Unstable Shelf Research Articles

Petrophysical Characteristics of Mauddud Formation in Selected Wells of Ratawi Oilfield, Southern Iraq

The Mauddud Formation is the most widespread Lower Cretaceous formation in Iraq, deposited along the NE margin of the Arabain Palte. The formation is widely distributed, covering nearly the entire territory of Stable and Unstable Shelf units. The study area is located in the Zubair subzone of the Mesopotamian zone within the Stable Shelf unit, approximately 70 km northwest of Basrah in southern Iraq. The main goal of this study is to evaluate the petrophysical characteristics of Mauddud Formation in the five wells (Ratawi-2, Ratawi-4, Ratawi-5, Ratawi-17, and Ratawi-19) in the Ratawi oilfield, southern Iraq. Open hole log analysis was utilized, and a series of calculations were applied to evaluate the reservoir properties, such as porosity, water saturation, and volume shale, that control the reservoir quality. The N-D cross plot diagram shows that limestone is the dominant lithology, and few shale contents is present in the upper and lower parts of the formation, while it is noticed that the volume of clay is constant throughout the formation in most of the wells, indicating that the formation is clean. Seven zones (A to G) have been identified and evaluated, depending mainly on full set logs to determine the most productive ones. Zones B, D, and F are classified as good reservoir zones with an average porosity of 21% and water saturation of 25%. A and C zones show reservoir and non-reservoir zones with porosity of 10% and water saturation of 40%. Finally, the remaining zones represented by E and G are classified as non-reservoir zones with a very low porosity of less than 4% and fully water-saturated.

Some Geomorphological Implications of Chemical Weathering in Sequences of Sedimentary Rocks in the Kirkuk Structure

This study was based on a review of a group of geomorphological features and characteristics within the Kirkuk anticline in the Low Folded Zone within the Unstable Shelf of Iraq. As well as identifying the role of the chemistry of the rocks that form the geological formations in the studied area and explaining the role of chemical weathering processes in shaping the geomorphological units. Each of these geomorphological units includes several landforms with different lithologies. These shapes were produced as a result of weathering, erosion, and sedimentation processes associated with structural, compositional, rock, and climatic factors. Literature. The exposed rocks in the sedimentation basin, from which different formations are formed, showed variation in their resistance to chemical and physical weathering processes. It has been noted that the chemical weathering of gypsum rocks is of the type of incipient weathering and that of limestone is of the type of incipient to moderate weathering. For the sandstones, they are of the moderate weathering type, while it is noted that the chemical weathering of the claystone and marl is of the extreme weathering type. This demonstrates the important role played by the type of rocks and their chemical composition in highlighting the role of various geomorphological processes in determining the nature of land units and forming the geomorphological features, in addition to the influence of various geological processes and the presence of structural units such as joints, fractures, and faults, as well as the influence of slope and various climatic factors.

Tectono-stratigraphic architecture, depositional systems and salt tectonics to strike-slip faulting in Kribi-Campo-Cameroon Atlantic margin with an unsupervised machine learning approach (West African margin)

Located in the Gulf of Guinea, the Kribi-Campo sub-basin belongs to the Aptian salt basins along the West African Margin. In this paper, we investigated the tectono-stratigraphic architecture of the basin, focusing on the role of salt tectonics and strike-slip faults along the Kribi Fracture Zone with implications for reservoir prediction.Using 2D seismic data and well data interpreted through sequence stratigraphy with integrated seismic attributes analysis with Python Programming and unsupervised Machine Learning, at least 6 s-order sequences, indicating three main stages of tectono-stratigraphic evolution were determined: pre-salt syn-rift, post-salt rift climax and post-rift stages. The pre-salt syn-rift stage with KTS1 tectonosequence (Barremian-Aptian) reveals a transform rifting along NE-SW transfer faults associated with N–S to NNE-SSW syn-rift longitudinal faults bounding a NW-SE half-graben filled with alluvial to lacustrine-fan delta deposits. The post-salt rift-climax stage (Lower to Upper Cretaceous) includes 2 s-order tectonosequences (KTS2 and KTS3) associated to the salt tectonics and Campo High uplift. During the rift-climax stage, the growth of salt diapirs developed syncline withdrawal basins filled by early forced regression, mid transgressive and late normal regressive systems tracts. The early rift climax underline some fine grained hangingwall fan or delta deposits and coarse grained fans from the footwall of fault scarps. The post-rift stage (Paleogene to Neogene) contains at least three main tectonosequences KTS4, KTS5 and KTS6-7. The first one developed some turbiditic lobe complexes considered as mass transport complexes and feeder channel-lobe complexes cutting the unstable shelf edge of the Campo High. The last two developed submarine Channel Complexes associated to lobes towards the southern part and braided delta to tidal channels towards the northern part of the Kribi-Campo sub-basin.The reservoir distribution in Kribi-Campo sub-basin reveals some channels, fan lobes reservoirs and stacked channels reaching up to the polygonal fault systems.

The Groundwater Balance Assessment in Holy Karbala, Central Iraq

Karbala is located in central Iraq, which is bounded by latitudes (32° 50' 15" - 32° 10' 15") and longitudes (43° 09' 41"– 44° 18' 56"), the area under study covers an area of 4,987 km2. It is a part of unstable shelf of the sedimentary plain zone and Al-Salman zone of the stable shelf, so it is a flat area, which gradually declines from the southwest towards the northeast. The geological formations which are exposed in the study area, having a range between middle Miocene and Pleistocene – Recent deposits. Two main aquifers were distinguished in the area, confined and unconfined one. Depending on the karbala meteorological station information (rainfall, temperature and humidity) from 1980 - 2019 utilizing Thornthwait formela's, the water overflow was accounted, appearing the renewed water store for the unconfined system, equalized to 111.0 *106 m3/year whereas the calculated constant volume of water for both systems was found to be equivalent to a total of 13.84 * 109 m3 However, after calculating the difference between the total water that in-coming the area (including, income subsurface runoff, recharge, fluctuation in monitoring wells and out-coming (including, discharge of pumping wells, outflow wells drainage, spring drainage, outcome subsurface runoff), the amount of change in the storage is found to be (+32.573 * 109 m3). The amount of positive change indicates the presence of excess water which can be added to both systems. The direction of the groundwater movements for the two main systems are highly matched between them as well as its similarity with the topographic surface.

Tectonically Stable Parts in Iraq Are Not Stable

Iraq is located in the extreme northeastern part of the Arabian Plate, which is in collision with the Iranian (Eurasian) Plate. The collision, which is still ongoing has created tens of folds some of which exhibit different types of faults. The exerted compressional forces are believed to be decreasing southwestwards as being far from the collision area (Suture Zone). Accordingly, all the existing tectonic and geological maps compiled by different authors and all the existing published articles, reports and books have considered two main tectonic domains in Iraq. The Stable Shelf and Unstable Shelf or Inner Platform and Outer Platform. The contact between these two main divisions follows almost the Euphrates River; towards the west of the river is the tectonically Stable area and towards the east and north is the tectonically Unstable area, which means the presence of different structural forms. In the current study, we have recognized tens of different Neotectonic evidence in the Stable part indicating that the area is tectonically not stable. Among those indications are abandoned valleys, development of sinkholes along certain lineaments, bending of valleys in right angles, and development of nick-points in valleys along certain lineaments.

Sedimentology, Mineralogy of Al-Dujaila River Sediments Project, Southeastern Kut City, Iraq

A sedimentological and mineralogical study was carried out on sediments of Al-Dujaila River Project, one of the branches of the Tigris River, southeastern Kut City, Iraq. The study aims to identify the nature and maturity of sediments in order to deduce the provenance of these sediments and the source area. The results of grain size analysis of ten river sediment samples indicated that the averages are: silt (44.97%), clay (34.06%), and sand (20.96%). According to Folk's classification (1974), the sediments are classified as sandy mud. A microscopic study of five sand fraction samples has shown the presence of light and heavy minerals. Light minerals (average 94.6%) include on average: a major share of rock fragments (64.8% including dominant carbonate, chert, igneous, metamorphic, and mudstone), quartz (24.1% including dominant monocrystalline and polycrystalline), feldspars (5% including orthoclase and plagioclase) while evaporates, and coated clays are subordinate. Heavy minerals (average 5.4 %) include opaques (average 54.2%) and non-opaques (average 45.8%) including pyroxene, amphibole, epidote, garnet, staurolite, chlorite, biotite, muscovite, zircon, tourmaline and rutile. Based on the mineralogical signatures, light and heavy minerals reflect metamorphic, mafic and felsic igneous rocks of the active margin of the unstable shelf in addition to carbonate, evaporate and mud of sedimentary rocks that could be sourced from the floodplain. According to sediment diversity and very poor grain sorting in the study area, as well as the values of indices of mineral maturity MI (0.34), MMI (0.76), and the ZTR (23.5%), all these results indicate that sediments are immature to extremely immature, which means the source area represents rather elevated topography, rapid erosion and transport in arid to the semi-arid environment and a short distance of transportation. The tectonic provenance of Al-Dujaila River sediments can be characterized as a lithic reworked of the recycled orogen as a result of the collision range of Taurus and Zagros Mountain range.

Microfacies Analysis and Diagenetic Effects of Middle Jurassic Succession in Rania and Sargelu Sections, Northern Iraq

The studied area covers two outcrops they are located within Sulaimaniya, northeastern of Iraq (Rania and Sargelu sections). Sargelu Sections are located in Sargelu village within Unstable Shelf, High Folded Zone, including Surdash anticline, while Rania Sectionis are located in Rania city near Hanjira village within the Unstable Shelf, High Folded Zone, including Shaweri anticline. The carbonates represent the major microfacies and constitute of lime mudstone microfacies, lime wackestone microfacies, Calcisphere-Posidonia lime wackestone submicrofacies, posidonia lime wackestone submicrofacies, lime packstone microfacies, Posidonia lime packstone submicrofacies, Posidonia-Ostacoda lime packstone submicrofacies, lime Crystalline Microfacies. The observations of the studied area show that the basin of the Sargelu Formation represents a deep part of a ramp system.These microfacies are variably affected by several diagenetic processes including mechanical and chemical compaction, cementation, recrystallization and dolomitization. The chert shows a high degree of quartz crystallinity which indicates a diagenetically product from the amorphous silica of the many radiolarians, remnant of which is preserved in several units of the Sargelu Formation

Mineralogy and Geochemistry of Sandstones from the Tanjero Formation, Bekhme Gorge Northeastern Iraq: Implications for Paleoweathering and Provenance

The Tanjero Formation is exposed on the Northern flank of the Perat anticline near the Northern entrance to the Bakhme gorge through which the waters of the Upper Zab flow. As for tectonics, it is located within the High Folded Zone of the Unstable Shelf. The Tanjero Formation is about 80 m. thick, it is bounded from the bottom by the Shiranish Formation. The formation consists of gray sandstone that contains gravel at the bottom followed by beds of marl, hard sandstone, and black claystone containing cushioning structures and small-scale cross-bedding are present. According to the Williams classification, theTanjero sandstones drop at the lithic wacke field. The provenance of these sandstones was investigated based on their minerals and geochemical composition. The geochemical analyses showed low silica, a negative correlation of silica with the most major oxides due to recycling sedimentary sources or weathering of silicates. The index of compositional variability indicates that the sandstones of the Tanjero Formation are immature clastic sediments and the high index of compositional variability values confirm that the clastic sediments occurred in the tectonically-active-settings area. Moderate chemical weathering has dominated in the studied area, which was inferred from the chemical index of alteration, the chemical index of weathering and the plagioclase index of alteration. Based on the tectonic discrimination diagrams, the Tanjero sandstones are quartzose sedimentary provenance, felsic igneous rocks source, transitional arc–lithic recycled setting, and located in the collision zone between the passive Arab margin and the effective Iranian-Turkish margin that formed the orogeny belt along the collision zone.

Sedimentological Study of Exposed Successions of the Sargelu Formation, Middle Jurassic, Northeastern, Iraq

The Middle Jurassic Sargelu Formation spreads out widely in North-Eastern Iraq, particularly within the High Folds Unstable Shelf Zone. The Sargelu Formation was studied in two exposed sections, Hanjira and Gorin, in the Northeastern part of Iraq. The Lower contact of the formation with the Sehkaniyan Formation and the Upper contact with the Naokelekan Formation in the two sections appears conformable. The thickness of the Formation in the Hanjira section is 40m. and in the Gorin section is 70 m. The sampling was done by taking samples from two sections and thin sections were made for all samples and were studied under a polarizing microscope. Three main microfacies donated as M, W, P, and eight submicrofacies were diagnosed which reflects the deposition of the formation within the FZ-1 zone known as the Deep Sea Basin and the FZ-2 known as the Deep Shelf.

Petrography and Geochemical Relationships of the Ultramafic Rocks in Galalah area within Erbil Governorate, NE Iraq

The current research to study the petrography, mineralogy and geochemical relationships of the ultramafic rocks in the Galalah area within Erbil Governorate, at the Unstable Shelf in the Imbricate Zone, to determine the origin of the ultramafic rocks. Dunite and Harzburgite are the most abundant rock bodies in the study area, and they represent most of the outer surface exposure of the ultramafic rock aggregates. The dunite rocks are characterized by pale brown color on the altered surface that is broken into olive green and dark green lithic. Dunite represents a homogenous lithologic feature that mainly consists predominately of olivine with accessory spinel and traces of orthopyroxene. While the harzburgite appears as a massive rock body consisting of olivine, orthopyroxene, and clinopyroxene. These rocks are mainly characterized by alteration to serpentinite, with accessory chromian spinel, secondary magnetite, chlorite, and talc. The studied ultramafic rocks are predominately rich in ferromagnesian minerals of less silica content, and other major elements affected by serpentinization are causing the deviation of elements. They have a strong decrease in sodium and calcium oxides relative to MgO and verified the silica and alumina with MgO and a slight increase in iron oxide. The low values of TiO2 in dunite and harzburgite are characteristic property of the Alpine type ophiolites during the primary process of the mantle in its upper part, before the tectonic emplacement of the ultramafic rocks, and also due to partial melting degree for the asthenospheric mantle. The MREE depletion relative to HREE and LREE may be attributed to the hornblende absence and the presence of olivine and pyroxenes minerals and/or to the source rock features. The U-shaped patterns of REE and their ratios are typical properties of ophiolitic ultramafic rocks, which are compatible with the supra-subduction zone. During the partial melting, the negative anomalies of Nb in ultramafic rocks with sequestration of the Nb concentration by sphene and ilmenite in various types of the source rocks have also been attributed to the crust contamination. These are also characterized by island arc conditions, and its depletion in the studied rocks may indicate the fore-arc tectonic environments

Mineral Composition and Provenance of Al-Chabbab Stream Sediments, Wasit, Southeastern Iraq

A mineralogical study was carried out on the sediments of Al-Chabbab stream, one of the seasonal tributaries of the Tigris River, southeast of Wasit, Iraq. This study includes the sediments of the Tigris River sited before and after the mouth of the Al-Chabbab stream. Light and heavy minerals are determined by using polarized microscope and X-Ray Diffraction technique. The light minerals are composed of quartz, rock fragments, and feldspar, which are the prevailing compositions in all samples. The quantity of monocrystalline quartz in the Tigris River was more than Al- Chabbab stream, which refered to the supplied of felsic sours rocks sediments to the Tigris River more than the sediments of Al-Chabbab stream. The average value of minerological maturity index and ZTR index of Al-Chabbab stream, Tigris and Al-Chabbab inflow samples indicates that clasts generally are sub-mature. The Tigris River clasts have high mineralogical maturity index, which refers to the long transportation. Heavy mineral accumulation of the recent sediments from Al-Chabbab inflow and the Tigris River is composed of opaque and transparent minerals including epidotes; pyroxenes; amphiboles (hornblende and glaucophane); zircon; garnet; tourmaline; rutile; kyanite; staurolite; flaky minerals (muscovite; biotite and chlorite) and celestite (glaucophane and celestite are absent in the sediment of Tigris River). Based on the mineralogical signatures, the light and heavy minerals reflect metamorphic, mafic and felsic igneous rocks, of the active margin of the unstable shelf, in addition to the carbonate, evaporite and mud rocks that could be sourced from the Euphrates, Fatha and Injana formations.

The Quantitative and Qualitative Assessment of Groundwater in Karbala Governorate, Iraq

Karbala governorate, however, neighborhood the western desert, which bounded by longitudes (43° 09' 41" – 44° 18' 56") and latitudes (32° 10' 15" – 32° 50' 15") with total area study of 4987 km2, represents part of sedimentary plain belongs to the unstable shelf and Salman zone belongs to the stable shelf. The main geological formations that exposed in the studied area represented by Al-Fatha Fn. (M. Miocene), Injana Fn. (U. Miocene), Dibdiba Fn. (Pliocene - pliestocene) and Quaternary Fn. (Pliestocene - Holocene). Two main underground reservoirs were distinguished based on the sedimentary facies and (four water reservoirs) as well. Quantitatively, the assessment was based on the climatic information (rainfall, temperature and humidity) for (39 years) for the period (1980 - 2019), so, by using Thornorite equation the water surplus was calculated representing the renewable storage of the unconfined aquifer which amounted to (110.9 * 106 m3/year), while the fixed storage for both systems (unconfined and confined) were calculated as (7.68 * 109 m3) and (6.16 * 109 m3) respectively, with total equivalent to (13.84 * 109 m3). While qualitatively, the assessment was based on utilizing the data bank information (151 wells) belongs to the general commission for groundwater (2013) in addition to some available field data. The results reveal that there some wells are within the permissible limits to be used for drinking purposes, which can be used for municipal after conducting biological tests on them, although they should not be used for agriculture. In general, it can be said that most of the water from the wells in the study area is suitable for agricultural use, with the exception of small scattered areas.

Geodiversity of Smaquli area as a potential geopark in Kurdistan region, Iraq

This research aims to spotlight abiotic elements of geodiversity in the Smaquli area and value and use as geoconservation through potential geopark. Smaquli area, situated in the southeastern part of Safen anticline, north of Iraq Kurdistan region, has a rich and diverse geological and geomorphological heritage, making it an interesting area for this study. This study aims to present the geodiversity of the Smaqule site as an opportunity to carry out future sustainable socio-economic activities in the geopark. The study includes fieldwork on the area's stratigraphy, structural geology, and geomorphology. Tectonically, the study area lay within the High Folded Zone of the Unstable Shelf of Iraq and was affected by the collision of Arabia-Eurasia Plates which started before 23–25 Ma in northern Zagros. The exposed rock unit formations in the Smaqule area range in age from Cretaceous to Paleogene. The oldest outcrop rock unit is the Qamchuqa Formation. Stratigraphy of the study area includes Qamchuqa, Bekhme, Shiranish, Tanjero, Kolosh, Gercus, and Pila Spi Formations. The study area is a mountainous area with different heights ranging from valleys to high ridges; this is due to structural controlling topography and differential erosion of the structures in the area and their different lithology of the rocks. Many geomorphological landforms are studied in the area, such as ridges, longitudinal and transverse valleys, Sulfur springs, caves, faults, drainage patterns, Badland, and an elongate lake. These features are very attractive landscapes for tourism and balneotherapy. This study highlights the area's geological significance to add to its known cultural value, local products, and tangible and intangible heritage. The study area is suitable for investment by the national and international tourism, creating employment opportunities for local people, and leading to socio-economic development. The Geosites Assessment Model (GAM) has been applied in this study to quantify the geotourism potential in the four geosites within the study area.

Structural Study of the Late Oligocene-Early Miocene Sequence in Khabaz Oil Field, NE of Iraq

Khabaz Oil Field is located in Kirkuk, about 20 Km southwest of Kirkuk City between Jambour and Bai Hassan oil fields. Tectonically, it is located on the Unstable Shelf within the Low Folded Zone (Zagros Fold Belt). Six wells in Khabaz oil field with two seismic lines (Line K8 and KK54) are used to conduct the geometric analysis, which include the description of fold and fault systems for the purpose of understanding the structural setting of Jeribe (Early Miocene) and Azkand (Late Oligocene) formations in this field. Khabaz structure is a double plunging positively inverted subsurface asymmetrical anticline influence the whole pre-Holocene sedimentary sequence. The interlimb angle of this structure ranges between 137º to 151º which is classified as a gentle anticline. The dip values of the axial surface range between 82 – 84º, so it can be classified as an upright fold with a general trend NW-SE. The core of the anticline is bounded by two high angle dipping reverse fault splay dipping toward each other. These faults pushed the core of the anticline upward with respect to the limbs of the structure. The Southwestern limb is affected by several high angle inverted faults that were possibly bifurcated from one or two major faults. The Northeastern limb is also influenced by a series of high angle reverse, some are dipping toward the core of the structure and few others are dipping toward the limbs. Some of these faults especially those influenced the southwestern limb of the anticline were inherited from the original normal faults that bounding the graben structure developed during the deposition of the Shiranish Formation. During the Late Plio-Plistocene contraction phase, the sense of slip on these faults were inverted and the faults migrated upward into the Tertiary sequence resulting in the formation of the positively inverted structure.

Evaluation of Tertiary Reservoir in Hamrin Oil Field, North Iraq

Hamrin oil field is one of the important oil field in northern Iraq. The field represent an asymmetrical anticline that extend North West-South East for more than 101 km, with width (4-7) km. Hamrin oil field was located at the south western boundary of foothill zone of the unstable shelf area according to the tectonic division of Iraq. The Tertiary reservoir represented by Jeribe and Euphrates formations as main reservoirs and Dhiban formation as secondary reservoir that represent an attractive petroleum completion target in Hamrin oil field. The aim of this study is to determine the petrophysical properties of these formations, using log data, because these properties affect the estimate of reserves (porosity and saturation) and well deliverability (permeability). This study shows that the petro physical properties of these formations were controlled by depositional environment, diagenesis and tectonic activity. The evaluation of the petro physical for tertiary reservoir in Hamrin oil field was necessary to choose the best interval for well completion.

Paleostress Analysis of the Northeastern Limb of Pulkhana Anticline /NE Iraq: Implications for Arabian Plate Tectonic Evolution

Pulkhana anticline is located in Tuzhurmatu area, about 50 km SE of Kirkuk city. The study area forms a part of the Zagros Folded Zone which is situated in the unstable shelf of Iraq within the physiographic zone called Foothill Zone (in the middle of Hemrin- Makhul subzone). The north eastern limb of the anticline reaches to 50ᵒ and the dip of the south western limb reaches to 70ᵒ. The core of the structure comprises the rocks of Fat’ha Formation surrounded by rocks of Injana and Mukdadiya Formations, whereas Bai-Hasan Formation forms the slopes of the low hills surrounding the anticline. These Formations range in age from Middle Miocene to Pliocene. More than 761 readings of joint planes were collected from 20 stations within 5 traverses in the study area. The study of joint sets and system was within Injana and Mukhdadiya formations, along traverses with 3-5 stations for each travers track. The results showed the presence of two sets of tension joints (bc, ac) and five sets of shear joints, through defining the maximum stress axis (σ1) and acute angle dividers for these conjugate joints. It was determined that two directions of Paleostress are present in the area, which are NE-SW and NW-SE. The direction of the first major stress (NE-SW) is orthogonal with, or normal to, the fold axis in the study area, which can be considered as a horizontal component which resulted from oblique collision of Arabian and Eurasian Plates. This old compressive stress is the reason behind the formation of the tension joint (ac) and shear joints, where the sets (ac) and system are perpendicular-semi perpendicular to the bedding plane, as they were formed at an early stage of folding. Also, the ) joint was formed in five tectonic stages with different time intervals. Joints formed in different tectonic stages, in the study area, are attributed to oblique collision of Arabian and Eurasian plates and counter clockwise rotation of Arabian plate relative to Eruasian plate.

Deep to shallow-marine sedimentology and impact of volcanism within the Middle Triassic Palaeo-Tethyan Semantan Basin, Singapore

The Middle Triassic Pulau Ayer Chawan Formation is a predominantly deep-marine, occasionally shallow-marine sedimentary succession, deposited in the Singapore sector of the Palaeo-Tethyan Semantan Basin. The formation provides an important record of the dynamic interplay between a siliciclastic sedimentary system and the products of an adjacent active volcanic arc. It is characterised by six sub-environments, including: deep-marine turbidite fan, deep-marine background sedimentation, subaqueous debris cone, shallow-marine, volcanically-sourced turbidite fan, and hyaloclastite mound or ridge. Turbidite fan deposits preserve the input of both siliciclastic and volcaniclastic sediments from the shelf, transported into the deep-marine environment by a suite of subaqueous sediment gravity flow processes, including: turbidity currents; mixed flow types (hybrid event beds); concentrated and hyper concentrated sediment gravity flows, and debris flows. Thick heterolithic successions of debrites were likely sourced through regular collapse of an unstable shelf. The presence of hybrid event beds, encountered within the deep-marine turbidite fans, supports a slope that was out-of-grade, and may have been actively retreating towards the hinterland. Together, these factors suggest regional-scale uplift of the eastern margins of the Semantan Basin during Triassic times, most likely facilitated through volcanic activity in the adjacent Palaeo-Tethys Sukhothai Arc. Evidence for contemporaneous, arc-related magmatism includes ubiquitous volcaniclastic sedimentary rocks within formation, including pyroclastic density current deposits and perhaps more-strikingly through the hyaloclastites of the Nanyang Member. The hyaloclastites formed through quenching of magmas delivered into the deep-marine setting from a series of sub-sea vents or mounds.

APPLICATION OF 18O AND 13C STABLE ISOTOPES COMPOSITION OF THE CARBONATE ROCKS OF THE JERIBE FORMATION EASTERN IRAQ; AN APPROACH TO DEFINE THE PALEO TEMPERATURE AND PALEO DEPTH

Stable isotopes 18O/16O and 13C/12C in the carbonate rocks of the Jeribe Formation are examined here to define the depositional characters in the basin includes paleo temperatures and paleo depth. The Jeribe Formation comprises a transgressive unit belongs to the Latest Eocene-Recent Megasequence (Ap11). Complete sections of the formation were studied in the core of Himreen structure in eastern part of Iraq. The Himreen structure lies in the outer platform margin of unstable shelf of the Arabian plate. The stable isotope (18O/16O and 13C/12C) of Jeribe Formation provides the first records of paleotemperature for the Neogene (middle Miocene Transgression) of the Southern Teythes, which indicate cooling during deposition. Microfacies study imply that the skeletal grains are composed of green and red algae, stromatolite and verities of benthic foraminifera. The non-skeletal grains are pellets and intraclasts. Analysis of microfacies suggests lagoon, reef, shoal and open marine environments. The depletion of both 18O and 13 C indicated shallowing at the contact with overlying and underlying formations in the shoal and lagoonal facies respectively. While in the middle part in the coral reef facies reveals elevation of the sea surface temperature. These suggest that the enrichment of both 18O and 13 C at the cool water temperature associated with upwelling and arise of sea level represented by reef and open marine facies.

The Transition Tectonic Zone Between the Two Parts of the Platform in Iraq: A Review Study

The changes of the tectonic boundary locations between the stable and unstable shelf on different version of the tectonic maps of Iraq is discussed. It is found that the location of the boundary varies due to philosophy and the type of the geological parameters. It is used the stratigraphic, geophysical, structural, geochemical, hydrological and others information in delineating the boundary. The deep crustal structures obtained by using gravity data show that the boundary shifted toward the west by about 100 km in southern Iraq. According to the review, and when taking in consideration all the geological and geophysical parameters from the lower crust to the earth surface, it is believed that the boundary is not a line but it is a tectonic crustal zone. This zone represents a transition zone between the main two regions of the platform in Iraq, and it is segmented to many subzones by transverse faults. In addition, it is believed that the data of the parameters of shallow geology confirm the eastern side of the main zone, while the lower crustal structures confirm the western side of the main zone.

Transition from storm wave‐dominated outer shelf to gullied upper slope: The mid‐Pliocene Orinoco shelf margin, South Trinidad

AbstractShelf‐edge deltas are a key depositional environment for accreting sediment onto shelf‐margin clinoforms. The Moruga Formation, part of the palaeo‐Orinoco shelf‐margin sedimentary prism of south‐east Trinidad, provides new insight into the incremental growth of a Pliocene, storm wave‐dominated shelf margin. Relatively little is known about the mechanisms of sand bypass from the shelf‐break area of margins, and in particular from storm wave‐dominated margins which are generally characterized by drifting of sand along strike until meeting a canyon or channel. The studied St. Hilaire Siltstone and Trinity Hill Sandstone succession is 260 m thick and demonstrates a continuous transition from gullied (with turbidites) uppermost slope upward to storm wave‐dominated delta front on the outermost shelf. The basal upper‐slope deposits are dominantly mass‐transport deposited blocks, as well as associated turbidites and debrites with common soft‐sediment‐deformed strata. The overlying uppermost slope succession exhibits a spectacular set of gullies, which are separated by abundant slump‐scar unconformities (tops of rotational slides), then filled with debris‐flow conglomerates and sandy turbidite beds with interbedded mudstones. The top of the study succession, on the outer‐shelf area, contains repeated upward‐coarsening, sandstone‐rich parasequences (2 to 15 m thick) with abundant hummocky and swaley cross‐stratification, clear evidence of storm‐swell and storm wave‐dominated conditions. The observations suggest reconstruction of the unstable shelf margin as follows: (i) the aggradational storm wave‐dominated, shelf‐edge delta front became unstable and collapsed down the slope; (ii) the excavated scars of the shelf margin became gullied, but gradually healed (aggraded) by repeated infilling by debris flows and turbidites, and then new gullying and further infilling; and (iii) a renewed storm wave‐dominated delta‐front prograded out across the healed outer shelf, re‐establishing the newly stabilized shelf margin. The Moruga Formation study, along with only a few others in the literature, confirms the sediment bypass ability of storm wave‐dominated reaches of shelf edges, despite river‐dominated deltas being, by far, the most efficient shelf‐edge regime for sediment bypass at the shelf break.