Microbial mat mediated structures in the Ediacaran Sonia Sandstone, Rajasthan, India, and their implications for proterozoic sedimentation

Abstract

A strong influence of microbial mats on the physics of Neoproterozoic sedimentation is explored within a 60 m-thick stratigraphic interval within the Sonia Sandstone, Jodhpur Group, western India. This marine interval is bounded by two terrestrial units, its base being marked by a transgressive lag and the top by an unconformity. Progradation from upper neritic, above fair-weather wave base to supralittoral settings was later terminated by a transgression; deposits of lower shoreface-upper shoreface transition thus overlie supralittoral aeolian sandstones, the basal contact of the former deposits being marked by another transgressive lag.A wide spectrum and abundant examples of microbial mat or mat-derived structures supports unusual cohesiveness within granular sand deposited in a high-energy marine environment. The cohesiveness is manifested in abundant preservation of several delicate primary structures and also in their replication in overlying beds, even after they were subjected to high-energy currents.A low rate of sedimentation and severely restricted sediment reworking resulted from prolific mat growth, and consequent depletion in the sediment budget was manifested in openUP (April 2008) bedform migration and evolution. These factors could also have influenced the sequencebuilding pattern in a distinctive way, as is already reported from several Meso-and Neoproterozoic successions. Ubiquitous mat growth thus had the potential to impart significant distinctions to Proterozoic clastic sedimentary successions.

Forced regressive wedge in the Mesoproterozoic Koldaha Shale, Vindhyan basin, Son valley, central India

“…The frequent amalgamation of coarse sandstones, inferred as storm units with or without erosion, also corroborates the near-coastal condition of deposition of these units (Bose et al, 2001. The rectangular to polygonal desiccation cracks in non-cohesive sandstone owe their origin to microbial mats (cf., Noffke et al, 2001;Sarkar et al, 2008Sarkar et al, , 2014Eriksson et al, 2010;Samanta et al, 2011Samanta et al, , 2015. The wrinkles on sandstone bed-tops may have originated by gentle shear by waves or through currents acting on cohesive mat layers (Sarkar et al, , 2014.…”

“…HSTs was due to the influence of microbial mats (cf., Sarkar et al, 2005Sarkar et al, , 2008Sarkar et al, , 2014Eriksson et al, 2010). Their study area possibly represents a more seaward part where a gradual transition from outer shelf to shoreface had taken place.…”

Neoproterozoic substrate condition vis-à-vis microbial mat structure and its implications: Sonia Sandstone, Rajasthan, India

“…Noteworthy is that these structures show close association with a wide spectrum of microbial mat-related structures (Gerdes et al, 2000;Parizot et al, 2005;Sarkar et al, 2008;Samanta et al, 2011), but do not share morphological similarities with any of them.…”

“…600 Ma Sonia Sandstone (Sarkar et al, 2008) of the Jodhpur Group (Marwar Supergroup), western Rajasthan, India are described. Though very restricted in occurrence, these possible bioturbations are found on the fresh surfaces of bedding plane exposures and are unique in their appearance and morphology, showing close resemblance to Phanerozoic counterparts.…”

A case study of microbial mat-related features in coastal epeiric sandstones from the Paleoproterozoic Pretoria Group (Transvaal Supergroup, Kaapvaal craton, South Africa); The effect of preservation (reflecting sequence stratigraphic models) on the relationship between mat features and inferred paleoenvironment

“…Various classification schemes have been proposed for preserved mat features in the clastic rock record (e.g., Noffke et al, 2001a;Schieber, 2004;Sarkar et al, 2008;Noffke, 2010); we here use that of Schieber (op. cit.…”