Permian brachiopod faunas of southeastern Mongolia: systematics, biostratigraphy, palaeogeographical and palaeobiogeographical implications

This research systematically studied Permian brachiopod fossils from southeastern Mongolia and correlated them with many places around East Asia. The research found that the fossil faunas are on the mixed affinities between high-latitude cool- to cold-water and low-latitude warm water species. Explanations are provided through southeastern Mongolia’s unique palaeogeographical and palaeoceanographical position in the Permian time.

Early Permian post-glacial bivalve faunas of the Itarare Group, Parana Basin, Brazil: Paleoecology and biocorrelations with South American intraplate basins

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Upper Mississippian Faunas of Western Montana

The author has made a study of an assemblage of fossils from the Blacktail Range near Dillon Montana with the purpose in view of attempting a correlation of that group with the fauna of the Big Snowy Group. Fossils have also been obtained from a limestone formation in northwestern Montana and from four different areas in the Amsden formation in central and western Mont­ana.

Abundance and preservation of radiolarian faunas of ODP Hole 122-761B (Table 1)

Sites 759 through 764 were drilled during Ocean Drilling Program Leg 122 on the Exmouth and Wombat plateaus off northwest Australia, eastern Indian Ocean. Radiolarian recovery was generally poor due to unsuitable lithofacies. A few Quaternary radiolarian faunas were recovered from most of the sites. Rare and poorly preserved Oligocene and Eocene radiolarian faunas were recovered from Holes 760A, 761B, 761C, and 762B. Poorly preserved Cretaceous radiolarians occur in samples from Holes 761B, 762C, 763B, and 763C. Chert intervals from Cores 122-761B-28X, 122-761C-5R, and 122-761C-6R contain moderately well-preserved Cretaceous radiolarian faunas (upper Albian, mid- to upper Cenomanian, and mid-Albian, respectively). Rare fragments of Upper Triassic radiolarians were recovered from sections in Holes 759B, 760B, and 764A. The only well-preserved pre-Quaternary radiolarians are in lower and upper Paleocene faunas (Bekoma campechensis Zone) recovered from Site 761, Sections 122-761B-16X-1 to 122-761C-19X-CC. The composition of these faunas differs somewhat from that of isolated coeval Paleocene faunas from Deep Sea Drilling Project sites in the Atlantic, Gulf of Mexico, tropical Pacific, eastern Indian Ocean, and near Spain and North Africa, as well as from several on-land sites in North America, Cuba, and the USSR.

Neogene benthic foraminiferal faunas of a southwest Pacific bathyal depth transect

Temporal changes in benthic foraminiferal assemblages were quantitatively examined (> 63 µm fraction) in four southwest Pacific deep-sea Neogene sequences in a depth transect between approximately 1300 and 3200 m to assist in evaluating paleoeeanographic history. The most conspicuous changes in benthic foraminiferal assemblages occurred in association with paleoclimatic changes defined at least in part by oxygen isotopic changes. The largest, centered at ~15 Ma (early Middle Miocene), is represented by an increase in the relative frequencies of Epistominella exigua, which underwent a major upward depth migration at that time. This was contemporaneous with the well-known positive oxygen isotopic shift in the early Middle Miocene. In Sites 588 and 590, most of the increase in relative abundances of E. exigua occurred during the middle to later part of the ~80 shift, following major growth of the east Antarctic ice sheet. Later assemblage changes occurred at 8.5 and 6.5 Ma. These associations indicate that the benthic foraminiferal assemblages in this depth transect largely adjusted to changes in deep waters related to Antarctic cryospheric evolution. In general, the Neogene benthic foraminiferal assemblages in this region underwent little change during the last 23 million years. This faunal conservatism suggests that deep-sea environments underwent relatively little change in the southwest Pacific during much of the Neogene. Although paleoceanographic changes did occur, partly in response to highlatitude cryospheric evolution, these were not of sufficient magnitude to create major deep-sea faunal changes in this part of the ocean. The benthic foraminiferal assemblages are dominated by individuals smaller than 150 µm. Most taxonomic turnover occurred in the larger (> 150 µm) size fractions.

Distribution of Pliocene diatom faunas in the Northwest Pacific

High-resolution quantitative diatom data are tabulated for the early part of the late Pliocene ( 3.25 to 2.08 Ma ) at DSDP Site 580 in the northwestern Pacific. Sample spacing averages 11 k.y. between 3.1 and 2.8 Ma, but increases to 14 to 19 k.y. prior to 3.1 Ma and after 2.8 Ma. Q-mode factor analysis of the middle Pliocene assemblage reveals four factors which explain 92.4% of the total variance of the 47 samples studied between 3.25 and 2.55 Ma. Three of the factors are closely related to modern subarctic, transitional, and subtropical elements, while the fourth factor, which is dominated by Coscinodiscus marginatus and the extinct Pliocene species Neodenticula kamtschatica, appears to correspond to a middle Pliocene precursor of the subarctic water mass. Knowledge of the modern and generalized Pliocene paleoclimatic relationships of various diatom taxa is used to generate a paleoclimate curve ("Twt") based on the ratio of warm-water (subtropical) to cold-water diatoms with warm-water transitional taxa (Thalassionema nitzschioides, Thalassiosira oestrupii, and Coscinodiscus radiatus) factored into the equation at an intermediate (0.5) value. The "Twt" ratios at more southerly DSDP Sites 579 and 578 are consistently higher (warmer) than those at Site 580 throughout the Pliocene, suggesting the validity of the ratio as a paleoclimatic index. Diatom paleoclimatic data reveal a middle Pliocene (3.1 to 3.0 Ma) warm interval at Site 580 during which paleotemperatures may have exceeded maximum Holocene values by 3 °- 5.5 °C at least three times. This middle Pliocene warm interval is also recognized by planktic foraminifers in the North Atlantic, and it appears to correspond with generalized depleted oxygen isotope values suggesting polar warming. The diatom "Twt" curve for Site 580 compares fairly well with radiolarian and silicoflagellate paleoclimatic curves for Site 580, planktic foraminiferal sea-surface temperature estimates for the North Atlantic, and benthic oxygen isotope curves for late Pliocene, although higher resolution studies on paired samples are required to test the correspondence of these various paleoclimatic indices.

Benthic foraminiferal faunas of Miocene to Holocene sediments of ODP Site 184-1143 from the southern South China Sea

Deep-sea benthic foraminiferal assemblages from Ocean Drilling Program (ODP) Site 1143 located in the southern South China Sea (SCS) were investigated to evaluate the relationship between faunal composition patterns and paleoceanographic changes during the last 6 million years (late Miocene to Holocene). We used multivariate statistics (correspondence analysis) to analyze carbon-flux-related changes in assemblage composition of benthic foraminifers. Additional proxies for carbon flux and deep-water ventilation include delta13C records of epifaunal Cibicidoides wuellerstorfi and infaunal Uvigerina peregrina var. dirupta and Melonis pompilioides, benthic foraminiferal accumulation rates (BFARs), diversity indices, and relative abundances of indicator species. We observe three significant benthic faunal changes in the southern South China Sea during the last 6 million years. Strong fluctuations in BFAR and relative abundance of productivity indicator species between glacial and interglacial stages after the mid-Pleistocene revolution (MPR) at approximately 0.9 Ma, indicating stronger seasonal carbon flux fluctuations, are accompanied by the extinction of such species as Stilostomella spp. Increases in carbon flux indicator species are coupled with an overall decrease in benthic foraminifer diversity around 3.0 Ma in the late Pliocene. This may indicate increasing carbon flux in a period of productivity maximum caused by enhanced offshore upwelling from intensified winter monsoon wind strength.

Foraminifer faunas in the Tagus Prodelta

Pluri-annual proxy records of marine sediment cores from the Tagus Prodelta off Lisbon, Portugal, have been generated to gain insight into the climatic and hydrographic changes in the area during the twentieth century. The study includes benthic and planktonic foraminiferal faunas and the stable isotopic composition of one benthic (Uvigerina celtica) and two planktonic (Globigerina bulloides and Globorotalia inflata) foraminiferal species. Sea bottom and surface water temperatures were estimated based on the d18O values of these species and compared with instrumental data. The foraminiferal fauna and the isotope-based temperature record indicate increasing temperatures throughout the last century. The immigration of a new species, Saidovina karreriana, to the area around 100 years ago indicates changes in the trophic conditions and water mass properties, which are probably at least partly due to anthropogenic pollution.

Age determination and foraminiferal faunas in sediment core MD99-2275

A high-resolution study of palaeoceanographic changes off North Iceland during the time period 8600-5200 cal year BP is based on benthic and planktonic foraminiferal assemblages. The core material (MD99-2275) was obtained from about 440 m water depth on the eastern part of the North Icelandic shelf. Changes in the faunal composition are interpreted to be mainly caused by variations in the strength of the relatively warm, high-salinity Irminger Current and the cold East Icelandic Current, which have been shown to be linked to the climatic changes in the North Atlantic region. Environmental proxies at that site are particularly sensitive to palaeoceanographic changes due to its position close to the marine Polar Front. Benthic assemblages show that relatively cold conditions prevailed at the base of the record. An increase in the influence of Atlantic water masses at the sea floor is seen at around 8400 cal year BP, whereas the surface waters were relatively warm already at 8600 cal year BP. The warming was interrupted by a cold event at around 8100-8000 cal year BP, registered both in the bottom and surface waters and correlated with the so-called 8.2 kyr cooling event. Both the benthic and the planktonic faunal compositions indicate that the Irminger Current had maximum influence in the area between 8000 and about 7300 cal year BP, followed by a gradually decreasing influence through the remaining part of the studied time interval. It is suggested that the contribution of Atlantic water masses from the east and north-east to the Arctic Surface waters off North Iceland increased after around 7000 cal year BP, and that this was further intensified after 6200 cal year BP. At present, the Arctic Surface Water north of Iceland consists of Polar waters, intermittently with direct influence from the East Greenland Current, mixed with Atlantic waters derived from the eastern part of the Nordic Seas. A comparison of the mean values of selected environmental proxies in the interval 8600-5200 cal year BP with the upper part of the same core shows that the water masses north of Iceland were considerably warmer during the Holocene thermal maximum than during the last 2000 cal year. In general, results from core MD99-2275 are in accordance with other marine records from the North Icelandic shelf and the northern North Atlantic region, although a detailed comparison on a centennial time scale is hampered by problems with spatial as well as temporal changes in the marine reservoir ages in the region.