Genera Of Benthic Foraminifera Research Articles

Multi‐proxy approach of the stratigraphy, geochemistry, and sedimentology of Eocene Margalla Hill Limestone: Case study from Muzaffarabad area, Sub‐Himalayas, Pakistan

To investigate the sedimentological characteristics of the Margalla Hill Limestone (MHL), a multi‐proxy approach including geochemical, mineralogical, and micropalaeontological investigations were carried out. Using detailed field observations and petrographic investigation of the studied section, five microfacies were dentified. Total organic carbon (TOC) values of the limestone are generally low (0.10–0.96%) and highly degraded, as observed from the low hydrogen index (i.e., 17–349 mg HC/g TOC). TOC is mainly Type‐III and Type‐IV organic matter that reflects a continental source or highly weathered marine organic matter (OM) with minor Type‐II which corresponds to algal or bacterial OM. The values of Tmax range from 419 to 512°C for most of the samples, which lies within the mature stage. Major element abundances do not vary significantly in the studied unit and are mainly linked to variations in clay contents. Trace elements (V, Cr, Mn, Zn, Ni, Cu, Th, Rb, U, and Zr) of the MHL depict a mainly detrital origin for shales, and overall decrease in trace element's concentration suggests a change from physical to chemical weathering. The rate of sedimentation as determined by the Th/U ratio indicates a regular to irregular low rate of sedimentation, from base to top of the studied section. The redox conditions, as reflected in the variation of Cr (V/Cr), using the V/Cr ratio with Ni + V indicate that the MHL was deposited under oxic‐dysoxic conditions. Chemical Index of Alteration, Chemical Index of Weathering, Plagioclase Index of Alteration, and Weathering Index of Parker showed that the source region was subjected to intense chemical weathering likely under tropical palaeoclimatic conditions with abundant rainfall. The limestone consists mainly of calcite followed by minor quartz and dolomite. Clay mineralogy revealed that the clay fraction is dominated by kaolinite, smectite, mica, and chlorite. The microfossils of various genera of benthic foraminifera have been identified. Based on benthic foraminifera, an Early Eocene (SBZ‐8; Middle Ilrdian 2) age has been assigned to the MHL.

Altered impact glass from the Devonian Norwood Member of the Antrim Shale, southeast Michigan

The presence of microtektites, indicative of a single short-lived event, may be a useful tool for constraining the timing of barren and monotonous beds thereby enabling more accurate long-distance correlation. While the Paleozoic Laurentian epeiric seas have been studied for more than a century, their geologically complex histories, large areal expanse, and seeming monotony of contained barren stratigraphic units precludes simple extrabasinal correlation. Recent investigations of the Upper Devonian succession in western New York have yielded evidence of extraterrestrial impact events in the form of microtektites. Geothermal well spoils from the coeval Antrim Shale (Norwood Member) of the Michigan Basinwere collected and completely digested. Sediments retrieved from these spoils (shale, clay, and limestone) contain four genera of benthic foraminifera, algal cysts, and other microfossils confirming a Devonian age. The sediments also contain microspherules inferred to be microtektites similar to those recovered from western New York and are potentially evidence of a large impact event. The microspherules may be a useful inter-basin marker event within the Late Devonian beds in North America that has gone previously unreported.

Facies, depositional environments, and anatomy of the Subis build-up in Sarawak, Malaysia: implications on other Miocene isolated carbonate build-ups

Isolated carbonate build-ups of Miocene age are important hydrocarbon reservoirs in SE Asia and globally. The architecture of the build-up rim and fore-reef talus is poorly understood. The Subis build-up is one of the cycle I–II carbonate outcrops exposed along the coastal Sarawak in an area of 5 × 6 km2, with an exposed thickness of 390 m. This provides an opportunity to document the composition and architecture of rim and talus deposits in an isolated build-up as an analogue for similar gas-bearing structures located offshore Central Luconia, in Malaysia, which were neither drilled nor cored so far. This paper documents sedimentological characteristics, lateral and vertical facies relationships, of the marginal sections of a build-up in a large quarry exposing the Subis Limestone. The Subis Limestone is composed of massive and branching corals, coralline red algae, benthic foraminifera, bivalves, gastropods, echinoids, and occasionally bryozoans and sponges. Eight microfacies types and four environments were defined to describe the Subis Limestone: outer talus, inner talus, reef rim, and lagoon. Nine genera of benthic foraminifera were interpreted, confirming an early Miocene age (cycle II) of the succession. Three major backstepping events were observed at the build-up, where they developed inward towards the center of the build-up.

Les ostracodes et foraminifères associés des dépôts de l’Éocène moyen et supérieur de la coupe de Jebel Serj (Tunisie centrale). Intérêt biostratigraphique, paléoécologique et paléobiogéographique

The ostracod fauna collected from the Cherahil formation that crops out at the Jebel Serj section (central Tunisia) contains 24 species belonging to 12 genera. These ostracods are associated with 9 genera of benthic Foraminifera (including 4 Nummulites species) and 7 genera of planktonic Foraminifera. The biostratigraphic study of ostracod assemblages results to the recognition of 6 biozones which are correlated with Lutetian-Priabonian. The Shannon Weaver, Margalef and equitability indices point to internal platform netritic conditions, with minor fluctuations in depth and oxygenation. The palaeobiogeographic distribution of ostracod species found in the study area of Central of Tunisia establishes a good connexion with the basins developed in Northern Africa (Tunisia, Algeria, Libya and Mauritania) and the Middle East (Egypt and Jordan).

Respiration rates and biovolumes of common benthic Foraminifera (Protozoa)

The respiration rates of five genera of benthic Foraminifera were determined by Cartesian diver microrespirometry. Across all genera studied, the rate averaged 11·3×10−3μl O2individual−1h−1at 10°C. Estimates of foraminiferal mean biovolumes ranged from 0·66 to 6·54×106μm3, giving an overall mean volume-specific respiration rate of 7·36 × 10−9μl O2h−1μm−3. For non-symbiont-bearing Foraminifera, in general, volume-specific rates (log μl O2h−1μm3) are best described by the equation, −0·98 × (log cell biovolume, μm3)−2·01. The respiration results show that these benthic Foraminifera respire some ten times more rapidly than naked amoebae of equivalent size. The combination of high respiratory rates and the often large standing stocks of Foraminifera encountered, suggests that these organisms may contribute significantly to total microbial benthic respiration.

Morphology and Time/Depth Distribution of Uvigerina peregrina: Continental Slope, Eastern Margin, United States: ABSTRACT

Uvigerina is one of the most important genera of benthic foraminifera for biostratigraphic and paleoenvironmental investigations of continental margin sediments from bathyal water depths. The authors present morphological and distributional evidence for distinct subpopulations within Uvigerina peregrina from the continental slope of the eastern US. A detailed record of U. peregrina distribution in the western North Atlantic over water depths from 700 to 4400 m was determined for the last 25 k.y. Modern U. peregrina is found in core tops from water depths of 700-3000 m, reaching its acme between 1300 and 1800 m. During the glacial maximum (18 k.y.B.P.), this species occupied depths from at least 2800 to 4350 m. Beginning 16 k.y.B.P., Uvigerina disappeared from both the shallow and deep parts of its range, until the last remnants of this glacial-age population disappeared 7.6 k.y.B.P. from a depth of 3600 m. Fourier shape analysis shows that the modern and glacial-age U. peregrina are morphologically distinct. These observations indicate the following: (1) modern Uvigerina has occupied depths below 1800 m only during the last 4 k.y.; (2) the lack of continuity between modern and glacial-age specimens suggests that separate subpopulations or morphotypes of this species existed; (3) water massmore » properties in the western North Atlantic are a major control on the distribution of Uvigerina; (4) paleobathymetric reconstructions using Uvigerina should consider what morphotypes are the basis for the depth zonation.« less