POMAR, LUIS¹, ANTONIO OBRADOR², and MARCELLO TROPEANO^3
1Universitat de les Illes Balears, Palma, Spain
²Universitat Autonoma de Barcelona, Bellaterra, Spain
³Universita di Bari, Bari, Italy

Abstract: Sub-Wavebase Cross-Bedded Grainstones on a Distally Steepened Carbonate Ramp, Upper Miocene, Menorca, Spain

Cross-bedded grainstones on carbonate ramps and shelves are commonly related to shorelines, shoals or shelf breaks. But coarsegrained cross-bedded grainstones of the Lower Tortonian carbonate platform of Menorca (Balearic islands) were deposited away from the shoreline and below the "wave-sweep base."

Excellent exposures along continuous outcrops on the sea cliffs reveal the depositional profile and 3-D distribution of the different facies belts. Basinward from the shoreline, fan deltas and beach deposits pass into 5km-wide gently dipping bioturbated dolopackstone, then into 100's-m-long 12-20°-dipping dolograinstone clinobeds and then into subhorizontal finegrained basinal dolowackestone-packstone.

In this Miocene example, coarse-grained grainstone, other than beach deposits, exist at four different settings:

(1) near the platform edge, where cross-bedded dolograinstone deposited by currents roughly parallel to the shoreline at 30-40-m estimated water depth, are interbedded with the gently dipping bioturbated dolopackstone;
(2) on the upper slope, where clinobeds are composed mostly of in-situ rhodoliths and red-algae fragments;
(3) lower on the slope, where very coarse intraclasts, molluscs, rhodoliths and other skeletal fragments infill slide/slump scars as upslope-backstepping bodies (antidunes) and are incased in planktonic-foram dolowackestones; and
(4) at the toe of the slope, where coarse-grained skeletal dolograinstones indicate bedform migration parallel to the platform margin, induced by wind-driven currents at more than 100-m estimated water depth.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas