محيط رسوبي و چينه نگاري سكانسي پشته هاي گلي در بخش زيرين سازند مبارك (شمال خاور شهميرزاد سمنان )

Depositional Environment and Sequence Stratigraphy of the Mud Mounds in the Lower Mobarak Formation (Northeast of Shahmirzad)

Unit 2 of the Mobarak Formation (Middle Tournaisian), in the Shahmirzad section consists of thin to medium-bedded shale and limestone. Towards the top of this succession, mud mounds consisting of core (bioclastic mudstone-wackestone) and flanking (crinoidal wackestone-packstone) facies are recognized. The mounds are covered by packstone-grainstone capping facies. Their underlying sub-mound facies include dark grey, thin-bedded pelagic limestone/shale with calciturbidite interbeds. The occurrence of the mud mounds between the deeper marine sub-mound facies and the shallow marine capping facies, the presence of the open marine skeletal grains and the absence of ooids and green algae indicate that the mud mounds were deposited in the upper slope of a distally steepened ramp. The mud mound facies represent a fourth-order cycle of an early high stand systems tract of a depositional sequence.