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Late Cretaceous and Cainozoic bathyal Ostracoda from the Central Pacific (DSDP Site 463)
ELSEVIER
Marine Micropaleontology 37 ( 1999) 13I- 147 www.elsevier.com/locate/marmicro
Late Cretaceous and Cainozoic bathyal Ostracoda from the Central Pacific (DSDP Site 463) Ian Boomer * Department of Geography, University of Newcastle, Newcastle, NE1 7RU, UK
Received 16 September 1998; accepted 8 March 1999
Abstract Cainozoic deep-sea ostracod assemblages from the summits of Mid-Pacific guyots point to high levels of endemism possibly as a result of their bathymetric separation from the surrounding sea floor. However, the interpretation of these fossil assemblages is hampered by the paucity of comparative material from surrounding non-guyot sites. Fifteen ostracod assemblages from DSDP Site 463 (Late Cretaceous-Pleistocene) were studied to compare with those from nearby guyots. Three distinct fauna1 assemblages are recognised at Site 463: Assemblage A (Maastrichtian-Eocene), Assemblage B (Oligocene-Upper Miocene) and Assemblage C (Upper Miocene-Pleistocene) although the palaeoenvironmental significance of these units is unclear. Sixty-two ostracod species are identified, the thirteen most abundant are discussed
in the taxonomic section, five of which are described as new. Between 30 and 100% of the species encountered in each sample are considered as endemic to Site 463, while some of the remaining species were previously thought to be endemic to individual guyots. Similarly high levels of endemism on nearby guyots probably reflect an incomplete knowledge of deep-sea ostracod faunas rather than the establishment of geographically or bathymetrically restricted populations. The presence of globally pandemic and geographically widespread taxa on sites such as the Mid-Pacific Mountains, surrounded by abyssal depths which lie below the CCD, indicates that some fauna1 exchange or migration of ostracods does take place. This must be achieved within the intermediate waters and probably occurs passively. 0 1999 Elsevier Science B.V. All rights reserved. Keywords: Ostracoda; endemism; deep-sea; diversity; Pacific
1. Introduction This work arises from studies of Late Cretaceous and Cainozoic deep-sea Ostracoda (ostracods) from guyot sites in the Pacific (Larwood and Whatley, 1993; Boomer and Whatley, 1995, 1996; Larwood et al., 1996; Whatley and Boomer, 1995). Thirteen Indo-Pacific guyot sites have been investigated based on material collected by the Deep Sea Drilling * Fax: +44- 191-2225421; E-mail: [email protected]
Project (DSDP) and the Ocean Drilling Program (ODP). Five sites from ODP legs 143 and 144 were the subject of research by the present author with a view to investigating the apparently high levels of endemism attained by ostracod faunas on the summits of bathymetrically isolated Pacific guyots and also to determine the effects of regional and global palaeoceanographical events on the ostracods (Boomer and Whatley, 1995, 1996; Whatley and Boomer, 1995). This followed the study of ostracods from Horizon Guyot (composite of two cores,
0377-8398/99/$ - see front matter 0 1999 Elsevier Science B.V. All rights reserved. PII: SO377-8398(99)00015-S
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DSDP sites 171 and 44), Ita Mai Tai Guyot (DSDP Site 200) and a number of guyots in the Emperor Seamount Chain (Larwood and Whatley, 1993). The guyot sites drilled during ODP legs 143 and 144 are in the Mid-Pacific Mountains and the Marshall Islands, respectively. Their summits are typically at a present day water depth of between 1000 and 1500 m and are generally surrounded by bathyal sea floor at depths of about 2500 to 2000 m. In comparison, Horizon Guyot (DSDP sites 171 and 44) is almost completely surrounded by abyssal floor below 5000 m. The ostracods are of particular interest since they do not possess a planktonic larval stage, therefore, the occurrence of benthonic ostracods in some deepsea settings can be difficult to explain. Abyssal plains which lie below the CCD surround the Mid-Pacific Mountains (MPM), thus the calcite-shelled ostracods cannot migrate freely across the ocean floor. Not only are the ostracods present along the MPM and other apparently isolated bathyal sites worldwide but regionally and globally pandemic taxa are included in the assemblages indicating that some migration must be occurring although the mechanism remains unclear. Steineck et al. (1990) discussed the presence of distinct ostracod assemblages associated with experimental wood islands emplaced at 1800 to 4000 m water depth. Although the fauna was distinct from the usual deep-sea benthonic dwelling ostracods the observation of similar assemblages at distant sites indicates effective methods of long distance dispersal. They suggested as possible vectors: (1) entrainment in high-energy bottom flows; (2) transport as viable eggs in fish guts; (3) ‘hitch-hiking’ on larger vertebrates or invertebrates (or their demersal larvae); (4) active swimming or crawling; (5) deployment of organic threads to harness currents more effectively (Steineck et al., 1990, p. 311). Whatever methods are employed it is clear that fauna1 exchange takes place between distant bathyal sites, even those separated by abyssal depths below the CCD which are inimical to ostracod survival. The guyot studies listed above report levels of endemism, i.e. the percentage of species in a sample which are believed to be unique to that site. It is clear that such studies are influenced by the availability of comparative information from the surrounding region.
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The more sites that are investigated the more previously ‘endemic’ species we encounter. Thus levels of endemism are partly an artefact of sampling. The ostracod assemblages which become established on guyot summits are generally some hundreds of metres shallower than the surrounding sea floor although in some cases this difference can be quite considerable. A number of MPM guyot sites have been investigated but as yet the intervening plateau has not. This work describes a reconnaissance set of Late Cretaceous to Pleistocene samples from such a site (DSDP Site 463, Leg 62) to compare with assemblages from the MPM guyots (Leg 143) as well as guyots in the nearby Marshall Islands (Leg 144). Globally and regionally pandemic deep-sea ostraced assemblages have been described by a number of authors (Steineck et al., 1988; Whatley and Ayress, 1988). These studies suggest that close faunal similarities can be expected from adjacent (nonguyot) deep-sea sites. Similarly equidistant guyot sites, however, have revealed much higher levels of endemism (Boomer and Whatley, 1996). Preliminary comparisons of endemism between Site 463 and five nearby guyot summits is given in Boomer and Whatley (1996). They show that diversity at all sites ranges from about 10 to 40 species while endemism ranges from about 40 to 100% of the recorded species, the assemblages at Site 463 are apparently just as ‘unique’ as those on the guyot summits. The Mid-Pacific guyots are volcanic summits which were emergent or near emergent in the mid- to Late Cretaceous (data from reef complex sediments); this study is therefore concerned with latest Cretaceous and Cainozoic fauna1 records from the pelagic sediments capping the guyots. Only two previous papers have described deep-sea ostracods from the equatorial Mid-Pacific. Steineck et al. (1988) detailed the Oligocene-Quaternary ostracods from DSDP Leg 85 (5 sites), describing two ecozones: an Oligocene-Lower Miocene ecozone with stable palaeoceanographical conditions, high diversity and low fauna1 turnover, and a Middle Miocene-Quatemary ecozone. The latter ecozone was divided into a lower subzone with high fauna1 turnover and an upper subzone with a depauperate, psychrospheric (cold, deep-water) assemblage
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adapted to corrosive bottom-water conditions. It is not possible to draw detailed comparisons between the present study and that of Steineck et al. (1988) since that paper dealt only with species whose adults are greater than about 400 km in length, no small cytherurid ostracods having been described from Leg 85. In many deep-sea assemblages the Cytheruridae are often the most diverse ostracod family. Steineck and Yozzo (1988) detailed the evolution of the Bradleya johnsoni lineage from the Late Eocene to Recent sediments of Leg 85, however, the genus is not common in the present study.
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Site 463
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I 2. Background and methods Hole 463 (Deep Sea Drilling Project, Leg 62) was drilled in a water depth of 2525 m in the MidPacific Mountains (21”21.01’N, 174”40.07’E, Fig. 1). The hole was cored to a depth of 822.5 m with 36.6% recovery overall (Shipboard Scientific Party, 1981) although recovery for the interval in this study was >90% (Fig. 2). The youngest unit encountered, forming the greatest part of this study, was predominantly nannofossil ooze, 47 m thick (Early Eocene-
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Non-recovery within core Fig. 2. Lithological and stratigraphical section of top part of Site 463. Depth of samples indicated by black arrowheads. Individual cores l-9 marked together with non-recovery.
Fig. 1. Location map showing the central Pacific region with the 2000 m isobath marked. The location of DSDP Site 463 is marked as are the guyot sites investigated during ODP legs 143 and 144 (after Boomer and Whatley, 1995).
Pleistocene age). A further three samples were taken from the upper part of the next oldest unit which was composed of foram-nannofossil ooze and chalk (late Maastrichtian age, Fig. 2). In all, fifteen 50 cm3 samples were taken from this sequence. All samples were washed over a 200-mesh
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sieve to remove the mud fraction and then air-dried; they were dry-sieved through 60- and loo-mesh sieves. The two largest fractions were completely picked (i.e. all ostracods >125 urn) under a binocular microscope and arranged in fauna1 slides. The number of left and right valves of each species in a sample was recorded, and the higher number, added to the number of articulated carapaces was taken as a record of the minimum number of individuals present in that sample. It is these values that are given in the distribution range chart (Fig. 3). A very few specimens showed evidence of abrasion or dissolution. These were not included in the specimen counts as they are probably reworked. Total specimens recovered per sample were generally low, only 4 of the 15 samples yielded more than 100 individuals. This is a common problem when dealing with deep-sea Ostracoda, particularly in terms of diversity. Some of the results may not therefore be statistically significant, this must be borne in mind when interpreting the data. Figured specimens were coated with gold and photographed under the Cambridge 140 SEM at Aberystwyth. All figured specimens and fauna1 slides are deposited in the collections of the Department of Palaeontology, Natural History Museum, London to which the catalogue number prefix OS applies. The stratigraphical distribution and abundance of each taxon is recorded in Fig. 3. The samples yielded varying abundances of Ostracoda, shown in Fig. 4A. Species diversity for the ostracods has been reported in two ways. First, as the number of species recorded in a given sample (i.e., as number of species present in the sample, here referred to as simple species diversity) and, second, as ‘compound’ (cumulative) values calculated by adding to the simple species diversity those taxa which are temporarily absent from a sample possibly due to the nature of the sampling, here marked by an asterisk. This is necessary because of the oftenlow abundance of individual ostracods in deep-sea environments. We may of course be witnessing ‘real’ absences due to environmental controls but the asterisks help to indicate total stratigraphical range. Both
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the simple and compound values are plotted on the species diversity graph (Fig. 4B).
3. Fauna1 evolution at Site 463 The stratigraphical distribution of the ostracod assemblages at Site 463 is outlined in Fig. 3. This study is based on a reconnaissance set of samples and there are inevitably some large stratigraphical gaps (notwithstanding the sedimentary hiatuses, see Fig. 4), as such the first and last appearances of taxa are not well constrained. However, three distinct faunal assemblages can be discerned from the stratigraphical data presented in Fig. 3 and these are summarised in Fig. 4. The assemblages are hereafter referred to as A (the oldest), B and C (the youngest). Since 41 of the 62 species recorded are considered to be endemic to this site it is difficult to make palaeoenvironmental conclusions based on the assemblage composition. Most of the genera present are recorded from shallow marine (< 10 m) through to bathyal (and in some cases abyssal) depths worldwide. During the Late Cretaceous to Recent interval many important global oceanographical changes have taken place and these are reflected in deepsea ostracod assemblages (Benson, 1990). Recently, Cronin and Raymo (1997) indicated the importance of sea-surface conditions (climate, productivity) in driving biological changes in the deep sea, with particular reference to ostracods. The three assemblages described below are distinctly different and must reflect the complex interplay of a number of environmental factors. 3.1. Assemblage
A
Assemblage A (4 samples, late MaastrichtianEocene), is characterised by low diversity samples dominated by the suborder Platycopina. High percentages of Platycopina have also been recorded from the Lower Palaeocene interval of ODP Site 865 (Boomer and Whatley, 1995) and this may be of regional significance. The reconstruction of the sub-
Fig. 3. Stratigraphical distribution of species recovered. Asterisk (*) indicates inferred Numbers indicate minimum number of individuals present (see text),f= fragment.
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Fig. 4. Fauna1 data plotted against age in millions of years. (A) Total number of specimens recorded in sample. (B) Number of species recorded (solid line) and compound diversity which includes asterisked records (dotted line). (C) Percentage of each sample constituted by the most common species, or dominance (solid line), and percentage of species thought to be endemic to this site (dotted line). (D) Percentage of Platycopina (solid line) and Krithidae (dotted line). (E) Number of species originations or first appearances (solid line) and extinctions (dotted line) for each sample. Hatched area on left hand column indicates presence of hiatuses.
sidence history of Site 463 indicates a palaeodepth of 1700 to 1300 m (Shipboard Scientific Party, 1981) for the Maastrichtian to Eocene interval (Barrera et al., 1997 suggest a palaeodepth of 1000-1500 m for the latest Cretaceous at Site 463) while the reconstruction for Site 865 (Bralower et al., 1995) suggests a palaeodepth reconstruction of 1300-1500 m for the Palaeocene-early Eocene interval. Thus, the assemblages are clearly deep-sea. Whatley (1992) associated high relative abundances and fauna1 dominance of Platycopina with decreased levels of dissolved oxygen at or about the sediment-water interface. High percentages of Platycopina in Assemblage A (Fig. 4D) are unlikely to reflect the influence of the Oxygen Minimum Zone at these depths but they may indicate sluggish circulation or the production of poorly oxygenated intermediate waters at that time. Palaeoceanographic studies from the region, however, suggest that this
was not the case. The platycopids may indicate oxygen depletion resulting from high surface productivity although there is no supporting evidence for this. Barrera et al. (1997) reported that the latest Cretaceous period witnessed vigorous oceanic circulation with different sources of deep and intermediate waters ‘competing’. The influence of these sources were variously controlled by changes in climate and sea level. They note one particular interval at about 7271 Ma during which oxygen and carbon isotopes indicate a period of particularly cool intermediate waters in the low latitude Pacific region. Before and after this event, they conclude, thermohaline circulation in this region may well have been controlled by the flow of relatively warm, high salinity water plumes. This process would have resulted in cool intermediate waters which would have mainly formed at high latitudes. Barrera et al. further conclude that
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during such warm climatic periods of Earth history, oceanic circulation may well have been quite dynamic due to the lack of distinct density differences within the oceans. Platycopids are not particularly common in deepsea environments today. One possible explanation for their dominance in these Mid-Pacific sites comes from studies of Recent reefal ostracod assemblages in tropical and subtropical regions (e.g. Jellinek, 1993; Yassini et al., 1993; Whatley et al., 1995). These settings yield abundant and diverse ornamented Platycopina similar to those recorded from the latest Mesozoic and earliest Cainozoic of sites 463 (this work) and 865 (Boomer and Whatley, 1995). In these pre-psychrosphere times (pre 38 Ma), some shallow water reefal taxa may well have been able to adapt to the gradual subsidence of the Late Cretaceous reef complexes. Shallow-water reefal ostracod assemblages of Palaeocene age (including ornamented platycopids) are known from the Emperor Seamounts in the northern Pacific (Malz, 1981). However, the post-Palaeocene sequences on the Emperor Seamounts are either truncated or interrupted by volcanism thus obscuring the fate of these shallow water taxa. 3.2. Assemblage
B
Assemblage B (5 samples, Oligocene-Late Miocene) is initially marked by a sharp increase in species originations (19 new species, Fig. 4E) and a concomitant diversity increase (from 6 to 24 species), while its uppermost limit is marked by an increase in extinctions (17 last occurrences) accompanied by a diversity decline (from 23 to 7 species). Ostracod abundance is at its highest during this interval. The assemblages show an initial decline in the importance of the Platycopina which is mirrored by the appearance, for the first time in this sequence, of the family Krithidae which constitutes the most abundant taxa in Assemblage B. Throughout the sequence the Platycopina and Krithidae follow an inverse relationship in terms of their relative abundance for most of the samples, together they constitute the bulk of each assemblage (Fig. 4D). Krithe is often one of the most numerically abundant taxa in bathyal ostracod faunas today and it dominates many Neogene assemblages. Thus, we are
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seeing the beginning of the establishment of modern deep-sea faunas. One of the key differences between Assemblage A and Assemblage B is that the two are separated by the establishment of the psychrosphere at about 40-38 Ma (Benson, 1975) although there were many other global oceanic temperature and circulation fluctuations during the Palaeogene which may have driven evolutionary changes in the intermediate water benthos. Zachos et al. (1994) discuss changing sea surface temperatures (SST) and vertical temperature profiles during the early Cainozoic and note that a marked temperature fall occurred between the latest Palaeoceneeearliest Eocene and the Late Eocene-earliest Oligocene. Such changes must have had significant effects on benthonic assemblages. Boomer and Whatley (1995) note a marked ostracod diversity crash at the Palaeocene-Eocene boundary at Site 865, an event also witnessed in deep-sea foraminifera (Thomas, 1990a). The possible mechanisms behind this fauna1 crisis are discussed in a number of papers (e.g. Thomas, 1990a; Eldholm and Thomas, 1993) which allude to the possible influence of tectonic events in the North Atlantic (known to be an important region in driving global oceanic circulation). Following the initial peak in species appearances in Assemblage B, the number of originations decreases and the rest of this interval is characterised by increased extinction. This may indicate the displacement of the original population by an immigrant fauna. This period includes a Late EoceneLate Miocene hiatus in sedimentation (Fig. 4). The sample immediately following this stratigraphical gap, which marks the upper limit of Assemblage B, however, sees all of the fauna1 indices continuing at a similar level (Fig. 4). This supports the work of Benson (1990, fig. 2) which indicates that the main ostracod diversity crash in this region occurred in the Late Miocene. The crash is also noted at Site 873 (Boomer and Whatley, 1996, fig. 6) and Site 171/44 (Larwood and Whatley, 1993, fig. 7). 3.3. Assemblage
C
Assemblage C (6 samples, Late Miocene-Pleistocene) is marked by depauperate, low diversity assemblages with little fauna1 turnover. Diversity falls from over 20 species in the uppermost sample of
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Assemblage B to less than ten species within a relatively short period of time and specimen abundance also drops markedly in this interval. Assemblage C initially shows an increase in the numerical importance of the Platycopina at the expense of the Krithidae but this pattern is quickly reversed through the Late Pliocene-Pleistocene interval when the Platycopina are absent and the Krithidae constitute 30-40% of the assemblages. Assemblage C is typical of modern globally pandemic psychrospheric ostracod faunas (Benson, 1975).
4. Conclusions Despite the fact that only 15 samples were taken from the Cretaceous-Pleistocene interval, it is possible to recognise three distinct fauna1 assemblages. The Late Cretaceous-early Cainozoic interval (Assemblage A) is dominated by ornamented platycopids which may reflect low oxygen levels near the sediment-water interface in this part of the Pacific Ocean. They may be a remnant of Earlymid-Cretaceous shallow water reefal faunas which adapted to deeper water conditions during subsidence of the region. Assemblage B marks a decline in the importance of the Platycopina with increases in ostracod abundance, diversity and rate of fauna1 turnover. Steineck et al. (1984) described a similar deep-sea ostracod assemblage from the Palaeogene of Barbados and commented that those faunas were part of a circum-equatorial (Tethyan) deep-sea fauna which had established a cosmopolitan distribution due to the latitudinal flow of warm saline bottom waters during this period. The existence of warm saline bottom waters at this time remains a matter of debate. It is probable that a short-lived (end Palaeocene) shift in deep water formation from high to low latitudes did occur but the conditions were soon reversed. Several less intense and shorter duration events may also have occurred during the Late Palaeocene and Early Eocene (Thomas, 1990b, 1992). There is little evidence to support the prolonged existence of circum-equatorial, warm, saline bottom waters referred to by Steineck et al. (1984). Assemblage C, with low diversity, low abundance and low fauna1 turnover equates to the upper sub-
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unit, upper Ecozone of Steineck et al. (1984) and reflects the establishment of the psychrospheric ostraced fauna. This assemblage is typical of modem bathyal ostracod faunas. At least 30% of the species encountered from each sample at Site 463 have not previously been recorded and these are currently considered to be endemic. All of the species in the oldest sample (463 9-3, 33-40 cm; upper Maastrichtian) are considered to be endemic (Fig. 4C), however, it important to note that there are few studies of deep-sea Maastrichtian ostracods from the central Pacific with which this material can be compared. The apparently high levels of apparently endemic taxa at Site 463 (Fig. 4C) supports the premise that, as yet, our knowledge of deep-sea faunas from this region is incomplete. This is of particular importance to studies which allude to the high endemicity of deep-sea ostracod guyot assemblages. If our knowledge of the abyssal and bathyal ‘background’ fauna is incomplete then our interpretation of guyot endemism may be misleading. The high endemicity of assemblages from guyot summits may not be as unique as had been thought since every new site in the region, whether guyot or not, yields on average 30-40% new taxa. As our knowledge base increases so it becomes clear that deep-sea benthonic ostracods are capable of migrating over considerable distances, despite being unable to survive in water below the CCD. This dispersal capability is attested by the presence of the same species in deep water sites in the Pacific and Atlantic (including guyots). Although the distribution mechanisms are unknown it must be achieved passively within the intermediate waters. A better test of ostracod endemism will only be achieved through studies of pelagic guyot sediments from sites which are surrounded entirely by abyssal waters which lie below the CCD.
Acknowledgements The author wishes to thank Professor Robin Whatley for his guidance during the work and for reading an early draft of this manuscript. The technical assistance of Messrs D. Griffiths and G. Hughes, Dr R. Jones and Miss M. Curry is gratefully acknowl-
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edged. This research was initially undertaken during the tenure of a NERC ODP Special Topic award at the University of Wales, Aberystwyth. The author wishes to thank Ellen Thomas, Alan Lord and an anonymous referee for their critical assessment of the paper.
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Subclass OSTRACODA Latreille, 1806 Order PODOCOPIDA Miiller, 1894 Suborder PLATYCOPINA Sars, 1866 Family CYTHERELLIDAESXS, 1866 Genus Cytherellu iones, 1849 Cytherella postagrena Boomer, sp. nov. (Plate 1, 5, 8,9)
Appendix A. Taxonomy In all, 62 separate taxa have been identified in the present study, 48 are illustrated in Plates l-3 and Fig. 5. Thirteen of the most abundant taxa are discussed in the following taxonomic section of which six are erected as new species. Abbreviations: M = male; F = female; A = adult (sex not discernible); RV = right valve; LV = left valve; CAR = carapace (e.g. FRV = female, right valve). All specimens adult, unless otherwise stated. All specimens are deposited in the collections of the Department of Palaeontology, Natural History Museum, London.
Cytherella sp. 2 Boomer and Whatley, 1995. Holotype: OS14689 FRV (Plate 1, 8). Type locality and horizon: Deep Sea Drilling Project Leg 62, Site
463, Mid-Pacific Mountains, Central West Pacific (21”21.01’N, 174’40.07’E); upper Maastrichtian, Core 9, Section 3, Interval 33-40 cm. Etymology: With reference to the net-like reticulation on the posterior region of the valves. Diagnosis: A weakly inflated species of Cytherella with compressed anterior and postero-ventral margins. Lateral surface smooth or bears very faint anastomosing ribs which are best developed peripherally, a weak net-like reticulation is developed posteriorly.
Fig. 5. Transmitted light drawings of selected taxa. For abbreviations see Appendix A. (a) Krithe sp. A. LV, 850 pm. (b) Argilloecia sp. C. LV, 540 pm. (c) Krithe sp. A. RV, 700 urn. (d) Argilloecia sp. B. RV, 525 pm. (e) Argilloecia sp. B. LV, 490 pm. (f) Argilloecia sp. C. RV. 590 urn. (g) Australloecia cf. A. micra. RV, 425 urn. (h) Bairdoppilata sp. A. RV. 1180 pm. (i) Argilbecia sp. C. LV, 560 urn.
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Material: 31 valves 2 carapaces. Description: Dorsal margin slightly convex, ventral margin bears
a distinct oral concavity. Anterior margin very broadly rounded, posterior margin more angular being particularly sharply truncated in the females (Plate 1, 8) compared with males (Plate 1, 5. 9). Valves distinctly swollen posteriorly in females, extending to posterior margin, less so in males where the posterior margin is compressed. Remarks: This species has also been recorded from the Palaeocene of ODP Site 865, Cytherella sp. 2 (Boomer and Whatley, 1995). Cytherella posterospinosa Boomer, sp. no”. (Plate 1, l-4) Cytherella sp. 8 Boomer and Whatley, 1995. Holotype: OS14685 FRV (Plate 1, 1). Qpe locality and horizon: Deep Sea Drilling Project Leg 62, Site
463, Mid-Pacific Mountains, Central West Pacific (21”21.01’N,
Plate 1 For abbreviations and repository see Appendix A. All specimens adult and all views external lateral unless otherwise stated. 14. Qtherella posterospinosa Boomer, sp. nav. EoceneMiocene. 1,4. Holotype. FRV 0314685. x45. I. Int. lat. x4. 4. MRV 0814686. x50. 2. MLV 0814687. x51. 3. 5, 8, 9. Cytherella postagrena Boomer, sp. nav. MRV 0314688. x49. 5. Holotype. FRV 0814689. x49. 8. MRV 0846890. x46. 9. Cytherella sp. A. ACAR 0814691. 6, I. Dorsal view. x45. 6. Left lat. x51. 7. Cytherella sp. C. ARV 0S14692. x51. IO. 11. Bairdoppilata sp. A. ALV 0814693. x25.5. Zubythocypris sp. A. ACAR OS14694 right lat. x49. 12. Bairdoppilata sp. B. ARV 0314695. x33. 13. 14. Aratrocypris sp. A. ALV 0814696. x 102. 15-17. Krithe sp. A. FRV 0814697. x47. 15. FLV 0814698. x48. 16. 17. MLV 0314699. x46. 18. 23. Argilloecia sp. A. ARV OS 14700. x62.5. 18. 23. ALV OS14701. x64. 19, 24. Argilloecia sp. B. 19. ARV 0814702. x64. ALV 0814703. x73. 24. 20. 25. Argilloecia sp. C. 20. ARV OS 14704. x79. ALV 0314705. x79. 25. 21, 22. Australloecia cf. A. micra Bonaduce et al. 21. ARV 0314706. x73. ALV os14707. x 102. 22.
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174YO.07’E); upper Maastrichtian, Core 6, Section 2, Interval 61-68 cm. Etymology: With reference to the development of conjunctive spines along the postero-lateral surfaces. Diagnosis: A tumid species of Cytherella with regular reticulation which is particularly well developed on the posterior third of valve, the reticulation bears many short, blunt backward pointing conjunctive spines. Material: 166 valves. Description: Carapace oval to quadrate in lateral view. Anterior
and posterior margins broadly rounded, ventral margin sinuous with marked concavity at mid-length, dorsal margin sinuous with small peak at mid-length. Greatest height anteriorly. A large number of small posteriorly directed conjunctive spines are associated with the reticulae in the posterior part of the valves. Reticulation fades anteriorly but is present on most of the lateral surfaces, grading to fine ribbing along the margins in the anterior half. Median adductor muscle scar sulcus is prominent in some specimens and non-reticulate. Remarks: This species has also been recorded from the Middle Eocene to Lower Oligocene of ODP Site 865 (Boomer and Whatley, 1995) with a probable reworked specimen in the Lower Miocene sediments of that site. The specimens from Site 865 are slightly more heavily reticulated along the mid-lateral surface than in the present material. Suborder PODOCOPINA Sam, 1866 Superfamily BAIRDIACEA Sam, 1888 Family BAIRDIIDAESars, 1888 Genus Buirdoppiluta Coryell, Sample and Jennings, 1935 Bairdoppilata sp. A (Plate 1, 11; Fig. 5h) Material: 51 valves. Description: A large, ovate species with poorly developed ante-
rior and postero-ventral marginal flanges, postero-ventral margin serrated. Lateral surface bears a few normal pores, otherwise no external features recognised. Greatest length just below midheight, greatest height at or just in front of mid-length. Ventral margin broadly rounded, dorsal margin lacks distinct cardinal angles. Remarks: This species is similar to Bairdoppilata sp. 1 Boomer and Whatley, 1995 from the Middle Eocene to Lower Oligocene of ODP Site 865 which can be distinguished by the greater number of normal pores on the lateral surfaces and the slightly more extended posterior process. Baintoppilata sp. B (Plate 1, 13) Material: 25 valves. Description: A distinctly elongate species with a narrow, com-
pressed antero-marginal flange and almost no posterior flange. Greatest length close to sinuous ventral margin. No normal pores observed on lateral surface. Remarks: Smaller than Bairdoppilata sp. A; this species is also more elongate in lateral view and lacks the distinct normal pore canals on the lateral surfaces. This species is restricted to Assemblage B. Superfamily CYPRIDACEA Baird, 1845 Family PONTOCYPRIDIDAE Muller,1894
142
I. Boomer/Marine
Micropaleontology 37 (1999) 131-147
I. Boomer/Marine
Micropaleontology 37 (1999) 131-147
143
Genus Argilloecia Sam, 1866.
Genus Australoecia McKenzie, 1967
Argilloecia sp. A (Plate 1, 18, 23; Fig. 5b and d) Material: 51 valves. Description: This species is distinguished by its relatively elon-
Australoecia cf. A. micra (Bonaduce et al., 1975) (Plate 1, 21,
gate carapace. Antero-marginal flange small, apparently truncated dorsally. Dorsal margin short and straight with the greatest height anteriorly. Postero- and antero-dorsal margins convex. Argilloecia sp. B (Plate 1, 19, 24; Fig. 5e and f) Material: 14 valves. Description: Carapace distinguished by well developed dorsal
cardinal angles and strongly sinuous ventral margin in lateral view. Postero- and antero-dorsal margins straight.
22; Fig. 5g and i) Material: 24 valves, 1 carapace. Remarks: This species is similar to one described by Bona-
duce et al. from the Recent of the Mediterranean. That species is known from Quatemary sediments in the Southwest Pacific Ocean (Whatley and Ayress, 1988). The present species differs from the type description in possessing a more broadly rounded posterior margin and a slightly higher carapace relative to the length. Superfamily CYTHERACEA Baird, 1850 Family KRITHIDAE Mandelstam in Bubikyan, 1958 Genus Krirhe Brady, Crosskey and Robertson, 1874
Plate 2 For abbreviations and repository see Appendix A. All specimens adult and all views external lateral unless otherwise stated. Henryhowella cf. H. asperrima (Reuss). 1, 2, 4. FRV OS14708. 1,4. x61. 1. Int. lat. x61. 4. MRV 0814709. x65. 2. Henryhowella cf. H. dasyderma Brady. FRV OS3, 6. 14710. x42. 3. FRV int. lat. x45. 6. Bradleya sp. A. ARV OS14711. x39.5. 5. Poseidonamicus dinglei Boomer, sp. no”. I, 8, 9. ARV OS14712. I, 9. x54. 7. Holotype. Int. lat. x54. 9. ALV OS14713. x57. 8. Pennyella sp. A. FLV 0314714. x46. 10. 11. Poseidonamicus sp. B. ARV OS14715. x49. Pennyella sp. B. MRV 0814716. 12, 15. hit. lat. x54. 12. x49. 15. Pennyella sp. C. ARV 0S14717. 13, 14. x44. 13. Int. x56. 14. Abyssocythere paratrinidadensis Boomer, sp. non l&18,21 Holotype. ALV 0814718. x51. 16. ARV 0814719. 17, 18. x51. 17. Int. x55. 18. RV juv, A-l? 0814720. x51. 21. Bathycythere bermudezi (Van den Bold, 1946). ALV 19, 20. 0314721. Int. x30. 19. x30. 20. Kuiperiana cf. K. bathymarina Ayress, Coles and 22. Whatley. ALV OS 14722. x 114. Pariceratina ubiquita Boomer. ARV 0S14723. x52. 23. Profundobythere bathytatos Coles and Whatley. 24. ARV 0814724. x78.
Krithe sp. A (Plate 1, 15-17; Fig. 5a and c) Material: 488 valves. Remarks: Numerically this is the most abundant single taxon in
the present study with over 400 individual valves recovered in the Oligocene to Upper Miocene interval. The species is similar to K&he dolichodiera Van den Bold, 1946 but differs externally in the outline of the posterior margin. Furthermore, the present species has a different anterior vestibule and antero-dorsal radial pore canal pattern (see Coles et al., 1994 for re-description of K. dolichodiera and discussion of the genus). Family
CYTHERURIDAE
Mtlller, 1984
Genus Hemiparacytheridea Hemiparacytheniiea
Herrig, 1963
ayressi Boomer, sp. nolz (Plate 3, 7, 9-l 1)
Hemiparacytheridea sp. 30 Boomer and Whatley, 1995. Hemiparacytheridea sp. 31 Boomer and Whatley, 1995. Holotype: OS14732 ALV (Plate 3, 9). Type locality and horizon: Deep Sea Drilling Project Leg 62, Site
463, Mid-Pacific Mountains, Central West Pacific (21”21.01’N, 174’40.07’E); upper Maastrichtian, Core 6, Section 2, Interval 61-68 cm. Etymology: In honour of Dr Michael Ayress (formerly ANU), for his work on Pacific deep-sea Ostracoda. Diagnosis: A quadrate, alate species of Hemiparacytheridea with irregular, corrugate reticulae. Material: 54 valves. Description: Carapace quadrate in lateral outline with straight, parallel ventral and dorsal margins. Anterior margin slightly convex, posterior margin drawn out into caudal process along the dorsal margin. Anterior margin compressed with narrow margin bearing up to three short spines, posterior margin broadly compressed. Carapace bears robust alae which are terminated laterally by an irregular rib running from the anterior margin until it forms a sharp, backward pointing, projection posteriorly. A weak, vertical, median sulcus is present. Lateral surfaces omamented by coarse irregular ribbing and secondary, fine intercostal punctation. Ribbing forms small raised area antero-dorsally and slight dorsal projection along the postero-dorsal margin. Remarks: The species has been recorded from the PalaeoceneEocene interval of ODP Site 866 (Boomer and Whatley, 1995)
144
I. Boorner/Marine
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37 (1999) 131-147
1. Boomer/Marine
Micropaleontolog?
with another possible record (single specimen) from the Lower Oligocene of Site 865 (authors unpublished information). Those specimens possess more dominant ribbing. although in all other respects they appear identical. Family TRACHYLEBERIDIDAE
Sylvester-Bradley.
Genus Abyssocythere Benson.
197
Abyssocylhere parattinidadensis, 18, 21)
1948
I Boomer,
sp. non (Plate 2, 16-
Steineck et al., 1985. ALV (Plate 2, 16). Type locality and horizon: Deep Sea Drilling Project, Leg 62, Site 463, Mid-Pacific Mountains, Central West Pacific (21”21 .Ol’N. 174”40.07’E): upper Maastrichtian, Core 9, Section 3, Interval 3340 cm. Etymolog!: With reference to the close similarity between this species and A. trinidadensis (Van den Bold, 1957). ?Abyssocythere
trinidadensis
Holorype: 0314718
37 (I 999) 131-147
145
Diagnosis: Differs from A. trinidadensis in the form of the distinctive, raised, ‘box-like’ postero-dorsal reticulum which is open ventrally in the present species and is completely enclosed in the former species. Material: 21 valves. Description: All internal and external features are typical of the genus (see Benson, 1971). The present specimens are well preserved and show a delicate pattern of reticulae on much of the external surfaces but particularly the antero-lateral region. The dorsal spines are perhaps better developed than in the holotype of A. trinidadensis. however, this may be a preservational feature. In all other respects the present material is similar to A. trinidadensis. Steineck et al. (1984) tigured a specimen of A. trinidadensis from the Eocene of Barbados which also appears to have an ‘open’ postero-dorsal reticulum and is. therefore. con-specitic with the present material.
Genus Henryhowella Puri, 1957 He~lrvhowellcccf. H. osperrima (Reuss, 1850) (Plate 2. 1. 2, 1). 39 valves. Remarks: This species is similar to H. asperrima (Reuss). described from bathyal Miocene sediments of the Vienna Basin, in possessing a sub-central tubercle and postero-lateral longitudinal swellings of the carapace. Type material of the species has recently been re-figured by Kempf and Nink (1993). Although similar in outline and ornament to H. asperrinw the present specimens are 20% smaller than the mean size for the species given by Kempf and Nink. The well developed hinge elements in the figured specimen (Plate 2, 4) confirms that they are adult and they are therefore assigned to H. cf. H. asperrima. A second species of HentThowella, H. cf. H. dasyderma Brady (Plate 2, 3, 6) has been recorded in the Upper Miocene-Pleistocene of Site 463, and closely resembles the species described by Brady ( 1880) from the Southeast Pacific. Material:
Plate 3 For abbreviations and repository see Appendix A. All specimens adult and all views external lateral unless otherwise stated. 1. Eucythrre sp. .A 41 V OS14725 ~92. 2. Eucythere sp. B. ARV 0S14726. x96. 3. Eucythere sp. C. ARV 0814721. x85. 4. Eucythere sp. D. ALV 0S14728. x88. 5. Hemiparacytheridea mediopunctata Coles and Whatley ARV 0814729. x127. Hemiparacytheridea cf. H. mediopunctata Coles 6. and Whatley. ARV 0814730. x90. ayressi Boomer, sp. nor. 7.9, IO, II Hemiparacytheridea ARV 0814731. 7. Il. Dorsal view. x97. I. x91. II. Holotype. ALV OS 14732. 9, 10. 8. Hemiparacytheridea sp. A.? ARV 0S14733. x96. Semicytherura cf. S. pulchra Coles and Whatley. 12. 15. ALV OS14734. x 100. 12. ARV 0814735. x 100. 15. Parahemingwayella downingae Coles and Whatley. 13. ALV OS14736. x 119. 14. Aversovalva sp. B. ALV 0814737. x97. 16, 17. Aversovalva formosa Coles and Whatley. 16. ARV int. 0S14738. x 110. ALV 0S14739. x99. 17. 18. 19. Cytheropteron sp. A. ARV OS 14740. x80. 18. ALV specimen lost. 19. Cytheropteron sp. D. 2&23. ARV 0S14741. x78. 20. 21. ALV OS14742. x 82. 22. ALV int. 0814743. x86. 23. Juv RV (A- I ) specimen lost. 24. Cytheropteron sp. E. ALV 0314744. x75. Cytheropteron sp. G. ALV 0814745. x77. 25. Cytheropteron sp. F. ALV 0814746. x83. 26.
Genus Pennyella
Neale. 1975
Pennyella
sp. B (Plate 2, 12, 15)
Material:
12 1 valves.
Remarks: Three species of Pennyella have been recorded in the present study. Pennyella sp. A, recorded from the Maastrichtian of Site 463. is probably ancestral to both Pennyella sp. B and Pennyeilu sp. C. Pennvellu sp. B is the most abundant of the three and is distinguished by the presence of a well developed series of spines along the anterior and postero-ventral compressed margins and also along a ventro-lateral carina. The species bears a well developed postero-dorsal knob and a serrated dorsal margin, both typical for the genus. A sub-central tubercle is present,
Genus Poseidonamicus Benson.
1972.
Poseidonamicus dinglei Boomer, sp. nav. (Plate 2. 7-9) Holotype:
OS 147
I2 ARV (Plate 2, 7).
Deep Sea Drilling Project Leg 62, Site 463. Mid-Pacific Mountains, Central West Pacific (21”21.01’N, 174”40,07’E): upper Maastrichtian, Core 9. Section 3, Interval 33-40 cm. E~molo~~: In honour of Dr. R.V. Dingle (Geological Institute, Copenhagen University) for his work on deep-sea Ostracoda. T,?appr locali@ and horizon:
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Diagnosis: A species of Poseidonamicus with regular reticulae, strong marginal and ventro-lateral ribs. The admarginal region bears a few fine radial ribs but little or no punctation. Material: 160 valves, 1 carapace. Description: Carapace elongate, quadrate in lateral view with a very broadly rounded anterior margin and triangular to arcuate posterior margin. Greatest height at anterior cardinal angle. The anterior-most two or three reticulae immediately above the ventro-lateral carina are more deeply developed than any other features of the ornament. Anterior and postero-ventral margins bear well developed spines. Interior details as for genus. Remarks: The present species bears similarities to the P. anteropunctatus group described by Whatley et al. from the Cainozoic of the Southwest Pacific. Z? dinglei is distinguished by the stronger development of the marginal ribs. Postero-dorsally the marginal rib is distinctly thickened in the LV while in the RV the anterodorsal cardinal region displays a sinuous outline.
References Barrera, E., Savin, S.M., Thomas, E., Jones, C.E., 1997. Evidence for thermocline-circulation reversals controlled by sealevel change in the latest Cretaceous. Geology 25 (8), 715718. Benson, R.H., 1971. A new Cenozoic deep-sea genus, Abyssocythere (Crustacea, Ostracoda, Trachyleberididae) with descriptions of five new species. Smithson. Contrib. Paleobiol. 7, l-25. Benson, R.H., 1975. The origin of the psychrosphere as recorded in changes of deep-sea ostracode assemblages. Lethaia 8, 6983. Benson, R.H., 1990. Ostracoda and the discovery of global Cainozoic paleoceanographical events. In: Whatley, R., Maybury, C. (Eds.), Ostracoda and Global Events. Chapman and Hall, pp. 41-58. Bonaduce, G., Ciampo, G., Masoli, M., 1975. Distribution of Ostracoda in the Adriatic Sea. Pubbl. Staz. Napoli 40 (Suppl.), l-305. Boomer, I., Whatley, R., 1995. Cainozoic Ostracoda from guyots in the Western Pacific: Leg 143, Holes 865B and 866B. Proc. ODP Sci. Results 143, 75-86. Boomer, I., Whatley, R., 1996. Ostracod endemism on midPacific guyots from ODP legs 143 and 144. In: Moguilevsky, A., Whatley, R. (Eds.), Microfossils and Oceanic Environments. University of Wales, Aberystwyth Press, pp. 403-412. Brady, G.S., 1880. Report on the Ostracoda dredged by H.M.S. Challenger During the years 1873-1876. Reports on the Voyage of H.M.S. Challenger, pp. 1-184. Bralower, T.J., Zachos, J.C., Thomas, E., Parrow, M.N., Paull, C.K., Kelly, D.C., Premoli-Silva, I., Sliter V, W., 1995. Late Paleocene to Eocene Paleoceanography of the Equatorial pacific Ocean: Stable Isotopes recorded at ODP Site 865, Allison Guyot. Paleoceanography 10, 841-865. Coles, G.P., Whatley, R., Moguilevsky, A., 1994. The ostracod genus Krithe from the Tertiary and Quatemary of the North Atlantic. Palaeontology 37, 71-120.
Cronin, T.M., Raymo, M.E., 1997. Orbital forcing of deep-sea benthic species diversity. Nature 385, 627-642. Eldholm, O., Thomas, E., 1993. Environmental impact of volcanic margin formation. Earth Planet. Sci. Lett. 117. 319329. Jellinek, T., 1993. Zur Gkologie und Systematik rezenter Ostracoden aus dem Bereich des kenianischen Barriere-Riffs. Senckenbergia Lethaea 73 (l), 83-225. Kempf, E.K., Nink, C., 1993. Henryhowella asperrima (Ostracoda) aus der Typusregion (Miozan: Badenian; Wiener Becken). Sonderveroff. Geol. Inst. Univ. Koln 70, 95-l 14. Larwood, J.G., Whatley, R.C., 1993. Tertiary to Recent evolution of Ostracoda in isolation on seamounts. In: McKenzie, K.G., Jones, P. (Eds.), Ostracoda in the Earth and Life Sciences. Balkema, pp. 53 l-549. Larwood, J.G., Whatley, R., Boomer, I., 1996. Seamount ostracod evolution: evidence from Horizon Guyot, Central Pacific Ocean (DSDP sites 44 and 171) and the Ninetyeast Ridge. East Indian Ocean (DSDP) Site 214) In: Moguilevsky, A., Whatley, R. (Eds.), Microfossils and Oceanic Environments, pp. 385-402. Malz, H., 1981. Pallozane Ostracoden von den Emperor Seamounts, NW-Pazifik. Zitteliana 7, 3-29. Shipboard Scientific Party, 1981. Western Mid-Pacific Mountains. Init. Rep. DSDP 62, 33-156. Steineck, P.L., Yozzo, D., 1988. The Late Eocene-Recent Brad&a johnsoni Benson lineage (Crustacea, Ostracoda) in the Central Equatorial Pacific. J. Micropalaeontol. 7, 187- 199. Steineck, P.L., Breen, M., Nevins, N., O’Hara, P., 1984. Middle Eocene and Oligocene deep-sea Ostracoda from the Oceanic Formation, Barbados. J. Paleontol. 58, 1463-1496. Steineck, P.L., Dehler, D., Hoose, E.M., McCalla, D., 1988. Oligocene to Quatemay Ostracods of the Central Equatorial Pacific (Leg 85, DSDP-IPOD). In: Hanai, T., Ikeya, N., Ishizaki, K. (Eds.), Evolutionary Biology of Ostracoda: its Fundamentals and Applications. Kodansha, Tokyo, pp. 597617. Steineck, PL., Maddocks, R.F., Turner, R.D., Coles, G., Whatley, R., 1990. Xylophile Ostracoda in the deep sea. In: Whatley, R., Maybury, C. (Eds.), Ostracoda and Global Events. Chapman Hall, London, pp. 307-319. Thomas, E., 1990a. Late Cretaceous-early Eocene mass extinctions in the deep sea. In: Sharpton, V.L., Ward, P.D. (Eds.), Global Catastrophes in Earth History; An Interdisciplinary Conference on Impacts, Volcanism and Mass Mortality. Geol. Sot. Am. Spec. Pap. 247,481-495. Thomas, E., 1990b. Late Cretaceous through Neogene deepsea benthic foraminifers (Mud Rise, Weddell Sea, Anarctica). Proc. ODP Sci. Results 113, 571-594. Thomas, E., 1992. Cenozoic deep-sea circulation: Evidence from deep-sea benthic foraminifera. A.G.U. Antarct. Res. Ser. 56, 141-165. Van den Bold, W.A., 1957. Ostracoda from the Paleocene of Trinidad. Micropaleontology 3, 1-l 8. Whatley, R.C., 1992. The platycopid signal: a means of detecting kenoxic events using Ostracoda. J. Micropalaeontol. 10, 18 l185.
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Whatley, R.C., Ayress, M., 1988. Pandemic and endemic distribution patterns in Quatemary deep-sea Ostracoda. In: Hanai, T., Ikeya, N., Ishizaki, K. (Eds.), Evolutionary Biology of Ostracoda: its Fundamentals and Applications. Kodansha, Tokyo, pp. 739-758. Whatley, R.. Boomer, I., 1995. Cenozoic Ostracoda from guyots in the western Pacific: Leg 144, Holes 871A, 872C and 873B. Proc. ODP Sci. Results 144, 87-96. Whatley, R.C., Cooke, P.C.B., Warne, M.T., 1995. The Ostracoda
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from Lee Point on Shoal Bay, Northern Australia: Part 1 Cladocopina and Platycopina. Rev. Esp. Micropaleontol. 27 (3), 69-89. Yassini, I., Jones, B.G., Jones, R.M., 1993. Ostracods from the Gulf of Carpentaria, northeastern Australia. Senckenbergiana Lethaea 73 (2), 375-406. Zachos, J.C., Scott, L.D., Lohmann, K.C., 1994. Evolution of early Cenozoic marine temperatures. Paleoceanography 9 (2) 353-387.
Marine Micropaleontology 37 ( 1999) 13I- 147 www.elsevier.com/locate/marmicro
Late Cretaceous and Cainozoic bathyal Ostracoda from the Central Pacific (DSDP Site 463) Ian Boomer * Department of Geography, University of Newcastle, Newcastle, NE1 7RU, UK
Received 16 September 1998; accepted 8 March 1999
Abstract Cainozoic deep-sea ostracod assemblages from the summits of Mid-Pacific guyots point to high levels of endemism possibly as a result of their bathymetric separation from the surrounding sea floor. However, the interpretation of these fossil assemblages is hampered by the paucity of comparative material from surrounding non-guyot sites. Fifteen ostracod assemblages from DSDP Site 463 (Late Cretaceous-Pleistocene) were studied to compare with those from nearby guyots. Three distinct fauna1 assemblages are recognised at Site 463: Assemblage A (Maastrichtian-Eocene), Assemblage B (Oligocene-Upper Miocene) and Assemblage C (Upper Miocene-Pleistocene) although the palaeoenvironmental significance of these units is unclear. Sixty-two ostracod species are identified, the thirteen most abundant are discussed
in the taxonomic section, five of which are described as new. Between 30 and 100% of the species encountered in each sample are considered as endemic to Site 463, while some of the remaining species were previously thought to be endemic to individual guyots. Similarly high levels of endemism on nearby guyots probably reflect an incomplete knowledge of deep-sea ostracod faunas rather than the establishment of geographically or bathymetrically restricted populations. The presence of globally pandemic and geographically widespread taxa on sites such as the Mid-Pacific Mountains, surrounded by abyssal depths which lie below the CCD, indicates that some fauna1 exchange or migration of ostracods does take place. This must be achieved within the intermediate waters and probably occurs passively. 0 1999 Elsevier Science B.V. All rights reserved. Keywords: Ostracoda; endemism; deep-sea; diversity; Pacific
1. Introduction This work arises from studies of Late Cretaceous and Cainozoic deep-sea Ostracoda (ostracods) from guyot sites in the Pacific (Larwood and Whatley, 1993; Boomer and Whatley, 1995, 1996; Larwood et al., 1996; Whatley and Boomer, 1995). Thirteen Indo-Pacific guyot sites have been investigated based on material collected by the Deep Sea Drilling * Fax: +44- 191-2225421; E-mail: [email protected]
Project (DSDP) and the Ocean Drilling Program (ODP). Five sites from ODP legs 143 and 144 were the subject of research by the present author with a view to investigating the apparently high levels of endemism attained by ostracod faunas on the summits of bathymetrically isolated Pacific guyots and also to determine the effects of regional and global palaeoceanographical events on the ostracods (Boomer and Whatley, 1995, 1996; Whatley and Boomer, 1995). This followed the study of ostracods from Horizon Guyot (composite of two cores,
0377-8398/99/$ - see front matter 0 1999 Elsevier Science B.V. All rights reserved. PII: SO377-8398(99)00015-S
132
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DSDP sites 171 and 44), Ita Mai Tai Guyot (DSDP Site 200) and a number of guyots in the Emperor Seamount Chain (Larwood and Whatley, 1993). The guyot sites drilled during ODP legs 143 and 144 are in the Mid-Pacific Mountains and the Marshall Islands, respectively. Their summits are typically at a present day water depth of between 1000 and 1500 m and are generally surrounded by bathyal sea floor at depths of about 2500 to 2000 m. In comparison, Horizon Guyot (DSDP sites 171 and 44) is almost completely surrounded by abyssal floor below 5000 m. The ostracods are of particular interest since they do not possess a planktonic larval stage, therefore, the occurrence of benthonic ostracods in some deepsea settings can be difficult to explain. Abyssal plains which lie below the CCD surround the Mid-Pacific Mountains (MPM), thus the calcite-shelled ostracods cannot migrate freely across the ocean floor. Not only are the ostracods present along the MPM and other apparently isolated bathyal sites worldwide but regionally and globally pandemic taxa are included in the assemblages indicating that some migration must be occurring although the mechanism remains unclear. Steineck et al. (1990) discussed the presence of distinct ostracod assemblages associated with experimental wood islands emplaced at 1800 to 4000 m water depth. Although the fauna was distinct from the usual deep-sea benthonic dwelling ostracods the observation of similar assemblages at distant sites indicates effective methods of long distance dispersal. They suggested as possible vectors: (1) entrainment in high-energy bottom flows; (2) transport as viable eggs in fish guts; (3) ‘hitch-hiking’ on larger vertebrates or invertebrates (or their demersal larvae); (4) active swimming or crawling; (5) deployment of organic threads to harness currents more effectively (Steineck et al., 1990, p. 311). Whatever methods are employed it is clear that fauna1 exchange takes place between distant bathyal sites, even those separated by abyssal depths below the CCD which are inimical to ostracod survival. The guyot studies listed above report levels of endemism, i.e. the percentage of species in a sample which are believed to be unique to that site. It is clear that such studies are influenced by the availability of comparative information from the surrounding region.
37 (1999) 131-147
The more sites that are investigated the more previously ‘endemic’ species we encounter. Thus levels of endemism are partly an artefact of sampling. The ostracod assemblages which become established on guyot summits are generally some hundreds of metres shallower than the surrounding sea floor although in some cases this difference can be quite considerable. A number of MPM guyot sites have been investigated but as yet the intervening plateau has not. This work describes a reconnaissance set of Late Cretaceous to Pleistocene samples from such a site (DSDP Site 463, Leg 62) to compare with assemblages from the MPM guyots (Leg 143) as well as guyots in the nearby Marshall Islands (Leg 144). Globally and regionally pandemic deep-sea ostraced assemblages have been described by a number of authors (Steineck et al., 1988; Whatley and Ayress, 1988). These studies suggest that close faunal similarities can be expected from adjacent (nonguyot) deep-sea sites. Similarly equidistant guyot sites, however, have revealed much higher levels of endemism (Boomer and Whatley, 1996). Preliminary comparisons of endemism between Site 463 and five nearby guyot summits is given in Boomer and Whatley (1996). They show that diversity at all sites ranges from about 10 to 40 species while endemism ranges from about 40 to 100% of the recorded species, the assemblages at Site 463 are apparently just as ‘unique’ as those on the guyot summits. The Mid-Pacific guyots are volcanic summits which were emergent or near emergent in the mid- to Late Cretaceous (data from reef complex sediments); this study is therefore concerned with latest Cretaceous and Cainozoic fauna1 records from the pelagic sediments capping the guyots. Only two previous papers have described deep-sea ostracods from the equatorial Mid-Pacific. Steineck et al. (1988) detailed the Oligocene-Quaternary ostracods from DSDP Leg 85 (5 sites), describing two ecozones: an Oligocene-Lower Miocene ecozone with stable palaeoceanographical conditions, high diversity and low fauna1 turnover, and a Middle Miocene-Quatemary ecozone. The latter ecozone was divided into a lower subzone with high fauna1 turnover and an upper subzone with a depauperate, psychrospheric (cold, deep-water) assemblage
I. Boomer/Marine
Micropaleontology
adapted to corrosive bottom-water conditions. It is not possible to draw detailed comparisons between the present study and that of Steineck et al. (1988) since that paper dealt only with species whose adults are greater than about 400 km in length, no small cytherurid ostracods having been described from Leg 85. In many deep-sea assemblages the Cytheruridae are often the most diverse ostracod family. Steineck and Yozzo (1988) detailed the evolution of the Bradleya johnsoni lineage from the Late Eocene to Recent sediments of Leg 85, however, the genus is not common in the present study.
133
37 (1999) 131-147
Site 463
Core 0
Ib
Depth
1
Ws9 10
_ Ib IS==
2
Pleistocene
Upper Pliocene
I I 20
I 2. Background and methods Hole 463 (Deep Sea Drilling Project, Leg 62) was drilled in a water depth of 2525 m in the MidPacific Mountains (21”21.01’N, 174”40.07’E, Fig. 1). The hole was cored to a depth of 822.5 m with 36.6% recovery overall (Shipboard Scientific Party, 1981) although recovery for the interval in this study was >90% (Fig. 2). The youngest unit encountered, forming the greatest part of this study, was predominantly nannofossil ooze, 47 m thick (Early Eocene-
I 30 I-
I
I 40I-
I I I
5CI-
’ Upper
6CI-
Maastrichtian
7()-
Foram-Nannofossil Ooze + Chalk
Nannofossil Ooze
Non-recovery within core Fig. 2. Lithological and stratigraphical section of top part of Site 463. Depth of samples indicated by black arrowheads. Individual cores l-9 marked together with non-recovery.
Fig. 1. Location map showing the central Pacific region with the 2000 m isobath marked. The location of DSDP Site 463 is marked as are the guyot sites investigated during ODP legs 143 and 144 (after Boomer and Whatley, 1995).
Pleistocene age). A further three samples were taken from the upper part of the next oldest unit which was composed of foram-nannofossil ooze and chalk (late Maastrichtian age, Fig. 2). In all, fifteen 50 cm3 samples were taken from this sequence. All samples were washed over a 200-mesh
1. Boomer/Murine
134
Micropaleontology
37 (1099) 131-147
NNINP ZONES EPOCH (Rotary
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sieve to remove the mud fraction and then air-dried; they were dry-sieved through 60- and loo-mesh sieves. The two largest fractions were completely picked (i.e. all ostracods >125 urn) under a binocular microscope and arranged in fauna1 slides. The number of left and right valves of each species in a sample was recorded, and the higher number, added to the number of articulated carapaces was taken as a record of the minimum number of individuals present in that sample. It is these values that are given in the distribution range chart (Fig. 3). A very few specimens showed evidence of abrasion or dissolution. These were not included in the specimen counts as they are probably reworked. Total specimens recovered per sample were generally low, only 4 of the 15 samples yielded more than 100 individuals. This is a common problem when dealing with deep-sea Ostracoda, particularly in terms of diversity. Some of the results may not therefore be statistically significant, this must be borne in mind when interpreting the data. Figured specimens were coated with gold and photographed under the Cambridge 140 SEM at Aberystwyth. All figured specimens and fauna1 slides are deposited in the collections of the Department of Palaeontology, Natural History Museum, London to which the catalogue number prefix OS applies. The stratigraphical distribution and abundance of each taxon is recorded in Fig. 3. The samples yielded varying abundances of Ostracoda, shown in Fig. 4A. Species diversity for the ostracods has been reported in two ways. First, as the number of species recorded in a given sample (i.e., as number of species present in the sample, here referred to as simple species diversity) and, second, as ‘compound’ (cumulative) values calculated by adding to the simple species diversity those taxa which are temporarily absent from a sample possibly due to the nature of the sampling, here marked by an asterisk. This is necessary because of the oftenlow abundance of individual ostracods in deep-sea environments. We may of course be witnessing ‘real’ absences due to environmental controls but the asterisks help to indicate total stratigraphical range. Both
135
the simple and compound values are plotted on the species diversity graph (Fig. 4B).
3. Fauna1 evolution at Site 463 The stratigraphical distribution of the ostracod assemblages at Site 463 is outlined in Fig. 3. This study is based on a reconnaissance set of samples and there are inevitably some large stratigraphical gaps (notwithstanding the sedimentary hiatuses, see Fig. 4), as such the first and last appearances of taxa are not well constrained. However, three distinct faunal assemblages can be discerned from the stratigraphical data presented in Fig. 3 and these are summarised in Fig. 4. The assemblages are hereafter referred to as A (the oldest), B and C (the youngest). Since 41 of the 62 species recorded are considered to be endemic to this site it is difficult to make palaeoenvironmental conclusions based on the assemblage composition. Most of the genera present are recorded from shallow marine (< 10 m) through to bathyal (and in some cases abyssal) depths worldwide. During the Late Cretaceous to Recent interval many important global oceanographical changes have taken place and these are reflected in deepsea ostracod assemblages (Benson, 1990). Recently, Cronin and Raymo (1997) indicated the importance of sea-surface conditions (climate, productivity) in driving biological changes in the deep sea, with particular reference to ostracods. The three assemblages described below are distinctly different and must reflect the complex interplay of a number of environmental factors. 3.1. Assemblage
A
Assemblage A (4 samples, late MaastrichtianEocene), is characterised by low diversity samples dominated by the suborder Platycopina. High percentages of Platycopina have also been recorded from the Lower Palaeocene interval of ODP Site 865 (Boomer and Whatley, 1995) and this may be of regional significance. The reconstruction of the sub-
Fig. 3. Stratigraphical distribution of species recovered. Asterisk (*) indicates inferred Numbers indicate minimum number of individuals present (see text),f= fragment.
presence
of species
although
not recorded.
136
I. Boomer/Marine
B
A Number of Specimens
Recorded
37 (1999) 131-147
C % Dominance (solid) & % Endemism
Diversity
(solid) & Compound
8
a
Micropaleontology
D % Platycopina (solid) & % Krithidae
3 0
E Originations (solid) & Extinctions
E
Diversity
100 200
300
20
8 40
50
100
50
100
10
20
$
Oligocene
-t
60 -
Fig. 4. Fauna1 data plotted against age in millions of years. (A) Total number of specimens recorded in sample. (B) Number of species recorded (solid line) and compound diversity which includes asterisked records (dotted line). (C) Percentage of each sample constituted by the most common species, or dominance (solid line), and percentage of species thought to be endemic to this site (dotted line). (D) Percentage of Platycopina (solid line) and Krithidae (dotted line). (E) Number of species originations or first appearances (solid line) and extinctions (dotted line) for each sample. Hatched area on left hand column indicates presence of hiatuses.
sidence history of Site 463 indicates a palaeodepth of 1700 to 1300 m (Shipboard Scientific Party, 1981) for the Maastrichtian to Eocene interval (Barrera et al., 1997 suggest a palaeodepth of 1000-1500 m for the latest Cretaceous at Site 463) while the reconstruction for Site 865 (Bralower et al., 1995) suggests a palaeodepth reconstruction of 1300-1500 m for the Palaeocene-early Eocene interval. Thus, the assemblages are clearly deep-sea. Whatley (1992) associated high relative abundances and fauna1 dominance of Platycopina with decreased levels of dissolved oxygen at or about the sediment-water interface. High percentages of Platycopina in Assemblage A (Fig. 4D) are unlikely to reflect the influence of the Oxygen Minimum Zone at these depths but they may indicate sluggish circulation or the production of poorly oxygenated intermediate waters at that time. Palaeoceanographic studies from the region, however, suggest that this
was not the case. The platycopids may indicate oxygen depletion resulting from high surface productivity although there is no supporting evidence for this. Barrera et al. (1997) reported that the latest Cretaceous period witnessed vigorous oceanic circulation with different sources of deep and intermediate waters ‘competing’. The influence of these sources were variously controlled by changes in climate and sea level. They note one particular interval at about 7271 Ma during which oxygen and carbon isotopes indicate a period of particularly cool intermediate waters in the low latitude Pacific region. Before and after this event, they conclude, thermohaline circulation in this region may well have been controlled by the flow of relatively warm, high salinity water plumes. This process would have resulted in cool intermediate waters which would have mainly formed at high latitudes. Barrera et al. further conclude that
I. Boomer/Marine
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during such warm climatic periods of Earth history, oceanic circulation may well have been quite dynamic due to the lack of distinct density differences within the oceans. Platycopids are not particularly common in deepsea environments today. One possible explanation for their dominance in these Mid-Pacific sites comes from studies of Recent reefal ostracod assemblages in tropical and subtropical regions (e.g. Jellinek, 1993; Yassini et al., 1993; Whatley et al., 1995). These settings yield abundant and diverse ornamented Platycopina similar to those recorded from the latest Mesozoic and earliest Cainozoic of sites 463 (this work) and 865 (Boomer and Whatley, 1995). In these pre-psychrosphere times (pre 38 Ma), some shallow water reefal taxa may well have been able to adapt to the gradual subsidence of the Late Cretaceous reef complexes. Shallow-water reefal ostracod assemblages of Palaeocene age (including ornamented platycopids) are known from the Emperor Seamounts in the northern Pacific (Malz, 1981). However, the post-Palaeocene sequences on the Emperor Seamounts are either truncated or interrupted by volcanism thus obscuring the fate of these shallow water taxa. 3.2. Assemblage
B
Assemblage B (5 samples, Oligocene-Late Miocene) is initially marked by a sharp increase in species originations (19 new species, Fig. 4E) and a concomitant diversity increase (from 6 to 24 species), while its uppermost limit is marked by an increase in extinctions (17 last occurrences) accompanied by a diversity decline (from 23 to 7 species). Ostracod abundance is at its highest during this interval. The assemblages show an initial decline in the importance of the Platycopina which is mirrored by the appearance, for the first time in this sequence, of the family Krithidae which constitutes the most abundant taxa in Assemblage B. Throughout the sequence the Platycopina and Krithidae follow an inverse relationship in terms of their relative abundance for most of the samples, together they constitute the bulk of each assemblage (Fig. 4D). Krithe is often one of the most numerically abundant taxa in bathyal ostracod faunas today and it dominates many Neogene assemblages. Thus, we are
137
seeing the beginning of the establishment of modern deep-sea faunas. One of the key differences between Assemblage A and Assemblage B is that the two are separated by the establishment of the psychrosphere at about 40-38 Ma (Benson, 1975) although there were many other global oceanic temperature and circulation fluctuations during the Palaeogene which may have driven evolutionary changes in the intermediate water benthos. Zachos et al. (1994) discuss changing sea surface temperatures (SST) and vertical temperature profiles during the early Cainozoic and note that a marked temperature fall occurred between the latest Palaeoceneeearliest Eocene and the Late Eocene-earliest Oligocene. Such changes must have had significant effects on benthonic assemblages. Boomer and Whatley (1995) note a marked ostracod diversity crash at the Palaeocene-Eocene boundary at Site 865, an event also witnessed in deep-sea foraminifera (Thomas, 1990a). The possible mechanisms behind this fauna1 crisis are discussed in a number of papers (e.g. Thomas, 1990a; Eldholm and Thomas, 1993) which allude to the possible influence of tectonic events in the North Atlantic (known to be an important region in driving global oceanic circulation). Following the initial peak in species appearances in Assemblage B, the number of originations decreases and the rest of this interval is characterised by increased extinction. This may indicate the displacement of the original population by an immigrant fauna. This period includes a Late EoceneLate Miocene hiatus in sedimentation (Fig. 4). The sample immediately following this stratigraphical gap, which marks the upper limit of Assemblage B, however, sees all of the fauna1 indices continuing at a similar level (Fig. 4). This supports the work of Benson (1990, fig. 2) which indicates that the main ostracod diversity crash in this region occurred in the Late Miocene. The crash is also noted at Site 873 (Boomer and Whatley, 1996, fig. 6) and Site 171/44 (Larwood and Whatley, 1993, fig. 7). 3.3. Assemblage
C
Assemblage C (6 samples, Late Miocene-Pleistocene) is marked by depauperate, low diversity assemblages with little fauna1 turnover. Diversity falls from over 20 species in the uppermost sample of
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Assemblage B to less than ten species within a relatively short period of time and specimen abundance also drops markedly in this interval. Assemblage C initially shows an increase in the numerical importance of the Platycopina at the expense of the Krithidae but this pattern is quickly reversed through the Late Pliocene-Pleistocene interval when the Platycopina are absent and the Krithidae constitute 30-40% of the assemblages. Assemblage C is typical of modern globally pandemic psychrospheric ostracod faunas (Benson, 1975).
4. Conclusions Despite the fact that only 15 samples were taken from the Cretaceous-Pleistocene interval, it is possible to recognise three distinct fauna1 assemblages. The Late Cretaceous-early Cainozoic interval (Assemblage A) is dominated by ornamented platycopids which may reflect low oxygen levels near the sediment-water interface in this part of the Pacific Ocean. They may be a remnant of Earlymid-Cretaceous shallow water reefal faunas which adapted to deeper water conditions during subsidence of the region. Assemblage B marks a decline in the importance of the Platycopina with increases in ostracod abundance, diversity and rate of fauna1 turnover. Steineck et al. (1984) described a similar deep-sea ostracod assemblage from the Palaeogene of Barbados and commented that those faunas were part of a circum-equatorial (Tethyan) deep-sea fauna which had established a cosmopolitan distribution due to the latitudinal flow of warm saline bottom waters during this period. The existence of warm saline bottom waters at this time remains a matter of debate. It is probable that a short-lived (end Palaeocene) shift in deep water formation from high to low latitudes did occur but the conditions were soon reversed. Several less intense and shorter duration events may also have occurred during the Late Palaeocene and Early Eocene (Thomas, 1990b, 1992). There is little evidence to support the prolonged existence of circum-equatorial, warm, saline bottom waters referred to by Steineck et al. (1984). Assemblage C, with low diversity, low abundance and low fauna1 turnover equates to the upper sub-
37 (1999) 131-147
unit, upper Ecozone of Steineck et al. (1984) and reflects the establishment of the psychrospheric ostraced fauna. This assemblage is typical of modem bathyal ostracod faunas. At least 30% of the species encountered from each sample at Site 463 have not previously been recorded and these are currently considered to be endemic. All of the species in the oldest sample (463 9-3, 33-40 cm; upper Maastrichtian) are considered to be endemic (Fig. 4C), however, it important to note that there are few studies of deep-sea Maastrichtian ostracods from the central Pacific with which this material can be compared. The apparently high levels of apparently endemic taxa at Site 463 (Fig. 4C) supports the premise that, as yet, our knowledge of deep-sea faunas from this region is incomplete. This is of particular importance to studies which allude to the high endemicity of deep-sea ostracod guyot assemblages. If our knowledge of the abyssal and bathyal ‘background’ fauna is incomplete then our interpretation of guyot endemism may be misleading. The high endemicity of assemblages from guyot summits may not be as unique as had been thought since every new site in the region, whether guyot or not, yields on average 30-40% new taxa. As our knowledge base increases so it becomes clear that deep-sea benthonic ostracods are capable of migrating over considerable distances, despite being unable to survive in water below the CCD. This dispersal capability is attested by the presence of the same species in deep water sites in the Pacific and Atlantic (including guyots). Although the distribution mechanisms are unknown it must be achieved passively within the intermediate waters. A better test of ostracod endemism will only be achieved through studies of pelagic guyot sediments from sites which are surrounded entirely by abyssal waters which lie below the CCD.
Acknowledgements The author wishes to thank Professor Robin Whatley for his guidance during the work and for reading an early draft of this manuscript. The technical assistance of Messrs D. Griffiths and G. Hughes, Dr R. Jones and Miss M. Curry is gratefully acknowl-
I. Boomer/Marine
Micropaleontology 37 (1999) 131-147
edged. This research was initially undertaken during the tenure of a NERC ODP Special Topic award at the University of Wales, Aberystwyth. The author wishes to thank Ellen Thomas, Alan Lord and an anonymous referee for their critical assessment of the paper.
139
Subclass OSTRACODA Latreille, 1806 Order PODOCOPIDA Miiller, 1894 Suborder PLATYCOPINA Sars, 1866 Family CYTHERELLIDAESXS, 1866 Genus Cytherellu iones, 1849 Cytherella postagrena Boomer, sp. nov. (Plate 1, 5, 8,9)
Appendix A. Taxonomy In all, 62 separate taxa have been identified in the present study, 48 are illustrated in Plates l-3 and Fig. 5. Thirteen of the most abundant taxa are discussed in the following taxonomic section of which six are erected as new species. Abbreviations: M = male; F = female; A = adult (sex not discernible); RV = right valve; LV = left valve; CAR = carapace (e.g. FRV = female, right valve). All specimens adult, unless otherwise stated. All specimens are deposited in the collections of the Department of Palaeontology, Natural History Museum, London.
Cytherella sp. 2 Boomer and Whatley, 1995. Holotype: OS14689 FRV (Plate 1, 8). Type locality and horizon: Deep Sea Drilling Project Leg 62, Site
463, Mid-Pacific Mountains, Central West Pacific (21”21.01’N, 174’40.07’E); upper Maastrichtian, Core 9, Section 3, Interval 33-40 cm. Etymology: With reference to the net-like reticulation on the posterior region of the valves. Diagnosis: A weakly inflated species of Cytherella with compressed anterior and postero-ventral margins. Lateral surface smooth or bears very faint anastomosing ribs which are best developed peripherally, a weak net-like reticulation is developed posteriorly.
Fig. 5. Transmitted light drawings of selected taxa. For abbreviations see Appendix A. (a) Krithe sp. A. LV, 850 pm. (b) Argilloecia sp. C. LV, 540 pm. (c) Krithe sp. A. RV, 700 urn. (d) Argilloecia sp. B. RV, 525 pm. (e) Argilloecia sp. B. LV, 490 pm. (f) Argilloecia sp. C. RV. 590 urn. (g) Australloecia cf. A. micra. RV, 425 urn. (h) Bairdoppilata sp. A. RV. 1180 pm. (i) Argilbecia sp. C. LV, 560 urn.
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Material: 31 valves 2 carapaces. Description: Dorsal margin slightly convex, ventral margin bears
a distinct oral concavity. Anterior margin very broadly rounded, posterior margin more angular being particularly sharply truncated in the females (Plate 1, 8) compared with males (Plate 1, 5. 9). Valves distinctly swollen posteriorly in females, extending to posterior margin, less so in males where the posterior margin is compressed. Remarks: This species has also been recorded from the Palaeocene of ODP Site 865, Cytherella sp. 2 (Boomer and Whatley, 1995). Cytherella posterospinosa Boomer, sp. no”. (Plate 1, l-4) Cytherella sp. 8 Boomer and Whatley, 1995. Holotype: OS14685 FRV (Plate 1, 1). Qpe locality and horizon: Deep Sea Drilling Project Leg 62, Site
463, Mid-Pacific Mountains, Central West Pacific (21”21.01’N,
Plate 1 For abbreviations and repository see Appendix A. All specimens adult and all views external lateral unless otherwise stated. 14. Qtherella posterospinosa Boomer, sp. nav. EoceneMiocene. 1,4. Holotype. FRV 0314685. x45. I. Int. lat. x4. 4. MRV 0814686. x50. 2. MLV 0814687. x51. 3. 5, 8, 9. Cytherella postagrena Boomer, sp. nav. MRV 0314688. x49. 5. Holotype. FRV 0814689. x49. 8. MRV 0846890. x46. 9. Cytherella sp. A. ACAR 0814691. 6, I. Dorsal view. x45. 6. Left lat. x51. 7. Cytherella sp. C. ARV 0S14692. x51. IO. 11. Bairdoppilata sp. A. ALV 0814693. x25.5. Zubythocypris sp. A. ACAR OS14694 right lat. x49. 12. Bairdoppilata sp. B. ARV 0314695. x33. 13. 14. Aratrocypris sp. A. ALV 0814696. x 102. 15-17. Krithe sp. A. FRV 0814697. x47. 15. FLV 0814698. x48. 16. 17. MLV 0314699. x46. 18. 23. Argilloecia sp. A. ARV OS 14700. x62.5. 18. 23. ALV OS14701. x64. 19, 24. Argilloecia sp. B. 19. ARV 0814702. x64. ALV 0814703. x73. 24. 20. 25. Argilloecia sp. C. 20. ARV OS 14704. x79. ALV 0314705. x79. 25. 21, 22. Australloecia cf. A. micra Bonaduce et al. 21. ARV 0314706. x73. ALV os14707. x 102. 22.
141
174YO.07’E); upper Maastrichtian, Core 6, Section 2, Interval 61-68 cm. Etymology: With reference to the development of conjunctive spines along the postero-lateral surfaces. Diagnosis: A tumid species of Cytherella with regular reticulation which is particularly well developed on the posterior third of valve, the reticulation bears many short, blunt backward pointing conjunctive spines. Material: 166 valves. Description: Carapace oval to quadrate in lateral view. Anterior
and posterior margins broadly rounded, ventral margin sinuous with marked concavity at mid-length, dorsal margin sinuous with small peak at mid-length. Greatest height anteriorly. A large number of small posteriorly directed conjunctive spines are associated with the reticulae in the posterior part of the valves. Reticulation fades anteriorly but is present on most of the lateral surfaces, grading to fine ribbing along the margins in the anterior half. Median adductor muscle scar sulcus is prominent in some specimens and non-reticulate. Remarks: This species has also been recorded from the Middle Eocene to Lower Oligocene of ODP Site 865 (Boomer and Whatley, 1995) with a probable reworked specimen in the Lower Miocene sediments of that site. The specimens from Site 865 are slightly more heavily reticulated along the mid-lateral surface than in the present material. Suborder PODOCOPINA Sam, 1866 Superfamily BAIRDIACEA Sam, 1888 Family BAIRDIIDAESars, 1888 Genus Buirdoppiluta Coryell, Sample and Jennings, 1935 Bairdoppilata sp. A (Plate 1, 11; Fig. 5h) Material: 51 valves. Description: A large, ovate species with poorly developed ante-
rior and postero-ventral marginal flanges, postero-ventral margin serrated. Lateral surface bears a few normal pores, otherwise no external features recognised. Greatest length just below midheight, greatest height at or just in front of mid-length. Ventral margin broadly rounded, dorsal margin lacks distinct cardinal angles. Remarks: This species is similar to Bairdoppilata sp. 1 Boomer and Whatley, 1995 from the Middle Eocene to Lower Oligocene of ODP Site 865 which can be distinguished by the greater number of normal pores on the lateral surfaces and the slightly more extended posterior process. Baintoppilata sp. B (Plate 1, 13) Material: 25 valves. Description: A distinctly elongate species with a narrow, com-
pressed antero-marginal flange and almost no posterior flange. Greatest length close to sinuous ventral margin. No normal pores observed on lateral surface. Remarks: Smaller than Bairdoppilata sp. A; this species is also more elongate in lateral view and lacks the distinct normal pore canals on the lateral surfaces. This species is restricted to Assemblage B. Superfamily CYPRIDACEA Baird, 1845 Family PONTOCYPRIDIDAE Muller,1894
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143
Genus Argilloecia Sam, 1866.
Genus Australoecia McKenzie, 1967
Argilloecia sp. A (Plate 1, 18, 23; Fig. 5b and d) Material: 51 valves. Description: This species is distinguished by its relatively elon-
Australoecia cf. A. micra (Bonaduce et al., 1975) (Plate 1, 21,
gate carapace. Antero-marginal flange small, apparently truncated dorsally. Dorsal margin short and straight with the greatest height anteriorly. Postero- and antero-dorsal margins convex. Argilloecia sp. B (Plate 1, 19, 24; Fig. 5e and f) Material: 14 valves. Description: Carapace distinguished by well developed dorsal
cardinal angles and strongly sinuous ventral margin in lateral view. Postero- and antero-dorsal margins straight.
22; Fig. 5g and i) Material: 24 valves, 1 carapace. Remarks: This species is similar to one described by Bona-
duce et al. from the Recent of the Mediterranean. That species is known from Quatemary sediments in the Southwest Pacific Ocean (Whatley and Ayress, 1988). The present species differs from the type description in possessing a more broadly rounded posterior margin and a slightly higher carapace relative to the length. Superfamily CYTHERACEA Baird, 1850 Family KRITHIDAE Mandelstam in Bubikyan, 1958 Genus Krirhe Brady, Crosskey and Robertson, 1874
Plate 2 For abbreviations and repository see Appendix A. All specimens adult and all views external lateral unless otherwise stated. Henryhowella cf. H. asperrima (Reuss). 1, 2, 4. FRV OS14708. 1,4. x61. 1. Int. lat. x61. 4. MRV 0814709. x65. 2. Henryhowella cf. H. dasyderma Brady. FRV OS3, 6. 14710. x42. 3. FRV int. lat. x45. 6. Bradleya sp. A. ARV OS14711. x39.5. 5. Poseidonamicus dinglei Boomer, sp. no”. I, 8, 9. ARV OS14712. I, 9. x54. 7. Holotype. Int. lat. x54. 9. ALV OS14713. x57. 8. Pennyella sp. A. FLV 0314714. x46. 10. 11. Poseidonamicus sp. B. ARV OS14715. x49. Pennyella sp. B. MRV 0814716. 12, 15. hit. lat. x54. 12. x49. 15. Pennyella sp. C. ARV 0S14717. 13, 14. x44. 13. Int. x56. 14. Abyssocythere paratrinidadensis Boomer, sp. non l&18,21 Holotype. ALV 0814718. x51. 16. ARV 0814719. 17, 18. x51. 17. Int. x55. 18. RV juv, A-l? 0814720. x51. 21. Bathycythere bermudezi (Van den Bold, 1946). ALV 19, 20. 0314721. Int. x30. 19. x30. 20. Kuiperiana cf. K. bathymarina Ayress, Coles and 22. Whatley. ALV OS 14722. x 114. Pariceratina ubiquita Boomer. ARV 0S14723. x52. 23. Profundobythere bathytatos Coles and Whatley. 24. ARV 0814724. x78.
Krithe sp. A (Plate 1, 15-17; Fig. 5a and c) Material: 488 valves. Remarks: Numerically this is the most abundant single taxon in
the present study with over 400 individual valves recovered in the Oligocene to Upper Miocene interval. The species is similar to K&he dolichodiera Van den Bold, 1946 but differs externally in the outline of the posterior margin. Furthermore, the present species has a different anterior vestibule and antero-dorsal radial pore canal pattern (see Coles et al., 1994 for re-description of K. dolichodiera and discussion of the genus). Family
CYTHERURIDAE
Mtlller, 1984
Genus Hemiparacytheridea Hemiparacytheniiea
Herrig, 1963
ayressi Boomer, sp. nolz (Plate 3, 7, 9-l 1)
Hemiparacytheridea sp. 30 Boomer and Whatley, 1995. Hemiparacytheridea sp. 31 Boomer and Whatley, 1995. Holotype: OS14732 ALV (Plate 3, 9). Type locality and horizon: Deep Sea Drilling Project Leg 62, Site
463, Mid-Pacific Mountains, Central West Pacific (21”21.01’N, 174’40.07’E); upper Maastrichtian, Core 6, Section 2, Interval 61-68 cm. Etymology: In honour of Dr Michael Ayress (formerly ANU), for his work on Pacific deep-sea Ostracoda. Diagnosis: A quadrate, alate species of Hemiparacytheridea with irregular, corrugate reticulae. Material: 54 valves. Description: Carapace quadrate in lateral outline with straight, parallel ventral and dorsal margins. Anterior margin slightly convex, posterior margin drawn out into caudal process along the dorsal margin. Anterior margin compressed with narrow margin bearing up to three short spines, posterior margin broadly compressed. Carapace bears robust alae which are terminated laterally by an irregular rib running from the anterior margin until it forms a sharp, backward pointing, projection posteriorly. A weak, vertical, median sulcus is present. Lateral surfaces omamented by coarse irregular ribbing and secondary, fine intercostal punctation. Ribbing forms small raised area antero-dorsally and slight dorsal projection along the postero-dorsal margin. Remarks: The species has been recorded from the PalaeoceneEocene interval of ODP Site 866 (Boomer and Whatley, 1995)
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1. Boomer/Marine
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with another possible record (single specimen) from the Lower Oligocene of Site 865 (authors unpublished information). Those specimens possess more dominant ribbing. although in all other respects they appear identical. Family TRACHYLEBERIDIDAE
Sylvester-Bradley.
Genus Abyssocythere Benson.
197
Abyssocylhere parattinidadensis, 18, 21)
1948
I Boomer,
sp. non (Plate 2, 16-
Steineck et al., 1985. ALV (Plate 2, 16). Type locality and horizon: Deep Sea Drilling Project, Leg 62, Site 463, Mid-Pacific Mountains, Central West Pacific (21”21 .Ol’N. 174”40.07’E): upper Maastrichtian, Core 9, Section 3, Interval 3340 cm. Etymolog!: With reference to the close similarity between this species and A. trinidadensis (Van den Bold, 1957). ?Abyssocythere
trinidadensis
Holorype: 0314718
37 (I 999) 131-147
145
Diagnosis: Differs from A. trinidadensis in the form of the distinctive, raised, ‘box-like’ postero-dorsal reticulum which is open ventrally in the present species and is completely enclosed in the former species. Material: 21 valves. Description: All internal and external features are typical of the genus (see Benson, 1971). The present specimens are well preserved and show a delicate pattern of reticulae on much of the external surfaces but particularly the antero-lateral region. The dorsal spines are perhaps better developed than in the holotype of A. trinidadensis. however, this may be a preservational feature. In all other respects the present material is similar to A. trinidadensis. Steineck et al. (1984) tigured a specimen of A. trinidadensis from the Eocene of Barbados which also appears to have an ‘open’ postero-dorsal reticulum and is. therefore. con-specitic with the present material.
Genus Henryhowella Puri, 1957 He~lrvhowellcccf. H. osperrima (Reuss, 1850) (Plate 2. 1. 2, 1). 39 valves. Remarks: This species is similar to H. asperrima (Reuss). described from bathyal Miocene sediments of the Vienna Basin, in possessing a sub-central tubercle and postero-lateral longitudinal swellings of the carapace. Type material of the species has recently been re-figured by Kempf and Nink (1993). Although similar in outline and ornament to H. asperrinw the present specimens are 20% smaller than the mean size for the species given by Kempf and Nink. The well developed hinge elements in the figured specimen (Plate 2, 4) confirms that they are adult and they are therefore assigned to H. cf. H. asperrima. A second species of HentThowella, H. cf. H. dasyderma Brady (Plate 2, 3, 6) has been recorded in the Upper Miocene-Pleistocene of Site 463, and closely resembles the species described by Brady ( 1880) from the Southeast Pacific. Material:
Plate 3 For abbreviations and repository see Appendix A. All specimens adult and all views external lateral unless otherwise stated. 1. Eucythrre sp. .A 41 V OS14725 ~92. 2. Eucythere sp. B. ARV 0S14726. x96. 3. Eucythere sp. C. ARV 0814721. x85. 4. Eucythere sp. D. ALV 0S14728. x88. 5. Hemiparacytheridea mediopunctata Coles and Whatley ARV 0814729. x127. Hemiparacytheridea cf. H. mediopunctata Coles 6. and Whatley. ARV 0814730. x90. ayressi Boomer, sp. nor. 7.9, IO, II Hemiparacytheridea ARV 0814731. 7. Il. Dorsal view. x97. I. x91. II. Holotype. ALV OS 14732. 9, 10. 8. Hemiparacytheridea sp. A.? ARV 0S14733. x96. Semicytherura cf. S. pulchra Coles and Whatley. 12. 15. ALV OS14734. x 100. 12. ARV 0814735. x 100. 15. Parahemingwayella downingae Coles and Whatley. 13. ALV OS14736. x 119. 14. Aversovalva sp. B. ALV 0814737. x97. 16, 17. Aversovalva formosa Coles and Whatley. 16. ARV int. 0S14738. x 110. ALV 0S14739. x99. 17. 18. 19. Cytheropteron sp. A. ARV OS 14740. x80. 18. ALV specimen lost. 19. Cytheropteron sp. D. 2&23. ARV 0S14741. x78. 20. 21. ALV OS14742. x 82. 22. ALV int. 0814743. x86. 23. Juv RV (A- I ) specimen lost. 24. Cytheropteron sp. E. ALV 0314744. x75. Cytheropteron sp. G. ALV 0814745. x77. 25. Cytheropteron sp. F. ALV 0814746. x83. 26.
Genus Pennyella
Neale. 1975
Pennyella
sp. B (Plate 2, 12, 15)
Material:
12 1 valves.
Remarks: Three species of Pennyella have been recorded in the present study. Pennyella sp. A, recorded from the Maastrichtian of Site 463. is probably ancestral to both Pennyella sp. B and Pennyeilu sp. C. Pennvellu sp. B is the most abundant of the three and is distinguished by the presence of a well developed series of spines along the anterior and postero-ventral compressed margins and also along a ventro-lateral carina. The species bears a well developed postero-dorsal knob and a serrated dorsal margin, both typical for the genus. A sub-central tubercle is present,
Genus Poseidonamicus Benson.
1972.
Poseidonamicus dinglei Boomer, sp. nav. (Plate 2. 7-9) Holotype:
OS 147
I2 ARV (Plate 2, 7).
Deep Sea Drilling Project Leg 62, Site 463. Mid-Pacific Mountains, Central West Pacific (21”21.01’N, 174”40,07’E): upper Maastrichtian, Core 9. Section 3, Interval 33-40 cm. E~molo~~: In honour of Dr. R.V. Dingle (Geological Institute, Copenhagen University) for his work on deep-sea Ostracoda. T,?appr locali@ and horizon:
146
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Micropaleontology 37 (1999) 131-147
Diagnosis: A species of Poseidonamicus with regular reticulae, strong marginal and ventro-lateral ribs. The admarginal region bears a few fine radial ribs but little or no punctation. Material: 160 valves, 1 carapace. Description: Carapace elongate, quadrate in lateral view with a very broadly rounded anterior margin and triangular to arcuate posterior margin. Greatest height at anterior cardinal angle. The anterior-most two or three reticulae immediately above the ventro-lateral carina are more deeply developed than any other features of the ornament. Anterior and postero-ventral margins bear well developed spines. Interior details as for genus. Remarks: The present species bears similarities to the P. anteropunctatus group described by Whatley et al. from the Cainozoic of the Southwest Pacific. Z? dinglei is distinguished by the stronger development of the marginal ribs. Postero-dorsally the marginal rib is distinctly thickened in the LV while in the RV the anterodorsal cardinal region displays a sinuous outline.
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Cronin, T.M., Raymo, M.E., 1997. Orbital forcing of deep-sea benthic species diversity. Nature 385, 627-642. Eldholm, O., Thomas, E., 1993. Environmental impact of volcanic margin formation. Earth Planet. Sci. Lett. 117. 319329. Jellinek, T., 1993. Zur Gkologie und Systematik rezenter Ostracoden aus dem Bereich des kenianischen Barriere-Riffs. Senckenbergia Lethaea 73 (l), 83-225. Kempf, E.K., Nink, C., 1993. Henryhowella asperrima (Ostracoda) aus der Typusregion (Miozan: Badenian; Wiener Becken). Sonderveroff. Geol. Inst. Univ. Koln 70, 95-l 14. Larwood, J.G., Whatley, R.C., 1993. Tertiary to Recent evolution of Ostracoda in isolation on seamounts. In: McKenzie, K.G., Jones, P. (Eds.), Ostracoda in the Earth and Life Sciences. Balkema, pp. 53 l-549. Larwood, J.G., Whatley, R., Boomer, I., 1996. Seamount ostracod evolution: evidence from Horizon Guyot, Central Pacific Ocean (DSDP sites 44 and 171) and the Ninetyeast Ridge. East Indian Ocean (DSDP) Site 214) In: Moguilevsky, A., Whatley, R. (Eds.), Microfossils and Oceanic Environments, pp. 385-402. Malz, H., 1981. Pallozane Ostracoden von den Emperor Seamounts, NW-Pazifik. Zitteliana 7, 3-29. Shipboard Scientific Party, 1981. Western Mid-Pacific Mountains. Init. Rep. DSDP 62, 33-156. Steineck, P.L., Yozzo, D., 1988. The Late Eocene-Recent Brad&a johnsoni Benson lineage (Crustacea, Ostracoda) in the Central Equatorial Pacific. J. Micropalaeontol. 7, 187- 199. Steineck, P.L., Breen, M., Nevins, N., O’Hara, P., 1984. Middle Eocene and Oligocene deep-sea Ostracoda from the Oceanic Formation, Barbados. J. Paleontol. 58, 1463-1496. Steineck, P.L., Dehler, D., Hoose, E.M., McCalla, D., 1988. Oligocene to Quatemay Ostracods of the Central Equatorial Pacific (Leg 85, DSDP-IPOD). In: Hanai, T., Ikeya, N., Ishizaki, K. (Eds.), Evolutionary Biology of Ostracoda: its Fundamentals and Applications. Kodansha, Tokyo, pp. 597617. Steineck, PL., Maddocks, R.F., Turner, R.D., Coles, G., Whatley, R., 1990. Xylophile Ostracoda in the deep sea. In: Whatley, R., Maybury, C. (Eds.), Ostracoda and Global Events. Chapman Hall, London, pp. 307-319. Thomas, E., 1990a. Late Cretaceous-early Eocene mass extinctions in the deep sea. In: Sharpton, V.L., Ward, P.D. (Eds.), Global Catastrophes in Earth History; An Interdisciplinary Conference on Impacts, Volcanism and Mass Mortality. Geol. Sot. Am. Spec. Pap. 247,481-495. Thomas, E., 1990b. Late Cretaceous through Neogene deepsea benthic foraminifers (Mud Rise, Weddell Sea, Anarctica). Proc. ODP Sci. Results 113, 571-594. Thomas, E., 1992. Cenozoic deep-sea circulation: Evidence from deep-sea benthic foraminifera. A.G.U. Antarct. Res. Ser. 56, 141-165. Van den Bold, W.A., 1957. Ostracoda from the Paleocene of Trinidad. Micropaleontology 3, 1-l 8. Whatley, R.C., 1992. The platycopid signal: a means of detecting kenoxic events using Ostracoda. J. Micropalaeontol. 10, 18 l185.
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Whatley, R.C., Ayress, M., 1988. Pandemic and endemic distribution patterns in Quatemary deep-sea Ostracoda. In: Hanai, T., Ikeya, N., Ishizaki, K. (Eds.), Evolutionary Biology of Ostracoda: its Fundamentals and Applications. Kodansha, Tokyo, pp. 739-758. Whatley, R.. Boomer, I., 1995. Cenozoic Ostracoda from guyots in the western Pacific: Leg 144, Holes 871A, 872C and 873B. Proc. ODP Sci. Results 144, 87-96. Whatley, R.C., Cooke, P.C.B., Warne, M.T., 1995. The Ostracoda
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from Lee Point on Shoal Bay, Northern Australia: Part 1 Cladocopina and Platycopina. Rev. Esp. Micropaleontol. 27 (3), 69-89. Yassini, I., Jones, B.G., Jones, R.M., 1993. Ostracods from the Gulf of Carpentaria, northeastern Australia. Senckenbergiana Lethaea 73 (2), 375-406. Zachos, J.C., Scott, L.D., Lohmann, K.C., 1994. Evolution of early Cenozoic marine temperatures. Paleoceanography 9 (2) 353-387.