Late Triassic and Early Cretaceous sedimentary sequences of the northern Isfahan Province (Central Iran): stratigraphy and paleoenvironments

Resumen

This research gives a
general outline of the Upper Triassic and Lower Cretaceous sequences
cropping out north of Isfahan, Central Iran. Upper Triassic Nayband
Formation subdivided into the Gelkan, Bidestan, Howz-e-Sheikh,
Howz-e Khan and Qadir members. Two biostromal levels are documented
in the Bidestan and Howz-e-Khan members. Due to a suitable condition
in Late Triassic time including light, oxygen and nutrient, fauna
such as: corals, sponges, hydrozoas, bivalves, gastropods,
brachiopods, echinoderms and Dicroidium were flourished in water and
flora on land. The first appearance of Heterastridium spp. in level
of the Bidestan Member is apparently the first occurrence of this
taxon in Central Iran. Qadir Member has several key beds, one key
bed with land flora Clathropteris spp., and three key beds with
bivalve Indopecten glabra, dating as Rhaetian Stage. An angular
unconformity can be traced between Rhaetian sediments and red
conglomerates and sandstones of Lower Cretaceous Sequences in
Isfahan area which encompasses all Jurassic rocks. This gap can be
related to Cimmerian tectonic phase.