--> Abstract: Condensed Facies Successions: Recognition, Occurrence and Origins, by Paul Wright; #90078 (2008)
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Condensed Facies Successions: Recognition, Occurrence and Origins

Previous HitPaulTop Wright
BG Advance, BG Group, Reading, United Kingdom

In some successions metre-scale shallowing-upwards packages occur that appear to represent substantial sea-level changes of many 10's or even 100's metres amplitude. These are not the products of forced regressions and cannot be interpreted in terms of current standard facies models. The Coniacian (Cretaceous) R1S reservoirs of Tunisia provide a striking example whereby anoxic carbonate mudrocks with distal storm laminae are overlain by calcisphere limestones (analogous to shelf-edge upwelling zones), themselves overlain by shallow water rudist-halimedacean carbonates (reservoir intervals). This succession would not be in itself difficult to interpret if not for the fact that these changes occur in packages as little as 4m thick.

A model is proposed whereby such deposits are envisaged as having formed in what were effectively marine lakes, but not simple platform interior lagoons. A critical factor may have been atidality producing stratification, shallow anoxia and periodic nutrient enrichment by water body mixing. Limited wave action is another characteristic. Such processes are likely to be a signature for very shallow intraplatformal settings.

Other examples from the stratigraphic record of similar extremely condensed facies successions will be discussed.

 

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas