ABSTRACT: Progradation and Retrogradation Registered in Calciturbidites?

REIJMER, JOHN J. G., JULIANA S. L. EVERAARS, and WOLFGANG SCHLAGER, Vrije Universiteit, Amsterdam, The Netherlands

Thick successions of reef-rimmed carbonate platforms developed in the Dolomites of Northern Italy. The well-preserved paleogeography was characterized by small isolated carbonate build-ups with well-developed platform-to-basin transitions, which provide an excellent opportunity to be examined in their mutual relationship. Within the successions several sequences are visible in the foreslope environment reflecting progradation and retrogradation of the carbonate platform in response to sea-level fluctuations. At the Durrenstein outcrop these prograding and retrograding sections were analyzed on the compositional variation of the calciturbidites. In outcrop several differences in sedimentological characteristics were detected between prograding and retrograding basinal successions. Prog ading beds are characterized by coarse grain size, fining-upward beds, and a large number of carbonate lithoclasts. Discrete slump levels and convolute laminations in combination with small-scale faults have been identified as slope adjustment processes.

Retrograde systems show coarsening-upward beds, wavy bedding, relative low number of carbonate lithoclasts, and a high percentage of carbonate mud with ooids and oncolites. Liquified flow and mud flows containing small-scale faults are indicative of slope adjustment processes in this system. The differences between the prograding and retrograding systems can be explained by the contrast between mud-dominated as opposed to coarse grained systems.

Calciturbidites are excellent recorders of processes influencing the platform tops. Petrographical analysis of the calciturbidites will add information on the relationship between processes at the platform top and the progradation/retrogradation at the foreslope.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)