Refined Seismic Stratigraphy in Prograding Carbonates

POMAR, LUIS, Universitat de les Illes Balears, Palma de Mallorca, Spain

Complete exposure of the upper Miocene Reef Complex in the sea cliffs of Mallorca (Spain) allows for a more refined interpretation of seismic lines with similar progradational patterns. A 6 km long high-resolution cross section in the direction of reef progradation displays four hierarchical orders of accretional units. Although all these units are of higher order, they all exhibit similar characteristics as a third order depositional sequence and can likewise be interpreted as the result of high order sea-level cycles.

The accretional units are composed of lagoonal horizontal beds, reefal sigmoids and gently dipping slope deposits. They are bounded by erosion surfaces at the top and basinwards by their correlative conformities. These units show vertical facies shifts which define progradational low-stand, aggradation during rise, progradational high-stand and offlapping during subsequent sea level fall.

These architectural patterns are similar to progradational sequences seen on seismic lines. On seismic lines, the progradational pattern often shows the following geometrical details: (1) discontinuous climbing high-energy reflectors, (2) truncation of clinoforms by these high-energy reflectors with seaward dips, (3) transparent areas intercalated between clinoforms. Based on facies distribution in the outcrops of Mallorca the high-energy reflectors are interpreted as sectors where the erosion surfaces truncated the reef wall and are overlain by lagoonal sediments deposited during the following sea-level rise. The more transparent zones seem to correspond with areas of superposition of undifferentiated lagoonal beds. Offlapping geometries can also be detected in highest quality seismi lines. The comparison between seismic and outcrop data provides a more accurate prediction of lithologies, facies distribution, and reservoir properties on seismic profiles.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)