Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Facies Distribution and Morphologies of Miocene Carbonate Platform Deposits: The Role of Paleotopography, La Rellana Platform, Southeastern Spain
(1) Department of Geology, University of Kansas, Lawrence, KS.
A spectacular 2km exposure of the Upper Miocene La Rellana carbonate platform, SE Spain, is oriented perpendicular to the platform margin. Four sequences were deposited over erosional topography on Neogene volcanics, preserving a paleo-drainage divide (DD). The DD defines a southwestern area, 0.7km in length with steeply dipping (20°) substrate, and a northeastern area, 1.3km in length with gently dipping (5°) substrate. Comparison of sequences on either side of the DD shows the effect substrate slope has on stratal geometries and facies distribution during high-magnitude relative sea-level fluctuations. Sequence 1 developed on subaerially exposed volcanics southwest of the DD. It consists of heterozoan facies with coarse-grained red algal, bryozoan wackestone-packstone in beds that dip 15-25° and onlap the DD. An erosional surface caps the sequence. Sequence 2 is predominantly heterozoan facies with cross-bedded red algal, bryozoan, mollusk, and local Tarbellastraea and Porites coral-rich packstone. Southwest of the DD, beds dip 20-25° and onlap. Resedimented coral reef clasts occur at the base. In contrast, northeast of the DD, beds dip only 5-10° and onlap, but reef detritus is absent, and deposits are dominantly mollusk packstone and wackestone. The difference indicates predictable interactions between shallow water currents and paleotopography. Sequence 3 is composed of Tarbellastraea and Porites reef, forereef slope, and packstone-grainstone facies. Southwest of the DD, forereef slope deposits dominate and are composed of packstone-grainstone, with 15-20° progradational geometries that extend for 0.7km. Northeast of the DD, facies consist of reef core and forereef slope deposits with aggradational and 15-30° progradational geometries that extend for 1.3km. Different styles of progradation are likely predictable on the basis of current direction and substrate slope. Sequence 3 is capped by an erosional surface with evidence for subaerial exposure. Sequence 4 consists of four internal sequences, composed of oolitic, microbial, and coral reef facies, that drape the erosional topography. The draping geometries indicate a different effect of paleotopography during high-magnitude high-frequency sea level change in comparison to underlying sequences. The Rellana platform is a good analog for predicting the effect of paleotopography and sea-level change on facies in subsurface Miocene hydrocarbon targets, such as those in the South China Sea or Indonesia.