Usage of microbial mats in depostional environment interpretation and sea level changes: A study of carbonate deposits of members 1 to 2 of the Mila Group (Deh-Sufiyan Formation) in Central Alborz

Abstract

Carbonate deposits of members 1 to 2 of the Mila Group (Middle Cambrian) in Central Alborz that call Deh-Sufiyan Formation in this research, were studied in Shahmirzad, Tueh-Darvar, Mila-Kuh and Deh-Molla sections. These sediments were deposited in four facies belts on a carbonate ramp including basinal environments, outer ramp (deep subtidal sequences), mid ramp (shallow subtidal to lower intertidal sequences), and inner ramp (shoal and upper intertidal to supratidal sequences). Various microbialites were recognized in the shallow-water sediments (includes subtidal and intertidal) of this unit. Based on this study, microbial mats have various morphology of form and type of growth structure and inluding laminar to wavy-laminar, domal or hemispheroidal, bulbous, columnar, regular flabellate columns, unlaminated, loaf- to mound-shaped thrombolities. Facies associations of Deh-Sufiyan Formation are arranged in small-scale of peritidal, shallow subtidal, and deep subtidal cycles and microbial mats are the major features of them. The trends of vertical changes of facies in shallowing-upward and deepening-upward cycles and distribution of various types of microbialites in these cycles had been related to depostional environments and their postions on carbonate ramp. Basal classification method used in this study can provide valuable informations for application of microbiali mats in paleo-environmental and sequence stratigraphy analysis.

Keywords

• Microbial mats
• Deh-Sufiyan Ramp
• stromatolitic cycles
• Mila Group
• Deh-Sufiyan Formation