Depositional Environment of the Upper Triassic Baluti Formation in Gara Anticline, Kurdistan Region, North Iraq: Insight from Microfacies and Biomarker Characteristics

Abstract

The studied section is located in the core of the Gara Anticline, about 12 km southeast of Amedi Town. The Baluti Formation is generally composed of grey and green shale, calcareous, dolostone with intercalations of thinly bedded dolostones, dolomitic limestones, and silicified limestones which are occasionally brecciated. The petrographic study shows five main microfacies in the Baluti Formation namely; finely laminated dolomudstone, fossil-barren and lime mudstone, fenestral mudstone/packstone, peloids and ooids wackestone, and lithoclasts (intraclasts) grainstones. The mudstones facies with no fauna and radial-fibrous ooids can point to a protected and low energy environment. Moreover, fenestral structures are reliable criteria for identifying a tidal flat environment. The presence of the lithoclasts (intraclasts) with radial ooids and a few terrestrial fragments may represent a quiet environment, albeit one affected by infrequent storm deposits. As a supplementary to microfacies, the biomarker characterizations were used to deduce the depositional environment of the Baluti Formation. Biomarker parameters show that the Baluti Formation could be deposited in anoxic to suboxic environment, and organic matter input is more likely characterized by land plant organic matter. This study showed that the most likely paleoenvironments for the Baluti Formation were supratidal, intertidal, subtidal, and sand shoals setting. However, the lack and/or very low diversity of skeletal fauna, and the lack of subaerial exposure may indicate that some parts of the formation seem to be deposited in low energy and restricted environment (Lagoon).

Microfacies Analysis and Depositional Environment of Sarki Formation (Early Jurassic), Rawanduz Area, Kurdistan Region, Northern Iraq

“…Here the bioclasts and some of the ooids have been micritized especially on the rim of grains. This microfacies corresponds to SMF (17) according to Wilson [13], and indicating deposition in shoal environment [14].…”

“…Owing to the existence of microcrystalline and rare fossils, it grows in a peritidal subenvironment. In early diagenetic fine size of crystalline dolomite is also developed in intertidal and supratidal environments and indicating Sabkha evaporation [15,17]. Moreover, the occurrence of fine-crystal dolomites in Sabkha fine-grained micritic sediments indicate suitable places for nucleation of larger dolomite crystals [10,18].…”