Interpreting Soft Sediment Deformation and Mass Transport Deposits as Seismites in the Dead Sea Depocenter

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Structural style and evolution of a late Triassic rift basin in the Central High Atlas, Morocco: Controls on sediment deposition

Late Triassic continental sediments deposited in an active-rift setting are exposed in the Oukaimeden-Ourika Valley, located in the Central High Atlas Basin of Morocco. The Oukaimeden Sandstone Formation is dominated by ephemeral and perennial braided fluvial facies, and is an outcrop analogue for Triassic sandstone hydrocarbon reservoirs found in Atlantic margin and North African basins. This paper documents detailed analysis of the outcrop data to investigate the influence of tectonics on deposition and the interplay with climatic controls. The geodynamic evolution of the basin is interpreted to be influenced by Atlantic rifting to the west and the formation of the Tethys Sea to the north, which led to the development of ENE and NNE striking normal faults. The present-day fault and outcrop geometry reflects later inversion due to the Alpine compression that led to uplift of the High Atlas and subsequent erosion. The ENE trending rift-basin is bound by normal faults, which are probably in part reactivated older Hercynian structures. The facies distribution was controlled by a complex interplay of tectonic and climatic controls. Evidence for syn-sedimentary movement of both fault sets is observed, with stratigraphic thickening and associated progressive change in bedding dip. These faults controlled the basin dimension, geometry of the half-graben and created the accommodation for sediment deposition. The presence of breccia deposits close to the main ENE bounding faults indicates footwall erosion and deposition of basin margin fans. The location and orientation of the main fluvial system was controlled by these structures, and the main channel belts ran parallel and proximal to the controlling faults, whereas away from the main syn-depositional faults overbank deposits dominate. Smaller contemporaneous NNE oriented faults are generally shorter with less throw, and had only a limited influence on gross sedimentation patterns. These faults are interpreted to be syn-sedimentary, displaying characteristics that suggest basal detachment within the Triassic, and as such provide evidence for the extension direction during late Triassic time. A periodic change from ephemeral to perennial systems, with associated changes in architectural style, is potentially attributed to climatic control, although a structural influence cannot be dismissed. © 2009 John Wiley & Sons, Ltd

Crustal structure of central Lake Baikal : insights into intracontinental rifting

This paper is not subject to U.S. copyright. The definitive version was published in Journal of Geophysical Research 107, B7 (2002): 2132, doi:10.1029/2001JB000300.The Cenozoic rift system of Baikal, located in the interior of the largest continental mass on Earth, is thought to represent a potential analog of the early stage of breakup of supercontinents. We present a detailed P wave velocity structure of the crust and sediments beneath the Central Basin, the deepest basin in the Baikal rift system. The structure is characterized by a Moho depth of 39–42.5 km; an 8-km-thick, laterally continuous high-velocity (7.05–7.4 km/s) lower crust, normal upper mantle velocity (8 km/s), a sedimentary section reaching maximum depths of 9 km, and a gradual increase of sediment velocity with depth. We interpret the high-velocity lower crust to be part of the Siberian Platform that was not thinned or altered significantly during rifting. In comparison to published results from the Siberian Platform, Moho under the basin is elevated by <3 km. On the basis of these results we propose that the basin was formed by upper crustal extension, possibly reactivating structures in an ancient fold-and-thrust belt. The extent and location of upper mantle extension are not revealed by our data, and it may be offset from the rift. We believe that the Baikal rift structure is similar in many respects to the Mesozoic Atlantic rift system, the precursor to the formation of the North Atlantic Ocean. We also propose that the Central Baikal rift evolved by episodic fault propagation and basin enlargement, rather than by two-stage rift evolution as is commonly assumed.This project was jointly funded by the U.S. Geological Survey Coastal and Marine Program and the Russian Academy of Sciences

Kinematic and thermal evolution of the Moroccan rifted continental margin: Doukkala-High Atlas Transect

The Atlantic passive margin of Morocco developed during Mesozoic times in association with the opening of the Central Atlantic and the Alpine Tethys. Extensional basins formed along the future continental margin and in the Atlas rift system. In Alpine times, this system was inverted to form the High and Middle Atlas fold-and-thrust belts. To provide a quantitative kinematic analysis of the evolution of the rifted margin, we present a crustal section crossing the Atlantic margin in the region of the Doukkala Basin, the Meseta and the Atlas system. We construct a post-rift upper crustal section compensating for Tertiary to present vertical movements and horizontal deformations, and we conduct numerical modeling to test quantitative relations between amounts and distribution of thinning and related vertical movements. Rifting along the transect began in the Late Triassic and ended with the appearance of oceanic crust at 175 Ma. Subsidence, possibly related to crustal thinning, continued in the Atlas rift in the Middle Jurassic. The numerical models confirm that the margin experienced a polyphase rifting history. The lithosphere along the transect preserved some strength throughout rifting with the Effective Elastic Thickness corresponding to an isotherm of 450°C. A mid-crustal level of necking of 15 km characterized the pre-rift lithosphere. © 2010 by the American Geophysical Union