Chitinozoans from the middle Rhuddanian (lower Llandovery, Silurian) ‘hot’ shale in the E1-NC174 core, Murzuq Basin, SW Libya

Review of Palaeobotany and Palynology 198 (2013) 62–91

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Research paper

Chitinozoans from the middle Rhuddanian (lower Llandovery, Silurian) ‘hot’ shale in the E1-NC174 core, Murzuq Basin, SW Libya Anthony Butcher ⁎ School of Earth & Environmental Sciences, Burnaby Building, Burnaby Road, Portsmouth, PO1 3QL, UK

a r t i c l e

i n f o

Article history: Received 15 April 2011 Received in revised form 9 November 2012 Accepted 23 November 2012 Available online 14 December 2012 Keywords: chitinozoan Libya Rhuddanian Silurian Gondwana hot shale

a b s t r a c t Chitinozoans recovered from the E1-NC174 core, south-west Libya, are described. On the basis of key biostratigraphical taxa, including Belonechitina postrobusta, Belonechitina pseudarabiensis, Plectochitina pseudoagglutinans, Angochitina seurati and Sphaerochitina palestinaense, the entire core is suggested to be of Rhuddanian age, with the ‘hot’ shale constrained to the upper part of the range of Belonechitina postrobusta. The age of this ‘hot’ shale, and the significant decline of chitinozoan abundance within it, shows strong similarity with the middle Rhuddanian ‘hot’ shale occurring in the BG-14 core of southern Jordan. In total, nineteen different taxa are described from fifty samples, adding valuable data to the chitinozoan record for lower Silurian strata in northern Gondwana. © 2012 Elsevier B.V. All rights reserved.

1. Introduction High-resolution dating of the widespread, organic-rich shales deposited in many areas of Gondwana during the latest Ordovician–earliest Silurian is of great importance, given that these shales act as major hydrocarbon source rocks (e.g. Lüning et al., 2000). Chitinozoans have proven to be a valuable group for such biostratigraphical dating given their wide palaeogeographical distribution, relative faciesindependence (compared, for example, with graptolites), and high potential for recovery even from very small samples (e.g. Verniers et al., 1995; Paris, 1996; Paris et al., 2004; Paris and Verniers, 2005). The data presented herein form part of the results from an integrated high-resolution biostratigraphical study through the ‘hot’ shale interval in the E1-NC174 core, Murzuq Basin, south-west Libya, comprising detailed study of the graptolites (Loydell, 2012), chitinozoans (presented herein), acritarchs and carbon isotopes (both in prep.). The chitinozoan data are based upon 6655 specimens, representing high-resolution analyses of 50 samples through this core, and allowed for the identification of key biostratigraphical and abundance changes through an early Silurian ‘hot’ shale sequence. Florentin Paris undertook the first studies of chitinozoans from the subsurface of Libya, in papers recording Ordovician, Silurian and Devonian occurrences (Molyneux and Paris, 1985; Hill et al., 1985; Paris et al., 1985, respectively), and has published recently a detailed study on the palynology of early Silurian shales from the CDEG-2a borehole of

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the eastern Murzuq Basin (Paris et al., 2012) — an impressive personal span of twenty-seven years of chitinozoan research in Libya alone. Only the studies by Hill et al. (1985) and Paris (1988a, 1988b) included Llandovery taxa that can be synonymised with those recovered herein. The recent study by Paris et al. (2012) does not record any taxa from the CDEG-2a core that occur also in the E1-NC174 core, suggesting therefore that both occupy very specific stratigraphical positions, and that the taxa in each have very restricted ranges. Other studies on chitinozoans specifically from Libya have been conducted, but have focused mainly upon strata that are either younger or older than the age proposed for the E1-NC174 core (e.g. Tekbali and Wood, 1991; Jaglin and Paris, 1992, 2002), and thus have only long-ranging species in common (e.g. Ancyrochitina ancyrea (Eisenack, 1931); see discussion in Section 6). Loydell (2012) has provided the first published detailed graptolite biostratigraphical study of a ‘hot’ shale from North Africa, based upon sixty-seven samples from the E1-NC174 core (discussed in detail in Section 6). Loydell's samples included those analysed also herein for chitinozoans, and thus provide data by which the ages determined independently from both fossil groups may be compared. The E1-NC174 graptolites and chitinozoans contribute to the calibration of the biozonations based on these two groups for northern Gondwana (e.g. see Loydell, 2007; Butcher, 2009 for comparable work on the Rhuddanian of Jordan). 2. Geological setting The E1-NC174 core comes from an exploration well drilled in 1997, in the north-west central part of the Murzuq Basin, south-west Libya (Fig. 1). Previous work on this core was published by Lüning et al.

A. Butcher / Review of Palaeobotany and Palynology 198 (2013) 62–91

(2003) in which a ‘hot’ shale was identified at the base of the Tanezzuft Formation, based upon total organic carbon (TOC), gamma-ray, and pyrite framboid data. The term ‘hot’ refers to the high natural radioactivity in certain shale units due to an increase in authigenic uranium, and as such they can be recognised readily in well logs due to their high gamma-ray values (Lüning et al., 2000, 2005). In North Africa, Silurian ‘hot’ shales account for 80–90% of Palaeozoic sourced hydrocarbons, and are therefore of great economic importance (Lüning et al., 2000, 2005). During the latest Ordovician–earliest Silurian, Libya was situated on the northern margin of northern Gondwana, which experienced widespread organic-rich shale deposition at this time due to marine transgression caused by the melting of the Hirnantian ice sheets. Different models have been proposed for the deposition of these Silurian ‘hot’ shales, the most widespread model being that they were formed as sea levels submerged the palaeotopography resulting in organicrich shales being deposited in palaeovalleys and depressions, with anoxic environments forming due to restricted circulation (e.g. Lüning et al., 2000; Le Heron et al., 2009, Fig. 16). However, a different model was proposed by Loydell et al. (2009) for the middle Rhuddanian (lower Llandovery, Silurian) ‘hot’ shale in the BG-14 core from southern Jordan. They proposed, on the basis of sedimentary, palynological, taphonomic, and carbon isotope data, that the particular ‘hot’ shale studied was deposited during a minor marine regression. It is recognised therein, however, that this model has been proposed only for the middle Rhuddanian ‘hot’ shale and that others, such as those occurring in the Hirnantian persculptus and lower Rhuddanian ascensus-acuminatus graptolite biozones in Jordan, were deposited through processes related to marine transgression. 3. Material and methods The E1-NC174 core consists of 17.4 m of homogenous dark grey– black shales with millimetre–sub-millimetre lamination, and contains the entire ‘hot’ shale plus the underlying and overlying organicallylean shales. In order to define a shale as ‘hot’, it must record gamma-ray values of greater than 200 API (roughly correlating to a TOC of 3%, see Lüning et al., 2000): the ‘hot’ shale interval in the E1-NC174 core has TOC values up to 13%, and gamma-ray values up

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to c. 600 API. In addition to these high values, the presence of type II kerogen and high hydrogen indices indicate that this ‘hot’ shale is an excellent oil-prone source rock (Lüning et al., 2003, p. 301). Although the underlying and overlying black shales are categorised as ‘lean’, they are still rich in organic matter and abundant in often well-preserved organic-walled fossils. For the study, fifty samples were selected throughout the available core material, ranging from depths of 7232′2″ to 7293′10″, giving a total sampled thickness of 56′8″ (or 17.27 m). All sample depths stated herein are given in feet and inches, as these are the original units in which the core was drilled and logged. Samples were cleaned, weighed and subjected to the ‘standard’ hydrochloric–hydrofluoric acid processing technique, based largely on that described by Sutherland (1994) and modified by Butcher (2009) and Butcher et al. (2010). An additional step in the processing procedure had to be included due to problems encountered during preliminary scanning electron microscope (SEM) analyses, where organic volatiles remaining on the specimens caused apparent movement and imaging problems while in the SEM chamber. After advice from Ken Dorning (pers. comm., 2007), a tiny amount of Savona Natura detergent was added routinely to each sample immediately after the acid processing and neutralisation stage, and prior to sieving. The residue was then passed through 1000, 53 and 10 μm nylon sieve meshes in sequence, and washed with a 50:50 methanol– water solution to remove any remaining detergent prior to heavy liquid separation with sodium polytungstate at a specific gravity of 2.0 g cm-3. The 1000 −53 μm residue fraction of each sample was picked through using a stereo microscope, and where possible the first 250 chitinozoans encountered from each were extracted and mounted onto SEM stubs that had been prepared with black and white negative film stuck emulsion-side up. Stubs were sputter coated using a gold-palladium target, and analysed using a Jeol JSM-6100 SEM. Amorphous organic matter (AOM) was a hindrance to the picking and analysis of the chitinozoans, as it was very abundant in all samples (especially so within the ‘hot’ shale interval) and obscured or adhered to the specimens of interest. Various oxidisation techniques were tested in order to disassociate or remove the AOM, including Schulze's solution, hydrogen peroxide, sodium hypochlorite, and nitric acid, but none proved effective: they either had no effect, or affected the AOM but also damaged the chitinozoans. Ultrasonic

Fig. 1. Map of southern Libya showing the two major depositional basins and the location of the E1-NC174 core. From Loydell (2012, Fig. 1).

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treatment was also tested, but had to be conducted for such a long period of time that the chitinozoans also experienced damage. However, it was still very clear under the stereo microscope whether chitinozoans were ‘trapped’ within AOM, in which case they were still counted, but could not often be identified. Due to the large amounts of AOM within the ‘hot’ shale interval, often low numbers of chitinozoans were picked even when a considerable amount of extra time had been spent to try and recover the desired 250 specimens. While such lower numbers may affect the accuracy of relative abundance data for taxa within those samples through having a smaller data set, the calculations for the number of chitinozoans per gram is affected less so. 4. Preservation and abundance of chitinozoans in the E1-NC174 core The core samples that were selected for palynological processing in this study yielded an average of 66% (by mass) organic material (i.e. the material remaining after HCl-HF-HCl treatment, and separating out in sodium polytungstate). Within the abundant organic material recovered from the E1-NC174 core samples, chitinozoans were generally very abundant below the ‘hot’ shale (see Fig. 2). Jansonius and Jenkins (1978) considered 20 chitinozoans per gram a good yield: abundances up to c. 4000 per gram were recorded from the lower part of the E1-NC174 core. Similarly high abundances (c. 3000 chitinozoans per gram) were recorded by Paris et al. (1995, p. 77) from the ‘graptolitic black shales (high gamma-ray horizon) of the Qusaiba ‘hot shale’’ in central Saudi Arabia, Paris et al. (2012), up to c. 4000 specimens per gram) from the ‘dark grey shale’ within the CDEG-2a core of the Murzuq Basin, Libya, and by Butcher (2009) from below the ‘hot’ shale interval of the BG-14 core and within the ‘hot’ shale of the WS-6 core of southern and eastern Jordan (maximum values of c. 4760 and c. 5670 chitinozoans per gram respectively). Although the abundance of chitinozoans is high in the lower part of the E1-NC174 core, the samples are in fact dominated by AOM. Many palynomorphs and zooclasts can be recognised, such as the chitinozoans, sphaeromorphs and graptolite fragments, but the vast majority of organic material is in the form of AOM. All of the chitinozoans observed were of a translucent amber to brown colour and therefore are unlikely to have undergone very high thermal maturation. Chitinozoans have been used as thermal maturation indicators (e.g. Cole, 1994; Obermajer et al., 1996), but no such study was undertaken herein. Pyrite was commonly observed attached to chitinozoan specimens, occurring in the form of small framboids c. 5–10 μm in diameter (see Plate VI, Fig. 5). Most disassociated pyrite would have sunk into the mineral fraction during heavy liquid separation, but the density of the small framboids attached to the chitinozoan vesicles was insufficient to cause sinking of the chitinozoans (the mineral fraction of the heavy liquid was routinely checked for chitinozoans, to see if their sinking had indeed occurred). The hollow vesicles of the chitinozoans offer an ideal location for the formation of pyrite in these sediments, and when not directly visible, pyrite can often be seen to have distorted the walls of the chamber and neck from within. The abundance data for chitinozoans in samples from the E1-NC174 core are displayed on Fig. 2, and show a marked decrease within the ‘hot’ shale interval (detailed absolute and relative abundance data tables for individual taxa are provided in the Supplementary Material, Tables SM1 and SM2 respectively). The average abundance of chitinozoans in samples below the ‘hot’ shale is 793 chitinozoans per gram; it is 104 per gram above the ‘hot’ shale. The average value for the twenty-one samples within the ‘hot’ shale interval is 82, and is thus not markedly different from those samples above. However, this value for the ‘hot’ shale is strongly skewed by high values at the base and top of the interval, probably due to a gradual onset and cessation of the environmental conditions responsible for deposition of the ‘hot’

shale. If the average of the fifteen samples occurring in the middle of the ‘hot’ shale interval is taken (corresponding roughly to the highest TOC values), the value is only 20 chitinozoans per gram. From these values, it seems that the abundance of chitinozoans was high previous to the onset of ‘hot’ shale deposition, decreased to very low values during it, and then increased very gradually upon its cessation. A study of the chitinozoan abundance in samples above those studied herein would show at what level it begins to revert towards the values observed below the ‘hot’ shale, or if indeed it does at all. This marked decrease of chitinozoan abundance within the ‘hot’ shale is undoubtedly of significance. Paris et al.'s (1995) value of up to 3000 chitinozoans per gram was recorded from ‘within or close to’ the high gamma-ray horizon of the Qusaiba shale in central Saudi Arabia. Cole (1994) also recorded that chitinozoans (and graptolites) were abundant in samples from the high gamma-ray part of the Qusaiba shale in Saudi Arabia. Butcher (2009), however, found that abundances were generally lower within samples from the BG-14 core of Jordan shown to contain high TOC and S2 values by Lüning et al. (2005), though not as markedly as in the E1-NC174 core. Thus the pattern of chitinozoan abundance within ‘hot’ shales does not seem to be uniform. A possible explanation may be that the ‘hot’ shales of different areas of northern Gondwana were formed by different depositional processes. Batten (1996, p. 1031), noted that chitinozoans are often present in ‘generally low numbers and diversity in shales containing abundant amorphous matter…[suggesting] that not all were planktonic’, and combined with the high and low energy facies-dependent distribution of some species, suggested that the relationship between chitinozoans and depositional conditions requires further investigation. The preservation of chitinozoans in the E1-NC174 core was generally very good. Two main problems affected the identification of chitinozoans to specific, and even generic, level: the obscuring of morphological features by AOM adhering to the vesicle, and/or damage to the morphological features. As discussed above, AOM adhering to the vesicles can often completely obscure a specimen, so that only its general affinity to the group Chitinozoa can be stated (see Plate VI, Figs. 3–5, and Section 5 below). In terms of damage to the specimens, protruding basal processes, characteristic of the Ancyrochitininae, appear to be the most susceptible. Removal or damage to these processes renders identification difficult or often impossible, and is reflected by the large number of specimens herein assigned to Ancyrochitina? sp. indet. (see Supplementary Material). As a result of these preservational problems, identification of chitinozoan taxa within the E1-NC174 core is therefore biased against those species that are less robust, or possess fragile spines, processes, or other morphological features. As the standard chitinozoan classification scheme proposed by Paris et al. (1999) is based purely on morphological characters, damage to specimens is problematical. The absolute and relative abundances of species belonging to Ancyrochitina and Plectochitina in particular must thus be viewed cautiously in the present study. The high potential of damage to specimens of these genera means that their use globally as biozonal taxa must be considered carefully, as they may not be well-preserved and recognisable in all strata. More robust forms, such as Belonechitina postrobusta, possess greater value as index taxa as their high preservation potential favours confident recognition.

5. Systematic palaeontology of chitinozoans from the E1-NC174 core 5.1. Notes on systematic palaeontology The suprageneric classification scheme of Paris et al. (1999), and their morphological terms, have been adopted herein. The system of open nomenclature used herein follows that of Matthews (1973).

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Fig. 2. Diagram showing the relationship of absolute chitinozoan abundance to gamma-ray and TOC values within the E1-NC174 core. TOC and gamma-ray curves modified from Lüning et al. (2003, Fig. 4).

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Measurements of specimens were obtained using the freeware UTHSCSA ImageTool 3.0 software (The University of Texas Health Science Centre, San Antonio, Texas). All biometric measurements were taken on specimens as observed, with no correction factor applied for flattening. It was decided to provide only raw data, as correction factors are approximate and can be applied retrospectively to the raw measurements. When preserved in three-dimensions, the values for D, da and dn of the material of other authors have had an artificial flattening factor of ÷ 0.7 applied. Although subjective, this factor allows the measurements to be plotted against the raw dimensions of the material recovered herein. The principal measurements, recorded in micrometres (μm), are as listed below: L D da dn lc ln lapp dapp lsp dsp

Length of the vesicle Maximum diameter of the vesicle Diameter of the aperture Minimum diameter of the neck Length of the chamber Length of the neck (including collarette if present) Length of basal processes (appendices) Diameter of appendices/processes (at base) Length of spines on vesicle surface Diameter of spines (at their base)

All material was recovered from the Tanezzuft Formation, Murzuq Basin, south-western Libya, from the E1-NC174 core. The exact sample horizons from which each taxon was recovered are detailed in the Supplementary Material (Tables SM1 and SM2). Specimens are housed at the British Geological Survey (BGS, Keyworth, UK) and have been assigned according to the BGS catalogue system with the prefix ‘MPA’ for micropalaeontological residues (from each sample horizon), and ‘MPK’ for the individual microfossil specimens illustrated.

5.2. Systematic palaeontology Group Chitinozoa Eisenack, 1931 Order Operculatifera Eisenack, 1931 Family Desmochitinidae Eisenack, 1931 emend. Paris (1981) Subfamily Desmochitininae Paris, 1981 Genus Bursachitina Taugourdeau, 1966 restrict. Paris, 1981 Type species: Desmochitina bursa Taugourdeau and de Jekhowsky, 1960; p. 1225, pl. 7, Fig. 89 (holotype lost, according to Paris et al., 1999). Neotype = Desmochitina bursa Taugourdeau and de Jekhowsky, 1960; Taugourdeau (1967, p. 256, pl. 1, Fig. 3). Bursachitina sp. A Plate I, 1 Material: 34 flattened specimens, recovered from samples below the ‘hot’ shale interval. Description: The vesicle chamber is conical to sub-cylindrical, with a concave base and well-rounded basal margin (the base is inferred as being concave due to its inward flattening). The flanks are weakly concave, giving the impression of a weak flexure. The aperture is wide, non-flaring, and may show a degree of fine denticulate ornamentation around its margin. The surface of the vesicle is smooth, and no basal features could be discerned due to inward flattening of the base. Dimensions: See Table 1. Remarks: The specimens bear a close resemblance to Bursachitina sp. A of Al-Hajri and Paris (1998), but are differentiated by their overall smaller size, well-rounded basal margin, and weakly concave flanks. The weak ‘flexure’ observed in the specimens recovered is most probably due to the weakly concave nature of the flanks being enhanced

by flattening. The three specimens illustrated by Al-Hajri and Paris (1998, Fig. 3.3–3.4, 3.7) display weakly convex flanks and a less rounded basal margin: no description of the taxon was provided in their paper. Al-Hajri and Paris (1998, Fig. 2) recorded their taxon as occurring in the Qusaiba and Sharawra members of the Qalibah Fm, Saudi Arabia, in strata they assigned to part of the uppermost Llandovery and the lower Wenlock. The specimens recovered bear a resemblance in vesicle shape to Belonechitina pseudarabiensis Butcher, 2009 (and described below), but there was no evidence of abraded spines on the surface of Bursachitina sp. A that would suggest affinity to this species. Also, when picking the residues a few examples of this taxon were observed in chains of up to five individuals, joined aperture to base — they were adjoined weakly, and could not therefore be transferred to an SEM stub intact. Such preservation of weakly-linked chains makes it unlikely that the specimens had undergone abrasion that could have removed the spines, and also none of the specimens of B. pseudarabiensis recovered was found adjoined in chains.

Table 1 Biometric data for Bursachitina sp. A, based upon four flattened specimens recovered from the E1-NC174 core. All measurements are in micrometres (μm).

Mean Maximum Minimum

L

D

da

L/D

D/da

113 123 106

75 81 68

50 52 48

1.52 1.61 1.44

1.50 1.60 1.40

Desmochitininae gen. et sp. indet. Plate I, 2 Material: 17 flattened specimens, recovered from samples below, within, and above the ‘hot’ shale interval. Description: All material is flattened perpendicular to its equatorial plane, and therefore each specimen is preserved as a disc, bearing a characteristic circular structure around its centre (representing the aperture). No other features could be discerned. Dimensions: See Table 2. Remarks: Due to their very close resemblance to the abundant flattened sphaeromorphs occurring in samples throughout the core, and related difficulties in identification, specimens of the Desmochitininae were not picked quantitatively. Only rare specimens could be observed during picking through their possessing the characteristic circular aperture (visible as a central ring), but it is possible that others could have occurred that could not be distinguished from sphaeromorphs. Therefore, the abundance data provided for the Desmochitininae herein is qualitative rather than quantitative. Due to a lack of any features other than the aperture on the vesicle, and no true representation of its original shape (due to flattening), identification at generic or species level could not be attempted. The specimens, having a glabrous surface, could be assigned with confidence only to the subfamily Desmochitininae: generic assignation for this subfamily is based upon chamber shape, and as such it could not be attempted. It is unlikely that the specimens belong to the genera Bursachitina or Ollachitina, however, as these possess conical and cylindrical vesicles respectively: these would be unlikely to flatten into the disc shape observed. No carina was observed, and as such the specimens are not likely to belong to the genus Pterochitina, though it is possible that this has been removed through damage. Hill et al. (1985) recorded Calpichitina densa (Eisenack, 1962) from well D1-31 (north-east Libya), in strata they assigned to the upper Aeronian–upper Telychian, based partly upon the record of this species in the ‘uppermost Llandovery and early [sic.] Wenlock of Gotland (Laufeld, 1974)’ (Hill et al., 1985, p. 29). The specimens recovered herein

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are similar to those specimens of C. densa illustrated by Hill et al. (1985, pl. 14, Figs. 7, 14), but cannot be identified confidently as this taxon.

Table 2 Biometric data for Desmochitininae gen. et sp. indet., based upon five flattened specimens recovered from the E1-NC174 core. All measurements are in micrometres (μm).

Mean Maximum Minimum

D

da

D/da

89 123 70

40 52 33

2.23 2.60 2.24

Order Prosomatifera Eisenack, 1972 Family Conochitinidae Eisenack, 1931 emend. Paris (1981) Subfamily Belonechitininae Paris, 1981 Genus Belonechitina Jansonius, 1964 emend. Paris et al. (1999) Type species: Conochitina micracantha subsp. robusta Eisenack, 1959; pp. 9–10, pl. 3, Fig. 4. Belonechitina postrobusta (Nestor, 1980a) Plate II, 1–9 ?1974 Conochitina robusta Eisenack; Martin, p. 34, pl. 6, Figs. 206–208. .1978 Conochitina robusta Eisenack; Grahn, Fig. 4a–d, f–g. *1980a Conochitina postrobusta Nestor; p. 101, pl. 4, Figs. 1–4; pl. 5, Figs. 2–3. ?1985 Belonechitina postrobusta (Nestor)?; Hill et al., pl. 12, Fig. 4a–b. .1988 Belonechitina aspera (Nestor)?; Geng and Cai, pl. 1, Fig. 11. .1992 Belonechitina postrobusta (Nestor); Dufka, pl. 1, Figs. 7–9. .1993 Belonechitina postrobusta (Nestor); Dufka and Fatka, pl. 4, Figs. 4–5, 10, 13. .1994 Belonechitina postrobusta (Nestor); Nestor, p. 45, pl. 17, Figs. 1–7. .1995 Belonechitina postrobusta (Nestor); Grahn, Fig. 7j. .1995 Belonechitina postrobusta (Nestor); Verniers et al., Fig. 5c–d [cop. Nestor, 1980a] .1997 Belonechitina postrobusta (Nestor); Geng et al., p. 80, pl. 9, Fig. 2. .2000 Belonechitina postrobusta (Nestor); Grahn et al., pl. 1, Fig. 5. .2000 Belonechitina postrobusta (Nestor); Soufiane and Achab, pl. 2, Figs. 4, 11. .2003 Belonechitina postrobusta (Nestor); Loydell et al., Fig. 16a. .2009 Belonechitina postrobusta (Nestor); Butcher, p. 598, pl. 1, Figs. 2–3, 6–7. Holotype: Conochitina postrobusta Nestor, 1980a; pl. 4, Fig. 1a–b. Material: 1238 flattened specimens, recovered from samples below and within the ‘hot’ shale interval. Description: The vesicle chamber is sub-cylindrical to conical, with a flat or weakly concave base and rounded basal margin. The flanks are straight to slightly convex, with an inconspicuous to slight flexure. The aperture displays a slight degree of fine denticulation, and may flare slightly. The entire vesicle is evenly covered by small, simple, randomly distributed spines of 2−4 μm. Many of the spines display a widened base, often coalescent on the vesicle surface. The spines are generally better developed towards the base of the vesicle, in particular around the basal margin. The bases of all specimens are flattened inwards, and basal features cannot therefore be discerned. Dimensions: See Table 3 and Fig. 3. Remarks: Belonechitina robusta (Eisenack, 1931) differs from B. postrobusta by its more slender and more conical vesicle, and longer and high-rooted spines that are usually arranged in longitudinal rows. Belonechitina arabiensis Paris and Al-Hajri, 1995 and B. pseudarabiensis Butcher, 2009 possess much longer spines, and a generally shorter vesicle length than B. postrobusta. Belonechitina aspera (Nestor, 1980a) is similar to the smallest specimens of B. postrobusta in the populations studied by Nestor (1980a) and herein, but is differentiated by a strongly convex base.

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Nestor (1980a, pp. 101–102) described a large range of intraspecific variation in both the shape of the vesicle and the degree of ornamentation in B. postrobusta. The range of variation in overall vesicle shape was illustrated by Nestor (1980a, Fig. 2), and shows that while D remains reasonably constant, L is extremely variable, as is the absence, presence and degree of flexure. The degree of surface ornamentation was described by Nestor (1980a) as variable, with almost smooth specimens having been recovered from her material. Such intraspecific variation in both vesicle shape and ornamentation were encountered in the specimens of B. postrobusta recovered from the E1-NC174 core: examples of this range are illustrated in Plate II. As can be seen from the illustrations, the overall shape of the specimens recovered varies from short, wide, sub-cylindrical vesicles through to longer, narrower vesicles, displaying a prominent flexure. Many transitional forms between these two end-members were encountered, therefore demonstrating that the specimens recovered belong to one taxon with a large range of intraspecific variation (Fig. 3). Those specimens recovered displaying the longest, narrowest vesicles and those with a very pronounced flexure fall outside the limits of the species as illustrated by Nestor (1980a, Fig. 2; see Fig. 3 herein), but are considered as being a continuation of the intraspecific variation within B. postrobusta due to the relationship imposed by the intermediary specimens herein. Butcher (2009), described specimens that he assigned to ‘Belonechitina cf. postrobusta’, as they plotted distinctly separate from specimens of B. postrobusta sensu stricto. The biometric data envelopes of both forms described by Butcher (2009) are shown on Fig. 3, and it can be seen that three specimens from the E1-NC174 core fall within that for B. cf. postrobusta. It is clear, therefore, that the degree of morphological variation within the Belonechitina postrobusta ‘group’ is in need of clarification. There does not appear to be any definable stratigraphical significance to the different ‘forms’ or shapes of B. postrobusta in the E1-NC174 core, although the number of long narrow specimens does decrease in the highest samples from which the species was recovered. From the examples herein of B. postrobusta it can be seen that, in order to perform confident and accurate identification, as many specimens as possible must be examined in order to determine the intraspecific variation of a species. Indeed, without the presence of intermediary specimens of B. postrobusta in this study, it would be very hard to relate many of the specimens to the same taxon. The fact that many of the specimens exhibit conspicuous flexure causes a conflict in terms of the generic assignation of this species (in accordance with Paris et al., 1999), as Belonechitina belongs to the sub-family Belonechitininae of the family Conochitinidae, which is characterised by having an inconspicuous flexure. Although all of the specimens herein are flattened, and such preservation will exaggerate flexure, it is still clear that many specimens must still have had conspicuous flexure originally. However, this problem is likely to occur with the generic classification of any taxon displaying a wide degree of intraspecific variation, and therefore the judgement of the author must be used to decide upon the genus, based upon perhaps the most common form, or the usage of previous authors for consistency in the literature. Table 3 Biometric data for Belonechitina postrobusta (Nestor, 1980a), based upon eighty flattened specimens recovered from the E1-NC174 core. Values for lc and ln were taken only from those specimens in which a chamber was differentiated by weak flexure. An artificial flattening factor of ÷ 0.7 has been applied herein to the values for D and da of the three-dimensionally preserved holotype and type material (Nestor, 1980a). All measurements are in micrometres (μm).

Holotype Type material Mean Maximum Minimum

L

ln

lc

D

da

L/D

290 180–385 215 340 123

96 – 84 175 22

194 – 157 263 91

90 107–134 96 125 75

65 64–107 61 83 42

3.22 – 2.24 3.57 1.52

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Belonechitina pseudarabiensis Butcher, 2009 Plate I, 3 *2009 Belonechitina pseudarabiensis Butcher; p. 599, pl. 2, Figs. 1–11. Holotype: Belonechitina pseudarabiensis Butcher, 2009; pl. 2, Figs. 1–2. Material: 27 flattened specimens, recovered from samples below and within the ‘hot’ shale interval. Description: The vesicle chamber is conical to ovoid, with a flat base and rounded basal margin. The flanks are straight, or may adjoin the neck through a gentle flexure. The aperture flares slightly, and is surrounded by a simple, thin-walled collarette. The surface of the vesicle is covered with randomly distributed simple spines of an even density over the entire vesicle. The spines measure 2.5–7 μm long with a diameter of c. 0.5 μm, and are spaced c. 2.5 μm apart. A circular depression is apparent around the anti-apertural pole, but no mucron is present. Dimensions: See Table 4. Remarks: B. pseudarabiensis is distinguished from other Belonechitina species by the nature and density of spines covering the vesicle. B. arabiensis, recorded by Paris and Al-Hajri (1995) in well samples from the Arabian Plate, shows a similar vesicle shape, with spines of a similar length and diameter to those of B. pseudarabiensis. However, the spacing of the spines in the former is recorded by Paris and Al-Hajri (1995) as being approximately 5 μm apart, whereas a distance of 2.5 μm between spines was recorded in all specimens of B. pseudarabiensis. The density of the spines may be further quantified by counting the number of spines per unit of area: B. pseudarabiensis has a density of 72–136 spines per 25 μm 2, whereas the specimens of B. arabiensis illustrated by Paris and Al-Hajri (1995) have a density of 30–47 spines per 25 μm 2. The difference in spine density between the two taxa is therefore quite marked, and enables the two species to be differentiated: the spine density remains independent of other morphological features, such as the shape of the vesicle or the degree of flexure.

Table 4 Biometric data for Belonechitina pseudarabiensis Butcher, 2009, based upon eleven flattened specimens, recovered from the E1-NC174 core. All measurements are in micrometres (μm).

Holotype Type material Mean Maximum Minimum

L

ln

lc

D

da

dn

110 82–164 109 133 91

43 – 49 73 28

67 – 60 73 54

51 43–82 74 92 63

33 26–64 43 49 32

31 – 43 49 38

Subfamily: Conochitininae Paris, 1981 Genus: Clavachitina Taugourdeau, 1966 Type species: Rhabdochitina claviformis Taugourdeau, 1961; p. 150, pl. 4, Fig. 69. Clavachitina sp. A Plate I, 6 Material: 19 flattened specimens, recovered from samples below the ‘hot’ shale interval. Description: The vesicle chamber is claviform, with a well-rounded base and indistinct basal margin. The flanks are gently convex, and

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a weak flexure is apparent in some specimens (enhanced by flattening). The neck is more cylindrical, and flares very slightly at the aperture. The surface of the vesicle is generally smooth, although very small tubercules (less than 2 μm in height) are observed on the surface of some specimens. No basal features are apparent. Dimensions: See Table 5.

Table 5 Biometric data for Clavachitina sp. A, based upon four flattened specimens, recovered from the E1-NC174 core. All measurements are in micrometres (μm).

Mean Maximum Minimum

L

ln

lc

D

da

dn

257 286 227

139 176 115

118 134 110

77 90 70

48 53 40

41 47 37

Remarks: Although a weak flexure was observed in some of the specimens assigned to Clavachitina sp. A herein, it is enhanced by the flattening of the specimens. Therefore, the genus Clavachitina was selected for this taxon as, prior to flattening, the weak flexure observed would have been inconspicuous, thus allowing it to be placed into the family Conochitinidae, rather than the Lagenochitinidae (which display a conspicuous flexure, see Paris et al., 1999). Due to the paucity of material and lack of distinguishing features this taxon is retained in open nomenclature. Conochitina elongata Taugourdeau, 1963? Plate I, 7 Holotype: Conochitina edjelensis elongata Taugourdeau, 1963; pl. 3, Fig. 60. Material: 11 flattened specimens, recovered from samples below, within, and above the ‘hot’ shale interval. Description: The vesicle chamber is sub-conical, with a rounded basal margin and concave base (deduced from the inward flattening of the base in all specimens). The flanks are straight, and display no distinct flexure. The aperture flares slightly, and appears not to be denticulate. The surface of the vesicle is generally smooth, although very small elongate tubercules (less than 2 μm in height) are observed around the basal margin of some specimens. No basal features could be discerned, due to inward flattening of the base in all specimens. Dimensions: See Table 6. Table 6 Biometric data for Conochitina elongata Taugourdeau, 1963?, based upon four flattened specimens, recovered from the E1-NC174 core. All measurements are in micrometres (μm).

Holotype Mean Maximum Minimum

L

D

da

dn

L/D

D/da

205 142 163 132

65 59 65 55

– 39 41 38

– 35 40 30

3.15 2.39 2.51 2.32

– 1.50 1.60 1.46

Remarks: The specimens assigned to Conochitina elongata? herein have been retained in open nomenclature due to the paucity of material. Close similarity is observed between the material from the present study and specimens of Conochitina edjelensis elongata illustrated by Paris in Hill et al. (1985, pl. 13, Figs. 6, 11) and Euconochitina

Plate I. Scale bars represent 50 μm on all figures. All material is from the E1-NC174 core, Murzuq Basin, south-western Libya. 1. 2. 3. 4, 5. 6 7 8

Bursachitina sp. A; MPK14248, 7287′11−11½″. Desmochitininae gen. et sp. indet.; MPK14249, 7238′3″. Belonechitina pseudarabiensis Butcher, 2009; MPK14250, 7270′10″. Spinachitina sp. A; 4, MPK14251, 7244′2″. 5, detail of Fig. 4 showing nature of the basal processes. Clavachitina sp. A; MPK14252, 7291′6″. Conochitina elongata Taugourdeau, 1963?; MPK14253, 7242′7″. Euconochitina sp. A; MPK14254, 7286′7½″.

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the values for L/D and D/da for Euconochitina sp. A are lower and higher, respectively, than those for C. elongata? Achab (1981, pl. 3, Figs. 1–4; pl. 4, Figs. 6–9) illustrated specimens she named as Conochitina sp. 2, from the Gun River and Jupiter formations of Anticosti Island (Québec, Canada) with which Euconochitina sp. A herein bears some resemblance. The resemblance, however, is not strong enough to allow for confident identification, as the vesicle shape of Achab's (1981) Conochitina sp. 2 is rather less conical, and her specimens are generally longer (c. 200 μm). Subfamily Spinachitininae Paris, 1981 Genus Spinachitina Schallreuter, 1963 emend. Paris et al. (1999) Type species: Conochitina cervicornis Eisenack, 1931; p 89, pl. 2, Figs. 12–13, pl. 4, Fig. 5.

Fig. 3. Biometric plot of the ratios of L/D vs D/da for specimens of Belonechitina postrobusta (Nestor, 1980a), including data from the holotype and type material. In addition, ‘1’ = envelope of values for specimens of B. postrobusta recovered from the BG-14 core, Jordan, and ‘2’ = envelope of values for specimens of B. cf. postrobusta recovered from the BG-14 core, Jordan (both from Butcher, 2009).

elongata illustrated in Won et al. (2002, Fig. 8.27–8.28). The specimens recovered in this study differ from the type material of Taugourdeau (1963) in being somewhat shorter, and having a smaller value of L/D. In the same publication that C. edjelensis elongata (now C. elongata) was erected, Taugourdeau (1963, p. 137–138) also erected C. edjelensis edjelensis (now C. edjelensis), a closely related taxon with a shorter vesicle (L= 150 μm; D = 95 μm). However, the value of L/D determined from the holotype of C. edjelensis is 1.58, considerably lower than both the mean and minimum values for C. elongata? herein (see Table 6), suggesting the possibility that the specimens herein are an intermediary form between the two. Euconochitina sp. A Plate I, 8 Material: 13 flattened specimens, recovered from samples below, and questionably above, the ‘hot’ shale interval. Description: The vesicle chamber is sub-conical, with a well-rounded basal margin and concave base. The flanks are straight, and display no distinct flexure. The aperture is simple, and does not flare. The surface of the vesicle is smooth. No basal features are apparent on those specimens where the base can be seen clearly. Dimensions: See Table 7.

Table 7 Biometric data for Euconochitina sp. A, based upon three flattened specimens, recovered from the E1-NC174 core. All measurements are in micrometres (μm).

Mean Maximum Minimum

L

D

da

L/D

D/da

133 161 116

74 77 72

39 43 36

1.80 2.09 1.62

1.89 2.02 1.67

Remarks: Euconochitina sp. A is differentiated from Conochitina elongata? herein in that the former has a wider value for D than the latter, although the values for L and da are similar. Subsequently,

Spinachitina sp. A Plate I, 4–5 Material: 1 flattened specimen, recovered from sample 7244′2″ at the top of the ‘hot’ shale interval. Description: The vesicle chamber is sub-cylindrical, tapering gently towards the aperture, which flares very slightly. The base is assumed to be concave (from its inward flattening), with a sharply rounded basal margin. The maximum width of the vesicle is at the basal margin, with a conspicuous constriction in the vesicle occurring just above. The flanks are straight, and possess no flexure. The vesicle surface is smooth, and the aperture is unornamented. A characteristic ornamentation occurs around the basal margin, consisting of short, blade-like triangular processes. The basal processes measure 5.2 – 6 μm in length (i.e. away from the vesicle surface), with basal dimensions of 1.2–2 μm wide and 4.3–5 μm long (across the vesicle surface). The elongation of the processes is parallel to the longitudinal axis of the vesicle. Seventeen processes can be seen clearly on the uppermost side of the specimen, and therefore an approximate total number of 34 processes is extrapolated. Dimensions: See Table 8.

Table 8 Biometric data for Spinachitina sp. A, based upon a single flattened specimen, recovered from the E1-NC174 core. All measurements are in micrometres (μm).

(Single specimen)

L

D

da

dn

L/D

D/da

289

85

56

50

3.41

1.51

Remarks: Spinachitina sp. A differs from other species of Spinachitina in the characteristic nature of its basal processes. The genus Spinachitina has a range from the ‘Upper Ordovician–Lower Silurian’ according to Paris et al. (1999, p. 562). The specimen described herein has a very similar vesicle outline to specimens of Conochitina electa illustrated in Nestor's original description of that species (Nestor, 1980a, pl. VI, 1−3, and her Fig. 3). Nestor (1980a, p. 107) also mentioned that the surface of C. electa may be granulated and that it may bear variable ornamentation on the basal margin, including fine, irregular spines. However, due to the large and distinctive nature of the basal processes on the specimen herein, it is not assigned to C. electa but rather as a species of Spinachitina. Only one specimen of Spinachitina sp. A was recovered from a single sample (7244′02″) in the E1-NC174 core, out of a total number of 214 picked chitinozoans, suggesting that it is a very rare taxon. A further considerable amount of the residue remaining from sample

Plate II. Scale bars represent 50 μm on all figures. All material is from the E1-NC174 core, Murzuq Basin, south-western Libya. 1,2,3,4,5,6,7,8,9.

Belonechitina postrobusta (Nestor, 1980a); various specimens showing the wide range of intraspecific variation. 1, MPK14255, 7287′11−11½″. 2, MPK14256, 7286′7½″. 3, MPK14257, 7287′11–11½″. 4. MPK14258, 7279′6″. 5, MPK14259, 7287′11–11½″. 6, MPK14260, 7287′11–11½″. 7, MPK14261, 7256′3″. 8, MPK14262, 7290′6½″. 9, MPK14263, 7287′11–11½″.

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7244′02″ was picked through in addition to the quantitative pick, with the purpose of recovering more specimens of this taxon, but none was found. Including the additional residue picked, the abundance of Spinachitina sp. A was determined to be a maximum of one specimen per 4.11 grams, in a sample yielding an extrapolated total of 875 chitinozoans (of other taxa) per 4.11 grams. Family Lagenochitinidae Eisenack, 1931 emend. Paris (1981) Subfamily Ancyrochitininae Paris, 1981 Genus Ancyrochitina Eisenack, 1955a Type species: Conochitina ancyrea Eisenack, 1931; p. 88, pl. 4, Fig. 4 (holotype lost, according to Paris et al., 1999). Neotype=Ancyrochitina ancyrea (Eisenack, 1931); Eisenack (1955a p. 163), pl. 2, Fig. 7. Ancyrochitina ancyrea (Eisenack, 1931) Plate III, 1 Holotype: Conochitina ancyrea Eisenack, 1931; p. 88, pl. 4, Fig. 4 Material: 11 flattened specimens, recovered from samples below, within, and above the ‘hot’ shale interval. Description: The vesicle chamber is lenticular to conical, with a broadly rounded basal margin, and a flat to weakly concave base. The flanks are convex, and there is a distinct flexure, with a distinct to inconspicuous shoulder. The neck is cylindrical, and flares towards the aperture. The surface of the vesicle is generally smooth, although small tubercules (less than 2 μm in height) may occur sporadically on the neck. The basal margin displays long processes of varying length (c. 20–30 μm), that branch once or twice, and are c. 5 μm in diameter at the base. The processes extend outwards from the vesicle approximately perpendicular to the longitudinal axis, and generally branch parallel to it. No basal features are observed. Dimensions: See Table 9.

Table 9 Biometric data for Ancyrochitina ancyrea (Eisenack, 1931), based upon a single flattened specimen typical of the taxon, recovered from the E1-NC174 core. All measurements are in micrometres (μm).

Typical specimen

L

ln

lc

D

da

dn

115

57

59

77

35

31

Remarks: Ancyrochitina ancyrea (Eisenack, 1931) is one of the most commonly recorded chitinozoans in early Silurian strata. Although this is due in a large part to the abundance of the taxon and its long stratigraphical range, it is also, however, in part due to the problems of differentiating A. ancyrea from other species of Ancyrochitina. The original diagnosis of the species is actually quite specific, stating that ‘the most remarkable characteristic is…six long, curved thorns [the end of which] forks itself nearly regularly in two rolled up points, which can be divided again in the same way’ (Eisenack, 1931, p. 88, translated herein). Where the two-fold branching does not occur, the processes are described as resembling deer antlers. The specimens assigned to A. ancyrea herein all possess spines of this nature. The description and number of the spines were clearly described therefore by Eisenack (1931) for A. ancyrea, but were emended by Eisenack (1955b) to include a wider degree of variation, especially in the nature of the processes. The problem has arisen that the continual addition of specimens by subsequent authors, showing wider degrees of variation not deemed sufficient to erect a new taxon, has broadened the parameters of the species so much that Laufeld (1974) adopted the emended diagnosis of Eisenack (1955b), but with the restriction that specimens displaying processes branching in an antler-like or irregular way would not be included; he was concerned that ‘if that part of the diagnosis is adhered to the taxon will be of wastebasket character’ (Laufeld, 1974, p. 39).

The specimens recovered from the E1-NC174 core were not particularly well preserved, in that all of the specimens are flattened and display either damaged or broken basal processes, so an accurate analysis of their number and the nature of branching cannot be made (the poor preservation of basal processes in the Ancyrochitininae, and subsequent problems with identification is discussed under Ancyrochitina? sp. indet. below). The nature of the processes that have been preserved on the specimens herein closely resembles that of A. ancyrea, as does the size and shape of the vesicle: the specimens have therefore been deemed as conspecific with A. ancyrea. Due to its long stratigraphical range (see Section 6), and the uncertainty of the defining characteristics of the species, a detailed synonymy for A. ancyrea has not been included herein. Ancyrochitina? sp. indet. Plate III, 2−6 Material: 1108 flattened specimens, recovered from samples throughout the E1-NC174 core. Description: The specimens display a wide range of vesicle chamber shape, from lenticular to ovoid to conical, all with rounded to broadly rounded basal margins and a convex base. All specimens display a marked flexure, and straight to convex flanks. A shoulder may be absent, inconspicuous or conspicuous. The surface of the vesicle ranges from smooth to granulate, occasionally displaying a short spinose ornamentation, usually on the neck. Evidence of processes occurring around the basal margin is present, but virtually all original processes have been damaged or removed. Basal features are not apparent. Dimensions: Dimensions are not provided for specimens assigned to Ancyrochitina sp. indet., as these would be of little value. The specimens display a wide variation of dimensions, suggesting that a number of separate taxa is encompassed within Ancyrochitina? sp. indet. Remarks: Open nomenclature is retained at generic level, as although the nature of what remains of the basal processes appear to be characteristic of Ancyrochitina, it is possible that some specimens may belong to Plectochitina or Clathrochitina. Although the presence of a number of different taxa is certain (based upon the wide variety of vesicle shapes and dimensions), those specimens assigned to Ancyrochitina? sp. indet., after the removal of their basal processes, possess no characteristics allowing identification to a separate taxon. Certain specimens do display unusual or characteristic basal processes, and as such may prove to be distinct species, but preservation and/or a paucity of material does not allow for such assignation to be made. For example, some specimens display processes that resemble those of Ancyrochitina porrectaspina Nestor, 1994 (pl. III, Figs. 3−4), while others possess distinct mace-like processes unlike any seen on described taxa in the literature (pl. III, Figs. 5−6). Flattening of specimens of the Ancyrochitininae is likely to be the major cause of the removal of and damage to their processes, although it is possible that pyritisation also plays a significant role. Abundant pyrite was observed on many specimens, usually in the form of small framboids c. 5–10 μm in diameter (see pl. VI, Fig. 5). Such framboids formed the basis of a correlative technique for the recognition of ‘hot’ shale intervals in the E1-NC174 core (Lüning et al., 2003). Pyrite framboids were observed as occurring within the vesicle of chitinozoan specimens recovered in the present study, often distorting the outer surface of the chamber and neck. It is possible that microcrystalline pyrite formed within the basal processes of certain specimens, as those of the genus Ancyrochitina are described as ‘hollow’ by Paris et al. (1999, p. 563), and those of Plectochitina as ‘cell-like’ (Paris et al., 1999, p. 563) and ‘spongy’ (Nestor, 1994, p. 73). Pyrite occurring within the processes, and subsequently expanding through crystal growth, could certainly cause significant damage. Genus Plectochitina Cramer, 1964 Type species: Plectochitina carminae Cramer, 1964; p. 346, pl. 20, Fig. 21 (holotype lost, according to Paris et al., 1999). Neotype =

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Plectochitina carminae Cramer, 1964; Priewalder (1997 p. 77), pl. 2, Fig. 1; pl. 4, Figs. 1, 7–8. Plectochitina pseudoagglutinans Taugourdeau, 1963 Plate III, 7 *1963 Ancyrochitina fragilis pseudoagglutinans Taugourdeau; pl. 1, Figs. 1–4. .1967 Plectochitina pseudoagglutinans (Taugourdeau); Cramer, p. 125, pl. 5, Figs. 145–146. p1985 Plectochitina pseudoagglutinans (Taugourdeau); Hill et al., pl. 13, Fig. 8? [non pl. 12, Figs. 5a–b = P. cf. pseudoagglutinans]. ?1988 Ancyrochitina fragilis pseudoagglutinans Taugourdeau; McClure, pl. 9, Fig. 6. ?2000 Plectochitina pseudoagglutinans (Taugourdeau); GhavidelSyooki, Fig. 3a–b, d–f. ?2004 Plectochitina pseudoagglutinans (Taugourdeau); GhavidelSyooki and Winchester-Seeto, p. 175, Figs. 8a–b. . 2007 Plectochitina pseudoagglutinans (Taugourdeau); Ghavidel-Syooki and Vecoli, pl. 2, Figs. 1–2, 4. Holotype: Specimen as illustrated by Taugourdeau (1963, p. 130, pl. 1, Fig. 1). Material: 47 flattened specimens, recovered from samples above the ‘hot’ shale interval. Description: The vesicle chamber is conical, with a sharply rounded basal margin, and a concave base. The flanks are generally straight, but may display a weak concavity or convexity. The flexure is distinct, with no conspicuous shoulder. The neck is cylindrical, and flares towards the aperture. The vesicle surface is smooth, with occasional small tubercules (less than 2 μm in height) occurring on the neck. Around the basal margin occur 4–6 large processes, although the exact number occurring is difficult to observe due to their poor preservation. The processes are nodular, and occur just below the maximum width of the vesicle at the basal margin. Very few processes are preserved intact, but in those that are their length measures c. 44–73 μm, with a diameter at their base of c. 10–19 μm. No basal features are discernible, as the bases are flattened inwards in all specimens. Dimensions: See Table 10.

Table 10 Biometric data for Plectochitina pseudoagglutinans (Taugourdeau, 1963), based upon nine flattened specimens, recovered from the E1-NC174 core. All measurements are in micrometres (μm).

Holotype Mean Maximum Minimum

L

ln

lc

D

da

dn

190 131 159 94

– 72 108 45

– 59 85 33

100 85 97 76

– 40 47 34

– 34 39 26

Remarks: The type material illustrated by Taugourdeau (1963, pl. 1, Figs. 1–4) does not display any specimens with complete basal processes preserved, as is the general preservation of specimens from the E1-NC174 core. However, the general nature of the vesicle shape, and those remnants of preserved processes, has allowed for the material herein to be regarded as conspecific with Ancyrochitina fragilis pseudoagglutinans (Taugourdeau, 1963) (now Plectochitina pseudoagglutinans). Although the specimens herein have been synonymised with P. pseudoagglutinans, the standing of the species itself has been regarded as ‘doubtful…as in the original material all processes of the figured specimens appear to be broken’ (Priewalder, 1997, p. 76). In lieu of a complete re-evaluation of the type material of Taugourdeau (1963), the identification herein is retained,

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although it is recognised that a thorough review of all specimens and material previously recorded may redefine the parameters of the species. It is proposed herein that the two specimens of P. pseudoagglutinans illustrated by Paris, in Hill et al. (1985, pl. 12, Figs. 5a–b; pl. 13 Fig. 8) are two separate taxa. The specimen illustrated in plate 13, Fig. 8 of Hill et al. (1985) is retained as P. pseudoagglutinans, as it displays the characteristic conical chamber. The specimen illustrated in plate 12, Figs. 5a–b of Hill et al. (1985), however, possesses a distinctly ovoid chamber and thin processes. Taugourdeau (1963, p. 130), translation) stated that the chamber shape of P. pseudoagglutinans is ‘conical and generally very flat…occasionally ovoid (probably from deformation)’, but the specimen in plate 12, Figs. 5a–b of Hill et al. (1985) resembles more closely those specimens identified as ‘Ancyrochitina fragilis cf. pseudoagglutinans’ (Taugourdeau, 1963, pl. 1, Figs. 5–6), having a distinctly ovoid chamber. The specimen in plate 12, Figs. 5a–b of Hill et al. (1985) is therefore assigned herein to Plectochitina cf. pseudoagglutinans (see description for this taxon below). McClure (1988, pl. 9, Fig. 6) illustrated one specimen that he assigned to Ancyrochitina fragilis pseudoagglutinans (now Plectochitina pseudoagglutinans). The specimen displays broken processes of a similar nature to those of the material herein, and Taugourdeau's (1963) material. The overall shape of the vesicle, however, is rather different, with a neck flaring significantly from the flexure to the aperture, and therefore it is only questionably synonymised herein. Ghavidel-Syooki (2000, Fig. 3a–b, d–f) illustrated specimens of P. pseudoagglutinans that display thinner processes, with a bi-rooted base and an intra-connective membrane. Due to the poor preservation of the type material of Taugourdeau (1963), the specimens of Ghavidel-Syooki (2000) are not excluded from the species, but are retained questionably. Ghavidel-Syooki and Winchester-Seeto (2004) illustrated a single specimen assigned to P. pseudoagglutinans. The specimen displays rather smaller spines than the specimens recovered from the E1-NC174 core, and has a more rounded basal margin, but is considered conspecific herein. A confident synonymy is proposed for the specimens herein with those illustrated by Ghavidel-Syooki and Vecoli (2007, pl. 2, Figs. 1–4), as their specimens possess well-preserved, complete basal processes and the characteristic conical chamber and concave base very similar to the those seen in specimens recovered from the E1-NC174 core. Plectochitina cf. pseudoagglutinans sensu Taugourdeau, 1963 Plate III, 8 .1963 Ancyrochitina fragilis cf. pseudoagglutinans Taugourdeau; pl. 1, Figs. 5–6. p1985 Plectochitina pseudoagglutinans (Taugourdeau); Hill et al.; pl. 12, Figs. 5a–b [non pl. 13, Fig. 8 = ?P. pseudoagglutinans]. Material: 46 flattened specimens, recovered from samples below the ‘hot’ shale interval. Description: The vesicle chamber is ovoid, with a broadly rounded basal margin, and a flat to convex base. The flanks are weakly convex, with a distinct flexure and slight shoulder. The neck is cylindrical, and flares slightly towards the aperture. The vesicle surface is generally smooth, but may display small tubercules (less than 2 μm in height). Around the basal margin occur 4–6 long processes, although the exact number occurring is approximate due to their poor preservation. The processes are weakly nodular, and occur just below the maximum width of the vesicle at the basal margin. Very few processes are preserved intact, but those that are show variation in terms of their length and diameter. Processes are c. 35–81 μm long, with a diameter at their

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base of c. 6–16 μm. No basal features are discernible, as the bases are flattened inwards in all specimens. Dimensions: See Table 11.

Table 11 Biometric data for Plectochitina cf. pseudoagglutinans sensu Taugourdeau (1963), based upon seven flattened specimens, recovered from the E1-NC174 core. All measurements are in micrometres (μm).

Mean Maximum Minimum

L

ln

lc

D

da

dn

176 211 133

87 105 61

90 117 63

87 105 76

44 52 35

41 51 29

Remarks: Plectochitina cf. pseudoagglutinans is differentiated from P. pseudoagglutinans sensu stricto by the distinctly ovoid chamber and more slender processes possessed by the former. As described above for P. pseudoagglutinans, one of the specimens illustrated by Paris in Hill et al. (1985, pl. 12, Figs. 5a–b) resembles very closely the two examples of Ancyrochitina fragilis pseudoagglutinans (now Plectochitina pseudoagglutinans) illustrated by Taugourdeau (1963, pl. 1, Figs. 5–6), as does the material assigned to P. cf. pseudoagglutinans herein. As they referred both of their illustrated specimens to P. pseudoagglutinans, Hill et al. (1985) do not record a difference in the stratigraphical occurrence of the conical (sensu stricto) and ovoid (cf.) forms as defined herein. In the E1-NC174 core, P. cf. pseudoagglutinans occurs below the ‘hot’ shale interval, while P. pseudoagglutinans occurs only above it, thus further indicating a differentiation between the taxa. No other such stratigraphical differentiation has been recorded in previous studies, however. Plectochitina sp. indet. Plate IV, 1−4 Material: 8 flattened specimens from throughout the E1-NC174 core. Description: Specimens of the genus Plectochitina with an ovoid to conical chamber and distinct flexure, characterised by basal processes of a spongy and/or nodular nature. Description: As for Ancyrochitina? sp. indet. above, specimens assigned to Plectochitina sp. indet. are so poorly preserved as to make identification to species level impossible. Identification to generic level is possible for these specimens, however, as they preserve clear evidence of the nodular and/or spongy processes that are characteristic of the genus (e.g. pl. IV, Figs. 1−4). Though only eight specimens were recovered herein, it is likely that many more belonging to the genus Plectochitina exist within those assigned to Ancyrochitina? sp. indet., but cannot be separated out due to the basal scars not preserving sufficient detail. Subfamily Angochitininae Paris, 1981 Genus Angochitina Eisenack, 1931 Type species: Angochitina echinata Eisenack, 1931; p. 82, pl. 1, Fig. 7 (specimen is lost, according to Paris et al., 1999). Neotype = Angochitina echinata Eisenack, 1964; p. 139, pl. 29, Fig. 10.

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Angochitina seurati Paris, 1988b Plate IV, 5–9 .1985 Angochitina sp. A Hill et al.; pl. 13, Figs. 1a–b, 2a–b, 4. *1988b Angochitina seurati Paris; p. 77, pl. 12, Figs. 1a–b, 2, 3. Holotype: Angochitina seurati Paris, 1988b; pl. 12, Fig. 2. Material: 71 flattened specimens, recovered from samples below and above the ‘hot’ shale interval. Description: The vesicle chamber is ovoid and elongate, with a broadly rounded basal margin, and a convex base. The flanks are convex, and possess a gentle flexure without an obvious shoulder. The neck is cylindrical, and possesses a collarette that flares towards the aperture, which may display fine denticulation. The vesicle surface bears a characteristic pilose ornamentation of very fine, simple spines that are randomly distributed over the entire vesicle surface. The spines measure c. 9–13 μm in length, and c. 0.4–0.8 μm in diameter. No basal features are apparent. Dimensions: See Table 12.

Table 12 Biometric data for Angochitina seurati Paris, 1988b, based upon 26 flattened specimens. A coefficient of correction of 0.7 was applied by Paris (1988b) to values of D, da and dn to compensate for the effects of flattening: this has been reversed herein for the type material so that the values may be compared with the material recovered in the present study.

Holotype Type material Mean Maximum Minimum

L

ln

lc

D

da

dn

L/D

252 154–274 180 240 139

137 – 83 146 38

115 – 98 134 71

80 57–83 70 76 61

57 34–63 49 61 39

– – 36 46 27

3.15 – 2.58 3.15 2.01

Remarks: Angochitina seurati is distinct from other species of Angochitina due to its fine pilose surface ornamentation. Although apparently fragile, the relatively short nature of the spines and their abundant distribution over the vesicle surface results in a high preservation potential for at least some of the characteristic ornamentation to be preserved: it may be that the spines display a high degree of flexibility. Combined with the distinct vesicle shape of the species, the pilose ornamentation means that the taxon can be easily recognised. However, Paris (1988b, p. 78) notes that the ornamentation is ‘difficult to see with a light microscope, even at large magnification’, and therefore SEM analysis is required to ensure confident identification. The specimens recovered from the E1-NC174 core possess rather longer spines than those described for the type material by Paris (1988b, p. 77), although many intermediary variations were observed in the material from the present study, showing that they are indeed conspecific. Only very rare specimens of Angochitina seurati were recovered from below the ‘hot’ shale interval in the E1-NC174 core, but increased in abundance in samples at the very top of the ‘hot’ shale interval, and above it. It is therefore apparent that, in general terms, a large number of specimens should always be analysed in order to avoid missing these rare specimens and thus obtaining an inaccurate record of a species' range.

Plate III. Scale bars represent 100 μm on Fig. 1; 50 μm on Figs. 2, 3, 5, 7 and 8; 25 μm on Figs. 4 and 6. All material is from the E1-NC174 core, Murzuq Basin, south-western Libya. 1. 2, 3, 4, 5, 6.

7. 8.

Ancyrochitina ancyrea (Eisenack, 1931); monospecific cluster of specimens, MPK14264, 7239′6″. Ancyrochitina? sp. indet.; 2, typical specimen showing evidence of basal processes removed through damage, MPK14265, 7266′7½″. 3, specimen showing basal processes resembling those of Ancyrochitina porrectaspina Nestor, 1994, MPK14266, 7239′6″. 4, detail of Fig. 3 showing nature of the processes. 5, specimen showing mace-like basal processes, MPK14267, 7283′7″. 6, detail of Fig. 5 showing nature of the processes. 7. Plectochitina pseudoagglutinans (Taugourdeau, 1963); MPK14268, 7238′3″. 8. Plectochitina cf. pseudoagglutinans sensu (Taugourdeau, 1963); MPK14269, 7287′11–11½″.

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Genus Fungochitina Taugourdeau, 1966 Type species: Conochitina fungiformis Eisenack, 1931; p. 89, pl. 2, Fig. 17 (specimen is lost, according to Paris et al., 1999). Neotype = Conochitina fungiformis subsp. spinifera Eisenack, 1962; p. 310, pl. 14, Fig. 15 (proposed by Paris et al., 1999). Fungochitina sp. A Plate V, 1 Material: 71 flattened specimens, recovered from samples below the ‘hot’ shale interval. Description: The vesicle chamber is conical, with a rounded basal margin, and a concave base (inferred through its inward flattening). The flanks are convex, or weakly concave in rare instances, and possess a conspicuous flexure with a slight shoulder. The neck is cylindrical, flaring slightly towards the aperture. The vesicle surface bears a characteristic ornamentation of long, thick simple spines that are randomly distributed over the entire vesicle surface. The spines measure c. 5–11 μm in length, and c. 1–2.5 μm in diameter. Larger, more robust spines occur around the basal margin, and may display distal bifurcation. No basal features are discernible, due to the inward flattening of the base in all instances. Dimensions: See Table 13. Table 13 Biometric data for Fungochitina sp. A, based upon nine flattened specimens, recovered from the E1-NC174 core. All measurements are in micrometres (μm).

Mean Maximum Minimum

L

ln

lc

D

da

dn

121 134 106

50 61 32

71 86 50

77 87 70

39 45 30

35 40 27

Remarks: Although the specimens recovered from the E1-NC174 core possess large basal spines that could suggest an assignation to the genus Ancyrochitina, it was considered herein that the spinose ornamentation was a more characteristic feature, and combined with the conical shape of the vesicle, the specimens were therefore assigned to Fungochitina. Fungochitina sp. A is distinct from other species of Fungochitina by the nature of its long spinose ornamentation. Belonechitina arabiensis Paris and Al-Hajri, 1995 bears some similarity, but it differs through less pronounced flexure, and the spines being defined as less than 4 μm in length. Fungochitina sp. B Plate V, 2 Material: 27 flattened specimens, recovered from samples above, within the top of, and questionably below, the ‘hot’ shale interval. Description: The vesicle chamber is conical, with a sharply rounded basal margin, and a concave base (inferred through its inward flattening). The flanks are weakly concave to weakly convex, and possess a conspicuous flexure with a very slight shoulder. The neck is wide, cylindrical, and does not appear to flare towards the aperture. The vesicle surface bears a characteristic ornamentation of simple spines that are randomly distributed over the entire vesicle surface, but are less developed on the neck. The spines measure c. 5–7.5 μm in length, and c. 0.6–1 μm in diameter. The spines may be partially or almost completely removed by damage, leaving some specimens virtually smooth. No basal features are discernible, due to the inward flattening of the base in all instances. Dimensions: See Table 14.

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Table 14 Biometric data for Fungochitina sp. B, based upon nine flattened specimens, recovered from the E1-NC174 core. All measurements are in micrometres (μm).

Mean Maximum Minimum

L

ln

lc

D

da

dn

106 121 94

52 65 43

55 63 47

87 97 82

40 43 33

37 40 32

Remarks: Fungochitina sp. B differs from Fungochitina sp. A as the former has a short, sharply conical chamber, wide non-flaring neck, and lacks the basal processes of the latter. It differs from other species of Fungochitina through the same criteria. Although the majority of specimens recovered from the E1-NC174 core possess the characteristic spinose ornamentation, many show a partial or almost complete removal of spines, presumably through post-depositional damage. A similar phenomenon was illustrated by Butcher (2009, pl. 2, Figs. 3–6, 10) for Belonechitina pseudarabiensis Butcher, 2009. The removal of distinctive ornamentation can result in problems of identification, although Fungochitina sp. B has a characteristic vesicle shape. Subfamily Cyathochitininae Paris, 1981 Genus Cyathochitina Eisenack, 1955b emend. Paris et al. (1999) Type species: Conochitina campanulaeformis Eisenack, 1931; p. 86, pl. 2, Fig. 2 (specimen is lost, according to Paris et al., 1999). Neotype = Conochitina campanulaeformis Eisenack; Eisenack (1962) p. 297, pl. 14, Fig. 5. Cyathochitina campanulaeformis (Eisenack, 1931) Plate V, 3 Holotype: Conochitina campanulaeformis Eisenack, 1931; p. 86, pl. 2, Fig. 2. Material: 123 flattened specimens, recovered from samples below, within, and above the ‘hot’ shale interval. Description: The vesicle chamber is conical, with a cylindrical neck. The basal margin is sharp to rounded, with a flat to concave base. There is a distinct flexure, and the flanks may be straight to slightly convex, with a slight to inconspicuous shoulder. The neck is cylindrical, and does not flare towards the unadorned aperture. The surface is smooth to weakly granulate, occasionally bearing sporadic tubercules (less than 2 μm in height). A carina occurs at the basal margin, and varies from being distinct (5–7 μm wide), to a simple thickening of the basal margin. A basal scar of low, concentric circular shape occurs on the base; no mucron is present. Dimensions: See Table 15.

Table 15 Biometric data for Cyathochitina campanulaeformis (Eisenack, 1931), based upon three flattened specimens, recovered from the E1-NC174 core. All measurements are in micrometres (μm).

Holotype Butcher (2009) Mean Maximum Minimum

L

ln

lc

D

da

dn

275 132–318 250 254 242

101 – 112 121 106

174 – 138 146 132

168 69–243 170 175 166

60 33–100 74 76 72

– – 69 73 63

Plate IV. Scale bars represent 50 μm on Figs. 1, 3, 5, 7 and 8; 25 μm on Figs. 2 and 4; 10 μm on Figs. 6 and 9. All material is from the E1-NC174 core, Murzuq Basin, south-western Libya. 1, 2, 3, 4. 5, 6, 7, 8, 9.

Plectochitina sp. indet.; 1, specimen showing short basal processes, MPK14270, 7287′11–11½″. 2, detail of Fig. 1, showing nodular nature of processes. 3, specimen showing long basal processes, MPK14271, 7239′6″. 4, detail of Fig. 3, showing nodular nature of processes. Angochitina seurati, Paris, 1988b; 5, typical specimen, showing partial preservation of pilose ornamentation, MPK14272, 7237′2″. 6, detail of Fig. 5, showing the nature of the surface ornamentation. 7, specimen from the lower part of the core, MPK14273, 7289′4″. 8, specimen showing better preservation of pilose ornamentation, MPK14274, 7237′2″. 9, detail of Fig. 8, showing detail of the surface ornamentation.

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Remarks: Cyathochitina campanulaeformis differs from Cyathochitina kuckersiana (Eisenack, 1934) as the latter displays a wide, thin carina, and generally concave flanks. Cyathochitina calix (Eisenack, 1931) is differentiated through its more elongate vesicle, having an L:D ratio of 2.2–2.5:1. C. campanulaeformis is one of the most common chitinozoans in mid Ordovician to early Llandovery strata and, therefore, many specimens have been illustrated and described in the literature, hence a detailed synonymy has not been included herein. Butcher (2009) conducted a detailed analysis of 356 specimens of C. campanulaeformis sensu stricto, and possible synonymous forms, recovered from Rhuddanian strata in Jordan. The study revealed a very wide range of intraspecific variation, with end-members linked through a series of intermediary forms, that encompass the difference between the specimens recovered from the E1-NC174 core, and the holotype of Eisenack (1931). A summary of the biometric measurements recorded by Butcher (2009) is provided in Table 15. Cyathochitina kuckersiana (Eisenack, 1934) Plate V, 4 Holotype: Conochitina kuckersiana Eisenack, 1934; p. 62, pl. 4, Fig. 14. Material: 14 flattened specimens, recovered from samples below and above the ‘hot’ shale interval. Description: The vesicle chamber is conical, with a cylindrical neck. The basal margin is sharp, with a flat base. The ratio L:D is between c. 1.1 and 1.5:1. There is a distinct flexure, and the flanks are straight to concave, with a slight to inconspicuous shoulder. Faint longitudinal ribbing (in relation to the axis of symmetry) is often observed on the neck and flexure. The neck is cylindrical, and flares very slightly towards the unadorned aperture. The surface is smooth to weakly granulate, with some weak radial ribs apparent on the anti-apertural part of the chamber. A wide (c. 18–25 μm), thin carina occurs at the basal margin. A concentric circular basal scar may occur. Dimensions: See Table 16.

Table 16 Biometric data for Cyathochitina kuckersiana (Eisenack, 1931), based upon a single flattened specimen typical of the taxon, recovered from the E1-NC174 core. All measurements are in micrometres (μm).

Holotype Butcher (2009) Typical specimen

L

ln

lc

D

da

dn

L/D

356 169–279 236

178 – 108

178 – 128

211 124–231 152

56 52–89 62

– – 59

1.69 1.08–1.69 1.55

Remarks: Cyathochitina kuckersiana differs from Cyathochitina campanulaeformis (Eisenack, 1931) in the presence of a wide carina, and often concave flanks. Cyathochitina calix (Eisenack, 1931) lacks the wide carina, and displays a much more elongate chamber (L:D=2.2–2.5:1). A wide range of intraspecific variation was reported by Butcher (2009) for C. kuckersiana, as for C. campanulaeformis (see above). The holotype of Eisenack (1934) shows a very long vesicle length, but the overall proportions and defining characteristics are the same as for the specimens from the E1-NC174 core. Subfamily Lagenochitininae Paris, 1981 Genus Lagenochitina Eisenack, 1931 emend. Paris et al. (1999)

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Type species: Lagenochitina baltica Eisenack, 1931; p. 80, pl. 1, Fig. 1 (specimen is lost, according to Paris et al., 1999). Neotype = Lagenochitina baltica Eisenack, 1959; p. 2, pl. 3, Fig. 6. Lagenochitina sp. A Plate V, 5 Material: 19 flattened specimens, recovered from samples below the ‘hot’ shale interval. Description: The vesicle chamber is claviform, with a cylindrical neck that flares slightly at the aperture. The basal margin is broadly rounded, with a convex base. There is a distinct but gentle flexure, and the flanks are weakly convex, with a slight to inconspicuous shoulder. The vesicle surface is smooth to weakly granulate (with tubercules less than 2 μm in height), No basal features are apparent. Dimensions: See Table 17. Table 17 Biometric data for Lagenochitina sp. A, based upon three flattened specimens, recovered from the E1-NC174 core. All measurements are in micrometres (μm).

Mean Maximum Minimum

L

ln

lc

D

da

dn

L/D

237 246 232

94 108 83

144 156 127

92 99 85

52 56 46

44 45 43

2.59 2.73 2.38

Remarks: Lagenochitina sp. A is differentiated from Lagenochitina sp. B herein as the latter has a shorter, more ovoid to spherical chamber, and a thinner neck. From other specimens of Lagenochitina, it differs through its characteristic claviform chamber. Although only a relatively small number of specimens were recovered from the E1-NC174 core, and fewer still studied biometrically (largely due to damage to the neck of specimens), a range of intraspecific variation is apparent, in terms of the angle of the flanks of the chamber. Although the specimens all possess a claviform chamber, some display flanks that taper more sharply, creating a slightly shorter chamber. These shorter-chambered specimens, however, are still distinct from specimens of Lagenochitina sp. B herein, due to their claviform rather than ovoid to spherical chamber. Lagenochitina sp. B Plate V, Fig. 6 Material: 141 flattened specimens, recovered from samples below, and questionably within, the ‘hot’ shale interval. Description: The vesicle chamber is spherical to ovoid, with a cylindrical neck that flares slightly at the aperture. The basal margin is inconspicuous, with a convex base. There is a distinct but gentle flexure, and the flanks are strongly convex, with a slight to inconspicuous shoulder. The vesicle surface is smooth to weakly granulate (with tubercules less than 2 μm in height), No basal features are apparent. Dimensions: See Table 18. Remarks: Lagenochitina sp. B is differentiated from Lagenochitina sp. A herein as the latter has a claviform chamber, and a wider neck. From other specimens of Lagenochitina, it differs through the characteristic shape of its chamber. Damage has often occurred to the necks of the specimens of Lagenochitina sp. A recovered from the E1-NC174 core, possibly due to a thin vesicle wall and/or thinning at the aperture (due to an inconspicuous collarette).

Plate V. Scale bars represent 50 μm on all figures. All material is from the E1-NC174 core, Murzuq Basin, south-western Libya. 1. 2. 3. 4. 5. 6. 7, 8.

Fungochitina sp. A; MPK14275, 7287′11–11½″. Fungochitina sp. B; MPK14276, 7244′2″. Cyathochitina campanulaeformis (Eisenack, 1931); MPK14277, 7239′6″. Cyathochitina kuckersiana (Eisenack, 1934); MPK14278, 7239′6″. Lagenochitina sp. A; MPK14279, 7293′10″. Lagenochitina sp. B; MPK14280, 7270′10″. Sphaerochitina palestinaense Grahn et al., 2005; 7, MPK14281, 7238′3″. 8, detail of Fig. 7, showing the nature of the chamber surface.

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Table 18 Biometric data for Lagenochitina sp. B, based upon nine flattened specimens, recovered from the E1-NC174 core. All measurements are in micrometres (μm).

Mean Maximum Minimum

L

ln

lc

D

da

dn

203 239 170

112 154 72

91 110 69

87 98 67

43 56 34

37 45 30

Genus Sphaerochitina Eisenack, 1955a emend. Paris et al. (1999) Type species: Lagenochitina sphaerocephala Eisenack, 1932; p. 271, pl. 12, Fig. 14 (specimen is lost, according to Paris et al., 1999). Neotype= Sphaerochitina sphaerocephala (Eisenack, 1955a; p. 162), pl. 1, Fig. 6. Sphaerochitina palestinaense Grahn et al., 2005 Plate V, 7–8 .1985 Sphaerochitina sp. B Hill et al.; pl. 14, pl. 1, Figs. 11a–b. .2000 Sphaerochitina sp. B Grahn et al.; pl. 3, Fig. 10. .2001 Sphaerochitina sp. B Le Hérissé et al.; pl. 3, Fig. 9. *2005 Sphaerochitina palestinaense Grahn et al.; p. 189, pl. 1, Figs. 10–11. Holotype: Sphaerochitina palestinaense Grahn et al., 2005; pl. 1, Fig. 10. Material: 91 flattened specimens, recovered from samples above, and questionably within the top of, the ‘hot’ shale interval. Description: The vesicle chamber is spherical to ovoid, with a long cylindrical neck that flares into a collarette at the aperture, which may be finely denticulate. The basal margin is inconspicuous, with a convex base. There is a distinct but gentle flexure with a slight to inconspicuous shoulder. The vesicle surface is covered with small tubercules less than 2 μm in height, that are often better developed on the chamber. No basal features are apparent. Dimensions: See Table 19.

Table 19 Biometric data for Sphaerochitina palestinaense Grahn et al., 2005, based upon fourteen flattened specimens, recovered from the E1-NC174 core. All measurements are in micrometres (μm).

Holotype Type material Mean Maximum Minimum

L

ln

lc

D

da

dn

L/D

234 223–384 222 293 190

140 – 126 162 104

94 – 90 120 71

55 75–117 68 84 60

55 50–67 44 57 35

– – 32 40 25

4.25 – 3.25 4.59 2.64

Remarks: Sphaerochitina palestinaense is differentiated from other species of Sphaerochitina by its long neck and pronounced collarette. The specimens of Sph. palestinaense recovered from the E1-NC174 core show remarkably close biometric values with the type material, except that they possess a slightly wider maximum diameter. Grahn et al. (2005, p. 192) provided both raw and artificially restored measurements, and the former were used for comparison herein: it is thus interpreted that there is a small degree of intraspecific variation in the chamber diameter, while all other characteristics remain stable. Due to the thin membranous nature of the prominent collarette it is prone to damage, and therefore an exact value for the maximum length of the vesicle in many specimens recovered from the E1-NC174 core could not be determined. Sphaerochitina solutidina Paris, 1988b Plate VI, 1−2 ?1985 Sphaerochitina sp. A Hill et al.; pl. 12, 10a–b; pl. 14, Figs. 9a–b, 13.

?*1988b Sphaerochitina solutidina Paris.; p.78, pl. 12, Figs. 7, 8a–b. ?2000 Sphaerochitina solutidina Paris.; Grahn et al., pl. 3, Fig. 8. ?2005 Sphaerochitina solutidina Paris.; Grahn et al., pl. 1, Fig. 9. ?2006 Sphaerochitina solutidina Paris.; Grahn, Fig. 5f [cop. Grahn et al., 2000, pl. 3, Fig. 8]. Holotype: Sphaerochitina solutidina Paris, 1988b; pl. 12, Fig. 8a. Material: 123 flattened specimens, recovered from samples below and above the ‘hot’ shale interval. Description: The vesicle chamber is spherical to ovoid, with a cylindrical neck that flares towards the aperture, which may be finely denticulate. The basal margin is inconspicuous, with a convex base. There is a distinct but gentle flexure with a slight to inconspicuous shoulder. The vesicle surface is covered with small tubercules less than 2 μm in height, and c. 1–2 μm diameter, that are often better developed on the chamber. No basal features are apparent. Dimensions: See Table 20.

Table 20 Biometric data for Sphaerochitina solutidina Paris, 1988b?, based upon four flattened specimens, recovered from the E1-NC174 core. All measurements are in micrometres (μm).

Holotype Type material Mean Maximum Minimum

L

ln

lc

D

da

dn

134 105–178 138 161 119

54 – 64 72 57

80 – 73 88 60

77.00 64–94 78.00 84.00 73.00

38.00 28–49 42.00 49.00 36.00

– – 35.00 42.00 29.00

Remarks: Sphaerochitina solutidina is differentiated from other species of Sphaerochitina by its very small, dense ornamentation, and short neck (relative to Sphaerochitina sphaerocephala). The specimens recovered from the E1-NC174 core do not possess such a fine or densely spaced ornamentation as the type material of Paris (1988b). Paris (1988b, p. 78) gives a diameter for the tubercules of 0.5 μm, densely spaced with up to 80–100 tubercules per 100 μm 2, which does not match that of the specimens from the E1-NC174 core: open nomenclature is thus retained. Chitinozoa gen. et. sp. indet. Plate VI, 3–5 Material: 3395 flattened specimens, recovered from samples throughout the E1-NC174 core. Description: The specimens display a wide range of vesicle chamber shape, and bear affinities to both the Conochitinidae and Lagenochitinidae, but remain unidentifiable due to severe damage, adhesion of AOM, or a combination of the two. Some surface ornamentation may be observed, but in all cases does not allow for confident identification at either the generic or species level. Dimensions: Dimensions are not provided for specimens assigned to Chitinozoa gen. et. sp. indet., as these would be of little value. A very wide range of dimensions is observed in the specimens. Remarks: Open nomenclature is retained at the suprageneric level due to the absence of any characteristic morphological features. Those specimens that possessed an indication of basal processes, and a conspicuous flexure, were assigned to Ancyrochitina? sp. indet. The abundance of AOM in all of the samples studied from the E1-NC174 core is attributed as the main cause for such a large number of specimens assigned to Chitinozoa gen. et sp. indet. Specimens that do not have AOM adhering to them are generally very well preserved, while specimens with large amounts of AOM adhering to them are most often unidentifiable (see pl. VI, Figs. 3–4). The AOM is very strongly adhering to those specimens that it covers, and cannot be easily separated from them without causing severe damage.

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6. Chitinozoan biostratigraphy of the E1-NC174 core 6.1. Previous chitinozoan studies from Libya As stated in the Introduction, the number of previous chitinozoan studies published on Llandovery strata in northern Gondwana is rather limited compared to other parts of the geological column. Of the taxa recorded from the E1-NC174 core, only two species are cosmopolitan, Belonechitina postrobusta and Conochitina elongata, with the remaining taxa not having been recorded outside of northern and western Gondwana (see Table 21, and occurrences listed below in Section 6.2). The occurrence of Sphaerochitina palestinaense and Sphaerochitina solutidina in Libya, Paraguay and Brazil suggests a strong faunal affinity between northern and western Gondwana during the early Llandovery. Florentin Paris undertook the first studies of chitinozoans from the subsurface of Libya, in papers recording Ordovician, Silurian and Devonian occurrences (Molyneux and Paris, 1985; Hill et al., 1985; Paris et al., 1985 respectively). As these were the first investigations in the area, many species were retained in open nomenclature, and were later reassessed and analysed systematically by Paris (1988a, 1988b). However, certain taxa were recognised by Paris in Hill et al. (1985) as existing species, most notably ‘Belonechitina postrobusta?’ and Ancyrochitina laevaensis, both identified as early Rhuddanian species by Nestor (1980a), and Plectochitina pseudoagglutinans and ‘Conochitina edjelensis elongata’, recorded from the middle to upper Llandovery of the Edjelé region of the Sahara (Taugourdeau, 1963). A. laevaensis was recorded by Paris (in Hill et al., 1985) as occurring with B. postrobusta? in well cuttings from sample 3750′–3773′ in the A1-81 core (eastern Libya), thus indicating an earliest Rhuddanian age (i.e. ascensus-acuminatus graptolite Biozone). It should be noted, however, that the sample from which they were recorded is 23 ft thick, and thus the co-occurrence of the two species may not be accurately represented. The absence of A. laevaensis in samples containing B. postrobusta in the E1-NC174 core may reflect the poor preservation potential of their processes (see discussion on chitinozoan preservation in Section 4). Hill et al. (1985) did not erect any biozones based upon the chitinozoan, miospore, and acritarch data from their study, but rather suggested ‘maximum age ranges’ for three of the cores studied, ranging from the uppermost Ordovician to the lower Telychian (see their Fig. 8). Paris (1988a, 1988b), however, performed more detailed sampling of five wells from north-eastern Libya (A1-81, A1-46, D1-31, E1-81 and I1C-81), and with the incorporated data of Hill et al. (1985), identified chitinozoan taxa indicative of an early Rhuddanian to late Telychian age. Three new species of chitinozoan, Angochitina seurati, Sphaerochitina solutidina, and Spinachitina libyensis, were erected by Paris (1988b) from early Silurian samples, all of which were previously recorded and illustrated but retained in open nomenclature by Hill et al. (1985). Due to the increased sampling density and based on a systematic review of the taxa, Paris (1988a) erected four local concurrent-range chitinozoan biozones for the Llandovery in north-eastern Libya (see his Fig. 8). The Conochitina vitrea-Spinachitina libyensis Biozone was erected for lowermost Rhuddanian strata (A1-81, E1-81 and I1C-81 wells), the Angochitina seurati–Plectochitina pseudoagglutinans Biozone for the middle Rhuddanian (E1-81 and I1C-81 wells), the Conochitina armillata-Cyathochitina sp. B Biozone for the upper Aeronian to lowermost Telychian (D1-31 well), and the Margachitina margaritana–Pterochitina deichaii Biozone for the middle to upper Telychian (A1-46 well). Paris (1988a, p. 65) stated, however, that ‘the available samples were too widely spaced with regard to the total thickness of the Llandoverian succession in northeast Libya… [and] do not constitute the complete sequence of biozones…The chitinozoan biozonation of the Llandovery of northeast Libya is still therefore provisional’.

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The A. seurati–P. pseudoagglutinans Biozone of Paris (1988a) was limited to one core sample in the E1-81 well, and one side-wall core in the I1C-81 well, but was recognised by Paris (1988a, p. 67) as being ‘useful for biostratigraphical purposes since A. seurati…has a restricted range, and its distinctive morphology makes it easy to recognize’. Indeed, the distinctive morphology of the species allowed it to be recognised in samples from the E1-NC174 core, although its range was rather longer in the core than in those studied by Paris (1988a): this increased range is not unexpected, due to his record of the species being from only two samples. Of the chitinozoan assemblage within the A. seurati–P. pseudoagglutinans Biozone of Paris (1988a), Angochitina seurati, Plectochitina pseudoagglutinans and Sphaerochitina solutidina are all species that were recorded from the E1-NC174 core also. Paris et al. (2012) conducted a palynological and palynofacies analysis of the Tanezzuft Formation shales from the CDEG-2a core, eastern Murzuq Basin, Libya. On the basis of chitinozoans and acritarchs, the strata therein were dated to the Rhuddanian−early Aeronian, with part of the fragilis and the nuayyimensis chitinozoan biozones recognised. However, within their paper Paris et al. (2012) did not record any specimens of Belonechitina postrobusta, nor a gamma-ray peak within the Rhuddanian: the significance of this will be discussed further below. Outside of Libya, those studies of early Silurian strata in Saudi Arabia (McClure, 1988; Paris et al., 1995; Al-Hajri and Paris, 1998), Jordan (Butcher, 2009), Iran (Ghavidel-Syooki, 2000; Ghavidel-Syooki and Winchester-Seeto, 2004; Ghavidel-Syooki and Vecoli, 2007), the Sahara region (Taugourdeau and de Jekhowsky, 1960; Taugourdeau, 1962, 1963), and Brazil and Paraguay (Grahn et al., 2000; Le Hérissé et al., 2001; Grahn et al., 2005; Grahn, 2006) all recorded taxa that were also recovered from the E1-NC174 core. Details of these taxa, and the ages assigned to them by the authors, are discussed below. 6.2. Recorded occurrences of taxa recovered from the E1-NC174 core Below are detailed previous records of those taxa recovered from the E1-NC174 core that allow direct comparison, based upon data in the published literature. Fig. 4 shows the range and approximate abundance of each taxon recovered in the E1-NC174 core, with absolute and relative abundance data for each sample depth presented in the Supplementary Material (Tables SM1 and SM2). 6.2.1. Belonechitina postrobusta (Nestor, 1980a) Stratigraphical range: Rhuddanian. B. postrobusta is restricted to the Rhuddanian, thus making it an important taxon in the recognition of earliest Llandovery strata. Indeed, according to Soufiane and Achab (2000, p. 98), ‘B. postrobusta is a widespread species occurring in the high latitude…as well as in the low latitude regions…and is not apparently influenced by environmental factors’. Given the species' stratigraphical importance, details of the most important previous records are provided below. • Martin (1974): ascensus-acuminatus to lowermost vesiculosus graptolite biozones; Deerlijk Fm, Deerlijk 404 well, southern Brabant Massif, Belgium. Martin (1974) recorded specimens recovered from the Deerlijk 404 well that she assigned to Conochitina (now Belonechitina) robusta, and that were later synonymised with B. postrobusta by Nestor (1990, p. 82). Martin's (1974) study is particularly useful in that her samples were the subject of a detailed graptolite study (Maletz, 1999). The samples shown to yield B. postrobusta by Martin (1974) were assigned to the ascensus-acuminatus and lowermost vesiculosus graptolite biozones by Maletz (1999), based upon the presence of all three index species, as well a diverse assemblage of associated graptolite species. Martin (1974) recorded

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a peak relative abundance of >20% for B. postrobusta in the vesiculosus Biozone, as compared with 1–5 and 5–20% in the underlying ascensus-acuminatus Biozone. Grahn (1978, 1998): ascensus-acuminatus to cyphus graptolite biozones; Rastrites Shale, Östra Tommarp section and Södra Sandby boring, southern Sweden. Grahn (1978, p. 11) recorded specimens of Conochitina (now Belonechitina) robusta (synonymised with B. postrobusta by Nestor, 1990) from strata referred to as being from the ‘Zone of Glyptograptus persculptus’. Grahn (1998) recorded the occurrence of both graptolites and chitinozoans from the same strata as previously studied by Grahn (1978), but provided no illustrations or descriptions of the taxa (hence omission from the synonymy list herein). In Grahn (1998), B. postrobusta is recorded as occurring only with graptolites indicative of the ascensus-acuminatus, vesiculosus and cyphus graptolite biozones (e.g. P. acuminatus, D. confertus, C. vesiculosus and ‘M’. revolutus). There is no evidence supporting the earlier suggestion of Grahn (1978) that the strata belong to the persculptus graptolite Biozone, and therefore the range of B. postrobusta as recorded by Grahn (1978, 1998) is interpreted as being from the ascensus-acuminatus to cyphus biozones. Nestor (1980a): ‘O. vesiculosus zone’; lower Juruu Stage, Ikla core, Estonia. Nestor (1980a, p. 101) recorded Conochitina (now Belonechitina) postrobusta throughout the Juruu Stage of Estonia, with a peak abundance in its upper part in strata ‘probably corresponding to the O. vesiculosus zone’. Hill et al. (1985): Rhuddanian to lower Aeronian; well A1-81, Core 3, eastern Libya. Hill et al. (1985, p. 27) recorded the occurrence of B. postrobusta? in samples that they assigned to the Rhuddanian–lower Aeronian, based upon acritarch data. They state on their p. 38 that ‘Belonechitina postrobusta is restricted to the Early Llandovery’. Geng and Cai (1988): ascensus-acuminatus to vesiculosus graptolite biozones?; Yangtze region, China. Specimens recorded as Belonechitina aspera? by Geng and Cai (1988) were synonymised with B. postrobusta by Nestor (1990). Geng and Cai (1988, Fig. 2) correlated their ‘?Belonechitina aspera’ Biozone with the ascensus-acuminatus and vesiculosus graptolite biozones, although the basis of this correlation is not known. Nestor (1990, 1994): ascensus-acuminatus to vesiculosus or cyphus graptolite biozones; Juruu Stage, seventeen cores, Estonia and northern Latvia. The data in Nestor (1990) were displayed simply on a range chart, and suggested a correlation with the ascensus-acuminatus to acinaces (upper vesiculosus) graptolite biozones for B. postrobusta, based upon graptolite data that Viiu Nestor (pers. comm.), recognised as ‘a bit rough for correlation’. Nestor (1994) recorded a similar range for B. postrobusta, of ascensus-acuminatus to vesiculosus zone age, based upon the notion of Kaljo et al. (1984) that the confertus graptolite Biozone of the Baltic correlates directly with the British vesiculosus graptolite Biozone. However, Loydell et al. (2003, p. 223) discussed the fact that the diagnostic graptolites of the Baltic confertus graptolite Biozone (D. confertus and D. swanstoni), upon which the biozone was largely based, both have ranges extending into the overlying cyphus graptolite Biozone. This is extremely significant as Nestor and many subsequent authors have based their chitinozoan biozone correlations upon this partly incorrect confertus = vesiculosus correlation: in fact the confertus graptolite Biozone must be stated as being correlatable with the vesiculosus or cyphus graptolite biozones.

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Nestor (1994) recorded that the occurrence of B. postrobusta is sporadic in samples from the ascensus-acuminatus graptolite Biozone, whereas in the confertus graptolite Biozone it is abundant: this increased abundance of B. postrobusta in the vesiculosus or cyphus graptolite biozones is similar to that recorded by Martin (1974) (see above). Dufka (1992): upper ascensus-acuminatus to cyphus graptolite biozones; ‘lower Silurian’, Prague Basin, Barrandian area, Czech Republic. Dufka (1992), Table 1) recorded B. postrobusta in five samples from the Prague Basin, assigned to the acuminatus, vesiculosus and cyphus graptolite Biozones. The basis of this correlation, however, was not stated, but given the excellent graptolite record in Bohemia is likely to be correct. Dufka and Fatka (1993): upper ascensus-acuminatus to upper cyphus graptolite biozones; Želkovice Fm, Prague Basin , Czech Republic. B. postrobusta was recorded by Dufka and Fatka (1993, text-Fig. 1) in samples from the acuminatus, vesiculosus and cyphus graptolite biozones, with the correlation being based upon graptolite data from Štorch (1986). Dufka and Fatka (1993) recorded a questionable occurrence of this species from the lowermost Aeronian triangulatus graptolite Biozone, but the specimen is not described or illustrated, and therefore cannot be confirmed. Grahn (1995): cyphus graptolite Biozone; File Haidarborrningen 1 and Närborrningen 1 boreholes, Gotland. Specimens of B. postrobusta were recorded from strata assigned to the cyphus graptolite Biozone, on the basis of graptolite data provided to Grahn by Hermann Jaeger (pers. comm. 1987, 1991, in Grahn, 1995, p. 58). Geng et al. (1997): ascensus-acuminatus to cyphus graptolite biozones; Kaochiapien Fm, well N-4, Taixian, and the Lungmachi Fm, Dazhongba section, Yichang, Yangtze region, China. B. postrobusta was recorded from the vesiculosus graptolite Biozone in the Dazhongba section by Geng et al. (1997), but from strata assigned to the early Aeronian gregarius graptolite Biozone in well N-4. The age recognition of the gregarius graptolite Biozone in well N-4 was based upon the occurrence of Glyptograptus cf. sinuatus and Coronograptus gregarius in the strata by Geng et al. (1997, p. 6). However, both Rickards (1976) and Kaljo et al. (1984) record the first occurrence of both of these graptolite species as being at the base of the cyphus graptolite Biozone, and therefore within the upper Rhuddanian. A Rhuddanian age for the sample horizons in well N-4 is further corroborated by the occurrence of Plectochitina nodifera in the samples: a typically early Rhuddanian chitinozoan species (see Verniers et al., 1995). Geng et al. (1997, p. 6) indeed suggest that the specimens of both P. nodifera and B. postrobusta occurring in the gregarius graptolite Biozone are in fact reworked from older strata, and therefore not of early Aeronian age. Nestor (1999): ascensus-acuminatus and/or vesiculosus to cyphus graptolite biozones; Solvik Fm, Oslo region, Norway. Nestor (1999) recorded badly preserved specimens of B. cf. postrobusta from the lower part of the Solvik Fm. The strata were correlated with the ascensus-acuminatus and/or vesiculosus graptolite biozones, based partly upon graptolite data from Worsley et al. (1983), and by correlation of the lithological succession in Estonia (hence the expansion herein of the range to include the cyphus graptolite Biozone, based on the discussion of the confertus= vesiculosus to cyphus graptolite Biozones above). Grahn et al. (2000): ‘uppermost Rhuddanian’; Vargas Peña Fm, well RD-116, Paraná Basin, Paraguay. Grahn et al. (2000, text-Fig. 8) recorded B. postrobusta from one sample in the lower part of the RD-116 well, Paraguay, and assigned the

Plate VI. Scale bar represents 100 μm on Fig. 4, and 50 μm on Figs. 1, 2, 3 and 5. All material is from the E1-NC174 core, Murzuq Basin, south-western Libya. 1, 2. 3, 4, 5.

Sphaerochitina solutidina Paris, 1988b?; 1, MPK14282, 7290′6½″. 2, more elongate form, MPK14283, 7242′7″. Chitinozoa gen. et sp. indet.; 3, specimen showing AOM adhering to the vesicle, obscuring any diagnostic features, MPK14284, 7269′11½″. 4, ?two specimens within a cluster of AOM, MPK14285, 7277′6″. 5, damaged specimen showing pyrite framboids within the chamber and neck, MPK14286, 7238′3″.

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Fig. 4. Range charge for chitinozoan taxa recovered from the E1-NC174 core, with gamma-ray data and the ‘hot’ shale interval identified. Gamma-ray curve modified from Lüning et al. (2003, Fig. 4).

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Table 21 Summary of the palaeogeographical occurrence of the chitinozoan taxa recovered from the E1-NC174 core. Long-ranging cosmopolitan taxa have been omitted. Star indicates taxa restricted to the E1-NC174 core. NORTHERN GONDWANA Libya, E1-NC174 core Bursachitina sp. A Belonechitina postrobusta Belonechitina pseudarabiensis Clavachitina sp. A Conochitina elongata Euconochitina sp. A Spinachitina sp.A Plectochitina pseudoagglutinans Plectochitina cf. pseudoagglutinans Angochitina seurati Fungochitina sp. A Fungochitina sp. B Lagenochitina sp. A Lagenochitina sp. B Sphaerochitina palestinaense Sphaerochitina solutidina

★ ● ● ★ ●? ★ ★ ● ● ● ★ ★ ★ ★ ● ●?

Other Libyan cores

Elsewhere in northern Gondwana

South American WESTERN GONDWANA

OUTSIDE GONDWANA

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associated assemblage to a local B. postrobusta chitinozoan Biozone. The biozone was correlated to the ‘uppermost Rhuddanian’ by Grahn et al. (2000, p. 166), upon the Rhuddanian occurrence of B. postrobusta as recorded by previous authors. • Soufiane and Achab (2000): vesiculosus to cyphus graptolite biozones; Becsie Fm, Jupiter 24 mile Camp composite section, Anticosti Island, Québec, Canada. Soufiane and Achab recorded B. postrobusta from the Becsie Fm in two outcrop sections, and correlated its co-occurrence with Conochitina electa with the vesiculosus graptolite Biozone. The basis of this correlation is that in Nestor (1990, 1994), the B. postrobusta chitinozoan Biozone comprises the co-occurrence of the index species and C. electa, whereas the overlying C. electa chitinozoan Biozone is defined by the disappearance of B. postrobusta, and the abundant occurrence of C. electa. However, by incorporating the B. postrobusta correlation of Nestor (1990, 1994), Soufiane and Achab (2000) have intrinsically incorporated the error of the vesiculosus=confertus graptolite biozone correlation (as previously described). Therefore, Soufiane and Achab's (2000) correlation with the vesiculosus graptolite Biozone must be expanded to incorporate the possibility of a cyphus graptolite Zone age. • Loydell et al. (2003): lower cyphus graptolite Biozone; Remte Fm, Aizpute-41 core, Latvia. B. postrobusta was recorded in the Aizpute-41 core by Loydell et al. (2003), in which graptolite control allowed for direct correlation of the B. postrobusta chitinozoan Biozone with the lower part of the cyphus graptolite Biozone. The precise range of B. postrobusta could not be stated confidently due to a barren sequence of several metres occurring immediately below the samples containing the species. • Butcher (2009): upper ascensus-acuminatus to vesiculosus graptolite biozones; Mudawwara Fm, BG-14 core, southern Jordan. Specimens of B. postrobusta displaying a similarly large range of intraspecific variation as the material recovered in the present study were recovered by Butcher (2009) from black shale samples in Jordan. Correlation with the graptolite biozonal scheme was based upon direct evidence from the same horizons as sampled for chitinozoans: the graptolite species N. apographon and Pa. acuminatus allowed for correlation of the lower samples with the upper ascensus-acuminatus graptolite Biozone, while D. confertus, A. atavus and P. obesus allowed for correlation of the highest sample with the vesiculosus graptolite Biozone (Lüning et al., 2005; Loydell, 2007). A peak abundance for B. postrobusta was observed by Butcher (2009) in the vesiculosus graptolite Biozone sample: in the lower samples the species has a relative abundance of 2–12%, while in the highest sample

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it reaches 33%. The peak abundance of the species at this level corresponds with that observed by both Martin (1974) and Nestor (1990, 1994). 6.2.2. Belonechitina pseudarabiensis Butcher, 2009 Stratigraphical range: Lower to middle Rhuddanian. • Butcher (2009): middle ascensus-acuminatus to vesiculosus graptolite biozones; Mudawwara Fm, BG-14 and WS-6 cores, southern and eastern Jordan. B. pseudarabiensis was recorded by Butcher (2009) from the Mudawwara Fm of two boreholes in Jordan. The specimens recovered from the BG-14 core were assigned by Butcher (2009) to the upper ascensus-acuminatus and vesiculosus graptolite biozones on the basis of direct graptolite evidence (Loydell, 2007). The specimens recovered from the WS-6 core by Butcher (2009) were assigned to the lower part of the middle ascensus-acuminatus graptolite Biozone, based upon the occurrence of graptolites, including A. ascensus, recorded by Loydell (2007). The graptolite age for the WS-6 core proposed agreed with that suggested by Andrews (1991), on the basis of a graptolite assemblage that also included A. ascensus, although the graptolites recorded by Andrews (1991) are not described or illustrated, being from an unpublished Palaeoservices Ltd report by R. B. Rickards. 6.2.3. Conochitina elongata Taugourdeau, 1963? Stratigraphical range: Middle Rhuddanian–lower Telychian? Given the questionable identification of the specimens herein as C. elongata, only a summary of previous stratigraphical records of the species is provided below. The age assignations are as stated in the original publications. • • • • • • • • •

Taugourdeau (1963): middle–upper Llandovery; Sahara region. Cramer (1967): Llandovery; north-western Spain. Nestor (1980b): middle Llandovery; Estonia. Verniers (1982): upper Aeronian–lower Telychian: Belgium. Hill et al. (1985): Aeronian–lower Telychian; A1-46, D1-31, and E1-81 cores, eastern Libya. Asselin et al. (1989): middle Rhuddanian (vesiculosus–lower cyphus graptolite biozones); Québec, Canada. Dufka (1992): middle Rhuddanian–lower Telychian: Czech Republic. Paris et al. (1995): upper Aeronian–lower Telychian; central Saudi Arabia. Paris (1996): Aeronian–lower Telychian; northern Gondwana.

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• Geng et al. (1997): upper Rhuddanian–upper Telychian (cyphus, lapworthi, and insectus graptolite biozones); Yangtze region, China. • Soufiane and Achab (2000): upper Rhuddanian; Anticosti Island, Québec, Canada. • Grahn et al. (2000): Aeronian–lower Telychian; Brazil and Paraguay. • Won et al. (2002): upper Aeronian–lower Telychian; Alaska. • Grahn et al. (2005): upper Aeronian–lower Telychian; north-eastern Brazil. 6.2.4. Ancyrochitina ancyrea (Eisenack, 1931) Stratigraphical range: Ordovician?–Devonian? A. ancyrea (Eisenack, 1931) sensu stricto has been recorded in strata from the Ordovician to Devonian (Sutherland, 1994). However, as emended by Eisenack (1955a) and further restricted by Laufeld (1974), it has become a species characteristic of the Silurian, and along with Cyathochitina campanulaeformis, it is one of the most frequently recorded Rhuddanian taxa. 6.2.5. Plectochitina pseudoagglutinans (Taugourdeau, 1963) Stratigraphical range: Lowermost Rhuddanian–upper Telychian. The species is restricted to Northern Gondwana. • Taugourdeau (1963): middle–upper Llandovery; Sahara region. The age assignation of Taugourdeau (1963) is based upon correlation with the samples analysed by Taugourdeau and de Jekhowsky (1960) and Taugourdeau (1962), and is based largely upon lithostratigraphical data, due to the rarity of characteristic fossils (Taugourdeau and de Jekhowsky, 1960, p. 1205). • Cramer (1967): upper Llandovery; northern León, Spain. Cramer's (1967) age assignation was based upon Taugourdeau's (1963) record of the species. • Hill et al. (1985): middle–upper Llandovery; D1-31? and E1-81 cores, eastern Libya. Hill et al. (1985, p. 27) based their age assignation upon Taugourdeau's (1963) record of the species. • McClure (1988): earliest Rhuddanian–Aeronian; Qusaiba Mbr, Tabuk Fm, north-western Saudi Arabia. McClure (1988) recorded P. pseudoagglutinans from the Qusaiba Shale, and dates this to the convolutus graptolite Biozone (middle Aeronian) based upon the occurrence of Lituigraptus convolutus. However, the graptolite data were not described or illustrated by McClure, and the exact level from which the specimens of P. pseudoagglutinans were recovered was not stated. Lüning et al. (2005) later dated the Qusaiba shale to approximately the earliest Rhuddanian to Aeronian. Qusaiba Member graptolites from the convolutus Biozone were described by El-Khayal (1987). • Paris (1988a): lowermost Rhuddanian–upper Telychian; A1-46, A1-81, D1-31, E1-81 and I1C-81 wells, north-eastern Libya. Paris (1988a) recorded P. pseudoagglutinans from strata correlated through the occurrence of the species, and co-occurring species such as Ancyrochitina laevaensis, with the previous recorded occurrences of Nestor (1980a), Paris (1981), and Taugourdeau (1962, 1963). Paris (1988a, p. 67) erected the ‘Angochitina seurati–Plectochitina pseudoagglutinans Concurrent-Range Biozone’ based upon the overlapping ranges of the index species (with A. seurati being the younger species). The biozone was tentatively assigned to ‘part of the Rhuddanian’ by Paris (1988a, p. 67), based upon the co-occurrence of the two index species in core samples between those correlated by other chitinozoan data from previous studies (e.g. Taugourdeau, 1962; Nestor, 1980a). However, Paris (1988a) recorded a total range for P. pseudoagglutinans from the lowermost Rhuddanian to the upper Telychian, based upon its occurrence in numerous core samples. However, no description or illustrations of the species were provided by Paris (1988a, b). • Paris et al. (1995): uppermost Aeronian–lower Telychian; central

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Saudi Arabia. The total range of P. pseudoagglutinans recorded by Paris et al. (1995, Fig. 2) as being uppermost Aeronian to lower Telychian, based upon the comparison of the chitinozoan assemblage in which it occurs with those recorded in previous studies (e.g. Taugourdeau and de Jekhowsky, 1960; Dufka, 1992). The last occurrence of Cyathochitina was recorded by Paris et al. (1995, p. 84) in the strata from which P. pseudoagglutinans was recovered, and was used to suggest an upper age limit for the strata as the Telychian crispus graptolite Biozone: Cyathochitina was reported as disappearing in this biozone in Belgium by Van Grootel (unpublished PhD thesis, cited in Paris et al., 1995), but has been recorded from the Wenlock of Sweden (Grahn, 1998) (see discussion in Loydell et al., 2007). Verniers et al. (1995): middle Aeronian–upper Telychian; global. In their review of chitinozoan assemblages globally, Verniers et al. (1995, Fig. 3) provide a range for P. pseudoagglutinans of middle Aeronian–upper Telychian. Al-Hajri and Paris (1998): upper Llandovery?; Qusaiba and Sharawra members, Qalibah Fm, north-western Saudi Arabia. P. pseudoagglutinans was recorded by Al-Hajri and Paris (1998, Fig. 2) as occurring in the uppermost Qusaiba and lowermost Sharawra members in Saudi Arabia. A graptolite fauna suggesting the lower Telychian turriculatus graptolite Biozone was recorded from the middle part of the Qusaiba Mbr by Philippe Legrand (pers. comm. 1991, 1993, in Al-Hajri and Paris, 1998). Although Al-Hajri and Paris (1998) assigned an ?early Wenlock age to the base of the overlying Sharawra Mbr, from which they also recorded P. pseudoagglutinans, ‘Some reworking is not excluded for Llandovery species recorded in the Sharawra Member (e.g. Plectochitina pseudoagglutinans…’ (Al-Hajri and Paris, 1998, p. 5). Ghavidel-Syooki (2000): Aeronian–Telychian; Sarchahan Fm, Zagros Basin, southern Iran. Ghavidel-Syooki (2000) assigned an Aeronian to Telychian age to the strata yielding P. pseudoagglutinans, on the basis of a comparison of the chitinozoan fauna with previous occurrences elsewhere (Nestor, 1994; Paris et al., 1995; Verniers et al., 1995), acritarchs (GhavidelSyooki, 1997), and unpublished graptolite data. Ghavidel-Syooki and Winchester-Seeto (2004): Telychian; Sarchahan Fm, Zagros Basin, southern Iran. P. pseudoagglutinans is one of the most abundant chitinozoan taxa recorded by Ghavidel-Syooki and Winchester-Seeto (2004, Fig. 9). It occurs in strata to which they assigned a Telychian age, on the basis of graptolite data from immediately underlying strata (Rickards et al., 2000) and correlation of the chitinozoan taxa with Nestor (1994), Paris et al. (1995) and Verniers et al. (1995). Ghavidel-Syooki and Vecoli (2007): upper Aeronian?–middle Telychian?; Member I, Niur Fm, north-eastern Iran. The strata in which Ghavidel-Syooki and Vecoli (2007) recorded P. pseudoagglutinans were assigned tentatively as corresponding to the upper Aeronian to middle Telychian Eisenackitina dolioliformis chitinozoan Biozone of Verniers et al. (1995), based upon the previously described stratigraphical occurrences of the chitinozoan taxa encountered therein.

6.2.6. Plectochitina cf. pseudoagglutinans sensu (Taugourdeau, 1963) Stratigraphical range: the two previously recorded occurrences of P. cf. pseudoagglutinans (as defined herein) were not differentiated from the occurrence of P. pseudoagglutinans by their authors, and therefore the stratigraphical range of P. cf. pseudoagglutinans outside of the E1-NC174 core is from the middle to upper Llandovery (Taugourdeau, 1963; Hill et al., 1985). 6.2.7. Angochitina seurati Paris, 1988b Stratigraphical range: middle Rhuddanian? to lower Telychian?

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Angochitina seurati has a very limited palaeogeographical and stratigraphical occurrence, having been reported only from Libya (Hill et al., 1985; Paris, 1988a, 1988b) and Saudi Arabia (Paris et al., 1995). • Hill et al. (1985): middle–upper Llandovery; E1-81 core, eastern Libya. Angochitina seurati (as Angochitina sp. A) was recorded by Hill et al. (1985, p. 27) from one sample in the E1-81 core, where it was noted as ‘abundant’. The co-occurrence of the taxon with species such as Plectochitina pseudoagglutinans and Conochitina elongata, that were recorded by Taugourdeau (1963) from the ‘middle and upper Llandovery’, was used as the basis for the age assignation of Hill et al. (1985). • Paris (1988a, 1988b): ‘part of the Rhuddanian’; E1-81 and I1C-81 wells, north-eastern Libya. Angochitina seurati and Plectochitina pseudoagglutinans were used as the index species of a concurrent range biozone erected for the strata studied in Libya by Paris (1988a, 1988b) (see discussion above for P. pseudoagglutinans). The biozone was recognised from only one sample in each of the E1-81 and I1C-81 wells, and no direct biostratigraphical control was available. The biozone was thus ‘tentatively referred to part of the Rhuddanian, since typical Aeronian chitinozoan species are still lacking’ (Paris, 1988a, p. 67). A lack of samples from between the first evidence of the Angochitina seurati–Plectochitina pseudoagglutinans chitinozoan Biozone and the last occurrence of index taxa from the preceding Conochitina vitrea-Spinachitina libyensis chitinozoan Biozone resulted in a stratigraphical gap of 200 ft in the I1C-81 well, and 262 ft in the E1-81 well, thus further impeding age constraint of the biozone. • Paris et al. (1995): vesiculosus graptolite Biozone?; central Saudi Arabia. The range of Angochitina seurati was given by Paris et al. (1995, Fig. 2) as being entirely within their Lagenochitina nuayyimensis Total Range chitinozoan Biozone. According to Paris et al. (1995, p. 83) independent graptolite control was available for the L. nuayyimensis chitinozoan Biozone, in the form of ‘Graptolite assemblages belonging to the local Neodiplograptus africanus Saharan zone, and referred to the acinaces Zone by P. Legrand (pers. commun. 1992)’. In the same personal communication, Philippe Legrand also suggested that the biozone may begin as early as the atavus (= lower vesiculosus) graptolite Biozone (Paris et al., 1995, p. 83). No details of the graptolite species used for this correlation were provided, as the subsurface graptolite material from Saudi Arabia was ‘still under study’. Paris et al. (1995, p. 82), did state that ‘any age assignment proposed here for the local chitinozoan biozones of subsurface Llandovery material from central Saudi Arabia must be regarded as tentative’, due to their acknowledgement that age assignment is ‘based upon indirect evidence, i.e. local graptolite control or by comparison with well controlled chitinozoan bearing sequences’. • Verniers et al. (1995): cyphus graptolite Biozone; global. Verniers et al. (1995, p. 654) recorded Angochitina seurati as occurring in their ‘Conochitina electa Biozone’, in which it occurs in the same time interval as Belonechitina postrobusta. The C. electa chitinozoan Biozone was correlated by Verniers et al. (1995) with the upper Rhuddanian cyphus graptolite Biozone, on the basis of the first record of C. electa being from the lower part of this graptolite biozone. There is thus a conflict in terms of the age range provided for Angochitina seurati between that of Paris et al. (1995) and Verniers et al. (1995), who defined the B. postrobusta chitinozoan Biozone (below the C. electa chitinozoan Biozone) on the basis of the confertus=vesiculosus biozonal graptolite correlation (see previous discussion under ‘Remarks’ for B. postrobusta). It would therefore be assumed that, as Verniers et al. (1995, p. 654) cited Paris et al.'s (1995) data for the occurrence of Angochitina seurati, that the species' occurrence in the vesiculosus graptolite Biozone (described above) would be recognised, as would its inclusion in the B. postrobusta

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chitinozoan Biozone. The confertus graptolite Biozone, however, was shown by Loydell et al. (2003) to correlate with the vesiculosus or cyphus graptolite biozones, and therefore this revision may account for the occurrence of Angochitina seurati in both of these graptolite biozones, although this was not recognised by Verniers et al. (1995). 6.2.8. Cyathochitina campanulaeformis (Eisenack, 1931) Stratigraphical range: Middle Ordovician to ?late Telychian. C. campanulaeformis is recorded from strata ranging in age from the Llanvirn to the late Llandovery (see Jenkins, 1969; Laufeld, 1971; Grahn, 1981a, 1981b; Mullins and Loydell, 2001), and a review of its range is therefore not provided herein. The genus Cyathochitina was recorded as having a highest occurrence in the lower part of the crispus graptolite Biozone of Telychian age in Belgium (Van Grootel, unpublished PhD thesis cited in Paris et al., 1995), although specimens identified as Cyathochitina sp. aff. campanulaeformis were recorded by Grahn (1998) from Sweden, in strata stated therein to be not older than Wenlock in age. Cyathochitina campanulaeformis was also questionably recorded by Nestor (1994), Table 1) in Estonia and North Latvia, from her Angochitina longicollis chitinozoan Biozone. This biozone was correlated therein to the turriculatus, crispus, griestonensis and the lowermost spiralis graptolite biozones, indicating an early to late Telychian age. 6.2.9. Cyathochitina kuckersiana (Eisenack, 1934) Stratigraphical range: Middle Ordovician to lower Llandovery. C. kuckersiana has almost as long a range as C. campanulaeformis, and a large number of recorded occurrences, but is less well represented in Silurian strata (see Jenkins, 1970; Grahn, 1981a, 1981b; Nestor, 1994). 6.2.10. Sphaerochitina palestinaense Grahn et al., 2005 Stratigraphical range: Upper Rhuddanian to upper Telychian? Sphaerochitina palestinaense has a limited recorded occurrence, described below. • Hill et al. (1985): upper Aeronian–lowermost Telychian; D1-31 well, north-eastern Libya. Sph. palestinaense (as Sphaerochitina sp. B) was recorded by Hill et al. (1985, p. 27) from two samples in the D1-31 well, that they assigned to the upper Aeronian to lowermost Telychian, based upon correlation of co-occurring chitinozoan species (e.g. Plectochitina pseudoagglutinans, Conochitina elongata) with the material of Taugourdeau (1963) (as described previously herein). The upper limit of the range of Sph. palestinaense was further limited by Hill et al. (1985, p. 27) based on the absence of specimens of the genus Cyathochitina (see previous discussion). However, the higher of the two samples containing Sph. palestinaense does not contain Cyathochitina spp. (according to Hill et al., 1985, p. 27), and could therefore be younger. Paris (1988a, p. 67) noted, however, that specimens of the genus Cyathochitina are known to be rare in coeval strata, and thus retained an earliest Telychian age for both samples. • Grahn et al. (2000): upper Rhuddanian–Telychian; Vargas Peña and Cariy formations, RD-116 well, Paraná Basin, Paraguay. Sph. palestinaense (as Sphaerochitina sp. A) was recorded by Grahn et al. (2000) in the lowest sample with B. postrobusta. According to Grahn et al. (2000, p. 166), the total range of B. postrobusta is restricted to the ‘uppermost Rhuddanian’ in the Paraná Basin, and thus this also serves as the earliest age for the occurrence of Sph. palestinaense. The Aeronian–early Telychian age was suggested by Grahn et al. (2000, p. 166) on the basis of the occurrence of Sph. palestinaense in their Conochitina elongata chitinozoan Biozone, the index species of which they correlated with previous records to this age. • Le Hérissé et al. (2001): upper Aeronian–lower to middle Telychian; Tianguá Fm, Serra Grande Group, 2-SL-1-MA well, northern Brazil.

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Le Hérissé et al. (2001) recorded Sph. palestinaense (as Sphaerochitina sp. A) from well cuttings of the Tianguá Fm in the 2-SL-1-MA core. The Tianguá Fm was dated by Le Hérissé et al. (2001, p. 31) as ‘late Aeronian – early–middle Telychian’, based upon the ‘lack of late Telychian species [of chitinozoan]…that commonly occur in the Amazon and Paraná Basins, and absence of species diagnostic for the Rhuddanian (e.g. Belonechitina postrobusta) and early Aeronian’. A ‘middle or earliest late Llandovery’ age for the Tianguá Fm was also suggested by Le Hérissé et al. (2001, p. 25), based upon the identification of Climacograptus cf. scalaris scalaris from core 52 of the 1-BJ-1-PA well (Hermann Jaeger, pers. comm. in Le Hérissé et al., 2001). • Grahn et al. (2005): upper Aeronian–lower Telychian; Upper Ipu, Tianguá, and lower Jaicós formations, 1-BJ-1-PA, 1-FM-1-MA, 2-PM-1-MA, 1-PD-1-MA, 9-PAF-7-MA, 2-Sl-1-MA and 1-PA-1-MA wells, Parnaíba Basin, north-eastern Brazil. Sph. palestinaense was erected by Grahn et al. (2005) for specimens occurring in cuttings from seven wells in the Parnaíba Basin. A late Aeronian to early Telychian age for the strata was proposed by Grahn et al. (2005) based upon the occurrence of taxa such as Sph. palestinaense (as synonymised by Grahn et al., 2005), Conochitina elongata, Conochitina proboscifera, and from previous studies by Grahn (1992) and Le Hérissé et al. (2001, see above). • Grahn (2006): upper Rhuddanian–middle Sheinwoodian; western Gondwana. In a review of western Gondwanan Ordovician and Silurian chitinozoan biozones, Grahn (2006, Fig. 6) gives the range of Sph. palestinaense as upper Rhuddanian to middle Sheinwoodian. A Wenlock age for the species has not been recorded previously (see occurrences discussed above), and no explanation or data were provided by Grahn (2006) to suggest why this higher range was given. Sph. palestinaense is noted as appearing in the uppermost part of the Belonechitina postrobusta chitinozoan Biozone (Grahn, 2006, p. 7), but is not stated as occurring in any of the succeeding biozones. A Sheinwoodian highest occurrence is therefore not recognised herein for the species, as there are currently no data by which it can be corroborated. 6.2.11. Sphaerochitina solutidina Paris, 1988b Stratigraphical range: Lower Rhuddanian–lower Telychian. Sphaerochitina solutidina has a limited recorded occurrence, described below. Although the specimens recovered from the E1-NC174 core were retained in open nomenclature, details of previous records of the taxon are described below, as the specimens may prove to be synonymous. • Hill et al. (1985): middle–upper Llandovery (lower Telychian?); D1-31 and E1-81 wells, north-eastern Libya. As described previously for taxa recorded by Hill et al. (1985), correlation of the strata in which Sph. solutidina was recorded was based largely upon the occurrence of C. elongata and P. pseudoagglutinans, which was correlated with data from Taugourdeau (1963), providing a ‘middle and late’ Llandovery age. The absence of specimens of Cyathochitina in samples above those yielding Sph. solutidina was cited as evidence that the strata were not younger than the lowermost Telychian (see discussions above). • Paris (1988a,b): Rhuddanian–upper Aeronian; A1-81, D1-31, E1-81 and I1C-81 wells, north-eastern Libya. Paris (1988a, p. 66) recorded Sph. solutidina from strata correlated to the Rhuddanian–upper Aeronian, based upon the correlation of co-occurring taxa, such as ‘a form similar to Ancyrochitina laevaensis’ that was correlated with the lowermost Rhuddanian of Estonia (Nestor, 1980a), and Plectochitina pseudoagglutinans, recorded from the ‘middle and late’ Llandovery strata of the Sahara (Taugourdeau, 1963). Sph. solutidina was shown by Paris (1988a, p. 66) to have a peak abundance near the base of his ‘C. vitrea–S. libyensis’ biozone, tentatively correlated therein to the lowermost Rhuddanian. • Paris et al. (1995): upper Rhuddanian–lower Telychian?; central

Saudi Arabia. Although they did not illustrate or describe any specimens of Sph. solutidina, Paris et al. (1995, Fig. 2) recorded the range of the species as being from the upper Rhuddanian to the lower Telychian, where it has its peak abundance. Based upon the overlapping range of Sph. solutidina with Angochitina hemeri, Paris et al. (1995, p. 81) erected the ‘S. solutidina-A. hemeri concurrent range biozone’, which coincides with the peak abundance of Sph. solutidina, and is correlated with the lower Telychian. This correlation was based largely on graptolite evidence from the KAHF-1 well of Saudi Arabia providing an Aeronian age (triangulatus–sedgwickii graptolite biozones) for the preceding ‘C. alagarda-P. paraguayensis’ chitinozoan Biozone (Philippe Legrand, pers. comm. in Paris et al., 1995, p. 84). The highest occurrence of specimens of the genus Cyathochitina within strata assigned to the Sph. solutidina-A. hemeri chitinozoan Biozone provided further evidence to Paris et al. (1995, p. 84) that it can be assigned to the lower Telychian (based on the last occurrences of Cyathochitina spp. elsewhere, see Paris et al., 1995, p. 84). This upper age constraint provided by Cyathochitina, however, was demonstrated to be incorrect by the recorded occurrence of Cyathochitina sp. aff. campanulaeformis in strata assigned to the Wenlock in Sweden (Grahn, 1998). • Grahn et al. (2000): upper Aeronian–‘Aeronian-Telychian transition’; Vargas Peña Fm, RD-116 well, Paraná Basin, Paraguay. Sph. solutidina was stated by Grahn et al. (2000, p. 166) to be a characteristic species of their ‘Total Range Zone of Conochitina elongata’, that they assigned to the Aeronian and lower Telychian on the basis of the occurrence of the index species elsewhere (as described previously). Sph. solutidina was recorded only from the RD-116 well on text-Fig. 8 of Grahn et al. (2000), from two samples within the ‘Late Aeronian’ of the Vargas Peña Fm. The species was shown on text-Fig. 9 of Grahn et al. (2000) to have a range restricted to the middle sub-biozone of their C. elongata Biozone. The middle sub-biozone of the C. elongata chitinozoan Biozone of Grahn et al. (2000, p. 168) is named as the ‘Concurrent Range Subzone of Conochitina proboscifera and Spinachitina harringtoni n. sp.’, for which it is stated that ‘it is easily distinguished through the co-occurrence of Conochitina proboscifera, Cyathochitina cf. kuckersiana… Sphaerochitina silurica n. sp., and Sphaerochitina solutidina’. The C. proboscifera-S. harringtoni sub-biozone of Grahn et al. (2000, p. 171) is stated as ranging ‘from the upper Aeronian to the Aeronian–Telychian transition’. The first appearance of Sph. solutidina in the RD-116 well is coincident with that of C. proboscifera, and reflected by its assignment to the abovementioned sub-biozone (Grahn et al., 2000, p. 168). Although C. proboscifera was stated as being ‘a widespread and common Telychian to Sheinwoodian species’ by Grahn et al. (2000, p. 170), its first occurrence was recorded as early as upper Aeronian by Grahn and Paris (1992), Grahn (1995, 1998), Nestor (1994), and Geng et al. (1987, 1997). This age was therefore considered by Grahn et al. (2000, p. 171) to correspond to the base of the C. proboscifera-S. harringtoni sub-biozone, and therefore to the first occurrence of Sph. solutidina in the Paraná Basin. The upper limit of the C. proboscifera-S. harringtoni sub-biozone of Grahn et al. (2000, p. 168, 171) (and therefore the upper limit of the range of Sph. solutidina) was defined by the first occurrence of Desmochitina cf. D. densa (marking the base of the succeeding ‘Concurrent Range Subzone of Conochitina proboscifera and Desmochitina cf. D. densa’), in strata they assigned to the lowermost Telychian. The disappearance of specimens belonging to the genus Cyathochitina in the C. proboscifera-D. cf. densa sub-biozone further indicated to Grahn et al. (2000, p. 171) that the strata are not younger than the lowermost Telychian, although this constraint has been shown to be incorrect (see previous discussions).

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• Grahn et al. (2005): upper Aeronian–lower Telychian; Tianguá Fm, 1-BJ-1-PA well, Parnaíba Basin, north-eastern Brazil. Sph. solutidina was recorded from the Tianguá Fm in one well (1-BJ-1-PA) in north-eastern Brazil. The Tianguá Fm was dated to the upper Aeronian to lower Telychian by Grahn et al. (2005) (see discussion above for Sph. palestinaense). • Grahn (2006): upper Aeronian; western Gondwana. In constructing a ‘formal Ordovician–Silurian chitinozoan biozonation for western Gondwana’ (Grahn, 2006, p. 509), the ‘Spinachitina harringtoni Range Biozone’ was formally defined, and the ‘Sphaerochitina solutidina Range Subzone’ was defined within its upper part (Grahn, 2006, p. 515). The base of the ‘Sphaerochitina solutidina Range Subzone’ was defined by the ‘FOB [first occurrence biohorizon] of Sphaerochitina solutidina’ (Grahn, 2006, p. 515), with its top being defined by the base of the succeeding ‘Pogonochitina djalmai Interval Zone’ (marked by the first occurrence of the index species). Diagnostic species of the ‘Sphaerochitina solutidina Range Subzone’ included Conochitina sp. A, Plectochitina sp. C and Sphaerochitina sp. C (all sensu Grahn et al., 2000): all were recorded as having the same stratigraphical range in coeval strata as Sph. solutidina by Grahn et al. (2000), and were used by Grahn (2006, p. 515) to restrict the Sph. solutidina chitinozoan Biozone to the upper Aeronian. It is interesting to note that no mention of Conochitina proboscifera is made by Grahn (2006) in the definitions of either the Spinachitina harringtoni or the Sphaerochitina solutidina chitinozoan biozones, as the species was an important correlative taxon used by Grahn et al. (2000) for strata of this age (see above). The stratigraphical ranges of the other chitinozoan taxa recorded by Grahn et al. (2000) formed the basis of the correlation of Grahn's (2006) S. harringtoni and Sph. solutidina chitinozoan, but no explanation as to the omission of C. proboscifera from the biozones was provided by Grahn (2006).

6.3. Age of the ‘hot’ shale in the E1-NC174 core An important chitinozoan present in the E1-NC174 core is Belonechitina postrobusta, which has a high relative abundance in most samples, from the lowest sample up to its last appearance at 7245′7″, near the top of the ‘hot’ shale. B. postrobusta is the biozonal index taxon for the Rhuddanian postrobusta chitinozoan Biozone of Verniers et al. (1995) and elsewhere (e.g. Nestor, 1994), and is present in high abundance in the middle Rhuddanian vesiculosus graptolite Biozone (e.g. Martin, 1974; Nestor, 1980a). A position in the upper part of the range of B. postrobusta is suggested herein for the ‘hot’ shale, as none of the characteristic lowermost Silurian taxa were found in the samples studied (e.g. Spinachitina fragilis, Ancyrochitina laevaensis, Plectochitina nodifera), although these taxa were recorded from below the ‘hot’ shale in the BG-14 core of southern Jordan (Butcher, 2009). Associated with B. postrobusta, but occurring in fewer samples, is B. pseudarabiensis, a species recorded by Butcher (2009) from the lower to middle Rhuddanian of Jordan. Angochitina seurati also occurs in samples throughout the E1-NC174 core. It occurs in low abundance below the ‘hot’ shale, is more abundant above, and has a range from the middle Rhuddanian to the lower Telychian: the taxon was used by Paris (1988a) to erect a biozone within the middle Rhuddanian of north-east Libya. A diverse assemblage of chitinozoan taxa is present in the lower part of the core. Several of these have been left in open nomenclature. Some have short stratigraphical ranges and thus may prove to be of value if found at similar levels in other sections. Chitinozoan abundance plummets within the ‘hot’ shale (see Fig. 2, and Table SM1). Therefore, the upper limits of stratigraphical ranges of taxa appearing below the ‘hot’ shale and disappearing within it are unlikely to be their true last occurrences.

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At the top of and above the ‘hot’ shale chitinozoan abundance recovers and the assemblage is very different from that lower in the core, with the first appearance of six taxa. The most significant of these is Sphaerochitina palestinaense, a species with a first recorded occurrence in the upper Rhuddanian. These data agree with Loydell's (2012) detailed study of the graptolites from the E1-NC174 core, in which analysis of over 500 graptolite specimens from sixty-seven samples led to the recognition of the Normalograptus tilokensis, Neodiplograptus africanus, and Neodiplograptus fezzanensis graptolite biozones in the core. The graptolite taxa recovered, both endemic and cosmopolitan, independently constrained the age of the core to being entirely Rhuddanian, with the ‘hot’ shale interval being of mid Rhuddanian age. In summary, the chitinozoan biostratigraphical data herein are consistent with the entire core being of Rhuddanian age, thus agreeing with Loydell (2012) in contradicting the suggestion of Lüning et al. (2003) that the base of the core may lie within the uppermost Ordovician. The ‘hot’ shale itself clearly lies within the upper part of the range of Belonechitina postrobusta indicating that it is not of early Rhuddanian age, but is from the middle Rhuddanian. This is supported by the presence of chitinozoans that appear first in the upper Rhuddanian above the ‘hot’ shale. It is interesting to note that, in their recent study of the CDEG-2a core from the eastern Murzuq Basin, Paris et al. (2012) did not recover any specimens of Belonechitina postrobusta, which is abundant throughout the majority of samples from the E1-NC174 core: in fact, there appear to be no taxa that are common between the two cores. In conjunction with this, there is also no prominent gammaray peak recorded in the Rhuddanian for the CDEG-2a core, and as such this raises the possibility of an unconformity within that core to account for these two prominent absences. Such absence of a postrobusta Biozone would fit well with the published data, as Paris et al. (1995, Fig. 2) do indeed record a ‘B. postrobusta (Interval range)’ Biozone for strata in the Llandovery of central Saudi Arabia, occurring between their ‘S. fragilis (Total range)’ and ‘L. nuayyimensis (Total range)’ biozones.

7. Conclusions Detailed analysis of the 6655 chitinozoans recovered from the E1-NC174 core has constrained independently the age of the ‘hot’ shale in the E1-NC174 core to the middle Rhuddanian, based upon key taxa with stratigraphically restricted ranges. Many of the taxa recovered herein have only scant previous recorded occurrences due to the relative paucity of published studies on Llandovery strata in northern Gondwana, and therefore this high-resolution study adds valuable data to the records of such taxa. The ‘hot’ shale itself shares many similarities with that occurring in the BG-14 core of southern Jordan, as studied in detail by Loydell (2007), Butcher (2009) and Loydell et al. (2009): it also is of middle Rhuddanian age (significantly, within the stratigraphical range of B. postrobusta), and records a sharp decline in chitinozoan abundance within the ‘hot’ shale interval (coinciding with the highest gamma-ray readings). High-resolution biostratigraphical studies such as these are of great importance in correctly identifying and constraining Lower Palaeozoic ‘hot’ shales, especially given their high economic value as hydrocarbon source rocks. Lüning et al. (2005) and Loydell (2007), for example, were able to demonstrate through such high-resolution biostratigraphical studies that the ‘lower hot shale’ in the lower Silurian of Jordan is in fact two discrete ‘hot’ shale intervals of early and mid Rhuddanian age. It is clear, therefore, that such high-resolution biostratigraphical techniques are essential for future studies of Palaeozoic ‘hot’ shales. Supplementary data to this article can be found online at http:// dx.doi.org/10.1016/j.revpalbo.2012.11.009.

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Acknowledgements This study forms part of a project funded by ENI, undertaken at the University of Portsmouth (UK), and the sponsors are thanked for allowing the publication of these data. The author is very grateful to the reviewers of the manuscript, Jacques Verniers and Esther Asselin, for their detailed comments, and Thijs Vandenbroucke also for his additional comments. David Loydell is thanked for much consultation and advice, and Ken Dorning also for advice on tackling problems with volatiles that arose during laboratory processing. This paper is a contribution to the International Geoscience Programme (IGCP) Project 591 – ‘The Early to Middle Paleozoic Revolution’. References Achab, A., 1981. Biostratigraphie par les chitinozoaires de l'Ordovicien Supérieur Silurien Inférieur de l'Île d'Anticosti, résultats préliminaries. In: Lespérance, P.J. (Ed.), Field meeting, Anticosti-Gaspé, Québec, II: Stratigraphy and Palaeontology. Subcomission on Silurian Stratigraphy. 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