Diagenesis of the pre-Ordovician Hijam Fm. (Hi2), Wadi Amdeh, Saih Hatat, north Oman

The upper part of the pre-Ordovician (late Precambrian?) Hijam Formation (Hi2 Member) is the proposed research object. It will be studied in the Amerat region where it is well exposed in Wadi Amdeh. Hi2 displays limestone and dolostone, both showing signs of intense, mainly selective silicification by dark silica. A single preliminary observation points to possible dedolomitization. Moreover, Hi2 exhibits veins, filled with calcite or dark silica as mentioned above or white silica or both alternating calcite and silica. Field work will determine (1) cross-cutting relationships between different veins and rock types, (2) and different vein types, as well as (3) vein orientations. Field work and microscopic study of relict/replacement fabrics will reveal the relative order of diagenetic replacements. These methods are flanked by cathodoluminescence analyses which will shed light on the cement stratigraphy. To get a more comprehensive understanding of the diagenetic conditions and environments, origin of cement precipitation fluids and the timing other analyses will be utilized: isotope of C, O and Sr; major, minor and trace element; fluid inclusions. In our work we will consider possible deformation and heating effects of the late Paleozoic Hercynian Orogeny, and the late Cretaceous Semail Ophiolite emplacement on the vein formation within the Hi2 Member as well as their effects in remobilizing relevant diagenetic fluids. The proposed research will close a gap in the poorly understood Hi2 Member. Moreover, our research may lead to an improved understanding of the also poorly understood Hercynian Orogeny in terms of orientation of the corresponding principal stress direction. It will also provide Oman?s oil industry with an increased knowledge of late Precambrian(?) and Phanerozoic diagenetic fluids and their possible migration paths as a cause for reducing pore space (e.g., factures becoming mineralized veins) or as a cause for increasing pore space (e.g., by dolomitization). This is significant as the Hajeer Fm., a hydrocarbon source rock in the subsurface, is the lateral equivalent of the Hijam Fm.

The upper part of the pre-Ordovician (late Precambrian?) Hijam Formation (Hi2 Member) is the proposed research object. It will be studied in the Amerat region where it is well exposed in Wadi Amdeh. Hi2 displays limestone and dolostone, both showing signs of intense, mainly selective silicification by dark silica. A single preliminary observation points to possible dedolomitization. Moreover, Hi2 exhibits veins, filled with calcite or dark silica as mentioned above or white silica or both alternating calcite and silica. Field work will determine (1) cross-cutting relationships between different veins and rock types, (2) and different vein types, as well as (3) vein orientations. Field work and microscopic study of relict/replacement fabrics will reveal the relative order of diagenetic replacements. These methods are flanked by cathodoluminescence analyses which will shed light on the cement stratigraphy. To get a more comprehensive understanding of the diagenetic conditions and environments, origin of cement precipitation fluids and the timing other analyses will be utilized: isotope of C, O and Sr; major, minor and trace element; fluid inclusions. In our work we will consider possible deformation and heating effects of the late Paleozoic Hercynian Orogeny, and the late Cretaceous Semail Ophiolite emplacement on the vein formation within the Hi2 Member as well as their effects in remobilizing relevant diagenetic fluids. The proposed research will close a gap in the poorly understood Hi2 Member. Moreover, our research may lead to an improved understanding of the also poorly understood Hercynian Orogeny in terms of orientation of the corresponding principal stress direction. It will also provide Oman?s oil industry with an increased knowledge of late Precambrian(?) and Phanerozoic diagenetic fluids and their possible migration paths as a cause for reducing pore space (e.g., factures becoming mineralized veins) or as a cause for increasing pore space (e.g., by dolomitization). This is significant as the Hajeer Fm., a hydrocarbon source rock in the subsurface, is the lateral equivalent of the Hijam Fm.

The lithological description and facies interpretation by Villey et al. (1986a) is the latest detailed publication concerning the Hijam Fm. There is an unpublished Final Year Project Theses by Al-Mamari (2015) which is a preliminary inventory on the diagenetic replacements, based on field and thin section studies. References: Al-Mamari, Y.Y.A. (2015): Compositional Diagnosis of the Hijam Dolomite in the Amerat Region (Oman Mountains), Oman.- Final Year Project Thesis, 53 pp., Muscat (Sultan Qaboos University). Arndt, M., Virgo, S., Cox, S.F., Urai, J.L. (2014): Changes in fluid pathways in a calcite vein mesh (natih Formation, Oman Mountains): insights from stable isotopes.- Geofluids, doi: 10.1111/gfl.12083, Wiley. Bechennec, M, Rabu, D. and Hutin, G. (1986): Geological Map of Rustaq, 1:100,000 sheet NF40-3D, Explanatory Notes, 69 pp.Hacker, B.R., Mosenfelder, J.L. and Gnos, E. (1996): Rapid emplacement of the Oman ophiolite: Thermal and geochronologic constraints.- Tectonics, 15, 1230-1247. Tucker, M.E. (2001): Sedimentary Petrology.- 3rd edition, 262 p. (Blackwell). Roberson, A.H.F. (2007): Overview of tectonic settings related to the rifting and opening of Mesozoic ocean basins in the Eastern Tethys: Oman, Himalayas and Eastern Mediterranean regions.- In: Karner, G.D., Manatschal, G. and Pinheiro, L.M. (eds.), Imaging, Mapping and Modelling Continental Lithosphere Extension and Breakup, Geological Society, London, Special Publication, v. 282, 325-388. Vandeginste, V., John, C.M., Manning, C. (2013): Interplay between depositional facies, diagenesis and early fractures in the Early Cretaceous Habshan Formation, Jebel Madar, Oman.- Marine and Petroleum Geology, 43, 489-503. Villey, M., Le Metour, J. and De Gramont, X. 1986a. Geological Map of Fanjah 1:100,000, BRGM sheet no. 40-3F, Explanatory Notes, 68 pp. Villey, M., Le Metour, J. and De Gramont, X. 1986b. Geological Map of Fanjah 1:100,000, BRGM sheet no. 40-3F.