engleski

Rudist mud mounds and biostromes from Upper Cretaceous of Istria (Croatia)

Beside biostromes which are the most common appearance of rudist congregations, in Upper Cretaceous of Istria rare rudist mud-mounds and atypical biostromes were investigated. Aim of this work is to present lithofacies characteristics of such forms and to determine role of rudists in their formation. Mud mounds, which appears in relatively more open subtidal close to peritidal condition, are result of interaction between acomodation space and amount of in situ baffled sediment. Shallowing and decrease of accomodation space are indicated with densley packed fragments of radiolitids at the top of congregations, together with their lateral migration marked by cross lamination or presence of horizontal lamination. Depending on the availability of accomodation space, from relatively open towards protected part of subtidal they occur as (1) mud mound without visible bedding, (2) bedded mud mound and (3) biostromal variate of mud mound. The last one represent transition towards typical rudist biostromes.

Rudists, Mud mound, Biostrome, Upper Cretaceous, Istria, Croatia.

nije evidentirano