HR: 10:50h
AN: GP41D-03    [PDF]
TI: Initial India-Asia Collision: Sedimentologic, Paleomagnetic and Paleontologic Evidence From the Ghazij Formation, Balochistan, Pakistan
AU: * Clyde, W C
EM: will.clyde@unh.edu
AF: Dept. Earth Sciences, University of New Hampshire, 56 College Rd., Durham, NH 03824 United States
AU: Khan, I H
EM: ikhan@cisunix.unh.edu
AF: Dept. Earth Sciences, University of New Hampshire, 56 College Rd., Durham, NH 03824 United States
AU: Khan, I H
EM: ikhan@cisunix.unh.edu
AF: Geological Survey of Pakistan, Sariab Rd., Box 15, Quetta, 00000 Pakistan
AU: Gingerich, P D
EM: gingeric@umich.edu
AF: Dept. Geological Sciences and Museum of Paleontology, University of Michigan, 1109 Geddes Rd., Ann Arbor, MI 48109 United States
AB: Initial continental collision between India and Asia is thought to have caused significant changes to global climate and biota, yet its timing and biogeographic consequences are uncertain. Structural and geophysical evidence indicates initial collision during the early Paleogene, but sedimentary evidence of this has been controversial owing to the intense deformation and metamorphism along the suture zone. Modern orders of mammals that appeared abruptly on northern continents coincident with the global warming event marking the Paleocene-Eocene boundary are hypothesized to have originated on the Indian subcontinent, but no relevant paleontologic information has been available to test this idea. Here we present sedimentologic, paleomagnetic, and paleontologic results that show the lower Eocene Ghazij Formation of western Pakistan records continental sedimentation and mammalian dispersal associated with initial India-Asia collision. Sedimentologically, the Ghazij exhibits a clear transition from shallow-marine facies in the lower part, to paralic deltaic facies in the middle part, and continental fluvial facies in the upper part. Paleomagnetic data indicate that Ghazij deposition occurred just before a pronounced decrease in the sea-floor spreading rate of the Indian Ocean. Large fossil mammal assemblages show strong endemism in the middle part of the formation but increasing cosmopolitanism and affiliation with northern continents higher in the formation. Our results support the hypothesis that initial continent-continent contact occurred near the Paleocene-Eocene boundary along the northwest edge of the Indo-Pakistan plate and that subsequent closure occurred diachronously along the rest of the suture. However, it appears that during initial collision, modern orders of mammals dispersed into India rather than out of it.
DE: 1520 Magnetostratigraphy
DE: 1525 Paleomagnetism applied to tectonics (regional, global)
DE: 8105 Continental margins and sedimentary basins
DE: 9320 Asia
DE: 9604 Cenozoic
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting