NW-SE Normal Faults Research Articles

Integration of seismic and well log data for evaluating the upper cretaceous reservoirs of Horus oil field, Alamein Basin, Northern Western Desert, Egypt

Horus field stands out as one of the main oil-rich areas in Alamein Basin. Formation and evolution of Horus field were influenced by tectonic processes occurring from Jurassic to Cretaceous periods. The main objectives of this study are to characterize structural elements, identify hydrocarbon potential, and pinpoint promising zones within Early Cretaceous rocks for hydrocarbon accumulations in Horus reservoirs. By utilizing high-quality 2D seismic reflection sections enhanced with structural smoothing attribute, which help eliminate random noise while preserving structural details and horizon geometry, building a 3D structural model becomes facile. Analysis of well logging data provides a comprehensive understanding of Cretaceous reservoirs, simplified by 3D static reservoir modeling to depict their varying ranges and anisotropies. 3D structural model shows that the trap of Horus field is linked to a structural uplift in an ENE-WSW trend, bordered to north and south by sediment-filled lows. This anticlinal ridge within the model is segmented into blocks by a series of NW-SE normal faults. 3D static reservoir models reveal high-quality reservoirs in Upper Bahariya and Abu Roash (G) Dolomite, characterized by substantial thicknesses of net pay zones. 3D static modeling of Cretaceous reservoirs guides the oilfield development and optimizes production strategies in Horus area.

Integrated seismic, petrophysical, and geochemical studies for evaluating the petroleum system of the Upper Bahariya-Abu Roash G sequence in the Karama Field, Abu Gharadig Basin, North Western Desert, Egypt

The main aim of this study is to delineate the hydrocarbon potential and evaluate the petroleum system elements of the Cenomanian Abu Roash G (AR/G) and the Upper Bahariya Members in the Karama Field. It lies at the southeast borders of the Abu Gharadig Basin, a well-known basin in the W.D. to the NE of Africa. We accomplish this study by analyzing a total of thirty 2D seismic profiles, a complete data set of well logs for five wells, and their geochemical data. The workflow starts with illustrating the dominant subsurface structural features, defining the main potential reservoirs and their parameters, and checking the maturity of the probable source rocks. The seismic interpretation indicated that the research area had been influenced by a NE-SW anticlinal structure accompanied by a set of WNW-ESE and NW-SE normal faults that are controlled by the positive compression inversion process that dominated during the Late Cretaceous. Analyzing and processing the well log data sets suggest that the reservoirs of the Abu Roash G (AR/G) and the Upper Bahariya Members are characterized by poor to good reservoir settings with net-pay thickness reaching up to 13–50 feet in the different wells (av. Effective porosity (∅eff) = 17.7 % and 15.6% for the AR/G and the Upper Bahariya Members, av. Shale volume (Vsh) = 17.4 % and 13.6 %, av. Water saturation (Sw) = 38.9 % and 39.8 %, while av. Hydrocarbon saturation values (So) = 60.2 % and 61.1%, respectively). The geochemical and maturity analyses assisted in determining the potential mature source rocks of the Jurassic Khatatba Shale (TOC = 0.70–5.67%; S1+S2 = 0.43–5.97 mg/g, Ro = 0.54–1.06 %) with some contribution from the Cretaceous sources (Alam El-Bueib and Bahariya Formations). Studying elements of the petroleum regime of the Karama Field indicates that the trapped hydrocarbons are structurally controlled by three-way dip closures, horst blocks, sealing faults, and vertical sealing by impervious shale and limestone beds. This case study could be applied to similar analogs in other oil fields in the Egyptian Western Desert to delineate their hydrocarbon potential and structural setting.

A Failed Rift in the Eastern Adventure Plateau (Sicilian Channel, Central Mediterranean)

Widespread volcanism has been known in the Sicilian Channel for a long time, even if some submarine volcanoes have only recently been discovered. Most of this volcanism formed along the NNE-trending transfer zone known as the Capo Granitola–Sciacca Fault Zone, while others, such as the islands of Pantelleria and Linosa, are associated with the continental rift zone that has developed since the early Pliocene in the central part of the Sicilian Channel through the formation of three deep tectonic troughs (Pantelleria, Linosa and Malta). However, the origin of a group of five volcanoes (here called “Tetide volcanic cluster”) that form a NW-SE alignment on the eastern edge of the Adventure Plateau is not yet known. In this work, we hypothesize that this volcanic alignment may represent the remnants of a failed rift attempt that was unable to generate another tectonic trough in the Sicilian Channel. Based on seismic sections and gravimetric data, three phases in the formation of this volcanic alignment can be identified: (i) a major magmatic intrusion in the early Pliocene associated with a NW-SE normal fault that formed during the opening of the Pantelleria graben, leading to the uplift and deformation of the host sedimentary rocks; (ii) a late Pliocene-Quaternary tectono-magmatic quiescent phase; and (iii) a renewed magma intrusion through fissures or cracks that led to the formation of the volcanoes in the late Quaternary. This process was not able to cause significant extension and only limited volcanism, which is why the “Tetide volcanic cluster“ is interpreted as the morphological expression of a failed rift.

Magnetic response contrast of Oligo-Miocene basaltic magmatism and structural control during its ascent at the northern tip of the Red Sea Rift

Oligo-Miocene volcanic activity has occurred along the northern Egyptian margin of the Red Sea Rift system, leading to the creation of small-volume monogenetic volcanoes. This research delves into the morphology and setting of these rift-related volcanics by combining aeromagnetic data, remote sensing, and field verification. Basaltic exposures in the study area were mapped using False Color Composite (FCC) and band ratios in Landsat 8 OLI data. In a map view, these mappable volcanic rocks appear as discrete semi-circular basaltic bodies and as discontinuous dikes. The basaltic bodies are aligned along ENE and NW-oriented zones, with most dikes orientated NW-SE. Multiple isolated high magnetic zones with NE and NW orientations were identified. Most basaltic outcrops coincide with high magnetic zones except for Gabal Abu Treifiya along the Cairo-Suez Road. The integration and combination of three layers of surface and subsurface structure patterns reveal an array of variance. The dominant trend of surface and deeper structural lineaments is NW-SE and NE-SW respectively. In contrast, shallow structural lineaments have NW-SE, NE-SW, E-W, and N–S trends. Long linear grabens result from the pairing of NW-SE normal faults. The basaltic occurrences such as Qattamiya and Abu Treifiya are located at the intersection of the NW-SE and E-W normal faults along the NW-SE linear grabens. The field investigation at both locations reveals a polyphase magmatic feeding system manifesting in the surface today as coherent and volcaniclastic rock units. This suggests a diverse range of eruptive styles through a complex feeder system that involves more than one volcanic cone. Though the two areas have good basaltic exposures, yet they have different magnetic responses. The severe alteration of Abu Treifiya's volcanic rocks into nonmagnetic minerals assemblage of zeolite, smectite, calcite, and hydrolysis of basaltic glass diminishes the expected high magnetic anomaly. This study contributes to our knowledge of Rift-related volcanism and the factors influencing the distribution of these volcanic materials.

Geophysical appraisal and hydrocarbon potential of the Pre-Cenomanian and Miocene reservoirs in the onshore and offshore Gulf of Suez Basin

The purpose of this study is to geophysically assess the petroleum potential of the Pre-Cenomanian (Nubia sandstones) as well as the Miocene oil reservoirs in the Rabeh field and Edfu-Saqqara field, located in the Gulf of Suez Basin. This will serve as a supplementary source for future exploration in the onshore and offshore Gulf of Suez Basin. This research utilizes the wireline logs of twelve drilled wells, eight of them drilled in Rabeh field, onshore southern Gulf of Suez Basin (RE-8, RE-22, RE-25, RE-2, RE-4, Nageh-1, South Malak-1 & Tawoos-1) and the rest four wells (Edfu A-3, Edfu A-5A, GS323-1 A & GS323-4 A) drilled in Edfu-Saqqara field, offshore central Gulf of Suez Basin. Moreover, twenty seismic profiles covering the Rabeh field were structurally interpreted. This interpretation exposed that the basement rocks are severely intersected by numerous NW–SE normal faults, along with minor E–W faults. The presence of these faults has a great role in forming suitable structural traps for holding hydrocarbon. Based on the qualitative and quantitative appraisal of the well logging data, Nubia, Nukhul and Rudies formations display positive petrophysical signs for being a potential reservoir in the studied fields. These reservoirs display respectable net pay thickness varying between 21 and 550 ft (i.e. 6.5–166.5 m), good net-to-gross ratio (0.01–0.90), excellent effective porosity (0.12–0.20), little shale content (0.03–0.20), minor water saturation (0.05–0.40) and high hydrocarbon saturation (0.60–0.95). The created lateral distribution maps for the considered petrophysical parameters in the Rabeh Field suggest that the drilling efforts should be essentially directed in the southeastern side of the Rabeh field to access the high-quality Nubia sandstone reservoirs.

Multiple compression directions and basinal response in a rhomb-shaped terrestrial basin: The Cuevas de Cañart syncline (Iberian Chain, eastern Spain)

Rhomb-shaped basins have been commonly attributed to strike-slip tectonics, linked to fault bends and jogs (pull-apart basins). The case-study presented in this work (Las Cuevas de Cañart basin, Iberian Chain) is a 2 km × 5 km continental basin that shows a particular combination of geometric and sedimentary features. It shows a syncline geometry with steeply-dipping limbs, thickness of syn-tectonic sedimentary continental filling of about 1000 m, high amplitude/wavelength ratio, and different fold trends, some of them oblique to the main trend of the Iberian Chain. All these features make it an interesting case of a mixed-type basin, sharing both compressional and strike-slip features. The Cuevas de Cañart basin shows a Mesozoic, pre-compressional sequence linked to the extensional processes dominating in the marginal zones of the Maestrazgo basin, with a series up to 1500 m thick of limestones, sandstones and shales. These units overlie a detachment level (Upper Triassic Keuper facies) and show thickness variations controlled by NW-SE and NE-SW striking normal faults. During the Cenozoic compression, both fault systems were re-activated, and newly formed E-W folds (perpendicular to one of the dominant shortening directions) also appeared in the southern basin margin. The detailed structural study of this basin evidences the role of different types of structures (basement faults, thrusts formed under different compression directions) and the relevance of the detachment level in the evolution of compressional basins and thin-skinned fold-and-thrust belts.

Hydrochemical changes in thermal waters related to seismic activity: The case of the 2020–2021 seismic sequence in Granada (S Spain)

Between the end of December 2020 and August 2021, 3110 earthquakes were recorded in the Granada Depression in southern Spain, with 353 of them being felt by the population. The highest concentration of earthquakes occurred between January 23rd and February 23rd, 2021, during which five out of six of the highest magnitude earthquakes (greater than 4.1 Mw) were recorded. This shallow seismicity is associated with NW-SE normal active faults, specifically the Santa Fe fault. Hydrochemical sampling was carried out at two deep, upwelling, and thermal boreholes located near the epicentral zone between January 27th, 2021 and July 18th, 2022, to analyze the response of a set of hydrochemical parameters during and after the earthquakes. The methodology employed different statistical tools, including Principal Components Analysis (PCA), PHREEQC modeling as well as Piper and Langelier-Ludwig diagrams, to determine the hydrochemical evolution during the seismic sequence and the parameter variations in relation to the number and magnitude of the earthquakes. The results showed significant variations in almost all of the parameters analyzed, with greater variations in SO4, Cl, Fe, Ca, Zn, and Al. During the days with the highest number of earthquakes of the highest magnitude, there was a rapid increase in Cl, SO4, SiO2, and Mg, while F, T, EC, and pH decreased. Peaks in SO4 seemed to anticipate earthquakes of greater magnitude that could be related to the preseismic dilatation which allows for an inflow of deep sulphated source water into the aquifer system. PCA and hydrochemical diagrams showed appreciable differences between the two boreholes, which could be related to the sampling distance from the epicentral zone. The results suggest the need for a hydrochemical monitoring network in the region, which has the highest seismic hazard in Spain.

Structural and petrophysical characteristics of the Turonian “AR/G″ reservoirs in heba field (Western Desert, Egypt): Integrated approach for hydrocarbon exploration and development

The evaluation of the Turonian “AR/G″ reservoirs in the Heba field, located in the eastern part of the Abu Gharadig Basin in the Western Desert of Egypt, is a crucial aspect of hydrocarbon exploration and development in the region. To achieve this, a comprehensive analysis of wells and seismic data was conducted. The seismic interpretation revealed that the Upper Cretaceous dextral wrenching tectonic has influenced the Heba field and extends throughout the northern Western Desert. Through the integration of seismic attributes, such as RMS and Sweetness, and well log correlation during the mapping phase, an ENE-WSW faulted anticline structure was identified in the study area. This geological feature was found to be plunging towards the NW direction and stretches throughout the study area, although it is fragmented by several NW-SE and WNW-ESE normal faults with lengths ranging from 1 to 10 km. The well log analysis of the AR/G Member has identified two proposed oil zones (Zone 1 and Zone 2), both exhibiting good reservoir quality across all examined wells. These oil zones are characterized by low to moderate shale volume (15%–40%), high total porosity (20%–28%), moderate effective porosity (15%–17%), moderate water saturation (40%–67%), and low bulk volume of water (6%–9%). These findings suggest that the AR/G Member has the potential to be a productive hydrocarbon reservoir. Integrating the structural and petrophysical characteristics of the “AR/G″ reservoirs can greatly assist in identifying suitable locations for oil exploration and development in the study area. This integrated approach enhances the ability to predict the behavior and production potential of the “AR/G″ reservoirs in the Heba field (Western Desert, Egypt).

Formation evaluation utilizing a new petrophysical automation tool and subsurface mapping of the Upper Cretaceous carbonate reservoirs, the southern periphery of the Abu-Gharadig basin, Western Desert, Egypt

The southern periphery of the Abu-Gharadig basin in the Northern Egyptian Western Desert is characterized by some subsurface geological challenges related to the carbonate reservoir's quality, which requires precise petrophysical evaluation and seismic structural interpretation. Therefore, we conducted a subsurface mapping and formation evaluation for the Upper Cretaceous carbonate reservoirs in the Southwest Abu Sennan (SWS) area utilizing seismic reflection profiles and borehole geophysical data. Seismic mapping of the Upper Cretaceous carbonate reservoirs (Abu Roash (AR)/B,/D, and/F) revealed 3-way folds with NE-SW trends divided by NW-SE normal fault trends presenting significant chances for exploration. These closures were filled by hydrocarbons generated from the Jurassic source rocks. Formation evaluation was performed using the new petrophysical tool “Gaialog” which was coded using Python. Petrophysical parameters for the recognized net pay intervals of AR/B, AR/D, and AR/F carbonate reservoirs showed that the effective porosity (φeff: Phie) and the hydrocarbon saturation (Sh) increases towards the East to Southeast direction while the water saturation (Sw) increases to the Northwest of the study area. The highest net pay and the effective porosity were found in the Eastern part of the study area. The study procedures can be applied in neighboring areas to evaluate and understand similar reservoirs.

Geophysical assessment for the oil potentiality of the Abu Roash “G” reservoir in West Beni Suef Basin, Western Desert, Egypt

The current study evaluates the hydrocarbon potentiality of the sandstone intervals of the Abu Roash “G” Member in Beni Suef Basin, Egypt. This evaluation has been performed through seismic interpretation for thirty seismic profiles and petrophysical appraisal for Fayoum-2X well (Fayoum oil field) and Yusif-4X well (Yusif oil field). The seismic interpretation presented the prevalence of the Lower Cretaceous NW-SE normal faults followed and linked with a major Late Cretaceous ENE strike-slip fault affected the Beni Suef Basin. This strike-slip fault is accompanied by a significant flower structure and releasing bend in the middle part of the studied area. The entrapment styles in both Fayoum and Yusif oil fields are considered by the existence of NW-SE trending horst closures bounded by the NW-SE faults. The petrophysical analysis exhibits good reservoir quality for the sandstones of Abu Roash “G” Member in the examined fields with low shale volume (5–20%); high effective porosity (15–25%), relatively low water saturation (35–55%) and pay thickness varies between 14 ft and 16 ft. Although the Abu Roash “G” Member exhibits lateral facies changes across the Beni Suef Basin, this study highlights the hydrocarbon potentiality of its entire sandstones for further exploration and development purposes in both Fayoum and Yusif oil fields. Core-based petrophysical analysis and detailed sedimentological analyses for the reservoir zones within Abu Roash “G” Member at Beni Suef Basin are highly recommended to emphasize the effect of the lateral facies change on the reservoir properties along the whole basin which will affect the development plans. The integration of multiscale datasets which includes seismic, different types of well logs, core is giving a precise picture about the reservoir units. Altogether are figuring out the detailed composition of reservoir sedimentology and quality by using the core information, investigate the hydrocarbon potentiality using the well logging evaluation, deducing their trapping mechanism, and controlling structures using the seismic datasets and the spatial distribution is define based on the correlation between different wells, depositional and structural conditions.

Insights on the active Southern Matese Fault system through geological, geochemical, and geophysical investigations of the CO2 gas vent in the Solopaca area (southern Apennines, Italy)

The south-eastern sector of the Matese Massif (southern Apennines, Italy) includes several nonvolcanic gas (mainly CO2) vents. The gas emissions in the northern part (Ciorlano-Ailano sector) have been associated with the Southern Matese Fault system, whereas a similar relationship is not evident in the southern part (Telese-Solopaca sector). Hence, we investigated the latter area (hills north of Solopaca town) through a multidisciplinary study of the principal CO2-degassing vent (Santantuono spring). The main goal is to reconstruct the structural architecture of the area and study the role of the fault array in conveying the gas migration to the surface. In particular, an integrated approach that combines structural and stratigraphic investigations with CO2 flux and geoelectrical surveys is proposed to shed light on the relationships between near-surface faults and gas rising. The main results from the geological-structural investigation suggest that thrust faults are the oldest structures, mainly verging to NNW, crosscut by high-angle N-S and younger NW-SE normal faults. This understanding is supported by the results of the CO2 flux survey, which records the highest flux values in correspondence with the mapped young normal faults, especially at their intersections. Moreover, the hypothesized tectonic and stratigraphic structure at depth is entirely consistent with the 3D geoelectrical model of the survey area provided by a 3D electrical resistivity tomography investigation, which also identifies the main NW-SE striking fault as the preferential pathway for gas migration. Finally, we suggest that the reconstructed NW-SE faults are the prolongation of the active Southern Matese Fault system bounding the SW Matese Massif margin defined by different segments with dominant normal kinematics and several gas vents.

Seismic interpretation and hydrocarbon assessment of the post-rift Cenomanian Bahariya reservoir, Beni Suef Basin, Egypt

The geophysical interpretations for a collection of high-quality 2D seismic data plus well logging data for six drilled wells exposed the structural controls and the hydrocarbon potentiality of the Beni Suef Basin, north Western Desert, Egypt. The created structural map on the top of the Early Cenomanian Bahariya Formation (the significant oil reserve in north Western Desert), exhibits a series of NW–SE normal faults as well as a master ENE strike-slip major fault. The extensional faults formed horst structures while the strike-slip fault created a negative flower structure in the central part of the study area. These structural features represent the main petroleum traps within Beni Suef Basin. The reservoir quality was assessed through the petrophysical analysis of the Bahariya Formation in wells; Azhar A2, Azhar E-2X, Azhar E3, Yusif-4X, Fayoum-2X and Beni Suef W-1X. This analysis proved that the Lower Bahariya unit has better reservoir quality than the Upper Bahariya reservoir, with shale volume less than 10%; effective porosity between 10 and 20%, water saturation between 25 and 75% and total pay thickness between 11 and 88 ft. The obtained results encourage drilling more exploratory wells in Beni Suef Basin to enhance the productivity from the sandstones of the Lower Bahariya reservoir.

Sedimentology, geomorphology, structural controls, and detrital zircon ages of the Itiquira River diamond placer deposits, Mato Grosso, western Brazil

The Itiquira River, Mato Grosso state (western Brazil), hosts several diamond placer deposits, mined intermittently over the last century. It runs over volcanic and sedimentary rocks of the Paraná Basin until it discharges in the northern Pantanal Basin. The bedrocks were deposited in marine, continental desertic, alluvial deltaic, and fluvial environments. The meanders of the Itiquira River are controlled by NE-SW, ENE-WSW, NNW-SSE, N–S, and NW-SE fractures and normal faults, developed in response to the evolution of the Paraná Basin and by neotectonics, linked with the development of the Pantanal Basin since the Paleogene. The Itiquira River middle valley, in which the diamondiferous placers are found, is controlled by NE-SW structures inherited from the Neoproterozoic Transbrasiliano Lineament. The landscape comprises dissected plateaus and structure-controlled valleys formed by Cretaceous, Paleogene, and Neogene planation processes. The diamonds occur in the muddy-sandy matrix of the current stream bed and older terraces gravels. In the Itiquira River, the diamond deposits are related to the following traps: point bars, cut-and-fill channels, pockets, and potholes. Sapphire, garnet (including kimberlitic), ilmenite, zircon, rutile, gold, and iron oxides are documented as heavy minerals in the gravels. Detrital zircon dating of grains extracted from the Itiquira River diamond deposits resulted in the ages of 2057, 1184, 873, 645–508, 307–207, and 144-142 Ma. The potential zircon sources are the Goiás Magmatic Arc granitoids, Paraguay Belt metavolcanics and granites, and Serra Geral Formation volcanics. The ages between 307 and 207 Ma are likely to be from an unknown (possibly kimberlitic) source. The Itiquira River tectonic, geomorphological, and sedimentological evolutions suggest potential sources for the diamond placers and paleoplacers.

Latest Jurassic–Early Cretaceous synrift evolution of the Torrelapaja Subbasin (Cameros Basin): implications for Northeast Iberia palaeogeography

The reconstruction of the latest Jurassic–Early Cretaceous evolution of the Torrelapaja Subbasin (Cameros Basin, Spain) resulted in the characterization of three synrift sequences (SS-1, SS-2 and SS-3) bounded by major unconformities. Three major NW–SE normal faults combined with smaller scale faults of variable direction (around NE–SW) controlled the sedimentation. The complex geometry of the Torrelapaja Subbasin indicates a main extension direction of NE–SW, and a secondary NW–SE extension. Sedimentation of the Tithonian–middle Berriasian SS-1 occurred in alluvial fan systems, grading upwards to carbonate palustrine-lacustrine environments. A new vertebrate site with large size sauropod bones has been found in the middle part of SS-1. The lower boundary of the uppermost Hauterivian–lower Barremian SS-2 is locally a palaeokarst, with sedimentary infill including three new fossil sites with remains of ornithopod, sauropod and theropod dinosaurs. Sedimentation of SS-2 encompasses distal alluvial terrigenous facies with local palaeosoils and palustrine-lacustrine limestones grading upwards to middle-distal alluvial facies. After a late Barremian–early Albian stratigraphic gap, sedimentation resumed in coastal flat environments represented by the mudstones with intercalated skeletal (oyster-rich) sandy limestones with carbonaceous plant remains of the SS-3. A middle–late Albian age assignment of SS-3 based on regional correlation is supported by strontium isotopic data. This unit marks the first Early Cretaceous marine incursion in the area from the northern Atlantic realm. This is a notable change of the previous palaeogeographical reconstructions which established that the first marine encroachment occurred in the early Aptian and was sourced from Tethysian domains.

New constraints on tectonism and magmatism from the eastern sector of the Trans-Mexican Volcanic Belt (Chignahuapan Horst, Puebla, México)

The Quaternary Acoculco (<2.7 my) and Los Humeros (<46 ky) calderas, located in the eastern sector of the Trans-Mexican Volcanic Belt (TMVB), are separated by a regional structure known as the Chignahuapan Horst (ChH). The tectonic and magmatic evolution of the ChH comprises four stages: 1) Upper Cretaceous-Paleocene Laramide orogeny, related to the deformation of sedimentary successions; 2) a sedimentary hiatus followed by the initial stage of the TMVB (Middle Miocene); 3) a Miocene NE-SW oriented extension responsible for the NW-SE normal faults that controlled the volcanic processes and the emplacement of calc-alkaline magmas that formed the Aquixtla sequence; 4) a magmatic hiatus prolonged until 1.6 ± 0.15 my; 5) Pliocene-Quaternary normal faults controlled the emplacement of tholeiitic-transitional magmas and the monogenetic volcanism distribution that formed the Apizaco-Chignahuapan sequence.Coevally to the Miocene NE-SW and Pliocene-Quaternary NW-SE tectonic extensional phases, NE-SW and NW-SE transfer faults were developed. NE-SW normal faults and NW-SE strike-slip faults correspond to fault systems optimally oriented with the current stress field, thus, these faults can be considered as potentially active structures controlling magma emplacement and the distribution of volcanic structures at the surface.

Normal fault reactivation during multiphase extension: Analogue models and application to the Turkana depression, East Africa

We present crustal scale physical analogue models of multiphase rifting to provide new constraints on the role exerted by faults formed during early extension on structures developed during later episodes of rifting. Our laboratory experiments (sand mixture is used to simulate the upper crust and PDMS-Corundum mixture is used to simulate the lower crust) are inspired by the Turkana depression in the East African Rift System, a natural case of rift zone developed through multiple extensional phases. The models reproduce a first rifting phase with NE-SW extension direction followed by a phase of W-E trending extension. In the experiments, we varied the amount of extension during the initial phase, which caused variations in the development and prominence of sets NW-SE normal faults, representing pre-existing faults to be potentially reactivated during the later rifting phase. Our model results indicate that the amount of extension in the early phase is critical in controlling the reactivation: the greater the amount of extension in the 1st-phase, the more important early faults are, and the easier these 1st-phase normal faults are reactivated during the 2nd-phase. At a local scale, fault reactivation may result in faults with a typical zigzag pattern, whose importance increases with the increase in the amount of extension during the early phase. Extrapolation of model results to the Turkana depression suggests that large-scale fault reactivation is unlikely to have occurred in the region, possibly implying that the Cretaceous-Early Paleogene extension was limited in the central part of Turkana depression. Results have been also extrapolated to other regions interested by multiphase rifting, such as basins in the North Sea rift.

New Macroseismic and Morphotectonic Constraints to Infer a Fault Model for the 9 (Mw6.1) and 11 January (Mw7.3) 1693 Earthquakes (Southeastern Sicily)

This study deals with the earthquakes which occurred in southeastern Sicily in 1693 (January 9 and 11, Mw ≈ 6.1 and 7.3, respectively). Although they have been largely studied, robust and commonly accepted seismic sources are still missing. We performed a revision of the 1693 macroseismic data and, for the fore and main-shocks, modeled new NNE-SSW trending seismic sources. In the Hyblean Plateau area, we carried out an analysis of DEM and aerial photos to map tectonic features. Then, we performed field surveys on the main faults, and a morphotectonic study with the aim of characterizing the activity of mapped faults. The study revealed the presence of three main fault systems. The first is the Palazzolo-Villasmundo Fault System, composed of NNE-SSW and NE-SW trending north-west-dipping normal faults. Some of these faults could be reactivated as reverse faults. The second is the Augusta-Floridia Fault System, made of NNW-SSE and NW-SE normal faults. The third is composed of faults which have never been mapped before: the Canicattini-Villasmundo Fault System that shows both a segmented and stepping pattern, almost N-S trending and west-dipping normal faults; some of these faults show a left-lateral movement. The morphotectonic study demonstrated that the fault systems are active. Furthermore, both strike and kinematics of the studied faults well match with the regional stress field characterized by a NW-SE σ1, which in the study area is probably both affecting some pre-existing faults, the Palazzolo-Villasmundo and the Augusta-Floridia Fault Systems, and causing the formation of new faults, the Canicattini-Villasmundo Fault System. The latter system lies across the Hyblean Plateau with a total length of 35 km and, due to its aligned segmented pattern, it can be the surface expression of a master fault that seems dividing the Hyblean Plateau in two blocks. Moreover, the Canicattini-Villasmundo Fault System well fits the southern part of the 1693 revaluated seismic sources and matches with a current alignment of shocks mainly characterized by left-lateral focal mechanisms on almost N-S fault planes. Considering the possible rupture length in depth, it could manage to release Mw ≈ 7.1 earthquakes, representing a valuable candidate source for the 1693 earthquakes.

Tectonic and magmatic controls on the evolution of post-collapse volcanism. Insights from the Acoculco Caldera Complex, Puebla, México

The Acoculco Caldera Complex (ACC; 2.7–0.06 Ma) is located in the eastern part of the Trans Mexican Volcanic Belt, México. The ACC produced three major explosive eruptions: the Acoculco andesitic ignimbrite (AI; 2.7 Ma; Syn-caldera), Piedras Encimadas rhyolitic ignimbrite (1.3 Ma; Late post-caldera), and the Tecoloquillo rhyolitic ignimbrite (TI; 0.8 Ma; Late post-caldera). Faulting has been active since the Pliocene to the present; the regional stress regime developed a NW-SE normal fault system (graben-horst structures) where the ACC was built on the Rosario-Acoculco horst.We investigated the depth of the Acoculco and Tecoloquillo magmatic chambers with H2O-CO2 content in glass inclusions, magmatic processes (magma mixing), and origin of magmas with major oxides-trace-element geochemistry and mineral chemistry. Magma chambers for TI and AI magmas are isolated from each other and located approximately 6–10 km depth. We related the local stress field to the magmatic processes that modified the AI (syn-caldera) and TI (post-caldera) magmas of the ACC. The extensional regime promoted the ascent of calc-alkaline magma and stopped by a local compressive stress regime (transfer zones; Acoculco fault), generating an entrapment zone (1.5–2.5 kbar). The new ascent of calc-alkaline magmas from a deep reservoir provoked magma mixing that triggered the AI eruption and the collapse of the magma chamber roof. The collapse event destroyed the feeding conduits and created new ascent paths that favored the formation of a new plumbing system. The ascent of melt used the pre-existing structures, probably deep graben-horst NE-SW faults, allowing peralkaline magma ascent that stopped in the entrapment zone. The new alkaline and calc-alkaline magma injection caused magma mixing that catalyzed the TI explosive eruption through NE-SW trending structures forming the TI plumbing system.

Reservoir characterization and 3D modeling of the Aptian Alamein Formation in North Razzak area (North Western Desert, Egypt)

Improving exploration and development techniques of fossil fuels are essential for continuous reserves development. Although there are many oil discoveries in the Razzak Area (North Western Desert, Egypt), there are also many dry wells. Therefore, the tectonic setting and reservoirs characterization of the study area has to be fully understood. Twenty 2D highly filtered stack zero-phase seismic sections and logging data of four wells were analyzed. According to seismic sections and structure contour maps (both time and depth), there is one major structural high (horst). It is a part of the regional Jurassic rift system. The NE Jurassic rifts continued during the deposition of the Early Cretaceous strata as growth faults and have been rejuvenated or continued during the closure of the Neotethys Ocean. During the Late Cretaceous, the compressional stress resulting from the collision between African and Eurasian plates has led to the inversion of the Razzak basin, where some segments of the main faults are transformed from normal to reverse and the hanging walls formed plunging drag fold, which was dissected by a set of NW-SE normal faults. Four prospective closures in the Razzak Field were highlighted. Based on integrated petrophysical tools (Gamma Ray, Sonic Log, Resistivity Deep, Neutron Porosity, and Bulk Density) in four wells (NRZK-1, NRZK2, NRZK-3, and NRZK-4), the Aptian Alamein Formation (mainly dolomite) was interpreted to be a good reservoir and can be subdivided into two zones (Upper Alamein and Lower Alamein) with different reservoir quality. In addition, 3D structure, facies, and petrophysical models were built based on integrated geological and petrophysical data. The results indicated that integrating both seismic profiles with logging data, even from a small number of wells, is highly valuable in evaluating reservoir quality and defining future prospective.

Geomorphology and spatial distribution of monogenetic volcanoes in the southern Puna Plateau (NW Argentina)

Monogenetic volcanoes are the most common volcanic landforms on Earth. Several works have shown that the study of geomorphology and spatial distribution of such small volcanoes reveals important aspects related to the volcanic field, from eruption dynamics to tectonic processes. The Altiplano-Puna Plateau (15° to 27° S, Central Andes) comprises the largest non-collisional plateau on Earth. Characterized by intensive deformation, uplift, and volcanism, this region is marked by the presence of hundreds of mafic monogenetic volcanoes. Despite its discrete occurrence, the monogenetic volcanoes show a close relationship with large scale, lithospheric foundering events in the region. In this contribution we applied a Geographic Information System (GIS) approach in order to build the first complete catalog of monogenetic landforms present in the southern Puna Plateau (24° 30′ to 27° 00′ S, NW Argentina), exploring their evolution and relationship with geotectonic events. Combining spatial analysis with a geomorphological study of each volcano, it was possible to identify the presence of 285 monogenetic volcanoes in the region, which could be grouped in seven clusters. Southern Puna shows a predominance of cinder cones and lava domes, suggesting a small influence of water in the eruption dynamics. Despite its high clustering degree, southern Puna monogenetic vents present a low density (8.3 × 10−3 vents/km2) when compared to other monogenetic fields around the world. In addition, Puna Plateau cones show a close relationship with monogenetic cones associated with an extensional environment, considering their back-arc context. Based on relative and available absolute ages, it was possible to map the volcanism evolution through time. The results indicate that the first monogenetic volcanoes appeared in the central region of the Plateau (Sierra de Calalaste), mainly associated with large-scale NNE-SSW reactivated faults. The activity then expanded (Antofalla and Antofagasta regions) and, finally reached the borders of the Plateau (Pasto Ventura and Arizaro regions), which show volcanoes associated with NW-SE normal faults.