Microfacies and diagenesis of the reefal limestone, Callovian Tuwaiq Mountain Limestone Formation, central Saudi Arabia (original) (raw)
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During diagenetic stages, the aragonitic skeletons and the inter/intra-corallite cement of the upper Jurassic corals of Hanifa Formation either dissolved or subjected to diagenetic alterations including cementation, micritization, recrystallization, silicification, dolomitization and dedolomitization. The proposed sequence of diagenetic stages is as follows: early marine diagenesis, early meteoric and mixing zone diagenesis, late meteoric diagenesis, and shallow burial diagenesis. Each stage is characterized by certain diagenetic processes. The source of sulfate solutions for dedolomitization in the studied corals is the dissolved anhydrite deposits of the Arab–Hith Formations, sometime before their erosion. A possible source of silica, needed for the formation of chert and chalcedony, is the sponge spicules dispersed in many carbonates of the Hanifa Formation.
Arabian Journal of Geosciences, 2012
The Neogene carbonate rocks have relatively small exposure relative to the siliciclastic and evaporite rocks in Rabigh and Ubhur areas, north Jeddah, Red Sea coastal plain of Saudi Arabia. The Miocene carbonates form small hills in both areas, which conformably overlie the siliciclastics, whereas the Pleistocene coral reefs form terraces facing the Red Sea in Rabigh area. The Neogene carbonates are represented by the following microfacies types: (1) dolomitic, oolitic, foraminiferal packstone; (2) sandy, dolomitic, intraclastic, foraminiferal packstone; (3) dolomitic and oolitic wackestone; (4) dolomitic, foraminiferal, intraclastic wackestone; (5) dolomitic mudstone; (6) coral boundstone; and grainstone. The diagenetic processes affecting these carbonates are compaction, dissolution, aggrading neomorphism, and replacement that took place during deposition, shallow burial, and uplift. Pervasive dolomitization by the seepage reflux mechanism is responsible for the mimic replacement of the calcite of the original component of the limestone with dolomite. Sediments, biota, and lithofacies characteristics of the studied carbonate rocks of Rabigh and Ubhur areas indicate the presence of three facies zones; these are (1) FZ 5 platform margin reefs, (2) FZ 6 (platform margin sand shoals), and (3) FZ 7 platform interior-normal marine. The standard microfacies types are represented by (1) SMF 12, limestone with shell concentration; (2) SMF 15, oolitic wackestone and packstone; and (3) SMF 18, bioclastic grainstone and packstone with abundant benthic foraminifera.
The Campanian Hajajah Limestone Member of the Aruma Formation was formed during two regressive episodes. Each of them formed of three depositional facies, from base to top: 1) intra-shelf basin facies, made up of fossiliferous green shale and mudstone with ostracods and badly preserved foraminifers. 2) fore-reef facies, consists of hard, massive, marly coralline limestone. The upper part is rich with low divers, badly to moderate preserved, solitary and colonial corals, and, 3) back reef and near-shore facies, consists of fossiliferous sandy dolomitized, bioturbated limestone with abundant reworked corals, bi-valves, gastropods, and aggregate grains. On the basis of field observations, micro-and macrofossils and microfacies analysis, the Hajajah Limestone Member was deposited in distal marine settings below storm wave base in a low-energy environment changed upward to fore-reef framework in an open marine environment with moderate to high energy conditions and terminated with shallow marine facies with accumulation of skeletal grains by storms during regression.
Journal of African Earth Sciences, 2017
In order to document the microfacies analysis and diagenetic alterations of the Middle Jurassic Dhruma Formation at southwest Riyadh City of central Saudi Arabia, a stratigraphic section was studied in detail at Khashm adh Dhi'bi area. Mudstones, wackstones, packstones, grainstones and boundstones are the main microfacies types in the studied area. These microfacies types with field investigations and fossil content indicated an environment ranging from deep shelf to organic buildup on platform margins for the studied carbonates. Cementation and recrystallization, dissolution, fragmentation and compaction, silicification, dolomitization, and bioerosion were the main diagenetic alterations affected the carbonate rocks of the Dhruma Formation. Cementation and recrystallization are represented by equant calcite crystals, Dog-tooth fringes of thin isopachous calcites and blocky low Mg-calcites. Gastrochaenolites, Trypanites and Meandropolydora spp. were the most bioeroders in coral heads and large bivalves and hardgrounds. These bioeroders indicated a long post-mortem period during the early diagenetic stage.
Eighteen scleractinian coral species belonging to 13 genera, 8 families and 4 suborders have been identified from the lower and upper parts of the Upper Jurassic (Oxfordian) Hanifa Formation at Jabal Al-Abakkayn, central Saudi Arabia. Actinastrea bernensis, A. crassoramosa, Coenastraea hyatti, Stylina kachensis, Cryptocoenia slovenica, C. wegeneri, Isastrea hemisphaerica, I. bernensis, Montlivaltia cornutiformis, M. frustriformis, Collignonastraea jumarensis, Ovalastrea michelini and Vallimeandropsis davidsoni are believed to be recorded for the first time from the Jurassic rocks of central Arabia. Most corals have massive hemispherical and globular forms, and few corals have dendroid and conical growth forms. They occur as small, isolated patches, about 0.5m thick and about 10–30m wide, in argillaceous reefal limestones. The identified corals show Africa, north America, northern, southern and western Europe, and southern or eastern Asia corals. The low diversity and abundance as well as the small size of colonies are attributed to inimical palaeoecological factors throughout the reefoids formation such as muddy substratum, water turbidity, high rate of sedimentation.
Marine Geology
Quaternary deposits of the Midyan coast of Saudi Arabia include coral-bearing limestones interbedded with sheet-flow siliciclastic sands and gravels, interpreted as braid-delta fan deposits. The limestones and their contained faunas provide evidence of periodic local stabilization of gravel surfaces and effective starvation of siliciclastic supply. Some indicate growth and deposition in waters a metre or so deep whereas others were substantially deeper. An additional group reflects initial deposition in shallow waters with resedimentation downslope by storm or other 'delta-front' processes. The surfaces of the fans provided morphological and environmental analogues to fore-and back-reef situations in which corals, calcareous coralline algae, molluscs, and echinoderms flourished, but in this area did not form independent reefs. The dominant controls on the changes from siliciclastic-to carbonate-dominated deposition were not transitional, and primarily related to channel and fan-lobe migration rather than tectonic or eustatic sea level changes. Similar variations in the distribution of siliciclastic sediments may control carbonate occurrence in other mixed sequences.
Proceedings of the Geologists' Association, 2017
Four Middle-Upper Jurassic sections from central Saudi Arabia have been investigated to evaluate microfacies types and macro-invertebrate paleocommunities and to interpret their paleoecology and paleoenvironments. The studied Jurassic successions are part of the Middle-Upper Callovian Tuwaiq Mountain Limestone and the Middle-Upper Oxfordian Hanifa Formation. Three main facies were recorded, including mud-supported microfacies, grain-supported microfacies and boundstones. A data matrix comprising 48 macrobenthic species in 35 samples collected from four sections were grouped into fifteen assemblages and one poorly fossiliferous interval by means of a Q-mode cluster analysis. The recorded macrofaunal assemblages have been subdivided into low-stress and high-stress on the basis of hydrodynamic conditions, substrate type, nutrient supply and hypoxia. The low-stress assemblages occur in (a) high-energy paleoenvironments with firm substrates; (b) high-energy shoals with unstable substrates of low cohesion and in (c) low-energy open marine environments with soft-substrates. The moderate-to high-stress assemblages occur in (a) oligotrophic environments with reduced terrigenous input in shelf lagoonal or in restricted inner ramp settings; (b) low-energy, soft substrate environments with hypoxia below the sediment-water interface; and, in (c) high-energy shoals and shelf lagoonal environments. The temporal distribution patterns of epifaunal and infaunal bivalve taxa are controlled by variations in water energy, substrate characteristics and productivity level. The reported litho-and biofacies confirmed that the Callovian Tuwaiq Mountain Limestone and the Oxfordian Hanifa Formation were deposited across wide spectrum of depositional environments, ranging from restricted lagoon to moderately deeper open marine basin, and providing the perfect conditions for macrofossils.
Diagenesis in live corals from the Gulf of Aqaba. I. The effect on paleo-oceanography tracers
… et Cosmochimica Acta, 2000
The effect of early diagenesis on trace element abundance in coral skeleton was studied in live coral heads (Porites) from the Nature Reserve Reef (NRR), Elat, Gulf of Aqaba, northern Red Sea. Petrography of the corals shows diagenetic features of dissolution, recrystallization, and secondary aragonite precipitation (pore filling), which are most extensive in the oldest part of the coral. Coral porewaters were extracted with a special setup and were analyzed for chemical composition. The total alkalinity and Sr deficit in pore water as compared to reef water is consistent with both precipitation of secondary aragonite and recrystallization of primary skeleton. The present rate constant of pore filling by secondary aragonite was estimated by a water replacement experiment to be 0.0015 y Ϫ1 , which equals to pore filling rate of 1.5 Ϯ 0.3 kg aragonite per year. The corals show clear seasonal fluctuations in Sr/Ca ratios that are interpreted as reflecting changes in sea surface temperature (SST). Yet, the secondary aragonite is characterized by a significantly higher Sr/Ca ratio than the average ratio in primary aragonite. Thus, measuring a mixed sample of pristine and secondary aragonite may produce erroneous (about 2°C lower) SST estimates by the Sr/Ca thermometers.
Journal of African Earth Sciences, 2018
The Jurassic succession in Saudi Arabia represents the most prolific succession in the world. However, a detailed microfacies and paleoenvironmental model description, high-frequency cycles (HFC) analysis, and paleoenvironmental reconstruction of the main source rock interval for the Jurassic reservoirs, the Callovian Tuwaiq Mountain Formation (TMF) are poorly documented. This article reports on a study of the TMF, and discusses the succession of the microfacies, paleoenvironments, HFC, and depositional sequences, and paleoenvironmental constrains. On the basis of detailed field and lab work, 8 microfacies were recognized and interpreted to be deposited in four facies belts representing the inner part of a rimmed carbonate platform including: deep lagoon, shallow lagoon, shoal and peritidal and tidal flat. Within the deep and shallow lagoonal settings, patch reefs form massive platy and domal coral colonies. The patch reef size increased by shifting from deep lagoon toward shallow lagoon settings as the conditions became more favorable for flourishing (harder substrate and more water clarity). While, by shifting from shallow lagoon to shoal settings, the patch reef size decreased till a point where no patch reefs were found as the conditions became unfavorable for flourishing (more restrictions and increase in salinity). The siliciclastic input was minute and could have been derived from tidal channels and/or windblown dust from the Arabian Shield. The stacking pattern of the microfacies revealed that the TMF represents a regressive cycle (3 rd order depositional sequence), which is formed by repeated aggrading to prograding medium and small scale cycles. The HFC analysis gave an estimated duration of a small cycle about 45 ACCEPTED MANUSCRIPT Kyr. This drives to an average rate of carbonate accumulation of 0.0455 m/Kyr. Therefore, medium and small scale cycles are possibly belonging to 4 th and 5 th order depositional cycles, respectively, which are orbitally driven by high frequency eustatic fluctuations (Milankovitch cycles "obliquity"). The paleoenvironmental reconstruction revealed that the deposition occurred under the influence of occasional storm events with normal marine euhaline salinity and becomes more restricted towards the proximal part (lagoon to tidal flat). Highlights Tuwaiq Mountain Formation deposited in the inner part of a rimmed carbonate platform It is composed of four facies belts deep and shallow lagoon, shoal, and peritidal and tidal flat Tuwaiq Mountain Formation represents a regressive 3 rd depositional sequence It is composed of repeated aggrading to prograding 4 th and 5 th order cycles Cyclicity was driven by orbitally driven high frequency eustatic fluctuations (Milankovitch cycles; i.e. obliquity) Highlights Tuwaiq Mountain Formation deposited in the inner part of a rimmed carbonate platform It is composed of four facies belts deep and shallow lagoon, shoal, and peritidal and tidal flat Tuwaiq Mountain Formation represents a regressive 3 rd depositional sequence It is composed of repeated aggrading to prograding 4 th and 5 th order cycles Cyclicity was driven by orbitally driven high frequency eustatic fluctuations
Thirty three benthic foraminiferal species belong to 23 genera and 16 families have been recorded from the coral reefs of the Callovian Tuwaiq Formation, Khashm Al-Qaddiyah area, Central Saudi Arabia. Three species: Astacolus qaddiyahensis, Nodosaria riyadhensis, Siderolites jurassica are believed to be new. Nearly all identified foraminifera are of Atlantic-Miditeranean affinity. The foraminiferal assemblage recorded in the present work is mixed of open marine, moderately deep marine conditions associations and shallow to deep lagoon. The reefal part of upper Twiaq Formation may have been deposited in shallow water of lower to middle shelf depth (20–50 m) as indicated by abundant corals and benthic foraminifera. The coral fauna and bearing benthic foraminifera indicated moderate water energy.