MESOZOIC DELTAIC SYSTEM AND SEQUENCE STRATIGRAPHIC MODEL OF THE LOWER JURASSIC DATTA FORMATION ALONG THE WESTERN SALT RANGE, PAKISTAN

Abstract

In this research, the Early Jurassic Datta Formation from three outcrop sections of the western Salt Range has been extensively studied to elucidate facies architecture, sedimentary features, diagenetic features, sequence stratigraphy, and depositional model. Datta Formation is well exposed with massive thickness in the western Salt Range and the Trans Indus Ranges, while tapering in the central Salt Range further eastward, it dies out. Its mainly dominated by variegated sandstone, siltstone, shale, fire clays, laterites, and carbonates. Seven lithofacies has been identified and interpreted in the Datta Formation, i.e., (i). Fluvial Meandering Lithofacies (JDL-01), (ii). Braided Fluvial Lithofacies (JDL-02), (iii). Lateritic Lithofacies (JDL-03), (iv). Flood Plain Lithofacies (JDL-04), (v). Siliciclastic Lagoon Lithofacies (JDL-05), (vi). Carbonates dominant Lagoon Lithofacies (JDL-06), (vii). Swamps related Deltaic Lithofacies (JDL-07). Sequence stratigraphic analysis is primarily based on recognizing sequence surfaces, finning-coarsening upward trends, and types of facies. Two transgressive-regressive cycles are identified in the south-eastern section (Kassan Nala and Kaowali sections), while four sequences are identified in the Nammal Gorge section. These sequences are started with the underlying sequence boundary of LST and ended with the sequence bounding surface after HST. Datta Formation is possibly deposited in fluvial to deltaic environments in the study area, revealing a prograding delta with a shoreline oriented in the SW-NE direction and the siliciclastic detritus fed the fluvial system running over the Indian cratonic basement in the direction of N-NW. The lower part of the formation is deposited in fluvial settings, probably in the incised valley. The point bar sequences result from meandering channel facies and show association with overlying flood plain/overbank facies. Moreover, the lagoonal facies mainly covered the upper part of the formation and displayed mixed lithologies of delta plain to delta front setting. However, the repetition of these lithofacies in the study area at several points indicates the recurrence of depositional phases. The carbonaceous shales and coal streaks are evident by the presence of swamp or marshy lands. These conditions meet the criteria of deltaic settings. Furthermore, several laterites and fire clay horizons are also argue periodic sub-aerial exposure of the depositional area. Thus it is concluded that the depositional area lies in a fluvial to deltaic setting with major distributary channels and their flood plain in the adjoining delta plain to delta front part.