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Location of eight outcrop sections in the Oman Mountains. The Dhruma Formation was investigated in another outcrop section in Jabal Madar towards the southeast of the Oman Mountains (data not shown in figure 1; satellite picture from google maps, 12/2015).
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As an example of an epeiric carbonate ramp depositional system, the world-class outcrops of the Middle Jurassic Dhruma Formation were studied in the Oman Mountains (Sultanate of Oman). An integrated approach was followed: facies analyses were combined with quantitative sequence-stratigraphic methods as well as bio- and chemostratigraphy. Deposition...
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... study area ( Fig. 1), which consists of a large anti- cline that enables detailed investigation of Permian to Cretaceous strata ( Glennie et al., 1974), is located ca 100 km to the west-southwest of Muscat in the Oman Mountains. Eight outcrop sections were logged along the northern flank of the Oman Mountains, where the type section of the Dhruma Formation ...
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... low-energy facies in the Dhruma Formation of Oman are key to understanding the range of palaeoenvi- ronments and thus the present cyclicity, mudstones were sampled at several locations (Wadi Sahtan, Wadi Bani Awf and Wadi Bani Kharus; Fig. 1) to identify if they were deposited in a fore-or backshoal environment. About 100 g of each of the nine samples obtained were processed for palynology at Petroleum Development Oman using standardized ...
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... peritidal lithofacies association (LFA 1) comprises carbonates, which show dominantly micritic textures and a minor quartz content. They are sometimes interbedded with thin, several centimetres thick sandstone sheets ( Fig. 10) with a lateral consistent thickness of at least hundreds of metres to kilometres. Peritidal facies were deposited in a wide spectrum of energy conditions, lead- ing to a diverse sedimentary record ranging from low- energy mudrocks (Fig. 11), to medium-energy microbial laminites and stromatolites (Fig. 12), as well as rippled wacke-to ...
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... minor quartz content. They are sometimes interbedded with thin, several centimetres thick sandstone sheets ( Fig. 10) with a lateral consistent thickness of at least hundreds of metres to kilometres. Peritidal facies were deposited in a wide spectrum of energy conditions, lead- ing to a diverse sedimentary record ranging from low- energy mudrocks (Fig. 11), to medium-energy microbial laminites and stromatolites (Fig. 12), as well as rippled wacke-to packstones, to high-energy events which show scour fills and occasionally cross-bedding. Peritidal facies of the Dhruma Formation show a rather low biodiver- sity comprising gastropods, bivalves, undefined shell debris, foraminifera and ...
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... centimetres thick sandstone sheets ( Fig. 10) with a lateral consistent thickness of at least hundreds of metres to kilometres. Peritidal facies were deposited in a wide spectrum of energy conditions, lead- ing to a diverse sedimentary record ranging from low- energy mudrocks (Fig. 11), to medium-energy microbial laminites and stromatolites (Fig. 12), as well as rippled wacke-to packstones, to high-energy events which show scour fills and occasionally cross-bedding. Peritidal facies of the Dhruma Formation show a rather low biodiver- sity comprising gastropods, bivalves, undefined shell debris, foraminifera and peloids. Individual facies are generally homogeneous in composition and ...
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... Low-Energy Zone Z lithofacies association (LFA 2) extends over 100s of kilometres and is dominated by lime-and dolo-mudstones ( Figs 13 and 14), occasionally with a minor clay content. In some places, thin (less than 10 cm thick) packstone sheets with a lateral extent of hundreds of metres to kilometres can be observed. ...
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... is common in Zone Z with abundant Thalassinoides trace fossils suggesting a marine shelf environment (Seilacher, 2007). Mud-and wackestones are often bioturbated and contain gastropods, bivalves, echinoderms or undefined shell debris (Figs 15 and 16) as well as abiogenic compo- nents such as peloids and coated grains. ...
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... low-energy conditions in combination with a very low carbonate productivity, probably due to clastic input from the hinterland, lead to the formation of mud- stones with a minor clay content (facies type: Mtb). These beds tend to be thinly bedded (Mtb, Fig. 14) and show only a low biodiversity and no bioturbation. The clay content is often reflected in a slight increase in the gamma-ray signal. Thin packstone sheets can probably be interpreted as storm ...
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... and are of a lagoonal to shoal-margin set- ting. Centimetres to decimetres thick, graded layers occa- sionally containing mud clasts at the base, are interpreted as storm deposits which were able to reach low-energy Zone Z. Wacke-to packstones are either dominated by bivalves, peloids and shell hash with subordinate bra- chiopods and gastropods (Fig. 17) or oncoids (Fig. 18). As oncoids of the Dhruma Formation are usually equidi- mensional, they were probably formed by continuous rolling above the wave base (Ratcliffe, ...
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... to shoal-margin set- ting. Centimetres to decimetres thick, graded layers occa- sionally containing mud clasts at the base, are interpreted as storm deposits which were able to reach low-energy Zone Z. Wacke-to packstones are either dominated by bivalves, peloids and shell hash with subordinate bra- chiopods and gastropods (Fig. 17) or oncoids (Fig. 18). As oncoids of the Dhruma Formation are usually equidi- mensional, they were probably formed by continuous rolling above the wave base (Ratcliffe, ...
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... Mixed cycle type (Fig. 26) • Low-energy cycle type (Figs 27 and 28) • Medium-energy cycle type (Figs 29 and 31) • High-energy cycle type (Figs 32 and 33) ...
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... variations in the thickness of medium-energy cycles are caused by limited accommodation space in CoSe1 (Fig. 2), discussed further in a forthcoming paper covering correlations between 29 outcrop sections and the subsurface of Oman. Low-energy textures vary between mud-and wackestones and high-energy texture between pack-and grainstones (Fig. 31). Medium-energy cycles are not always dominated by transgressive features but are sometimes symmetrical (Fig. 31, upper ...
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... (Fig. 2), discussed further in a forthcoming paper covering correlations between 29 outcrop sections and the subsurface of Oman. Low-energy textures vary between mud-and wackestones and high-energy texture between pack-and grainstones (Fig. 31). Medium-energy cycles are not always dominated by transgressive features but are sometimes symmetrical (Fig. 31, upper ...
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... conditions, their occurrence suggests that these are the most distal deposits within the Dhruma Formation and thus are a candidate to define the position of the zone of maximum flooding of the upper composite sequence. The bio-component diversity is variable throughout the section and appears to correspond to high-frequency sequences. As shown in Fig. 41, the diversity increases towards the zone of maximum flooding of each high-fre- quency sequence and decreases towards their boundary. Furthermore, an overall increase in biodiversity can be observed towards the top of the formation, most likely due to increasing open marine conditions, while rather restricted marine conditions in the ...
Citations
... The Saiq-Mahil boundary (Early Triassic) remains controversial, with various interpretations proposed by different researchers (Koehrer et al., 2010;Baud and Richoz, 2013). The Mahil KS1 Formation of the Lower Triassic, well-exposed in the Saiq Plateau and Wadi Sahtan regions in the Northern Oman Mountains (Fig. 1a-d), is regarded as an epeiric platform sequence deposited within a passive continental margin on the Arabian Plate (Walz et al., 2013;Eltom et al., 2017;Schlaich and Aigner, 2017). ...
... Rights reserved. (Tasli et al. 2008;Gardosh et al. 2011;Eid et al. 2015;Han et al. 2016;Ismanto et al. 2019;Schlaich and Aigner 2017). B Paleogeographic map of the Middle Jurassic along the eastern margin of Pangea with marked approximate location of study areas (modified from Han et al. 2016;Ismanto et al. 2019) Field observations show patchy dolomitization, suggesting that it is formed along weak zones (burrow-related void spaces, fractures, stylolites, and parallel bedding planes) (Fig. 2B-F). ...
... The present study in the Trans Indus Ranges and western extension of Hill Ranges, Pakistan can be compared with other significant studies in the western coastline of Tethys which include South Turkey (Tasli et al. 2008), Central Saudi Arabia (Ismanto et al. 2019), Oman (Schlaich and Aigner 2017), the East Mediterranean (Gardosh et al. 2011), and the Southern Tibet, China (Han et al. 2016) and is depicted in Fig. 14. ...
... In Oman, the middle Jurassic period can be described as phase of shallow carbonate platform with a relatively gentle slope (Schlaich and Aigner 2017). The Dhruma Formation in Oman, which spans the entire Middle Jurassic, has a total thickness of 238 m and generally exhibits a pattern of increasing sediment grainsize from bottom to top (Schlaich and Aigner 2017). ...
The middle Jurassic Samana Suk Formation is well exposed in Himalayan foreland fold and thrust belt forming a good hydrocarbon reservoir of the Indus Basin; however, the combined sedimentological and geochemical studies are not conducted so far. An integrated approach using field, petrographic, geochemical, and isotopic studies was used to better understand the depositional and diagenetic processes within the formation. The formation is predominantly composed of thin to medium-bedded limestone with intercalation of shale. Field observations reveal sedimentary and diagenetic features such as cross bedding, sole marks, ripple marks, convolute bedding, stylolites, dissolution marks and patchy dolomitization. Microfacies associations include mudflat microfacies associations (mudstone MF-1, dolo-mudstone MF-2), lagoonal microfacies associations (siliciclastic bio-packstone MF-3, peloidal bioclastic packstone MF-4, bioclastic wackestone MF-5, and peloidal wackestone MF-6), barrier/shoal microfacies association (peloidal grainstone MF-7, ooidal–peloidal bioclastic grainstone MF-8, ooidal grainstone MF-9, and bioclastic peloidal grainstone MF-10). The above-mentioned microfacies associations suggest the deposition in the ramp settings (mudflats, lagoonal and shoal). The diagenetic features include: micritization, mechanical/chemical compaction, dissolution, neomorphism, cementation, dolomitization and fracturing. Selective replacement of grain dominated facies represents fabric retentive replacive dolomite RD-I formed at the early phase, followed by matrix replacive dolomite RD-II. Late-stage diagenetic alteration is marked by fabric-destructive dolomite RD-III. Geochemical data show a consistent decrease in salinity from the early to late diagenetic phases characterized by elevated Na and K concentration and reduced Fe and Mn concentration. Furthermore, stable isotopic data of limestone and dolomite phases show non-depleted δ¹³ C values ranging from + 0.26 to + 1.86‰ VPDB suggesting no external supply of carbon after the deposition of the carbonate units. The non-depleted δ¹⁸ O values ranging from − 1.96 to − 0.45‰ VPDB of dolomite phases represents seawater signatures, and hence may have formed in surface processes of marine water in mudflat settings/evaporitic conditions. Paleogeographically, Samana Suk Formation exhibits similar depositional conditions with the western coastline of the Tethys.
... For this reason, the Jurassic provides an excellent model for the depositional processes and sedimentological heterogeneity of ancient carbonate ramps worldwide (Beydoun 1986;Sharland et al. 2001). Epeiric carbonate ramps are a common type of depositional system, although the distribution of facies, geometries and fine-scale complexity are still only poorly known in the Jurassic of the Arabian Plate (Schlaich and Aigner 2017). ...
... . A progressive increase in δ 13 C values is noted near the top of the niortense zone within units D2 and lowermost D3, with an average of 2‰ (VDB) in the lower part of the succession, similar to records in the northwestern Tethyan and the Arabian basins(O'Dogherty et al. 2006;Schlaich and Aigner 2017;Al-Mojel et al. 2018). Similar records have also been documented in the UAE(Hönig and John 2015. ...
The lithofacies, microfacies, and depositional environments of the Dhruma Formation were studied at the type locality at Khashm adh Dhibi to better understand the sedimentology and depositional history on the Arabian Platform. Twelve lithofacies were identified that can be grouped into four lithofacies associations corresponding to depositional paleoenvironments ranging from peritidal to open marine. The vertical distribution of the lithofacies and their corresponding depositional settings allow for the division of the Dhruma Formation into six 3rd-order sequences (DS1–DS6), each bounded by sharp vertical facies changes, and/or hiatuses. Abrupt negative shifts in both δ¹³Ccarb and δ¹⁸Ocarb values coincide closely with the placement of sequence boundaries on the Arabian Platform. This suggests that the carbonates in these zones underwent meteoric diagenesis during episodes of subaerial exposure. Comparison of the sequence stratigraphy interpreted from the vertical distribution of facies with published eustatic sea-level curves improves our understanding of the eustatic sea-level variation and/or local tectonics in forming both local hiatuses and regional unconformities.
... Deskripsi singkapan dimaksudkan untuk mengidentifikasi ciri-ciri utama, seperti bidang perlapisan, gradasi, struktur sedimen, fosil dan geometri [2]; [3]; [4]. Pengamatan mikroskopis terhadap tekstur, komposisi (persentase cangkang terfragmentasi dan/atau tidak terfragmentasi, persentase bahan mikrit dan terrigenous, komposisi ukuran butir), jenis allochem, kandungan diagenetik dan mikrofosil memberikan panduan untuk menemukan fasies karbonat, energi indeks, stratigrafi urutan dan lingkungan pengendapan [4]; [5]; [6]. Investigasi lapangan dan pengamatan mikroskopis telah diterapkan pada fasies dan interpretasi pengendapan karbonat purba beberapa cekungan di Asia [3]; [4]; [7]; [8] termasuk Indonesia [9]. ...
ABSTRAK (10 PT) Daerah penelitian berada di daerah Sindangsari dan Sekitarnya, Kecamatan Cimerak Kabupaten Pangandaran, Provinsi Jawa Barat. Daerah penelitian masuk pada Formasi Pamutuan yang tersingkap pada Selatan peta lembar Karangnunggal, Formasi Pamutuan berumur Miosen Tengah dengan lingkungan pengendapan laut dangkal. Perbedaan proses sedimentasi dan hubungan antara formasi pada beberapa lokasi diduga akibat pengaruh paleogeografi awal. Hal tersebut menjadi suatu hal yang menarik untuk dikaji dan sesuai dengan tujuan penulisan artikel ini karena dapat memberikan gambaran spesifik terhadap perkembangan lingkungan pengendapan daerah penelitian. Untuk memahami proses sedimentasi Formasi Pamutuan maka dalam penelitian ini dilakukan analisis fasies dan lingkungan pengendapan. Metode yang digunakan dalam penelitian ini meliputi pengumpulan data dengan melakukan pemilihan sampel representatif, melalukan deskripsi petrologi dan petrografi sehingga dapat menentukan suatu fasies seperti litologi. Berdasarkan analisis data didapatkan empat fasies batuan fasies Litic Greywake dan Mudrock, fasies Bounstone, fasies Packstone dan fasies Mudstone. Fasies-fasies tersebut diendapkan pada empat lingkungan pengendapan yang saling berganti yaitu sand shoals, reef margin, slope dan toe of slope. Analisis mikrofosil menunjukkan batuan karbonat dari Formasi Pamutuan di daerah penelitian diendapkan pada N 13-N 14 (Miosen Tengah) pada lingkungan Neritik Tengah-Neritik Luar (100-200 meter). Kata kunci : fasies, lingkungan pengendapan, pamutuan, pegunungan selatan, Pangandaran ABSTRACT (10 PT) The research area is in the Sindangsari and surrounding areas, Cimerak District, Pangandaran Regency, West Java Province. The study area is included in the Pamutuan Formation, which is exposed in the South of the Karangnunggal map sheet, the Middle Miocene Pamutuan Formation, with a shallow marine depositional environment. Differences in sedimentation processes and the relationship between formations at several locations are thought to be due to the influence of early palaeogeography. This is an interesting study because it can provide a specific description of the development of the depositional environment in the study area. In order to understand the Pamutuan Formation's sedimentation process, facies and depositional environment analyses were carried out in this study. The method used in this study included collecting data by selecting representative samples and carrying out petrological and petrographic descriptions to determine facies such as lithology. Based on data analysis, four rock facies were obtained; Greywacke lithic and Mudrock, Bounstone, facies Packstone, and Mudstone. These facies were deposited in four alternating depositional environments: sand shoals, reef margin, slope, and toe of the slope. Microfossil analysis shows that carbonate rocks from the Pamutuan Formation in the study area were deposited at N 13-N 14 (Middle Miocene) in the Middle Neritic-Outer Neritic environment (100-200 meters). PENDAHULUAN (10 PT) Indonesia memiliki jumlah batuan karbonat yang cukup melimpah keberadaanya. Batuan karbonat sebagian besar terbentuk di kompleks paparan karbonat di dataran pasang surut, laguna, beting dan cekungan; beberapa juga ditemukan di lingkungan terestrial. Proses pembentukan batuan ini lebih rumit dibandingkan batuan silisiklastik karena pada dasarnya proses pembentukannya tidak semata-mata sedimentasi. Suksesi geometri
... A compilation of Middle Jurassic global δ 13 C data reveals distinctive patterns in both marine and continental records, in which four PCIEs during the Aalenian, the early Bajocian, at the Bathonian-Callovian boundary, and at the Callovian-Oxfordian boundary interspersed with three NCIEs at the Aalenian-Bajocian boundary, at the Bajocian-Bathonian boundary, and in the middle Oxfordian (e.g., Bartolini and Cecca, 1999;Jenkyns et al., 2002;Hesselbo et al., 2003;O'Dogherty et al., 2006;Schlaich and Aigner, 2017;Fig. 9). ...
The breakup of Pangaea and the rapid opening of the Ligurian and Central Atlantic oceans during the Middle Jurassic resulted in widespread volcanism accompanied by significant shifts in global environments, climates, and floras. Although major volcanism is a plausible driver of such global changes, linking these phenomena in the Middle Jurassic is hindered by a lack of detailed sedimentary records from which to evaluate cause and effect. Here, we link Middle Jurassic environmental, climatic, and floral changes with volcanism using records from the Dameigou section of the Qaidam Basin on the Qinghai-Tibet Plateau. High-resolution chemostratigraphic (δ13Corg patterns) and biostratigraphic (palynological fossils) data reveal three negative organic carbon isotope excursions (NCIE) at the Aalenian-Bajocian boundary, the Bajocian-Bathonian boundary, and in the middle of the Callovian, respectively. The first two NCIEs (NCIE-I and NCIE-II) were accompanied by relatively warm and humid climatic conditions and coal accumulation. In contrast, the third NCIE (NCIE-III) was accompanied by warm but dry climatic conditions, a decrease in coal accumulation, a decline in plant diversity, the significant decline in fern spore diversity and abundance, and a rapid increase in the abundance of Classopollis pollen (based on petrological, palynological, PCA, Hydrophyte/Xerophyte ratio, and nMDS data). Four sedimentary mercury anomalies (Hg/Al2O3 spikes) have temporal coincidence with the three NCIEs and climate warming events, suggesting a volcanic origin for these. We suggest that volcanism was a key driver of Middle Jurassic change, with major pulses releasing large amounts of CO2 and Hg into the atmosphere, resulting in Hg loading, NCIEs, climatic warming, and floral changes in terrestrial strata. Our multi-proxy study provides new insights into the links between volcanism and terrestrial environmental, climatic, and floral changes during the Middle Jurassic.
... The Lower Triassic Mahil Formation, well-exposed in the Saiq Plateau and Wadi Sahtan areas in the Northern Oman Mountains (Fig.1), is the first epeiric platform sequence deposited on the passive continental margin of the Arabian Plate (Walz et al., 2013;Eltom et al., 2017;Schlaich and Aigner, 2017).The Lower Mahil Formation is an outcrop equivalent to the subsurface Kuff KS-1 Formation; the Khuff Formation is an example of a very low-gradient homoclinal carbonate ramp (Alsharhan and Kendall, 1986;Al-Aswad, 1997;Insalaco et al., 2006;Knaust, 2009;Baud et al., 2010;Koehrer et al., 2010Koehrer et al., , 2011Koehrer et al., , 2012Bendias et al., 2013;Fontana et al., 2013;Walz et al., 2013;Amel et al., 2015).Deposition of the Khuff Formation shelf occurred in shallow-to open-marine conditions, but shallow-water conditions were the most common (Alsharhan and Kendall, 1986;Bendias et al., 2013;Peyravi et al., 2015).Minor detailed studies of the microfacies and depositional environment were published about the Khuff Formation KS-1 cycle in Oman, despite its relevance in the oil and gas industry.The major aim of this study is to provide a detailed description of a time-equivalent outcrop to the subsurface Khuff KS-1 Formation in the Saiq Plateau and Wadi Sahtan areas.The specific aims are to: (i) define the microfacies characteristics and distribution, (ii) establish a robust framework for the depositional environment model, and (iii) provide a reference for the hydrocarbon exploration and development of the Khuff Formation KS-1 in the northern Oman Mountains. ...
This study presents a detailed microfacies analysis of the Lower Triassic Mahil Formation (Khuff outcrop equivalent (KS-1)) in Jabal Akhdar, at the Saiq Plateau and Wadi Sahtan areas of Northern Oman.Two sections were measured and sedimentologically logged along a depositional dip profile emphasizing color, lithology, grain components, bed thickness, the nature of bed contact, lateral continuity of beds, and fossil content.One hundred and eighty fresh rock samples were collected from various lithofacies.The collected samples were thin-sectioned after blue epoxy was impregnated, and then they were half stained with Alizarin Red S and Potassium Ferricyanide for mineralogical identification.The point-counted compositions were determined by counting 300 points for each thin section to reconstruct the original components, obtain precise quantification, develop representative microfacies, and construct the depositional model for the Lower Mahil Formation.Accordingly, eighteen microfacies types representing different carbonate ramp environments were identified; two are only recognized in the Wadi Sahtan logged section, ten are restricted to the Saiq Plateau logged section, and six are common for both sections.The Lower Mahil Formation consists of backshoal (inner ramp) to foreshoal (mid-ramp) carbonate facies, with shoal (ramp crest) facies restricted to the Saiq Plateau logged section.The backshoal facies was characterized by abundant non-skeletal grains with breccia.The shoals were predominantly oolitic and intraclastic packstone-grainstone.Foreshoal carbonate facies, on the other hand, has mixed skeletal and non-skeletal grains with weakly developed hummocky cross-stratified beds. The shallow-water foraminiferal and oolitic packstone/grainstone facies are the potential reservoir intervals, whereas the wackestone facies is the non-reservoir intervals within the Lower Mahil Formation. The detailed sedimentological and microfacies analysis helped characterize the Lower Mahil Formation for better recognizing the potential reservoir vs. no-reservoir. This study can be a key reference to correlate the Lower Mahil Formation locally and regionally.
... The Arabian Plate was located at 25° south of the equator in the Permian and moved 15° further north towards the equator during the Triassic (Scotese 2001;Ziegler 2001;Schlaich and Aigner 2017). The plate tilted northwards due to rifting and subsidence that followed the breakup of Pangea in the Early Jurassic (Grabowski and Norton 1995;Schlaich and Aigner 2017). ...
... The Arabian Plate was located at 25° south of the equator in the Permian and moved 15° further north towards the equator during the Triassic (Scotese 2001;Ziegler 2001;Schlaich and Aigner 2017). The plate tilted northwards due to rifting and subsidence that followed the breakup of Pangea in the Early Jurassic (Grabowski and Norton 1995;Schlaich and Aigner 2017). During the Jurassic, the Arabian Plate was stationary and occupied an equatorial position on the southern margin of the Neo-Tethys Ocean (Murris 1981;Al-Husseini 1997;Al-Fares et al. 1998;Ziegler 2001) (Fig. 1a). ...
... Dolomite, which was originally a low-energy mudstone facies, is composed of fine sucrosic preserving dolomite crystal rhombs. Dolomudstone facies described from the Dhruma Formation in Oman was interpreted as restricted tidal flat or shallow lagoon deposits (Schlaich and Aigner 2017;Schlaich et al. 2018). ...
Stable oxygen (δ18O) and carbon (δ13C) isotope data obtained from outcrops of the Middle Jurassic Dhruma Formation in central Saudi Arabia were investigated to assess paleoenvironments and determine impacts of diagenesis on the primary isotopic signals archived in the sedimentary rocks. Eleven identified facies in the succession are interpreted as inner to middle carbonate ramp deposits. These facies are grouped into low- to moderate-energy lagoonal, intertidal, moderate-to-high-energy shoal complex, and low-energy open marine settings. The δ13C variations facilitate the identification of six isotopic intervals and two negative excursion peaks in the sequence. The δ18O is less variable than the δ13C, and its record shows a long-term positive trend in the Late Bajocian Niortense through the lower part of the Parkinsoni Zone. Bivariate plots of δ13C and δ18O records reveal that most studied samples are within the northwestern Tethyan marine isotope region. However, a few samples clustered within the burial diagenesis zone. Low values of correlation coefficients (<0.5) between δ13C and δ18O and heavier values of both isotopes compared to their average Jurassic meteoric water values rule out the influence of meteoric water diagenesis. Higher concentrations of Sr than Mn, low Mn/Sr ratios, and lack of any strong relationship between δ18O and elemental ratios such as Sr/Ca, Fe/Ca, and Mn/Sr support the absence of meteoric water influence on the isotope values. Coeval negative excursions at the Niortense/Garantiana boundary are likely due to eustatic sea-level fall. Likewise, coeval positive excursion and covariance of both isotopes are attributed to syndepositional diagenesis.
... The large shallow-water area, in such epeiric seas, can damp out tidal and wave energy that leads to predominantly mud-dominated coastal and shoreline depositional systems (cf. Enos 1983;Schlaich and Aigner 2017). Two types of carbonate platform can be distinguished in the succession, which are physically restricted carbonate platforms with favored the growth of microbes (oncoids), low-faunal diversity, containing a largely endemic benthic foraminiferal assemblages (Kaminski et al. 2018a) and lack of reef (Dhruma sequence; Appendix Fig. 21), and differentiated carbonate platform with normal-marine coral/stromatoporoid and high-faunal diversity (Tuwaiq sequence; Appendix Fig. 23). ...
... Whereas, the maximum marine transgression, accompanying normal-marine conditions and optimum carbonate production, would always present the highest species diversity (e.g., MFS Tuwaiq sequence; Appendix Fig. 23; Fig. 20; cf. Schlaich and Aigner 2017;Al-Mojel et al. 2020a). This Middle Jurassic highest species diversity interval is synchronous with the first development of a deep intrashelf basin with probably source rock in the near subsurface (Fig. 18). ...
The sequence stratigraphy of the Dhruma Formation and Tuwaiq Mountain Limestone (Bajocian to middle Callovian) is based on shallow cores and outcrop measured sections along a 600-km–long N-S transect west and south of Riyadh. Correlations were extended westward in the subsurface using gamma-ray wireline logs (500 km). For the first time, the study integrates sequence stratigraphic framework with detailed semiquantitative micropaleontological analysis that allows reappraisal of stratigraphic interpretation of main biofacies associations. The outcrops provide a continuous stratigraphic record of the Middle Jurassic transgression of a large (>1000 km) epeiric tropical platform from continental braided fluvial deposits to tidal or wave-dominated mixed carbonate-siliciclastic lagoonal deposits. These formed aggraded flat-topped platform wedges and thicken northward due to evident syndepositional differential subsidence. The carbonate platforms are mud-dominated and evolved from restricted carbonate platforms that contained microbes and low-faunal diversity (early Bajocian to early Bathonian) to normal-marine carbonate platforms hosting coral/stromatoporoid-rich strata and high-faunal diversity adjacent to a deeper intrashelf basin (middle Callovian). The succession consists of two 2nd-order sequences, Dhruma and Tuwaiq sequences, separated by an unconformity (middle Bathonian hiatus). Several composite and high-frequency sequences that have a subordinate maximum flooding surface (MFS) in the lower Bathonian (zigzag Zone) and a main MFS in the middle Callovian coronatum Zone. The depositional sequences are considered to be of eustatic origin as they match well with Tethyan sea-level cycles. The carbonates developed well during late transgressive and highstand systems tract (TST and HST) of the composite sequences controlled by back stepping of the siliciclastic sources.
... The Lower Triassic Mahil Formation, well-exposed in the Saiq Plateau and Wadi Sahtan areas in the Northern Oman Mountains (Fig.1), is the first epeiric platform sequence deposited on the passive continental margin of the Arabian Plate (Walz et al., 2013;Eltom et al., 2017;Schlaich and Aigner, 2017).The Lower Mahil Formation is an outcrop equivalent to the subsurface Kuff KS-1 Formation; the Khuff Formation is an example of a very low-gradient homoclinal carbonate ramp (Alsharhan and Kendall, 1986;Al-Aswad, 1997;Insalaco et al., 2006;Knaust, 2009;Baud et al., 2010;Koehrer et al., 2010Koehrer et al., , 2011Koehrer et al., , 2012Bendias et al., 2013;Fontana et al., 2013;Walz et al., 2013;Amel et al., 2015).Deposition of the Khuff Formation shelf occurred in shallow-to open-marine conditions, but shallow-water conditions were the most common (Alsharhan and Kendall, 1986;Bendias et al., 2013;Peyravi et al., 2015).Minor detailed studies of the microfacies and depositional environment were published about the Khuff Formation KS-1 cycle in Oman, despite its relevance in the oil and gas industry.The major aim of this study is to provide a detailed description of a time-equivalent outcrop to the subsurface Khuff KS-1 Formation in the Saiq Plateau and Wadi Sahtan areas.The specific aims are to: (i) define the microfacies characteristics and distribution, (ii) establish a robust framework for the depositional environment model, and (iii) provide a reference for the hydrocarbon exploration and development of the Khuff Formation KS-1 in the northern Oman Mountains. ...
This study presents a detailed microfacies analysis of the Lower Triassic Mahil Formation (Khuff outcrop equivalent (KS-1)) in Jabal Akhdar, at the Saiq Plateau and Wadi Sahtan areas of Northern Oman. Two sections were measured and sedimentologically logged along a depositional dip profile emphasizing color, lithology, grain components, bed thickness, the nature of bed contact, lateral continuity of beds, and fossil content.One
hundred and eighty fresh rock samples were collected from various lithofacies.The collected samples were thinsectioned after blue epoxy was impregnated, and then they were half stained with Alizarin Red S and Potassium Ferricyanide for mineralogical identification.The point-counted compositions were determined by counting 300 points for each thin section to reconstruct the original components, obtain precise quantification, develop
representative microfacies, and construct the depositional model for the Lower Mahil Formation. Accordingly, eighteen microfacies types representing different carbonate ramp environments were identified; two are only recognized in the Wadi Sahtan logged section, ten are restricted to the Saiq Plateau logged section, and six are common for both sections. The Lower Mahil Formation consists of backshoal (inner ramp) to foreshoal (midramp) carbonate facies, with shoal (ramp crest) facies restricted to the Saiq Plateau logged section.The backshoal facies was characterized by abundant non-skeletal grains with breccia. The shoals were predominantly oolitic and intraclastic packstone-grainstone. Foreshoal carbonate facies, on the other hand, has mixed skeletal and nonskeletal grains with weakly developed hummocky cross-stratified beds. The shallow-water foraminiferal and oolitic packstone/grainstone facies are the potential reservoir intervals, whereas the wackestone facies is the non-reservoir intervals within the Lower Mahil Formation. The detailed sedimentological and microfacies analysis helped characterize the Lower Mahil Formation for better recognizing the potential reservoir vs.no-reservoir. This study can be a key reference to correlate the Lower Mahil Formation locally and regionally.
... The Arabian plate, which formed part of the northeastern margin of the Gondwana supercontinent, experienced diastrophic tectonic events throughout much of its geological history (Haq et al. 1988;Haq and Al-Qahtani 2005;Faqira et al. 2009;Stewart 2016). In the Permian, it was located at approximately 258 south of the paleoequator, before it progressively shifted northwards during the Triassic and Jurassic (Scotese 2001;Ziegler 2001;Schlaich and Aigner 2017) to occupy a position close to the equator during the Mesozoic (Stampfli and Borel 2002;Golonka 2007;Seton et al. 2012;Stewart et al. 2016). This shift of position was accompanied by events that influenced the geology of the Arabian Plate. ...
The interaction of fluvial, tidal, and wave processes in coastal and paralic environments gives rise to sedimentary successions with highly varied styles of facies architecture; these are determined by the morphology and evolutionary behavior of the range of coastal sub-environments, which may be difficult to diagnose in subsurface sedimentary successions with limited well control.
This study presents depositional models to account for stratigraphic complexity in a subsurface fluvial to shallow-marine succession, the Middle Jurassic Dhruma Formation, Saudi Arabia. The study achieves the following: i) it examines and demonstrates sedimentary relationships between various fluvial, nearshore, and shallow-marine deposits, ii) it develops depositional models to account for the stratigraphic complexity inherent in fluvial to shallow-marine successions, and iii) it documents the sedimentology and the stratigraphic evolutionary patterns of the lower Dhruma Formation in the studied area of Saudi Arabia. The dataset comprises facies descriptions of 570 m of core from 14 wells, 77 representative core thin sections, 14 gamma-ray logs, and FMI image logs from 4 wells. These data are integrated with quantitative information from > 50 analogous systems from a wide range of modern and ancient settings, stored in a relational database. Stratigraphic correlations reveal the internal anatomy of the succession.
Facies associations are representative of fluvial channels, intertidal flats, pedogenically modified supratidal flats or floodplains, river-influenced tidal bars, weakly storm-affected shoreface and offshore-transition zones, storm-dominated delta-front and prodelta settings, and an open-marine carbonate-dominated shelf. These sub-environments interacted in a complex way through space and time. The vertical succession of the studied interval records an overall transition from coastal-plain deposits at the base to marine deposits at the top. As such, the succession records a long-term transgressive, deepening-upward trend. However, this general trend is punctuated by repeated progradational events whereby coastal sand bodies of fluvial, wave, and tidal origin prograded basinward during stillstands to fill bays along a coastline. The nature of juxtaposition of neighboring sub-environments has resulted in a sedimentary record that is highly complex compared to that generated by morphologically simple shoreface systems that accumulate more regularly ordered stratal packages.
