INITIAL SURVIVORSHIP OF NONMARINE MOLLUSCAN FAUNAS IN END-CRETACEOUS DECCAN INTERTRAPPEAN STRATA, INDIA

The record of nonmarine mollusks from the Deccan Plateau of peninsular India has remained poorly known since their initial study in the mid-1800s. With more than 100 localities now under study, mollusks are now reported from at least 14 localities from the Lameta Formation (Kl) (infratrappean) and 15 localities from the first three Deccan intertrappean (KDi) intervals in the states of Maharashtra (Chandrapur [Kl, KDi], Nagpur [KDi], Wardha [KDi], and Yavatmal [KDi] Districts) and Madhya Pradesh (Jabalpur [Kl], Sagar [Kl], and Chhindwara [KDi] Districts). Mollusks from two localities are now reported from an unnamed infratrappean unit and at multiple horizons from two localities from the Ir-bearing third intertrappean interval in the state of Gujarat (Kutch District [Kinf, KDi]). A main study area is along the eastern outcrop edge of the Deccan Traps in the Nand-Dongargaon Basin, where specimens are found in coarse and fine clastic sediments and commonly preserved as carbonate and chert steinkerns or external molds. Lacustrine paleoenvironments predominate all sections, but these conditions are variable, with marlstone beds varying in both clastic and faunal content. Channel deposits are rare, but still fossiliferous. Intertrappean molluscan-bearing sections average about 2 m, but vary in their fossil content and preservation based on local paleoenvironmental conditions and may covary in abundance with ostracodes. The K/P boundary has been preliminarily correlated in the above study area to be above all of the known molluscan occurrences. Only one intertrappean Paleocene molluscan locality (state of Uttar Pradesh) is presently known. The initial production of basalt lavas seems to have had little effect on the distribution and abundance of nonmarine mollusks existing in isolated intertrappean environments. The apparent lack of a fossil record interpreted just before (~350 Ka) the K/P boundary is part of ongoing investigations. Over 50 mollusk-bearing localities have yet to be assigned an intertrappean interval and many more mapped (Geological Survey of India) fossil localities have yet to be documented for their content or level. These records may permit further biostratigraphic organization and interpretation of the India end-Cretaceous extinction and survivorship record.