Ostracod Assemblages Research Articles

Ostracoda and Paleoenvironment of Holocene-Raised Beach Sediment in Skarvsnes, East Antarctica

Four sediment samples were collected from an outcrop of the Holocene-raised beach in Skarvsnes (Lützow-Holm Bay, East Antarctica) at an elevation of 0–10 m through a geomorphological survey conducted during the 46th Japanese Antarctic Research Expedition (JARE 46). These samples were used for grain size, CNS (carbon, nitrogen, and sulfur) elemental, and ostracod analyses. The 14C dating of an annelid tube collected from the same outcrop was also conducted using an accelerator mass spectrometry. The resultant age was estimated at approximately 5,800 cal. year BP. A total of 16 ostracod species belonging to 10 genera were identified for the first time from all study samples near Lake Suribachi-Ike, Lützow–Holm Bay, East Antarctica. The phytal species were found to be the most dominant, suggesting rich seagrass and/or seaweeds at that time. Autecological methods and modern analog technique of ostracod assemblages were used to estimate the paleoenvironment. The result from the modern analog technique suggested that the paleo-water depth of approximately 30 m at that time is the most probable estimation, implying the glacial-isostatic uplift of approximately 30–40 m (5.1–6.8 mm/year) until sample date.

Ostracods sensitivity to reconstructing water depths and oxygen levels: A case study from the Middle-Late Eocene of the Beni Suef area (Egypt)

Fifty-five ostracod species have been identified from 100 samples belonging to three stratigraphic sections in the Middle-Upper Eocene strata of the Beni Suef area (southern Tethys of Egypt). These ostracods have been used to subdivide the studied time interval into three zones that are correlated to the planktic foraminiferal zones E13 to E15. Based on clustering, non-metric Multidimensional Scaling (nMDS), and The Permutational MANOVA, sediment facies was found to be a significant factor controlling the ostracod fauna. Four assemblages were identified and their bio-ecological preferences were used to reconstruct paleoenvironments: 1) The upper Bartonian ostracod assemblage (El Fashn Formation) is dominated by Paracypris eskeri Bassiouni and Morsi and Novocypris eocenana Ducasse and is characterized by lower Shannon Diversity and higher ‘Dominance’ of stenohaline species with preference for lower oxygen levels and deeper neritic water depths; 2) The uppermost Bartonian (Qurn Member of Beni Suef Formation) is dominated by Paracypris eskeri Bassiouni and Morsi and Bairdia gliberti (Keij) indicating better oxygenated environmental conditions, supported by higher diversity values; 3) The lower Priabonian (Tarbul Member of Beni Suef Formation) is dominated by Novocypris eocenana Ducasse and has the lowest diversity, linked to the significant decrease of species with preference for highly oxygenated conditions; 4) The uppermost Priabonian (Maadi Formation) contains the most diverse assemblage and is characterized by a very low ‘Dominance’ and very high Shannon Index, where 26 species constitute the trophic nucleus and most of them are indicative of shallow water-depths and inner shelf settings in addition to preferences for high oxygen levels. The general increase in diversity and decrease in dominance is attributed to improved environmental conditions at shallower depths, where enhanced water mixing increased the oxygen available for biological demands. Moreover, the strong similarity of the recorded ostracod assemblages with those reported from other southern Tethyan sites reflects migration through the Atlantic and/or the trans-Sahara seaway, while the low similarity with the northern Tethys province (Europe) may be related on the one hand to their benthic nature, which may have limited their ability to move for longer distances, on the other hand to prevailing cooler waters to the north at higher latitudes. Water depth and associated environmental changes in respect to oxygen levels is interpreted to be the main factor controlling the distribution of the ostracods in the Beni Suef area.

Early Cretaceous Ostracoda (Crustacea) from south-central Araripe Basin, Brazil, with descriptions of seven new species.

A systematic study is made of Early Cretaceous (late Aptian/earlyAlbian) ostracod assemblages from the Santo Antnio section. This section is characterized by sediment belonging to the post-rift sedimentary sequence of the Romualdo Formation in the southern-central region of the Araripe Basin, Brazil and represents on of the first marine ingression in the interior of the continent, during the beginning of the formation of the Atlantic Ocean. The Santo Antonio section presents ostracods in greater diversity than previously known. Nineteen samples were analyzed, yielding a total of 8,370 specimens. Fifteen taxa were identified, including six brackish ostracods: Pattersoncypris salitrensis, Pattersoncypris angulata, Pattersoncypris micropapillosa, Damonella grandiensis, Alicenula cf. leguminella and Theriosynoecum cf. quadrinodosum; and nine typically brackish-marine species, including seven new ones: Dicrorygma cf. minuta, Dicrorygma (Orthorygma?) dimorpha, Mongolianella aptianensis sp. nov., Mantelliana speculum sp. nov., Paracypris undulareventralis sp. nov., Microceratina retangularis sp. nov., Perissocytheridea oculusutilis sp. nov., Perissocytheridea poruslinearis sp. nov. and Perissocytheridea florisdorsalis sp. nov. Therefore, the detailed taxonomic study brings a new understanding of marine ostracods around the upper Aptian/lower Albian boundary of the Araripe Basin.

Ostracoda Assemblages of the Hartha Formation (Late Campanian - Early Maastrichtian) from Balad (8) well, Central Iraq

Ostracoda Assemblages of the Hartha Formation (Late Campanian - Early Maastrichtian) from Balad (8) well, Central Iraq

Ostracods reveal the palaeoenvironmental changes in Laizhou Bay, Bohai Sea (eastern China) since the Late Pleistocene

Laizhou Bay is located in the Bohai Sea, eastern China. Since the Late Pleistocene, Laizhou Bay has gone through frequent transgressive and regressive activities and both marine and non-marine sediments have been deposited. In order to further understand the palaeoenvironmental changes since the Late Pleistocene, a core (DK06) was drilled on the coastal plain of Laizhou Bay. From this core, we obtained abundant well-preserved ostracod specimens. After environmental analysis and cluster analysis of these ostracods, four biofacies have been recognised: Biofacies I (shallow marine facies), Biofacies II (estuarine facies), Biofacies III (brackish water facies), Biofacies IV (freshwater facies). The studied ostracod assemblages suggest that the palaeoenvironment of Laizhou Bay went through four transgressions including three well-known marine transgressions during MIS 1, MIS 3 and probably MIS 5 and three regressions since the late Pleistocene, indicating substantial impact of glacial-interglacial sea level changes on the Bohai Sea coastal areas and their biota.

Paleoenvironmental Changes Since the Late Pleistocene Revealed by Ostracodes Record in Changmu Co., Western Tibet

A 4.9-m profile (BG-1) in Changmu Co., western Tibet, provides a continuous climate record from the Late Pleistocene to mid-Holocene on the basis of ostracode assemblages and shell trace elements. The results show six distinct climate change zones from 23.4 to 4.9 ka BP based on U-Th dating. The climate remained extremely cold until 13 ka BP because of the influence of the Last Glacial Maximum, which was indicated by the rare ostracodes occurring in this period. After that, the temperature rose gradually and the paleolake (Changmu Co.) enlarged. The ostracode assemblage during this period had high abundance and diversity, although the dominance of cold-water species and low Mg/Ca ratios indicate that the climate was still cold. More runoff water from a relatively warm climate entering into the lake, suggested by the increased U/Ca and Mn/Ca, led to a high lake level of 13–10.5 ka BP; this trend was also verified by the decreasing Sr/Ca values. The climate changed from humid to drought between 10.5 and 7.9 ka BP, which was inferred from the decreased abundance of ostracodes; however, there was a short humid period from 9.5 to 9.2 ka BP suggested by increased U/Ca and Mn/Ca ratios. A gradual transition to a humid environment began at 7.9 ka BP and ended at 5.3 ka BP. After this period, an extremely arid climate occurred after rising temperature and increasing evaporation, indicated by sharply increased Mg/Ca and Sr/Ca ratios. Eventually, the Changmu Co. paleolake shrank and dried up at some time after 4.9 ka BP. The changes in paleoclimate in Changmu Co. since the Late Pleistocene corresponded well to changes that occurred in the Westerlies-dominated Central Asia, suggesting that the climate in this region was mainly controlled by Westerlies circulation.

Biostratigraphy, palaeoecology, and palaeobiogeography of the Middle–Late Eocene ostracods, north‐west Fayoum area, Egypt

The present study focuses principally on the late Middle Eocene–early Late Eocene ostracods from two successions (Garet Umm Rigl section and Qasr El Sagha sections), in the northwestern portion of Fayoum area, Egypt. Stratigraphically, the studied successions are classified into three formations (from base to top), the Gehannam, Birket Qarun, and Qasr El Sagha (Temple Member). The recorded ostracod assemblage contains 33 species belonging to 20 genera and 9 families. According to their stratigraphic ranges, three local biozones are recognized, Asymmetricythere yousefi–Loxoconcha pseudopunctatella, Reticulina heluanensis–Leguminocythereis sadeki, and Trachyleberis nodosus nodosulcatus–Ruggeria (Keijella) glabella. The comparison of the proposed biozones with their equivalents inside Egypt denotes a Middle–Late Eocene age for the studied sections. Based on the character of investigated ostracods, three ecozones are distinguished. An inner–outer neritic environment is suggested for the first ecozone, inner‐middle neritic conditions for the second, while shallow water conditions are proposed for the third ecozone. In addition, this paper represents an attempt to detect the palaeobiogeographic provinces of Eocene ostracods by means of multivariate analyses (principle component analysis, Q‐mode cluster analysis and similarity index). These analyses are applied on a matrix composed of some selected Eocene species from 10 regions located at the southern Tethys and western Africa. The results identify three distinctive provinces, North Africa (Algeria, Tunisia, Libya, and Egypt), the Middle East (Jordan and Israel) and West Africa (Senegal, Togo, Ivory Coast and Nigeria). The distinctive affinities between these provinces suggests ostracod migration along the southern Tethys during the Eocene age.

New paleontological and biostratigraphical data (calcareous nannofossils, ostracods, brachiopods), correlations and lithostratigraphic units in the Urgonian facies (latest Hauterivian-Barremian) of the Swiss and French Jura Mountains: the Falaises Member and the Saars Formation (former “Gorges de l’Orbe Formation”)

From latest Hauterivian to latest Barremian, the Urgonian facies of the Swiss and French Jura Mountains are subdivided into three formations and five members: new Saars Formation (= former “Gorges de l’Orbe Formation” sensu Strasser et al., 2016; Pictet, 2021) with a new Falaises Member below the Montcherand and Bôle members of Pictet (2021), Rocher des Hirondelles Formation with Fort de l’Ecluse and Rivière members (Pictet, 2021, revised), and Vallorbe Formation (revised from Strasser et al., 2016 and the “Vallorbe Member” of Pictet, 2021). The latest Hauterivian-early Late Barremien Saars Formation includes three members 1) to 3): 1) Latest Hauterivian-Early Barremian Falaises Member with new Early Barremian nannoflora from the Corcelles Marls (much younger than the late Early Hauterivian nannoflora from the Uttins Marls of the type locality at Mont de Chamblon), primitive orbitolinids Praedictyorbitolina claveli Schroeder, 1994; and fossils/microfossils usually considered as Hauterivian markers: echinids Pseudholaster intermedius (Münster in Goldfuss, 1826), brachiopods Glosseudesia semistriata (Defrance, 1828), Lamellaerynchia hauteriviensis Burri, 1953 and Plicarostrum aubersonense Burri, 1956, and ostracods of the Assemblage 1 [Protocythere triplicata (Roemer, 1841), Rehacythereis bernardi (Grosdidier, 1964), Schuleridea clunicularis (Triebel, 1938), Schuleridea gr. thoerenensis (Triebel, 1938)]. 2) Early Barremian Montcherand Member with brachiopods Glosseudesia inexpectata Mojon, n. sp. and Glosseudesia ebrodunensis (de Loriol, 1864), and ostracods of the Assemblage 2 [Strigosocythere strigosa (Grosdidier, 1964), P. triplicata, and juvenile immature species markers of the next ostracod Assemblage 3]. 3) Early to early Late Barremian Bôle Member with adult ostracod markers of the Assemblage 3 [Rehacythereis geometrica (Damotte and Grosdidier, 1963), Bairdoppilata barremiana Mojon, n. sp., Bairdoppilata luminosa Kuznetsova, 1961; Neocythere (Centrocythere) gottisi Damotte and Grosdidier, 1963; Schuleridea derooi Damotte and Grosdidier, 1963; Schuleridea alata Kaye, 1965; Dolocytheridea intermedia Oertli, 1958]. 4) The Early to Late Barremian Fort de l’Ecluse Member/Rocher des Hirondelles Formation and Late Barremian Rivière Member/Vallorbe Formation are characterized by markers such as echinids Heteraster couloni (L. Agassiz, 1839), orbitolinids [Praedictyorbitolina carthusiana Schoeder et al., 1990; Eopalorbitolina charollaisi Schroeder and Conrad, 1967; Valserina broennimanni Schroeder and Conrad, 1967; Paleodictyoconus actinostoma Arnaud-Vanneau and Schroeder, 1976; Paracoskinolina maynci (Chevalier, 1961)], and typical ostracods of the Assemblage 4 [Strigosocythere chalilovi (Kuznetsova, 1961), Rehacythereis buechlerae (Oertli, 1958) only in the southern Jura and replaced by R. geometrica in the central Jura, Platycythereis rostrata Sauvagnat, 1999] extended in the latest Barremian-Early Aptian Fulie Member of the basal Perte-du-Rhône Formation defined by Pictet et al. (2016).

Changes in benthic microfossil assemblages before, during and after the early Toarcian biotic crisis in the Portland-Wight Basin (Kerr McGee 97/12-1 well, offshore southern England)

The uppermost Pliensbachian (Margaritatus Zone) - upper Toarcian (Pseudoradiosa Zone) sediments (silty and variably calcareous claystones, marlstones, silty sandstones, and sandy limestones) recovered from the Kerr McGee 97/12–1 well were deposited in the Portland-Wight Basin. The foraminiferal assemblages of these sedimentary succession are dominated by calcareous forms of the suborder Lagenina and locally Robertinina. Three main ecostratigraphic intervals have been identified, based on changes in the foraminiferal and ostracod assemblages that occurred before, during and after the sedimentation of the earliest Toarcian black, organic-rich, non-calcareous claystones. The ecostratigraphic interval I (upper Pliensbachian) is characterized by a diverse assemblage with specialist, opportunist and intermediate forms, but dominated by Lenticulina muensteri. The ostracods in this interval are dominated by Metacopina. This assemblage is interpreted to represent a phase that pre-dates the biotic crisis. The ecostratigraphic interval II, related to the deposition of the lower Toarcian black claystones, shows an abrupt increase in the opportunist form Reinholdella (91%) with very low diversity and a high abundance of specimens, mainly Reinholdella macfadyeni and R. dreheri. In this interval the ostracods Metacopina dissapear. The top of the black claystones is almost barren of foraminifera and ostracods (only two specimens recorded of Trochammina eoparva). This second interval represents the biotic crisis phase related to the Jenkyns Event. The ecostratigraphic interval III (upper part of the lower Toarcian through to the upper Toarcian) is characterized by an increase in the diversity and abundance of foraminifera, as well as the dominance of Lenticulina. The ostracod assemblage shows a turnover with respect to the upper Pliensbachian assemblage with dominance of Cytherocopina, Platycopina and Bairdiocopina. This assemblage is interpreted to reflect the increased availability of oxygen from deep-infaunal to epifaunal microhabitats and the return to normal conditions at the sea floor. The incidence of the global warming related to the Jenkyns Event in the biotic crisis is also considered. Ecostratigraphic fluctuations in microfossil assemblages from the Kerr McGee 97/12–1 well across the T-OAE event are comparable with those described from the Mochras Borehole (west Wales), the Lusitanian Basin (Portugal), and the Atlassic Basin (North Africa).

Ostracod assemblages from the Golubaya (Rybatskaya) Bay area on the outer northeastern Black Sea shelf over the last 300 years

A multi-proxy study of core Ash-2012-02 from the outer shelf of the northeastern Black Sea allowed us to define recent environmental changes, on a seven-year period resolution for the last 300 years. The age model of the core Ash-2012-02 based on radionuclide (210 Pb, 137 Cs, 241 Am) measurements suggests an average sedimentation rate of 1.4 mm/y and, consequently, a sedimentary record from end of the Little Ice Age to present. We subdivided the core section into five intervals mainly based on changes in relationships between ostracod species and their total abundance. Besides, the modern ostracod distribution on the northeastern Black Sea shelf was studied. Six main habitats with a specific ostracod species composition and environmental conditions have been investigated, as well as information on the temperature and salinity preferences for some ostracod species was provided. The ostracod species composition of assemblages remained similar throughout the core, but there were significant variations in the main ostracod species and the foraminiferal abundance. The hydrodynamic variations caused by climatic changes in the region are responsible for oxygen content in the bottom waters and affect the structure of the faunal assemblages. During the second half of the 20th century, an increasing trend of TOC and CaCO3 as well as considerable reduction in the ostracod diversity and the ostracod and foraminifera abundance are recorded in the muddy habitats, likely associated with unfavorable oxygen conditions and increased anthropogenic pressure.

Multi-proxy investigation of the post-evaporitic succession of the Piedmont Basin (Pollenzo section, NW Italy): A new piece in the Stage 3 puzzle of the Messinian Salinity Crisis

Paleoenvironmental reconstruction of the Mediterranean Basin at the end of the Messinian Salinity Crisis is contentious. One section that records this final phase (Stage 3) is the Pollenzo Section in the Piedmont Basin (NW Italy). Here, we present new stratigraphic, sedimentological, petrographic, micropaleontological (ostracods, calcareous nannofossils, foraminifera, dinoflagellates) and geochemical ( 87 Sr/ 86 Sr ratios) data from the Cassano Spinola Conglomerates (CSC) and interpret the paleoenvironment of this northernmost tip of the Mediterranean Basin. The CSC comprise three depositional units: members A and C, which were deposited subaqueously, and the intervening member B, which is continental. The CSC is topped by a ~ 50 cm-thick black layer, which is directly overlain by the open marine Argille Azzurre Formation of early Zanclean age. Our investigation reveals that member A is largely barren of autochtonous microfossils, except for an almost monospecific ostracod assemblage of Cyprideis torosa at the top, which indicates shallow-water (<30 m) conditions. Paratethyan ostracods and, possibly, taxa of calcareous nannofossils adapted to low-salinity water first occur in member C. 87 Sr/ 86 Sr ratios measured on ostracod valves from the member A/B transition (0.708871–0.708870) and member C (0.708834–0.708746) are lower than the coeval Messinian seawater values (~0.709024) and the 87 Sr/ 86 Sr ratios of a hypothetical lake filling Piedmont (>0.7090) estimated by means of the present-day 87 Sr/ 86 Sr signature of the Po river, the main drainage system of Northern Italy that receives the weathering products (including ions) of the Alps and Apennines. These values are likely to reflect the mixing of local high 87 Sr/ 86 Sr river water with low 87 Sr/ 86 Sr from the Mediterranean, which at the time was dominated by inputs from Eastern Paratethys, circum-Mediterranean rivers and Atlantic Ocean. Our results suggest that, at times during the final stage of the Messinian Salinity Crisis, the Piedmont Basin was hydrologically connected with the main Mediterranean Basin. At regional scale, this implies that the water level in the Mediterranean Basin was relatively high. • Piedmont Basin alternated subaqueous and continental conditions during MSC Stage 3. • 87 Sr/ 86 Sr values are inconsistent with subaqueous sedimentation in a local river-fed endorheic lake • Piedmont Basin-Mediterranean connection during times of Paratethyan ostracods spreading. • The Mediterranean water-level was occasionally relatively high during Stage 3.

OSTRACODS FROM THE LATE TRIASSIC (NORIAN) OF YUKON, CANADA: NEW TAXONOMIC AND PALAEOBIOGEOGRAPHIC INSIGHTS

The present work investigates the significance of Late Triassic ostracods from the Yukon Territory, Canada, and adds to the scientific knowledge of the taxonomy of these organisms during the Norian, which remain poorly documented and understood. Fifteen limestone samples representing distinct marine palaeoenvironments cropping out at Lime Peak, Stikinia terrane, provided 90 species, including 9 newly described: Alatobairdia? sohni n. sp., Bairdia aksala n. sp., B. taan n. sp., B. yukonensis n. sp., Cornutobairdia yukonella n. sp., Lobobairdia whitella n. sp., Mirabairdia canadia n. sp., Hungarella limella n. sp., Leviella riedeli n. sp. Most assemblages point to neritic conditions in the photic zone. A similarity analysis demonstrates the distinct composition of reef-related and algae-related ostracod assemblages. The ostracod-algae associations in Lime Peak reveal that the affinity of Bairdiidae for algae (Dasycladaleans in the case of Lime Peak) was already established in the Norian. A faunal link is identified during the Norian between eastern and western Panthalassa and Japan, in line with studies on other taxa. The flux of species between eastern Panthalassa and Tethyan areas appears very unbalanced in the Late Triassic with most migrations originating from the Tethys. Further data from other Middle and Upper Triassic Panthalassan localities and stages (i.e. Ladinian and Carnian) are needed to confirm whether this apparent trend is due to sampling bias or reflects real dispersal fluxes.

Результаты палеоэкологического анализа остракод из разреза верхнего берриаса у с. Алексеевка (Белогорский район, Республика Крым)

The results of the paleoecological analysis on ostracods of the upper part of Sultanovskaya Formation (Boissieri zone) in the section near v. Alekseevka are presented. Five ostracod assemblages reflecting changing conditions in the paleobasin are defined. It was established that the sedimentation in the Late Berriasian time occurred under conditions of a warm normally salty with a calm hydrodynamic regime of the basin, mainly in oxygen waters.

Environmental evolution of the Miocene palaeolake of Venta del Moro (Valencia, Spain): a study of foraminifers, thecamoebians (Arcellinida) and ostracods

ABSTRACT The Venta del Moro site (Valencia, Spain) is especially known for its rich content in Late Miocene fossil mammals but it also holds other fossil vertebrates, invertebrates and plants. A micropalaeontological study of a 70-cm long sedimentary section carried out in the lacustrine beds of the site has yielded 2 foraminifer, 7 thecamoebian and 19 ostracod taxa (two of these last probably new species). A constrained cluster analysis allowed the recognition of three consecutive zones based on their micropalaeontological content. The variation of the microfossil assemblages closely matches lithology and reflects environmental changes in a palaeolake that was subject to a gradual drying process. Anoxic bottom conditions at the base of the sequence (Zone 1) prevented the occurrence of aerobic benthic microorganisms. Later, the appearance of ostracods and thecamoebians (Zone 2) documents the increasing oxygenation of the lake and suggests a permanent freshwater to slightly brackish lake with low temperature and stream influence. The dominance of foraminifers and the changes in the thecamoebian and ostracod assemblages in the upper part of the sequence (Zone 3) reflect more stable and oxygenised conditions and probably increasing temperature and evaporation in oligohaline temporary waters, during the final drying phase of the lake.

Ostracod response to monsoon and OMZ variability over the past 1.2 Myr

We present the first continuous middle through late Pleistocene record of fossil ostracods from the Maldives in the northern Indian Ocean, derived from sediment cores taken at Site U1467 by Expedition 359 of the International Ocean Discovery Program (IODP). Site U1467 lies at 487 m water depth in the Inner Sea of the Maldives archipelago, an ideal place for studying the effects of the South Asian Monsoon (SAM) system on primary productivity, intermediate depth ocean circulation, and the regional oxygen minimum zone (OMZ). The Inner Sea acts as a natural sediment trap that has undergone continuous sedimentation for millions of years with minor terrestrial influence. Our record spans from Marine Isotope Stage (MIS) 35 to the present, covering the mid-Pleistocene transition (1.2–0.6 Ma) and the Mid-Brunhes Event (MBE, at ~480 ka) the time when ice age cycles transitioned from occurring every 40,000 years to 100,000 years. The ostracod data is interpreted alongside the existing datasets from the same site of sedimentological (grain-size) and XRF-elemental analyses, and new organic biomarker data also from Site U1467. These datasets support the paleoenvironmental interpretation of the ostracod assemblages. Ostracods are abundant and diverse, displaying a prominent change in faunal composition at the MBE related to the increase in the amplitude of glacial-interglacial cycles, which deeply affected the monsoon system and thereby the past oceanographic conditions of the Maldives Inner Sea. Furthermore, ostracods exhibit distinctly different assemblages across glacial-interglacial cycles, particularly after the MBE, and these changes convincingly correspond to variability of the OMZ. Glacial periods are characterized by ostracod indicators of well‑oxygenated bottom water due to the intensification of the winter monsoon and the contraction of the OMZ. Abundant psychrospheric ostracods during glacials suggests that a southern sourced water mass, such as Antarctic Intermediate Water (AAIW) and/or Subantarctic Mode water, bathed the Maldives Inner Sea during glacial periods. In contrast, interglacial stages are characterized by ostracod species and biomarker data that indicate low-oxygen conditions and sluggish bottom water circulation pointing to an expansion of the regional OMZ due to the strengthening of the summer monsoon. Our results highlight the sensitivity of ostracods to oceanographic and climate variability.

Ostracod Response to a Major Middle Jurassic Sea-Level Fall: A Case Study from Southern Tunisia (North Gondwana) with Implications on Regional Stratigraphy and Palaeoenvironmental Reconstruction

Marginal-marine to non-marine ostracod assemblages from the Bajocian (Mid-Jurassic) of southern Tunisia, precisely from the Krachoua Formation at the Kef El Anneba section near the Beni Kheddache area, are here described and tested for their utility to improve the stratigraphic accuracy and palaeoenvironmental reconstructions. This particular microfauna consists of 11 species belonging to 6 genera and represents 2 distinct types of species-rich assemblages from this time interval, allowing the interpretation of the depositional setting of the fossiliferous horizon from which the samples derive. The first ostracod assemblage is mainly composed of the brackish to shallow marine species Fastigatocythere sp. Mette, 1995; Vernoniella aff. V. bajociana Bate, 1965b; Paracypris sp. A, Paracypris sp. B, Fabanella sarda Malz et al., 1985; Marslatourella aff. M. bathonica Andreu, 1999; and Fabanella aff. F. bathonica Oertli, 1957. This ostracod biofacies reflects marginal marine (shallow platform, restricted lagoon) conditions in the studied area. In contrast, the second ostracod assemblage is exclusively dominated by the non-marine limnic species Alicenula sp., Theriosynoecum pusilla Rohr, 1976; Theriosynoecum aff. T. aveyronensis Rohr, 1976; and Theriosynoecum sp. Such ostracod biofacies reflects the establishment of (a) permanent freshwater lake(s) in the studied area, triggered by the total emersion of the Bajocian Krachoua platform, presumably as response to the short-term sea-level fall event JBj3 of Haq (2017). The recognized ostracod species from the upper part of the Krachoua Formation at Kef El Anneba section (Medenine area) are particularly similar to those already described from the neighbouring sections of Kezzani (Dhaher area) and Krachoua (Tataouine area), facilitating a stratigraphic calibration of the Krachoua Formation, as well as regional correlations of the respective Bajocian continental event within the southern Tunisian palaeogeographic domain. Moreover, the biogeography of the studied ostracod microfauna from the Mid-Jurassic of southern Tunisia provides further arguments to support the hypothesis of significant biological exchanges between Laurasian and Gondwanan islands, as recently demonstrated by means of a charophyte microflora, indicating that Peri-Tethyan biogeography remained relatively uniform during that time interval and challenging the previous assumption of their endemism.

Ostracoda (Crustacea) from the Lower Jurassic of northeastern Thailand: stratigraphic and paleoenvironmental implications

Freshwater ostracods were recovered from limestone strata belonging to the Nam Phong Formation exposed at Ban Non Tum section in Chaiyaphum Province, northeastern Thailand. The examined rocks were collected above the oldest known dinosaur footprints site in Thailand. All recovered ostracods belong to the Superfamily Darwinuloidea and were attributed to three species: Suchonellina sarytirmensis (Sharapova) in Mandelstam, 1947, Suchonellina. sp. A and Suchonellina sp. B. The ostracods represent the first known record of Jurassic darwinuloideans in Southeast Asia. The ostracod assemblage and microfacies are indicative of deposition in a shallow and low energy fluvio-lacustrine regime.

Disentangling the Impact of Global and Regional Climate Changes During the Middle Eocene in the Hampshire Basin: New Insights From Carbonate Clumped Isotopes and Ostracod Assemblages

AbstractWe present a novel multiproxy data set (bulk and clumped isotopes on gastropod shells and variations in ostracod assemblages) of the Hampshire Basin (Southern‐England) that sheds light on the connection between the North Sea and the Atlantic Ocean through the English Channel during the deposition of the Barton clay formation (latest Lutetian—Bartonian, middle Eocene; ∼41–40 Ma). During this time period, the English Channel operated as a gateway between the warmer Atlantic Ocean and the colder North Sea waters. High‐latitude water mixing combined with the regional hydrological cycle and sea‐level variations, may have contributed to mitigate the water temperatures in the Hampshire Basin, with an average recorded of ca. 25°C. In the uppermost part of the section the connection between the two water masses was limited or absent as evidenced by warmer (up to ca. 35°C) Atlantic Ocean temperatures in the Hampshire Basin. The large differences in average oxygen isotope composition of seawater (δ18Owater) recorded (from δ18Owater −1.7‰ to δ18Owater of −0.7‰) evidenced large salinity differences between the Atlantic Ocean and the North Sea. Ostracods suggest that the temporary connection between those two water masses was caused by relative regional sea‐level variations. This scenario could be partially linked to glacio‐eustatic sea‐level changes related to climate fluctuations probably associated with the MECO event.

Lake level controls the recurrence of giant stromatolite facies

AbstractStromatolites have often served as a diagnostic carbonate facies for deep‐time palaeoclimatic and geobiological studies because they may form under favourable environmental conditions for microbially mediated carbonate production. ‘Giant’ (&lt;5 m) stromatolites occur in the Laney Member of the Eocene Green River Formation in the Vermillion Creek section of the Sand Wash Basin (north‐west Colorado, USA). Giant stromatolite growth was hypothesized to have been promoted by both availability of large substrates as nucleation sites and physicochemical factors, including increased calcium carbonate mineral saturation states due to the generally warmer Eocene climate and a dynamic period in Lake Gosiute’s hydrological balance. Depositional horizons of giant stromatolites were observed at two distinct stratigraphic levels, which demonstrated that the formation of the giant morphotype was not a unique occurrence, and provided an opportunity to examine both onset and cessation of stromatolite development. Coincident increases in carbonate clumped isotope‐derived temperatures, the carbon and oxygen isotopic compositions of lake water (δ18Ow), carbonate mineral saturation states (Ω) estimated by ooid size, and salinity estimated by ostracod assemblages demonstrated that formation of giant stromatolites was facilitated by lake level drawdown. Decreased lake levels: (i) promoted carbonate precipitation; and (ii) positioned benthic microbial communities within the photic zone. Field and petrographic analyses revealed that the giants preserved micritic laminations, ‘trapped and bound’ grains, and aragonite fans, interpreted as reflecting contributions from both microbially mediated and abiotic carbonate mineral precipitation. Field and microscopic sedimentological and stable isotope data indicated that giant stromatolite growth ceased as a result of subaerial exposure of mounds during lake level lows. Although microbial mediation of carbonate chemistry was seemingly important for initiation of stromatolite growth, this work demonstrated that stromatolite macromorphology was dominantly controlled by availability of large substrates, lake level and resultant solute chemistry, i.e. increased Ω.

Late Quaternary evolution of the Metaponto coastal plain, southern Italy, inferred from geomorphological and borehole data

A multidisciplinary study of a sector of the Ionian coastal belt, southern Italy, mainly based on two new boreholes approximately 25 m (MSA) and 20 m (MSB) deep, was carried out in the frame of a wider geoarchaeological project. Stratigraphic and Paleoecological data, together with geomorphological observations, have been used in order to define the Late Quaternary morpho-sedimentary evolution and its relationships with tectonic and climate forcing. The analyses of core sediments and geomorphic interpretations allowed us to reconstruct the changes in depositional setting and physical landscape starting from the MIS 5.5. To this scope, new data about sedimentary facies, benthic foraminifera and ostracod assemblages, and a set of 14C ages spanning from about 33 to 15 kyr BP are here presented. All these data revealed a strong modification of the depositional setting within the coastal plain, as inferred by the presence of marine, transitional, and continental deposits, and suggest an anomalous position of sea-level reference points. Such anomalies are clustered in two homogenous arrays that can be explained only admitting a significant tectonic uplift in recent times (i.e. about 4 mm/yr over the last 15,000 years).