New Late Permian tectonic model for South Africa\u2019s Karoo Basin: foreland tectonics and climate change before the end-Permian crisis

Pia A Viglietti,Roger M H Smith,Bruce S Rubidge

doi:10.1038/s41598-017-09853-3

Pia A Viglietti, Roger M H Smith + Show 1 more

Open Access

https://doi.org/10.1038/s41598-017-09853-3

Copy DOI

Abstract

Late Permian Karoo Basin tectonics in South Africa are reflected as two fining-upward megacycles in the Balfour and upper Teekloof formations. Foreland tectonics are used to explain the cyclic nature and distribution of sedimentation, caused by phases of loading and unloading in the southern source areas adjacent to the basin. New data supports this model, and identifies potential climatic effects on the tectonic regime. Diachronous second-order subaerial unconformities (SU) are identified at the base and top of the Balfour Formation. One third-order SU identified coincides with a faunal turnover which could be related to the Permo-Triassic mass extinction (PTME). The SU are traced, for the first time, to the western portion of the basin (upper Teekloof Formation). Their age determinations support the foreland basin model as they coincide with dated paroxysms. A condensed distal (northern) stratigraphic record is additional support for this tectonic regime because orogenic loading and unloading throughout the basin was not equally distributed, nor was it in-phase. This resulted in more frequent non-deposition with increased distance from the tectonically active source. Refining basin dynamics allows us to distinguish between tectonic and climatic effects and how they have influenced ancient ecosystems and sedimentation through time.

Highlights

Late Permian Karoo Basin tectonics in South Africa are reflected as two fining-upward megacycles in the Balfour and upper Teekloof formations
Two second-order subaerial unconformities (SU) are present at the base and top of the Balfour Formation[1] and one third-order SU is noted in the middle of the Balfour Formation, which only attains a maximum thickness of 513 m
Our study extends the second-order SU at the base of the Balfour Formation west to the base of the Oukloof Member and northwards towards the basin’s forebulge (Figs 2 and 3), updates biostratigraphic ranges, and absolute dates[46, 47] show the SU are diachronous

Summary

Introduction

Late Permian Karoo Basin tectonics in South Africa are reflected as two fining-upward megacycles in the Balfour and upper Teekloof formations. Many of the upper and lower boundaries of lithostratigraphic groups are diachronous or have proximal and distal equivalents[1, 4, 35] This is reflected in the geologic record as the preservation of large-scale (second-order) fining upward depositional sequences bounded by subaerial unconformities (SU)[1, 36, 37]. These cycles are recognized in the Beaufort Group[39] by fluvial systems that are characterized by an initial pulse of high energy fluvial transport (e.g. sandstone-rich lithological unit), often underlain by an SU, followed by increasingly finer grained sediment as tectonic activity ceased[1] and river gradients declined This cyclicity is used to identify the position of SUs in Upper Cretaceous fluvial deposits in southern Utah[40, 41]. It discusses the implications of our increased understanding of Late Permian Karoo Basin dynamics and how to recognize the climatic overprint on foreland basin sequences

Methods

Results

Discussion

Conclusion