Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

Pratul Kumar Saraswati ¹, R. Ramesh ²

Affiliations
1 Department of Earth Sciences, I.I.T., Powai, Bombay 400076, IN
2 Physical Research Laboratory, Navrangpura, Ahmedabad 380009, IN

Abstract

Developments in stable oxygen and carbon isotope studies of the sediments from oceanic realm has established their potential use as stratigraphic markers. Whereas, other schemes of stratigraphic classifications for the Cenozoic sediments of Kutch are available, this paper attempts to establish the stable isotope stratigraphy of a part of the sequence. It is observed that the δ¹⁸0 and δ¹³C variation significantly correspond to the chronostratigraphic units of this area. The negative δ¹³C of the Kakdian Stage (Berwali Series) shifts characteristically to positive values in the Babian Stage (Berwali Series) and then swings back to negative values in the Bermoti Series. The Kakdian Stage and the Bermoti Series, both having negative δ¹³C, can be differentiated by their respective δ¹⁸O range.

Keywords

Stable Isotopes, Eocene-Oligocene, Stratigraphy, Kutch.

Full Text

     

Pratul Kumar Saraswati ¹

Affiliations
1 Department of Earth Sciences, I.I.T., Powai, Bombay-400 076, IN

Abstract

The biometric parameters of Lepidocyclina (Nephrolepidina) from the Oligocene - Early Miocene sections of Kutch, Saurashtra and Quilon are studied to evaluate their biostratigraphic importance. Following the biometric concept L. (N.) isolepidinoides is identified in the Early Oligocene sequence of Kutch and L. (N.) sumatrensis from the Early Miocene sections of Kutch, Saurashtra and Quilon. The nephrolepidines of Kutch appear to show agradual sustained change withintelVal of arrested evolution. The average value of parameter - A stagnated at about 42% during Oligocene and increased to nearly 46% in Early Miocene times. The value of C increased from 1.7 in Early Oligocene to 2.6 in Late Oligocene and 3.9 in Early Miocene. During this interval F increased from 1.2 to 2.7. The parameters A, C and F are found to be most dependable in inferring the relative age of the nephrolepidine assemblages from the studied localities. The staggering values of E and dc prevent them from a reliable use in biostratigraphy.

Keywords

Biometry, Lepidocyclina, Biostratigraphy Foraminifera.

Full Text

     

Pratul Kumar Saraswati ¹, Arun Kumar ²

Affiliations
1 Department of Earth Sciences, Indian Institute of Technology, Powai, Bombay 400 076
2 Department of Earth Sciences, Indian Institute of Technology, Powai, Bombay 400 076, IN

Abstract

Analysis of an Indo-Pacific species, Lepidocyclina (Nephrolepidina) sumatrensis shows that the protoconch diameter varies with latitude. The data plotted on the reconstructed continental positions for the Miocene epoch shows that forms away from the equator are characterised by progressively larger protoconch diameter. An average value of protoconch diameter >200μ is seen to occur from 15° to 30° latitude while those with <200μ are confined within 15° latitude. This observation can have potential use in inferring the climate of the geological past.

Full Text

   

Pratul Kumar Saraswati ¹

Affiliations
1 Department of Earth Sciences, Indian Institute of Technology, Powai, Bombay-400 076, IN

Abstract

No Abstract.

Full Text

   

Pratul Kumar Saraswati ¹

Affiliations
1 Department of Earth Sciences, Indian Institute of Technology, Bombay - 400076, IN

Abstract

Sea-level change is known to have influenced the evolution of marine life. It is examined here how faunal diversity and rates of taxic evolution are related to change in sea-level and stability of the sea-level cycles. Evolutionary metrics of Palaeogene larger foraminifera are calculated and stability of sea-level cycles are determined using number and average duration of third order cycles in each stratigraphic interval. Generic diversity and the rates of origin and extinction individually do not show one to one correspondence either with transgression-regression or with the stability of the sea-level cycles. The rate of extinction relative to the rate of origination, however, is found to be significantly affected by the stability of the sea-level cycles. The rate of extinction exceeds the rate of origin during the periods of low stability. Regression, assisted by unstable sealevel cycles and possibly sharp climatic deterioration caused extinction maxima of larger foraminifera in Late Eocene.

Keywords

Palaeontology, Foraminifera, Evolutionary Metrics, Eustasy, Palaeogene.

Full Text

     

kanchan Das Gupta ¹, Pratul Kumar Saraswati ¹, Utz Kramar ², C. N. Ravindran ³, Doris Stuben ², Zsolt Berner ²

Affiliations
1 Department of Earth Sciences, IIT Bombay, Mumbai - 400 076, IN
2 Institute for Mineralogie und Geochemie, Fritz-Haber-Weg 2, 76131 Karlsruhe, DE
3 Regional Geology Laboratories, ONGC, Panvel, Phase I, Mumbai - 410 221

Abstract

The clays of Karai Formation (Uttatur Group) contain well-preserved planktonic and benthic foraminifera of Albian-Turonian age. The pristine tests of planktonic and benthic foraminifera were analyzed for their oxygen isotopic compositions. The δ¹⁸0 values of planktonic foraminifera, comprising Whiteinella archaeocretacea, Marginotruncana sp., Rotalipora reicheli, Praeglobotruacana stephani and Globigerinelloides sp. indicate the maximum near-surface temperatures of 29°C. The bottom water temperature, estimated on benthic foraminifera1 species Gyroidinoides sp., Quadrimorphina sp., Gavelinella sp., Lenticulina sp. and Pleurustomella sp., is about 2. This is in agreement with the palaeoclimatic conditions inferred on fossil assemblages.

Keywords

Palaeotemperature, Stable isotopes, Foraminifera, Cretaceous, Cauvery Basin, TamilNadu.

Full Text

     

Pratul Kumar Saraswati ¹, kazuyuki Shimoike ², Kenji Iwao ², Arijit Mitra ³

Affiliations
1 Department of Earth Sciences, Indian Institute of Technology, Powai, Mumbai - 400 076, IN
2 Akajima Marine Science Laboratory, Aka, Zamami-son, Okinawa, 901 -33, JP
3 Department of Geology, Banaras Hindu University, Varanasi - 221 005, IN

Abstract

This paper examines the bathymetnc distribution of larger foraminiferal species on the reef flat and reef slope of Akajima Island, Iocated near Okinawa in the Ryukyu island arc of Japan, It also estimates the total skeletal carbonates contributed by larger foraminifeia in the reef sediments of this island. Three distinct assemblages are recognized with increasing water-depths: (i) Marginopora vertebralis and Baculogypsina sphaerulata are confined to reef flat, occurring at a water depth of 1.5 m (ii) Peneraplis planatus and Neorotalia calcar occur within 30 m bathymetry followed down depth by (iii) Operculina ammonoides, Nummulites venosus, Alveolinella quoyi and Baculagypsinoides spinosus between 30 and 60 m. Cycloclypeus is the deepest dwelling genus, making its first appearance at 60 m. Larger foraminifera contribute about 5.8% of the sediments accumulated on reef flat and reef slope of Akajima, which is significantly higher than the global average. There is considerable variation in relative contributions by miliolids and rotaliids on reef flat and reef slope. On the reef flat, miliolids contribute 64% of the total skeletal carbonates produced by larger foraminifera, whereas on reef slope it contributes only about 5%.

Keywords

Foraminifera, Coral Reef, Carbonates, Akajirna, Okinawa, Japan.

Full Text

     

Pramod Kumar ¹, Pratul Kumar Saraswati ¹, Santanu Banerjee ¹

Affiliations
1 Department of Earth Sciences, Indian Institute of Technology Bombay, Mumbai - 400 076, IN

Abstract

The Early Miocene succession of Kutch represents a mixed carbonate-siliciclastic depositional system. The carbonate part of the succession, characterized by high abundance of shallow marine benthic fauna, hosts typical shell concentrations (also referred as shell beds). The thickness of shell concentrations vary in scale from 5 cm to 100 cm and are separated by poorly fossiliferous to barren silty shales/siltstones. Based on taphonomic and sedimentological observations, shell concentrations are classified as lag, event, composite/multi-event and hiatal types. The occurrence of different types of shell concentrations in the background of sequence stratigraphic framework is the main theme for the present study. Overall, the shell concentrations occupy the middle part of the sequence i.e. upper part of the transgressive systems tract and lower part of the highstand systems tract. Lag concentrations are found in the lower part of the sequence while composite concentrations, the major contributors in the sequence, occur in upper part of the transgressive systems tract and in the lower part of the highstand systems tract. The hiatal concentrations are associated with maximum flooding surface while the position of event concentrations is independent of sequence stratigraphic framework. The shell concentrations occupy marine flooding surface or marine ravinement surface, thus mark parasequence boundaries.

Keywords

Shell Concentration, Mixed Carbonate-Siliciclastic System, Systems Tract, Early Miocene, Kutch, Gujarat.

Full Text

     

Jahnavi Punekar ¹, Pratul Kumar Saraswati ¹

Affiliations
1 Department of Earth Sciences, IIT Bombay, Mumbai – 400 076, IN

Abstract

A highly diverse assemblage of mammal and other continental vertebrate fossils is reported in recent years from Vastan lignite mine (21°25'47" N; 73°07'30" E). Its importance in testing palaeobiogeographic hypothesis of mammalian dispersal in to or out of India has necessitated a definite age of the sequence. Nummulites burdigalensis is the only age diagnostic foraminifer in the section. This species is widespread in the Indian sedimentary basins and used to mark Early Eocene strata. In the present study two subspecies of Nummulites burdigalensis, viz., Nummulites burdigalensis burdigalensis and Nummulites burdigalensis kuepperi, are distinguished which led to further biostratigraphic refinement. Their concurrence in the section implies basal Cuisian age and shallow benthic zone SBZ 10 (most likely the lower part). The examination of this species from Kutch indicates the occurrence of evolutionarily advanced subspecies Nummulites burdigalensis cantabricus of middle Cuisian age (SBZ 11). Contrary to some recent reports, the study rules out the occurrence of N. globulus or any other Ilerdian foraminifer from the mine section.

Keywords

Vastan lignite, Nummulites, Eocene mammals, Cambay Shale, Kutch.

Full Text

     

Pratul Kumar Saraswati ¹, Urbashi Sarkar ¹, Santanu Banerjee ¹

Affiliations
1 Department of Earth Sciences, IIT Bombay, Powai, Mumbai - 400 076, IN

Abstract

Three successive subspecies of Nummulites burdigalensis evolved from N. solitarius. These include N. burdigalensis keupperi, N. burdigalensis burdigalensis and N. burdigalensis cantabricus. The evolving lineage is traced in a borehole drilled through the Naredi Formation of Kutch. The associated taxa include N. solitarius and N. fraasi in the lower part and Assilina laxispira and A. spinosa in the upper part of the formation. The better stratigraphic resolution achieved by subspecies identification and the lately redefined Ilerdien Stage in the background of Early Eocene carbon isotope excursion marker, lead to constrain the age of Naredi Formation as Early Eocene, ranging from shallow-benthic zones SBZ6 to SBZ11.

Keywords

Nummulites, Eocene, Kutch Basin, Gujarat.

Full Text