Forced regression across the marine to continental transition in Jammu sub-basin: Implication to the Oligo-Miocene unconformity in the Himalayan foreland

摘要

Similar to the other sub-basins, marine to continental transition in Jammu foreland also shows the presence of a characteristic greenish gray, quartz arenite unit, locally termed as White Sandstone unit. Process based sedimentological and sequence stratigraphic work carried out across this White Sandstone unit suggest that this unit was deposited in a shoreface settings during a forced regression. The sharp base of the White Sandstone unit represents a surf diastem (a kind of regressive surface of marine erosion) and does not signify a >10 Myr unconformity. The gradational top of the unit, showing various degree of exposure and soil development, has been interpreted as type 1 sequence boundary. The White Sandstone unit, present along the entire stretch of the western Sub-Himalaya, also shows forced regressive nature in the Subathu sub-basin situated ~350 km SE of Jammu. So, the forced regression across the marine to continental transition in the entire western Himalayan foreland is a regional phenomena and not a local one. Contrary to the earlier works, which proposed the presence of an unconformity spanning >10Myr encompassing the Oligo-Miocene period, the present study showed that the unconformity, if present, is of small duration possibly spanning <40 kyr. These findings seriously question the earlier interpretations of accelerated exhumation and unloading of the mountain load in response to climate driven enhanced erosion or passage of the forebulge for the development of the Oligo-Miocene unconformity in the Himalayan foreland and its relation to Cenozoic tectonic-climate connection.