Recent years have seen the growth of new techniques that combine conventional stratigraphic and observational approaches to characterizing the type, scope, extent, timing, and effects of diagenetic processes with petrophysical measurements of their rock microstructure. These new Quantitative Diagenesis (QD) techniques can be used to predict post- and predolomitization porosities and permeabilities as well as track petrodiagenetic pathways. The objective of this paper is to use QD to calculate changes to the CO2 storage of a CCUS target for the first time. These QD approaches include porosity and permeability prediction resulting from varying degrees of dolomitization, calculation of porosity and permeability of the host rock before dolomitization, using petrodiagenetic pathways to track quantitatively the type, extent, and timing of diagenetic processes, and methods for determining the impact of fractures (the Fracture Effect Index, FEI). This paper reports the impact of dolomitization and fracturing on CO2 storage by considering the Butmah and Shiranish formations (NE Iraq). The Butmah Formation data show that the CO2 storage of the formation increased significantly 154.23 Mt (78%) due to dolomitization. The Shiranish Formation showed an increase in CO2 storage of 144.23 Mt (70%) from the almost unfractured rocks of its U.1(A) lithofacies (FEI = 0.31) to the highly fractured rocks of its U.4 lithofacies (FEI = 15.55). The main scientific contribution of this paper is that it shows for the first time that QD techniques can be used to calculate very significant changes in CO2 storage capacity concomitant with fracturing, dolomitization, and precipitation. Such techniques should therefore be employed when judging any legacy reservoir or aquifer in carbonates the potential CCUS use.

The Corinth Rift in Greece is very active, with high rates of extension, sedimentation and environmental change. International Ocean Discovery Program (IODP) Expedition 381 drilled three sites sampling syn-rift sediments, complementing previous fault and stratigraphic interpretations and providing the longest high-resolution stratigraphic record for an early phase rift. Sedimentation in the Gulf of Corinth started-2.0-2.5 Ma as an isolated basin, with the most recent rift phase starting at-0.75 Ma, marking a shift to increasingly orbitallycontrolled marine incursions. A wide range of paleoenvironmental conditions have been generated, reflected in the diverse microfossil assemblages and sedimentary lithologies. Drilling results highlight a recent acceleration of strain rate and fault activity connected to rapid strain localization, with linkage of the border fault system over 10s-100s kyr timescales. Over long timescales (100s kyr), these variations in fault slip rate control sediment accumulation. On shorter time scales (10s kyr), changes in accumulation rate and type of sediment are primarily controlled by glacial-interglacial climate change, with accumulation rates in glacial periods at least double that of interglacial periods, accompanied by enhanced basin stratification and dominance of non-marine faunal assemblages. The mud-dominated sediments have three stratal package types (bioturbated, bedded, laminated) that record distinct hydrological conditions linked to climate and sea level which influence the landscape and basin conditions. Results from the Corinth Rift are compared with other active basins and rift systems for a better understanding of the tectonic and climatic processes shaping these environments.

Abstract: Fractured carbonate reservoirs are of great importance in the oil industry due to their significant role in global oil reserves and complex nature, where the majority of these reservoirs are naturally fractured, making them complex and challenging for oil recovery. The detection and characterization of fractures are essential for understanding the reservoir's petrophysical properties and hydrocarbon recovery potential as they play a critical role in reservoir performance. In this paper we have used 3D seismic from the Razzak field in the Western Desert, Egypt, with a specific focus on the Alamein dolomite reservoir. The reservoir holds significance due to its prolific oil-bearing nature, and featuring widespread lateral distribution in the northern Western Desert. Additionally, its contribution to an active Mesozoic petroleum system emphasizes its importance. Using Petrel software, the Alamein top and visible faults were identified, leading to the creation of a structural map illustrating the WSW-ENE axes of the Alamein's structural culminations in the southern part of the horst block. Owing to an extensional force during the Jurassic period with a NE-SW orientation, resulting from rifting, was evident, marked by the formation of normal faults associated with the opening of the Neotethys in the NE-SW direction. In the interpretation of 3D seismic data for Alamein dolomite reservoir, only one major listric normal fault was identified. However, the presence of minor faults or fractures, not easily discernible with conventional seismic techniques, is plausible. To address this, volume attributes were applied to detect subtle changes in seismic properties: (i) the curvature operation calculated the dip and azimuth angles, aiding in identifying structural complexities like faults and fractures, (ii) the maximum curvature value highlighted areas of steeply dipping or folded structures, (iii) Edge detection emphasized sharp boundaries, yet no hidden fractures or minor faults were revealed. The variance attribute yielded limited information, but Ant tracking on the variance cube effectively identified hidden minor faults and fractures. Incorporating the Ant track attribute into FRACPAQ software provided an objective methodology for quantifying fracture patterns, revealing NW-SE-oriented fracture segments in contrast to the WSW-ENE orientation of the major fault. Consequently, seismic attributes will unveil concealed fractures, and the application of FRACPAQ will prove effective in furnishing data on fracture orientation and length statistics.Key words: FracpaQ; seismic attributes; fractured carbonate; Razzak fieldHow to cite: Elattar, H.A., Collier, R., and Glover, P. W. J.: Using FracPaQ and seismic attributes to assess seismic scale fractures in carbonate reservoirs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1674, https://doi.org/10.5194/egusphere-egu24-1674, 2024.

The diagenetic history of the Butmah Formation (Lower Jurassic) is very complex and affected by several diagenetic processes that worked effectively with fracturing control to create the final pore network. A microscopic study, core plug and well log analyses were combined in this study in order to describe, and differentiate between, the diagenetic and fracturing control that created the final pore system of the formation. The diagenetic processes of the Butmah Formation were studied in depth to describe the diagenetic stages and identify the elements that may compose a petrodiagenetic pathway illustrating its effect on the reservoir quality of the Butmah Formation. Accordingly, the Butmah Formation samples were divided into three petrophysical fields controlled mainly by fracturing and diagenesis, which were then used to develop a new method for estimating the pre-dolomitisation petrophysical properties of the dolomite samples and the post-dolomitisation petrophysical properties of the limestone samples. Consequently, the output of applying this method allows us to effectively begin to predict each of the elements that may compose a petrodiagenetic pathway for the Butmah Formation and make its reservoir characterisation integrated and more understandable. The new method provided a good prediction of matrix porosity and permeability, as well as allowing the estimation of reservoir properties of any other carbonate reservoir in petroleum development projects when there are no core samples in some formation intervals within boreholes.

The Shiranish Formation represents one of the most important fractured reservoirs in northern Iraq. In this work, the petrophysical properties of the formation have been fully characterised using microscopy, core analysis, and well log analysis using conventional methods as well as new quantitative diagenetic approaches. During this work we have developed methods to quantify a petrophysical heterogeneity index (chi), reservoir quality indicator (RQI), and fracture effect index (FEI) for each of the stratigraphic units of the formation. The FEI was calculated by dividing the difference between the mean permeability of the wireline log data and the mean permeability of the unfractured core plug samples by the difference between the mean porosity of the wireline log data and the mean porosity of the unfractured core plug samples. This study shows that the Shiranish Formation has a fracturing pore system in all the characterised units, but it is particularly well developed in U.4, which shows the best reservoir quality (A and B). The new methods developed in this study can be applied to any carbonate formation to provide a trustworthy way to obtain a reservoir quality indicator linked to the petrophysical heterogeneity of the studied formation.

The value of deep-water sedimentary successions as reliable records of environmental change has been questioned due to their long response times and sediment pathways leading to complex responses to climatic change and tectonic signals over differing timescales. We studied the Gulf of Corinth, Greece, to test the value of deep-water stratigraphic successions as records of external controls on sediment flux in a setting with short response times and transport distances. The confinement of the rift basin allows for a near-complete accounting of clastic sediment volumes. The recent acquisition of high-resolution seismic reflection data, utilisation of International Ocean Discovery Programme Expedition 381 cores and a robust chronological framework, enable evaluation of the stratigraphy at a high temporal resolution. Combining borehole and high-resolution seismic reflection data, distinct seismic units can be correlated to multiple paleoenvironmental proxies, permitting quantification of sediment flux variation across successive glacial-interglacial cycles at ca. 10 kyr temporal resolution. Trends in average sediment flux since ca. 242 ka show ca. 2-9 times greater sediment flux in cooler glacials compared to warmer interglacial conditions. The Holocene is an exception to low sediment flux for the interglacials, with ca. 5 times higher rates than previous interglacials. The short and steep configuration of the Sythas canyon and its fan at the base of an active submarine normal fault results in deep-sea deposition at all sea-level stands. In contrast, adjacent canyon systems shut down during warm intervals. When combined with palynology, results show that periods of distinct vegetation re-organisation correlate to sediment flux changes. The temporal correlation of sediment flux to palynology in the Gulf of Corinth over the last ca. 242 kyr is evidence that variability of sediment supply is largely governed by climate-related changes in hinterland catchments, with sea-level and tectonics being second-order controls on sediment flux variability. Sediment flux and depositional patterns over the last ca. 242 kyr reveal a strong link between climate cycles and sediment transport, with heightened flux during glacial periods. The Holocene interglacial shows unprecedented sedimentation due to anthropogenic impacts, highlighting the dynamic response of rift basin systems to environmental changes.image

This study presents the petrographical and petrophysical characteristics of the Cambro-Ordovician clastic reservoirs from the Risha field, northeastern Jordan. Routine core analysis, wireline logs, petrographic thin sections, scanning electron microscopy, and X-ray diffraction were integrated to characterize the gas reservoirs of the Risha, Dubeidib, and Umm Sahm formations (the equivalent of Sarah, Qasim, and Upper Saq formations of northern Saudi Arabia). These reservoirs are variably micro- and mesoporous, with permeability < 1 mD and dominantly < 6

Records of relative sea-level rise for the last deglaciation are mostly limited to coral reef records and geophysical model estimates, but observational data from regions with temperate climates is sparse. We present a new relative climatic and regional sea-level rise record for glacial Termination 1 (Marine Isotope Stages [MIS] 2-1) based on ostracode paleoecology from the upper 8 m of the International Ocean Discovery Program (IODP) Site M0080 collected on Expedition 381, in the Gulf of Alkyonides, eastern Corinth basin of the Mediterranean Sea. Results show a series of major faunal transitions from lacustrine (Ponto-Caspian, Lake Corinth) glacial-age assemblages to fully marine (Mediterranean) interglacial assemblages between 20 and 8 ka. During glacial and early deglacial intervals, the Gulf of Alkyonides was characterized by non-marine lacustrine conditions with episodic sediment input from coastal, saline lake environments. Relatively stable lake shoreline conditions marked by the distinctive Tuberoloxoconcha sp. Existed from -17.5 to 15 ka. During the peak deglacial interval, the Bolling-Allerod (B-A, -15-13.5 ka), rapid sea-level rise is indicated by a fully marine ostracode fauna colonization, which persisted from 13.5 to 7.5 ka (Late Pleistocene-Early to Middle Holocene). The transition from lacustrine to marine environments confirms that during the last glacial maximum (LGM) low sea level (130 - 125 m below present day), the Corinth-Alkyonides depocentres were lacustrine. Marine water breached the shallow Rion and Acheloos-Cape Pappas sills, which today are -50 -60 m deep, separating the Mediterranean and Corinth-Alkyonides system beginning about 15 ka. Based on Alkyonides sedimentation rates, mean rates of sea-level rise during the B-A flooding of the CorinthAlkyonides system are comparable to those obtained from coral reef sea level (SL) records, at least 10 -20 mm yr & DBLBOND;1. Changes in sedimentation and sill depths in this tectonically active region may have played a role in reconnection of the Mediterranean and Corinth/Alkyonides system over a prolonged period. However, the ages and scale of the faunal changes and their clear correspondence with previously published global sea-level curves and the regional sea-level curve based on deglacial land elevation changes predicted by the ICE-7G model suggests the M0080A deglacial is dominated by the glacioeustatic sea-level rise and records details of global climate changes during Termination 1. & COPY; 2023 Elsevier Ltd. All rights reserved.

Machine learning clustering methods offer the potential for recognition and separation of facies based on core or well-log data. This is a particular problem for carbonate rocks because diagenesis produces a wide range of rock microstructures and transport properties. In this work we use a large database of high quality poroperm, electrical, mercury injection capillary pressure and nuclear magnetic resonance spectroscopy measurements (307 core samples), representing 5 stratigraphically defined facies, as well as well log data to examine facies-recognition abilities using 8 different machine learning clustering approaches and a redundancy of 10 to ensure statistically valid results, resulting in a total of over 990 clustering runs. For a 3 cluster problem, we find that the Expectation Maximisation (92.57% success) and two types of Kmeans approaches (89.60% and 91.09%) provide the best methods. Further testing using the best of these shows that the quality of the input parameter (attribute) matters more than the number of attributes used, with the power of attributes in decreasing order being porosity, cementation exponent, permeability, pore throat diameter and free fluid index, implying that some attributes can degrade clustering performance. Further tests show that there should be at least as many attributes as clusters, in which case the machine learning can be left to choose the final number of clusters, providing the best performance in this work (69.35% success for a five cluster problem), otherwise it is best to constrain the cluster number by supervision. Application of the results from the previous testing to a mixed carbonate tight carbonate well from the Butmah formation shows satisfactory determination of 4 petrofacies by clustering (up to 91.65%) when compared to petrofacies determined manually. However, the greater challenge of clustering 9 reservoir quality classes defined using a ternary petrofacies approach did not provide a successful result (<38% success rate).

Continental rifted margins can have complex uplift histories related to different processes including footwall uplift by mechanical unloading, dynamic uplift and interaction with transfer margins.Deciphering uplift histories along rift flanks is integral to understanding the margin evolution as a whole.Here, a combination of drainage analysis and stream profile inverse modeling is utilized to estimate the rift flank uplift along the north-eastern Red Sea onshore margin.The drainage network was extracted from an ASTER DEM (~30 x 30 m-horizontal resolution) and the uplift history was calculated using an inverse model, which builds on the relationship between uplift, erosion and stream profile shape.Local relief, minimum erosion volumes and minimum erosion volume:catchment area ratios (Rva) were also calculated and compared to uplift estimates.Within the study area, small catchments represent footwall drainage and larger catchments are mostly associated with pre-rift structures and syn-rift accommodation zones.Uplift initiated in the southern part during early rifting (21-15 Ma) before shifting northward (12-0 Ma).This uplift distribution is reflected in Rva and relief maps.Earlyrift uplift is interpreted as a record of early-rift faulting with possible additional mantle support, whereas later uplift was driven by fault linkage and mantle upwelling (12-6 Ma) as well as transform tectonics (6-0 Ma).These modeling results are largely in agreement with other independent data (low-temperature thermochronology and dated carbonate terraces).Our workflow benefits from its utilization of ubiquitous drainage data.The combination of drainage analysis and inverse modeling proves to be more discerning than either one method in isolation, and may have application to analysis of other margins.

Syn-rift deep-water muds and mudstones preserve a relatively complete stratigraphic record of tectonic and climatic events. This paper investigates mud-dominated deposits and stratigraphy using core from International Ocean Discovery Program (IODP) Expedition 381 sites M0078 and M0079 in the Gulf of Corinth, Greece. Millimetre-scale logging defined several bed types: homogeneous and laminated mud beds, bioturbated beds, a variety of graded beds, and rare matrix-supported conglomerates and slumps. Homogeneous muds and light grey to black laminated muds record deposition from distal, waning low density turbidity currents and terminal mud-rich quasi-laminar or laminar plug flows. Graded beds, interpreted as turbidites, range from beds several millimetre to a few centimetres of mud with silt to fine sand bases, to metre-scale mud beds with coarser sand and pebble bases. Conglomerate and slumped beds record cohesive debris flows, transitional flows and slope failure. Three stratal package types are distinguished: bioturbated, bedded and laminated, recording distinct hydrological conditions. Bioturbated packages record interglacial marine conditions with well oxygenated waters. Bedded packages record hemipelagic processes and low energy density underflows in a mainly dysoxic, stratified, lacustrine setting (glacial phases). In laminated packages, white mm-scale laminae of calcite or aragonite from varved, hemipelagic sediments demonstrating seasonal variability in a dysoxic non-marine or transitional setting. Rift stratigraphy is linked to eustatically controlled connections to the global ocean across rift segment boundaries. The ca. 780 to 330 ka succession is dominated by laminated packages with thin bioturbated packages and distinct conglomerates and slumps, suggesting high sills, making ocean connections brief and transitional to lacustrine conditions prolonged. The ca. 330 ka to present succession shows well developed bioturbated and bedded packages, separated by thin laminated packages, suggesting brief transitions and well-developed marine conditions due to lower sills. Results indicate that structurally controlled rift segment boundaries exert a first-order control on syn-rift stratigraphic evolution, with fault segment growth and linkage driving intra-rift facies and sequence variability.

Abstract Grain-size analysis of the sediments in borehole M0079A, located in the Corinth Rift, was used to explore hydrodynamic conditions and provenance in the Late Pleistocene Corinth Rift. Grain-size populations that were sensitive to the sedimentary environments were characterized by frequency distribution, particle size–standard deviation and probability cumulative curves. Our results indicate the grain-size population component in the range 0.15–0.25 µm may be used as a sensitive proxy for hyperpycnal flows, which have commonly been triggered by river floods from the southern margin of the rift since c. 0.593–0.613 Ma. The high-density plumes derived from the longer rivers of the southern rift that were prevalent before c. 0.593–0.613 Ma. When sediment is supplied as hemipelagic deposition, the proportion of the total grain-size population that is in the 0.3–0.5 µm range becomes an index for suspension fall-out deposits. The core shows coarser sediments during the marine periods, and this may be linked to the current circulation related to the Ishtmia Strait opening. The study thus illustrates how the establishment of interbasinal straits can influence the details of sedimentary hydrodynamics in the deep-water axis of an adjacent depocentre.

A sedimentological investigation of Miocene deposits at the periphery of the Zagros foreland basin, Kurdistan Region, NE Iraq, reveals a cyclical arrangement of carbonate-evaporite ramp facies. The study aims to provide rare insight into the lateral variability of microfacies and environments of such systems' inner ramp and shoreline. Between 10 and 40 depositional cycles are preserved, separated by a flooding surface, and recording an overall basinward progradation. In each cycle, a shallowing-upward trend from a lower-energy calcareous mudstone and mudstone-wackestone carbonate microfacies at the base to a higher-energy packstone-grainstonerudstone or low-energy algal mat/stromatolitic carbonate microfacies above is evident. Evaporite deposits of supratidal sabkha origin cap each carbonate deposit. Red clastic sediments that advanced south-westward into the basin from the adjacent Zagros hinterland overlie each evaporite deposit. A flooding surface and return to calcareous mudstones mark the start of the next cycle. Outcrop and thin-section analysis of the carbonate deposits of each cycle reveals a shoaling-up to inner-ramp facies with varied environmental settings that developed under a range of hydrodynamic conditions. Microfacies analysis indicates that these environments included normal marine salinity open lagoons, hypersaline lagoons, restricted and shallow lagoons, sand shoals, intertidal and supratidal flats, supratidal ponds, and a coastal alluvial plain that included channelised deposits and palaeosols. The cyclical facies trend changes toward the top of the succession in that the relative rate of siliciclastic supply markedly increased, whereas the rate of carbonate and evaporite production decreased. Progradation and shoreline migration through time caused lateral and vertical facies changes and thickness variations over the succession. Repeated relative sea-level changes, associated changes in climate, and variations in sediment supply from the hinterlands during the collision of the Arabian and Iranian plates, combined with a variable rate of accommodation generation, are inferred to have controlled the preserved cyclicity.

The timing and character of coarse siliciclastic sediment delivered to deep-water environments in active rift basins is governed by the complicated interactions of tectonics, climate, eustasy, hinterland geology, and shelf process regime. The stratigraphic archives of deep-water syn-rift basin-fills provide records of palaeoenvironmental changes (e.g. climate and vegetation) in onshore catchments, particularly where they are connected by narrow shelves. However, a chronostratigraphically constrained record of climatic fluctuations and process responses in the hinterland source area recorded in deep-water deposits is rare. Here, we integrate a fully cored research borehole with outcrop exposures of deep-water syn-rift stratigraphy to reconstruct palaeoenvironmental change within the stratigraphy of the West Xylokastro Fault Block in the Corinth Rift, Greece. We used palaeomagnetic and palynological analyses from borehole core samples to develop a chronostratigraphic and palaeoenvironmental model, which we compare to global records of Early-Mid Pleistocene climate and eustatic change. This framework allows establishment of a chronostratigraphic and palaeoenvironmental context to stratigraphic variability encountered in outcrop and in the borehole. Our results show that the ∼240 m thick studied succession was deposited from ∼1.1 to 0.6 Ma across the Early-to Mid-Pleistocene transition. During the Early Pleistocene, obliquity-paced climatic variability is largely coherent with vegetation changes of forest coverage within catchments on the southern margin of the Corinth Rift. Large magnitude, eccentricity-paced cyclicity dominant after the Mid-Pleistocene Transition can alter sediment supply from onshore catchments during the warming stages of severe interglacials where expansion of forest cover may trap sediment within catchments. Conglomeratic grade sediment delivery to the deep-water is enhanced during glacial periods, interpreted to reflect sparse forest cover and large winter storms, and during semi-arid, grassland-dominated interglacial highstands during severe interglacials. Base-level rise during minor interglacials is easily outpaced by high sediment supply and is seldom represented stratigraphically. The study demonstrates the value of integrated palynological and sedimentological studies, whilst applying a conservative approach to interpretation when dealing with sparse palynological records from proximal deep-water stratigraphy. The case study provides conceptual models where climatic and vegetation changes can begin to be incorporated as a key control on sediment flux from onshore drainage basins to deep-water syn-rift successions.

This study examines the scaling relationship between fault length and displacement for the purpose of gaining a better understanding of the evolution of normal faults within the central Kenya Rift. 620 normal faults were manually mapped from a digital elevation model (DEM), with 30 m(2) resolution and an estimated maximum displacement of similar to 40-similar to 6030 m and fault lengths of 1270 - 60,600 m. To assess the contribution of fault populations to the strain accommodation from south to north, the study area has been divided into three zones of fault populations based upon their average fault orientations; zone 1 in the north is dominated by NNE striking faults, zone 2 in the centre of the rift is characterised by NNW to NNE fault trends, whereas zone 3 in the south is characterised by NNW striking fault systems. Extensional strain was estimated by summing fault heaves across six transects along the rift, which showed a progressive increase of strain from south to north. The fault length and displacement data in the three zones fit to a power law distribution. The cumulative distributions of fault length populations showed similar fractal dimension (D) in the three zones. The cumulative displacement distributions for the three zones showed a decrease in the Power-law fractal dimension with increasing strain, which implies that the strain is increasingly localized onto larger faults as the fault system becomes more evolved from south to north. Increasing displacement with increasing strain while the fault length remains almost constant may indicate that the fault system could be evolving in accordance with a constant length fault growth model, where faults lengthen quickly and then accrue displacement. Results of this study suggest that the process of progressively increasing fault system maturity and strain localization onto large faults can be observed even over a relatively small area (240 x 150 km) within the rift system. It is also suggested that patterns of fault growth can be deduced from the fractal dimension of cumulative distribution of fault size populations.

Interactions between footwall‐, hangingwall‐ and axial‐derived depositional systems make syn‐rift stratigraphic architecture difficult to predict, and preservation of net‐erosional source landscapes is limited. Distinguishing between deposits derived from fault‐scarp degradation (consequent systems) and those derived from long‐lived catchments beyond the fault block crest (antecedent systems) is also challenging, but important for hydrocarbon reservoir prospecting. We undertake geometric and volumetric analysis of a fault‐scarp degradation complex and adjacent hangingwall‐fill associated with the Thebe‐2 fault block on the Exmouth Plateau, NW Shelf, offshore Australia, using high resolution 3D seismic data. Vertical and headward erosion of the complex and fault throw are measured. Seismic‐stratigraphic and seismic facies mapping allow us to constrain the spatial and architectural variability of depositional systems in the hangingwall. Footwall‐derived systems interacted with hangingwall‐ and axial‐derived systems, through diversion around topography, interfingering or successive onlap. We calculate the volume of footwall‐sourced hangingwall fans (V HW ) for nine quadrants along the fault block, and compare this to the volume of material eroded from the immediately up‐dip fault‐scarp (V FW ). This analysis highlights areas of sediment bypass (V FW > V HW ) and areas fed by sediment sources beyond the degraded fault scarp (V HW > V FW ). Exposure of the border fault footwall and adjacent fault terraces produced small catchments located beyond the fault block crest that fed the hangingwall basin. One source persisted throughout the main syn‐rift episode, and its location coincided with: (a) an intra‐basin topographic high; (b) a local fault throw minimum; (c) increased vertical and headward erosion within the fault‐scarp degradation complex; and (d) sustained clinoform development in the immediate hangingwall. Our novel quantitative volumetric approach to identify through‐going sediment input points could be applied to other rift basin‐fills. We highlight implications for hydrocarbon exploration and emphasize the need to incorporate interaction of multiple sediment sources and their resultant architecture in tectono‐stratigraphic models for rift basins.

Deep-water syn-rift systems develop in partially- or transiently-linked depocentres to form complicated depositional architectures, which are characterised by short transport distances, coarse grain sizes and a wide range of sedimentary processes. Exhumed systems that can help to constrain the tectono-stratigraphic evolution of such systems are rare or complicated by inversion tectonics. Here, we document a mid-Pleistocene deep-water syn-rift system fed by Gilbert-type fan deltas in the hangingwall of a rift margin fault bounding the West Xylokastro Horst block, on the southern margin of the Gulf of Corinth, Greece. Structural and stratigraphic mapping combined with digital outcrop models permit observations along this syn-rift depositional system from hinterland source to deep-water sink. The West Xylokastro Fault hangingwall is filled by two distinct sediment systems; an axial system fed by coarse-grained sediment gravity flows derived from fault-tip Gilbert-type fan deltas and a lateral system dominated by mass transport deposits fed from an evolving fault-scarp apron. Abrupt changes in stratigraphic architecture across the axial system are interpreted to record changes in relative base level, sediment supply and tectonics. Locally, depositional topography and intra-basinal structures controlled sediment dispersal patterns, from bed-scale infilling of local rugose topography above mass transport complexes, to basin-scale confinement from the fault scarp apron. These acted to generate a temporally and spatially variable, heterogeneous stratigraphic architecture throughout the basin-fill. The transition of the locus of sedimentation from a rift margin to a fault terrace through the syn-sedimentary growth of a basinward fault produced regressive surfaces updip, which manifest themselves as channels in the deep-water realm and acted to prograde the system. We present a new conceptual model that recognises coeval axial and transverse systems based on the stratigraphic architecture around the West Xylokastro fault block that emphasizes the lateral and vertical heterogeneity of rift basin-fills with multiple entry points.

Models to explain alluvial system development in rift settings commonly depict fans that are sourced directly from catchments formed in newly uplifted footwalls, which leads to the development of steep-sided talus-cone fans in the actively subsiding basin depocentre. The impact of basin evolution on antecedent drainage networks orientated close to perpendicular to a rift axis, and flowing over the developing hangingwall dip slope, remains relatively poorly understood. The aim of this study is to better understand the responses to rift margin uplift and subsequent intrabasinal fault development in determining sedimentation patterns in alluvial deposits of a major antecedent drainage system. Field-acquired data from a coarse-grained alluvial syn-rift succession in the western Gulf of Corinth, Greece (sedimentological logging and mapping) has allowed analysis of the spatial distribution of facies associations, stratigraphic architectural elements and patterns of palaeoflow. During the earliest rifting phase, newly uplifted footwalls redirected a previously established fluvial system with predominantly southward drainage. Footwall uplift on the southern basin margin at an initially relatively slow rate led to the development of an overfilled basin, within which an alluvial fan prograded to the south-west, south and south-east over a hangingwall dip slope. Deposition of the alluvial system sourced from the north coincided with the establishment of small-scale alluvial fans sourced from the newly uplifted footwall in the south. Deposits of non-cohesive debris flows close to the proposed hangingwall fan apex pass gradationally downstream into predominantly bedload conglomerate deposits indicative of sedimentation via hyperconcentrated flows laden with sand- and silt-grade sediment. Subsequent normal faulting in the hangingwall resulted in the establishment of further barriers to stream drainage, blocking flow routes to the south. This culminated in the termination of sediment supply to the basin depocentre from the north, and the onset of underfilled basin conditions as signified by an associated lacustrine transgression. The evolution of the fluvial system described in this study records transitions between three possible end-member types of interaction between active rifting and antecedent drainage systems: (a) erosion through an uplifted footwall, (b) drainage diversion away from an uplifted footwall and (c) deposition over the hangingwall dip slope. The orientation of antecedent drainage pathways at a high angle to the trend of a developing rift axis, replete with intrabasinal faulting, exerts a primary control on the timing and location of development of overfilled and underfilled basin states in evolving depocentres.

A new reservoir quality ternary plot (RQTP) of effective porosity, shale volume, and matrix is presented in this study. We show it to be a useful tool for first-order estimation of the petrophysical zones and reservoir classes of each unit within a reservoir. Subsequently, we combine the RQTP results with permeability and fracturing intensity data in carbonate rocks to provide a better overall characterisation of reservoir quality. The approach has been applied to the Butmah Formation, a thick variable carbonate succession of Liassic (Lower Jurassic) rocks in north-western Iraq. The RQTP approach divides carbonate reservoirs into classes according to: (i) a measure of porosity, (ii) the fraction of shale, and (iii) the fraction of non-shale matrix. The outcome of applying this model to the Butmah Formation indicates that the best reservoir quality is identified in Unit 4, which consists of fine to medium dolomite rocks. These rocks are not associated with anhydrite cement or dissolved later due to late dissolution, presenting as clean carbonate with complex pore network heterogeneity. These types of rocks were classified as Rc2 and Rc3 using the RQTP Model. By contrast, the worst reservoir qualities (Rc7) were identified in Unit 1 which is composed of cemented limestone that shows low pore network heterogeneity (predominantly uniform pore sizes), low porosity, and poor permeability.

AbstractModels that aim to capture the interactions between sediment supply, base level and tectonism recorded in fan delta successions in rift basins have not considered the stratigraphic archive preserved in interfan areas; yet interfan stratigraphy can provide a complementary record to the fan delta axes. The exhumed Early–Middle Pleistocene Kerinitis and Selinous fan deltas, in the hangingwall of the Pyrgaki–Mamoussia (P‐M) Fault, Corinth Rift, Greece, offer an ideal laboratory for the assessment of interfan architecture. Furthermore, using the geometry of adjacent present‐day fan deltas, interfans are classified into three end‐members. The classification is based on their lateral separation, which determines the degree of interfingering of topset, foreset and bottomset deposits. Qualitative (facies, stratal geometries, nature of key surfaces) and quantitative (stratigraphic thickness, bedding dip, palaeocurrents, breakpoint trajectories) data were collected in the field and from unmanned aerial vehicle photogrammetry‐based 3D outcrop models of the exhumed fan delta successions. The ancient Kerinitis–Selinous interfan architectures record: (a) initial westward progradation of the Kerinitis fan delta into the interfan area (Phase 1), (b) subsequent progradation of the Selinous fan delta into the interfan area and asymmetric growth of both fan deltas eastward (Phase 2), (c) stratal interfingering of foresets from both systems (Phase 3), and (d) relative base‐level fall, erosion and reworking of sediments into the interfan area (Phases 4 and 5). The Kerinitis–Selinous interfan evolution is linked to initial net subsidence of the P‐M Fault (Phases 1–3) and subsequent net uplift (Phases 4 and 5) resulting from a northward shift in fault activity. The interfan area provides a more complete stratigraphic record than the proximal axial areas of the fan deltas of the early stages of basin uplift, through higher preservation potential and protracted submergence. Therefore, for the most comprehensive insight into basin evolution, interfan analysis should be undertaken in concert with analysis of the fan delta axes.