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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 49 (1965)

Issue: 3. (March)

First Page: 337

Last Page: 338

Title: Diapiric Structures and Upper Proterozoic to Lower Cambrian Sedimentation in the Flinders Ranges, South Australia: ABSTRACT

Author(s): C. R. Dalgarno, J. E. Johnson

Article Type: Meeting abstract


During deposition of the Adelaide System (Upper Proterozoic) and Lower Cambrian Series, which together exceed 50,000 feet in thickness, an incompetent dolomite-silstone sequence (Callanna beds) formed piercement structures which influenced sedimentation.

More than thirty discrete diapiric structures occur along fairly well-defined trends which are regarded as a basement fault system. Surface diameters of the eroded cores of the domes range up to several miles but the injection of carbonate-siltstone breccia has caused complication of some folds and resulted in irregular bodies with dike-like tongues.

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The main period of folding in the early Paleozoic has resulted in cross-sectional exposures of several diapirs. Bald cap structures and interdigitation of conglomerates with basin sediments along the flanks of the domes indicate repeated phases of diapir movement. Adjacent diapirs show evidence of uplift at widely different times from the glacial phase of the Late Proterozoic to the Early Cambrian.

Boulder trains derived from the core of one diapir (Enorama) successively onlap along the flank of the structure and the unconformity may be traced for several miles. The same stratigraphic units (Umberatana Group) on the opposite flank, are truncated by subsequent movements of the core.

An example of a structure of irregular form is the Arkaba diapir, which shows control over facies and thickness from the top of the Umberatana Group through the Wilpena Group to the Lower Cambrian.

Other structures (Frome and Wirrealpa diapirs) exist on an important hinge zone which controlled Lower Cambrian deposition. The Frome diapir shows repeated intervals of erosion near the Adelaide System-Cambrian boundary and offers exposures of both diapiric and depositional contacts. The Wirrealpa diapir and associated faults separate a Lower Cambrian sequence to the south, comprising two formations (2,000 feet in thickness) from an equivalent section to the north, of seven distinct units totalling 10,000 feet in thickness. The diapir core was eroded during this interval.

Exposed is a cross section of a graben which developed during the early Cambrian above a diapir (Oraparinna), the bounding faults of which controlled the development of an Archaeocyatha biohermal bank which intertongues with basinal facies.

Diapiric structures which affected late Proterozoic and early Paleozoic deposition have been recorded 750 miles to the northwest of this province from the Amadeus Basin in central Australia. Evaporitic deposits there are reported within the Bitter Springs Limestone which occurs below a late Proterozoic glacial unit.

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Copyright 1997 American Association of Petroleum Geologists