Naredi Fm

YpresianProgress in dating of Naredi Formation from 1971 to 2018The Naredi Formation was initially assigned Early Eocene age by Biswas and Raju (1971). Later, the lower part of the formation in the type section at Naredi was assigned Late Paleocene age (Biswas, 1992) due to the report of N. indicus (Pandey and Ravindran, 1988), a species that was originally described as a new variety of N. globulus from the uppermost Ranikot Fm beds of Pakistan. Saraswati et al. (2012) re-examined the species and opined that it is N. globulus nanus and referred this to shallow benthic-foraminifer zone SBZ8. It may also be noted that the uppermost Ranikot Fm is now referred to Early Eocene (Wakefield and Monteil, 2002). The section in the type area of the Naredi Fm represents only a part of the formation. A complete succession is found in a borehole, approximately 9 km southwest of the type section, where the lower part contains N. solitarius and N. fraasi and it was assigned to SBZ6 (see Saraswati et al., 2012). The zones SBZ5 and SBZ6 are indistinguishable because index species of both biozones co-occur (Scheibner and Speijer, 2009) and therefore the lowermost part of the Naredi Fm is referred to SBZ5 - SBZ6, at the base of the Ypresian. The planktic foraminifera are rare and represented by Chiloguembelina trinitatensis. Considering the associated larger foraminifera species, the basal part of the formation may correspond to planktic zone E2. In the borehole section, a hiatus of 7 Myr is estimated between the Deccan Traps Fm basalt (69 Ma to 63 Ma; Pande, 2002) and the overlying sediments of the Naredi Fm (SBZ5). The uppermost fossiliferous strata of the Naredi Fm contains N. burdigalensis cantabricus, Assilina spinosa and A. laxispira, and therefore referred to SBZ11 (Punekar and Saraswati, 2010; Saraswati et al., 2012). The associated planktic foraminifera includes Chiloguembelina crinita and Acarinina quetra. The planktic and larger benthic foraminifera constrains it to planktic zone E6. The topmost beds of the formation are unfossiliferous and therefore no definite age could be assigned. It is likely that the exclusion of Nummulites and Assilina from the upper few meters of the section is ecological and it may also be part of SBZ11. The Naredi Formation is thus assigned to Ypresian Stage and to the shallow benthic zones SBZ 5/6 to 11 and planktonic foraminifer zones E2 to E6. There is thus no evidence of marine Paleocene rocks in on-land Kutch, and the earliest marine transgression took place at the onset of the Ypresian (Source: Saraswathi et al., 2016). Strontium Isotope Stratigraphy (Dating): Anwar et al., 2013 suggested that the biostratigraphically constrained Sr isotope values indicate the Naredi Formation is of Early Eocene age spanning from 55 to 49.9±1.5 Ma.

Sarnavan, Bajpai and Raju (2008) recognized nine minor cycles of sea-level fluctuations in type section. The paleobathymetry ranges from non-marine to 45 m.

[Figure 5: Stratigraphic details of the Naredi Formation depositional cycles in Kutch (after P.K. Saraswathi et al., 2016)]