Quaternary ichnofacies model for paleoenvironmental and paleosealevel interpretations: a study from the Banas River Basin, western India

Integration of data from ichnological and other interdisciplinary sources from the Quaternary Banas River Basin (India) has permitted the reconstruction of a composite ichnofacies model for the interpretation of paleoenvironments and paleosealevels. A glacioeustatic transgressive-regressive system tract of the ancient Arabian Sea has been recognized from the superposition of ichnofacies. The Pleistocene shallow marine Psilonichnus ichnofacies (ichnogenus Psilonichnus, Skolithos, Arenicolites and Thalassinoides of infaunal polychaete, crab and bivalve origin), developed in the Vadpag-Vend segment of the lower Banas sequence, corresponds to interglacial high sea stands. The overlying late Pleistocene-Holocene continental Coprinisphaera-Scoyenia mixed ichnofacies (paleosol association of delicate surficial traces of terrestrial insects and river floodplain association of aquatic traces of worms and crustaceans), formed in the Radhanpur-Varahi segment of the upper Banas sequence, represents the Last Glacial regressive mode of sealevel. Levee-bound oriented crustacean burrows may be used as new ichnological tools to locate buried paleochannels and aquifers. The juxtaposition of levees with alternate worm burrow and barren zones and floodplains with gastropod and barren zones indicates monsoonal lows and highs in the Holocene. The overprinting of the Coprinisphaera elements on the Scoyenia forms has resulted from the Recent-sub-Recent environmental degradations (rising temperature, spread of desert, shrinking saltmarshes and weakened fluvial forces) probably related to global warming and other Greenhouse processes. The readable ichnological signatures of the Quaternary glacioeustatic sealevel fluctuations and consequent climatic changes qualify the Banas model for wider application.