Print this pageInput and Diagenesis of a Carbonate Slope (Bahamas): Response to Morphology Evolution and Sea Level Fluctuations
WESTPHAL, HILDEGARD, and JOHN J. G. REIJMER
Signals in sediment composition, mineralogy, organic matter, and diagenesis
are responses to changes in platform morphology (ramp vs. rimmed) and sea-level
fluctuations. Pliocene periplatform sediments of the western slope of the Great
Bahama Bank clearly reflect combined effects of these factors.
High-resolution component analysis reveals the differences in the sensitivity of the platform to sea level changes due to morphology: while the lower part of the upper Pliocene (deposited on the slope of a ramp) is composed of monotonous wackestones, the uppermost Pliocene sediments (deposited on the slope of a rimmed platform) show striking differences in composition (mudstones to grainstones). Here, the coarse lowstand deposits lack fine matrix derived from the platform interior.
In carbonates, acoustic impedance strongly depends on diagenetic alterations. Therefore the understanding of physical properties is crucial for the interpretation of seismic data. The dependence on diagenetic grade and style has been examined on SEM- and microscope-scale. It is shown that cementation (and therefore sonic velocity) is dependent on primary mineralogy and grain size distribution of the deposits (the diagenetic potential). Thus, sonic velocity is to great part dependent on sea level and morphology.
The combination of input and diagenesis data (XRD, TOC, component analysis, SEM) leads to a model of the dynamic evolution of a carbonate slope. It is shown that cyclicity observed in periplatform sediments is a function of (1) sea level, (2) morphology, and (3) interdependent diagenesis.