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Tertiary Tectonics and Sedimentation in the Salin (Fore-Arc) Basin, Myanmar

TREVENA, A. S., and R. J. VARGA, Unocal Science and Technology Division, Brea, CA, and I. D. COLLINS and U. NU, Unocal Myanmar, Yangon, Myanmar, in cooperation with Myanma Oil and Gas Enterprise, Yangon, Myanmar

Salin basin of central Myanmar is a Tertiary fore-arc basin that extends over 10,000 sq mi and contains 30,000+ ft of siliciclastic rocks. In the western Salin basin, Tertiary deltaic and fluvial formations contain thousands of feet of lithic sandstones that alternate with transgressive shallow marine shales. Facies and paleocurrent studies indicate deposition by north-to-south prograding tidal deltas and associated fluvial systems in a semi-restricted basin. Presence of serpentinite and volcanic clasts in Tertiary sandstones may imply that the basin was bounded to the east by the volcanic arc and to the west by a fore-arc accretionary ridge throughout much of the Cenozoic.

Salin basin is currently defined by a regional north/south-trending syncline with uplifts along the eastern and western margins. Elongate folds along the eastern basin margin verge to the east and lie above reverse faults that dip west; much of Myanmar's present hydrocarbon production is from these structures. Analogous structures occur along the western margin, but verge to the west and are associated with numerous hydrocarbon seeps and hand-dug wells. These basin-bounding structures are the result of fault-propagation folding. In the western Salin basin, major detachments occur within the shaly Tabyin and Laungshe formations. Fault ramps propagated through steep forelimbs on the western sides of the folds, resulting in highly asymmetric footwall synclines.

Stratigraphic and apatite fission track data are consistent with dominantly Plio-Pleistocene uplift, with limited uplift beginning approximately 10 Ma. Paleostress analysis of fault/slickenside data indicates that fold and thrust structures formed during regional east/west compression and are not related in any simple way to regional transpression as suggested by plate kinematics.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)