Neogene deep sea benthic foraminiferal diversity in the Indian Ocean: Paleoceanographic implications

The species diversity indices, as defined by the number of species,S; Shannon-Wiener index,H(S) and Buzas-Gibson index,É, of DSDP sites 219, 220, 237 and 238 were measured to determine the benthic foraminiferal diversity patterns in the Indian Ocean deep sea sequences during the Neogene. The Time-Stability hypothesis could satisfactorily explain the observed diversity patterns. The general patterns of diversity suggest environmental stability during the Neogene. However, few small fluctuations in diversity during the Middle Miocene (c.14·8 Ma), Late Miocene (c.6·0 Ma) and Late Pliocene (c.2·0 Ma) may possibly be the effects of Antarctic Bottom Water (AABW) activity in this region. The benthic foraminiferal diversity in the tropical Indian Ocean is more than the high latitudinal areas with comparable depths.     

Major change in Atlantic Deep and bottom waters 700,000 yr ago: Benthonic foraminiferal evidence from the South Atlantic

In the modern South Atlantic the transition between deep water and bottom water is marked by a clear change in the associated benthonic foraminiferal fauna. uvigerina and Globocassidulina characterize oxygen-poor Circumpolar Deep Water which has long been isolated from the surface. Planulina and miliolids are found associated with the more newly formed, oxygen-rich North Atlantic Deep Water. Antarctic Bottom Water is characterized by “Epistominella” umbonifera. Analysis of the benthonic foraminiferal faunas in two sediment cores recovered from the Vema and Hunter Channels in the western South Atlantic shows that the level of the transition between deep and bottom waters shallowed sharply about 700,000 yr ago. This rise indicates a sharp, sustained increase in the volume of bottom water flowing through the South Atlantic after this time. Prior to about 700,000 yr ago, the amount of Antarctic Bottom Water entering the western South Atlantic was greatly reduced and Circumpolar Deep Water apparently accounted for the bulk of northward flow. Production of southward-flowing North Atlantic Deep Water seems not to have been affected. The timing of this change in circulation regime suggests a possible causal link to similar changes in records of terrestrial and sea-surface climate.     

Palaeoceanographic development in Storfjorden,Svalbard, during the deglaciation and Holocene: evidence from benthic foraminiferal records

Brines can have a profound influence on the relative abundance of calcareous and agglutinated foraminiferal faunas. Here we investigated the distribution of benthic foraminiferal species in four cores from a brine‐enriched environment in Storfjorden, Svalbard. Stratigraphically, the cores comprise the last 15 000 years. The purpose of the study was to reconstruct changes in the palaeoecology and palaeoceanography of Storfjorden in relation to past climate changes, and to identify potential indicator species for brine‐affected environments. The benthic foraminifera in Storfjorden all have widespread occurrences in the Arctic realm. Calcareous species dominated Storfjorden during the deglaciation and early Holocene until c. 8200 a BP. However, agglutinated species increased in abundance whenever conditions became colder with more sea ice and stronger brine formation, such as during the Older Dryas, the Intra‐Allerød Cold Period and the Younger Dryas. Following a moderately cold period with numerous agglutinated foraminifera from c. 8200–4000 a BP, conditions became more changeable from c. 4000 a BP with repeated shifts between warmer periods dominated by calcareous species and colder periods dominated by agglutinated species. The warmer periods show a stronger influence of Atlantic Water, with reduced brine formation and less corrosive conditions at the sea bottom. Conversely, the colder periods show a stronger influence of Arctic water, with higher brine production and more corrosive bottom water. The distribution patterns of the calcareous species are basically the same whether calculated relative to the total fauna (including agglutinated specimens) or relative to calcareous specimens alone. Moreover, the patterns are similar to the patterns found elsewhere along western Svalbard in areas without the influence of brines. No particular species appear to be specifically linked to brine formation. However, the most persistent agglutinated species R. scorpiurus and A. glomerata are also the species most tolerant of the acidic bottom water that normally is associated with brine formation.     

Variation on Foraminiferal Composition in Cretaceous Black-Gray-Red Bed Sequence of Southern Tibet, China

An Upper Cretaceous black-gray-red bed sequence was deposited in the Tethys-Himalayan Sea where abundant foraminifera, especially planktons, were yielded. In the shallow shelf to the upper slope on the north margin of Indian plate was recorded an extinction-recovery-radiation cycle of foraminiferal fauna highly sensitive to paleoceanographical changes. The black unit, consisting of the Late Cenomanian-earliest Turonian beds, displays a major extinction, with keeled planktonic and many benthic species as the principal victims at the end of the Cenomanian when existed only low diversity, sin-face water-dwelling foraminifera. The gray unit spans a long-term recovery interval from the Turonian to the early Santonian with keeled planktonic foraminifera returning stepwise to the water colunm. The planktonic biota in the red unit, extremely abundant, indicate a biotic radiation during the Late Santonian and the Early Campanian, implying that the high oxygen levels had returned to all the oceanic depth levels,and that the water stratification disappeared, followed by the radiation of all depth-dwellers. The variation on foraminiferal faunas from the whole sequence refers to the extreme warm climate that appeared in the Middle Cretaceous and to the declined temperature toward the late epoch. Substantial deposits for this warming and cooling zones represent the black shales in the Middle Cretaceous and the red beds in the later period of the southern Tibet. The change in the foraminiferal composition corresponded to the formation of dysaerobic facies and to the development of high-oxidized circumstances.     

Cenomanian-Coniacian Sea-level Change and Dissolved Oxygen Fluctuations in Tethys-Himalaya: Evidences from Benthic Foraminifera of Gamba, Tibet

Benthic foraminifera, preserved in the Late Cretaceous organic carbon-rich sediments of Gamba, southern Tibet, provide high-resolution proxies for sea-level changes and dissolved oxygen fluctuations of southeastern Tethys. The fossils were statistically analyzed and divided into three faunas of "Cenomanian fauna", "Turonian fauna", and "Coniacian fauna". A middle neritic-upper bathal environment (50-250m) was estimated considering the ratios of planktonic and epifaunal benthic foraminifera (P/(P+E)), the morphological analysis according to the studies of recent foraminifera and the abundant distributions of depth-related species such as Alabamina creta, Laevidentalina sp., Praebulimina spp., Pleurostomella cf. naranjoensis, Pyrulina sp., Quinqueloculina spp., Haplophragmoides spp., etc. The result shows an almost parallel trend with the global transgressive and regressive cycles, but the former fluctuates more frequently at upper Cenomanian, which probably indicates tectonic instability of the continental margin. According to the benthic foraminiferal richness (BFN), Shannon-Weiner diversity (H(s)), as well as benthic foraminiferal oxygen index (BFOI), five periods of oxygen depleted conditions (dysoxic-anoxic) have been recognized. They correspond to the OAE2, the lower Turonian, the upper Turonian, the Turonian-Caniacian boundary event and the probably OAE3. In addition, the oxygen fluctuations in Gamba might be controlled directly by sea-level changes, while the paleoproductivity and oxygen conditions interacted with each other under oxygen deficiency environments.     

South Equatorial Current (SEC) driven changes at DSDP Site 237, Central Indian Ocean, during the Plio-Pleistocene: Evidence from Benthic Foraminifera and Stable Isotopes

This study attempts to analyse paleoceanographic changes in the Central Indian Ocean (Deep Sea Drilling Project Site 237), linked to monsoon variability as well as deep-sea circulation during the Plio-Pleistocene. We used factor and cluster analyses of census data of the 34 most dominant species of benthic foraminifera that enabled us to identify five biofacies: Astrononion umbilicatulum–Uvigerina proboscidea (Au–Up), Pullenia bulloides–Bulimina striata (Pb–Bs), Globocassidulina tumida–Nuttallides umbonifera (Gt–Nu), Gyroidinoides nitidula–Cibicides wuellerstorfi (Gn–Cw) and Cassidulina carinata–Cassidulina laevigata (Cc–Cl) biofacies. Knowledge of the environmental preferences of modern deep-sea benthic foraminifera helped to interpret the results of factor and cluster analyses in combination with oxygen and carbon isotope values. The biofacies indicative of high surface productivity, resulting from a stronger South Equatorial Current (Au–Up and Pb–Bs biofacies), dominate the early Pliocene interval (5.6–4.5 Ma) of global warmth. An intense Indo-Pacific ‘biogenic bloom’ and strong Oxygen Minimum Zone extended to intermediate depths (1000–2000 m) over large parts of the Indian Ocean in the early Pliocene. Since 4.5 Ma, the food supply in the Central Indian Ocean dropped and fluctuated while deep waters were corrosive (biofacies Gt–Nu, Gn–Cw). The Pleistocene interval is characterized by an intermediate flux of organic matter (Cc–Cl biofacies).     

Late Glacial–Holocene record of benthic foraminiferal morphogroups from the eastern Arabian Sea OMZ: Paleoenvironmental implications

The Arabian Sea is characterized today by a well-developed and perennial oxygen minimum zone (OMZ) at mid-water depths. The Indian margin where the OMZ impinges provides sediment records ideal to study past changes in the OMZ intensity and its vertical extent in response to the changes of monsoon-driven primary productivity and intermediate water ventilation. Benthic foraminifera, depending upon their adaptation capabilities to variation in sea floor environment and microhabitat preferences, develop various functional morphologies that can be potentially used in paleoenvironmental reconstruction. In this study, we analysed benthic foraminiferal morphogroups in assemblage records of the last 30 ka in a sediment core collected from the lower OMZ of the Indian margin (off Goa). In total, nine morphogroups within two broadly classified epifaunal and infaunal microhabitat categories are identified. The abundance of morphogroups varies significantly during the late Glacial, Deglacial and Holocene. It appears that monsoon wind driven organic matter flux, and water column ventilation governing the OMZ intensity and sea-bottom oxygen condition, have profound influence on structuring the benthic foraminiferal morphogroups. We found a few morphogroups showing major changes in their abundances during the periods corresponding to the northern hemisphere climatic events. Benthic foraminifera with planoconvex tests are abundant during the cold Heinrich events, when the sea bottom was oxygenated due to a better ventilated, weak OMZ; whereas, those having tapered/cylindrical tests dominate during the last glacial maximum and the Holocene between 5 and 8 ka BP, when the OMZ was intensified and poorly ventilated, leading to oxygen-depleted benthic environment. Characteristically, increased abundance of taxa with milioline tests during the Heinrich 1 further suggests enhanced ventilation attributed probably to the influence of oxygen-rich Antarctic Intermediate Water (AAIW).     

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。     

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.     

Assessing the suitability of benthic foraminiferal morpho-groups to reconstruct paleomonsoon from Bay of Bengal

Temporal changes in benthic foraminiferal morpho-groups were suggested as an effective proxy to reconstruct past monsoon intensity from the Arabian Sea. Here, in order to test the applicability of temporal variation in morpho-groups to reconstruct past monsoon intensity from the Bay of Bengal, we have documented recent benthic foraminiferal distribution from the continental shelf region of the northwestern Bay of Bengal. Based on the external morphology, benthic foraminifera were categorized into rounded symmetrical (RSBF) and angular asymmetrical benthic foraminifera (AABF). Additionally, a few other dominant groups were also identified based on test composition (agglutinated, calcareous) and abundance (Asterorotalids and Nonions). The relative abundance of each group was compared with the ambient physico-chemical conditions, including dissolved oxygen, organic matter, salinity and temperature. We report that the RSBF are abundant in comparatively warm and well oxygenated waters of low salinity, suggesting a preference for high energy environment, whereas AABF dominate relatively cold, hypersaline deeper waters with low dissolved oxygen, indicating a low energy environment. The agglutinated foraminifera, Asterorotalids and Nonions dominate shallow water, low salinity regions, whereas the calcareous benthic foraminiferal abundance increases away from the riverine influx regions. Food availability, as estimated from organic carbon abundance in sediments, has comparatively less influence on faunal distribution in the northwestern Bay of Bengal, as compared to dissolved oxygen, temperature and salinity. We conclude that the factors associated with freshwater influx affect the distribution of benthic foraminiferal morpho-groups in the northwestern Bay of Bengal and thus it can be used to reconstruct past monsoon intensity from the Bay of Bengal.     

中—新生代有孔虫古地理对西藏特提斯演变的动态响应

有孔虫化石资料是地质历史的真实记录,对不同地质时期古地理格局和生态环境的变迁具有动态响应。西藏特提斯构造带的演化、板块相对地理位置变迁等诸多问题一直是地学界关注的热点。研究西藏特提斯沉积盆地内有孔虫动物群的古生态特征和古地理分布,能够识别生物地理区系,进而恢复不同时期的大地构造演化格局。西藏地区中、新生代古生物地理区系的分化是西藏特提斯地质演变的具体反映。西藏南部早侏罗世产底栖大有孔虫Orbitopsella喜暖动物群,晚侏罗世出现双壳类Buchia喜冷动物群。由此推测,侏罗纪新特提斯洋扩张尤其是中大西洋的开张,将位于印度大陆北缘的特提斯喜马拉雅带,从早侏罗世较低纬度的温暖位置向南推移至较高纬度的低温地区。白垩纪中期Orbitolina有孔虫类群繁盛于特提斯北侧亚洲大陆的拉萨地块和羌塘盆地,但没有出现在印度大陆。这说明当时印度大陆已脱离冈瓦纳大陆向北漂移,受四周深水环境的阻隔,Orbitolina动物群未能向印度大陆扩散。此时深水环境中生活着浮游有孔虫Ticinella-Rotalipora动物群。Turonian晚期开始形成海退,拉萨地块的海洋环境基本消失。Coniacian-Campanian早期印度大陆北缘浮游有孔虫继续占优势,繁盛Marginotruncana-Globotruncana动物群。直至白垩纪末,印度和欧亚大陆之间的深海阻隔仍然存在,雅鲁藏布江缝合带两侧动物群一直存在根本性差异。印度大陆北缘发育着Orbitoides-Omphaloceclus 动物群,冈底斯南缘则以Lepidorbitoides-Pseudorbitoides动物群为特征。古新世Danian期生态环境发生变化,显示大印度与亚洲大陆发生初始碰撞(66~61 Ma)。Selandian期之后,缝合带两侧才出现相同的Miscellanea-Daviesina有孔虫类群,生物区系的分异基本结束。始新世早期缝合带两侧为完全相同的生物区系,共同发育底栖大有孔虫Nummulites-Discocyclina动物群。有孔虫古地理证据表明,大印度与欧亚大陆的初始碰撞在古新世早期发生,时间大致在Danian期,沿雅鲁藏布缝合带的深海演变为残留海环境。小个体货币虫Nummulites willcoxi和浮游有孔虫Globigerina ouachitaensis的存在,代表特提斯喜马拉雅最高海相沉积,时代属于始新世Priabonian晚期(35~34 Ma)。随后,特提斯喜马拉雅海封闭,海水完全退出西藏境内。     

西太平洋782A钻孔新生代的有孔虫

大洋钻探工程” 1 2 5航次的 782 A钻孔位于西太平洋菲律宾海东北部 ,井深 4 76.8m。基底为安山岩 ,上覆盖层为中始新统—更新统的沉积层 ,其中保存有低丰度的有孔虫。自下而上可划分出 8个浮游有孔虫带。由于出现 Catapsydrax dissimilis,C.stainforthi为 N5 、N6 带的带化石 ,表明本钻孔存在早中新世的地层。同时由于缺失浮游有孔虫带 P1 5 — P1 6 下部 ,N3上部—N4,N7—N1 1 带的带化石 ,说明在中始新世与晚始新世之间、晚渐新世与早中新世之间、早中新世与中中新世之间存在 3个沉积间断。钻孔中的有孔虫标志本区当时处于温暖亚热带环境。根据不同时期温度的变化 ,可划分出 5个阶段 ,包括 3个偏暖时期和 2个温凉时期。     

北京顺义早更新世有孔虫动物群的古生态及古环境

1975年我们报道了泥河湾盆地怀来及蔚县境内发现半咸水有孔虫化石,当时认为它们的层位可能属第四系上部,后来进一步工作证实应是泥河湾组上部沉积。1977年我们对华北平原第四纪海进海退现象作了初步报道,认为华北平原在早更新世时发生过海进(渤海海进),并引用陈方吉在北京东南发现海相介形虫资料,说明早更新世渤海海进时海水曾经到达这一地区。1978年李鼎容等在北京市顺义县早更新世地层中发现大量有孔虫化石。进一步证实北京地区早更新世确曾发生过海进,使我们解释怀来及蔚县所发现的半咸水有孔虫来源,有更多证据。这一发现,对于北京地区第四纪地层划分对比、新构造运动判别和古地理恢复有重大意义。     

晚上新世以来南海北部深部水团演化

对南海北部大洋钻探184航次1146站晚上新世以来底栖有孔虫属种组合的Q型因子分析, 发现底栖有孔虫组合以2.1Ma, 1.5Ma和0.7Ma为界, 分为Stilostomella-Globocassidulina subglobosa-Nodogenerina, Bulimina alazanensis, Uvigerina perigrina和Melonis barleeanus-Globobulimina affinis-Bulimina aculeata4个组合.结合底层水溶解氧含量和浮游、底栖有孔虫碳同位素分析, 认为底栖有孔虫组合的变化是南海底层水影响所致, 以及南海北部表层和底层海水营养盐含量变化的共同结果.      

Geo-environmental appraisal of the Meda creek,Saurashtra, Gujarat

Water chemistry, sediment texture, clay mineralogy and foraminiferal contents from the bottom of Meda creek were studied to assess the geo-environmental status of the creek. Water quality data for three seasons suggests domination of marine environment as pH remained above 8 and salinity above 35‰ throughout. Clay dominate the bottom sediments, except near mouth. Montmorillonite, illite and kaolinite are the major clay minerals in the sediments. In absence of any source rock in the catchment of the Meda creek, the presence of illite and kaolinite indicates their transportation and depositions from near coastal waters during high tides. Ammonia sp. is the most dominating foraminifera. Reworked forms as well as angular asymmetric forms of foraminifera were dominant in clay rich areas of the creek.     

Rapid climatic shifts of the northern Norwegian Sea during the last deglaciation and the Holocene

High resolution cores from the upper continental slope, northern Norwegian Sea, document rapid climatic fluctuations during the latest deglaciation and the Holocene. Based on down-core analysis of planktic and benthic foraminifera, stable oxygen and carbon isotopes, carbonate and organic carbon and radiocarbon dating, the following evolution is proposed: sea-ice cover broke up, the surface ocean warmed and an in situ benthic foraminiferal fauna was established at 12 500 BP. The Younger Dryas was characterized by reduced sedimentaion and foraminiferal production, due to surface ocean cooling. At the end of the Younger Dryas there were major shifts in both surface and bottom water conditions. The surface ocean warmed to temperatures similar to modern levels within < 100 years, reaching a maximum at about 9200 BP when foraminiferal production was high. A benthic foraminiferal assemblage indicative of bottom water conditions similar to present conditions was established at 10 000 BP. This was followed by a gradual decline in nutrients or an increase in ventilation of the bottom water throughout the Holocene. A gradual surface ocean cooling of c . 2°C ended around 6500 BP followed by a second warming that culminated at 2000 BP. The warming at the end of the Younger Dryas and the succeeding older Holocene temperature maximum correlate to a June insolation maximum in the northern hemisphere. In addition, fluctuating surface temperatures in the Holocene may be driven by variations in inflow of Atlantic Water.     

西藏特提斯喜马拉雅海相白垩纪—古近纪生物地层与重大地质事件研究进展

地质历史时期曾发过许多对生命的演化进程造成过重大影响与制约的全球性地质事件,白垩纪—古近纪就是一个重大地质事件频发的时期。随着冈瓦纳大陆在中生代时期的解体,全球海陆格局发生了根本的变化,地球的表层和岩石圈层均发生了重大的改变,由此引发了构造运动空前活跃,发生过诸如大洋缺氧事件(OAE)、大洋富氧事件(CORBs)、白垩纪/古近纪(K/Pg)生物大灭绝事件、古新世—始新世极热(PETM)事件、印度-亚洲板块碰撞、新特提斯洋的演化及最终消亡等一系列的全球性重大地质事件。对这些重大地质事件的研究,有助于加深我们对古海洋、古地理、古环境的认识。尝试追踪和捕捉这些重大地质事件,恢复和重建古地理,其基础是建立精确的年代地层格架。西藏南部保存了中国最为完整的海相白垩纪—古近纪沉积,完整地记录了上述的全球性重大地质事件,通过对札达、岗巴、定日、亚东、江孜、萨嘎和吉隆等地区高分辨率浮游和底栖有孔虫、介形虫、钙质超微化石和放射虫生物地层学研究,可直接约束全球性重大地质事件发生的时间,并为重建新特提斯洋古海洋环境和古地理提供证据。此外,在重大地质环境突变期间生物的演化过程,也可为探明极端环境变化发生时期气候-环境-生物之间的协同演化关系提供证据。本文系统总结了课题组为主的近年来对藏南白垩纪—古近纪海相地层中微体古生物学的研究成果及重要进展,并对未来研究提出展望。     

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.     

Palaeoenvironmental reconstruction of the Oligocene Afales Basin, Ithaki island, western Greece

Assemblages of benthic foraminifera from one clastic succession in the Afales Basin (Ithaki Island, western Greece) were investigated to reconstruct palaeoenvironmental conditions during the Oligocene. The section consists of alternating hemipelagic marls and detrital deposits, designated as flysch-like beds, attributed to biostratigraphic Zones P20 and P21. Planktic percentages are mostly high (66–80%). Benthic foraminiferal assemblages comprise calcareous and agglutinated taxa (up to 15%). The prevalence of epifaunal foraminifera indicates good ventilation of the bottom water resulting from basin morphology, which enabled the undisturbed flow of water throughout the basin. Palaeodepth estimates imply bathyal deposition, from about 800 to 1200 m deep. The benthic foraminiferal fauna is of high diversity along the section, as is expected in deep marine environments. The abundances of the most common foraminiferal taxa (Cibicidoides spp., Oridorsalis umbonatus, Gyroidinoides spp., Stilostomella spp., Nodosariidae, Nuttallides umbonifera) are quite variable and imply generally oligotrophic to mesotrophic environmental conditions with variable organic flux.     

Benthic foraminiferal biostratigraphy of the tertiary sediments from the Elazig and Malatya Basins,Eastern Turkey

Tertiary sequences in the Elazig and Malatya Basins, eastern part of Taurus Orogenic Belt, are investigated with the aim of defining the benthic foraminiferal biozones. Tertiary geological units from bottom to top are as follows: Basement rocks, Zorban Formation, Yildiztepe Formation, Suludere Formation, Gedik Formation (Malatya Basin); Elazig Magmatics, Keban Metamorphics, Harami Formation, Kuscular Formation, Seske Formation, Kirkgecit Formation (Elazig Basin). Middle-Upper Eocene Yildiztepe, Suludere and Gedik Formations; Upper Paleocene-Lower Eocene Seske Formation and Middle-Upper Eocene Kirkgecit Formation are all characterized by interbedded clastics and carbonate rocks. Six stratigraphic sections are studied in detail for foraminiferal biostratigraphy. Eight benthic foraminiferal biozones are reported. These are; Coskinolina rajkae biozone in the Late Paleocene (Thanetian), Assilina yvettae, Idalina sinjarica biozones in the Late Paleocene; Asterocyclina alticostata gallica biozone in the Early Eocene (Late Cuisian), Nummulites millecaput biozone in the Middle Eocene (Middle Lutetian), Nummulites aturicus biozone in the Middle Eocene (Late Lutetian), Nummulites perforatus biozone in the Middle Eocene (Bartonian), Nummulites fabianii biozone in the Late Eocene (Priabonian). Some key taxa are illustrated.