Cretaceous Sedimentation Along the Betic-Maghrebidian Alboran Margin (Gibraltar Arch Area, Southern Spain, Northern Morocco)

Philippe Olivier, Jurgen Thurow, Wolfgang Kuhnt

The continental margin of the former Alboran microcontinent was narrow and sediment starved. Hence it is well suited to study paleo-oceanography and paleoenvironment of shelf-to-slope sedimentation which is scarcely influenced by detrital overprint. Cretaceous sediments of the Alboran margin are now outcropping within four structural units (Malaguides, Dorsale, Predorsalian, Mauretanian) in the Gibraltar arch area. Sediments from carbonate platform, slope, proximal fan, distal fan, and pelagic deep-water environments were observed. Four evolutionary stages were discriminated: (1) buildup of a carbonate platform, formation of half-graben structures (rifting), breakup, and local oceanization (Late Triassic and Jurassic); pelagic sediments in the shelf-to-slope environment; 2) continuing pelagic sedimentation with local uplift (preflysch phase of Tithonian to Early Cretaceous; calciturbidites with ophiolite debris); (3) local deposition of thick clastic wedges (Barremian to late Albian), and (4) decreasing sedimentation rates and ceasing terrigenous input (late Albian), resulting in an overall pelagic environment (Cenomanian to Paleocene).

Two supra-regional black shale events are documented in the sedimentary sequences: (1) late Liassic, during the rifting stage, and (2) Cenomanian-Turonian, during a juvenile oceanic stage. Total organic carbon content is up to 30% in Liassic and 15% in Cenomanian-Turonian. In both cases, organic-rich deposits may reach 10 m thick. Attention is focused on sedimentation patterns on shelf-to-abyssal paleobathymetric settings during Cenomanian-Turonian. Within shelf sequences (Malaguides and Dorsale), condensation and stratigraphic gaps are common. Sediments include pelagic limestone and marlstone. The deeper sequences (Predorsalian and Maurentanian) exhibit organic-rich siliceous sedimentation intercalated in a calciturbidite sequence. Sedimentological, biostratigraphical, and geochemica characteristics of this sedimentation are briefly discussed.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.