Biostratigraphy, microfacies and sequence stratigraphic analysis of the Chorgali Formation, Central Salt Range, northern Pakistan

Abstract

In present study three sections of early Eocene Chorgali Formation were measured from Pail, Wanhar and Sar Kalan area, Central Salt Range, Punjab, Pakistan. At these localities the Chorgali Formation is about 12m, 8.8m and 15.1m thick, respectively. A total number of 53 samples were collected, 18 from Pail section, 18 from Wanhar section and 17 from Sar Kalan section. Eocene Chorgali Formation in this area is consisted of grey to pale grey limestone, greenish grey shale intercalations and argillaceous limestone. At Pail section nine various microfacies were recorded i.e., Mudstone microfacies (CGP1), Bioclastic mudstone microfacies (CGP2), Nummulites-Lockhartia wackestone microfacies (CGP3), Nummulitidae wackestone microfacies (CGP4), Bioclastic wackestone microfacies (CGP5), Alveolina-Nummulites wackestone microfacies (CGP6), Alveolina wackestone microfacies (CGP7), Nummulites-Alveolina wackestone microfacies (CGP8) and Intraclastic-peloidal packstone microfacies (CGP9).At Wanhar section five facies were recorded i.e., Rotaliidae wackestone microfacies (CGW1), Nummulitidae Wackestone microfacies (CGW2), Nummulites- Lockhartia wackestone microfacies (CGW3), Nummulites-Assilina wackestone microfacies (CGW4), Intraclastic-peloidal packstone microfacies (CGW5).At Sar Kalan section total four facies were recorded i.e., Bioclastic wackestone microfacies (CGSK1), Nummulites-Assilina wackestone microfacies (CGSK2), Nummulitidae wackestone microfacies (CGSK3), Intraclastic-peloidal packstone microfacies (CGSK4).The assemblage of larger foraminifera were recorded to describe the biota of the formation and to interpret the paleo-environments with implications of sequence stratigraphy. Field observations and microfacies analysis suggest that the deposition of Chorgali Formation at these localities probably took place in inner shelf conditions. Presence of shallow water benthic larger foraminifer's further support lagoon to bay environment of the genesis of the formation. The formation might have been deposited because of falling stage system tract (FSST), showing a progradational pattern of deposition. The basin ward shift of deposition indicates the regressive sequence.