Ecological control of sedimentary accommodation: evolution from a carbonate ramp to rimmed shelf, Upper Miocene, Balearic Islands

Stratal patterns and facies architecture develop in response to sediment flux and the available space for sediment accumulation (accommodation). In siliciclastic systems, these two parameters are independent. In carbonates, however. they are highly interdependent: (1) sediment input (production) highly depends on biological systems and consequently on intrabasinal conditions (nutrients. temperature. salinity, etc.). (2) Sediment dispersal depends on the production loci and on the interaction between the amount and type of sediment being produced and the hydraulic energy, additionally biological processes (binding, baffling, framework construction) and even cementation frequently modify it. (3) Accommodation is not an independent factor with respect to sediment input: type, efficiency and area of the carbonate factory depend on sea-level changes and sea-floor morphology. The base level for sediment to accumulate (accommodation) depends on the type and locus of sediment being produced. The Upper Miocene carbonate platforms of the Balearic Islands illustrate how changes in intrabasinal environmental conditions (nutrients and/or temperature) produce changes in stratal patterns and facies architecture if they affect the biological system. During Early Tortonian. carbonate production occurred both in the shallow euphotic zone (foramol) and in the deeper oligophotic zone (rhodalgal). originating a distally steepened ramp. During Late Tortonian and Early Messinian carbonate production mainly occurred in the euphotic zone where framework-producing biota (coral reefs) formed a rimmed platform. Although deposited under similar conditions of high-frequency sea-level fluctuations. these two types of platforms exhibit different internal facies architecture and distribution of heterogeneities, because of differences in base level. In carbonates, base level for sediment accumulation depends on the type and amount of sediment being produced, on the production loci and on the processes controlling sediment dispersal, Base level for the loose foramol-rhodalgal sediment associations of the ramp was controlled by wave- and storm-base and the associated currents, whereas base level for the frame work-dominated reef complex was sea level. Furthermore. the increase on effective accommodation space to allow the reef-rimmed shelf to prograde onto the distally steepened ramp. both platforms being depositional sequences, resulted from an ecological change rather than significant relative sea-level change, namely by the shift from grain- to framework-producing biota. The euphotic. framework-producing biota was able to fill the accommodation space existing between wave- and storm-base level and sea level that was not previously filled by the loose bioclasts. (C) 2001 Elsevier Science B.V. All rights reserved.