Microfacies, sedimentary environment and geochemistry of the Badamu Formation (Lower-Middle Jurassic) in Lut Block, East of Iran .

摘要

The Badamu Formation (Upper Toarcian-Middle Bajocian) mainly consists of limestone and shale and has is cropped out in east of Iran. The Badamu Formation conformably overlays Shemshak Formation and is underlaid sharply by Hojedk Formation in Kerman area and is underlaid gradually by Baghamshah Formation in Tabas and Southern Khorasan areas. The aim of this work is petrographical study of rocks and recognition of various microfacies that finally result in reconstruction and presenting depositional model and determine the paleoenvironment. Therefore, Southwest Esfak section with limestone lithology in Southern Khorasan province has been studied. Petrographical study of 50 thin sections of this formation revealed totally six carbonate microfacies within four microfacies belt including shallow marine, shoal, semi-closed lagoon and tidal channel. Comparison of these facies with standard ones indicates that Badamu Formation has been deposited in a homoclinal ramp including inner ramp, middle ramp and outer ramp sub-environments. Geochemical analysis of the limestone samples revealed high calcium and low magnesium content. Also, study of major and minor elements values determined that aragonite has been the original carbonate mineral of Badamu Formation limestones and these rocks have stabilized within a meteoric-pheratic and burial diagenetic environment. In addition, variations of Sr/Ca values versus Mn suggest that diagenetic alteration has occurred in a geochemically-opened system.