Sedimentation and tectonics of the Sylhet trough, Bangladesh

Research Article| November 01, 1991 Sedimentation and tectonics of the Sylhet trough, Bangladesh SAMUEL Y. JOHNSON; SAMUEL Y. JOHNSON 1U.S. Geological Survey, M.S. 939, Box 25046, Denver Federal Center, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar ABU MD. NUR ALAM ABU MD. NUR ALAM 2Geological Survey of Bangladesh, Segun Bagicha, Dhaka-1000, Bangladesh Search for other works by this author on: GSW Google Scholar Author and Article Information SAMUEL Y. JOHNSON 1U.S. Geological Survey, M.S. 939, Box 25046, Denver Federal Center, Denver, Colorado 80225 ABU MD. NUR ALAM 2Geological Survey of Bangladesh, Segun Bagicha, Dhaka-1000, Bangladesh Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1991) 103 (11): 1513–1527. https://doi.org/10.1130/0016-7606(1991)103<1513:SATOTS>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation SAMUEL Y. JOHNSON, ABU MD. NUR ALAM; Sedimentation and tectonics of the Sylhet trough, Bangladesh. GSA Bulletin 1991;; 103 (11): 1513–1527. doi: https://doi.org/10.1130/0016-7606(1991)103<1513:SATOTS>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Sylhet trough, a sub-basin of the Bengal Basin in northeastern Bangladesh, contains a thick fill (12 to 16 km) of late Mesozoic and Cenozoic strata that record its tectonic evolution. Stratigraphic, sedimentologic, and petrographic data collected from outcrops, cores, well logs, and seismic lines are here used to reconstruct the history of this trough.The Sylhet trough occupied a slope/basinal setting on a passive continental margin from late Mesozoic through Eocene time. Subsidence may have increased slightly in Oligocene time when the trough was located in the distal part of a foreland basin paired to the Indo-Burman ranges. Oligocene fluvial-deltaic strata (Barail Formation) were derived from incipient uplifts in the eastern Himalayas. Subsidence increased markedly in the Miocene epoch in response to western encroachment of the Indo-Burman ranges. Miocene to earliest Pliocene sediments of the Surma Group were deposited in a large, mud-rich delta system that may have drained a significant proportion of the eastern Himalayas.Subsidence rates in the Sylhet trough increased dramatically (3-8 times) from Miocene to Pliocene-Pleistocene time when the fluvial Tipam Sandstone and Dupi Tila Formation were deposited. This dramatic subsidence change is attributed to south-directed overthrusting of the Shillong Plateau on the Dauki fault for the following reasons. (1) Pliocene and Pleistocene strata thin markedly away from the Shillong Plateau, consistent with a crustal load emplaced on the northern basin margin. (2) The Shillong Plateau is draped by Mesozoic to Miocene rocks, but Pliocene and younger strata are not represented, suggesting that the massif was an uplifted block at this time. (3) South-directed overthrusting of the Shillong Plateau is consistent with gravity data and with recent seismotectonic observations. Sandstone in the Tioam has a marked increase in sedimentary lithic fragments compared to older rocks, reflecting uplift and erosion of the sedimentary cover of the Shillong Plateau. If the Dauki fault has a dip similar to that of other Himalayan overthrusts, then a few tens of kilometers of horizontal tectonic transport would be required to carry the Shillong Plateau to its present elevation. Uplift of the Shillong Plateau probably generated a major (∼300 km) westward shift in the course of the Brahmaputra River. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.