Shallow stratigraphy and structure of the Australian continental margin beneath the Timor Sea

Abstract

Shallow seismic sections from the 1967 B.M.R. marine geophysical survey of the Timor Sea were made with a Spark-array source and a Subot Hydrostreamer receiver along 4,500 miles of traverse across the outer shelf and upper slope of the Timor Sea. These sections were interpreted in terms of the stratigraphical section penetrated in Ashmore Reef No. 1 Well. The chief region-wide feature is a Late Miocene to Early Pliocene unconformity, which probably extends through a series of down-faulted blocks into the Timor Trough, which is consequently dated as no older than Late Miocene. Following uplift, erosion, and downfaulting of the Timor Trough in the Late Miocene, marine deposits, presumably carbonates, bypassed the shelf to build out over a subsiding shelf edge and uppermost slope to a maximum thickness of 2,000 ft., and coral reefs developed on structural hinges and anticlines. Long-continued growth of structures to the present day is shown by variations in the thickness of sediments across axes and by an antecedent shelf valley cut across an anticline. The upper slope has subsided at least 2,400 ft. since the Miocene; a series of prograding sediment layers in the southwest part of the area has accumulated since the Late Pliocene at a rate of 0.14 ft. 1,000 years ( 4 cm 1,000 years ) vertically, and 17 ft. 1,000 years ( 5 m 1,000 years ) horizontally.