The sedimentology and context of Late Ordovician glacial marine sediments from Sierra Leone,West Africa

Glacial marine deposits (the Waterfall Formation of the Saionia Scarp Group) from northern Sierra Leone, West Africa, correlate with sequences in Guinea and Senegal and indicate a Late Ordovician age. The sediments (150 m in thickness) are laminated mudstones (rhythmites) of alternating fine laminae and lenticular, graded, coarse laminae a few millimetres thick. Dispersed clasts of various rock types occur within the rhythmites, which also locally contain slump structures. Interbedded with the rhythmites and dropstones are turbidites, with sole structures, amalgamated and graded beds. Transport directions are from the north.Deposition from low-density melt-water suspension currents derived from a shelf glacier is suggested for the rhythmites, with the clasts emplaced by iceberg rafting.Underlying the glacial sediments are subarkoses with heavy-mineral laminae and cross-bedded, super-mature quartz arenites attributed to a shallow-water tidal origin.The occurrence of glacial marine sediments in Sierra Leone provides a southwestern boundary to the ice-sheet which is well-documented as covering much of the Sahara and Northwest Africa during Late Ordovician time, and further emphasizes the great area affected by this glaciation.     

The effects of the final stages of the Late Ordovician glaciation on marine palynomorphs (chitinozoans, acritarchs, leiospheres) in well Nl-2 (NE Algerian Sahara)

Palynomorph assemblages, especially chitinozoans and acritarchs, from the Upper Ordovician of well Nl-2 (north-east of the Algerian Sahara) are studied in order to precisely date the ultimate effects of the Late Ordovician glaciation and to document the impact of this major climatic stress on the diversity of the palynoplankton. References are made to stable isotope excursions and to global eustatic sea level variations in order to improve the local age determination. The Hassi el Hadjar Formation, i.e. glacio-marine diamictites, is interpreted as a transgressive event resulting from the melting of the northern Gondwana ice cap. It yields poorly preserved and moderately diverse chitinozoans of late Hirnantian age. Acritarchs are more abundant in the lower part of these "microconglomeratic clays", but display a low diversity and are badly preserved throughout the whole formation. Reworked individuals are recorded in both groups. The marine sediments of the M'Kratta Formation of latest Hirnantian age contain better preserved, more abundant and more diverse palynomorph assemblages, especially in the Upper Member. The composition of this palynoplankton indicates a fairly good faunal and phytoplankton recovery after the early Hirnantian climatic stress.The extinction of the Ordovician forms, and the appearance of Silurian type taxa occur only in the uppermost Hirnantian, i.e. following with a slight delay the glacial event. The overlying black shales of Wenlock age (lower part of the Oued Mehaiguène Formation) are indicative of marine anoxic environments. They yield a virtually exclusive, but enormous number of Tasmanacea. The very peculiar composition of this palynoplankton seems to be independent of the Late Ordovician glaciation and is most likely related to the factors that, later, generated and maintained anoxic conditions in this area.A new species of chitinozoan, Spinachitina oulebsiri sp. nov. from the latest Hirnantian M'Kratta Formation, is described and illustrated.     

Geological summary of the Busidima Formation (Plio-Pleistocene) at the Hadar paleoanthropological site, Afar Depression, Ethiopia

The Hadar paleoanthropological site in Ethiopia preserves a record of hominin evolution spanning from approximately 3.45 Ma to 0.8 Ma. An angular unconformity just above the ca. 2.95 Ma BKT-2 complex divides the sediments into the Hadar Formation (ca. 3.8-2.9 Ma) and the Busidima Formation (ca. 2.7-0.15 Ma). The unconformity is likely a response to a major tectonic reorganization in the Afar Depression, and activation of the As Duma fault near the Ethiopian Escarpment (west of Hadar) created a half-graben in which the Busidima Formation was deposited. The pattern and character of sedimentation in the region changed dramatically above the unconformity, as cut-and-fill channel conglomerates and silt-dominated paleosols that comprise the Busidima Formation stand in sharp contrast to the underlying deposits of the Hadar Formation. Conglomerate deposition has been related to both the perennial, axial paleo-Awash and ephemeral, escarpment-draining tributaries. Overbank silts have yielded fossils attributed to early Homo and Oldowan stone tools. Numerous tuffaceous deposits exist within the Busidima Formation, but they are often spatially limited, fine-grained, and reworked. Recent work on the tephrostratigraphic framework of the Busidima Formation at Hadar has identified at least 12 distinct vitric tephras and established the first geochemical-based correlations between Hadar and the neighboring project areas of Gona and Dikika. Compared to Gona and Dikika, where Busidima Formation sediments are exposed over large areas, the highly discontinuous sediments at Hadar comprise less than 40 m in composite section and are exposed over an area of <20 km², providing only snapshots into the 2.7-0.15 Ma window. The stratigraphic record at Hadar confirms the complex depositional history of the Busidima Formation, and also provides important details on regional stratigraphic correlations and the pattern of deposition and erosion in the lower Awash Valley reflective of its tectonic history.     

Cherty carbonate facies of the Montoya Group, southern New Mexico and western Texas and its regional correlatives: a record of Late Ordovician paleoceanography on southern Laurentia

The Upper Ordovician Montoya Group in southern New Mexico and westernmost Texas records predominantly subtidal deposition on a gently dipping carbonate ramp that was subsequently nearly entirely dolomitized. The medial unit of the Montoya Group, the Aleman Formation is unique because it contains abundant chert (10–70% by volume). The chert occurs as: (1) thin continuous beds of sponge spicules within mudstone or calcisiltite; (2) discontinuous, lenses or nodules within skeletal wackestones and packstones; or (3) as a replacement of skeletal grains and burrows. Coeval skeletal grainstones and muddy peritidal facies contain little chert. Phosphate (up to 5 wt.%) occurs within the underlying Upham Formation and the Aleman Formation as replacement of fossils and peloids. The abundance of chert and phosphate in these subtidal facies indicates they formed within a region of strong upwelling. Regional correlation with Upper Ordovician cherty units along the periphery of southern Laurentia and other low latitude continents suggests that upwelling was widespread and long-lived during the Late Ordovician. The upwelling is interpreted to record vigorous oceanic circulation produced by the onset of glaciation on Gondwana during this period. Late Ordovician relative sea-level curves around the periphery of Laurentia indicate correlative third-order (1–3 my duration) fluctuations that may provide a means for high-resolution global correlations. However, the mechanism(s) that produced these long-term fluctuations are unclear.     

Ancient forests and grasslands in the desert: Diet and habitat of Late Pleistocene mammals from Northcentral Sonora, Mexico

Despite high taxonomic diversity elsewhere in North America during the Pleistocene, vertebrate faunas are exceedingly rare in the region of northern Mexico. Térapa, a unique fossil site located in the present-day desert of Northcentral Sonora, Mexico (29°41′N, 109°39′W, 605 m elevation), contributes to our understanding of the paleoecology and paleoclimate of the region during the Late Pleistocene, ca. 43,000-40,000 cal. yr BP. At least 60 vertebrate taxa, including amphibians, turtles, a crocodilian, snakes, birds and many mammals, have been recovered from an 11-m thick sequence of fossiliferous sediments. The diversity and tropical affinity of these taxa suggest a more-forested environment than the thornscrub desert habitat present in this region today.Isotopic analyses of tooth enamel carbonate from ancient mammalian herbivores suggest that the Sonoran desert has undergone considerable climate change since the Late Pleistocene. Bulk carbon (δ¹³C) and oxygen (δ¹⁸O) isotopes from nine mammalian fossils indicate a habitat mosaic with variations in diet that include browsers, mixed feeders and C4 hyper-grazers (δ¹³C range of − 10‰ to 2‰). Unique to this site are δ¹³C tooth enamel values of − 6.1 and − 5.6 ‰ for the deer Odocoileus, which suggest a more variable diet than strict browsing, including possibly feeding on CAM and/or C4 plants. Serial sampling of carbon (δ¹³C) and oxygen (δ¹⁸O) isotopes for ancient mammal teeth with hypsodont dentitions (fossil Equus and Bison,) as well as δ¹⁸O meteroric water estimates from well-supported climatic models suggest a cooler and more equable environment at Térapa during the Late Pleistocene. These results also support previous habitat reconstructions inferred from the macrobotanical and packrat midden records of northern Sonora (Mexico). High-resolution stable isotope geochemistry indicates that: 1) ancient Térapa was covered with forest and grassland habitats that extended northward into Mexico by about 350 km relative to their present-day northern limits during the Late Pleistocene; and 2) an Amount Effect (AE) is demonstrated in the fossil record at Térapa even though the climate was less seasonal compared to the modern desert habitat.     

Reef reconstruction after extinction events of the latest ordovician in the Yangtze platform,South China

Summary Early Silurian reef reconstruction on the Yangtze Platform, in the northern part of the South China Block, is preceded by a combination of regional and global processes. During most of Ashgill time (Late Ordovician), the area was dominated by Wufeng Formation deep water graptolitic black shales. Reefs largely disappeard in the middle of the Ashgill Stage, from the northwestern margin of Cathaysian Land (southeastern South China Block), in advance of the Late Ordovician glaciation and mass extinction, due to regional sea-level changes and regional uplift, unrelated to the mass extinction itselt. Late Ordovician microbial mudmound occurrence is also found in the western margin of the Yangtze Platform, its age corresponding to theDicellograptus complexus graptolite biozone of pre-extinction time. On the Yangtze Platform, a thin, non-reef-bearing carbonate, the Kuanyinchiao Formation (=Nancheng Formation in some sites), thickness generally no more than 1m, occurs near several landmasses as a result of Hirnantian regression. Reappearance of the earliest Silurian carbonates consisting of rare skeletal lenses in the upper part of Lungmachi Formation, are correlated to theacensus graptolite biozone, early Rhuddanian of Shiqian, northeastern Guizhou, near Qianzhong Land. Carbonate sediments gradually developed into beds rich in brachiopods and crinoids in the lower part of Xiangshuyuan Formation, middle Rhuddanian. In the middle part of Xiangshuyan Formation, biostromes, containing abundant and high diversity benthic faunas such as corals, crinoids and brachiopods, show beginnings of reconstruction of reef facies. Substantial reef recovery occurred in the upper part of Xiangshuyuan Formation, lower Aeronian, as small patch reefs and biostromes. During the late Aeronian, carbonate sediments, especially reefs and reef-related facies, expanded on the upper Yangtze Platform, and radiation of reefs occurred in Ningqiang Formation, upper Telychian. The long period of reef recovery, taking several million years, remains difficult to explain, because redistribution of any refugia faunas would be expected to take place soon after the extinction. Reefs and reef-related facies subsequently declined after Telychian time due to regional uplift of the major portion of the Yangtze Platform. Carbonate facies are therefore uncommon in South China during the rest of Silurian time.     

新疆塔里木盆地奥陶纪冷水型胞石

文内描述了在新疆塔里木盆地覆盖区QB-1井(黑土凹线)和TZ-32井(却尔却克组)中发现的3种奥陶纪冷水型胞石.即Tanuchitina sp.cf.achabae Paris,Linochitina pissotensis Paris和Siphonochitina bella sp.nov.,时代为中到晚奥陶世。冷水型胞石在奥陶纪主要分布于冈瓦纳大陆北缘和英国等中高纬度地区,沿冈瓦纳大陆边缘向北的洋流将这些中高纬度的表层冷水型胞石带入低纬度的塔里木板块内,热带下沉作用能使它们在深水的盆地相中获得适宜的环境温度而得以生存。     

Miocene to Pliocene vegetation reconstruction and climate estimates in the Iberian Peninsula from pollen data

Pollen analysis of Miocene and Pliocene sediments from the Iberian Peninsula shows a progressive reduction in plant diversity through time caused by the disappearance of thermophilous and high-water requirement plants. In addition, an increase in warm-temperate (mesothermic), seasonal-adapted “Mediterranean” taxa, high-elevation conifers and herbs (mainly Artemisia) occurred during the Middle and Late Miocene and Pliocene. This has mainly been interpreted as a response of the vegetation to global and regional processes, including climate cooling related to the development of the East Antarctic Ice Sheet and then the onset of the Arctic Ice Sheet, uplift of regional mountains related to the Alpine uplift and the progressive movement of Eurasia towards northern latitudes as a result of the northwards subduction of Africa. The development of steppe-like vegetation in southern Iberia is ancient and probably started during the Oligocene. The onset of a contrasted seasonality in temperature during the Mid-Pliocene superimposed on the pre-existing seasonality in precipitation, the annual length of which increased southward. The Mediterranean climatic rhythm (summer drought) began about 3.4 Ma and caused the individualization of modern Mediterranean ecosystems. Quaternary-type Mediterranean climatic fluctuations started at 2.6 Ma (Gelasian) resulting in repeated steppe vs. forest alternations. A latitudinal climatic gradient between the southern and the northern parts of the Iberian Peninsula existed since the Middle Miocene.     

Paleogene terrigenous (flysch) sequences in Etoloakarnania region (W. Greece). Plankton stratigraphy and paleoenvironmental implications

Based on calcareous nannofossils and planktonic foraminifera1 biostratigraphic data from flysch sequences, we give evidence for the paleoenvironmental evolution of Gavrovo and Ionian foreland basins (External Hellenides, Etoloakarnania region). Our data suggest that the onset of clastic sedimentation in both foreland basins in the study area is chronostratigraphically placed at Late Eocene (from 36.2-34.4 Ma; nannofossil biozones NP19-20, planktonic foraminifera biozones P16-17). During the earliest Oligocene (NP21-22 nannofossil biozones/34.4-32.45 Ma), both basins represent restricted accumulation of sediments, mainly composed of clays and silts. The presence of thick flysch deposits, accumulated during Early Oligocene (33.4-30 Ma, nannofossil zone NP23), indicates an increasing rate of sediment supply. The flysch sequences in the Ionian basin are associated with a distal depositional environment, while in the same time the sedimentation in the external part of Gavrovo basin is related to a more proximal environment that is gradually deepening. On the contrary, the internal part of Gavrovo basin is characterised by deep-water facies, deposited in the Early Oligocene. At the end of Early Oligocene and the onset of Late Oligocene (nannofossil zone NP24/30-27.2 Ma, planktonic foraminifera zone P21), the deposition of coarse grained sediments in both basins indicates a shift to shallower depositional environment. The accumulation of fine-grained sediments during Late Oligocene (27.2-23.2 Ma, NP25 nannofossil biozone) in the Ionian basin marks the youngest flysch sediments in the Etoloakarnania region and specifies the time of the Gavrovo nappe emplacement on the Ionian zone. Moreover the emplacement of Pindos nappe on the Gavrovo zone is estimated between 30-27.2 Ma (NP24 biozone) as supported by the nannofossil analysis of samples in front of Pindos thrust.     

Palynofacies Analysis of Inner Continental Shelf and Middle Slope Sediments offshore Egypt, South-eastern Mediterranean

Marine palynological studies of Quaternary sediments usually focus on dinoflagellate and pollen assemblages for paleoceanographic and paleohydrographic interpretations of past events. This paper focuses on the use of palynofacies analysis for paleohydrological reconstructions of deltaic and deep sea environments to evaluate transport of organic matter to the ocean. These palynodebris data are used to interpret palaeoenvironmental and paleohydrographic changes in two marine cores from the continental shelf (core-1, 27 m water depth) and middle slope (core-2, 1030 m) offshore Egypt, south-eastern Mediterranean Sea, during the latest Pleistocene and the Holocene. The relative abundances of various types of sedimentary organic matter such as phytoclasts, zooclasts, amorphous organic matter and palynomorphs are related to paleohydrographic changes of the overlying water column. Based on the total palynodebris and organic carbon content, sediments of the inner continental shelf core are characteristic of a prodelta environment proximal to a fluvio-deltaic source and moderately distal oxic environments with enhanced structured organic matter preservation potential. In contrast, the palynodebris of the middle slope core show that the basal sediments (105-140 cm depth) indicate suboxic to dysoxic bottom water conditions, followed by anoxic-suboxic bottom water conditions for the interval from 30-85 cm, which represents the S1 Sapropel. The top sediments of core-2 (0-25 cm) were deposited under oxic bottom water conditions, suggesting good ventilation in the water column. A quantitative approach was also used for interpreting the Holocene sea-level changes, based on the correlation between phytoclast and organic matter abundances. Sedimentation rate in the continental shelf is varied, being relatively very low (6.7 cm/kyr) in the basal part and increased upward to be 20 cm/kyr (depth 115-120 cm). In the upper Gray clayey silt layer the sedimentation rate was high (about 40-45 cm/kyr) due to the high discharge from El Manzala Lagoon and Damietta Nile branch. In the middle slope depth the sedimentation rate was relatively low and uniform, around 14 cm/kyr.     

Ramp morphology controlling the facies differentiation of a Late Ordovician reef complex at Bachu,Tarim Block,NW China

A carbonate ramp in the shallow‐marine northwestern part of the Central Tarim Uplift, Bachu, NW China, exhibits an extraordinary Late Ordovician reef complex along the Lianglitag Mountains, exposed for a distance of about 25 km. Seven localities within the ‘Middle Red Limestone’ of the Upper Member of the Lianglitag Formation (Katian, Late Ordovician) illustrated the changes in biofacies and lithofacies: northern, seaward‐directed patch reefs are replaced towards the south by coeval grain banks. The patch reef units are dominated by microbial and calcareous algal components. The reefs at the northernmost locality are knoll‐shaped, kalyptra‐shaped or irregularly shaped with sizes of individual reefs increasing from about 2 m in height and diameter. Stratigraphically upward, reefs notably expand to larger structures by several mounds coalescing; they are generally about 10 m thick and tens of metres in lateral extent. The maximum thickness of the main patch reef is more than 30 m, and its diameter is around 100 m. The reefal units turn into biostromes with gentler relief southward and still further south grade into banks composed of peloids and coated grains. The southernmost locality is still a shallow‐water bank, and the coastline is not documented in the study area. The present evidence indicates that the Late Ordovician palaeo‐oceanography provided a number of environments for the optimal growth of carbonate build‐ups; microbial‐calcareous algal communities could thrive in areas where the innovative metazoan reef frameworks consisting of corals and stromatoporoids did not play a significant role. The ramp morphology, especially changes in water depth, controlled the configuration of the reef complex.     

Internal supporting structures of some Late Ordovician graptolites from South China revealed by micro-CT

Three-dimensionally preserved pyritic internal moulds of the Late Ordovician graptolites Appendispinograptus leptothecalis and Styracograptus chiai from the Upper Ordovician Wufeng Formation of the Daheba section, Hunan Province, South China, were imaged by micro-CT. The distinctive pea-shaped pits/dimples aligned in a zigzag line arising from the second/third thecal pair on the tubarium in these species are interpreted as the surface expression of the junction between the lateral thecal walls and the thickened internal cross-bars that support the nema. The relations between different internal structures such as the nema, median septum, aboral lists, interthecal septa and cross-bars are summarized, and examples of these supporting systems in different taxa are illustrated. The presence of isolated cross-bars in different diplograptid tubarium may suggest that they have evolved as a result of constructional restrictions.     

Late Ordovician vertebrates from the Bighorn Mountains of Wyoming, USA

Abstract:  Late Ordovician vertebrate faunas occur in clastic sedimentary units along the length of the Rocky Mountains from Colorado to Montana, and across the border into Canada. Most research has, however, been conducted on localities in the southern part of the outcrop belt, particularly the Harding Sandstone Formation of Colorado. Micropalaeontological sampling of the coeval South Piney Member (Winnipeg Formation) in the Bighorn Mountains of Wyoming has revealed an abundant vertebrate fauna. The vertebrate assemblage includes a low-abundance fauna of 13 conodont taxa that together indicate an undatus Chronozone age (mid-Mohawkian; mid-Caradoc; Late Ordovician). The pteraspidomorphs Astraspis desiderata Walcott and Eriptychius americanus Walcott are also present together with one new taxon, Eleochera glossa gen. et sp. nov., which is interpreted as a derived stem-gnathostome on the basis of its scale histology and morphology. The fauna bears a strong similarity to that of the Harding Sandstone but is of lower diversity. In particular, it lacks the fine-grained, deeper water component of the Harding Sandstone that contains, inter alia , thelodonts and stem-chondrichthyans.     

Probable calcified metaphytes in the latest Proterozoic Nama Group, Namibia: origin, diagenesis, and implications

Samples from the Huns Limestone Member, Urusis Formation, Nama Group, at two adjacent localities in southern Namibia contain thin foliose to arched, sheet-like carbonate crusts that are 100-500 micrometers thick and up to 5 cm in lateral dimension. Morphologic, petrographic, and geochemical evidence supports the interpretation of these delicate crusts as biogenic, most likely the remains of calcified encrusting metaphytes. The original sediments of the fossiliferous samples contained aragonitic encrusting algae, botryoidal aragonite cements, and an aragonite mud groundmass. Spherulites within the precursor mud could represent bacterially induced mineral growths or the concretions of marine rivularian cyanobacteria. Original textures were severely disrupted during the diagenetic transition of aragonite to low-magnesian calcite, but some primary structures remain discernible as ghosts in the neomorphic mosaic. Gross morphology, original aragonite mineralogy, and hypobasal calcification indicate that the crusts are similar to late Paleozoic phylloid algae and extant peyssonnelid red algae. Structures interpreted as possible conceptacles also suggest possible affinities with the Corallinaceae. Two species of Cloudina, interpreted as the remains of a shelly metazoan, are also known from limestones in the Nama Group. It is possible, therefore, that skeletalization in metaphytes and animals arose nearly simultaneously near the end of the Proterozoic Eon.     

Discovery of Anticostia uniformis from the Xiazhen Formation at Zhuzhai,South China and its stratigraphic implication

The Xiazhen Formation is an Upper Ordovician lithostratigraphic unit in the Jiangshan-Changshan-Yushan (JCY) area, which contains series of Late Ordovician reef successions. The reef successions of the Xiazhen Formation at Zhuzhai are critical for evaluation of the Late Ordovician marine diversity and palaeoecology. However, their age has long been uncertain and generally is regarded as of upper Katian, based on the occurrences of shelly fossils and correlation with the stratigraphic equivalent Changwu Formation. The newly discovered graptolite species Anticostia uniformis, in the Xiazhen Formation, together with the combined evidence of brachiopods and sedimentology, indicates an age range for the graptolite locality from the Dicellograptus complanatus Biozone to the Diceratograptus mirus Subzone of late Katian, but the graptolites do not rule out the possibility that it is Hirnantian.     

Early Acheulean technology in the Rietputs Formation, South Africa, dated with cosmogenic nuclides

An absolute dating technique based on the build-up and decay of ²⁶Al and ¹⁰Be in the mineral quartz provides crucial evidence regarding early Acheulean hominid distribution in South Africa. Cosmogenic nuclide burial dating of an ancient alluvial deposit of the Vaal River (Rietputs Formation) in the western interior of South Africa shows that coarse gravel and sand aggradation there occurred ca 1.57 ± 0.22 Ma, with individual ages of samples ranging from 1.89 ± 0.19 to 1.34 ± 0.22 Ma. This was followed by aggradation of laminated and cross-bedded fine alluvium at ca 1.26 ± 0.10 Ma. The Rietputs Formation provides an ideal situation for the use of the cosmogenic nuclide burial dating method, as samples could be obtained from deep mining pits at depths ranging from 7 to 16 meters. Individual dates provide only a minimum age for the stone tool technology preserved within the deposits. Each assemblage represents a time averaged collection. Bifacial tools distributed throughout the coarse gravel and sand unit can be assigned to an early phase of the Acheulean. This is the first absolute radiometric dated evidence for early Acheulean artefacts in South Africa that have been found outside of the early hominid sites of the Gauteng Province. These absolute dates also indicate that handaxe-using hominids inhabited southern Africa as early as their counterparts in East Africa. The simultaneous appearance of the Acheulean in different parts of the continent implies relatively rapid technology development and the widespread use of large cutting tools in the African continent by ca 1.6 Ma.     

The oldest known occurrence of the Foliomena fauna in the uppermost Darriwilian (Middle Ordovician) of South China

The oldest Foliomena fauna was, until now, known from the middle–upper Miaopo Formation (Nemagraptus gracilis Biozone, lower Sandbian, basal Upper Ordovician) of South China. In this study, the oldest record of the fauna is set back to the latest Darriwilian (upper Hustedograptus teretiusculus Biozone), represented by Foliomena jielingensis and some typical constituents of the Foliomena fauna from the basal Miaopo Formation at Jieling, northern Yichang, western Hubei Province, central China. The Miaopo Formation is characterized by its organic‐rich dark‐grey shale facies, unique in its localized distribution on the Yangtze Platform, and distinguished by its rich and diverse benthic and graptolitic faunas. This suggests an origin of the Foliomena fauna in periodically oxygen‐starved local depressions on the Yangtze Platform during the Middle–Late Ordovician transition.     

Survival of crinoid stems following decapitation: evidence from the Ordovician and palaeobiological implications

It was recently discovered that the stems of extant crinoids may survive after detachment of the crown, presumably feeding by the absorption of nutrients through the ectoderm. Previously, only one analogous, albeit morphologically dissimilar, pattern of crownless survival has been recognized from the fossil record. Certain Upper Ordovician (Cincinnatian) crinoid pluricolumnals from Kentucky, Ohio and Indiana, derived from the disparids Cincinnaticrinus spp., have rounded terminations reminiscent of some modern bourgueticrinid overgrowths. Such specimens have hitherto been interpreted as distal terminations of mature individuals that have become detached from their attachment structures and taken to an eleutherozoic existence. However, it is considered more probable that they represent overgrowths of the column following predatory decapitation. If this new interpretation is correct, then post-decapitation survival of crinoid stems is now recognized for most of the history of the crinoids, 'lethal' predation on crinoid crowns occurred at least as early as the Late Ordovician and ancient crinoid populations can no longer be determined merely by counting crowns.     

The Late Eocene ‘Whiskey Creek’ methane-seep deposit (western Washington State)

Summary Large limestone boulders are eroding from a landslide west of the mouth of Whiskey Creek, Clallam County, Washington State. These boulders are composed of micrite, carbonate cement, and densely-packed fossil bivalves. Siltstone in the landslide, and on the surfaces of the boulders, indicates that these limestones are derived from the lower part of the Pysht Formation. The molluscan taxa and their localised occurrence within limestone are typical features of ancient chemosymbiotic cold-seep communities. Formainiferans from both the siltstone and the limestone indicate that deposition occurred during Late Eocene time, at water depths of between 500 to 1,500 m. Lipid biomarkers, particularly isoprenoid hydrocarbons and fatty acids, with δ¹³C values as low as −101‰ PDB, reveal that the anaerobic oxidation of biogenic methane was an important component in the biogeochemical cycling of carbon in the ancient seep environment.     

Preliminary palynological investigation of Saudi Arabian Upper Ordovician glacial sediments

An Ordovician stratigraphically admixed palynomorph assemblage that contains palynomorphs eroded from Middle through Upper Ordovician strata characterizes the Hawban Member (restricted) of the Sarah Formation in central Saudi Arabia. This distinctive assemblage, combined with detailed sedimentology, helps identify the presence of Hirnantian Gondwanan glacial sediments on the Arabian Plate. Similar Ordovician admixed assemblages have been recognized from Upper Ordovician glacial sediments elsewhere along the Gondwanan margin. Within Saudi Arabia the composition of reworked assemblages depends upon the stratigraphic succession exposed to glacial erosion. Sylvanidium? hawbanense, which is one of the acritarchs found in glacial sediments, is newly described from Arabian Upper Ordovician strata.