Comparatively little work has been undertaken on how sedimentary environments and facies changes can influence detailed structural development in slump sheets associated with Mass Transport Deposits (MTD’s). The nature of downslope deformation at the leading edge of MTD’s is currently debated in terms of frontally emergent, frontally confined and open-toed models. An opportunity to study and address these issues occurs within the Dead Sea Basin, where six individual slump sheets (S1-S6) form MTD’s in the Late Pleistocene Lisan Formation. All six slumps, which are separated from one another by undeformed beds, are traced towards the NE for up to 1 km, and each shows a change in sedimentary facies from detrital-rich in the SW, to more aragonite-rich in the NE. The detrital-rich facies is sourced predominantly from the rift margin 1.5 km further SW, while the aragonite-rich facies represents evaporitic precipitation in the hyper saline Lake Lisan. The stacked system of MTD’s translates downslope towards the NE, and follows a pre-determined sequence controlled by the sedimentary facies. Each individual slump roots downwards into underlying detrital-rich layers and displays a greater detrital content towards the SW, which is marked by increasing folding, while increasing aragonite content towards the NE is associated with more discrete thrusts. The MTD’s thin downslope toward the NE, until they pass laterally into undeformed beds at the toe. The amount of contraction also reduces downslope from a maximum of ~50% to <10% at the toe, where upright folds form diffuse ‘open toed’ systems. We suggest that MTD’s are triggered by seismic events, facilitated by detrital-rich horizons, and controlled by palaeoslope orientation. The frequency of individual failures is partially controlled by local environmental influences linked to detrital input, and should therefore be used with some caution in more general palaeoseismic studies. We demonstrate that MTD’s display ‘open toes’ where distributed contraction results in upright folding and shortening rather than distinct thrusts. Such geometries may account for some of the contraction that is apparently missing when balancing seismic sections across large off shore MTD’s.
Bibliographical noteGIA acknowledges funding from the Carnegie Trust to undertake fieldwork for this project. SM acknowledges the Israel Science Foundation (ISF grant no. 1436/14) and the Ministry of National Infrastructures, Energy and Water Resources (grant no. #214-17-027). RW was supported by the Israel Science Foundation (ISF grant no. 1245/11). We thank Hugo Ortner and Pedro Alfaro for careful and constructive reviews.
- soft sediment deformation
- Dead Sea Basin