Late Westphalian palynomorphs from northern Saudi Arabia

REVIEW OF PALAEOBOTANY AND PALYNOLOGY ELSEVIER

Review of Palaeobotany and Palynology 89 (1995) 125 137

Late Westphalian palynomorphs from northern Saudi Arabia B. Owens, N. Turner British Geological Survey, Keyworth, Nottingham NG12 5GG, UK Received 8 February 1993; revised and accepted 24 September 1994

Abstract

Late Carboniferous (Westphalian D) miospore assemblages are reported from an exploration borehole in the northwestern part of Saudi Arabia. The presence of stratigraphically diagnostic monolete miospore genera are reported for the first time in the Arabian Peninsula. The study emphasises the need to examine cored sections to establish the biostratigraphical value of the extensive populations of zonate miospores (Cirratriradites, Vallatisporites and Kraeuselisporites) reported. A detailed review is presented of previous Late Carboniferous-Early Permian data in the Arabian Peninsula and comparisons are drawn with comparable datasets in North Africa and Western Europe.

1. Introduction

Whilst a degree of palynostratigraphic order has developed from the examination of Late Carboniferous-Early Permian p a l y n o m o r p h assemblages in the Euramerican Province based on studies in the United States, C a n a d a and both western and central Europe and in parts of the G o n d w a n a Province, i.e. Australia, Argentina and India, the situation in the region of the interface between these two provincial land masses remains largely unresolved. Comprehensive studies are few and any conclusions which have been drawn are often speculative, being based in the absence of any adequate independent biostratigraphical controls, on long range palynological correlations. Considerable work still remains outstanding in terms of documenting the large number of taxa which remain in open nomenclature. The present account reports the initial results of a more comprehensive review of this interval which will be undertaken throughout the K i n g d o m of Saudi Arabia. Previous investigations have been concentrated 0034-6667/95/$9.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0034-6667(95)00046-1

in the southern part of the Kingdom and in adjacent parts of O m a n and have been directed in part at trying to date the onset of the Late Palaeozoic glaciation in those regions. Glacial deposits are well known in the southern part of the Arabian Peninsula but are unrecorded in the literature in the northern part of the Kingdom. McClure (1980) has provided the most comprehensive overview of these deposits based on evidence from surface sections on the Tuwaiq Sedimentary Escarpment and from borehole sections in the Southern Tuwaiq region. McClure (1980) concluded that some of the evidence from the surface sections supported a probable aqua-glacial origin for the boulder beds, evidence also existed from the frequent occurrence of channelling and conspicuous cross-bedding to suggest an alternative fluvial origin. Evidence for the age from nonpalynological sources of these deposits which underlie the Khuff Formation of Permian age and in some cases rest directly on Basement is limited. Hudson (1958) and Hudson and Sudbury (1959) had suggested a comparable set of boulder beds in the Haushi Formation of southern O m a n as

126

B. Owens, N. Turner~Review of Pulaeobotany and Palynology 89 (1995) 125 137

being of Lower Permian age based on the presence of brachiopods and other shelly fossils. Hadley and Schmidt (1975) were unable to confirm this age on the sections at Khashm Khatmah in southern Tuwaiq where the boulder beds which are locally part of the Wajid Sandstone were suggested as being possible correlatives of the Tabuk Formation which extends from the Ordovician to the Devonian in age. Palynological evidence recovered by McClure from the Wajid Sandstone together with unpublished data accumulated by Cameron and reported by McClure is particularly important in establishing the age of these deposits. Assemblages recovered from borehole 4 located 65 km southeast of Khashm Khatmah were dominated by monosaccate pollen and highly ornamented trilete spores. McClure reported the presence of Cordaitina spp., Cristatisportes spp., Cyclogranisporites parvulus, Florinites sp., Nuskoisporites gondwanensis,

Potonieisporites neglectus, P. novicus, Punctatisporites gretensis, P. cf. obesus and "Wajidisporites" sp. Partly on the basis of the absence of any significant components assignable to the Carboniferous, McClure concurred with Cameron's earlier suggestion and proposed a Lower Permian (Sakmarian) age for the sampled interval. This result was compatible with earlier unpublished data from borehole 3 (200 km southeast of Khashm Khatmah) from which Cameron (quoted in McClure) reported a StephanianSakmarian age for assemblages containing abundant representatives of Nuskoisporites and Potonieisporites together with Cirratriradites splendens,

Illinites spectabilis, Leiotriletes directus, Platysaccus umbrosus and Punctatisporites gretensis. Cameron's conclusion on the age of this material was largely based on the comparisons drawn with the Lower Permian Greta Coal in Australia and ignored the absence of any of the characteristic accessory spores typical of the Stephanian in Western Europe. It appears justified to suggest that a Sakmarian age is more probable for these assemblages. This conclusion is further supported by the evidence from borehole 2 (near Qaryah) where McClure reported that assemblages from below the local equivalent of the Upper Permian Ruhaiya Limestone contained Complexisporites poly-

morphus, Vittatina Jbveolata, Costapollenites ellipticus and Striatosaccites bullaeJormis. Elsewhere in the Arabian Peninsula, Besems and Schuurman (1987) have recorded palynomorphs from what are considered mid-Stephanian Sakmarian sections with comparable boulder deposits in the Wadi A1 Khalata of southern Oman. Assemblages recovered are composed of abundant monosaccate pollen, trilete zonate spores and both striate and non-striate bisaccate pollen grains. Two broad based assemblages were recognised; the older, Assemblage A, appears closely comparable with that recorded from boreholes 3 and 4, both 200 km southeast of Khashm Khatmah by McClure but is accorded a middle-late Stephanian age by Besems and Schuurman. The upper Assemblage B which is characterised by abundant non-striate and striate bisaccate pollen of the genera Protohaploxypinus, Cycadopites and Vittatina together with frequent trilete spores, e.g. Punctatisporites spp., Apiculatisporis cornutus, Brevitriletes levis, Cirratriradites spp., Cristatisporites spp., Horriditriletes spp., Microbaculispora spp. and common Botryococcus was assigned a Sakmarian age but considered by Besems and Schuurman to be unrepresented in Saudi Arabia. Again comparisons were drawn between these assemblages and the Late Carboniferous Early Permian palynozonation scheme proposed by Kemp et al. (1977) in Australia. The Oman Assemblage A was equated with the Australian Unit II characterised by an abundance of Microbaculispora and assigned a middle late Stephanian age by Balme (1980) whilst Assemblage B was correlated with the Sakmarian Australian Unit III with its base being defined by a sudden quantitative increase in the representation of bisaccate pollen. Love (1994) has expanded the knowledge of this interval in Oman with an investigation of the A1 Khalata and Gharif Formations. The original twofold subdivision of Besems and Schuurman (1987) is expanded into five zonal units referred to as Assemblages. The oldest unit, the Potonieisporites Assemblage is assigned a late Westphalian-early Stephanian age and characterised by Punctatisporites spp., Leiotriletes spp., Potonieisporites spp. and Plicatispollenites with only rare specimens of

B. Owens, N. Turner/Review of Palaeobotany and Palynology 89 (1995) 125 137

Microbaculispora and Horriditriletes. Love correlated this unit with the Australian Unit I of Kemp et al. (1977). Direct evidence for a Westphalian age for the Assemblage is still difficult to justify. The younger Assemblages defined by Love compare closely in composition with Assemblage Groups A and B of Besems and Schuurman. No definitive evidence is available in the published literature to support the presence of Late Carboniferous deposits in the Arabian Peninsula. McClure (1980) has commented that "rocks of definite Carboniferous age occur in most of the holes in the area that are drilled deep enough." This statement is supported with a listing of genera recorded below assumed Sakmarian deposits in borehole 2 which included Densosporites, Cristatisporites, Lycospora, Gondisporites, Crassispora, Vallatisporites, Virkkipollenites, Nuskiopollenites and Vittatina. Whilst some of these genera do represent well documented Carboniferous components, the list includes several elements which are more typical of the Permian. Doubt must exist on this claim until this pre-Sakmarian material from borehole 2 can be re-examined and the validity of these generic identifications substantiated.

127

the A1 Khalata Formation (Fig. 2) but their precise age remained in doubt. Evidence from the present study indicates the youngest known Carboniferous miospores occur at 4200 ft. Previous unpublished investigations have suggested the interval between 3900 and 4210 ft was of Permian age but this data may be only a reflexion of caved Permian components being present in a sequence devoid of indigenous palynomorphs. The precise age of this unit will remain unresolved until a cored section is available for examination. The sands, siltstones and shales between 4210 and 4640 ft belong to the A1 Khalata Formation of late Westphalian-Stephanian age. Below 4640 ft sandstones become more common within the sequence and the succession to T D is assigned on palynological evidence to the Early Carboniferous Berwath Formation. Two strew mount slides prepared in the Saudi Aramco laboratories in Dhahran using conventional palynological sample preparation methods were examined for each sample interval. All slides including those containing material figured in this paper are housed in the Palaeontology Collections of the Natural History Museum, London, England.

2. Sample details 3. Stratigraphical palynology This investigation is based on a number of cutting samples recovered between 4200 and 4650 ft in well ST-8 drilled by The Saudi Arabian Oil Company in the northwestern part of the Kingdom, approximately 160 km W N W of Rafha and 530 km E N E of Tabuk (Fig. 1). The interval examined immediately overlies a number of short cored intervals from which Clayton (1995-this issue) has recorded Visean-?early Namurian miospores. Preliminary lithostratigraphic subdivision of the succession in well ST-8 has placed the base of the Unayzah Formation, the conventional base to the Permian System, at approximately 3700ft based on the commencement of carbonate deposits which become a dominant component in overlying Khuff Formation sequences. The interval of sands, siltstones and shales between 3700 and 4640 ft have been assigned provisionally to equivalents of

The palynomorph assemblages recovered from all ten samples investigated between 4200 and 4670 ft reveal considerable evidence of downhole caving from the overlying Permian Khuff and Unayzah Formations. For the purposes of this account all records of the striate and non-striate bisaccate pollen elements of the caved Permian microflora are omitted. The authors have, however, retained the records of a number of cingulizonate and zonate miospores in the account until more is known of the stratigraphical distribution of the group from the examination of cored late Westphalian-Permian intervals elsewhere in Saudi Arabia. Some representatives in this complex appear to be closely comparable to representatives of "Cirratriradites", Vallatisporites and Kraeuselisporites previously recorded in the Late Carboniferous and Permian of both the Gondwana and

128

B. Owens, N. Turner~Review of Palaeobotany and Palynology 89 (1995) 125 13 7 i

36 °

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i

40 °

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Fig. 1. L o c a t i o n o f well ST-8, n o r t h w e s t e r n S a u d i A r a b i a .

Euramerican Provinces whilst others appear to be undescribed. Subsequent investigations will clarify which of these components should be regarded as caved. The youngest of the p a l y n o m o r p h assemblages which was recovered from cuttings between 4200 and 4220 ft was dominated by caved striate and non-striate bisaccate pollen which accounted for more than 70% of the total population. The

remainder of the assemblage contained a number of taxa which include several components of Late Carboniferous aspect: Leiotriletes ~phaerotriangu-

lus, Calamospora parva, Cyclogranisporites aureus, Apiculatmporites spinulistratus, Microreticulatisporites sp., Laevigatosporites maximus, L. desmoinesensis, L. medius, L. minor, Punctatosporites minutus, P. rotundus, Thymospora thiessenii, T. obscura and Potonieisporites spp. These

B. Owens, N. Turner/Review of Palaeobotany and Palynology 89 (1995) 125-137

CARBONIFEROUS ~ ! KHALATA E Q U I V A L E N T ~ I I II I ~ lilllbllllllllllllllll:'l 1 iljllllll ~ ~ ' ~ " l i , i b ','k',',' • I}1J " l l ' t 'Il l [l l lI l tI t l ~I I

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Laevigatosporites maximus Laevigatosporites minor Torispora granulata Punctatisporites minutus Punctatosporites rotundu$ Potonieisporffes sp, Laevigatosporites medius Thymospora obscura Laevigatosporite$ desmoinesen$is Thymospora thiesseni Lat~ites

rotundus

Laevigatosporites vulgaris Punctatosporite$ oculu$ Spelaeotriletes arenaceus Calamospora mutabili$ Raistrickia saetosa Lophotriletes commissurali$ Cirratriradites rarus Reticulati~oorites reticulatus Speciososl~rite$ minutus Calamospora pallida Reticulatisporite$ po~,gonali$ Vesti~oora fenestrata Florinites visendus Kraeuselisporites cf ornatus CadioSl3ora magna Triquitrites bransonii Cyclogranisporffes orbiculus Thymoslx~a pseudothiasseni Spelaeotriletes triangulu$ Florinites junior Triquitrites protensus Punctatosporites granifer Crassispora kosankei Endo~oorites glol~'formi$ Laevigatosporites minutus Speciososporite$ minor Florinites mediapudens Auroraspora solisorta Spackmanites ellipticus Latensina trileta Lycospora pusilla Florinites pumicosu$ Latosporite$ globulus Raistrickia aculeata Pef~ersites ellipticu8

Fig. 2. Distribution of ?indigenous miospore species in Upper Carboniferous interval in well ST-8.

129

130

B. Owens, N. Turner/Review of Palaeobotany and Palynology 89 (1995) 125-137

components are unique in comparison to all previously documented Late Palaeozoic assemblages recorded in the Arabian Peninsula in that they contain stratigraphically significant taxa that have been previously extensively recorded from the late Westphalian-Stephanian deposits of Western Europe. Clayton et al. (1977) in summarising the distribution of the principal diagnostic miospores in Western Europe indicated that Laevigatosporites which is quantitatively significant in Westphalian and Stephanian deposits is also known to extend into the European Autunian with broadly similar distribution patterns being noted for Punctatosporites, Torispora and Thymospora. No element present in the assemblage allows for the designation of an age determination more precise than Late Carboniferous. The interval between 4370 and 4670 ft provided assemblages from a further nine cutting samples which are sufficiently similar in overall composition to allow their collective interpretation (Fig. 3). All of the elements recorded in the sample from 4200 4220 ft extend down into this interval in which the miospore populations are similarly dominated by monolete genera including Laevigatosporites, Latosporites, Punctatosporites and Speciososporites. The frequency levels of caved striate and non-striate bisaccate pollen are variable throughout this interval but these elements continue to be common components. A rich association of additional ancillary species are present in these assemblages including representatives of the following: Punctatisporites obliquus, Calamospora

microrugosa, C. mutabilis, C. pallida, Cadiospora magna, Granulatisporites microgranifer, Cyclogranisporites orbiculus, Lophotriletes microsaetosus, L. mosaicus, Apiculatisporis aculeatus, Anapiculatisporites spinosus, Raistrickia cf. aculeata, R. saetosa, Reticulatisporites reticulatus, R. polygonalis, Triquitrites bransonii, T. protensus, Lycospora pusilla, Densosporites anulatus, Crassispora kosankei, C. ovalis, Spelaeotriletes arenaceus, S. triangulus, Auroraspora solisorta, Endosporites globiformis, Florinites junior, F. pumicosus, iF. mediapudens, F. visendus, Latensina trileta, Laevigatosporites vulgaris, L. minutus, Latosporites rotundus, L. globulus, L. minutus, Punctatosporites oculus, P. granifer, Speciososporites minutus, S. minor,

Thymospora pseudothiessenii, Spackmanites ellipticus, S. sp. cf. S. irregularis and Peppersites ellipticus. In addition limited evidence was recorded in the form of representatives of Foveosporites insculptis, ValIatisporites cf. verrucosus and Spelaeotriletes cf. benghaziensis which suggests limited reworking of earlier Carboniferous deposits. These assemblages also contain a significant number of cinguli-zonate and zonate miospores which have been provisionally referred to the genera Cirratriradites, Vallatisporites and Kraeuselisporites. Some of these components are comparable to forms previously recorded from the Namurian-Westphalian interval in Western Europe (Cirratriradites rarus and Kraeuselisporites cf. ornatus) whereas others show a closer affinity to taxa recorded from the Late CarboniferousPermian of either Gondwanaland or North America (Cirratriradites africanus recorded by Kemp et al. (1977) from the Permian of Western Australia, Kraeuselisporites splendens recorded by Kemp et al. (1977) and Segroves (1970) from the Permian of Western Australia, K. kuttungensis described from probable Namurian equivalents in New South Wales by Playford and Helby (1968) and later reported from probable Westphalian equivalents in Western Australia by Powis (1984) and K. spinosus described from the Triassic of the Peace River area of western Canada by Jansonius (1962). The lack of detailed information on representatives of this morphological complex elsewhere in the Arabian Peninsula precludes any firm decision on whether these forms are indigenous to the studied material or caved from horizons higher in the well. Besems and Schuurman (1987) have recorded a range of zonate miospores from the Wadi A1 Khalata North section in Oman which encompass some of the morphological variants encountered in the material recorded in the present study. The Oman material which was left in open nomenclature was assigned to the genera Cirratriradites, Cristatisporites and Vallatisporites. The Wadi A1 Khalata North section was considered by Besems and Schuurman to belong to their Assemblage Group A of middle late Stephanian age. The complex also appears to be a common component of the Microbaculispora Assemblage recorded by Love (1994) from the Haushi Group

B. Owens, N. Turner~Review of Palaeobotany and Palynology 89 (1995) 125-137

SAMPLES

LU ('- CU'I-rlNGS nO ~--e CORES

PALYNOLOGICAL CHARACTERISTICS

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A N D N O N - S T R I A T E BISACCATE P O L L E N T O G E T H E R W I T H LATE C A R B O N I F E R O U S

Laevigatosporites, Latosporites, Punctatosporites, Thymospora, Reticulatisporites, Raistrickia, Cadiospora, Vestispora, Tricluitrites a n d Speciososporites GENERA INCLUDING

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NAMURIAN GENERA INCLUDING

Kraeuselisporites. Vallatisporites, Verrucosisporite$, Diatomozonotriletes, Spelaeotriletes, Pustulatisporites. Raistrickia, Auroraspora, Retusotriletes, Aratrisporite$ a n d Camptozonotriletes

4850

. . . . . . . . . . .

Fig. 3. Summary of distribution of stratigraphically diagnostic miospore taxa in the Carboniferous of well ST-8.

131

132

B. Owens, N. Turner~Review o f Palaeobotany a n d Palynology 89 (1995) 1 2 5 - 1 3 7

PLATEI

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B. Owens, N. Turner/Review of Palaeobotany and Palynology 89 (1995) 125 137

in Oman. Open nomenclature is again employed but a correlation with Assemblage Group A of Besems and Schuurman is again suggested.

4. Comparison with other areas

The record of late Westphalian-early Stephanian miospore assemblages in well ST-8 is unique in the Arabian Peninsula and therefore makes direct comparisons within the region difficult. The most comprehensive investigation previously carried out is that by Besems and Schuurman (1987) on the Wadi A1 Khalata sections in Oman. Assemblages recovered from those sections lack completely any representatives of taxa which in the paralic areas of northwest Europe are characteristic of the Westphalian or early Stephanian, most significant being the total absence of monolete miospores which are frequent components in the ST-8 assemblages. The Oman sections are dated as middle or late Stephanian to Sakmarian on the basis of correlations drawn with the zonal scheme proposed by Kemp et al. (1977) in Western Australia. The oldest of the Wadi AI Khalata assemblages (Assemblage Group A) was characterised by containing common zonate miospores assigned to the genera Vallatisporites, Cristatisporites and Cirratriradites in association with monosaccate pollen, e.g. Parasaccites, Plicatipollenites and

PLATE I All figures x 500 magnification.

1. Laevigatosporites maximus, ST-8, 4480-4500 ft, F M 680. 2. Laevigatosporites desmoinesensis, ST-8, 4520-4550 ft, FM 681. 3. Speciososporites minor, ST-8, 4520-4550 ft, FM 682. 4. Punctatisporites cf. obliquus, ST-8, 4520-4550 ft, F M 683. 5. Punctatosporites granifer, ST-8, 4520 4550 ft, F M 684. 6. Triquitrites protensus, ST-8, 4520-4550 ft, F M 685. 7. Triquitrites bransonii, ST-8, 4520 4550 ft, F M 686. 8. Triquitrites bransonii, ST-8, 4520-4550 ft, FM 687. 9. Kraeuselisporites cf. ornatus, ST-8, 4370-4430 ft, F M 688. 10. Cirratriradites rarus, ST-8, 4520-4550 ft, F M 689. 11. Cirratriradites rarus, ST-8, 4520-4550 ft, F M 670. 12. Kraeuselisporites sp., ST-8, 4370-4430 ft, F M 671. 13. Spackmanites ellipticus, ST-8, 4520 4550 ft, FM 672. 14. Spelaeotriletes arenaceus, ST-8, 4520 4550 ft, F M 673. 15. Reticulatisporites polygonalis, ST-8, 4370-4430 ft, F M 674. 16. Vestisporafenestrata, ST-8, 4520-4550 ft, F M 675.

133

Potonieisporites. Most of these taxa are known in the ST-8 well assemblages where they are considered to be present as a result of caving. If this assumption is correct it is probable that equivalents of the Wadi A1 Khalata sequence may occur above the studied interval in well ST-8. The alternative interpretation would be that glacio-fluvial Late Carboniferous conditions which gave rise to the A1 Khalata Formation in the southern part of the Arabian Peninsula and which are associated with a Gondwanan microflora did not extend as far north as the northern part of Saudi Arabia where deposits of approximately similar age were developed in more temperate or sub-tropical climatic regimes which were within the depositional range of miospores derived from the European-Asiatic paralic coal basin floral belt. This interface between the areas influenced by the advances and retreats of the developing Late Carboniferous Gondwanan glaciation would undoubtedly be a migrating belt in which one would anticipate both local and regional variations. Evidence available from the Cyrenaican Platform in northeast Libya provided limited support for this hypothesis. Loboziak and Clayton (1988) described a sequence of miospore biozones extending from the late Visean to the early Asselian (Permian) in that region. Whilst the data are largely derived from cored intervals in wells throughout the region, independent biostrati-

134

B. Owens, N. Turner/Review of Palaeobotany and Palynology 89 (1995) 125 137

graphic calibration was absent. The proposed biozonal units are coarse in scale with only two, the Plicatipollenites malabarensis-Cannanoropollis janakii and the Strotersporites indicus-Protohaploxypinus goraiensis biozones extending from the ?Serpukhovian ( = N a m u r i a n ) to the early Asselian (Permian). Monolete miospores were not recovered by Loboziak and Clayton and few comparisons are possible with the ST-8 assemblages. It is of interest to record, however, that Kraeuselisporites ornatus, Cirratriradites rarus and Vallatisporites ciliaris were reported in this sequence. A more detailed study (Brugman et al., 1988) in one of the wells in northeast Libya does, however, allow more detailed comment. The interval in well Al-19 to the southwest of Tobruk which extends across the Carboniferous-Permian boundary contained representatives of Potonieisporites spp., Laevigatosporites vulgaris, Punctatosporites minutus, Kraeuselisporites spp., Lycospora

recorded in the Saudi Arabian well ST-8. The presence of monosaccate and disaccate pollen in Palynozone XVII emphasises the need to examine additional cored samples from above the limit of the probable Westphalian deposits in the northern part of Saudi Arabia in order to ascertain which of the pollen components recovered in cutting samples should be regarded as indigenous. Coquel et al. (1988) in a review of revised palynological data on the Visean-Moscovian (Westphalian-early Stephanian) in the Rhadames Basin of western Libya also provided information on the late Westphalian sequences in the BecharAbadla Basin in the Algerian Sahara. It is significant to note (see also Coquel, 1985) their records from coal seam assemblages of Lycospora pusilla,

pusilla, Endosporites ornatus, Crassispora kosankei, Torispora securis, Spelaeotriletes spp., VaIlatisporites spp., and Cirratriradites rarus in the

to indicate a Westphalian C age, the absence of representatives of Thymospora preventing an assignment to Westphalian D. All of these BecharAbadla components were reported in the ST-8 assemblages. Coquel et al. commented that the Becha~Abadla assemblages represent an event during the Late Carboniferous during which Gondwanan influences appeared to recede but related this to the development of physical barriers in the Ougarta region to the south rather than inferring the existence of a possible regressive phase during the development of the Late Carboniferous Gondwanan glaciation. The strongest comparisons with the assemblages from well ST-8 are those which can be drawn with the detailed sequence of palynological events which have been established in the classic paralic Westphalian and limnic late WestphalianStephanian deposits of Western Europe. The scheme of palynological zones proposed by Clayton et al. (1977) summarised a number of local zonation schemes published earlier (Smith and Butterworth, 1967; Alpern et al., 1969; Loboziak, 1974). Westphalian C deposits in Western Europe are assigned to the Torispora securis-T, laevigata (SL) Zone and are characterised by the zonal taxa together with Vestispora fenestrata, Triquitrites

interval assigned to the Ghzelian(?)-Asselian. Again no independent biostratigraphical calibration is available to substantiate this conclusion and the age assignment is largely based on the presence of an accompanying diverse monosaccate and bisaccate pollen flora. As in the case of well ST-8, the Libyan data for well Al-19 is derived from cutting samples and caving cannot be eliminated. The most comprehensive scheme for palynological zonation of Carboniferous deposits in North Africa is that proposed by Massa et al. (1980) in the Rhadames Basin in western Libya. Assemblages from the upper part of the Dembaba Formation which were assigned to Palynozone XVII in the Massa et al. scheme were assigned a Moscovian (=Westphalian-early Stephanian) age on the basis of the occurrence of Laevigatosporites

vulgaris, Torispora securis, Punctatosporites granifer together with monosaccate and disaccate pollen grains of more Permian aspect. The common components of the Palynozone included Lycospora

pusilla, Retusotriletes incohatus, Vallatisporites ciliaris and Spelaeotriletes arenaceus. Broad comparisons can therefore be drawn with the sequence

Torispora securis, Laevigatosporites vulgaris, Punctatosporites granifer, Vestispora fenestrata, Cadiospora magna, Endosporites globiforrnis and Florinitesjunior which were taken by those authors

B. Owens, N. Turner~Review of Palaeobotany and Palynology 89 (1995) 125-137

spp., Laevigatosporites spp., Punctatosporites spp.,

Microreticulatisporites nobilis, Reticulatisporites reticulatus and Florinites junior. Although rare examples of Latensina trileta are recorded within the zone in the Netherlands, Thymospora is absent and it is therefore inappropriate to assign the ST-8 assemblages to that zone. The appearance of verrucose monolete spores of the genus Thymospora appears to be a more or less synchronous event at the base of Westphalian D in Western Europe and is used to define the base of the succeeding Thymospora obscura-T, thiessenii (OT) Zone. Clayton et al. commented that the extinction of Reticulatisporites reticulatus in Western Europe occurs just above the base of the OT Zone whilst Densosporites spp. becomes infrequent and Florinites junior, Microreticulatisporites nobilis and Crassispora kosankei disappear approximately in the middle of the zone. All of the other taxa characteristic of the preceding SL Zone continue through the OT Zone. The assemblages recorded from the OT Zone therefore appear to compare closely with those recorded from well ST-8, the principal difference being the absence in the European sections of Westphalian D age of a significant component made up of zonate miospores.

5. Conclusions (I) Comparison of the Late Carboniferous palynomorph assemblages recovered from well ST-8 with those recorded in Western Europe suggests a correlation with the early to middle parts of Westphalian D (OT Zone). (2) The assemblages appear unique to the Arabian Peninsula, containing significant representation of a number of monolete miospore genera. These assemblages appear to be missing from the palynological sequences reported in the Wadi A1 Khalata sections and in subsurface sections in Oman (Besems and Schuurman, 1987; Love, 1994) as well as from the Cyrenaica Platform of northeast Libya (Loboziak and Clayton, 1988; Brugman et al., I988). (3) Limited correlations can be drawn with the Rhadames Basin of western Libya (Massa et al.,

135

1980) and the Bechar Abadla Basin of the Algerian Sahara (Coquel, 1985; Coquel et al., 1988) where monolete taxa are recorded together with significant numbers of zonate taxa of the genera Kraeuselisporites, Vallatisporites and Cirratriradites. It is suggested that this component composed of zonate taxa within the assemblages may represent a local microfloral component which supplements the remainder of the assemblages which are of more conventional composition and of Western European aspect. (4) The palynological evidence indicates a major stratigraphic hiatus in well ST-8 above the cored interval at 4650 ft which extends from the early Namurian to late Westphalian C. The reason for this break requires the examination of additional cored well sections elsewhere in the Arabian Peninsula to ascertain whether it is tectonically controlled or the result of erosion during one of the early phases of Late Carboniferous glaciation. Elucidation of this problem may place in a new perspective results obtained elsewhere in the region, particularly in northeast Libya and Oman.

Acknowledgements Mrs. J Lines, British Geological Survey, is thanked for her assistance with the preparation of text figures. The authors publish with the permission of the Director, British Geological Survey (NERC).

Appendix 1. Author citation of taxa listed in text Apiculatasporites spinulistratus (Loose) Ibrahim, 1933 Apiculatisporis aeuleatus (Ibrahim) Smith and Butterworth, 1967 Apiculatisporis cornutus (Balme and Hennelly) Hoeg and Bose, 1960 Auroraspora solisorta Hoffmeister, Staplin and Malloy, 1955 Brevitriletes levis (Balme and Hennelly) Bharadwaj and Srivastava, 1969 Cadiospora magna Kosanke, 1950 Calamospora microrugosa (Ibrahim) Schopf, Wilson and Bentall, 1944 Calamospora mutabilis (Loose) Schopf, Wilson and Bentall, 1944

B. Owens, N. Turner~Review of Palaeobotany and Pa/ynology 89 (1995) 125 137

136

Calamospora pallida (Loose) Schopf, Wilson and Bentall, 1944 Calamospora parva Guennel, 1958 Cirratriradites africanus Hart, 1963 Cirratriradites rarus (Ibrahim) Schopf, Wilson and Bentall, 1944

Cirratriraditres splendens Balme and Hennelly, 1956 Complexi~porites polymorphus Jizba, 1962 Costapollenites ellipticus Tschudy and Kosanke, 1966 Crassispora kosankei (Potonie and Kremp) Bharadwaj, 1957 Crassispora ovalis Bharadwaj, 1957 Cyclogranisporites aureus (Loose) Potonie and Kremp, 1955 Cyclograni~sporites orbiculus Potonie and Kremp, 1955 Cyclogranisporites parvulus Staplin, 1960 Densosporites anulatus (Loose) Smith and Butterworth, 1967 Endosporites glob(formis (Ibrahim) Schopf, Wilson and

Punctatisporites obliquus Kosanke, 1950 Punctalosporites granifer Potonie and Kremp, 1956 Punctatosporites minutus Ibrahim, 1933 Punctatosporites oculus Smith and Butterworth, 1967 Punctatosporites rotundus Bharadwaj, 1957 Raistrickia cf. aeuleata Kosanke, 1950 Raistrickia saetosa (Loose) Schopf, Wilson and Bentall, 1944 Reticulatisporites polygonalis (Ibrahim) Smith and Butterworth, 1967

Endosporites ornatus Wilson and Coe, 1940 Florinites junior Potonie and Kremp, 1956 Florinites mediapudens (Loose) Potonie and Kremp, 1956 Florinites pumicosus (Ibrahim) Schopl; Wilson and Bentall,

Reticulatisporites reticulatus ( lbrahim) Ibrahim, 1933 Retusotriletes ineohatus Sullivan, 1964 Spackmanites ellipticus Habib, 1966 Spackmanites sp. cf. S. irregularis Ravn, 1986 Speciososporites minor Alpern, 1958 Speciososporites minutus Alpern, 1958 Spelaeotriletes arenaceus Neves and Owens, 1966 Spelaeotriletes cf. benghaziensis Loboziak and Clayton, 1988 Spelaeotriletes triangulus Neves and Owens, 1966 Thymoapora obscura (Kosanke) Wilson and Venkatachala, 1963 Thymospora pseudothiessenii (Kosanke) Wilson and

1944

Venkatachala, 1963

Florinites visendus (Ibrahim) Schopf, Wilson and Bentall, 1944 Foveoaporites insculptus Playford, 1962 Granulatisporites microgranifer lbrahim, 1933 Illinites spectabilis Leschik, 1956 Kraeuselisporites kuttungensis Playford and Helby, 1968 Kraeuselisporites ornatus (Neves) Owens, Mishell and

Thymospora thiessenii (Kosanke) Wilson and Venkatachala,

Bentall, 1944

Marshall, 1976

Kraeuselisporites cf. ornatus (Neves) Owens, Mishell and Marshall, 1976

Kraeuselisporites spinosus Jansonius, 1962 Kraeuselisporites splendens (Balme and Hennelly) Segroves,

1963

Torispora securis Balme, 1952 Triquitrites bransonii Wilson and Hoffmeister, 1956 Triquitrites protensus Kosanke, 1950 Vallatisporites ciliaris (Luber) Sullivan, 1964 Vallatisporites cf. verrucosus Hacquebard, 1957 Vestispora fenestrata (Kosanke and Brokaw) Wilson and Venkatachala, 1963 Vittatinajoveolata Tschudy and Kosanke, 1966

1970

Laevigatosporites desmoinesensis (Wilson and Coe) Schopf, Wilson and Bentall, 1944

Laevigatosporites Laevigatosporites Laevigatosporites Laevigatosporites

maximus (Loose) Potonie and Kremp, 1956 medius Kosanke, 1950 minor Loose, 1934 minutus (Ibrahim) Schopf, Wilson and

Bentall, 1944

Laevigatosporites vulgaris lbrahim, 1933 Latensina trileta Alpern, 1958 Latosporites globulus (Schemel) Potonie and Kremp, 1956 Latosporites minutus Bharadwaj, 1957 Leiotriletes directus Balme and Hennelly, 1956 Leiotriletes sphaerotriangulus (Loose) Potonie and Kremp, 1954 Lophotriletes microsaetosus (Loose) Potonie and Kremp, 1955 Lophotriletes mosaicus Potonie and Kremp, 1955 Lycospora pusilla (Ibrahim) Somers, 1972 Microreticulatisporites nobilis ( Wicher) Knox, 1950 Nuskoisporites gondwanensis Balme and Hennelly, 1955 Peppersites ellipticus Ravn, 1979 Platysaccus umbrosus Leschik, 1956 Potonieisporites neglectus Potonie and Lele, 1961 Potoniei~sporites novicus Bharadwaj, 1954 Punctatisporites gretensis Balme and Hennelly, 1956 Punctatisporites cf. obesus (Loose) Potonie and Kremp, 1955

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