Influence of Neo-Tectonic Activity in the Cuban Fold and Thrust Belt on the Slope and Margin Failures of Cay Sal and Great Bahama Bank

Abstract

The Bahamian archipelago is considered tectonically inactive but a fold growth analysis on the most distal anticline of the Cuban fold and thrust belt indicates continuous shortening throughout the Neogene. In addition, several structural elements around of Cay Sal Bank document recent movements. Deep-rooted faults with both thrust and wrench fault characteristics separate the platform from the adjacent basin. Two of these faults reach the seafloor, forming 30 km long and 50 m high scars on the seafloor. Anticlines that are dissected by faults display Holocene fold-growth strata. Both these features, together with recent earthquakes, document the neo-tectonic activity in this part of the archipelago. Multi-channel seismic and multi-beam data reveal for the first time a tectonic influence on the slope sedimentation of Great Bahama Bank (GBB) and Cay Sal Bank (CSB). Neo-tectonics does not change the general bank morphology but it is reflected in the slope development. GBB with its 450 km long margin that is nearly perpendicular to the Cuban fold and thrust belt displays the decreasing tectonic influence from south to north. In the proximity of the fold and thrust belt, large margin collapse features and associated mass transport complexes are common. Away from plate boundary only slope failures are observed that are likely not triggered by tectonic processes. Along eastern CSB the neo-tectonic activity is recognized in lateral displacements of slope canyons and vertical scars on the sea floor. On the north and eastern side of CSB, multichannel seismic data display deep-rooted faults terminating at various stratigraphic horizons, documenting the ongoing deformation related to the Cuban fold and thrust belt. Some of the faults displace the seafloor on the slope and in the basin. Bathymetric maps of the slopes display asymmetric canyons that are oriented oblique to smaller slope gullies and are in some places displaced laterally. This canyon geometry is interpreted to reflect an underlying fault pattern. The connection of faults to large mass wasting events is seen on seismic data where chaotic slump units terminate against buried faults. These slow tectonic movements in the Cuban fold and thrust belt are not enough to change overall platform architecture but influences the type and location of slope and margin failure.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015