Sedimentary Processes of Mixed Carbonate and Siliciclastic Slope Deposits, SE Spain

K. M. McColgin
University of Wisconsin–Madison, Dept. of Geology and Geophysics, Madison, WI

The degree of mixing of Lower Miocene carbonate and siliciclastic deposits in the Costa Blanca region of SE Spain lessens from shelf to basin. The primary goal is to determine the sedimentary processes involved in separating the carbonate and clastic components in a basinward direction. A depositional model applicable to this and other mixed systems will be developed based on the nature of the lithologic and geometric relations between mixed, carbonate, and clastic units.

The entire shelf to basin sequence from near-shore sandstone to turbidites is accessible and well preserved in a NW-SE transect over a distance of less than 15 km. Several stratigraphic sections will be correlated based on facies associations, aerial photos, geometric stratal relationships, and sequence stratigraphy to understand the genetic relationships of the strata. Petrographic work will also be used in this analysis.

Though the focus of this work is sedimentological, tectonics may be a driving mechanism for variability of mixing in the section. Through the Oligocene, the local stress regime was tensional, giving rise to a broad, shallow carbonate platform. Thrusting began in the early Miocene with the onset of compression, resulting in a shift from a passive margin to foreland basin setting. Preliminary field observations have shown that the drowning of the Oligocene platform was not accomplished in a single event, but rather there were smaller scale pulses within an overall deepening in the Aquitanian and lower Burdigalian. The depositional models developed in this study will better the understanding of mixed carbonate and siliciclastic slope systems in general, as well as the unconformity at the Oligocene/ Miocene boundary and the subsequent foreland basin development in this part of the Western Tethys.

AAPG Search and Discovery Article #90902©2001 AAPG Foundation Grants-in-Aid