Geology of the Cenozoic Indus Basin sedimentary rocks: Paleoenvironmental interpretation of sedimentation from the western Himalaya during the early phases of India-Eurasia collision

This study reassesses the stratigraphy, sedimentology, and provenance of the Indus Basin sedimentary rocks, deposited within the Indus Tsangpo Suture Zone (ITSZ) during the early phases of India-Eurasia collision. Using field observations, biostratigraphy, and petrographic and isotopic analyses we create a paleodepositional reconstruction within the paleotectonic setting of the early phases of India-Eurasia collision. We then re-examine existing constraints to the timing of India-Eurasia collision previously interpreted from the earliest occurrence of mixed Indian-and Eurasian-derived detritus in the succession. From mid-Cretaceous to early Paleocene times the Jurutze and Sumda Formations were deposited within an arc-bounded marine basin between the Dras and Kohistan-Ladakh Island arcs. The <51 Ma aged deltaic Chogdo Formation then filled the basin until deposition of the 50.8-49.4 Ma aged Nummulitic Limestone during a marine incursion, before continental facies developed in an evolving intermountain basin with the deposition of the Paleogene Indus Group. Within these systems, sediment was sourced from the Eurasian margin to the north and was transported southward into the suture zone. In this section, we see no unequivocal evidence of Indian Plate input to the sedimentary succession (and thus no evidence of mixed Indian-Eurasian-derived detritus indicative of India-Asia collision) until the upper stratigraphic horizons of the Indus Group, when facies are representative of an axial, northwesterly flowing river system. We suggest that the paleo-Indus River was initiated within the ITSZ during late Oligocene-early Miocene times. Sedimentation of the Indus Group continued until the late Miocene. Citation: Henderson, A. L., Y. Najman, R. Parrish, M. BouDagher-Fadel, D. Barford, E. Garzanti, and S. And (2010), Geology of the Cenozoic Indus Basin sedimentary rocks: Paleoenvironmental interpretation of sedimentation from the western Himalaya during the early phases of India-Eurasia collision, Tectonics, 29, TC6015, doi:10.1029/2009TC002651.