TS1.2 | Deformation, Fluid Flow and Diagenetic Processes involving Layered Rocks and Granular Media in the Shallow Crust
EDI
Deformation, Fluid Flow and Diagenetic Processes involving Layered Rocks and Granular Media in the Shallow Crust
Convener: Mattia PizzatiECSECS | Co-conveners: Giulio Viola, Stefano Tavani, Olivier Lacombe, Barbara MarchesiniECSECS, Alexis Cartwright-Taylor, Leonardo Del SoleECSECS
Orals
| Fri, 19 Apr, 14:00–15:40 (CEST)
 
Room K1
Posters on site
| Attendance Fri, 19 Apr, 16:15–18:00 (CEST) | Display Fri, 19 Apr, 14:00–18:00
 
Hall X2
Orals |
Fri, 14:00
Fri, 16:15
Sedimentary rocks and sediments, having different degrees of cementation and primary layered architectures, cover most of the Earth's surface with thickness ranging from a few meters to several kilometers deposited in different tectonic-geodynamic settings and depositional environments. The joint study of deformation mechanisms, strain localization, fluid flow patterns and diagenetic processes affecting sedimentary rocks has crucial importance for both scientific research and global economy. Sedimentary rocks represent strategic targets and prospects for resource supply (groundwater, geothermal energy, hydrocarbons, ore deposits), underground gas storage (anthropogenic CO2, H2), as well as risk evaluation (groundwater contaminant transport). The meso- and micro-structural analysis of brittle deformation structures, the quantification of petrophysical properties, the characterization of fluid flow patterns, and the reconstruction of fluid-rock interactions occurring in sedimentary rocks during diagenesis facilitate the evaluation of potential reservoir quality and its efficient exploitation. Moreover, primary layering of sedimentary rocks strongly influences fault geometries with mechanical stratigraphy and strength anisotropy playing a crucial role in defining the overall fault propagation process and mechanical behavior (aseismic creep vs seismic sliding).
We encourage you to contribute to this session by submitting original ongoing research lines, including field, laboratory, and computational modeling-based studies, dealing with the following topics:
- Analysis of brittle deformation (from outcrop to the micro-scale) affecting high to low porosity layered sedimentary sequences deformed in various tectonic settings, under different kinematics and depths.
- Relationships between brittle deformation structures (faults, deformation bands, joints, veins, and stylolites) and selective diagenetic processes (cementation, dissolution, and mineral replacement).
- Parameters controlling the strain localization in layered-anisotropic rocks, with implications for fault evolution in space and time, faulting style, and seismic activity.
- Definition and quantification of fluid flow patterns and pathways both via numerical modeling simulations as well as through direct measurements of petrophysical-hydraulic properties.
- Fluid-rock interactions associated with diagenetic processes active at different depths and time from rock deposition to final exposure.

Orals: Fri, 19 Apr | Room K1

Chairpersons: Mattia Pizzati, Barbara Marchesini, Giulio Viola
14:00–14:05
14:05–14:35
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EGU24-390
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ECS
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solicited
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Highlight
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On-site presentation
Emma Michie

A wide range of deformation and diagenetic mechanisms have been observed within faulted carbonate lithofacies.  These processes are known to influence the permeability of a fault, and hence the flow properties.  The mechanisms active during faulting are influenced by a range of factors, including: lithofacies, host porosity, host permeability, juxtaposition type, depth of burial, depth at time of faulting and kinematics.  Although we can estimate the fundamental controls on resulting fault rock permeability, the ability to predict flow properties within and surrounding faults in carbonates remains highly uncertain.  This presentation will discuss conditions for when a fault may act as a conduit or a potential barrier to flow, along with the gaps in current data and knowledge.

Further, conditions for when a permeability anisotropy may be created within the fault core of carbonate lithofacies will be presented, along with the implications for fluid migration across or along the slip surface.  A permeability anisotropy is observed within carbonate fault cores, dependent on lithofacies and juxtaposition.  The significant heterogeneity created when different lithofacies are juxtaposed outweighs the resulting permeability anisotropy that is created, such that no systematic permeability anisotropy can be defined.  However, when self- or similar juxtapositions occur, a systematic permeability anisotropy is recorded, creating a permeability that can be as much as over 5 orders of magnitude lower normal to fault strike than parallel to fault strike.  The permeability anisotropy is formed from differing mechanisms dependent on lithofacies; the intersections of shears with fractures/veins in recrystallised lithofacies, and oriented pores in high porosity grainstones.  This is similar to previous crystalline and siliciclastic studies.  The permeability anisotropy can act to allow flow in one orientation but prevent it in another.

How to cite: Michie, E.: Can we ever predict how fluids may flow within and surrounding faults in carbonates?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-390, https://doi.org/10.5194/egusphere-egu24-390, 2024.

14:35–14:45
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EGU24-2077
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Highlight
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On-site presentation
Fabrizio Agosta

Shallow-water carbonates include a variety of heterogeneities such as bed interfaces, laminations, stylolites, and pressure solution seams forming rock multilayers crosscut by high-angle strata-bound fractures. At a larger scale, bed package interfaces and other primary stratigraphic contacts exert a similar control compartmentalizing high-angle faults within discrete sedimentary units. The aforementioned heterogeneities commonly form within the depositional environments, and/or at specific diagenetic conditions under given burial depths. Mechanical compaction, dissolution, cement precipitation, and other physical/chemical processes hence alter the original framework of the carbonates, and contribute to the acquirement of their long lasting mechanical properties. To further investigate this topic, in other words to assess the time-dependent fracture stratigraphy of shallow-water carbonates, this presentation focuses on the influence exerted by tectonics on the mechanical layering of the Mesozoic platform carbonates of southern Italy. By analyzing outcrops lying along the axial zone of the southern Apennines fold-and-thrust belt, and within its forebulge area, published data are discussed altogether to decipher the control exerted by thrusting tectonics on the formation of mechanical interfaces within Lower Jurassic to Upper Cretaceous carbonates. Rocks exposed in the foreland domain include a number of high-angle fractures. These fractures are mainly bounded by bed interfaces, and their spacing values vary proportional to the bed thickness. Such a proportionality is exhibited by both mud- and grain-supported carbonate lithofacies, which show saturated to oversaturate conditions. Differently, carbonates lying in the axial zone of the southern Apennines belt are characterized by values of fracture density and intensity that do not vary proportionally with the bed thickness. In order to investigate the significance of the latter data, detailed microstructural analyses aimed at assessing the timing of pressure solution processes with respect to the diagenetic history and tectonic evolution of the carbonates are considered. Besides the effects of early embrittlement of the carbonate grainstone lithofacies, which occurred due to cement precipitation in phreatic marine environment that prevented the effects of localized dissolution at the grain-to-grain contacts, two main phases of pressure solution characterized the carbonates. The first one took place during Meso-Cenozoic sedimentary burial with formation of wave-like, bed-parallel surfaces. In cat, the continuous burial of the carbonates, down to depths of ca. 1.5 km, promoted the development of solution surfaces along the bed interfaces, and also within the single beds. Small, isolated, wave-like surfaces formed as isolated elements within the single carbonate beds. The second phase occurred during Upper Miocene thrusting tectonics, at depths of ca. 4 km, with formation of seismogram-like surfaces at low-angle to bedding. The latter surfaces consisted of both stylolites and slickolites with sub-vertical teeth, which cut across the pervasive blocky cements of the carbonates, dissolved the pre-existing veins, and formed laterally persistent surfaces throughout the carbonates. Accordingly, the combination of both pure shear (stylolites) and sub-simple shear (slickolites) strain caused formation of new mechanical interfaces in the carbonate beds, and therefore modified the thickness of single mechanical units throughout the Mesozoic carbonates.

How to cite: Agosta, F.: Evolving fracture stratigraphy properties of layered carbonates through time: examples from the southern Apennines fold-and-thrust belt, Italy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2077, https://doi.org/10.5194/egusphere-egu24-2077, 2024.

14:45–14:55
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EGU24-16378
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Highlight
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On-site presentation
Eric Salomon, Anna Nele Meckler, and Harald Stollhofen

In porous sandstone, fluids are guided by major features such as faults or lithologic discontinuities. At the local scale, deformation bands are common structures to baffle fluid flow in such rock. Potential flow-hindering structures less frequently reported of are veins in porous sandstone (Skurtveit et al., 2015, as a rare case), which may root in the circumstance that they do not appear very often and/or have simply been overlooked. 

We here present a case where calcite veins formed in the highly porous (up to 25 % porosity) and partially poorly lithified eaolian Lower Cretaceous Twyfelfontein Formation in NW Namibia. This sandstone was buried by the extrusion of voluminous Paraná-Etendeka flood basalts at around 130 Ma and was since then subject to exhumation. Calcite veins occur in roughly half of the visited outcrops of the Twyfelfontein Formation and their dominant parallel trend to the continental margin suggests a tectonic origin. As the host rock is void of carbonate framework material or cement, the veins must have formed through advective fluid circulation. An external source of the calcium may possibly be the alteration of overlying and intercalated basalt. The veins exhibit a remarkable multitude of textures ranging from blocky, colloform, to microcrystalline calcite generations, that have partially experienced brecciation. This argues for highly variable formation conditions, potentially spanning from normal fluid advection to boiling and injection (c.f., Moncada et al., 2012; Salomon et al., 2021). 

Preliminary clumped isotope data of the veins indicate a low temperature formation in the range of 19-61°C, which suggests overall shallow burial conditions. This is in agreement with the diagenetic paragenesis of the rock arguing for late stage vein formation, i.e. during exhumation of the rock. Upcoming U/Pb calcite dating is expected to bring greater clarity on this regard. A halo in the host rock surrounding the veins became calcite cemented due to the growth of calcite from the fractures into the sandstone body. This appearance demonstrates the following evolution: (1) fracturing of the sandstone, which enhances advective fluid flow in the rock body; (2) vein precipitation and near-vein host-rock cementation; and consequently (3) reduction of permeability in the fracture and adjacent wall rock. 

Due to their potential of forming effective barriers to fluid flow, we stress that their formation needs to be understood in greater detail. The variable vein textures indicate differing formation conditions, which sets the base for a more common occurrence of calcite veins in porous uncemented sandstone. 


References:

Moncada, D., et al. (2012). Journal of Geochemical Exploration 114, 20-35, doi:10.1016/j.gexplo.2011.12.001.

Salomon, E., et al. (2021). Journal of Structural Geology 153, 104463. doi:10.1016/j.jsg.2021.104463.

Skurtveit, E., et al., (2015). Petroleum Geoscience 21, 3-16, doi:10.1144/petgeo2014-031.

How to cite: Salomon, E., Meckler, A. N., and Stollhofen, H.: Calcite veins as local fluid flow barriers in reservoir rock? The odd occurrence of veins in highly porous aeolian sandstone in Namibia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16378, https://doi.org/10.5194/egusphere-egu24-16378, 2024.

14:55–15:05
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EGU24-17144
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ECS
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On-site presentation
Rebecca Kühn, Rüdiger Kilian, and Michael Stipp

The shortening of sediments in accretionary prisms is accomplished by localized faulting as well as non-localized deformation. While faulting is often easily recognized from seismic sections, accessing the amount and extent of non-localized deformation is rather challenging. In order to address this challenge, we explore samples from the active accretionary prism offshore Gisbourne, NZ at the Hikurangi margin which contains accreted sediments of Pliocene to recent age. Drilling at Site U1318F of IODP Expedition 375 recovered non- to semi-lithified sediments from a major accretionary fault, the Papaku Fault, including its hanging wall and footwall. The crystallographic preferred orientation (CPO) of the clay minerals is a measure for their alignment and was determined in 66 sediment samples from the drill core (250-500 mbsf) using high energy X-rays. The results show that the CPO strength of the clay mineral basal planes (00l) is in general weak and no depth-related trend can be observed. In the hanging wall of the Papaku Fault, (00l) pole figures have non-rotationally symmetric, unimodal density distributions displaying incomplete girdles. In the footwall, most (00l) pole figures exhibit unimodal, rotationally symmetric to weak girdle density distributions, with most maxima pointing parallel or subparallel to the drill core axis. Fault zone samples also exhibit rotationally symmetric, unimodal (00l) distributions, with maxima perpendicular to the fault plane.

We assume that pre-shortening and pre-faulting, sediments had a weak initial CPO related to sedimentation and compaction with a rotationally symmetric, unimodal (00l) distribution. The girdle shape of the distribution in the hangingwall and to a minor extent in the footwall is introduced by non-localized deformation which results in grain-scale folding. Accordingly, diffuse shortening was larger in the present-day hanging wall than in the present-day footwall. Furthermore, we interpret the CPO in the Papaku fault itself to be a result of sediment shearing, overprinting any pre-existing CPO. The position of the Papaku fault is compatible with fault initiation where diffuse shortening was unable to propagate sufficiently towards the foreland.

While our results also confirm existing tectonic models from this part of the Hikurangi margin, more importantly they demonstrate implications for strain distribution in fault and thrust systems as well as the usefulness of clay mineral CPO for unravelling deformation and tectonic processes in accretionary prism sediments.

How to cite: Kühn, R., Kilian, R., and Stipp, M.: Crystallographic preferred orientation of clay minerals in sediments from the Hikurangi accretionary prism offshore New Zealand, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17144, https://doi.org/10.5194/egusphere-egu24-17144, 2024.

15:05–15:15
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EGU24-20887
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Highlight
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On-site presentation
Atle Rotevatn, Vilde Dimmen, Hakan Heggernes, Matteo Demurtas, Haakon Fossen, Edoseghe Osagiede, and Thibault Cavailhes

The study of deformation, fluid flow and diagenesis within porous granular rocks includes processes spanning from the sub-millimetric pore and grain scale, to 10s to 100s km-long fault systems that delineate entire sedimentary basins and rift systems. Based on outcrop examples globally, we here show how selective, structurally controlled diagenesis is manifested across scales, discuss some of the key aspects of the governing processes involved and how such understanding may be used in attempts to subsurface predictions. Grain scale observations are focused on deformation within siliciclastic, carbonates and volcaniclastic rocks, allowing us to investigate the role of material properties in controlling how deformation is localized and accommodated. We further discuss how grain-scale deformation affects permeability, fluid flow and structurally controlled fluid-rock interaction. At the opposite end of the spectrum, we discuss the relations between deformation, fluid flow and diagenesis at the scale of basin bounding fault systems in rift basins. Finally, we address the significance of understanding structures as elements of structural networks, and how network properties may hold the potential for a more quantitative understanding of structurally controlled fluid flow.

How to cite: Rotevatn, A., Dimmen, V., Heggernes, H., Demurtas, M., Fossen, H., Osagiede, E., and Cavailhes, T.: Deformation, fluid flow and diagenesis in deformed granular rocks across scales, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20887, https://doi.org/10.5194/egusphere-egu24-20887, 2024.

15:15–15:25
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EGU24-3571
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On-site presentation
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Miao Luo, Paul Glover, and Piroska Lorinczi

Just how much do sorting, cementation and compaction control the porosity and permeability of rocks? In this work we start with making extremely accurate porosity and permeability measurements on binary grain mixtures, arriving at good agreement between them and theoretical results. These seemingly simple experiments are difficult to carry out with the degree of precision needed to test the models. We have developed a methodology allowing porosity and permeability to be measured to within ± 4.415% and ± 4.989% (at a flow rate of 5.13 cm3/s) of each value, respectively. The newly developed theoretical framework includes both the interstitiation mixing process and several replacement processes.

A major result of this work is that the theoretical models describing these two processes are independent of grain size and grain shape. The latter of these two findings infers that the models developed in this work are applicable to any shape of grain or type of packing, providing that a representative porosity of each size of grain pack is known independently, either experimentally or theoretically. Experimental validation has shown that the newly developed relationships for porosity described measurements of porosity for near-ideal binary mixtures extremely well, confirming that porosity is always reduced by binary mixing, and that the degree of reduction depends upon the size of the ratio between the two grain sizes.  

Calculation of permeability from the packing model has also been carried out. Six different permeability estimation methods have been used. It was found that the most accurate representations of the experimental permeability were obtained (1) when the exact RGPZ method was used with the porosity mixing models developed in this work, and (2) when the exact RGPZ method was used with the weighted geometric mean to calculate a representative grain size. For mixtures where there is a large difference in grain sizes, permeability (k) varies little for the ranges of mixtures from 28% to 100% of small grains (about 4*k), only increasing significantly as the fraction of small grains falls below 28% to zero (to 2 orders of magnitude in k) because the small grains then only partially occupy the space between the large grains. For mixtures of grains of similar sizes, the situation is remarkably different. The variation in permeability for small grain fractions between 100% and about 28% is much amplified (2 orders of magnitude in k), while the increase in permeability as the fraction of small grains falls from about 28% to zero is similar to the other case, and perhaps slightly less pronounced (about 1.5 orders of magnitude in k). This counterintuitive behaviour is important for the interpretation of how sorting affects permeability, implying a greater spread of permeabilities for rock composed of grains with a small difference in grain size.

How to cite: Luo, M., Glover, P., and Lorinczi, P.: Theory and modelling of the effects of grain sorting, compaction & cementation on porosity and permeability, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3571, https://doi.org/10.5194/egusphere-egu24-3571, 2024.

15:25–15:40

Posters on site: Fri, 19 Apr, 16:15–18:00 | Hall X2

Display time: Fri, 19 Apr 14:00–Fri, 19 Apr 18:00
Chairpersons: Mattia Pizzati, Barbara Marchesini, Stefano Tavani
X2.21
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EGU24-277
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ECS
Ian Bala Abdallah, Elisa Panza, Stefania Dastoli, Canio Manniello, Giacomo Prosser, and Fabrizio Agosta

Fracture and fault networks are characterised by complex spatial and dimensional properties that might affect the flow and accumulation of subsurface fluids. In geological applications, DFN models are commonly employed to compute the multiscale properties of fractured rock volumes in terms of porosity and equivalent permeability. In the present contribution, we focus on an outcrop-to-reservoir investigation of Mesozoic shallow-water carbonates exposed along the axial zone of the southern Apennines fold-and-thrust belt, FTB, Italy. The carbonates were originally deposited in lagoon-to-proximal ramp settings of the Paleo Apenninic Platform during Lower Jurassic–Upper Cretaceous times and include well-layered and massive associations of bed packages several m-thick. By integrating the results of both field and digital structural analyses, we build multiple DFNs to assess the hydraulic behaviour of geocellular volumes representative of the different scales of observation, and stochastically populated with high-angle fractures, small, and medium faults. Fractures are either strata-bound, SB, or non-strata-bound, NSB, and results compartmentalized within single-bed packages. Small faults crosscut multiple bed-packages and show a few cm-to-m throws, whereas medium faults displace multiple bed-package associations and have throws > 1m. Both small and medium faults exhibit high peaks of fracture density, P20, and intensity, P21, in correspondence with the releasing jogs disrupting mechanical interfaces such as bed package boundaries and pre-existing low-angle thrust faults. As data input for DFN modeling, the aperture values of the stochastic fractures are set as proportional to either fracture length (most favourable flow conditions) or to the square root of fracture length (least favourable conditions). At the outcrop scale, 5m-side DFN models show the highest values of fracture porosity among those considered in this work. These results are therefore consistent with both SB and NSB fractures forming the main repository for fluid accumulation. At larger scales, the 50m-side and 500m-side DFN models including small and medium faults, are characterized by higher values of equivalent permeability, which range between 10-2 and 10-1 mD. Considering the computed Kxx and Kyy values for the single geocellular volumes, near-isotropic horizontal conditions are assessed across all scales of investigation. Accordingly, altogether, high-angle SB and NSB fractures, small and medium faults form a system of well-connected network through the shallow-water carbonates. Interpreting these data in light of published values for platform carbonates in Italy, we interpret this multiscale horizontal permeability isotropy due to the severe exhumation (~ 4 to 5km) the studied carbonates went through during the Quaternary downfaulting of the southern Apennines FTB.

How to cite: Abdallah, I. B., Panza, E., Dastoli, S., Manniello, C., Prosser, G., and Agosta, F.: Fracture porosity and equivalent horizontal permeability computed for shallow-water carbonates of the southern Apennines fold-and-thrust belt, Italy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-277, https://doi.org/10.5194/egusphere-egu24-277, 2024.

X2.22
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EGU24-536
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ECS
Canio Manniello, Vincenzo La Bruna, Hilario Francisco Rego Bezerra, Renata Emily Brito Araùjo, Xavier Milton Morais, Emma Michie, Daniel Faulkner, Michael John Allen, Giacomo Prosser, and Fabrizio Agosta

Diagenetic and tectonic processes taking place in platform carbonates produce significant textural and mineralogical modifications through time, controlling the pore space in terms of dimension, geometry, shape, and connectivity of single pores, and influencing both total and effective porosity. Focusing on the different types of solution surfaces, this study is conducted on Lower Jurassic, Cretaceous, and Eocene, carbonates exposed at the Viggiano Mt. and Raparo Mt., southern Apennines, Italy. Microscale analyses show that the primary porosity of these rocks was occluded by pervasive blocky cements, which precipitated during burial diagenesis of the carbonates. We aim to assess the role exerted by the roughness of bed-parallel and low-angle to bedding solution surfaces, on the pore properties and permeability values of a variety of carbonate lithofacies such as mudstones, packstones, grainstones and rudstones. Specifically, we show the results of Nuclear Magnetic Resonance (NMR), gas-porosimetry and water-permeability tests conducted on plugs cored either orthogonal or parallel to bedding interfaces. All the study plugs show an amount of effective porosity lower than 5%, with mean values of ca. 3%. Excluding larger microfractures, and sporadic intrafossil and intercrystal molds, among the various types of solution surfaces we document that the rough, seismogram-type stylolites localize secondary porosity, while smooth, wave-type stylolites do not. The seimogram type stylolites, due to the non-selective carbonate’s dissolution, form a poorly connected vuggy porosity, and the NMR results the pores are subspherical to tubular (r<3 µm), with low aspect ratios (stiff pores), differently from the pores associated to open fractures (soft pores). Connectivity in the seismogram-type stylolites-related pores is due mainly to small microfractures forming capillary porosity (pore throat ca. r=1 µm). The results of permeability measurements at room pressure indicate that the amount of bed-perpendicular permeability is generally low (10-1 and 10-3 mD). The results of permeability measured at increasing confining pressure show that the in stylolite-dominated the bed-parallel samples have slightly higher values with respect to the bed-orthogonal ones and, at increasing confining pressure conditions, the permeability decreases of less than one order of magnitude. Differently, the fracture-dominated plugs show a permeability decrease of two orders of magnitude. These results are therefore consistent with a pore connectivity affected by open fractures only at shallow depths (<25 MPa) and influenced by both stylolites and primary pores at depths. Results of ongoing X-ray tomography analyses will better clarify the pore distribution along stylolites and at the fracture-stylolite intersections.

How to cite: Manniello, C., La Bruna, V., Bezerra, H. F. R., Araùjo, R. E. B., Morais, X. M., Michie, E., Faulkner, D., Allen, M. J., Prosser, G., and Agosta, F.: Pore space properties of solution surfaces in shallow-water carbonates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-536, https://doi.org/10.5194/egusphere-egu24-536, 2024.

X2.23
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EGU24-569
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ECS
Aygun Bayramova

On a global scale, the South Caspian is a basin where mud volcanoes are
most densely distributed. Numerous active volcanoes are registered here, both on
land and in the adjacent sea basin (Caspian Sea), which, as a result of their daily
activity, discharge water fluids to the Earth's surface.
In this work, using samples taken from coastal and island mud volcanoes, a
comparative study of the chemical compositions of the fluids expelled from the
salse and gryphon-type emissions, as well as their origin, including the
contribution of various stratigraphic units to the water formation processes.
According to our results, the contribution of the condensed waters of the
Caspian Sea was greater in the formation of Na-Cl type waters of mud volcanoes
in the South Caspian Basin. In addition, the origin of volcanic waters also formed
as a result of the contribution of shallow ‘low-mineralized’ pore fluids and deep-
seated ‘high-mineralized’ brines correlates well with the depths (1-5.5 km) of the
Productive Series strata.

How to cite: Bayramova, A.: A Comparative study of water fluids of coastal and island mud volcanoes: Acase study of the South Caspian Basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-569, https://doi.org/10.5194/egusphere-egu24-569, 2024.

X2.24
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EGU24-1240
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ECS
Mohammadreza Akbariforouz, Qi Zhao, and Chunmiao Zheng

The complexity of fault zone structure and faulting mechanisms significantly impact the permeability of fault zone rocks. Various factors, including the type and porosity of the host rock, the fault’s geometry, differential strain, the history of deformation, and the tectonic setting, can cause permeability to exhibit wide fluctuations. However, research into the permeability of complex fault zones is constrained by the scarcity of in situ measurements. Utilizing analytical relationships, laboratory tests, outcrop measurements, or numerical modeling often yields biased results, as they may not accurately represent real-world conditions. Moreover, the effects of fault branching and interconnections have not been thoroughly explored. This study compares the permeability of faulted carbonate rocks using a comprehensive database of in situ permeability tests. We investigate how a network of seven faults influenced permeability variations at different locations and depths by examining surface and subsurface data, including information from excavated tunnels. Our findings reveal that factors such as fault dips, length, fault structure, and rock characteristics can create diverse impacts on permeability. We observe permeability values in fault damage zones one to five orders of magnitude higher than those in the host rocks. The thickness and condition of damage zones shed light on the range of fault zone permeability. Furthermore, we find that faulted rocks with higher porosity and lower mechanical strength exhibit more substantial alterations in permeability. This study provides valuable insights into the behavior of faulted carbonate rocks.

How to cite: Akbariforouz, M., Zhao, Q., and Zheng, C.: Understanding the Heterogeneity and Anisotropy of Permeability in Carbonate Rocks Within a Fault Network, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1240, https://doi.org/10.5194/egusphere-egu24-1240, 2024.

X2.25
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EGU24-2265
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ECS
A Multiscale Characterization of Pore Network Heterogeneity and Its Influence on Reservoir Properties in the Permian Shihezi H8 Formation, Ordos Basin, China
(withdrawn after no-show)
Muhammad Toseef Adnan, Guishan Zhang, and Bin Chang
X2.26
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EGU24-2471
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ECS
Sebastian Mulder, Dmitry Bublik, and Johannes Miocic

Fluid extraction from geological formations for purposes of subsurface utilization leads to pore pressure drop in reservoirs and subsequent compaction and seismicity, especially in porous sandstones. Petrography controls the geomechanical properties of the reservoir, crucial for predicting a reservoir's response to fluid extraction and understanding its lateral variability. This study focuses on the Groningen gas field in the Netherlands, addressing its compaction-induced surface subsidence and seismic events resulting from gas depletion. Core samples were examined to delineate spatial petrographic trends and develop a microscale model of the Groningen gas field. Optical microscopy (OM) and scanning electron microscopy (SEM) were used to determine mineralogical compositions, textural relationships and diagenetic processes. Predominantly constituted of sublitharenites, the sandstones exhibit dolomite and quartz cement as primary authigenic cements. Variations in clay types—kaolinite, illite, and chlorite—were observed, influencing localized pore-filling cementation processes.  Across the field, mineral relations revealed notable trends: depth-related feldspar decrease, correlation between kaolinite and feldspar abundance, and elevated chlorite content towards the northern sector together with the presence of an early quartz cementation phase, which is also observed within aquifer cores. The dissolution of feldspar potentially impacts the structural integrity of the sandstones, while authigenic mineralization appears intricately linked to depositional facies and localized fault-related fluid movements. The timing and extent of these diagenetic processes emerged as pivotal factors dictating sandstone stability within the reservoir. This comprehensive analysis enhances our understanding of Groningen's reservoir heterogeneity, offering critical insights to predict and manage subsurface responses to extraction-induced pressure changes. By providing predictive models, this study facilitates the evaluation of reservoir behavior and aids in mitigating risks associated with compaction-induced subsidence and seismicity.

How to cite: Mulder, S., Bublik, D., and Miocic, J.: Petrographic Heterogeneity and Sandstone Evolution in the Groningen Gas Field: Implications for Reservoir Geomechanics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2471, https://doi.org/10.5194/egusphere-egu24-2471, 2024.

X2.27
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EGU24-3975
Penecontemporaneous polygonal faulting triggered by sand overloading onto unconsolidated clays in the northern South China Sea
(withdrawn after no-show)
Qingfeng Meng and Fang Hao
X2.28
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EGU24-4381
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ECS
Vincenzo Moretto, Leonardo Del Sole, Manuel Curzi, Luigi Dallai, Gianluca Vignaroli, Giulio Viola, Fabrizio Balsamo, Luigi Riccardo Berio, Georg Grathoff, Lurence Noel Warr, and Luca Aldega

Multiple episodes of brittle deformation tend to increase the structural complexity of fault zones. This commonly results in the development of juxtaposed and non-coeval distinct Brittle Structural Facies (BSF) formed at different times, depths, and temperature. Indeed, these BSFs are characterized by an irregular distribution of inherited, syn-kinematic, and post-kinematic minerals, whose study provides useful information about the temperature conditions of (de)formation, and the origin of fluids circulating within faults. We combined X-ray diffraction (XRD) analyses and polytype determinations of whole-rock and several grain-size fractions (6-10 μm, 2-6 μm, 0.4-2 μm, 0.1-0.4 μm, and <0.1 μm), with H-isotope data of 76 fault rocks and 6 protoliths from two structurally and well-characterized fault zones with different kinematics: the Carboneras strike-slip fault zone (Betic Cordilleras, SE Spain) and the Kornos-Aghios Ioannis extensional fault zone on the Lemnos Island (North Aegean Trough, Greece). Mineralogical and geochemical data allowed us to (1) reconstruct the distributions of syn/post-kinematic minerals in distinct BSFs, (2) constrain their formation temperature, and (3) unravel the origin of fluids involved during faulting. In the Carboneras fault rocks, we distinguished a protolithic mineralogical assemblage consisting of quartz, carbonates, K/Na-micas (2M1 polytype), chlorite, kaolinite, and Fe/Ti-oxides, a syn-kinematic assemblage composed of mixed layers chlorite-smectite and illite-smectite (1Md polytype), and a post-kinematic assemblage made up of smectite, chlorides, and sulphates. The coexistence of randomly (R0), short-range (R1), and long-range (R3) ordered illite-smectite in different BSFs indicates contrasting formation temperatures. Bulk samples generally display δ2H values (V-SMOW) between -15‰ and -60‰ (with a few exceptions at -90‰), while their respective <2μm fractions show δ2H values between -10‰ and -60‰. The combination of mineralogical and geochemical data from the Carboneras fault zone depicts a complex history of multiple brittle events occurring at different temperature conditions, wherein parental fluids of mostly meteoric origin infiltrated into the fault zone and interacted with the host rocks at various degrees and depths. In the fault rocks of Lemnos Island, we identified a host-rock mineralogical assemblage composed of quartz, feldspars, carbonates, K-mica (2M1 polytype), chlorite, R0 illite-smectite, anatase, and Fe-oxides and hydroxides, a syn-kinematic assemblage made up of R3 illite-smectite (1Md polytype), and kaolinite, and a post-kinematic assemblage characterized by halite and gypsum. Bulk samples display δ2H values (V-SMOW) between -70‰ and -140‰, while their respective <2μm fractions show δ2H values between -60‰ and -85‰. Such results indicate that Kornos-Aghios Ioannis fault rocks formed during a deformation event with predominantly hydrothermal fluids circulating into the fault zone (>160°C). This multidisciplinary approach represents an innovative point of view for studying fluid circulation, mineral crystallization, and temperature evolution in complex fault zones, and it can be applied to both orogen scale faults and smaller fault systems.

How to cite: Moretto, V., Del Sole, L., Curzi, M., Dallai, L., Vignaroli, G., Viola, G., Balsamo, F., Berio, L. R., Grathoff, G., Warr, L. N., and Aldega, L.: Tracing the origin of parental fluids and paleo-temperature distribution in fault zones: case studies from the Carboneras Fault (Spain) and Lemnos Island (Greece), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4381, https://doi.org/10.5194/egusphere-egu24-4381, 2024.

X2.29
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EGU24-5693
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ECS
Giovanni Freda, Silvia Mittempergher, Fabrizio Balsamo, Mattia Pizzati, Raffaele Di Cuia, and Angelo Ricciato

Deformation may exert a positive or negative impact on rock strength, stiffness and porosity depending on the initial properties of the rock. In porous rocks, deformation bands (DBs) reduce both porosity and permeability, and potentially increase rock strength and stiffness. In low porosity (tight) rocks, deformation occurs via shear and opening-mode fractures, thus enhancing permeability and deteriorating strength and stiffness.

In this study we describe field observations and laboratory analyses to characterize sub-vertical deformation bands in the porous carbonates of the Calcarenite di Gravina Fm. exposed in Matera and Gravina in Puglia, Southern Italy. Matera and Gravina in Puglia are located at the boundary between the Apulian foreland and the foredeep of the Southern Apennines thrust belt. Both study areas consist of an asymmetrical horst structure involving the Cretaceous (Senonian) tight carbonates of the Apulian platform (Calcare di Altamura Fm.) unconformably overlain by Plio-Pleistocene shallow-marine coarse-grained lithic sandstone and grainstone (Calcarenite di Gravina Fm.). The Calcarenite di Gravina Fm. is dominated by pervasive DBs organized into 2 main sets dipping at high angle and striking N-S and NNE-SSW, except in some limited areas where the DBs form a complex network with the presence of a secondary set, striking NW-SE, showing mutual crosscutting relationships. The DBs have a positive relief, due to their relatively higher resistance to erosion, and appear whitish, tabular with some slight undulations, 10’s of meters long in map view, continuous and steeply inclined (from 75° to 90°). These structures have thicknesses from few mm up to a few cm depending on the facies of the calcarenite. At the outcrop scale the DBs don’t seem to accommodate significant shear offsets. A total of 53 oriented samples were collected for thin sectioning, petrophysical, and microstructural analysis. We acquired porosity measurements using a Hg-intrusion porosimeter, which showed that the DBs have an average porosity of 11%, while for the host rock is 38%. 29 Blue-impregnated thin sections of host rocks and DBs were analysed by standard microscopy, cathodoluminescence (CL), and a scanning electron microscope (SEM). The analysis of the CL images shows that the clast size distributions are similar in the DBs and host rock, and they are not crushed or fractured. Furthermore, while in the host rock the clasts are randomly oriented, in the DBs they are iso-oriented with the long axis describing low angles to the band.

Our work shows that these DBs are characterized by the absence of grain size reduction with a strong preferred orientation of long axes without significant fragmentation. These data may indicate that DBs formed in high porosity conditions, at very shallow depths. Moreover, given the strong difference between the petrophysical properties of the host rock and DBs and the apparent abundance and continuity of the DBs, they would provide a significant anisotropy in the flow pathways of the calcarenite.

How to cite: Freda, G., Mittempergher, S., Balsamo, F., Pizzati, M., Di Cuia, R., and Ricciato, A.: Microstructural characterization of deformation bands in shallow porous carbonates of Apulian Platform, Southern Italy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5693, https://doi.org/10.5194/egusphere-egu24-5693, 2024.

X2.30
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EGU24-9013
Daniel Moraetis, Aris Leontaritis, Andreas Scharf, Charalampos Fassoulas, Stylianos Zacharias, Kosmas Pavlopoulos, Frank Mattern, Asma Alnaqbi, Xuan Yu, Christos Pennos, Kostas Adamopoulos, Hamdan Hamdan, and Nikolaos P. Nikolaidis

Here we present the results of surface and subsurface (caves) geological mapping in the Lefka Ori Massif. The structural field data collection and the stratigraphy analysis were supported by the IGCP-715 project in collaboration of the Speleological Association of Crete (SPOK) and the Gourgouthakas 2023 exploration team. The overall structure of the Lefka Ori Massif consists of a roughly E-W trending open anticline. Regional uplift is related to compressional and extensional events during the Late Oligocene to present. The primary lithologies of the Lefka Ori Massif are comprised of the Plattenkalk Unit and the Trypali Unit. The Plattenkalk Unit contains (1) black brecciated karstified marbles/dolostones with interbedded stromatolites (Triassic), (2) white to gray marbles/dolostones (Triassic-Lias), and (3) thin bedded marbles (Dogger-Oligocene). Black dolostones and brecciated marbles (with stromatolite fragments) are building up the overlying Trypali Unit (Late Triassic-Lias).

The results from the structural analysis in the Lefka Ori Massif highlight 3 sets of faults, which are of (A) E-W striking thrust faults, (B) dextral NNW-SSE strike-slip faults and (C) E-W striking steep dip-slip faults. A regional thrust (hereafter "Pachnes Thrust") has a vertical displacement of 1000 m and duplicates the Plattenkalk Unit stratigraphy (sections 1 and 2) in the Lefka Ori Massif. The hanging wall consists of Plattenkalk units 1 and 2, while the footwall comprises the Plattenkalk unit 3. The Pachnes Thrust has an apparent horizontal displacement of approximately 12 km. The cross-cutting relationship of the thrust with the strike-slip faults indicate that the faults are coeval. The steep dip-slip faults are still of an unknown relative age but certainly most of them appear as normal, younger faults. The Pachnes Thrust is folded around a roughly E-W trending open fold axis. The Late Oligocene green and red, calcschist sediments in the footwall of the Pachnes Thrust indicates the maximum age of thrusting.

The third deepest cave in Lefka Ori Massif (Sternes Cave, depth -616 m) contains a system of galleries reaching a total length of 5.6 km. This karst system of subhorizontal galleries is well explained by the Pachnes Thrust as it parallels the thrust. Likewise, the Pachnes Thrust has been delineated in the deepest cave (Gourgouthakas) at a depth of -700 m. In addition, the accepted hydrology in the Lefka Ori Massif is defining an upper fast flowing reservoir and a lower slow flowing reservoir. The physical model for these two reservoirs is explained by the hanging wall 1 and 2 lithologies (fast flowing reservoir) and the footwall lithology 3 (slow flowing reservoir) of the Pachnes Thrust.

The Pachnes Thrust in Lefka Ori Massif probably correlates with the recorded southward thrusting and nappe stacking due to convergence between the African and Eurasian plates (Oligocene-Early Miocene). The deformed Pachnes Thrust plane is coeval with the southward thrusting, due to the uplift and exhumation phases during extension described in the literature. The present findings are offering new evidence of the tectonic evolution and the exhumation of the high pressure metamorphosed rocks in the Hellenic Subduction Channel.

How to cite: Moraetis, D., Leontaritis, A., Scharf, A., Fassoulas, C., Zacharias, S., Pavlopoulos, K., Mattern, F., Alnaqbi, A., Yu, X., Pennos, C., Adamopoulos, K., Hamdan, H., and Nikolaidis, N. P.: A new geological model for the Lefka Ori Massif in the accretionary wedge of the Hellenic Subduction Zone. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9013, https://doi.org/10.5194/egusphere-egu24-9013, 2024.

X2.31
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EGU24-10510
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ECS
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Highlight
Marco Mercuri, Fabrizio Agosta, Michele Fondriest, Luca Smeraglia, Andrea Billi, Stefano Tavani, and Eugenio Carminati

Understanding the origin and distribution of damage within carbonate-hosted fault zones is crucial, yet it remains a complex challenge, which hampers the overall assessment of their mechanical and hydraulic structure. In carbonate-hosted fault zones, shattered to intensely brecciated non-cohesive rocks have been reported. Although their origin has been related to the propagation of multiple seismic ruptures, great uncertainties persist regarding their interpretation and distribution.

The NW-SE striking, approximately 15 km long Roccapreturo Fault, in the central Apennines of Italy, is an intriguing case study where non-cohesive fault rock domains occur within its footwall damage zone. These domains elongate in a NE-SW direction for ~200 meters from the main slip surface.

We employed a multiscale approach to better understand the distribution and origin of the non-cohesive fault rocks. The fault geometry and throw distribution along the main fault segments were characterized through fault-perpendicular geological cross-sections. Virtual outcrop models of key exposures, located in and around an abandoned quarry, were constructed using Structure from Motion-Multiview Stereo photogrammetry. These models utilized photos taken with a Mavic Mini 2 drone. The interpretation of virtual outcrop models, combined with classical fieldwork, allowed us to map the damage and minor fault strands.

The Roccapreturo Fault displaces Cretaceous rocks originally deposited in various depositional environments. Along its strike, from NW to SE, the fault intersects rocks from internal or restricted carbonate platform, margin, and proximal slope to basin depositional environments. Notably, non-cohesive fault rocks are exposed between the margin and proximal slope rocks. This area coincides with the maximum throw of the fault, which is ca. 600 meters, and with the intersection with a system of pre-existing NE-SW-striking steeply dipping faults.

At the outcrop scale, faults exhibit two preferred orientations, parallel and perpendicular to the main slip surfaces of the Roccapreturo Fault, respectively. The former ones show predominant dip-slip kinematics, while the latter ones show both dip-slip and strike-slip kinematics.

We interpret the distribution of non-cohesive fault rocks along the Roccapreturo Fault as influenced by its intersection with the NE-SW fault system, where most of the slip accumulated. Accordingly, the pre-existing NE-SW faults accommodated transtensional slip during latest extensional deformation and coeval rock exhumation from depth. The transition of the Cretaceous depositional environments, which was accommodated by the NE-SW-striking faults, therefore highlights the pivotal role of pre-existing anisotropies in dictating the distribution of damage, particularly of non-cohesive fault rocks, in carbonate hosted faults.

How to cite: Mercuri, M., Agosta, F., Fondriest, M., Smeraglia, L., Billi, A., Tavani, S., and Carminati, E.: Influence of pre-existing faults on damage distribution in carbonate fault zones: the case study of the Roccapreturo Fault, central Apennines, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10510, https://doi.org/10.5194/egusphere-egu24-10510, 2024.

X2.32
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EGU24-17174
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ECS
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Highlight
Hakan Heggernes, Atle Rotevatn, Matteo Demurtas, Casey W. Nixon, and Haakon Fossen

Networks of deformation bands in porous granular rocks represents potential low-permeable baffles to fluid flow in subsurface reservoirs. However, little work addresses the network properties of such networks, like spatial intensity, network connectivity and network geometry. Motivated by this, we here present an investigation of two-dimensional, horizontal exposures of deformation band networks within the Jurassic Entrada Sandstone in the San Rafael Desert (Utah). We analyse the geometry and topology (i.e. a network represented as nodes and branches) of the studied networks to: 1) characterise deformation band orientation, connectivity and areal intensity; 2) assess spatial topological variability; 3) elucidate large scale variation across the study area; 4) evaluate effective network permeabilities. Effective deformation band network permeability is calculated by incorporating a topological measure of network connectivity into the permeability calculations. Deformation band networks show distinct topological signatures, typically being dominated by Y-nodes, and IC- and CC-branches. Depending on the orientation of deformation bands and numbers of different sets of deformation bands within each studied network, both topology and areal intensity vary. Low proportion of isolated II-branches reflects the evolution of deformation bands through bifurcation and abutment, creating Y-nodes, to form interconnected networks. We document great spatial variability I network connectivity and topology within individual networks. Similarly, the effective permeability within well-connected (parts of) the studied deformation band networks (>1.5 connections per branch) significantly reduce effective permeabilities, whereas areas within the networks with low connectivity offer higher-permeable pathways for tortuous fluid flow.

How to cite: Heggernes, H., Rotevatn, A., Demurtas, M., Nixon, C. W., and Fossen, H.: Spatial variability in topology, connectivity and permeability within deformation band networks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17174, https://doi.org/10.5194/egusphere-egu24-17174, 2024.

X2.33
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EGU24-19192
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ECS
The Influence of Bioturbation on Sandstone Brittleness: A Comparative Analysis of Massive Sandstone versus Bioturbated Sandstone (Ordovician Qasim Formation-Saudi Arabia)
(withdrawn)
Moaz Salih, Hassan Eltom, Andrew La Croix, Shahin Dashtgard, Mutasim Osman, and Mazin Bashri