Browsing by Author "M.S. Srinivasan"

Now showing 1 - 20 of 23

A journey through morphological micropaleontology to molecular micropaleontology
(2007) M.S. Srinivasan
Micropaleontology has undergone a remarkable change over the past 150 years. With the recognition ofbiostratigraphic utility of microfossils in petroleum exploration, micropaleontology received a new impetus from the early descriptive stage to noticeable and exciting trends in the early part of the 20th century. The changes have been primarily in the areas of systematics of smaller benthic foraminifera, biostratigraphy and precision in paleoecology mainly to cater the needs of oil companies. This marks the first major milestone - the development of Industrial micropaleontology. A dazzling shift in micropaleontology occurred in the seventies and eighties with the advent of intensive scientific ocean drilling programmes and availability of new instrumentation and analytical techniques to study microfossils. In addition, efforts to evolve multiple microfossil biostratigraphies and their integration with other fields such as magnetostratigraphy, stable isotopic stratigraphy, carbonate stratigraphy, computer application and more recently with molecular biology opened up multifaceted approach to micropaleontological research. This was indeed another important milestone in the history of development of micropaleontology. This led to a qualitative change in research emphasis in the areas of correlation, paleobiogeography, plankton evolution, paleoclimatology and paved way for new research areas like paleoceanography and molecular micropaleontology. Of late, microfossils have emerged as a very powerful and reliable tool to trace past variations in monsoon and to characterize tsunamigenic sediments. Thus, the subject of micropaleontology is becoming more and more important branch of Earth System Science for finding solutions to contemporary issues and that its future is indeed very bright.
Correlation of Late Cenozoic marine sections in Andaman-Nicobar, northern Indian Ocean, and the equatorial Pacific.
(1979) M.S. Srinivasan; R.J. Azmi
A large number of overlapping stratigraphic sections exposed on the Andaman-Nicobar Islands contain an almost complete Early Miocene to Quaternary sequence of tropical planktonic foraminiferal zones. 20 zones based on the ranges of planktonic foraminifera are defined. 24 datum levels are established, many of which are comparable with those established for the equatorial Pacific and are thus important for interregional correlation. The stratigraphic ranges of several species such as Globigerinatella insueta, Globigerinoides conglobatus, Globoquadrina conglomerata and Protentella bermudezi are significantly different from those reported from the equatorial Pacific. -from Authors
Deep sea benthic foraminiferal response to the Pliocene palaeoenvironments of the northern Indian Ocean
(Universite Claude Bernard Lyon I, 2000) Ajai K. Rai; M.S. Srinivasan
The benthic foraminiferal contents of two DSDP sites 219 (Arabian Sea) and 237 (Mascarene Plateau) have been analysed in order to understand paleoceanographic changes in the northern Indian Ocean during Pliocene. Uvigerina proboscidea is the most dominant taxon with intervals of marked fluctuations in its abundance at both the sites reflecting relatively higher surface water productivity with changing magnitudes during Pliocene. Earliest Pliocene (c. 5.6 to 5.0 Ma) is the interval of distinct increase in the surface water productivity in response to more SW Indian Ocean monsoonal upwelling. The faunal assemblage during c. 5.0 to 4.0 Ma suggests relatively warm, oxygenated and more saline bottom waters and moderately low surface water productivity in the Arabian Sea region. This was also broadly the period of global warmth and higher eustatic sea level. The surface water productivity during c. 4.0 to 3.4 Ma at site 219 was moderately higher. However, site 237 is characterized by strong bottom currents and relatively lower surface productivity. Further, the latest Pliocene (c. 2.5 Ma onwards) is characterised by significantly higher surface water productivity induced by higher rates of SW Indian Ocean monsoonal upwelling which corresponds with the onset of major Northern Hemisphere glaciation. These paleoenvironmental changes are suggested to be mainly responsible for several last occurrences of benthic foraminiferal taxa near the Pliocene/Pleistocene transition.
Deep-Sea Drilling Project Leg 90: The South Pacific Cenozoic
(1983) J.P. Kennett; C. Von Der Borch; P.A. Baker; C.E. Barton; A. Boersma; W.C. Dudley Jr.; J.V. Gardner; D.G. Jenkins; W. Lohman; R. Morin; R. Martini; R.B. Merrill; C.S. Nelson; C. Robert; M.S. Srinivasan; R. Stein; A. Takeuchi
[No abstract available]
Early Neogene multiple microfossil biostratigraphy, John Lawrence Island, Andaman Sea
(2000) O.P. Singh; M.S. Srinivasan; V. Sharma
Planktic foraminifera, calcareous nannofossils and radiolaria were examined from Early Neogene sequence of John Lawrence Island, Andaman Sea in order to compare and contrast the stratigraphic ranges of various microfossil groups to achieve a better biostratigraphic resolution. Based on stratigraphic ranges of planktic foraminifera, the examined samples from the South Point section of John Lawrence Island are referable to the upper part of the Globigerinatella insueta Zone and lower part of Praeorbulina glomerosa Zone of Srinivasan (1988). These zones also correspond to Globigerinoides bisphericus (M4b) Zone and Praeorbulina sicana-Praeorbulina glomerosa (M5a) Zone of Berggren et al. (1995) delineating the Early / Middle Miocene boundary. The boundary between these two zones demarcates the Jarawaian / Inglisian Stage (Early / Middle Miocene) boundary. The calcareous nannofossil assemblage recovered from the examined samples is assigned to Helicosphaera ampliaperta (NN4) Zone of Martini (1971), whereas radiolarian studies reveal the samples to be referable to Calocycletta costata Zone of Reidel and Sanfilippo (1970). Berggren et al. (1995b) estimated and age range of 16.7-16.1 Ma for planktic foraminiferal zones (M4b-M5a) and 18.3-15.6 Ma for the calcareous nannofossil zone (NN4). According to Nigrini (1985) the radiolarian Calocycletta costata Zone ranges in age from 17.3-15.7 Ma. A comparison of above estimated ages reveals the age data based on planktic foraminifera to be more precise than the calcareous nannofossils and radiolaria. Thus, based on comparative age data the sequence examined at John Lawrence Island represents the upper part of calcareous nannofossil Helicosphaera ampliaperta (NN4) Zone and also the upper part of the radiolaria Calocycletta costata Zone. The inconsistency in the distribution and abundance of any single microfossil group throughout the examined section shows the need for employing multiple microfossil biostratigraphic approach. The study reveals that various microfossil groups serve as complimentary to each other for attaining enhanced biostratigraphic resolution.
Early Pliocene closing of the Indonesian Seaway: evidence from north-east Indian Ocean and tropical Pacific deep sea cores
(1998) M.S. Srinivasan; D.K. Sinha
Deep sea cores from sites 214 and 758A (Ninetyeast Ridge, north-east Indian Ocean), 761B (Wombat Plateau, north-east Indian Ocean) and 586B (Ontong Java Plateau, Tropical Pacific) are ideally located for comparison of late Neogene planktic foraminiferal biogeography and paleoceanographic records of tropical Indian and Pacific oceans to infer the timing of closing of the Indonesian Seaway. A consistent stratigraphy was developed between sites 214 and 586B using graphic correlation and was integrated with the paleomagnetic time scale of Berggren et al. (1985) to provide an accurate chronology to compare interocean stratigraphic ranges of late Neogene planktic foraminifera. Tropical planktic foraminifera occur throughout each sequence at all sites. At each site the Miocene-Pliocene boundary is defined by the first appearance of Globorotalia tumida (5.2 Ma), the early/late Pliocene boundary by the first appearance of Globigerinoides fistulosus (3.2 Ma) and the Pliocene-Pleistocene boundary by the last appearance of G. fistulosus (1.6 Ma). Neogene planktic foraminiferal assemblages at sites 214, 758A, 761B and 586B are generally similar until the beginning of the Pliocene (5.2 Ma) when the faunal record indicates divergence. A notable difference is complete absence of early Pliocene taxon Pulleniatina spectabilis from all the Indian Ocean sites. This difference suggests that the Indonesian Seaway became an effective biogeographic barrier to planktic foraminifera at the beginning of the Pliocene. However, there is still exchange of surface waters through this Seaway. Earlier studies suggested a Middle to Late Miocene occurrence for this biogeographic barrier. P. spectabilis evolved from P. primalis in the equatorial Pacific at about 5.2 Ma. It is a short-ranging early Pliocene species spanning about 1.3 m.y. and occurred only in Pacific, unlike earlier suggestions of a broader distribution into the Indian Ocean.
Improved correlation of the late Neogene planktonic foraminiferal datums in the equatorial to cool subtropical DSDP sites, southwest Pacific: application of the graphic correlation method
(1991) M.S. Srinivasan; D.K. Sinha
Sequential order of planktonic foraminiferal datums has been established for the Late Neogene of five DSDP sites examined in the southwest Pacific. A critical analysis reveals many of the datums to be time transgressive and thus not useful for correlation. Therefore, to evaluate the reliability of the datums for cross-latitudinal correlation, Shaw's graphic correlation method has been applied. The results show that the datums can be broadly grouped under two categories, namely: first order datums and second order datums. -from Authors
Influence of Antarctic Bottom Water (AABW) and monsoonal activity in the central Indian Ocean over past 5 million years: Benthic foraminiferal record at DSDP Site 238
(2007) Ajai Kumar Rai; M.S. Srinivasan; Abhayanand Singh Maurya
This study quantitatively analyzes Pliocene-Pleistocene benthic foraminifera from DSDP Site 238 in the central Indian Ocean. A Q-mode factor analysis of 28 most abundant species defines three significant faunal assemblages reflecting different environmental characteristics. The Cibicides wuellerstorfi-Oridorsalis umbonatus assemblage (Factor 1) represents well oxygenated bottom waters with active currents and intermediate to low supply of organic matter. The Uvigerina proboscidea assemblage (Factor 2) indicates a continuously high flux of organic matters to the sea floor in response to increased surface water productivity. The Nuttallides umbonifera assemblage (Factor 3) is associated with Antarctic Bottom Water (AABW) and reflects cold, oligotrophic, increased carbonate corrosiveness and high oxygen concentration. In most of the past 5 Ma (i.e. 5-4.2 Ma, 2.8-1.8 Ma and 1.2 Ma to Recent) the dominant occurrences of Cibicides wuellerstorfi-Oridorsalis umbonatus assemblage represent active bottom water currents with more ventilation and relatively low trophic levels reflecting the influence of NADW at abyssal depths in the central Indian Ocean. The early Late Pliocene (c. 3.6-2.8 Ma) and Early Pleistocene (c. 1.8-1.2 Ma) are two significant intervals of prominent faunal change, which indicate entirely different deep-sea conditions. The prominent occurrence of Nuttallides umbonifera assemblage during 3.6-2.8 Ma reflects cold, corrosive and well-oxygenated bottom waters possibly in response to increased flow of AABW towards the central Indian Ocean at abyssal depths. The Early Pleistocene (c. 1.8-1.2 Ma) is characterized by distinct occurrence of the Uvigerina proboscidea assemblage reflecting higher surface productivity. The widespread, intensified monsoon system during Early Pleistocene causes increased upwelling and higher surface productivity, which also enhanced the supply of organic carbon to the ocean floor. © Geol. Soc. India.
Micropaleontology: Principles and applications
(Springer International Publishing, 2015) Pratul Kumar Saraswati; M.S. Srinivasan
This book will help readers learn the basic skills needed to study microfossils especially those without a formal background in paleontology. It details key principles, explains how to identify different groups of microfossils, and provides insight into their potential applications in solving geologic problems. Basic principles are addressed with examples that explore the strengths and limitations of microfossils and their geological records. This overview provides an understanding of taphonomy and quality of the fossil records, biomineralization and biogeochemistry, taxonomy, concepts of species, and basic concepts of ecology. Readers learn about the major groups of microfossils, including their morphology, ecology, and geologic history. Coverage includes: foraminifera, ostracoda, coccolithophores, pteropods, radiolaria, diatoms, silicoflagellates, conodonts, dinoflagellates, acritarch, and spores and pollens. In this coverage, marine microfossils, and particularly foraminifera, are discussed in more detail compared with the other groups as they continue to play a major role in most scientific investigations. Among the various tracers of earth history, microfossils provide the most diverse kinds of information to earth scientists. This richly illustrated volume will help students and professionals understand microfossils, and provide insight on how to work with them to better understand evolution of life, and age and the paleoenvironment of sedimentary strata. © Springer International Publishing Switzerland 2016.
Miocene planktonic foraminiferal biogeography and paleoceanographic development of the Indo-Pacific region
(Geological Society of America, 1985) James P. Kennett; Gerta Keller; M.S. Srinivasan
Biogeographic patterns of Pacific planktonic foraminifera have been quantitativelymapped for two time-slices in the early Miocene (22 and 16 Ma) and one in the lateMiocene (8 Ma). Important differences are apparent between the early and late Miocenethat resulted from changes in surface water circulation within the Pacific Ocean andbetween the tropical Pacific and Indian Oceans.In the early Miocene, tropical Pacific planktonic foraminifera were dominated bydifferent taxa in the eastern and western areas, but by the late Miocene the assemblageswere similar across the entire tropical Pacific. East to west faunal differences wereprobably due to differences in the surficial water-mass structure and temperature. It islikely that a deeper thermocline existed in the west favoring shallow water dwellers suchas Globigerinoides and Globigerina angustiumbilicata, and a shallower thermocline inthe east favoring slightly deeper-dwelling forms, especially Globorotalia siakensis andG. mayeri. During the late Miocene a trans-equatorial assemblage developed, dominatedby Globorotalia menardii-G. limbata and Globigerinoides groups. These faunalchanges are interpreted to reflect both the development, during the middle Miocene, ofthe Equatorial Undercurrent system when the Indonesian Seaway effectively closed andthe general strengthening of the gyral circulation and Equatorial Countercurrent thatresulted from increased Antarctic glaciation and high-latitude cooling during the middleMiocene.The trans-equatorial planktonic foraminiferal distribution patterns typical of thelate Miocene did not persist to the present-day oceans when east-west differences areagain evident. However, these differences in modern assemblages are exhibited withinforms that usually inhabit deeper waters. There is a successive changing dominancefrom west to east of Pulleniatina obliquiloculata to Globorotalia tumida to Neogloboquadrinadutertrei. The modern west to east differences in these deeper-dwelling formsreflect an intensification of the Equatorial Undercurrent system and its shallowing towardsthe east to depths well within the photic zone. Shallow-water forms, such asGlobigerinoides, maintain trans-tropical distribution patterns in the modern ocean un-like the early Miocene that lacked an effective equatorial countercurrent system in thePacific.The distribution of faunas in the North Pacific indicates that the gyral circulationsystem was only weakly developed in the early Miocene, but was strong by the lateMiocene. In the northwest Pacific, temperate faunas were displaced northward as theKuroshio Current intensified in the late Miocene. In the South Pacific, more distinctlatitudinal faunal provinces appeared during the middle to late Miocene along with anorthward expansion of the polar-subpolar provinces and contraction of the tropicalprovince. These faunal changes resulted from the continued areal expansion of the polarand subpolar water masses as Australia drifted northward from Antarctica and from thesteepening of pole to equator thermal gradients related to increased Antarctic glaciation.
Neogene deep sea benthic foraminiferal diversity in the Indian Ocean: Paleoceanographic implications
(Springer India, 1992) Ajai K. Rai; M.S. Srinivasan
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. © 1992 Indian Academy of Sciences.
Neopleurostomella, a new foraminiferal genus from DSDP Site 219, Arabian Sea
(1992) M.S. Srinivasan; A.K. Rai
A detailed qualitative and quantitative investigation of foraminifera from DSDP Site 219 (Arabian Sea) has enabled us to identify a new, distinctive benthic foraminiferal genus, Neopleurostomella, in the Middle Miocene to Early Pliocene deep sea sequences. -Authors
New bivalves from the Miocene of Little Andaman Island, Bay of Bengal
(2002) S. Kanjilal; M.S. Srinivasan
The present paper reports large sized internal moulds of seven new and exotic bivalves from the Miocene rocks of Little Andaman Island in the Bay of Bengal. The fauna (comprising five taxa) include one new subfamily (Trapezicardiinae n.subfam.), one new genus (Trapezicardium n.gen.) one new subgenus (Megalaevicardium n.subgen. under Laevicardium Swainson), and three new species [viz., Glycymeris (Glycymerita) gigantica n.sp., T. laiensis. n. gen. and n.sp., and L. (M.) hutbayensis n.subgen. and n.sp.].
Ocean circulation in the tropical Indo-Pacific during early Pliocene (5.6-4.2 Ma): Paleobiogeographic and isotopic evidence
(2000) M.S. Srinivasan; D.K. Sinha
A comparison of late Neogene planktic foraminiferal biogeography and stable isotopic records of shallow dwelling and deep dwelling planktic foraminifera from DSDP sites 214 (Ninetyeast Ridge, northeast Indian Ocean) and 586B (Ontong-Java Plateau, western Equatorial Pacific) provides a clue to the nature of the ocean circulation in the tropical Indo-Pacific during early Pliocene. The present study reveals that the late Neogene planktic foraminiferal data from the eastern and western sides of the Indonesian Seaway are very similar. The only distinct inter-ocean difference however is the absence of Pulleniatina spectabilis from the Indian Ocean. This species makes its first evolutionary appearance in the Equatorial Pacific at about 5.6 Ma (Early Gilbert reversed) and ranges up to 4.2 Ma (Top Cochiti subchron). The complete absence of Pulleniatina spectabilis from the Indian Ocean is attributed to blocking of westward flow of tropical waters of the Pacific to the Indian Ocean resulting in a major change in ocean circulation in the tropical Pacific and Indian oceans during 5.6 to 4.2 Ma. In order to understand the nature of this blockage, isotopic depth ranking of selected planktic foraminifera was carried out which reveals that the Indonesian Seaway became an effective biogeographic barrier to deep dwelling planktic foraminifera and thus it may be interpreted that the shallow sills that mark the Seaway in modern times were present as early as 5.6 Ma. The distribution of Pulleniatina spectabilis throughout the Equatorial Pacific reveals that Modern Equatorial Pacific Under Current (Cromwell Current) flowing towards east at a depth of 200-300 m (which is also the depth habitat of Pulleniatina spectabilis) was present at the beginning of the Pliocene (5.6 Ma). As a sequel to the blocking of the Indonesian Seaway and the resultant interruption in the flow of central Equatorial Current System of the Pacific to the west there was an increase in the western Pacific Warm Pool Waters and strengthening of the gyral circulation in the Pacific and Indian Oceans. This eventually triggered the intensification of the Asian Monsoon System. © Printed in India.
Palaeotectonic implications of increased late Eocene-early Oligocene volcanism from South Pacific DSDP sites
(1985) J.P. Kennett; C. Von Der Borch; P.A. Baker; C.E. Barton; A. Boersma; J.P. Cauler; W.C. Dudley Jr.; J.V. Gardner; D.G. Jenkins; W.H. Lohman; E. Martini; R.B. Merrill; R. Morin; C.S. Nelson; C. Robert; M.S. Srinivasan; R. Stein; A. Takeuchi; M.G. Murphy
Late Eocene-early Oligocene (42-35 Myr) sediments cored at two DSDP sites in the south-west Pacific contain evidence of a pronounced increase in local volcanic activity, particularly in close association with the Eocene-Oligocene boundary. This pulse of volcanism is coeval with that in New Zealand and resulted from the development of an Indo- Australian / Pacific Plate boundary through the region during the late Eocene. The late Eocene / earliest Oligocene was marked by widespread volcanism and tectonism throughout the Pacific and elsewhere, and by one of the most important episodes of Cenozoic climatic cooling. © 1985 Nature Publishing Group.
Pleistocene oceanographie changes indicated by deep sea benthic foraminifera in the northern Indian Ocean
(Springer India, 1994) Ajai K. Rai; M.S. Srinivasan
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 of U. 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 of U. proboscidea and more diverse and equitable benthic fauna. The lower depth range for the occurrence of Bulimina 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 of Stilostomella lepidula occurs close to the Early/Late Pleistocene boundary. © 1994 Indian Academy of Sciences.
Quaternary climatic changes indicated by planktonic foraminifera of Northern Indian Ocean
(1993) A.D. Singh; M.S. Srinivasan
The relative abundances of planktonic foraminifera, the changes in their coiling and the isotopic record from deep sea cores of some crucial sites in Northern Indian Ocean indicate climatic fluctuations for the past 3.0 million years (Late Pliocene to Pleistocene). The abundance of temperate forms like Globigerina spp. together with sporadic occurrence of a polar species Neogloboquadrina pachyderma during specific time intervals suggest cooling episodes. Warmer intervals are marked by the dominance of tropical assemblages including Globigerinoides spp., Globorotalia s.l., Pulleniatina and Globoquadrina. On the basis of the planktonic foraminiferal frequency changes, four intervals of major climatic cooling have been recognized-one in the Late Pliocene (2-3 m.y.), three in the Pleistocene immediately above the Pliocene/Pleistocene boundary (1.6 m.y.), at 0.6 m.y., and during the late Pleistocene. Marked shift in coiling directions within Pulleniatina populations and Globorotalia s.l. is observed to coincide with the frequency changes. There was marked increase of δ l8O values in oxygen isotopic record of foraminiferal tests around 2-3 m.y. (Late Pliocene) and within the Pleistocene. Major faunal turnover accompanied by changes in coiling synchronous with the isotopic shifts, suggest these faunal changes to be climatically induced.
Response of Northern Indian Ocean deep-sea benthic foraminifera to global climates during Pliocene-Pleistocene
(1990) Anil K. Gupta; M.S. Srinivasan
The Northern Indian Ocean (DSDP Site 214) benthic foraminifera have been examined quantitatively to understand their response to the global climatic events and to determine the history of bottom-water circulation in the Northern Indian Ocean during Pliocene-Pleistocene.Uvigerina spp.,Cibicides kullenbergi, C. wuellerstorfi, Globocassidulina pacifica, G. subglobosa, Oridorsalis umbonatus andBulimina alazanensis are the dominant members of the benthic assemblage and reveal significant changes in distribution patterns. Based on benthic foraminiferal frequency changes, four intervals of major faunal and climatic turnover have been recognized at 5.2-5.1 Ma, 3.9-3.2 Ma, 3.2-3.1 Ma and 3.1-0.6 Ma. The interval between 5.2-5.1 Ma is marked by widespread Antarctic glaciation, deep-sea hiatuses, bottom-water cooling, increased upwelling, high sedimentation rates, highestUvigerina abundances and intensified bottom-water circulation. During 3.9-3.2 Ma the bottom waters were warmer and bottom-water activity waned, with a sharp decline inUvigerina abundance and increase inCibicides. The interval between 3.2-3.1 Ma was a time of bottom-water cooling and coincides with a global benthic positive oxygen isotopic shift, Antarctic ice volume increase and possible initiation of Northern Hemisphere glaciation. The Late Pliocene and Pleistocene interval (3.1-Recent) is punctuated by major changes in benthic foraminiferal assemblages, warm/cold cycles, major glacial/interglacial intervals, increase in polar ice volume and intensification of upwelling. On the basis of cumulative percentages ofUvigerina andCibicides, nine intervals of major bottom-water cooling have been inferred in the Pliocene and two in the Pleistocene at Site 214 reflecting the major changes in bottom-water circulation. © 1990 Elsevier Science Publishers B.V.
Stratigraphy and depositional environments of Neogene limestones of Andaman- Nicobar Islands, Northern Indian Ocean.
(1981) M.S. Srinivasan; B.K. Chatterjee
Carbonate rocks are widespread on the Andaman-Nicobar Islands, northern Indian ocean, ranging in age from Early Miocene to Pleistocene. Lithologically they range from deep water to shallow water calcarenites. Thin section analysis of the limestones has revealed a number of major lithofacies. They exhibit sequential changes in their fabrics, biogenic and clastic constituents. Depths of deposition ranged from high energy, shallow neritic at the beginning of Early Miocene to progressively lower bathyal. The sudden influx of glass shards in the later Early Miocene suggests explosive volcanism in neighboring areas. During this interval of basinal subsidence, the limestones received abundant argillaceous material from subaerial erosion of nearby volcanic terrain. Differing conditions in Late Miocene may be attributed to tectonism in the Andaman sea region. Thereafter, younger limestone facies of Plio-Pleistocene age, reflect a shoaling upwards.-from Authors Miocene Pleistocene lithofacies fabrics biogenic clastic constituents tectonism Indian ocean
The future of geology
(2012) M.S. Srinivasan
[No abstract available]