Aruma Formation Research Articles

Controls on fracture propagation in bioturbated carbonate rocks: Insights from the Aruma formation, central Saudi Arabia

Previous research has explored the linkage between bioturbation, porosity, and permeability in carbonate reservoir rocks. The impact of bioturbation on natural fractures in such rocks remains relatively unexplored, however, but is crucial for effective subsurface resource management. This study focuses on the relationship between bioturbation and fracture characteristics in a well-exposed outcrop, the upper Cretaceous Khanasir Member of the Aruma Formation, central Saudi Arabia. The approach includes field investigation, petrography, imaging analysis, and CT scanning to quantify the relationship between burrows and fracture characteristics at scales from thin section to outcrop scale. At the outcrop scale, the Khanasir Member comprises three distinct units based on their fracture and burrow characteristics. These units reveal two primary categories of fractures: (1) burrow-related fractures, influenced and controlled by bioturbation; and (2) non-burrow-related fractures, unaffected by bioturbation. The characteristics of fractures within these units are influenced by multiple factors including: if burrows are filled; composition of the burrow fillings; mineralogy of host rock matrix; texture of the host rock matrix; and burrow percentage. The interplay of these factors affects fracture attributes such as density, length, and spacing, all of which have a direct impact on fluid flow behavior within subsurface reservoirs.

Evaluation of using micronized saudi calcite in ilmenite-weighted water-based drilling fluid

A high-density water-based drilling fluid (WBDF) is crucial for maintaining wellbore stability, controlling formation pressures, and optimizing drilling performance in challenging subsurface conditions. In the present research, the effect of micronized calcium carbonate (calcite), extracted from the Aruma formation outcrop, is evaluated as one of the additives that could be added to the ilmenite-weighted WBDF to enhance and optimize its properties. Various concentrations of Calcite microparticles were introduced into identical fluid formulations to assess their impact. The concentrations ranged from 0, 10, 20, to 30 lb/bbl, providing a comprehensive examination of the effects of calcite microparticles across a spectrum of concentrations within the fluid. The results highlighted that adding Barite microparticles to the WBDF revealed a notable enhancement in rheological properties. Specifically, the yield point demonstrated an increase of 37%, 37%, and 11% for concentrations of 10, 20, and 30 lb/bbl of calcite, respectively. Equally significant, high-pressure-high-temperature (HPHT) filtration analysis indicated a considerable enhancement for the fluids containing calcite microparticles. A reduction of 14.5%, 24.6%, and 13% were observed in HPHT filtrate for concentrations of 10 lb/bbl, 20 lb/bbl, and 30 lb/bbl respectively. Simultaneously, there is a reduction in filter cake thickness by 20%, 40%, and 20%, respectively. No ilmenite settling was observed in the sample containing 20 lb/bbl of calcite, unlike the other concentrations. These diverse results strongly suggest that the optimal concentration for calcite microparticles is 20 lb/bbl. The combined utilization of the optimal concentration of calcite microparticles alongside the established additives proves to be an effective strategy for optimizing the ilmenite-weighted WBDF performance in terms of both thermal stability and rheological behavior.

Characterizing the Attributes of Large Burrows in the Upper Cretaceous Aruma Formation: Insights From Ground Penetrating Radar

Characterizing the Attributes of Large Burrows in the Upper Cretaceous Aruma Formation: Insights From Ground Penetrating Radar

Micronized calcium carbonate to enhance water-based drilling fluid properties

Advanced drilling technique requires competent drilling fluids. This study tests micronized calcium carbonate (CaCO3) as a water-based drilling fluid (WBDF) additive. CaCO3 microparticles were extracted from Aruma formation outcrop and studied for structural, colloidal stability, morphology, and particle size distribution. WBDF systems were prepared with varying quantities of CaCO3 microparticles, including 0, 15, 30, and 45 lb/bbl, respectively. The addition of CaCO3 microparticles was investigated in terms of the rheological, high pressure-high temperature (HPHT) filtration, barite sagging, density, and pH. The results showed that CaCO3 microparticles are stable at a pH greater than 8. Moreover, fluid containing CaCO3 microparticles exhibited an enhancement in rheological properties. The yield point increased by 29%, 34%, and 37% for 15, 30, and 45 lb/bbl of CaCO3 respectively. In addition, the HPHT filtration also showed that CaCO3 has a significant improvement in both filtration loss and filter cake thickness. The filter cake thickness decreased by 17%, 40%, and 65% at 15, 30, and 45 lb/bbl of CaCO3 respectively. Static and dynamic sag maintained in a safe range at 30 lb/bbl of CaCO3 microparticles. This study showed that using CaCO3 microparticles along with conventional fluid additives improved the thermal stability and rheological properties of drilling fluid.

Bioturbated strata in the Upper Cretaceous Aruma Formation, central Saudi Arabia: An analog for aquifers and hydrocarbon reservoirs with large burrows

The upper Cretaceous Aruma Formation in Central Saudi Arabia exhibits Thalassinoides-bearing strata resembling a bioturbated carbonate reservoir with large burrows. These burrows possess distinct stratigraphic characteristics. Certain intervals within the formation feature open or partially filled Thalassinoides, creating three-dimensional permeability pathways, while others contain Thalassinoides filled with low-permeability sediments. This comprehensive study investigates the paleoenvironment, ichnological features, bulk permeability influence, and stratigraphic variations of these bioturbated intervals. Incorporating field observations, laboratory analyses (including petrography, geochemical assessments, petrophysical measurements, and computed tomography scanning [CT]), we present the division of the studied interval into three biogenically influenced fluid flow media (BIFM 1–3). BIFM 1 comprises solution-enlarged open Thalassinoides (average shaft diameter: 5 cm) hosted within a mud-dominated matrix. BIFM 2 consists of Thalassinoides with mud-dominated infills (average shaft diameter: 3 cm) embedded in a dolomite matrix. BIFM 3 exhibits compacted open Thalassinoides. These BIFM units demonstrate burrow percentages ranging from 10% to 45%, featuring interconnected networks. The identified units reflect diverse depositional settings, ranging from open marine to restricted lagoon, and distinct stratigraphic positions. By highlighting the sedimentological and stratigraphic controls on the petrophysical properties of carbonate strata containing Thalassinoides with large burrows, this research contributes to the prediction of super-permeability zones in analogous settings.

Depositional environment and sequence stratigraphy of the Upper Cretaceous Aruma Formation, NE Riyadh, Saudi Arabia

The Campanian to Maastrichtian Aruma Formation represents a distinctive depositional system of the carbonate-dominated ramp along the Arabian plate. Sedimentologic characteristics and stratigraphic relations are integrated with carbon and oxygen stable-isotope data to interpret the depositional environments in a sequence stratigraphic framework. One siliciclastic facies association (FA1) and eight carbonate microfacies (MF 1–8) belonging to four facies belts (FB1–4) were identified. Facies characteristics support accumulations on a carbonate ramp environment that extends from offshore/outer ramp to middle and inner ramp settings. Stable-isotope data are correlated to the oscillating global sea-level curve and global excursions’ events in order to refine the sequence stratigraphy of the Aruma Formation. Carbon-isotope chemostratigraphy shows remarkable long-time excursions, which are correlated to the two global negative excursions (Late Campanian event “LCE” and Campanian–Maastrichtian boundary event “CMBE”) as well as the positive δ13 C excursion of Middle Maastrichtian event “MME” and the uppermost negative δ13 C excursion toward the K–Pg boundary. The negative shift in the δ13 C values associated with relatively positive values in the δ18 O herald three marked sea-level falls, which can be coincided with global sequence boundaries. The merged surfaces TS1/SB1 and TS2/SB2 can be correlated to the Campanian events KCa3 (80 Ma) and KCa6 (75.4 Ma), respectively. The coplanar surface TS3/SB3 matches well with the Maastrichtian event KMa3 (69.4 Ma). The positive values of δ13 C and/or negative values of δ18 O coincide with periods of maximum transgressions. The minor pulses are mostly attributed to cyclic fourth-order sequences. The established sequence stratigraphic architecture and depositional model of the outcrop data herein will be useful in regional correlations with analogous subsurface successions along the Arabian plate and enhancement of potential petroleum explorations.

Isotope stratigraphy (87Sr/86Sr,13C) and depositional sequences of the Aruma Formation, Saudi Arabia: Implications to eustatic sea‐level changes

Lithofacies characteristics, depositional architecture (facies tracts and depositional sequences), stable isotopes (δ18O and δ13C), and87Sr/86Sr ratios were analysed from the Aruma Formation at the Khashm Buwaibiyat section (north‐east Riyadh, Saudi Arabia). The Aruma Formation consists of three formal members (base to top), Khanasir, Hajajah, and Lina members. Based on87Sr/86Sr and δ13C data, the lower age of the regionally distributed Aruma Formation (Khanasir Member) is now proposed as Late Campanian. This age assignment is supported by the identification of a distinct δ13C negative excursion (=Epsilon Event; Upper Campanian), and a globally conformable range of87Sr/86Sr values (0.707604–0.707703). Additionally, a review of previous fauna (ammonites and nannofossils) also favours this age assignment. The87Sr/86Sr values (0.707817–0.707848) from the upper part of the Hajajah Member reflects a Late Maastrichtian signature as also noted by the presence of a long‐term δ13C decrease. Additionally, based on lithofacies and depositional architecture for the Aruma Formation, nine facies types are identified. These are grouped into four facies associations (restricted peritidal, lagoon inner ramp, shoal transgressive lag, and coral reefs), reflecting four third‐order depositional sequences (transgression–regression cycles). These reflect strong influence of both eustatic sea‐level rise and regional tectonics (resulting in widespread unconformities and long‐time gaps). The shallowing and deepening of the sea level is inferred using sequence stratigraphy (system tracts) and lithofacies variations. This data suggests a gradual rise in sea level from the Upper Campanian to the Maastrichtian with an intervening fall around the Campanian‐Maastrichtian boundary.

Foraminifera from the Aruma Formation of Central Saudi Arabia

The Aruma Formation is well exposed in central Saudi Arabia as a thin northwest-southeast trending outcrop. It consists of a carbonate-dominated succession dated asCampanian to Paleocene. Of the three members, theKhanasir and Hajajah are confirmed as being Cretaceous, but the uppermost Linah Shale Member is assigned a Paleocene age. Dolomitization and differential erosion of the Aruma has left exposures for which the lithostratigraphy can only be confirmed by biostratigraphy. At the study location, the Khanasir Member contains the dasyclad algae Cymopolia tibetica, radiolitid rudist fragments and rare small rotalid and miliolid foraminifera. The HajajahMember is confirmed by the presence of the characteristic larger benthonic foraminiferal assemblage including Loftusia persica, Omphalocyclus macroporus, Rotalia trochidiformis and Fissoelphidium cf. operculiferum of Maastrichtian age. The sparse microfossil assemblages indicate deposition undifferentiated shallow marine, normal salinity, probably lagoon depositional setting.

Turonian microcrinoids from the lower Aruma Formation of Saudi Arabia

Pelagic microcrinoids assigned to the genus Roveacrinus identified in thin-sections of carbonates of the Turonian lower Aruma Formation of Saudi Arabia provide the first documented occurrence of these microfossils in the Arabian Peninsula. The species include Roveacrinus cf. alatus Douglas 1908, Roveacrinus sp., Roveacrinus geinitzi Schneider 1989, Roveacrinus cf. geinitzi, Roveacrinus aff. rugosus Douglas 1908, Roveacrinus sp. A., Roveacrinus aff. geinitzi Schneider 1989 and Roveacrinus cf. derdereensis. The Turonian range is based on the presence of planktonic foraminifera Heterohelix moremanni, H. globulosa and Marginotruncana sigali in the absence of Rotalipora spp., although possible Cenomanian forms are present within one deep marine microfacies assemblage. The biofacies containing the often abundant Roveacrinus fragments consists typically of abundant calcareous dinoflagellate cysts Calcisphaerula innominata with less common Pithonella ovalis, and rare Bonitocardiella conica, rare to common planktonic foraminifera and rare benthonic foraminifera including Marssonella turris and Gavelinella spp. This assemblage, within very fine-grained packstones, suggests a deep marine depositional environment with low energy, normal salinity conditions. Deep marine sediments, that include Heterohelix moremanni and forms that may be transitional to H. globulosa, include roveacrinids that compare with the Cenomanian species R. derdereensis and these may prove to be supplementary useful age indicators in such environments. Although their association with pelagic microfossils would suggest a planktonic lifestyle, a definite paleoenvironmental interpretation seems elusive by most authors although there is a direct association between the roveacrinoid abundance and flooding surfaces and high-productivity events. Roveacrinid fragments have been recovered from calcareous mudstones of the Ruwaydha and Tuwayil members of the Aruma Formation that overlie upper Cenomanian grainstones of the MishrifMember of theWasia Formation. A regionally significant unconformity separates the Mishrif Formation from the Aruma Formation, of which the basal Aruma represents a significant deep marine transgression. The episodic microcrinoid distribution potentially provides regionally correlative bioevents in addition to their possible relationship with the oceanic anoxic event OAE 2.

Campanian–Maastrichtian unconformities and rudist diagenesis, Aruma Formation, central Saudi Arabia

The Upper Cretaceous Aruma Formation is widely distributed in central Saudi Arabia and consists of three members, from base to top, the Khanasir Limestone Member, the Hajajah Limestone Member, and the Lina Shale Member. It disconfomably overlies the Cenomanian Wasia Formation (middle Turonian, the “Wasia-Aruma break”). Two unconformities were recorded within and at the top of the Aruma Formation: (a) “the lower Campanian unconformity” between the Khanasir Limestone Member and the Hajajah Limestone Member and (b) “the pre-Cenozoic unconformity” between the Lina Shale Member and the Paleogene Umm er Radhuma Formation. The comparison between these unconformities and those recorded on the Arabian Plate was emphasized. A lenticular rudist biostrome in the uppermost part of the Khanasir Limestone Member consists mainly of the radiolitids and sparse canaliculated rudists in life position. However, rudists are entirely fragmented in the lower limestone and are very rare in the upper limestone of the Hajajah Limestone Member. Loose right valves of radiolitids from the Campanian Khanasir Member have underwent diagenetic alterations, such as fragmentation and compaction, micritization, bioerosion, and micritic calcite cement, which indicates marine diagenetic stage, while very limited silicification, dolomitization, and dissolution suggest the meteoric diagenetic environments with arid climates. Isopachus and equant calcite cement and neomorphism may be showed the fresh pharetic zone related with subaerial unconformities.

Solitary corals of the Campanian Hajajah Limestone Member, Aruma Formation, Central Saudi Arabia

Fourteen species of the solitary corals belonging to eight genera and six families were identified and illustrated from the Campanian – Maastrichtian Aruma Formation, northeast of Riyadh, Saudi Arabia. Cunnolites (Plesiocunnolites) riyadhensis, Actinoseris riyadhensis and Asteroseris arabica are believed to be new. Genus Cunnolites dominates the identified fauna with six species namely Cunnolites (C.) reussi, C. (P.) orbignyi, C. (P.) longifossata, C. (P.) scutellum, C. (C.) profundus and C. (P.) riyadhensis (n. sp.). The other species belong to Aulosmilia cuneiformis, Rennensismilia inflexa, Rennensismilia sp., Acrosmilia conica, Actinoseris riyadhensis (n. sp.), Asteroseris arabica (n. sp.), Montlivaltia sp. and Conicosmilotrochus sp. The solitary corals have various growthforms from cupolate to flabellate, trochoid, ceratoid, cylindrical and patellate. The studied taxa inhabit soft substrate in turbid water environment with low rate of sedimentation. Borings and scars are rare, encrustations occur on the lower surfaces of some specimens. Partial mortality, overgrowths, disorientation or any records of life impedences due to sedimentation and unstable substrate were not observed in the studied specimens. Pedestals and columnar growths are also absent. Bioerosion is observed in some specimens in the form of pittings produced by predators.

Cymopolia eochoristosporica Elliott, 1968 (green alga, Dasycladale) from the upper Maastrichtian of the Tarbur Formation (SW Iran)

The poorly known dasycladalean alga Cymopolia eochoristosporica Elliott, 1968 is reported for the first time from the upper part of the Tarbur Formation (Zagros Zone, SW Iran) assigned to a late Maastrichtian age. It was reported so far from the Maastrichtian Aruma Formation of Saudi Arabia (type-locality), the Maastrichtian Simsima Formation of Oman, and the Maastrichtian (e.g., Zongshan Formation) of Tibet. All these Maastrichtian occurrences belong to the southern Tethyan margin, with special concentration within the Arabian plate, evidencing its palaeobiogeographic as well as biostratigraphic importance. C. eochoristosporica occurs in algal-foraminiferan wackestones together with other dasycladaleans (e.g., Salpingoporella pasmanica Radoičić) and halimedaceans, benthic foraminifera (Broeckina, Tarburina, Laffiteina, Gyroconulina, Loftusia, Omphalocyclus), rudists, gastropods, as well as corals. As a peculiarity, the calcification of the alga is made up of light-brownish calcite, presumably replacement of the original aragonitic composition. The dasyclad-bearing deposits are assigned to an internal infralittoral, possibly polyhaline depositional setting.

New record of Durania cornupastoris (rudist) from the Campanian of the Aruma Formation, Riyadh, Saudi Arabia: Description and biogeographic remarks

A Radiolitidae (rudist, bivalvia), Durania cornupastoris (Des Moulins) is a well-known species defined as an index fossil from the Turonian (mostly middle-upper) deposits in the Mediterranean Tethys and also in the USA. This study includes new rudist materials and well-preserved samples of the species from the Campanian Khanasir Limestone Member of the Aruma Formation outcropping around the Riyadh (Saudi Arabia) region. Durania cornupastoris is characterized by the many finely ribbed, generally flat, sometimes slightly or pronounced concave posterior and ventral radial bands and bulge interband with thick costae similar to the external ornament of the rest of the right valve surface. The width of the radial bands are variable. A comparison of the species with the well-known Durania species such as Durania arnaudi (Choffat), Durania gaensis (Dacqué) and Durania apula Parona is considered. The broadening of the stratigraphic range up to the Campanian and biogeographic distribution into the eastern part of the Arabo-African plate of the species are also emphasized.

Facies development and paleoenvironment of the Hajajah Limestone Member, Aruma Formation, central Saudi Arabia

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, bivalves, 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.

Stratigraphy and depositional environments of the Upper Cretaceous Aruma Formation, Central Saudi Arabia

The Upper Cretaceous Aruma Formation in central Saudi Arabia is subdivided into three members. The Khanasir Member at the base is characterized by dasycladecean-rudist biofacies. The middle Hajajah Member is characterized by coral-stromatoporoid biofacies, while the upper Lina shale Member contains few badly preserved molluscs. Fifty macrofossils species have been identified from the studied section, 25 of them belong to gastropods, 17 belong to scleractinian corals, and 8 species belong to bivalves. The identified macrofossils have close affinity to Tethyan faunas and previously known from the Cretaceous rocks in Asia, Africa, and Europe. The most recorded microfacies types are wackestones, packstones, and floatstones with green algae, benthic and rare planktonic foraminifers, ostracods, and corals. The studied section revealed a major Campanian-Maastrichtian marine transgression followed the continental siliciclastics of the Wasia Formation with progressive deepening upward, from a shallow marine lagoonal environment to relatively more open marine conditions.

Applications of chemostratigraphy in Cretaceous sediments encountered in the North Central Rub’ al-Khali Basin, Saudi Arabia

The following study was undertaken on inorganic geochemical data acquired for 832 core and cuttings samples taken from Cretaceous sediments encountered in 11 wells in the North Central Rub’ al-Khali Basin, Saudi Arabia. The study sections extend from Khafji Member at the base of the Wasia Formation to the basal part of the Aruma Formation. The principal objective of the study was to produce a chemostratigraphic scheme for these wells, though a comparison was also made with a previous lithostratigraphic scheme.Although ICP–OES (Inductively Coupled Plasma–Optical Emission Spectrometry) and ICP–MS (Inductively Coupled Plasma–Mass Spectrometry) were used to acquire data for 50 elements, the chemostratigraphic scheme is based on changes in the following ‘key’ elements and ratios: Ca, Al, Zr, P/Y, Zr/P, Zr/Y, Zr/Nb, Mo and Zr. The scheme comprises a hierarchical order of five zones, 18 subzones and four divisions, with the zones labelled C1, C2, C3, C4 and C5 in ascending stratigraphic order. The definition of these zones are mainly based on changes in Ca and Al reflecting variations in bulk lithology as a response to changes in base level. Zone C1 is dominated by elevated Al and low Ca concentrations and represents calcareous mudrocks deposited in a lagoonal–prodelta environment. An increase in base level led to the formation of highly calcareous rudistic limestones deposited in a shallow marine environment, with a further increase in base level resulting in the deposition of calcareous mudrocks with high Al values in zone C3. Zone C4 comprises rudistic limestones (with elevated Ca and low Al) deposited in shallow marine conditions, while C5 is dominated by calcareous mudrocks and argillaceous limestones deposited in a prodeltaic paleoenvironment. Although the definition of zones mainly relates to changes in base level/bulk lithology, more subtle changes in provenance are modelled using the P/Y, Zr/P, Zr/Y and Zr/Nb ratios which are used to define most subzones and divisions. Variations in this ratio are almost entirely dependent on changes in source/provenance.Although all of the zones and most of the subzones are correlative between the study wells it is noted that different criteria are used to define the zone C2 and C4 subzones in the eastern and western wells of the study area. This suggests that separate sediment sources were responsible for the delivery of clastic material to these carbonate ‘reefs’ during the deposition of these subzones.One important conclusion from this study is that there are close links between the chemostratigraphic and lithostratigraphic correlations but the former offers a much higher level of resolution.

Gastropods from the Campanian–Maastrichtian Aruma Formation, Central Saudi Arabia

The gastropod fauna of the Upper Cretaceous Aruma Formation in central Saudi Arabia comprises fifteen species belonging to fifteen genera, fourteen families, and five clades. The species are not abundant at any individual stratigraphic level but are equally and irregularly scattered in the formation. The studied species come mainly from the Hajajah Member of Upper Cretaceous Aruma Formation in central Saudi Arabia. Calliomphalus orientalis (Douvillé, 1916); Coelobolma corbarica Cossmann, 1918; Turritella (Torquesia) figarii Quaas, 1902; Neoptyxis olisiponensis (Sharpe, 1850) and Otostoma (Otostoma) divaricatum (d’Orbigny, 1847) are recorded from the Upper Cretaceous of central Arabia for the first time. The identified species have a close affinity to the Tethyan fauna known from other parts in Asia, Africa and Europe. Herbivores and predators are the dominant trophic groups which may indicate shallow marine lagoonal and relatively open marine environment.

Sequence stratigraphy of Aqra Formation (Late Upper Campanian–Maastrichtian) in Geli Zanta corge, Northern Iraq

The Aqra Formation represents a succession that was deposited over most of Northern Iraq and adjacent regions. In north Iraq, in the core of NW–SE trending Aqra anticline, a 438-m-thick section of the Aqra Formation crops out at Geli Zanta corge. The base of the Aqra Formation is not exposed here. The upper contact is unconformably overlain by Paleocene–Lower Eocene formations (Kolosh and Khurmala formations). A hundred and one samples were collected from the section and used for biostratigraphic and microfacies analysis. According to the occurrence of larger Foraminifera (Orbitoides media and Orbitoides apiculata) and planktonic Foraminifera (Abathomphalus mayaroensis), Late Upper Campanian–Maastrichtian age was determined for Aqra Formation. Fifteen facies were distinguishable throughout the formation, representing tidal flat (supratidal), restricted marine shelf (lagoon) and shelf margin rudist reef, and its related debris. These environments were used to interpret three depositional sequences which correlate with those of Aruma Formation (KSA), Simsima Formation (UAE) in Arabian Plate, and with Iraqi formation sequences. Three maximum flooding surfaces were recognized as MFS 175, MFS 180, and MFS 190.

Sequence stratigraphy of the Late Campanian – Early Maastrichtian Shiranish Formation, Jabal Sinjar, northwestern Iraq

ABSTRACTThe Late Campanian – Maastrichtian Shiranish Formation consists of deep-marine marls and limestones that were deposited in northern and central Iraq. In northwestern Iraq, in the core of EW-trending Jabal Sinjar, a 430-m-thick section of the Shiranish Formation crops out. The base of the Shiranish section is not exposed here. It is unconformably overlain by Paleocene – Lower Eocene formations: Sinjar Formation along the northern part of the Jabal, and Aaliji Formation along its eastern side. Eighty samples were collected from the section and used for facies analysis and biostratigraphic calibration. Previous studies of planktonic foraminifera recognized four biozones, which were confirmed in the present study: Globotruncanita calcarata Interval Zone, Globotruncanella havanensis-Rosita fornicata Partial Range Zone, Globotruncana aegyptiaca Interval Zone and Gansserina gansseri Interval Zone. These zones are here calibrated in several geological time scales. Six facies were distinguishable throughout the section, representing shallow-marine, middle-shelf, outer-shelf and upper-bathyal environments. These environments were used to interpret six depositional sequences. The older five Shiranish sequences are fourth order and grouped into one third-order sequence, while the sixth and youngest Shiranish Sequence was of third order. This suggests that the studied section was deposited in about 5 million years between ca. 76.0–74.4 and 69.5–69.8 Ma. The correlation between the Shiranish sequences and those of the Aruma Formation in Saudi Arabia implies that the northern Arabian Platform was regionally flooded starting in the Late Campanian and ending in the Maastrichtian. In the study area, an unconformity straddles the Cretaceous – Tertiary (K/T) boundary and represent a hiatus of ca. 10 or more million years.

Stratigraphy of the Valanginian? to Early Paleocene succession in central Saudi Arabia outcrops: Implications for regional Arabian sequence stratigraphy

ABSTRACT On the basis of regional lithostratigraphic field mapping, and biostratigraphic and sequence stratigraphic interpretations, the definitions and ranks of the Late Valanginian? to Paleocene rock units that crop out in central Saudi Arabia were revised. The definition of the Late Valanginian? to Early Aptian Biyadh Sandstone is inconsistent with that of the same-named formation in subsurface Saudi Arabia. In outcrop, only the lower Dughum member of the Biyadh Sandstone corresponds to the subsurface Biyadh Sandstone. Accordingly, the Biyadh Sandstone at outcrop was redefined so as to correlate to the same-named subsurface formation; the term Dughum member is considered obsolete. Above the redefined Biyadh Sandstone, the Sallah Formation at outcrop (previously Sallah member of Biyadh Sandstone) yielded the Aptian and/or earliest Albian? ammonite Hypacanthoplites cf. milletianus d’Orbigny; it correlates (in part or completely) to the undifferentiated-Aptian Shu’aiba Formation in Abu Jifan field. The overlying Huraysan Formation (previously Huraysan member of Biyadh Sandstone) is assigned an Albian age based on its stratigraphic position above the Sallah Formation and below the Upper Albian and Cenomanian Majma Formation (previously Majma member of Wasia formation). The Huraysan Formation correlates by stratigraphic position and lithology to the Khafji and Safaniya members of the Wasia Formation in subsurface Saudi Arabia. The Majma Formation may correlate to the Mauddud, Wara and lower part of the Ahmadi members of the subsurface Wasia Formation in Saudi Arabia. The successively overlying Qibah and Malihah formations (previously Qibah and Malihah members of Wasia formation) complete the Cenomanian and Early Turonian succession below the pre-Aruma unconformity. These two formations may correlate to the upper part of the Ahmadi, Rumaila and Mishrif members of the subsurface Wasia Formation in Saudi Arabia. In central Saudi Arabia, the pre-Aruma unconformity is overlain by the Upper Campanian and Lower Maastrichtian Khanasir Member of the Aruma Formation. The Upper Maastrichtian Hajajah and Paleocene Lina members form the upper part of the Aruma Formation. In contrast, the subsurface Aruma Formation in Saudi Arabia may extend to the Coniacian Stage. The Biyadh Sandstone consists of coastal-plain clastics deposited during several transgressive-regressive sequences. It overlies the pre-Biyadh unconformity, which is represented by west-cutting regional erosion that reaches down to the Jurassic Dhruma and underlying Marrat formations. The overlying Sallah Formation represents a transgressive-regressive sequence deposited in lagoonal and tidal settings, and includes limestone beds with marine fauna. The overlying Huraysan Formation consists of fluvial, fining-upward clastics and is, together with older units, regionally eroded by the pre-Majma unconformity. The associated pre-Majma hiatus probably occurred in the Late Albian and is characterized by the Az Zabirah Bauxite, a deposit that reflects a pedogenic episode that occurred in tropical humid conditions. The fluvial and marginal marine clastics of the Majma Formation, and marine clastics and carbonates of the Qibah Formation, can together be characterized in terms of three flooding events. The Malihah Formation was deposited in mixed proximal settings (tidal to fluvio-deltaic) and exposed (paleosols with bauxite). It represents a regression associated with the eastward tilting of the Arabian Plate during Turonian tectonism along the Neo-Tethyan margin. Central Saudi Arabia remained exposed during the Late Turonian through Middle Campanian, during which times the pre-Aruma Bauxite formed. The Aruma Formation is characterized by four third-order sequences; one in the Khanasir Member, two in the Hajajah Member – all of Late Cretaceous age, and the Paleogene Lina sequence.