Species diversity variations in Neogene deep-sea benthic foraminifera at ODP Hole 730A,western Arabian Sea

Deep-sea benthic foraminifera are an important and widely used marine proxy to understand paleoceanographic and paleoclimatic changes on regional and global scales, owing to their sensitivity to oceanic and climatic turnovers. Some species of benthic foraminifera are sensitive to changes in water mass properties whereas others are sensitive to organic fluxes and deep-sea oxygenation. Benthic faunal diversity has been found closely linked to food web, bottom water oxygen levels, and substrate and water mass stability. The present study is aimed at analyzing species diversity trends in benthic foraminifera and their linkages with Indian monsoon variability during the Neogene. Species diversity of benthic foraminifera is examined in terms of number of species (S), information function (H), equitability (E) and Sanders’ rarefied values, which were combined with relative abundances of high and low productivity benthic foraminifera at Ocean Drilling Program Hole 730A, Oman margin, western Arabian Sea. The Oman margin offers the best opportunity to understand monsoon-driven changes in benthic diversity since summer monsoon winds have greater impact on the study area. The species diversity was higher during the early Miocene Climatic Optimum (～17.2–16.4 Ma) followed by a decrease during 16.4–13 Ma coinciding with a major increase in Antarctic ice volume and increased formation of Antarctic Bottom Water. All the diversity parameters show an increase during 13–11.6 Ma, a gradual decrease during 11.6–9 Ma and then an increase with a maximum at 7 Ma. Thereafter the values show little change until 1.2 Ma when all the parameters abruptly decrease. The benthic foraminiferal populations and diversity at Hole 730A were mainly driven by the Indian monsoon, and polar waters might have played a minor or no role since early Neogene period as the Arabian Sea is an enclosed basin.     

Paleoenvironmental and biostratigraphic significance of uvigerinids and other foraminifera from the Bhuban Formation,Assam-Arakan Basin,Mizoram

Planktic and benthic foraminifera including uvigerinids are documented from the Upper Bhuban Formation, exposed at Thingdawl village, Kolasib district, Mizoram. The foraminiferal assemblage is poorly preserved and consists of index fossils useful for precise biochronology and interpretation of the depositional environment. A total of ten benthic and six planktic foraminiferal species are described. Six species belong to the genus Uvigerina, four to Ammonia, one species each of Globorotalia, Globigerinoides, Clavatorella, Praeorbulina and two species of the genus Orbulina. Based on lithological and foraminiferal assemblage, middle neritic to upper part of outer neritic paleobathymetry is inferred for the deposition of this part of the Upper Bhuban Formation. The foraminiferal assemblage suggests late Early Miocene to early Middle Miocene, (∼16 Ma) equivalent to planktic foraminiferal zones N8-N9 for the Upper Bhuban Formation.     

Diversity of recent planktonic foraminifera in the southern Indian Ocean and Late Pleistocene paleotemperatures

Planktonic foraminiferal assemblages have been examined in 25 trigger core top samples and 51 piston core top samples collected between latitudes 28° S and 55° S and longitudes 79° E and 120° E from the southern Indian Ocean during cruises of the U.S.N.S. Eltanin. Samples taken from water depths exceeding 4000 m and/or showing evidence of calcium carbonate dissolution were eliminated from further analysis. The final piston core data set consists of 34 samples; the trigger core data set containing 21 samples. A close relationship exists between changes in the planktonic foraminiferal assemblages in the surface sediments and surface water temperatures. Species diversity values were computed for each of the core top assemblages using the Shannon-Wiener Index and the Brillouin Index, each of which takes into consideration the number of species and the proportionment of individuals among the species. The Shannon and Brillouin diversity values for all samples are positively correlated (correlation coefficient (r) = +.999). Regression analysis of latitude versus Shannon diversity values in the trigger core samples clearly shows a decrease in diversity with increasing latitude (r = ?.979). Furthermore, a strong correlation (r = +.977) exists between decreasing species diversity (Shannon) and decreasing average summer-winter temperature of the overlying surface waters. A paleotemperature equation derived from the relationship of diversity in trigger core samples and surface water temperature was used to generate paleotemperature curves for five trigger cores and a 6 m piston core of Late Pleistocene age, located beneath the present position of the Subtropical Convergence. A 7–8° C temperature range is suggested between the interglacial and glacial episodes in this Late Pleistocene sequence, and probably reflects latitudinal shifts of the Subtropical Convergence and Australasian Front during the Late Pleistocene.     

南海北部近6 Ma以来中层水体演化的底栖有孔虫证据

本文对南海北部陆坡SH7B孔底栖有孔虫群落结构组成及壳体氧碳同位素值变化特征进行研究,旨在了解该区晚中新世以来的中层水体演化历史。利用因子和聚类分析对该钻孔128个样品中的35个底栖有孔虫优势属种的相对百分含量数据进行统计分析,识别出4个组合:Globocassidulina subglobosa-Stilostomella spp.（Gs-St）,Chilostomella mediterranensis-Globobulimina spp. (Cm-Gl),Hoglundina elegans-Pyrgo spp. (He-Py),Melonis affinis-Pyrgo spp. (Ma-Py)。晚中新世晚期至上新世早期（5.8~2.8 Ma）相对高海平面温暖期,SH7B孔底栖有孔虫为相对稳定的Gs-St组合,反映了低到中等营养物质供给的低氧水体环境。其中5.8~3.79 Ma底栖有孔虫壳体碳同位素偏负和强烈的碳酸盐溶解现象在全球其他海区均有发现,指示当时南海北部陆坡底层水体低氧环境可能受到因全球大洋环流格局变化影响的太平洋偏腐蚀性的缺氧中层水体影响。3.79~2.8 Ma底栖有孔虫丰度和喜氧类表生种含量逐渐增加,指示水体流通性趋于增强,水体氧含量稍有增加。晚上新世2.4 Ma以来,底栖有孔虫组合与氧碳同位素值波动变化频繁,反映了中等到高表层输出生产力的富氧到缺氧中层水体环境,南海北部陆坡底栖有孔虫的分布主要受陆源有机质输入量的多寡和南海中深层水体的循环状况共同控制。     

Pleistocene oceanographie changes indicated by deep sea benthic foraminifera in the northern Indian Ocean

An attempt has been made to understand the Pleistocene bottom water history in response to the paleoclimatic changes in the northern Indian Ocean employing quantitative analyses of deep sea benthic foraminifera at the DSDP sites 219 and 238. Among the 150 benthic foraminifera recorded a few species show dominance with changing percent frequencies during most of the sequence. The dominant benthic foraminiferal assemblages suggest that most of the Pleistocene bottom waters at site 219 and Early Pleistocene bottom waters at site 238 are of North Indian Deep Water (NIDW) origin. However, Late Pleistocene assemblage at site 238 appears to be closely associated with a water mass intermediate between North Indian Deep Water (NIDW) and Antarctic Bottom Water (AABW). Uvigerina proboscidea is the most dominant benthic foraminiferal species present during the Pleistocene at both the sites. A marked increase in the relative abundance ofU. proboscidea along with less diverse and equitable fauna during Early Pleistocene suggests a relative cooling, an intensified oceanic circulation and upwelling of nutrient rich bottom waters resulting in high surface productivity. At the same time, low sediment accumulation rate during Early Pleistocene reveals increased winnowing of the sediments possibly due to more corrosive and cold bottom waters. The Late Pleistocene in general, is marked by relatively warm and stable bottom waters as reflected by low abundance ofU. proboscidea and more diverse and equitable benthic fauna. The lower depth range for the occurrence ofBulimina aculeate in the Indian Ocean is around 2300 m, similar to that of many other areas.B. aculeata also shows marked increase in its abundance near the Pliocene/Pleistocene boundary while a sudden decrease in the relative abundance ofStilostomella lepidula occurs close to the Early/Late Pleistocene boundary.     

A brief review of Agenian rhinocerotids in Western Europe

The Agenian is the earliest Neogene European Land Mammal Age. It encompasses the mammalian zones MN1 (23.03–22.7 Ma) and MN2 (22.7–20.0 Ma) and roughly coincides with the Aquitanian standard age. Agenian mammalian assemblages from Western Europe encompass a mixture of rhinocerotid taxa of Oligocene affinities and of Miocene newcomers, mostly recorded in France, Germany, Switzerland, and to a lesser extent, Spain. Rhinocerotidae are documented by seven species referred to five genera (Pleuroceros pleuroceros, Protaceratherium minutum, Plesiaceratherium aquitanicum, Mesaceratherium paulhiacense, Diaceratherium lemanense, D. asphaltense, and D. aginense), further attesting to a low suprageneric diversity. Their systematics, morphology, ecology, stratigraphical and geographical ranges are detailed in the present article. Occurrences and geographical ranges of all seven rhinocerotid species are illustrated on palaeogeographical maps of the circum-Mediterranean region at 23 Ma (MN1) and 21 Ma (MN2). The richest Agenian localities (Paulhiac, MN1; Laugnac, MN2) record a specific diversity similar to that of Orleanian rhinocerotid assemblages, with up to five/six associated species. All Agenian rhinocerotid species from Western Europe are endemic to the concerned region, which is consistent with the complete geographic isolation of Western Europe by earliest Miocene times. However, all five genera are documented by twin species in coeval localities of South and Central Asia, which implies (1) vicariant speciation events by latest Oligocene times and (2) the existence of intermittent pathways for terrestrial megamammals such as rhinocerotids during the concerned interval.     

Stratigraphy and sedimentology of phosphate-rich sediments in Malta and south-eastern Sicily (latest Oligocene to early Late Miocene)

The Maltese archipelago and south‐eastern Sicily include an Uppermost Oligocene to Upper Miocene hemipelagic sedimentary succession representing the Malta‐Hyblean plateau, which limits the eastern Mediterranean to the west. This succession hosts a unique and well‐exposed series of condensed and allochthonous phosphate‐rich beds, which were formed in a sedimentary regime of erosion, sediment reworking and frequent gravity‐flow deposition. The combination of nannofossil biostratigraphy and ⁸⁷Sr/⁸⁶Sr isotope stratigraphy allows for the precise attribution of ages to the phosphate deposits and for the distinction of three periods of major phosphogenesis. The first phase occurred between 24·5 and 21 Ma and 25 and 18·9 Ma (clustering of ages between 25 and 22·5 Ma) on Malta and Sicily, respectively. The second and third phases of phosphogenesis are documented from the Maltese Islands and are dated as 17·2 to 13·1 Ma and 10·9 to 9·8 Ma, respectively. The phosphate‐rich beds are associated with hiatuses and phases of important condensation which, for the oldest phosphogenic period, envelop the time period of 23·2 to 22 Ma for the Fomm Ir Rhi Bay section (Malta) and from 19·1 to 16·3 Ma for the sections of Sampieri and Modica (Sicily). For the second phase of phosphogenesis on the Maltese Islands, a consistent hiatus was found which embraces the time period of approximately 17 to 15 Ma. Also the third phase of phosphogenesis appears to be associated with a major hiatus, which probably envelops the time period between 12·5 and 10·9 Ma, but a better age control is needed here. The correspondence in timing of the Maltese‐Sicilian phases of phosphogenesis with major phases of phosphogenesis outside the Mediterranean realm, to maxima in oceanic phosphorus‐burial rates and maxima in the δ¹³C benthic foraminiferal record suggests that the palaeoceanographic evolution of the eastern Mediterranean was well in phase with that of other ocean basins until at least the early Late Miocene, despite its increasing isolation due to the gradual closure of the Eurasian‐Arabian Strait and progressive sea‐level fall.     

Palaeomagnetic evidence for the Gondwanian origin of the Taurides and rotation of the Isparta Angle,southern Turkey

The Taurides, the southernmost of the three major tectonic domains that constitute present‐day Turkey, were emplaced following consumption of the Tethyan Ocean in Late Mesozoic to mid‐Tertiary times. They are generally assigned an origin at the northern perimeter of Gondwana. To refine palaeogeographic control we have investigated the palaeomagnetism of a range of Jurassic rocks. Forty‐nine samples of Upper Jurassic limestones preserve a dual polarity remanence (D/I=303/−9°, α₉₅=6°) interpreted as a primary magnetization acquired close to the equator and rotated during emplacement of the Taurides. Result from mid‐Jurassic dolerites confirm a low palaeolatitude for the Tauride Platform during Jurassic times at the Afro–Arabian sector of Gondwana. Approximately 4000 km of Tethyan closure subsequently occurred between Late Jurassic and Eocene times. Although related Upper Jurassic limestones and Liassic redbeds preserve a sporadic record of similar remanence, the dominant signature in these latter rocks is an overprint of probable mid‐Miocene age, probably acquired during a single polarity chron and imparted by migration of a fluid front during nappe loading. This is now rotated consistently anticlockwise by c. 30° and conforms to results of previous studies recording bulk Neogene rotation of the Isparta region following Lycian nappe emplacement. The regional distribution of this overprint implies that the Isparta Angle (IA) has been subject to only small additional closure (<10°) since Late Miocene time. A smaller amount (c. 6°) of clockwise rotation within the IA since Early Pliocene times is associated with an ongoing extensional regime and reflects an expanding curvature of the Tauride arc produced by southwestward extrusion of the Anatolian collage as a result of continuing northward motion of Afro–Arabia. Copyright © 2002 John Wiley & Sons, Ltd.     

Lithostratigraphy and planktonic foraminiferal biostratigraphy of the late Eocene-Middle Miocene sequence in the area between Wadi Al Zeitun and Wadi Al Rahib,Al Bardia area,northeast Libya

The present study deals with the lithostratigraphy and planktonic foraminiferal biostratigraphy of the Late Eocene-Middle Miocene sequence in the Al Bardia area, northeast Libya. The lithostratigraphical studies carried out on three stratigraphical surface sections, namely Wade Al Rahib, Wadi Al Hash and Wadi Al Zeitun, led to the recognition of three rock units from base to top: (1) the Al Khowaymat Formation (Late Eocene-Early Oligocene); (2) the Al Faidiyah Formation (Late Oligocene-Early Miocene); and (3) the Al Jaghboub Formation (Early-Middle Miocene). The planktonic foraminiferal biostratigraphical analysis led also to the recognition of nine planktonic foraminiferal zones ranged in age from Late Eocene to Early Miocene with one larger foraminiferal zone of Middle Miocene age. These are, from base to top, as follows: Truncorotaloides rohri Zone (Late-Middle Eocene, Lutetian), Globigerinatheka semiinvoluta and Turborotalia cerroazulensis s.l. Zones (Late Eocene, Priaborian), Cassigerinella chipolensis/Pseudohasitgerina micra Zone (Early Oligocene, Rupelian), Globigerina ciperoensis ciperoensis, Globorotalia kugleri Zones (Late Oligocene, Chattian), Globigerinoides primordius Zone (Early Miocene, Aquitanian), Globigerinoides altiaperturus/Catapsydrax dissimilis and Globigerinoides trilobus Zones (Early Miocene, Burdigalian), and the larger benthonic foraminiferal zone, Borelis melo melo Zone (Middle Miocene, Langhian to Serravallian). The study of planktonic foraminifera proved the existence of a regional unconformity between the Early and Late Oligocene, with the Middle Oligocene deposits being absent (absence of Globigerina ampliapertura and Globorotalia opima opima Zones), and another, smaller unconformity located between the Late Eocene and Early Oligocene, in which the uppermost part of the Late Eocene is missing.     

Shallow water agglutinated foraminiferal response to Late Cretaceous–Early Paleocene sea-level changes in the Dakhla Oasis,Western Desert,Egypt

The Late Cretaceous (Maastrichtian) to early Paleocene (Thanetian) shallow water (<100 m) agglutinated foraminifera from a section at Dakhla Oasis (Western Desert, Egypt) were analyzed for their assemblage, species and genera distribution, diversity, depositional environment, community structure and palaeobathymetry with respect to regional tectonics, climate and global eustasy. Data suggest an equitable benthic environment with low species dominance deposited in a brackish littoral and/or marsh setting. Sea level curves using characteristic benthic foraminiferal species, genera and assemblages corroborate quantitatively generated estimate and statistical analysis. Data suggests that in the absence of or of an impoverished benthic foraminiferal fauna, a high resolution agglutinated foraminiferal dataset can be as good a predictor of the benthic community structure and environment, as its calcareous counterpart, at least for shallow settings (<100 m). Present data also provides a good window in better understanding the distribution and interrelationship between the three dominant genera, Haplophragmoides, Trochammina and Ammobaculites. Faunal changes at boundaries (Cretaceous/Paleogene, Danian/Selandian and Selandian/Thanetian) are also evaluated.     

Palaeomagnetism of igneous rocks of the Lake District (Caledonian) terrane,Northern England: palaeozoic motions and deformation at a leading edge of Avalonia

The Lake District terrane of northern England comprises Upper Cambrian–Silurian sediments and volcanics accumulated at the northern margin of the Avalonian Plate during growth and demise of the Iapetus Ocean. Ocean closure and suturing resulted in Late Ordovician and Acadian tectonism and were accompanied by emplacement of a large regional batholith. Palaeomagnetic study of intrusive igneous rocks, including application of thermal demagnetization, field tests and principal component analysis, identifies a history of Ordovician to Devonian magnetization. Late plutons (Shap and Skiddaw granites and/or aureoles) record a shallow dipolar (A3) axis (mean declination/inclination (D/I=278/+17°) dating from emplacement in late Early Devonian times (c. 395 Ma). Although this axis is recorded as a sporadic overprint in older rocks, no pervasive remagnetization is attributable to batholith emplacement. Instead, the Carrock Fell Complex Layered Gabbros have a mid- to late Ordovician (A1) remanence (D/I)=17·4/−58·1°, 36 samples, α₉₅=4·8°) predating regional F2 folding. Later events in this igneous complex comprise the Carrock Fell Granophyre with a post-folding Ordovician remanence, and Round Knott Dolerite with a remanence linked to hydrothermal alteration late in the Ordovician magmatic episode. A Late Ordovician (Ashgill) palaeofield is also defined by remanence (A2) in the Threlkeld–St John's Microgranite and aureole (438 Ma, D/I=236·5/63·3°, 41 samples, α₉₅=4·7°). Other intrusions carrying a remanence predating the Acadian deformation include the Great Cockup Picrite (458 Ma, D/I=43·2/−31·8°, 31 samples, α₉₅=7·7°) and basic intrusives in the aureole of the Eskdale Granite (429 Ma, D/I=174·5/25·8°, 32 samples, α₉₅=8·8°). Collectively the palaeomagnetic data from this terrane identify a hairpin in the apparent polar wander path during Late Ordovician (Caradoc–Ashgill) times corresponding to ‘soft’ closure of the Iapetus suture and accompanying deformation. The same motion is recognized in contemporaneous data from the Welsh Caledonides where declinations are rotated by c. 55° relative to contemporaneous results from the Lake District. Adjustment for this (probable late Acadian) rotation beings fold trends of the Paratectonic Caledonides into alignment and identifies a parallel mid- to late Ordovician destructive plate margin comprising forearc (Lake District) and backarc (North Wales). This arc was oriented latitudinally in mid-southerly latitudes during formation and the bulk of the magmatism occurred during a single normal-polarity chron. The relationships between magnetization and folding in both the Lake District and Welsh Borderlands identify the importance of Late Ordovician deformation along this arc during collision of Avalonia and Laurentia. Arc-related volcanism was succeeded in Silurian times by parallel foreland basins embracing the Welsh Basin and southern Lake District as the Laurentian Plate overrode the Avalonian Plate. © 1997 John Wiley & Sons, Ltd.     

Benthic foraminiferal turnover across the Paleocene–Eocene Thermal Maximum (PETM) event in Eastern Desert,Egypt

Benthic foraminiferal fauna are analyzed quantitatively and qualitatively at three stratigraphic sections in Eastern Desert of Egypt (Serai, Duwi, and Um El Huetat). These sections embrace the Paleocene–Eocene Thermal Maximum (PETM) interval which is represented by the occurrence of five distinctive beds. These beds constitute the Dababiya Quarry Member at the lower part of Esna Formation. The occurrence of them indicates an expanded and relatively continuous record across the P/E boundary. The organic-rich clay layer (bed no. 1 of the Dababiya Quarry Member) marks the start of the PETM event. This bed is characterized by the extinction of all benthic foraminiferal fauna except for the occurrence of rare agglutinated foraminiferal species. The presence of these species indicates an oceanic anoxic event at the sea floor. High concentration of phosphatic contents including fish remains occurred in the middle part of the PETM (bed nos. 2 and 3 of the Dababiya Quarry Member) with the continuous absence of benthic foraminiferal fauna except for few specimens at the top of bed 3. Bed nos. 4 and 5 of the Dababiya Quarry Member represent the upper part of the PETM and the initial stage of sea floor recovery. Low diversity and abundance of benthic foraminiferal taxa occurred within these beds, represented by Valvulineria scrobiculata, Lenticulina midwayensis, Loxostomoides appliane, and Siphogenerinoides eleganta. This phenomenon continues upward during the post-PETM event. The Paleocene velasco-type benthic foraminifera Angulogavelinella avnimelechi and Coryphostoma midwayensis species are extinct within the advent of the PETM event. The benthic foraminiferal assemblages at the studied sections are dominated by midway-type fauna with little representative of velasco-type fauna. The velasco-type species are represented with high abundance at Serai section and with low densities at Um El Huetat section, while at Duwi section, they rarely occurred. This suggests outer neritic-upper bathyal (150–400 m) setting at Serai section and mostly middle-outer neritic (50–150 m) setting at Um El Huetat and Duwi sections.     

Differential response at the seafloor during Palaeocene and Eocene ocean warming events at Walvis Ridge,Atlantic Ocean (ODP Site 1262)

The Latest Danian Event (LDE, c. 62.1 Ma) is an early Palaeogene hyperthermal or transient (<200 ka) ocean warming event. We present the first deep‐sea benthic foraminiferal faunal record to study deep‐sea biotic changes together with new benthic (Nuttallides truempyi) stable isotope data from Walvis Ridge Site 1262 (Atlantic Ocean) to evaluate whether the LDE was controlled by similar processes as the minor early Eocene hyperthermals. The spacing of the double negative δ¹³C and δ¹⁸O excursion and the slope of the δ¹⁸O–δ¹³C regression are comparable, strongly suggesting a similar orbital control and pacing of eccentricity maxima as well as a rather homogeneous carbon pool. However, in contrast to early Eocene hyperthermals, the LDE exhibits a remarkable stability of the benthic foraminiferal fauna. This lack of benthic response could be related to the absence of threshold‐related circulation changes or better pre‐adaptation to elevated deep‐sea temperatures, as the LDE was superimposed on a cooling trend, in contrast to early Eocene warming.     

Paleoceanography and climate of the Badenian (Middle Miocene, 16.4–13.0 Ma) in the Central Paratethys based on foraminifera and stable isotope (δ18O and δ13C) evidence

Benthic foraminifera and stable isotopes analyses revealed changes emerging in the paleoceanographic scenery in the Paratethys. The percentage of inbenthic, oxyphylic taxa and diversity in the benthic foraminiferal assemblage showed increasing food supply (organic matter), decreasing oxygen level and growing stress on the sea floor. Oxygen isotopes measured in planktonic and benthic foraminifera pointed to strengthening stratification during the Badenian period. The carbon isotopes indicated intensified accumulation of light marine organic matter. This increasing stratification trend is especially pronounced by Late Badenian (13.5–13 Ma) when surface water oxygen isotope values are rather negative. A simple two-layer circulation model was worked out for the Badenian Paratethys explaining these characteristic environmental changes. An antiestuarine (lagoonal) circulation is assumed for the Central Paratethys during the Early (16.4–15 Ma) and mid Badenian (15–13.5 Ma). The mid Badenian period of time comprises the short episode of evaporite formation in the Carpathian Foredeep and the Transylvanian Basin. Evidence presented here supported a reversal of circulation to estuarine type after the deposition of salts by Late Badenian (13.5–13 Ma). The Early Badenian antiestuarine circulation is suggested to associate with the high temperatures of the Mid-Miocene Climatic Optimum, and the Late Badenian estuarine circulation with the cooler period following it.     

Evolution of the Paleocene-Early Eocene larger benthic foraminifera in the Tethyan Himalaya of Tibet, China

The Paleocene-Early Eocene larger benthic foraminifera (LBF) in the far eastern Neo-Tethyan Ocean of Tibet still remain poorly known. Here, we present a novel, high-resolution larger foraminiferal biozonation from the shallow-water limestones in Tibet, which will improve our current understanding of the larger foraminiferal evolution in the eastern Neo-Tethyan Ocean. Based on one continuous section at Tingri and three separate sections at Gamba, ten Shallow Benthic Zones (SBZ 1–10) have been designated in Tibet by following the principle of Oppel Zone. In contrast to those in Europe, the Paleocene LBFs in Tibet are characterized by high diversification of Lockhartia, Kathina, Daviesina, Miscellanea, Ranikothalia, and Operculina and show progressively increasing diversity of genera and species during SBZ 2–5. Adult dimorphism and large shell size of some LBFs as well as differentiation of the diversity between genera and species initiated as early as SBZ 3. It suggests that the occurrence of the Larger Foraminifera Turnover (LFT) was probably not synchronous in the entire Neo-Tethyan Ocean, because in Europe, the LFT was generally thought to occur at the beginning of SBZ 5. During the Early Eocene, the LBFs in Tibet decreased markedly on the generic level and increased on the species level, and some new genera (Alveolina, Orbitolites, Nummulites, Assilina, Discocyclina) have gained predominance in Tibet. It is nearly identical to the evolution of the LBFs in Europe and indicates a high-degree homogenization of the LBFs in the entire Neo-Tethyan Ocean. Furthermore, the Paleocene-Eocene (P-E) boundary in shallow-water environments has been clearly identified by us, and it is situated in the upper part of SBZ 5 and associated with no evident biotic turnover of shallow benthic foraminiferal communities. The possible diachroneity of the LFT in the Neo-Tethyan Ocean and the evident lagging of the Paleocene-Eocene Thermal Maximum (PETM) behind the LFT imply that the LFT could only be the result of a natural evolutionary process and has no linkage with the PETM. Notably, a transient but distinct larger foraminiferal extinction and origination (LFEO) event has been found in Tibet, which is characterized by a sudden disappearance of all Paleocene lamellar-perforate LBFs, such as Lockhartia, Kathina, Daviesina, Miscellanea, Ranikothalia, and Operculina, and the initial dominance of the Early Eocene porcellaneous-walled Alveolina. The LFEO marks the boundary between SBZ 5 and 6, and might only occur in the low-latitude areas of the Neo-Tethyan Ocean. Surprisingly, the LFEO coincides with the initial recovery of the Carbon Isotope Excursion (CIE), and their synchronicity implies that some possible mechanisms causing the rapid recovery of the CIE probably had also led to the LFEO in the shallow-water environments.     

Biostratigraphy and depositional environment of the Miocene limestone bed of Baripada,Mayurbhanj district,Odisha: Foraminiferal,sedimentological and bulk organic geochemical evidences

Baripada Marine Beds (BMB) have been studied extensively in terms of its mega fossil content. However, not much has been discussed about the foraminiferal content and the organic matter assemblage in these beds. The fossiliferous sequence of BMB consists of sandstone, shale and limestone units. The present study is persued on the limestone unit of BMB. Foraminiferal, thin section and rock-eval pyrolysis studies were performed on the 33 surface samples collected from five sections of Jamdapal and Mukurmatia region along the Budhabalang river bank. Foraminifera are less abundant in the samples of Jamdapal, whereas Mukurmatia is comparatively rich. First appearance datum of Globorotalia menardii[ranges since middle Miocene (12.6 Ma); FAD at planktic foraminiferal zone N12] and last appearance datum of Neogloboquadrina continuosa [ranges between early Miocene (23.2 Ma) to late Miocene (8.3 Ma); FAD at planktic foraminiferal zone N4B and LAD at N16] together suggest that the limestone unit was deposited in between 12.6 to 8.3 Ma within the upper Miocene. Also, the association of shallow water benthic foraminifera (Species of Ammonia, Asterorotalia, Bolivina, Buliminella, Cibicides, Challengerella, Criboelphidium, Cribononion, Elphidium, Hanzawaia, Nonionella) and planktic foraminifera (Globigerina falcoensis, Globigerina woodi, Globorotalia menardii, Neogloboquadrina continuosa) together with oyster bank and shark teeth suggest deposition of limestone within well oxygenated, tropical, shallow water, open marine condition (within 40m water depth). Lithological and thin section studies together with global sea level fluctuation history advocate that upper Miocene marine transgression promoted the formation of this unit. Bulk organic geochemical data obtained by the rock-eval pyrolysis studies on selected samples indicate a low total organic carbon (TOC), with low hydrogen index (HI), high oxygen index (OI). The organic facies is characterised by type-IV kerogen with major contribution from near shore terrestrial plants. This also suggests deposition in shallow, oxygenated environments that did not promote significant accumulation and preservation of organic content in sediments.     

Palaeogeographical implications of CretaceousBenthic Foraminifera recovered by the Deep Sea Drilling project in the Western South Atlantic ocean

Albian/Cenomanian benthic foraminiferal faunas recovered by the DSDP in the western South Atlantic Ocean (Leg 36) are described and analyzed from the palaeogeographic and palaeo-environmental points of view. In doing this the author compares Leg 36 assemblages in the western South Atlantic Ocean with coeval benthic foraminiferal faunas recovered in the eastern South Atlantic Ocean (Leg 40) and in the eastern Indian Ocean (Legs 26 and 27). The specific composition of these assemblages, except for Leg 27, is virtually the same. Consequently, they are considered to indicate the same depositional water depth at all relevant sites studied, whether located in the Angola Basin, the northern flank of the Walvis Ridge, the eastern margin of the Falkland Plateau or on the Naturaliste Plateau. All the assemblages indicate shallow environments around 100 m and not exceeding 300–400 m in the deepest parts, corresponding to the inner shelf and the inner part of the outer shelf. By contrast the foraminiferal associations of Leg 27 (especially Site 259) indicate a greater depth, of the order of 200–600 m (but not exceeding 1000 m) corresponding to upper slope of Sliter & Baker (1972) and Sliter (1972). These bathymetrical conclusions are in remarkable accord with those of Sliter (1976), based on planktic Foramini fera of Leg 36.Late Cretaceous (Campanian-Maastrichtian) material with benthic Foraminifera was limited to two positive samples; however, these faunas indicate much the same palaeo-environment as do the planktic ones analyzed by Sliter (1976).     

Evolution of Chinese Neogene Rhinocerotidae and Its Response to Climatic Variations

Chinese Neogene Rhinocerotidae has quite a complete record and its temporal range is the Early Miocene to Late Pliocene. The samples include 25 species in 4 tribes of 2 subfamilies. They are used as a foundation for the study of the evolution of the family and its relation to climatic changes. Taxonomic diversity, new records and extinctions are estimated for each Chinese Neogene mammal faunal unit (NMU). The diversity of Chinese Rhinocerotidae varies noticeably throughout the Neogene and is recognized within five stages: the Middle Miocene and Late Miocene are stages of high diversity and the Early Miocene, early Late Miocene and Pliocene are stages of low diversity. Rhinocerotid diversity and morphology are closely related to environmental factors and particularly sensitive to changes in ambient temperature and humidity. The interpretation of climatic variation reflected in the evolution of Rhinocerotidae corresponds precisely with the conclusions drawn from other workers and provides new evidence fen     

伦坡拉盆地西部丁青湖组新发现凝灰岩锆石U- Pb年龄及其地层学意义

伦坡拉盆地丁青湖组沉积时代的确定对于研究青藏高原中部的古高度和古气候具有重要的地质意义,但由于没有精确的年龄数据,其顶部是否跨入了新近系,一直以来都存在争论。作者在伦坡拉盆地西部鄂加卒地区开展野外调查过程中,在该剖面中部和上部新发现两套凝灰岩夹层,对凝灰岩进行了LA-ICP-MS锆石U-Pb定年,获得了两件凝灰岩样品的形成年龄分别为24.05±0.24Ma(MSWD=1.07,n=24)和22.64±0.33Ma(MSWD=0.45,n=17),时代分别为晚渐新世和早中新世。根据凝灰岩锆石U-Pb年龄和前人研究成果,将鄂加卒剖面的细碎屑岩地层重新厘定为丁青湖组,并将丁青湖组的沉积时代定为渐新世-中中新世。根据丁青湖组地层厚度及沉积速率估算,该组沉积持续时间在21～23Ma之间,其顶部地层的年龄在11～13Ma左右。由此可见,伦坡拉盆地接受连续沉积一直持续到了中中新世,这比过去普遍认识的晚始新世-渐新世时期青藏高原中部的古高度和古气候变化时间更晚。前人在该地区发现的近无角犀化石、攀鲈鱼化石、棕榈科叶片化石以及孢粉化石等研究结果共同证实,青藏高原中部渐新世晚期的古海拔高度低于～2500～3000 m。因此,该区晚渐新世-早中新世温暖潮湿的气候特征很可能是受到了印度洋气流穿透的影响,而且该影响可能一直持续到了中中新世,从而造就了该时期青藏高原生物的多样性。     

Biostratigraphy of oligocene succession in the High Folded Zone,Sulaimani, Kurdistan region,Northeastern Iraq

Oligocene and Lower Miocene sediments from High Folded Zone of Iraqi Zagros have been studied paleontologically at south of Sulaimaniyah, Kurdistan Region, NE Iraq. The identified fauna are consisted of (25) genera and species of benthonic and (16) species of planktonic foraminifera. The fauna comprises relatively abundant foraminiferal assemblages of moderate diversity. Based on the stratigraphic distribution of these species, two biozones have been recognized which are Nummulites—Rotalia and Globoquadrina dehiscens zones. These biozones indicate that the studied sections of Basara and Khewata are of Late Oligocene–Early Miocene age. Based on the microfossils, it has been found that the age of sediments is equivalent to or represents Anah and Serikagni Formations. Some previous studies described Oligocene rocks (Kirkuk Group) as interior sag basin. In the present study, the occurrence of the group inside High Folded Zone and its rich fauna content are used for the discussion of the sag basin versus normal marine water.