Diagenesis of Palaeozoic-Mesozoic Tethys Ocean Carbonate succession- Oman Mountains

This paper studies the uppermost unit of Kharus Formation (Cambrian) and the Autochthonous Akhdar Group (Permian-Triassic), which unconformably covers the pre-Permian strata. The petrographic and geochemical as well as field observations indicate that the succession underwent different stages of dolomitization that produced rocks inheriting the original host rock textures and structures (fabric-preserving dolomitization) and rocks with complete obliteration of the pre-existing textures (fabric-destroying dolomitization). Dolomites that retain the original fabric of the limestone are indicators of the host rock mineralogy, i.e., whether it was made up of high Mg-calcite or aragonitic allochems and indicate early dolomitization. The top part of the Kharus Formation consists of pervasively dolomitized units, whereas dolomites belonging to the Autochthonous Akhdar Group display variable degrees of structural and textural preservation. The evidence suggests very early dolomitization in a relatively short time interval for the Permian-Triassic carbonates. The preserved depositional features in the Permian-Triassic carbonates indicate deposition in shallow marine environments with variable energy levels. Seven facies are inferred: stromatolites, mudstones, wackestones, intraformational breccias, grainstones, packstones and grain/packstones. Petrographic as well as field observations exclude evidence of evaporites within Palaeozoic-Mesozoic rocks. Five paragenetic phases are determined to explain the type of dolomitization and to indicate the type and severity of diagenesis that affected the Palaeozoic-Mesozoic Tethys Ocean carbonates from the Oman Mountains.

Assessment of Groundwater Resources in Water Spring Areas Using Geophysical Methods, Northern UAE

The Khatt, Madab, and Al Ghmour Springs are important springs in UAE. They are located in the foothills of the Oman Mountains. The water temperature of these springs is relatively high (approximately 39 °C). Overexploitation of fractured aquifers negatively affected the waterflows from these springs. The outflows from these springs are time-dependent and range from 10 to 50 L/s (until 1998) to 1–10 L/s (until 2010). To assess the current conditions of the spring areas, relevant data were carefully reviewed, analyzed, and stored in a GIS database. A 3D-geological model was developed for the Khatt Springs area, which allowed different types of visualizations, calculations, and predictions. In addition, a 2D earth resistivity imaging survey was performed to evaluate the available groundwater resources, characterize the major faults/fractures feeding these springs, and to determine the locations of saturated fractures and karsts and the thicknesses of the unconsolidated materials in the wadis. Borehole and drilling information from observation wells were utilized to enhance the analysis of the earth resistivity imaging data. The described procedures and acquired results indicated that it was possible to determine the locations of two production wells for feeding Al Ghmour Springs with water during drought periods to keep it alive.

Novelly discovered post-mid-Eocene sinistral slip in the eastern Oman Mountains: widely distributed shear with wrench-fault assemblage related to Arabia-India convergence

<p>The geology of the Oman Mountains was shaped by the SW-directed obduction of allochthonous deep-sea rocks (Hawasina), trench-facies rocks (Haybi) and oceanic lithosphere (Semail Ophiolite) onto Arabian autochthonous shelf carbonates during the Late Cretaceous. Locally, the resulting obduction orogen was overprinted by significant post-obductional extension. NNE-directed extension occurred during at least two episodes which took place from the latest Cretaceous to early Eocene and late Eocene to Oligocene/Miocene, respectively. Moreover, the Oman Mountains, between the eastern Batinah Coastal Plain and the Sur area (Qalhat Fault) display numerous ~N/S-oriented folds and reverse faults. These structures overprinted mid-Eocene to at least Oligocene/Miocene formations (i.e., the Seeb to Barzaman formations).</p><p>Detailed structural/field work and satellite image analyses provide ample evidence that these ~N/S-compressional features are cogenetic with ~WNW to NW-striking sinistral faults. All these post-mid-Eocene structures are part of one major left-lateral WNW- to NW-striking shear zone from the Batinah Coastal Plain in the NW to the Batain area in the SE. Sinistral shearing is localized along the southwestern margin of the Saih Hatat Dome, crosses the Fanja area and continues to the northern part of the Jabal Akhdar Dome (Jabal Nakhl Subdome). The straight southwestern margin of the Saih Hatat Dome may correlate with a Permo-Triassic major extensional fault, active during the Pangea rifting. Shearing also affected rocks northeast of this zone, i.e., within the Salma Plateau and the Rusayl Embayment. Thus, shearing affected an area of 250 km by 40 km in width. We term this shear zone hereafter the “Hajar Shear Zone” (HSZ). The amount of sinistral shearing is unknown due to the absence of markers and wide strain distribution, but is likely to be at the order of a few tens of kilometers.</p><p>The cause for the WNW-directed sinistral shearing is the overall E/W-directed shortening between the Arabian and Indian plates. During shortening, a pre-existing WNW-striking basement fault zone was reactivated, creating the HSZ. A G-Plates reconstruction between the two plates reveals an ~8° counter-clockwise rotation of India (with respect to fixed Arabia) between 32.5 and 20 Ma, resulting in ~150 km E/W-shortening between both plates at the easternmost tip of Arabia. The area northeast of the HSZ underwent most E-W-shortening. The 150 km interplate E/W-shortening is the maximum value for sinistral shearing along the HSZ and other faults. Some of the shortening may have been absorbed offshore Oman across the Owen Basin and/or along the continental/oceanic transitions of both plates.</p>

A textbook example of triply-folded Ediacaran carbonates – insights into geodynamics and geomorphology (Hat Plateau, Jabal Akhdar Dome, Oman Mountains)

<p>The Jabal Akhdar Dome (JAD) of the Oman Mountains contains superbly exposed sedimentary Neoproterozoic formations in its core. Carbonates of the Hajir Formation are resistant against erosion in the prevailing semi-arid conditions unlike the subjacent and overlying siliciclastic formations. Structural fieldwork and satellite image analyses reveals that the central-western JAD (Hat Plateau) was affected by three folding events. Each event produced its own fascinating fold style with associated structures. The widely exposed Hajir carbonates displays these folds spectacularly. The geomorphology of these carbonates reflects the folds with differently oriented rides and troughs as anti- and synclines, respectively. Thus, the JAD acted as a natural laboratory where the 3D fold styles can be directly linked to the geomorphology and vice versa.</p><p>A previously unrecognized folding event (F1) produced overturned NNE-verging tight folds. The fold amplitude ranges between tens and hundreds of meters, and the overall non-plunging fold axes trend ESE. The F1 folds are associated with a gently to moderately SSW-ward dipping penetrative axial plane cleavage. Open to tight upright kilometric F2 folds refolded the F1 structures. The F2 folds are overall non-plunging and NE/NNE-trending, and contain a penetrative sub-vertical axial plane schistosity, parallelly oriented to the F2 axes. The youngest folding event (F3) produces one open and broad anticline. The F3 fold axis trends WNW through the Hat Plateau and the anticline contains a WNW-striking sub-vertical spaced axial plane schistosity.</p><p>The deformation style of the F2 folds and related structures changes abruptly along a NNE-oriented zone at the western end of the Hat Plateau. West of this, the F2 structures are ENE-oriented while east of it the orientation is NE to NNE. Furthermore, the amplitude of the F2 folds decreases from ~3 km in the west to <1 km in the east. We relate this sudden change of the F2 style to the western flank of a pre-existing subsurface basement horst. We suggest that this NNE-striking horst is the northern continuation of the Makarem-Mabrouk High/Horst below the JAD. The eastern horst shoulder would be at the eastern margin of the JAD and parallel to the Semail Gap. A buttressing effect along the western horst’s shoulder during NW/SE to WNW/ESE-directed F2 shortening would explain the dramatic change in the F2 style.</p><p>In summary and in 3D terms, the F1 folds were originally oriented parallel to the present F1 anticline, i.e. before the F2 deformation, while the F2 folds strike almost perpendicularly to this direction. The F1 and F2 folding episodes associated with the abrupt change in F2 style are depicted in a steric block diagram, which visualizes the complex findings, allowing for a 3D understanding of the structures.</p>