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The Mesozoic Structural Evolution Of The Merrimelia Field, Southern Cooper - Eromanga Basin, South Australia.

Menpes, Sandra Ann

Honours Degree, 1988

University of Adelaide

Abstract

The Merrimelia structure is an anticlinal feature separating the Nappamerri and Patchawarra troughs of the Cooper Basin. Five isopach maps, based on both wireline log and seismic data were constructed, along with several stratigraphic cross-sections, to determine the timing and intensity of Mesozoic structural activity in the Merrimelia region. The focus of this activity is a north-east - south-west thrust fault marking the boundary between the Merrimelia High and the Patchawarra Trough.

A period of Late Triassic, wrench-induced compression reactivated the Merrimelia High, resulting in the erosion of between 250 and 300 feet of Nappamerri section, the equivalent of which is preserved in the adjacent Patchawarra Trough. The north-east - south-west compression created a broad anticline, with the Merrimelia 23 area emerging as the structural crest.

Structural growth is a feature of the Nappamerri Formation and the Westbourne Formation. Activity during deposition of the Jurassic Westbourne Formation may be attributed to the transfer of increased plate margin stresses to the continental interior.

Regional thickening to the north-west is characteristic of tectonically quiescent periods until the inception of the Murta Lake system in the Early Cretaceous. Some of the thickness increase off-structure must also be attributed to the compaction of variable thicknesses of underlying Permian sediments, particularly during Nappamerri deposition.

An east - west compressional event in the Early Tertiary reactivated the Merrimelia anticline, with the area in the vicinity of Merrimelia #6, #10, and #11 representing the structural crest, and consequent oil trap.

Australian School of Petroleum
THE UNIVERSITY OF ADELAIDE

SA 5005 AUSTRALIA

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