Multiple dolomitization events of the Lower Carboniferous Um Bogma Formation, west central Sinai, Egypt

Abstract

The Lower Carboniferous Urn Bogma Formation in west-central Sinai , Egypt displays extensive and pervasive dolomitization. The combined petrographic/isotopic/stratigraphic investigations of the dolomite succession in the studied area reveal the presence of two distinct dolomite types: dolomite type (1) is confined to the basal part of the succession being associated with economic ferro-manganese deposits, and dolomite type (II) is located near the upper part of the succession. Silt, clay and marl beds vertically separate the two dolomitic units .The dominance of ooid and benthic fossil ghosts in the basal dolomite type (1) supports the suggestion that the CaCO J precursor has been formed under shallow agitated subtidal setting. The terrigenous beds that overlie this basal unit indicate that that the area has been brought into a meteoric realm during a subsequent lowstand period even before the emplacement of the upper part of the formation . During this period considerable stabilization of the initial metastable CaCO J phases into diagenetic low-Mg calcites has presumably took place.The persistent stratigraphic distribution of dolomite type (II) throughout the entire area and the typical marine 8 nC values (+ 1.1 and 2.9%0 POB) are consistent with platform-wide pumping system within a subtidal setting. Early stabilization of the initial CaCO J fabrics of the basal carbonate unit impeded their dolomitization during this stage. Subsequent shallow burial stabilization of dolomite type (II) is assessed from the well-developed stylolites, the non-planar crystal boundaries, the undulose extinction, the low porosity and the relatively depleted 8 180 (-5 .1 to -7%0 POB ) values. The initiation of dolomite type (I) was a post-burial process as indicated from the euhedral planar crystal boundaries, the high intercrystalline porosity and the absence of any compaction fabrics. The oxygen (3.3 to 4.7%0 POB) and carbon (+ 1.9 to 3.40/00 POB) isotopic values of this type of dolomite are possibly inherited from the CaCO J precursor where dolomitization took place from more or less unmodified marine water during period of minimum sea level fluctuations.

Sedimentological and geochemical characteristics of the late middle Eocene dolostone succession, Kachchh, western India

“…A negative correlation of Sr with SiO 2 ( r 2 = −0.58) suggests that the Sr was also supplied from the seawater contrary to silica. In case of penecontemporaneous and shallow‐burial dolomitization, seawater is recorded as the major source of Mg (e.g., F. I. Khalaf et al, ; Land, ; Lee & Friedman, ; Sena et al, ; Shaaban, Holail, & Rashed, ; Warren, ). Thus, it is suggested that the MgO and Sr were supplied from seawater, while the rest of the oxides were supplied in suspension and dissolved states from the meteoric water.…”

Gold and Base Metals Associated with Uranium Mineralization in Some Lower Carboniferous Rock Units in the Wadi Abu El Mogheirat Area, Southwestern Sinai, Egypt

“…Gibbsitic marl and black gibbsite from the middle Um Bogma Formation show high enrichment in Co, Cu, Mn, Ni, Pb and Zn (levels exceeding 1000 ppm, with even more than 10000 ppm for Mn). Mn-Fe ore constitutes an important fraction of rocks in the Um Bogma Formation (Kora et al, 1994;Shaaban et al, 2005;Khalifa and Arnous, 2012;Rabeh, 2016).…”