Provenance, Sedimentology, and Tectonic Setting of Ancient Sandstones and Conglomerates in a Continental Rift Basin: Espanola Basin, Rio Grande Rift, New Mexico

William Cavazza

The Miocene fill of the Espanola basin half-graben is composed of two lithosomes with different provenance, paleocurrents, sandstone and conglomerate petrology, and sedimentary facies. Lithosome A has westward paleocurrents, basement-derived detrital composition, and represents sedimentation in a braid plain-sand flat-ephemeral lake system. Lithosome B has south-southwest-directed paleocurrents, a large volcaniclastic and sedimentary clastic detrital component, and represents a perennial fluvial system. Despite being derived from the unfaulted side of the Espanola half-graben, both lithosomes display upward-fining megasequences (100-400 m thick), comparable to similar megasequences derived from tectonically active basin margins. Thus, vertical arrangement of sedimentary d posits along the unfaulted margin of an asymmetrical rift basin can be determined by tectonism along the opposite, deeper margin. Continental rifts are ideal settings for detailed provenance studies. Variety of lithologies in the sediment source area (basement, sedimentary cover, and volcanic strata) provides "petrologic tracers" to delineate the sediment paleodispersal system. For the Miocene fill of the Espanola basin, integration of petrologic (sandstone point-counting, conglomerate clast-counting) and sedimentologic (paleocurrent and facies analyses) techniques resulted in identification of two genetically significant rock bodies not corresponding to previously established lithostratigraphic units.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.