Earthquake-induced soft sediment deformation (SSD) structures from the Bilara limestone formation, Marwar basin, India

Abstract

The Neoproterozoic Bilara limestone Formation of the Marwar Group, Rajasthan, India exposes metresthick layers of soft sediment deformation (SSD) structures at different stratigraphic levels which could be traced over hundreds of metres on the outcrop scale. The SSD structures include disharmonic folds, lowangle thrusts, distorted laminae, fluidisation pipes, slump and load structures, homogeneities, diapirs, etc. Whereas SSD structures suggesting tensional stress, viz., intrastriatal graben, fluidisation, slump, etc. dominate in the lower part of the Bilara succession, features implicating compression, viz., folds, lowangle thrust are prevalent in the uppermost part. Since SSD structures are mostly confined within the algal laminites, we interpret that enhanced micritic fluid pressure below early cemented algal carbonate played a major role in laminae deformation. Depending on the degree of lithification and pore-water pressure, deformation features formed either plastically or led to diapiric injection at enhanced pore water pressure. Separated by near-horizontal underformed strata, the SSD layers, traceable over hundreds of metres, are interpreted as products of seismic shacking. Considering the time frame of the Marwar basin, i.e., the Precambrian-Cambrian transition, the SSD horizons present within the Bilara succession may hold the potential for the correlation with SSD structures reported from the time-correlative stratigraphic successions present in erstwhile adjoining tectonic terrains, e.g., China, Siberia, etc.

Recognising surface versus sub-surface deformation of soft-sediments: Consequences and considerations for palaeoseismic studies

“…Maltman, 1994a, Festa et al, 2016Alsop et al, 2019). SSD can be triggered by either external deformation (allogenic/exogenic triggers), such as tectonics and earthquakes, or by processes that develop in the depositional environment (autogenic/endogenic triggers), including rapid sedimentation and floods (e.g., Chakraborty et al, 2019). These different triggers have been discussed by Moretti and Sabato (2007); Moretti and Van Loon (2014) and Van Loon (2014).…”