Paleoslope, Sea Level and Climate Controls on Upper Miocene Ramp to Fringing Reef Depositional Sequences, SE Spain

Evan K. Franseen, Robert H. Goldstein

Upper Miocene carbonates from Las Negras, Spain demonstrate the important interaction between sea level position, paleotopography, and climate for accumulation of depositional sequences (DS). Paleoslope combined with relative sea level fluctuations were the major controls. Platform evolution also reflects a changing climate from a more temperate ramp to a tropical fringing reef complex.

During accumulation of onlapping ramp strata (DS1A, DS1B), sea level was at a high or rising position. DS1B is characterized by six fining upward subtidal cycles perhaps controlled by a combination of overall high but fluctuating sea level, low sedimentation rates related to temperate climate, or deposition only in the distal toe of slope setting. The subtidal coarse-grained and fine-grained carbonate cycles lap out against volcanic basement without any indication of facies changes approaching the lap out. Therefore, this carbonate ramp is different than most; carbonate sediments must have been generated upslope but bypassed downslope into areas with low basement paleoslope. Sediments piled up and onlapped at the toe of slope to create a ramp that filled in much of the basement paleot pography.

Similar processes are reflected in later strata of DS2 and the megabreccia marking the base of DS3. However, these units had reefs forming in upslope areas, and relative falls in sea level caused transport downslope to accumulate only on areas of low paleoslope created by deposition of DS1A,B. On these gently sloping surfaces, DS3 fringing reef strata accumulated to form steep fore-reef slope topography through reef aggradation, progradation, and downstepping. With sea level just above the gently sloping surfaces, DS3 strata were preserved in only these areas. During later deposition of the Terminal Carbonate Complex, sea level position allowed for accumulation of shoaling upward carbonate cycles on relatively flat substrates created by DS3 deposition or post-DS3 erosional truncation. /P>

Although this research shows that sea level and climate played a role in carbonate deposition, it illustrates that substrate paleoslope may have played a dominant role in controlling platform morphology.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995