The Eocene succession of Garo Hills, Assam, India

Abstract

SUMMARYBased on the distribution of several stratigraphically important species three distinct larger foraminiferal zones are recognized in the Middle-Upper Eocene succession of Garo Hills, Assam, India. A comparison of these zones with larger foraminiferal assemblages from other Middle-Upper Eocene successions in the Indian region is attempted and observations are made on the demarcation of the Middle and Upper Eocene boundary and the classification of the Upper Eocene succession in this region.

The youngest marine deposits preserved in southern Tibet and disappearance of the Tethyan Ocean

“…These units are succeeded by the Barail Formation (Samanta, 1965(Samanta, , 1968(Samanta, , 1969Singh and Pratap, 1983;Alam et al, 2003;Lokho and Tewari, 2011). The Sylhet Limestone Group yields Nummulites, Assilina and Discocyclina assemblages, which indicate shallow marine deposition similar to that in the lesser Himalaya region.…”

“…The Kohat Formation consists of shale and limestone in the lower part, and Nummulites limestone and Alveolina limestone in the middle and upper part, respectively (Pivnik and Wells, 1996). The Nummulites, Assilina and Alveolina assemblages Afzal et al (2009), Mathur et al (2009), Mirza et al (2005, Samanta (1968), Singh and Pratap (1983), Tripathi et al (1988), Tripathi and Mamgain (1986), Wan (1987Wan ( , 1990, Willems (1993), Willems et al (1996).…”

“…The Sylhet Limestone Group yields Nummulites, Assilina and Discocyclina assemblages, which indicate shallow marine deposition similar to that in the lesser Himalaya region. The Kopili Formation consists of shale and marl, with abundant foraminifers and molluscs in the lower part and is poorly fossiliferous in the upper part, indicating a change from shallow marine to deltaic sedimentation (Samanta, 1968;Najman et al, 2008). Some species from the Sylhet Limestone also appear in the upper part of the Zhepure Formation.…”

“…South of the eastern Himalayan syntaxis, the collision-related final marine sediments outcrop as the lower Eocene Rengging Formation and the upper lower Eocene to Middle Eocene Yinkiong Formation in the Siang window region of Assam-Arakan Basin (Tripathi et al, 1978(Tripathi et al, , 1981Tripathi and Mamgain, 1986;Tripathi et al, 1988;Acharyya, 2007;Acharyya and Saha, 2008). Even younger final marine deposits occur in the Bengal basin, where the Sylhet limestone and overlying Kopili Formation are of Middle to upper Eocene age (Samanta, 1965(Samanta, , 1968(Samanta, , 1969Singh and Pratap, 1983;Alam et al, 2003).…”

Bartonian orthophragminids with new endemic species from the Pirkoh and Drazinda formations in the Sulaiman Range, Indus Basin, Pakistan

“…Larger benthic foraminifera (LBF), such as nummulitids, orthophragminids, alveolinids and rotaliids, constitute the dominant faunal element in these deposits (Afzal, Wıllıams, Leng, Aldrıdge, & Stephenson, 2011;Hottinger, 2014;Racey, 1995;Schaub, 1981;SerraKiel et al, 1998;Zhang, Willems, & Ding, 2013), which are generally referred to as 'Nummulitic limestone' . The middle Eocene shallow-marine deposits with prolific development of LBF are exposed in some parts of the Indian Subcontinent: in the Sulaiman and Kirthar ranges in Pakistan, Kutch and Cambay basins in western India, and in the Assam-Meghalaya regions in eastern India (Eames, 1952a(Eames, , 1952bNagappa, 1959;Nuttall, 1926;Özcan, Saraswati, Hanif, & Ali, 2016 and references therein; Samanta, 1968;Samanta & Lahiri, 1985). In the Sulaiman Range, to the west of Himalayas, the middle Eocene deposits, informally named 'Discocyclina beds' , are known for the abundant occurrence of orthophragminids and nummulitids and also for the remains of sea cows and archaeocete whales, described from the Drazinda Formation (Gingerich, Arif, Bhatti, Anwar, & Sanders, 1997 and references therein).…”