Paleoarchean terrestrial to shallow marine sedimentation on Singhbhum Craton, eastern India (the Western Iron Ore Group)

Abstract

Distinguishing shallow-marine and terrestrial (fluvial) sedimentary deposits is often difficult in the absence of fossils and challenging in deformed and metamorphosed early Precambrian terrains. Herein we report for the first time a > 3.4 Ga shallow marine to terrestrial deposit from the Western Iron Ore Group (WIOG), Singhbhum Craton, India. The WIOG sedimentary succession, lying below a ~ 3.4 Ga banded iron formation, has been divided into three facies associations: a lower alluvial fan-fluvial association, a middle shallow-marine association, and an upper fluvial association. The bottommost conglomerate–very coarse- to coarse-grained sandstone constitutes the alluvial fan-braided fluvial association. Sandstones of the facies association two bears mud drapes and herringbone cross-stratification and thus indicates tidal influence. These shallow-marine sandstones bear wave ripples, ladderback ripples, and adhesion structures and indicate an intertidal depositional environment. The overlying fluvial facies association is characterized by several fining-upward cycles of conglomerate–coarse- to medium-grained sandstones with large-scale trough cross beds, parallel lamination and penecontemporaneous deformation structures and minor shale, indicating the braided nature of the postulated river system. The WIOG succession indicates an overall shallowing-up trend because of sea level fall. The sedimentary structures and texture of the WIOG fluvial deposit are very similar to recent fluvial deposits and are likely to have formed by similar sediment transportation and depositional processes in a tectonically stable sedimentary basin.