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Slumping as a record of regional tectonics and palaeoslope changes in the Satpura Basin, central India

Khan Merajuddin, Khangar Ranjit G., Raychowdhury Nilasree, Babhare Anand T.

Geologos

2021

Vol. 27, No. 2

93--103

Soft-sediment deformation structures play an important role in interpreting regional tectonics and basin evolution during slumping events. The Satpura Basin is interpreted as pull-apart with a monoclinal northerly palaeoslope throughout its evolution. The basin formed as a result of sinistral strike-slip faulting, induced by the ENE–WSW-trending Son-Narmada South fault in the north and the Tapti North fault in the south. We have analysed the slump folds within the basalmost Talchir Formation and related these to regional tectonics and palaeoslope changes in the Satpura Basin. The glaciofluvial strata of the Talchir Formation, exposed in the southern part of the Satpura Basin, record intricacies of folds created during slumping. Several fold styles can be distinguished, within alternations of competent sandstone and incompetent shale layers, some of which indicate buckling. Upright folds, resulting from pure shear, underwent rotation of their axial planes and fold axes during simple shear-dominated progressive deformation when the slump moved downslope. The soft-sediment deformation structures that we have studied show refolding patterns that closely resemble comparable folds known from lithified rocks. These layers with refolded structures are overlain by undeformed sediments, which proves that they are the product of a single ongoing slumping process, rather than of successive deformation events. Our analysis of their fold axes and axial planes, together with fold vergences and thrust directions within the slumps, suggests a mean slumping direction towards the southwest. Analyses of slump folds and their relationship with regional tectonics have allowed us to reinterpret basin evolution history. The southwesterly trending palaeoslope of the basin suggest that the slope of the basin was not uniform throughout its evolution. At the opening, the oblique slip fault, which trended NE–SW, generated due to movement along the ENE–WSW basin bounding faults, was more active and triggered slumping event within the Talchir deposits in the basin. With progressive overlapping of the basin-bounding faults, the Satpura Basin gradually tilted towards the north.

Slump folds within mid-Miocene crevasse-splay deposits : a unique example from the Tomisławice lignite opencast mine in central Poland

Widera Marek

Geological Quarterly

2020

Vol. 64, No. 3

711--722

Non-tectonic, soft-sediment deformation structures occur in mid-Miocene crevasse-splay deposits exposed in the Tomisławice lignite opencast mine in central Poland. The crevasse-splay cross-stratified siliciclastic deposits are underlain by continuously folded and relatively thick lignite beds, and overlain by a thin undisturbed layer of lignite. Only the middle part of the crevasse-splay succession is deformed plastically in the form of folds, while the lower and uppermost beds are undeformed. Most of the intraformational deformation structures are recumbent folds, while only a few can be classified as upright folds in the initial stage of their evolution. The origin of these folds is associated here with a penecontemporaneous slumping process caused by liquefaction of sandy-muddy sediments. The slumping was triggered by an increase in the inclination of heterolithic layers caused by the compactional subsidence of an organic-rich substrate - peat. This type of subsidence occurred following a sudden siliciclastic load on top of the underlying and poorly-compacted peat/lignite seam. The initiation and development of the slump folds can be explained by differentiated loading, compaction and liquefaction processes, and the introduction of a tectonic agent is unnecessary.