بررسي روند تكاملي اربيتولين هاي سازند داريان در منطقه دشتك، زون زمين ساختي زاگرس مرتفع

Evolutionary Study of the Orbitolinids in the Dariyan Formation, Dashtak Area, High Zagros Zone

Orbitolinids are among the most important group of foraminifera which are of high importance in sediment biostratigraphy of the Early-Mid Cretaceous sequences. Concerning the origin of orbitolinids, there are different ideas, the most important and newest of which has been introduced by Cherchi and Schroeder that shows 4 different phylogenetic lineages in this group. Six species belonging to the genera Mesorbitolina Schroeder and Praeorbitolina Schroeder were identified through the Dariyan Formation of the Dashtak area. Based on appearance and stratigraphic distributions of orbitolinids in the Dashtak stratigraphic section and comparison with Cherchi and Schroederʹs evolutionary model, Praeorbitolina wienandsi - Mesorbitolina ovalis-periva phylogenetic lineage is herein suggested for the upper part of the Dariyan orbitolinids in the studied area comprising part of the Praeorbitolina cormyi - Mesorbitolina aperta Cherchi and Schroeder phylogenetic lineage. The most important changes in the phylogenetic lineage, reperesented herein are as follows: the change in the position of embryonic apparatus, the shape of protoconch and subembryonic zone, size increase in embryonic apparatus and protoconch, increase in number of subembryonic and deuteroconch partitions.