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Mass Transport Deposits in Offshore Morocco, Safi Haute Mer Area
Dallas Dunlap1, Lesli Wood1, and Lorena Moscardelli1
Search and Discovery Article #50089 (2008)
Posted August 27, 2008
*Adapted from oral presentation at AAPG Annual Convention, San Antonio, Texas, April 20-23, 2008
1Bureau of Economic Geology, University of Texas Jackson School of Geosciences, Austin, TX
Recent detailed mapping in a 1,064-km2 3D seismic survey acquired in offshore Morocco revealed the presence of at least three regional mass transport complexes (MTCs) within the Cretaceous interval of the Safi Haute Mer area, as well as several smaller, younger MTCs. Their extent (up to 100 km2) and thickness (350 ms) are strongly influenced by surrounding structural features associated with regional tectonics and salt mobilization. Although the MTCs are characterized by chaotic, mounded seismic facies, seismic attribute analysis shows some internal organization. Depositional architectures identified within these units include (1) large-magnitude lateral erosional edges, (2) internal syndepositional thrusts, and (3) kilometer-scale, transported mega-blocks. Detailed analysis of the internal architecture of the mega-blocks has revealed the presence of discrete, low-sinuosity, single-thread channels that average 90 m in width. Clear expression of stacked channel complexes within the mega-blocks indicates that they have preserved their original stratigraphy. Analysis of surrounding highs shows similar-scale channelization, indicating that the blocks may have come from relatively close by. In addition to the larger MTCs, an important number of smaller and younger MTCs have been identified in the study area that are composed of essentially localized slumps and slides. On the basis of limited data, these deposits are thought to be Late Cretaceous or earliest Tertiary in age.
Two working hypotheses address possible triggering mechanisms for generation of these MTCs: (1) Associated step relief along a narrow shelf, presence of salt tectonics, and frequent occurrence of large earthquakes in the area. (2) Mega-tsunamigenic forces associated with the K-T impact in the Yucatan Peninsula. Both hypotheses are currently under consideration.
· Numerous depositional morphologies are identifiable in seismic within the SHM area. Some include sediment waves, slope channel complexes, major sediment fairways, and mass transport deposits.
· The Cretaceous SHM mass transport complex is composed of multiple seismic facies and multiple episodes of mass failure.
· It spans the entire SHM study area (~1100 sq km) and may span over 20,000 sq km of offshore Morocco. It ranges up to 500 ms thick.
· Large rafted blocks ranging up to +/- 4 sq km in size show preserved stratigraphy and seismic morphologies with low sinuosity, braided channel systems unlike those found in older or younger strata within the study area.
· It is possible that this MTC was derived from upslope; generated by either regional tectonic activity or possibly as a result of the End Cretaceous Impact Event and resulting tsunamigenic waves, which have been modeled to range between 20 m and 200 m in height.
· Similar tsunamigenic-generated mass transport deposits are found in offshore Mexico and form reservoir for one of the largest oil fields in the world.
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Seismic data provided by Government of Morocco and Vanco Energy, Inc.