GREEN, DARRYL, University of New Orleans, LA

ABSTRACT: High-Frequency Cyclicity Recorded in Back-Reef-Lagoon Units, Upper Miocene Reef Complex, Mallorca, Spain

Coral-reef lithofacies in the Upper Miocene Reef Complex of southwestern Mallorca, Spain, record four orders of magnitude (1M-4M) of sea-level fluctuations of a frequency higher than 3rd-order cycles (Pomar, 1991). Based on reef geometries and erosion surfaces, estimated amplitudes of Mediterranean sea-level oscillations during the Late Miocene were less than 15 m (4M), 20-30 m (3M), 60-70 m (2M), and about 100 m (1M). Back-reef-lagoon units exposed in the Cap Blanc area record 3M and 4M cyclicity of a 2M aggradational event.

Along 2 Km of continuous sea-cliff outcrops parallel to the direction of reef progradation and 1.5 km perpendicular to progradation, the lagoonal complex is divided into (a) a lower part comprising two units that are laterally equivalent to two 3M aggradational reefs and (b) an upper part that has no laterally equivalent reef. The lower part (a), which onlaps a 2M down-stepping reef, is composed of 10-m-thick 3M units of outer- to mid-lagoonal grainstone-wackestone bounded by subaerial surfaces that trace into discontinuities bounding the 3M reef units. Within the 3M units are 2- to 5-m-thick 4M units bounded by submarine and subaerial discontinuities. The upper part (b) is 5-12 m of inner-lagoonal grainstone-wackestone with stromatolites and root zones.

In the Upper Miocene Reef Complex of Mallorca, lagoonal units record 2M-4M events associated with aggradational-progradational barrier reefs, but do not record the downstepping progradation that characterized much of this reef complex. Little or no lagoonal deposits are associated with the offlaping-progradational fringing reefs. The lagoonal complex, therefore, ischaracterized by vertical sequences that reflect shoaling-upward or aggradation, but evidence of extensive progradation ("strongly regressive" sequences) is absent.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.