Relationships between deformation and basin evolution in the intracratonic Amadeus Basin, central Australia

Abstract

Tectonic subsidence curves based on the sedimentary record are used here to study basin evolution and to indicate deformational periods in the history of the intracratonic Amadeus Basin in central Australia. The basin developed during an initial period of extension at about 900 Ma in the Late Proterozoic (Stage 1), was subjected to another period of extension at about Proterozoic-Cambrian boundary time when there was also a shortening event on the southwest margin (Stage 2), and was shortened during the Late Devonian-Early Carboniferous (Stage 3). Stage 1 extension in the southwest and northwest corners of the basin was associated with rift basin sediments and volcanics previously regarded as basement to the Amadeus succession. In the metamorphic Arunta Complex on the northern margin of the basin, a dolerite dyke swarm is considered to have been emplaced during this event. Extension in a N-S direction associated with Stage 2 occurred only in the northern part of the basin; at the same time a major compressional event, the Petermann Ranges Orogeny, was occurring along the southern margin. In the north, the sediment fill at this time firstly thickens rapidly towards the northern margin and then thins dramatically at the margin, implying a half-graben structure and the presence of a major bounding fault. In the southwest, the Petermann Ranges Orogeny caused detachment of the sediments above the salt horizon in the Bitter Springs Formation, northward transport, folding of the sediment pile, and formation of major basement-cored nappes. During Stage 3 a foreland basin associated with southward-directed overthrust sheets of the Alice Springs Orogeny formed in the northern part of the basin. Horizontal shortening was of the order of 50–100 km and hence the present basin margins are structural rather than depositional. The structures that developed during this stage dominate the structural pattern of the basin.