Extensional Tectonics and Carbonates in the Central Domain, Gulf of California, México
East-west extensional tectonics in the Gulf of California, Central Domain, occurred during the middle-to early-late Miocene. The best example of this extension is Bahía Concepción (BC), a fault-bounded extensional basin, and accommodation zone. Units within the mainly volcanic, Oligocene-Miocene Comondú Group dip in opposite directions on the margins of the basin. This is a result of the major extensional episode that generated normal faults on the surface and listric detachment faults at depth. This event produced depocenters as half-grabens for mostly nearshore marine carbonate deposits. On the BC and at Punta San Antonio, the extensional episode uplifted granodiorite basement along a detachment. Extension on the BC zone was responsible for development of a half-graben structure, first flooded in early Pliocene time. The oldest marine sedimentary unit present in the region is the late Miocene-early Pliocene Tirabuzón Formation. The tectono-sedimentary evolution of the Bahía Concepción region is recorded by: 1) pre-rift strata of the Comondú Group; 2) a syn-rift stage with syntectonic siliciclastic / evaporite /carbonate deposits; 3) post-rift strata, represented by the late Miocene to Pliocene flat-lying, marine mostly carbonate sedimentary units. In the central region, the islands and coastal basins of marine sediments are primary evidence for deep rifting. Basin development and marine incursion are diverse across the central Gulf region, with basins active from Upper Miocene through Early Pleistocene time. Areas within the Loreto Embayment and north to BC show a pattern of old/deep basins to the South and East with young/shallow basins to the North and West and greater synchrony in marine incursion. This pattern supports the concept of an east to west stepping of transtensional stress accommodation across older extensional structures.
Most of the sedimentary marine record exposed on the islands and coastal basins along the eastern margin within the Gulf of California is composed of shallow-water carbonate ramps of biogenetic material, particularly rhodalgal biocalcarenite, as well as other biogenic sedimentary material such as fragments of mollusks and corals. The whole region in California Peninsular and associated islands bears a resemblance to structure and sedimentation patterns for the Gulf of Suez and the north-western Red Sea as described by Bosworth et al, (1998).
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California