Occurrence of Tidalites in the Mesoproterozoic Subtidal-Intertidal Flat, Lalsot Sub-basin, North Delhi Fold Belt, Rajasthan, India

Abstract

The Mesoproterozoic Bayana Formation (Alwar Group) in the Lalsot sub-basin, North Delhi Fold Belt, NW India, is represented by (i) conglomerate-rich alluvial fan-braided river deposits near the lower part, followed by (ii) reworked conglomerate-sandstone deposits with significant tidal influences in the middle part and (iii) predominant tide-wave influenced marginal marine deposits in the upper part, in an overall fining-up succession. Tidalites are well-preserved in the upper part of the siliciclastic Bayana succession, and are reported here as one of the oldest records of tidal depositional systems within the Aravalli cratonic area, NW India. Tidalites are represented by tidal bundles, tidal beddings and tidal rhythmites. Tidal bundles, associated with reactivation surfaces indicating time–velocity asymmetry, sigmoidal bundles, herring-bone cross-strata, are abundant in sand-dominated facies succession formed in subtidal condition. Tidal beddings and tidal rhythmites are preserved in mud-dominated facies successions and are commonly associated with asymmetric/symmetric ripple forms, and desiccation cracks, indicating intertidal flat depositional setting. Time-series analysis of continuous rhythmic foreset bundles manifests neap–spring tidal cycles with synodic month lengths of27.4 lunar days. Systematic analysis of the architecture of the tidalites signifies rapid shift in sedimentation from subtidal to intertidal flat in a meso- to macro-tidal setting. Transition from immature fan-fluvial depositional system in the basal part to matured subtidal-intertidal system in the upper part of the overall retrogradational Bayana succession signifies base level change under the influence of sea level fluctuations and/or basinal subsidence in the Mesoproterozoic Lalsot sub-basin.