Upper Miocene Reef Complex of Mallorca, Balearic Islands, Spain

Luis Pomar

The late Tortonian-Messinian coral reef platform of south Mallorca onlaps a folded middle late Miocene carbonate platform on which progradation of up to 20 km occurs. Vertical sea cliffs (up to 100 m high) superbly show the last 5 km of this progradation and complement the numerous water-well cores from the island interior.

The Mallorca reef presents the most complete facies zonation of the Miocene reefs of the western Mediterranean. The reef wall framework is up to 20 m thick and shows (1) erosional reef flat with reef breccia and small corals; (2) spur-and-grove zone with large, massive corals; (3) deep buttresses and pinnacles with terraces of branching corals; and (4) deep reef wall with flat, laminar coral colonies, branching red algae, and Halimeda sands.

The upper reef slopes are made of Halimeda sands with wedges of red algae and mollusk coquina. The back-reef lagoon is subdivided into two zones: (1) the outer lagoon consisting of the rampart zone and patch reefs with a variety of coral growth forms and abundant red algae, mollusks, bryozoans, and echinoderms and (2) the inner lagoon with foram-rich oolite shoals, mudbanks, stromatolitic flats, and swamps.

The coral reef platform consists of a series of progradational-accretional sequences and erosion surfaces of different orders of magnitude. The first-order sequence is bounded by significant erosion surfaces with breccias, major facies shifts, and vertical accretion. The second-order sequences show accretional events of up to 100 m thick with 1 to 2 km of progradation, and the third-order sequences occur in packages of tens of meters. Individual reef units are bounded by minor erosional surfaces and define the fourth-order sequences. This composite accretional-progradational architecture implies cyclic variations of relative sea level. Episodes of sea level rise were responsible for the vertical accretion. Sea level falls produced the erosional surfaces; most progradation occurred dur ng lowering sea level episodes. This sedimentological framework of the Mallorca reef suggests late Miocene glacio-eustatic fluctuations of sea level similar to the Quaternary.

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