Paleo-fluids characterisation and fluid flow modelling along a regional transect in Northern United Arab Emirates (UAE)

Abstract

In the Northern Emirates, Jurassic and Lower Cretaceous platform carbonates of the Musandam parautochthonous units are tectonically overlain by siliciclastic units of the Hawasina-Sumeini allochthon, which derive from the former paleo-slope domain and a more distal basinal portion of the Arabian margin of the Tethys, respectively. All these tectonic units display numerous evidences of paleo-fluid circulations, accounting for dolomitisation and recrystallisation of the rock matrix (Musandam Platform units), as well as cementation of fractures. Polymict breccias of Upper Cretaceous Ausaq Formation which underlay the sole thrust of the Hawasina-Sumeini allochthon also record episodes of hydraulic fracturing, whereas fluid inclusion data indicate precipitation at high temperature in relation to paleo-fluid flow. Petrography of thin-sections (conventional and cathodoluminescence microscopic techniques) as well as fluid inclusion and stable isotopes analyses, were combined with microtectonic studies. These analytical data document (1) the paragenetic sequence of diagenetic products for the Musandam Platform (which constitutes a carbonate reservoir analogue) and Sumeini units of the Dibba Zone, as well as (2) the nature of the paleo-fluids circulating along fractures and the sole thrust of the Hawasina-Sumeini allochthon. The main results of this petrographic approach are qualitative, evidencing (1) the rapid and vertical transfer of hot fluids in the vicinity of the former slope to platform transition, accounting for episodes of hydrothermal dolomitisation, as well as (2) early (i.e. pre-orogenic) and late (i.e. post-orogenic) episodes of emersion of the carbonate units, accounting for additional interactions with meteoric fluids and karstification. In order to better link these diagenetic events with the overall burial, thermal and kinematic evolution of the Arabian margin, basin modelling with Ceres2D, including fluid flow and pore-fluid pressure modelling, was subsequently performed along a regional transect (D4) located in the vicinity of the samples localities and cross-cutting the Northern Oman Mountains from Dibba in the east up to the Arabian Gulf in the west. New subsurface constraints provided by deep seismic profiles were used to constrain the architecture of the cross-section, and to test various hypotheses on the lateral and vertical connection, timing and hydrodynamic behaviour of the faults. This Ceres basin modelling also provides new quantitative estimates of the paleo-fluid pathways, of the timing and velocities of the fluid transfers and of the evolution of pore-fluid pressures. Ultimately, this integration of petrographic studies on surface samples and coupled kinematic and fluid flow basin modelling provides an updated scenario for the succession of tectonically controlled episodes of fluid rock interactions, namely dolomitisation and karstification recorded in the Mesozoic platform carbonates of the Northern Emirates.

Rift and salt-related multi-phase dolomitization: example from the northwestern Pyrenees

“…Therefore, tectonics exerted strong control on the fluid circulation and associated dolomitization by creating pathways through faults and fracture networks as well as along the diapir boundaries. This consequently had an important effect on the diagenetic evolution of the carbonate platform in accordance with other studies conducted in similar tectonic settings (Callot et al, 2010;Gonzalez et al, 2012;Roure et al, 2005Roure et al, , 2010Vilasi et al, 2009).…”

Relationship between karstification and burial dolomitization in Permian platform carbonates (Lower Khuff — Oman)

“…The deposition of these extensive platform carbonates was initiated from Middle Permian to Early Triassic times (Callot et al, 2010;Weidlich and Bernecker, 2011) triggered by the rifting of the Neo-Tethys ocean (Koehrer et al, 2011;Pillevuit, 1993;Stampfli and Borel, 2002) and the fragmentation of the supercontinent Pangaea (Ruban et al, 2007;Sharland et al, 2001). The more than 2000 km wide extension of the platform allows the study of stratigraphically equivalent sediments to Oman in the subsurface of Bahrain, UAE, Qatar, Saudi Arabia and Kuwait (Weidlich and Bernecker, 2011) (subsurface Khuff Formation).…”

Origin of Drusy Dolomite Cement in Permo-Triassic Dolostones, Northern United Arab Emirates

“…Fluid-inclusion microthermometry of drusy mosaic dolomite and the subsequently precipitated calcite cement indicate formation from hot brines during compressional tectonic events in conjunction with the obduction of Oman ophiolites [16,36]. However, it is not immediately clear whether the drusy mosaic dolomite has been precipitated as cement [13] or formed by dolomitization of drusy mosaic calcite by the hot basinal brines [15,37].…”

“…The origin of such dolomite is not fully explored, particularly regarding whether it is a primary precipitate or formed by dolomitization of precursor drusy calcite cement. The fluid flow and related diagenetic evolution, particularly dolomitization of carbonate succession in northern United Arab Emirates (UAE), is interpreted to be controlled by the tectonic evolution of the region [16,17].…”