Himalayan Geology, Vol. 41 (1), 2020, pp. 73-80, Printed in India
Paleoenvironment of the Sokolowia shell beds, Upper Part of the Ziarat Formation, Northern Iran
SAMIRA TAGHDISI NIKBAKHT1, SEDIGHEH ZIRJANIZADEH2, AZAM ZAREH3, MEHDI HADI4, AMIR SALAHI4, YAGHUB NASIRI2,4*
1Department of Geology, Faculty of Sciences, University of Hormozgan, Bandar Abbas, Iran
2Geology Department, Faculty of Science, University of Gonabad, Gonabad, Iran
3Department of Geology, Payam Noor University, Shiraz, Iran
4Department of Geology, Faculty of Sciences, Ferdowsi University of Mashhad, Mashhad, Iran
*Email (Corresponding author): ya.nasiri@mail.um.ac.ir; y.nasiri.1365@gmail.com
Abstract: The Sokolowia shell beds in the Ziarat Formation (Middle Eocene) have been distinguished into primary biogenic, fair-weather wave and proximal storm tempestite concentration of varied taphonomic and sedimentologic characteristics. The existence of normal grading, sharp and erosional base in the uppermost part of the Ziarat Formation indicate proximal tempestites between the storm wave-base and fair-weather wave-base. Disarticulated and intensely fragmented Sokolowia shells were concentrated above the fair-weather wave-base. These are convex-up, exceedingly fragmented; poorly sorted large shells in calcareous marl were formed under strong hydrodynamic energy above the storm weather base. Articulated shells in silty mudstone matrix, without fragmentation and abrasion, were accumulated in lagoon environment attributing to in-situ concentration. These shell concentrations are recognized in distinct positions within the depositional sequence of the Ziarat Formation.
Keywords: Shell bed, Alborz Basin, Iran, Middle Eocene, Ziarat Formation.