The Beduh Formation (Lower Triassic) is a rhythmic succession of mudstones and fine-grained to very fine grained sandstones, cropping out in the Northern Thrust Zone, Kurdistan, Iraq. This lithostratigraphic unit is traditionally interpreted as offshore to lower-shoreface facies of a homoclinal ramp system. Facies and sequence-stratigraphic analysis identifies two third-order depositional sequences. These two sequences are restricted within type 2 sequence boundary at the bottom of the formation and type 1 sequence boundary at the top. Each sequence comprises transgressive (TST) and highstand (HST) systems tracts. The analysis of high-frequency (meter-scale) cycles, which is based on the high-resolution sequence stratigraphy analysis of third-order sequence, records five shallowing-upward and three deepening-upward cycles within the Beduh succession at Nazdur section and two shallowing-upward and five deepening-upward cycles in Sararu section. The thicknesses of shallowing-and deepening-upward cycles range from 2 to15 m. This work represents a first study in the understanding of the sedimentary and stratigraphic evolution for one of the common Triassic formations exposed in the Northern Thrust Zone. Our sequence-stratigraphic approach contributes to the understanding of the relationship between depositional model and sea-level changes.
The samples of the mineralization of Pb-, Zn-, and Fe-sulfides were collected from three localities (Dure, Lefan, in the northern Thrust zone; and Sinjar, in the Foothill zone) in Northern Iraq. The geochemical recognition using X-ray diffraction (XRD) affirms the presence of the ore deposit sulfides (pyrite, sphalerite, galena, smithsonite, and cerussite). The characterization of mineral chemistry using electron microprobe analysis (EMPA) gives a clear and exact percentage of each element in each mineral. Fluid inclusions are mostly liquid H 2 O and/or water vapor, which may also contain lesser soluble salts and slightly ore elements. Some fluid inclusions contain CO 2 vapor. This occurrence suggests the presence of two immiscible phases due to boiling at the time of their trapping. They are of epithermal system. The homogenization temperatures and salinities obtained for fluid inclusions can be comparable to those reported for the Mississippi Valley Type (MVT) lead-zinc deposits. It is concluded from the petrographic evidence, fluid inclusions and stable isotope data that lead-zinc mineralization was formed due to deeply circulating high-temperature fluids (brines) within the source basin, or later on by tectonic processes, which possibly contribute in leaching metals from either the diagenesis of host rocks or dewatering of deeper buried siliciclastic beds.
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