engleski

Taxonomy of rudists from the Campanian transgressive sediments of Brašljevica, Orešje and Kalnik Mt., Northern Croatia.

Rudists are common fossils in transgressive Upper Cretaceous deposits in three localities placed in northwestern part of Croatia. They appearances coincide with the beginning of transgressive sequence through floatstones-thickets. Within rudist community Vaccinites, Hippurites and Hippuritella could be differentiated according to their general or generic morphological elements. The sediments from Orešje and Brašljevica are determined as of the Campnian age, according to Sr-isotope composition of rudist shells and nannofossil community obtained from the marly sediments directly overlaying rudists-bearing sediments. Morphological elements (ligamental ridge, teeth, pillars, length of the contour around the inner margin of the outer shell layer and the ratio between this length and the distance between the sutures of the pillars) from the transverse shell sections permit different species to be defined within the family. Transverse sections of analyzed Vaccinites, Hippurites and Hippuritella specimens show, for every genus specific values of the angle between teeth and the ligamental ridge, between ligamental ridge and the E pillar (P2), and the ratio between the length of the contour and the pillar suture distance. These measurements, subjected to Cluster analysis (Ward's and Unweighted pair-group methods), represent ground for possible taxonomic determination of the vaccinitids from three different localities.

Rudists; Upper Cretaceous; transgressive sediments; Croatia

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