Sedimentary evolution of the Garau Basin (Lower-Middle Cretaceous): Implications from the facies analysis, depositional environment and palaecological conditions

Facies analysis of Garau Formation exposed in Lurestan Basin, High Zagros, folded belt Zagros led to indentification of three facies associations, representing basin plain, turbidite floor fan to outer ramp of a distally steepened ramp system. Basin plain deposits in central Lorestan Basin include plagic and hemi-plagic and turbidity deposits were developed in southern part of the Lorestan area. Analysis of depositional environment and facies of the Garau Formation reflect a three stage evolution model: 1) Early stage is represented by ramp drowning and basin plain expansion in an anoxic to dysoxic, low energy conditions with high productivity; 2) The activation of turbidity currents in the basin floor. These intervals are coincided with Leupoldina bloom and Oceanic Anoxic Event 1a (OAE1a). The middle part of the Garau Fm. is interpreted as fine-grained pelagic turbidites on base of their flat shape, sharp base, transitional top, Buma sequence and composition, which are composed mainly of intercalation of gravity flows and pelagic/hemipelagic deposits. The relative influence of sea level falls may result in an increase in sharp activation of turbidity currents and deposition of floor fans. 3) Stage 3 is represented by the recovery in the effectiveness of carbonate factory, favoured by the progressive shallowing of the depositional system and an increase in the abundance of pelagic foraminifers. These deposits reflect the shutdown of the turbidity and subordinate mass flows of the feeder system in the mainland and drowning of calciturbidites stage 2, likely as the result of a relative sea-level rise.