Comparison of tidalites in siliciclastics and carbonate systems: An outstanding example from Proterozoic Simla Basin, Western Lesser Himalaya

Significant progress has been achieved in the research of tide-dominated environments in the past two decades. This study highlights both the importance and diversity of tidal deposits. Development of better tools for... [ view full abstract ]

Significant progress has been achieved in the research of tide-dominated environments in the past two decades. This study highlights both the importance and diversity of tidal deposits. Development of better tools for recognizing tidalites (e.g., tidal bundles and tidal rhythmites) has also revealed that such deposits are much more common and extensive than previously thought. Several examples of ancient tidalites have been reported from all over the globe in previous literatures. But comparison of tidalites recorded in both siliciclastics and carbonates has not commonly been sited so far. The Proterozoic Simla Group, Lesser Himalaya serves a unique example in this regard. An attempt has been made in the present work to differentiate sedimentary facies and architectural elements of tidalites in both siliciclastics and carbonates depositional systems recorded in the basin. Lithofacies and microfacies analysis led to identification of 11 lithofacies and 4 architectural elements from the siliciclastics, 6 lithofacies and 3 architectural elements from the carbonates. The most diagnostic features for comparison of the two tidalite systems are sedimentary structures, textures, and architectural elements. Physical features such as flaser-lenticular bedding, mud/silt couplets, tidal rhythmites, tidal channels, tidal bundles, cross stratified successions, tidal bars and microbial structures are common to both the environments. Architecture of these tidalites attests to sedimentation in shallow subtidal to intertidal flat facies, affected by intermittent reworking by open marine waves/storms. Seventeen facies attributes were categorized into two major facies belts (FA1 and FA2). FA1 represents a prograding muddy pro-delta deposit whereas FA2 bears the signature of an inner-mid carbonate ramp deposit. Facies distribution indicates development of highstand systems tract (HST). The aggradational to progradational bedsets record the history of slow rise in sea level.

KeyWords: Proterozoic, Simla Basin, tidalites, inner-mid carbonate ramp, prodelta, highstand systems tract (HST)