Morphometric evaluation of diverse ripple structures in the Alwar Group at Jamwa Ramgarh in NE Rajasthan, North Delhi Fold Belt, NW India

In this study we describe a complex set of well-preserved ripple structures from the Alwar Group quartzites (quartz arenite) of Mesoproterozoic Delhi Supergroup in NW India. Exposed in a road section near Jamwa Ramarh (to the east of Jaipur city), a large abundance and diversity in ripple shape, size, wave amplitude and mode of occurrence is unique for a small geographic area. The studied ripples are predominantly symmetric in shape, showing bifurcations, sinuous types, pointed crest with rounded trough, etc. Occasional current and criss-cross, and mega ripples are also present. Their symmetric shape suggests a wave dominant environment. The Vertical Form Index (VFI) values or Ripple Index values below 15 further rule out any possibility of a wind origin for them. The criss-cross and interference ripples point toward the presence of a high energy river system in the vicinity. The statistical analysis of ripple morphological parameters indicates deposition of quartz arenite under shallow water conditions (< 3 m depth). Based on various morphometric analyses, we infer continental shelf with variable depth for the development of these wave ripples. Based on the crest-line criterion, the inferred paleocurrent direction was from the NW.