TAPHONOMIC FEATURES OF LENTICULINA AS A TOOL FOR PALEOENVIRONMENTAL INTERPRETATION OF MIDSHELF DEPOSITS OF THE UPPER JURASSIC (PREBETIC ZONE, SOUTHERN SPAIN)

摘要

Taphonomic analysis of Lenticulina from the Upper Jurassic foraminiferal assemblages of midshelf environments was carried out in a marl-limestone rhythmite of the Prebetic. Size, fragmentation-corrasion, microboring, encrustations, recrystallization, mineralization, sedimentary infillings, and cementation of tests were analyzed by thin section. Encrustations, microborings, and dominance of micritic infillings in the tests are indicative of long exposure on the sea bottom related to low-sedimentation rates. In contrast, the frequency of sparitic cements and reelaborated tests is indicative of higher-sedimentation rates, which are also increased by the input of sediment winnowed from shallower areas. The stratigraphic distribution of these taphonomic features reveals trends in sedimentation rates and sediment input that may be interpreted according to the sequence stratigraphy proposals for the Prebetic. During transgression, increasing relative distance from shore produces a lower-sedimentation rate and prolonged exposure of the fossil remains. This results in increased amounts of microborings, encrustations, and micritic infillings, while fragmentation and the proportion of the reelaborated tests of Lenticulina decrease. Rapid burial is related to increasing sediment input and sedimentation rates and can be associated with aggradation and progradation during the development of a highstand systems tract and a shelf margin wedge. A higher-sedimentation rate explains the scarcity of encrustations and microborings and the abundance of sparitic cements. A higher allochthony of Lenticulina is indicated by the locally high values of fragmentation and reelaborated tests. This taphonomic analysis is useful in monotonous epicontinental lithofacies as marl-limestone rhythmites can reveal features indicative of depositional developments that can be fitted to sequence stratigraphic models.