Facies mosaic and diagenetic patterns of the early Devonian (Late Pragian–Early Emsian) microbialite‐dominated carbonate sequences, Qasr Member, Jauf Formation, Saudi Arabia

Abstract

The Al-Jawf area of northern Saudi Arabia provides spectacular outcrops of Early Devonian carbonate bioherms in the Wadi Murayr and Dumat Al-Jandal areas. These carbonate bioherms belong to the Qasr Member of the Late Pragian-Early Emsian Jauf Formation (~405 Ma) and are surrounded by a bioclastic carbonate succession. The Qasr Member is the first major carbonate unit of the Palaeozoic succession in Saudi Arabia that mainly consists of microbialite carbonates and metazoan reefs exhibiting distinct mound features. These bioherm complexes and their associated carbonate facies are pervasively dolomitized. Stratigraphic, petrographic and geochemical analyses were conducted to determine the facies distribution and interpret their depositional and diagenetic processes. A total of 11 facies are identified from a range of depositional environments within a carbonate platform system, ranging from tidal flats, lagoon, shoal, patch reefs to reef front. The main diagenetic processes are carbonate cementation and dolomitization. Dolomitization occurred as both fabric preserved (mostly in grain-dominated facies) and fabric destructive (mud-dominated facies). The microbialites and coralline sponges facies show poor reservoir with visual porosity less than 5%, but this succession may have a potential to serve as a good source for the underlying and overlying facies. Ooid and peloidal grainstone facies show fair to good visual porosity that locally exceeds 10% with intergranular porosity as the dominant type. However, in the most studied samples, vuggy and intraparticle porosities are observed as the dominant type.

Structural diagenesis and dolomitization of Cenozoic post-rift carbonates in the Red Sea rift basin: A multiproxy approach

“…A sandy carbonate layer in the middle strata followed this layer, with thin laminated mud layers. An abundance of Borelis melo has been observed in this stratum, confirming its Miocene age (Hughes, 2014;Koeshidayatullah et al, 2016). The last unit is marked by a very thick (10.75 m) floatstone coral unit at the bottom, followed by a 3-m wackestone to the top (Figure 2).…”

“…The creation of micrite envelopes by microboring organisms surrounding skeletal and non-skeletal grains may provide a substrate for a developing marine cement (Al-Ramadan et al, 2019). The depositional environment of the carbonate host rock is suggested to have been deposited in the platform interior to platform margin carbonate facies, characterized by a highly heterogeneous vertical succession (Koeshidayatullah et al, 2016;Al-Ramadan, 2017;Al-Ramadan et al, 2019). The dolomitization process is interpreted to be near-surface, early formed dolomite, based on its fabric-preserving mimetic texture (e.g., Sibley and Gregg, 1987;Swart, 2015).…”

“…This dolomitization results in intergranular pores that are important for the oil and gas reservoir. In addition to creating pores, the considerable dolomitization also helped to preserve them (Koeshidayatullah et al, 2016).…”

Quantitative evaluation of the roles of ocean chemistry and climate on ooid size across the Phanerozoic: Global versus local controls

“…The vast expanse of the ramp and the large supply of nuclei (e.g. Sumner & Grotzinger, 1993;Koeshidayatullah et al, 2016) may also explain the lower Ω in the Lower Triassic epicontinental carbonates of the Middle East (Saudi Arabia and Iran) by providing a larger area favourable for shallow carbonate precipitation at both the micro-scale and macro-scale. Such a concept could also be applied to systems of other ages in vast epicratonic seas.…”