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Sequence Stratigraphy, Sedimentology, Biostratigraphy And Palaeontology of the Eastern Warburton Basin (Palaeozoic), South Australia

Sun, Xiaowen

Doctor of Philosophy, 1996

University of Adelaide

Abstract

The Warburton Basin is one of the least known basins in Australia in terms of its stratigraphy, depositional history and relationships with adjacent basins. It contains a complex succession of volcanic, carbonate and siliciclastic rocks which represent a mosaic of non-marine to marine environments. The primary purpose of this study is to provide an improved stratigraphic framework, sedimentary and tectonic history of the eastern Warburton Basin, and develop new petroleum play concepts. An integrated basin analysis approach has been applied. This has involved a multidisciplinary study ranging from biostratigraphy, structural geology, sequence stratigraphy, sedimentology, volcanology, and reservoir and trap prediction.

A systematic palaeontological study of more than one thousand trilobite, conodont and other fossil specimens has resulted in recognition of eight new trilobite species: Austrasinia dailyi, Amphoton moornbaensis, Dorypyge gidgealpaensis, Horonastes oepiki, Hypagnostus shergoldi, Lisania changi, Solenoparia gatehousei and Solenoparia changi. Eight Cambrian and three Early Ordovician faunal assemblages have been established, ranging from early Middle Cambrian Late Templetonian/Floran to Early Ordovician Lancefieldian stages. These faunal assemblages can be correlated with the well-established northern Australian biostratigraphic assemblages, and those on other continents. The refined biostratigraphy provides a foundation for sequence stratigraphy in the basin. It serves as a guide for seismic mapping and wire-line log correlation across tectonically deformed regions with poor seismic quality of the Warburton Basin.

Two phases of volcanism have been differentiated according to their lithofacies and geochemical characteristics. The early phase is dominated by basin-wide, rhyodacitic volcanics with minor basalt during the Early Cambrian. In contrast, the late phase is dominated by locally-distributed, basaltic volcanics during the Middle to early Late Cambrian. The within-plate nature of the basalt indicates renewed continental rifting or a localised deep-seated fracture zone.

Two major depositional systems and various environments are recognised. The older is a carbonate-dominated shelf-to-basin system, with environments varying from lagoonal, peritidal, and shelf-edge, to slope apron and basin transitions. The younger is a mixed carbonate-siliciclastic shallow marine system, with environments varying from carbonate and siliciclastic shoals to storm influenced muddy shelf. Five stages of sedimentary history and palaeogeography from the Early Cambrian to Early Ordovician have been reconstructed. A warm water, low latitude palaeogeography is indicated by high biological activity; especially benthic microbial production, abundant peloids, ooids and other coated grains; shallow marine sea floor cementation, early peritidal dolomitisation; and distinctive upward-shoaling cycles.

Four major post-depositional structural styles are interpreted mainly based on seismic data. The most prominent is a thrust fault system initially formed in the Warburton Basin, that created a series of imbricate slices, and hence repeat sections. Within the Warburton Basin, three major unconformities separate four seismic packages which can be differentiated by distinctive reflection configurations, amplitudes, frequencies and interval velocities. An understanding of structural style, seismic package matching by reflection character, and biostratigraphic control, enable regional correlation of these packages across largely undrilled and tectonically deformed parts of the eastern Warburton Basin. This permits reconstruction of pre-deformation geometry of this part of the basin. The four seismic packages mainly include four major, thick and regionally distributed lithostratigraphic units: Mooracoochie Volcanics, Kalladeina Formation, "Innamincka Red Beds", and "Mudrangie Sandstone".

The seismic package mainly composed of carbonate rocks of the Kalladeina Formation shows regionally parallel-layered, and locally mounded reflection patterns, and locally wedge-filling geometry. This seismic facies analysis confirms and complements the reconstruction of carbonate shelf-to-basin palaeoenvironments and basin architecture derived from facies analysis of well-logs, cores and cuttings.


Australian School of Petroleum
THE UNIVERSITY OF ADELAIDE

SA 5005 AUSTRALIA

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