Ostracod Content Research Articles

New insights on the latest Messinian-to-Piacenzian stratigraphic series from the Dahra Massif (Lower Chelif Basin, Algeria): Lago Mare, reflooding and bio-events

Geological investigations carried out on the Dahra Massif have revealed sedimentary changes and bioevents characterizing the post-gypsum detrital sediments (from Messinian to Piacenzian), which are followed by the Trubi equivalent Pliocene marls or white marly limestones. Structured into two superimposed steps, the late Messinian deposits yielded two successive ostracod assemblages. They indicate a brackish environment for the lower and a fairly open shallow brackish environment for the second. Based on their ostracod content, assemblage 1 (Cyprideis, Loxoconcha muelleri) corresponds to the Lago Mare biofacies 1 of the Apennine foredeep, which is correlated with the Lago Mare 1 episode dated between 5.64 and 5.60 Ma. Assemblage 2 (Loxocorniculina djafarovi) is referred to the Lago Mare biofacies 2 described in the same region. It is correlated with the Lago Mare 3 episode, dated between 5.46 and 5.33 Ma. Moreover, the stratigraphic succession is marked by a major discontinuity indicated by a hardground, separating step 1 from step 2 and corresponding to the ostracod assemblages 1 and 2, respectively. This discontinuity is considered here to be equivalent to the Messinian Erosional Surface, already evidenced in the region and widely known around the Mediterranean Basin. These late Messinian deposits and their ostracod assemblage 2, notably the detrital sedimentation with Ceratolithus acutus, Globorotalia margaritae, Reticulofenestra cisnerosii document a marine incursion into the Lower Chelif Basin, corresponding to the latest Messinian marine reflooding of the Mediterranean Basin, that happened before the earliest Zanclean R. cisnerosii occurrence. Finally, the bioevents evidenced in the Dahra Massif, reinforce the evidence of the late Messinian Lago Mare 3 episode, and support the ante-Zanclean age of the marine reflooding of the Mediterranean. The overlying deposits are marked by coral constructions (cf. Cladocora cf. caespitosa, Dendrophyllia sp) never described before and covering the entire early Zanclean, testifying the existence, at that time, of warm enough conditions, which may correspond to the marine isotopic stage TG5.

Paleobiogeographic affinities and paleoecological significance of paleogene ostracods from Eastern Benin Basin, Southwestern Nigeria

Ditch cutting samples from the studied section of the RC-4 Hole, eastern Benin (Dahomey) Basin were studied for their ostracod content. 3671 ostracod fauna belonging to 22 species were recovered and analysed with a view to determining ostracod paleobiogeographic affinities and paleoecological conditions within this part of the basin during the Paleogene. Ostracod assemblages of the studied section bear close affinities to those of some North and West African basins. Species such as Bairdia ilaroensis, Leguminocythereis spp., Bairdia malzi, Paracosta kefensis, Xestoleberis tunisiensis, Buntonia jordanica, Aegyptiana duwiensis and Leguminocythereis lokossaensis identified from the RC-4 hole suggest shallow neritic conditions. Paracosta kefensis and Paracosta parakefensis occur in high abundance indicating marine upwelling conditions. Many of the species recovered in this study have also been identified from Iullemeden and southern Tethys basins (e.g. Sirte Basin) suggesting ostracod migration from Benin Basin (Gulf of Guinea) to southern Tethys basins through the Paleogene shallow Trans – Saharan Seaway. A distinct ostracod turnover at the top of the limestone unit (Ewekoro Formation) is related to the Paleoceneo Eocene Thermal Maximum (PETM) – a climatic phenomenon characterised by 5 – 8 C global temperature rise at the end of the Paleocene.

Turonian and Coniacian Ostracods from the Gafsa Basin (central-southern Atlas of Tunisia) and the Gulf of Gabes (eastern coast of Tunisia): Biostratigraphic, paleoevironmental and paleobiogeographic implications

Three hundred thirty-nine samples were collected from the Turonian-Coniacian succession that crops out in the Gafsa Basin and drilled in the Gulf of Gabes; these samples come from four outcrops and four wells and they were examined for their ostracod content. Sixty-two species belonging to twenty-nine genera were identified. They are subdivided into two major groups: smooth - species dominated assemblages and ornamented - species dominated assemblages. In the present work, five research goals are pursued: 1) to document the ostracod biodiversity encountered in the studied outcrops and wells, 2) to establish their biostratigraphic distribution, 3) to suggest a zonation mainly based on ostracods and correlated directly with the equivalent planktic foraminiferal zones, 4) to attempt a paleoenvironmental reconstruction based on the application of paleoecological characteristics of the identified ostracod assemblages. Finally, paleobiogeographical relationships were carried out between the Tunisian ostracods and those recorded in different regions of the Tethyan realm.

Paleoenvironmental and paleobiogeographic implications of Middle Miocene Ostracods from the Al Khums area, northwestern Libya

This paper studies the Middle Miocene ostracods from three different outcrops in the Al Khums area, northwestern Libya. Lithologically, these outcrops belong to the Al Khums Formation, and are considered synchronous due to the great similarity in their ostracod content. Twenty seven ostracod species, belonging to 22 genera and 13 families, were identified. Although the age of the Al Khums Formation cannot be precisely constrained based on its ostracod assemblage, the presence of the larger benthic foraminiferan subspecies Borelis melo melo allows to assign to the sequence a Middle Miocene age. The identified ostracods indicate that the depositional environment was shallow marine. This conclusion is also supported by the co-occurrence of algae, large oysters and corals. Multivariate analyses were applied to the present data to distinguish the paleobiogeographical provinces of the studied ostracod species. The results indicate that there are two distinguished bioprovinces: (1) The South Tethyan bioprovince (STP) including Algeria, Libya and Egypt, and (2) The North Tethyan bioprovince (NTP) including Spain, Italy, Malta, France, Turkey and Greece. Similarities between the ostracod assemblages of these bioprovinces suggest a good marine connection between both sides of the Mediterranean Sea during the Middle Miocene.

Variation of the mid-latitude westerlies and Indian summer monsoon since the last deglaciation: Evidence from grain-size data from Linggo Co, central Tibet

The mid-latitude westerlies and Indian summer monsoon (ISM) have a significant impact on the water budget and general environment of the Tibetan Plateau (TP), and much work has been conducted in order to characterize variations in these two atmospheric circulation systems on various time scales. However, the nature of the interplay between the Asian summer monsoon and the westerlies during the last deglaciation remains controversial. In this study, a sediment core from Linggo Co, a closed lake in the central TP, was analyzed for grain size and ostracod content. The results suggest that environmental change in the Linggo Co basin during the past 17 ka can be divided into four stages: during Stage 1 (17–11.7 ka) Linggo Co was a shallow lake characterized by high amplitude hydrological fluctuations. Strong winds prevailed in winter, correlative with cold events in the North Atlantic region, and indicating the dominance of the westerlies. During Stage 2 (~11.7 ka), in the early Holocene, Linggo Co expanded rapidly and there was the disappearance of the shallow-water ostracod species Limnocythere inopinata together with a decrease in mean grain-size. These changes indicate that ISM was enhanced and that it was the dominant atmospheric circulation affecting TP rather than the westerlies. During Stage 3 (10–8 ka) Linggo Co experienced several intervals with a negative water budget, which may be attributed to a weakening of the weaken ISM or to the reduced influx of glacial meltwater as a result of the influence of cold climatic events. During Stage 4, after 8 ka, Linggo Co shrank progressively in parallel with a gradual weakening of the ISM and finally a transition to the present environment occurred at ~2.5 ka. A comparison of the record from Linggo Co and other records from the TP reveals that prior to 16.5 ka the mid-latitude westerlies was the dominant atmospheric circulation system controlling the entire TP. From 16.5 to 11.5 ka, the mid-latitude westerlies still controlled the central-northern TP; however, the ISM controlled the southern TP, which had a similar climatic pattern to the present day. During the early-middle Holocene, the ISM was the dominant system affecting the entire TP; however, its influence was considerably reduced during the late Holocene, which was probably accompanied by a strengthening of the westerlies.

Quantative analysis and paleoecology of Middle to Upper Eocene Ostracods from Jebel Jebil, central Tunisia

One hundred and seventy collected samples from Jebil section have been carefully studied for their ostracod content and referred to 41 species belonging to 20 genera. Their vertical distribution allowed to distinguish five successive associations of ostracod assemblages; two of which are correlated with the Early Lutetian, one with the Late Lutetian, another association with the Bartonian and the last one with the Priabonian. Community structure of the collected ostracod fauna has been studied; three indices have been calculated for each sample: Shannon (diversity), Margalef (richness) and Equitability indexes. In the lower and the middle part of the Formation, they indicate a stable environment supporting high diversity ostracod communities; whereas in the upper portion the environmental conditions were unstable characterized by low diversity. The results of a multivariate statistical method, using the cluster analysis and the Detrended Correspondence Analysis of the 41 ostracod species and the 170 samples, have led to conclude that the most effective environmental factor in the study area is the paleodepth and of less importance oxygenation and salinity. Thus, it allowed to distinguish four palaeoenvironmental intervals within the Cherahil Formation: the first one represented by taxa that are known from the shallower parts of the shelf; the second interval includes the majority of the encountered species of inner neritic shelf with normal salinity; the third one, corresponding to an outer neritic domain; and the last interval refers to a circalittoral environment, is comprised mainly of Cytherella angulata and of Soudanella laciniosa triangulata.

Late Miocene sedimentary environments in south-western Amazonia (Solimões Formation; Brazil).

In Miocene times a vast wetland existed in Western Amazonia. Whereas the general development of this amazing ecosystem is well established, many questions remain open on sedimentary environments, stratigraphical correlations as well as its palaeogeographical configuration. Several outcrops located in a barely studied region around Eirunepé (SW Amazonas state, Brazil) were investigated to obtain basic sedimentological data. The observed deposits belong to the upper part of the Solimões Formation and are biostratigraphically dated to the Late Miocene. Vertically as well as laterally highly variable fine-grained clastic successions were recorded. Based on the lithofacies assemblages, these sediments represent fluvial deposits, possibly of an anastomosing river system. Sand bodies formed within active channels and dominant overbank fines are described (levees, crevasse splays/channels/deltas, abandoned channels, backswamps, floodplain paleosols). Lacustrine environments are restricted to local floodplain ponds/lakes. The mollusc and ostracod content as well as very light δ18O and δ13C values, measured on ostracod valves, refer to exclusively freshwater conditions. Based on palaeontological and geological results the existence of a long-lived lake (“Lake Pebas”) or any influx of marine waters can be excluded for that region during the Late Miocene.

The upper Bedoulian and lower Gargasian Ostracoda of the Aptian stratotype: Taxonomy and biostratigraphic correlation

In the vicinity of Saint-Saturnin-les-Apt (Vaucluse, SE France), which is included in the area of the historic Aptian stratotype of Apt-Gargas, are four sections in a succession that permits the study in a very detailed and continuous way of the last beds of the upper Bedoulian and those of the lower Gargasian. The Ostracod content of the microfauna is relatively important and in a satisfactory state of preservation. 46 species have been indexed of which three are new: Cytherella circumrugosa nov. sp., Cytherelloidea bedouliana nov. sp. and Parexophthalmocythere (Parexophthalmocythere) sp. Until the present day, our comprehension of this group of microfossils in this stratigraphic interval was very fragmentary, not just in the Apt region but also in the Bedoulian historic stratotype area (Cassis-la Bedoule). This new study made it possible to determine a good number of species not previously reported in the stratotypes, to refine the generic status of many forms and to place some of them in open nomenclature. The completion of a chronologic distribution chart collated with a recently published foraminiferal zonation (Cabri, Luterbacheri and Ferreolensis zones) shows very clearly the bipartite distribution of a good part of the Ostracod fauna. Accordingly, two ensembles are recognized, one at the end of the upper Bedoulian (index species Protocythere bedoulensis), the other characterizing the lower Gargasian, identified by the appearance and development of Parataxodonta inornata. The two groups are sharply separated by an episode of impoverished microfaunas at the base of the Gargasian.

Recent ostracods from the Persian gulf

Fourteen bottom samples from the north-western part of the Persian Gulf (Iranian side), ranging in depth from 32 to 54 m, have been analysed for their ostracod content. Of a total of 50 species identified seven taxa are new (Aglaiocypris pellucida, Cytherella bigemina, Cytherella retroflexa, Cytherella sericea, Heinzmalzina ocellata, Paijenborchella calcarina andSagmatocythere nupta). Compared to a previous sampling in 1965, eight additional ostracod species occur in the modern Persian Gulf. Water depth and substrate may be the most important factors controlling the distribution of some ostracod species. The fauna demonstrates strongest affinities with that of the Red Sea and the Indo-West Pacific. Contrary to previous statements, none of the recorded species in this study is shared with the Mediterranean fauna, except for the cosmopolitanCyprideis torosa.

Late Quaternary climate history of the Bolivian Altiplano

Abstract Sediment cores and outcrops from the Bolivian Altiplano are used to interpret late Pleistocene/Holocene paleoclimates and lake evolution based on a multi-proxy approach (ostracod content, palynology, sedimentology, and radiocarbon dating). Despite the different sensitivity of the lacustrine basins to environmental changes, interpreting the records in terms of paleohydrology, climate, and more especially timing of events is difficult. Notwithstanding these problems, Lake Titicaca in the north and Lake Pocoyu (Lake Poopo, salars of Coipasa and Uyuni) in the south reveal a similar evolution in general trends through the course of time. During the Minchin phase (until 30–26 kyr BP), the Altiplano was wetter than present. The Last Glacial Maximum (ca. 26–14 kyr BP), marked by cooler, drier conditions, was followed by a return to a wetter climate, interrupted by short arid events, between ca. 14 and 10.5 kyr BP. Another cycle of aridity, between 10.5 and 8 kyr BP, took place abruptly just after the humid Tauca phase. The mid-Holocene is interpreted as climatically unstable, with an alternation of humid and dry episodes. Since 3.9 kyr BP, wetter conditions have persisted and intensified to the present. The data are interpreted in terms of changes in inter-tropical convergence zone extension (summer precipitation) and in polar air mass intensity (winter precipitation).

Tertiary ostracods of Gebel Withr, southwestern Sinai, Egypt: pal˦ontology, biostratigraphy and pal˦obiogeography

The exposed Early Eocene-Early Miocene interval in the study area yields considerable amounts of ostracods. A detailed investigation of the ostracod content has led to the recognition of 79 species and subspecies, five of which are reported as new species. They are Semicytherura bassiounii, Semicytherura gammudii, Pterygocythere withrensis, Paracosta reymenti and Cativella bulgi. An attempt to reconstruct a local ostracod biozonation has led to the recognition of six biostratigraphical zones. These biozones are arranged from the youngest to the oldest as follows: Leguminocythereis bopaensis-Leguminocythereis bicostata Assemblage Zone; Reticulina saitoi-Trachyleberis nodosus Assemblage Zone; Asymmetricythere yousefi-Cytherella piacabucuensis Assemblage Zone; Leguminocythereis africana-Buntonia faresi Assenblage Zone; and Grinioneis haidingeri-Pokornyella deformis minor Assemblage Zone. The palaeobathymetric estimates for these assemblages reveals a great deal from the inner neritic to the upper bathyal environments. The cosmopolitan distribution of the recorded species proved to be useful for pal˦obiogeographic reconstruction. This reveals that there was a direct connection throughout the Tethyan realm and a connection between the Tethyan North Africa and West Africa via the Trans-Saharan Seaway, at least until the end of the Palaeocene, through which the migration of benthic organisms had occurred.

The late Pleistocene ostracod record of the crater lake sediments from Lago di Albano (Central Italy): changes in trophic status, water level and climate

Four cores (ranging between ca. 9 and ca. 14 m in length) from Lago di Albano in Central Italy were studied for their ostracod content, as well as algal and bacterial pigments, CaCO3 and concentration of organic matter. Cores PALB 94 1E and PALB 94 1C from Site 1, located at the bottom of a steep slope at 70 m water depth, where oxygen concentration is below 6 mg l-1, spans the Holocene and the late Pleistocene until 28 kyr B.P. (calibrated age). The other cores, PALB 94 6A and PALB 94 6B taken at a depth of 30 m, where oxygen is 7--11 mg l-1, represent mainly Pleistocene deposits.

Lagoonal to Reefal Ostracod Assemblages from Holocene and Recent Deposits, Chesterfield Islands and Northern New Caledonia (Southwestern Pacific)

Lagoonal to Reefal Ostracod Assemblages from Holocene and Recent Deposits, Chesterfield Islands and Northern New Caledonia (Southwestern Pacific)