ABSTRACT: Early Cretaceous Sequence Stratigraphy and Sea Level on Southern Exmouth Plateau, NW Australia

Ron Boyd, ODP Leg 122 Scientific Party

Permian-Jurassic rifting of northwest Australia resulted in the development of a passive continental margin flanking the northeast Indian Ocean. On this margin, a relatively thin synrift to postrift sedimentary sequence was deposited on the southern Exmouth Plateau. A sequence stratigraphy analysis of the Early Cretaceous sedimentary succession on the southern Exmouth Plateau was derived from a synthesis of extensive industry and ODP (Ocean Drilling Project) seismic stratigraphy, wireline logs, lithostratigraphy, and biostratigraphy. Results indicate that during breakup, the southern Exmouth Plateau was a transform margin. Between the Tithonian and Valanginian, a continental slope/margin system deposited over 1500 m of clastic sediments in less than 15 m.y., over a 300-km wide depositional wedge. Over the plateau, wireline log sequences correlate rapidly deposited progradational sets of seismic clinoforms and cored sandstone intervals of turbidite deposition. Intervals of slower deposition occupy condensed sections of thin glauconitic limestones and belemnite-rich mudstones. The high density and quality of regional seismic and stratigraphic data, the proximity to previously published and dated sequence boundaries, and the continuous ODP core allows the Exmouth Plateau to be used as a test for the concept of global sea level cycles. Southern clastic supply decreased into the Aptian-Cenomanian and cyclic deposition of deep-water mudstones continued during subsidence of the earlier shelf margin wedge. Between the Albian and Cenomanian, deposition gradually b came dominated by pelagic carbonates.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990