Nummulitids, lepidocyclinids and Sr-isotope data from the Oligocene of Kutch (western India) with chronostratigraphic and paleobiogeographic evaluations

György Less,Gianluca Frijia,Ercan Özcan,Pratul K Saraswati,Mariano Parente,Pramod Kumar

doi:10.1080/09853111.2018.1465214

Abstract

Due to its intermediate geographical position between the Mediterranean and W Pacific, the Oligocene shallow-marine sequence of Kutch (India) is of key importance in paleobiogeographical interpretations. Larger benthic foraminifera (LBF) are a fundamental link for the correlation between the Mediterranean shallow benthic zones (SBZ) and the W Pacific ‘letter stages’. LBF were re-evaluated by morphometric studies of the internal test from five stratigraphic sections of the Maniyara Fort Formation. Based on their significant affinity to coeval fauna in the Mediterranean, they were assigned to W Tethyan SBZ zones, supported by Sr-isotope stratigraphy. In the Basal Member, traditionally considered as early Rupelian, we identified Nummulites bormidiensis, N. kecskemetii and Heterostegina assilinoides assigning it to the early Chattian SBZ 22B Zone. The Coral Limestone Member, previously considered as late Rupelian, is also assigned to this zone, for the presence of N. bormidiensis, Eulepidina formosoides-dilatata and Nephrolepidina morgani-praemarginata. Its early Chattian age (26.5–29 Ma) is further supported by Sr-isotope data. Miogypsinoides complanatus and Spiroclypeus margaritatus in the Bermoti Member (the top of the formation) document the late Chattian SBZ 23 Zone and the Sr-isotope data (22.5–24 Ma) place it close to the Oligocene–Miocene boundary.

Highlights

The 30–35 m thick Oligocene succession of the Maniyara Fort Formation (Kutch Basin, western India) represents a mixed carbonate-siliciclastics sequence deposited in a shallow marine setting on the western margin of the Indian subcontinent
The formation is subdivided into four members, which are, from bottom to top: (a) The Basal Member (4–4.5 m thick), whose larger foraminiferal assemblages mainly consist of reticulate Nummulites, and subordinate Heterostegina and Operculina (Op. complanata)
There exists a general agreement among Indian stratigraphers (e.g. Biswas, 1992; Raju, 2011) that the lower three members of the Maniyara Fort Formation belong to the Rupelian, whereas the Bermoti Member is generally referred to the Chattian

Summary

Introduction

The 30–35 m thick Oligocene succession of the Maniyara Fort Formation (Kutch Basin, western India) represents a mixed carbonate-siliciclastics sequence deposited in a shallow marine setting on the western margin of the Indian subcontinent. It is very rich in larger benthic foraminifera (LBF), whose distribution – according to most previous works (as summarized e.g. by Biswas, 1992; Raju, 2011 and Catuneanu & Dave, 2017) – covers almost the entire duration of the Oligocene period.

Methods

Results

Conclusion