LATE CRETACEOUS-PALEOCENE MICROBIOTA FROM DECCAN VOLCANIC PROVINCE, PENINSULAR INDIA

Abstract

This dissertation reports on biostratigraphic, paleoenvironmental, paleoecologic and biogeographic aspects of end Cretaceous-early Paleocene intertrappean deposits, based on investigations carried out in nine selected sections across the Deccan Traps volcanic province of peninsular India. These investigations (Dayapar, Virani, Lakshmipur, Anjar in District Kutch, Gujarat; Jhilmili in District Chhindwara and Phulsagar in District Mandla, both in Madhya Pradesh; Nahardi in District Jhalawar, Rajasthan; Papro in District Lalitpur, Uttar Pradesh; Duddukuru in East Godavari District, Andhra Pradesh) provide new insights into our understanding ofecosystems that existed during the Deccan Traps volcanic episode. The discovery of planktic foraminifers and brackish water ostracods in the Deccan intertrappean deposits at Jhilmili in central India is one of the most important highlights of this dissertation with major implications for central India's paleogeography during the K-T transition. The discovery indicates that the main Deccan province, generally considered to be terrestrial in nature, may also contain intervals of brackish to marine deposition. The recovered assemblage comprises a number of early Danian (P1a) planktic foraminifers (including Parasubbotina pseudobulloides, Subbotina triloculinoides, Praemurica taurica and Globigerina (E.) pentagona) and a brackish water ostracod species (Neocyprideis cf. N. raoi) The discovery has a two-fold significance. First, it reveals a marine seaway in central India during the Maastrichtian - early Paleocene and second, it supports that the K-T boundary is at or near the end of the main phase of Deccan volcanism (e.g., top of the Ambenali Formation) consistent with recent results from Rajahmundry (Keller et ah, 2008; Jay and Widdowson, 2008). The proposed marine incursions during the K/T transition may possibly have followed the Narmada and Tapti rift zones where a major transgression is already known to have existed during the Cenomanian- Turonian (Bagh Beds). The recovery of a freshwater ostracod assemblage (12 spp.), for the first time from the Paleocene-aged Deccan intertrappean deposits of Papro (District Lalitpur, Uttar Pradesh) is another important find being reported in this doctoral investigation. The assemblage, with strikingly similarities to those previously documented from a number of Maastrichtian Deccan intertrappean deposits, including some with dinosaur remains (such as Dayapar and Anjar in Kutch), shows that the intertrappean freshwater ostracods were one of the least affected communities, at least qualitatively, across the Cretaceous-Tertiary transition. Paleoecologically, the analysis of Deccan intertrappean ostracods from widely separated sections (Nahardi, Dayapar, Phulsagar, and Papro) reveals an admixed assemblage suggestive of a lacustrine system that comprised a core of permanent water and a periphery that was subject to intermittent desiccation during dry seasons. A preliminary attempt was made for the first time to analyze the carbon and oxygen stable isotopes of ostracod shells recovered from the Lakshmipur intertrappean deposits of Kutch. Although essentially tentative, the study suggests that evaporative conditions prevailed intermittently during the deposition of Lakshmipur intertrappeans. However, this tentative conclusion needs supportive evidence from the presence of evaporative minerals. Investigations of biogeographic aspects of the intertrappean freshwater ostracods have helped to reconcile a long standing apparent conflict between the geophysical and paleontological data. These freshwater ostracods show strong endemism at species level and do not indicate close Asian affinities as previously claimed. At the generic level, the intertrappean ostracods are cosmopolitan and show nearly as much affinity with European and North American Cretaceous ostracods as they do with other Asian faunas. The extensive ostracod endemism suggests India's geographic isolation around the K-T boundary time, consistent with the traditional geophysical data that show India as northward moving island continent during this interval.