Evidences of Tempestite and Turbidite deposits in Pabdeh Formation, north and southwest of Zagros Basin

Pabdeh Formation in studied area (northwest of Zagros Basin and north Dezful Embayment) comprises alternation of thin to Thic limestones (lime mudstone, wackestone, packstone and grainstone) and dark to light gray shale beds, rich in planktonic microfauna. Vertical stacking of these facies suggests that depositional environment of the type section evolved gradually from an outer ramp with planktonic facies and anoxic to suboxic conditions in to a mid ramp with high energy oolitic shoal facies and inner ramp with lagoonal facies. In the mid ramp, strong storms were important for sediment transport and sedimentation. Storm deposits (carbonate tempestite facies) with their unique sedimentary structures such as erosional basal contact, hummocky cross-stratification, normal grading, ripply cross-lamination, ripple mark on top of each event bed, couplets of fine (lime mudstone) and coarse (shell-lags) laminae, deposited in this suite. Based on the same studies in the northwest of Zagros Basin, suggest a shallowing-upward trend of the facies deposited in a distally steepend carbonate ramp, wherein the depositional setting evolved from an outer ramp with pelagic and turbidite facies (Microfacies 4B and 4C) and reducing condition to oxygen depleted waters (TOC>2.5%) that gradually changed into middle ramp where marine currents (e.g. turbidity currents) had important roles in sediment reworking and redeposition.