Lithofacies Analysis Research Articles

Facies analysis, provenance and tectono-depositional evolution of the Ediacaran Hammamat molasse sediments, Umm Tawat area, North Eastern Desert, Egypt

The Ediacaran Hammamat Sediments in the Umm Tawat basin of the Egyptian North Eastern Desert are exposed with an ENE-trend, along with the Dokhan Volcanics and various phases of intrusive rocks. Different lithofacies of molasse-type deposits exist, with a debate about their tectono-depositional setting, provenance, and diagenesis versus metamorphism. In this study, we present a new insight into the facies and evolution of Umm Tawat sediments using an integrated structural, sedimentological, and mineralogical approach. Lithofacies analysis revealed their deposition in continental suites of alluvial fans, braided fluvial channels, and lacustrine environments. The sediments were derived from proximal heterogeneous sources of intermediate and acidic igneous rocks and a subordinate sedimentary provenance conveyed from uplifted basin margin hinterlands. Petrographic, SEM-EDX, and XRD data imply that the HS were affected by diagenesis to very low-grade metamorphism and local thermal metamorphism in contact with the intrusive younger granite. Carbon smears possibly derived from organic matter in shale were observed. Two reconstructed paleostress phases derived from fault slip data with the sedimentological analysis constrain the tectono-depositional evolution of the Umm Tawat molasse basin. We propose an early development of ENE-asymmetric sedimentary depocenter associated with the N–S-directed extensional strike-slip stress regime. Syn-tectonic deposition of the Hammamat Sediments occurred during this phase in three stages with variable sediment provenance and accommodation/sediment influx ratios. This phase was accompanied by the three phases of younger granites and the Dokhan volcanics. Positive inversion with N–S-directed compressional strike-slip stress regime caused ENE-to NE-folding and reverse reactivation for the pre-existing ENE-trending dextral faults. Up on the regional correlation, the Ediacaran Umm Tawat molasse basin differs somewhat from other molasse basins in the central Eastern Desert regarding their facies and tectono-depositional model. This basin probably formed as a continental intra-arc basin located in the northern region of the Nubian Shield.

Facial composition of the deposits of the productive strata based on qualitative interpretation of the log data

As is known, most of the discovered oil and gas fields in Azerbaijan are associated with terrigenous deposits; thus, the successful discovery of new fields largely depends on determining the genesis of terrigenous formations.
 Determining the genesis of reservoir deposits allows apetroleum geologist to more accurately predict the reservoir’sshape and change its main parameters in both lateral and vertical directions.This information also allows us to choose a rational drilling operationsystem in the field. Comprehension of the genesis of the productive stratum deposits is also important in developing oil and gas fields.
 The research of the genesis of deposits of productive series is of great interest given the acceleration of exploration and evaluation of their oil and gas potential. In this regard, using the ««qualitative logging facies models» proposed by V.S. Muromtsev in the article, the sections of the wells of the Garbi Absheron, Shimali Absheron, Khazri, and Arzu structures of the North Absheron zone of the uplift PS suites «Fasila», «Upper Kirmaky Clayey» (UKC) and on the sedimentary rocks of the «Upper Kirmaky Sandy» (UKS) formation, a lithofacial analysis of sedimentary rocks was carried out, the genesis of sedimentary rocks was established, and an explanation of the results obtained was given.
 Geophysical logging data of the borehole potential curve of intrinsic polarisation were used to build spatial models and 3D models. The constructed models allow us to attribute various shapes of the well potential curve (WP) to deposits of a defined facies composition.
 In the research work, the total thickness of facies for the UKC and UKS suites was calculated, three-dimensional spatial models were built considering the variation in their thickness by structuresof the North Absheron zone of the uplift, and 3D models were built by the structures located on them.The facies composition of the sediments of the layers in the «Fasila», «UKC» and «UKS» formations was determined based on created models selected by their appearance and forms of display from WP diagrams of well sections in the Garbi Absheron, Shimali Absheron, Khazri, and Arzu structures.
 These models are major for accurately calculating oil and gas reserves in the area, for drilling and designing new wells, and refining the operation scheme.

LATE PALEOZOIC – MESOZOIC TECTONIC EVOLUTION AND PROSPECTS OF HYDROCARBON EXPLORATION IN THE ALAKOL SEDIMENTARY BASIN (KAZAKHSTAN)

Based on the analysis of stratigraphic, lithofacies, and geological and geophysical data, consideration is being given to the main stages in the formation of the basement and cover structures of the Alakol sedimentary basin. For this region, there was developed the substantiation of a scheme of tectonic zoning and there were proposed structural characteristics of faults and lithofacies features of the section. Evidence was found of a complex, multi-stage tectonic evolution. There were discovered potentially promising stratigraphic oil and gas complexes of the Late Paleozoic and Mesozoic. The deep-seated structure of the region is illustrated by a geological and geophysical section, spatially coincident with the "Turkestan" seismic profile. Based on the lithological and paleogeographic reconstructions, there were identified four major tectonic boundaries: Cambrian-Ordovician, Devonian-Carboniferous, Permian-Early Triassic, and Middle Triassic-Cretaceous. The correlation of the stratigraphic range of the hydrocarbon potential of the Alakol basin has been carried out. The criteria for forecasting hydrocarbon accumulations were substantiated.

Paleoproterozoic rift-related volcanism of the Karrat Group, west Greenland: New insights from lithofacies analysis and geochemistry of the Kangilleq Formation

Mafic volcanic rocks of the Paleoproterozoic Kangilleq Formation of the Karrat Group of West Greenland represent a submarine mafic volcanic sequence, erupted and deposited on the Rae craton of Greenland. The formation ranges from <100 m-thick to ∼500 m-thick, and consists of mafic volcaniclastic rocks, pillow lavas and massive basalt lavas that have undergone greenschist facies metamorphism, yet preserve primary volcanic textures such as pillows, drainage cavities, lobes, flow banding, autoclastic breccias, hyaloclastite, scoria and layering.Rocks of the Kangilleq Formation overlie the Archean Qeqertarssuaq Complex and are interleaved with and overlain by the ca. 1950 Ma Nûkavsak Formation. Based on detailed (1:200) mapping and high-precision geochemistry, rocks of the Kangilleq Formation are subdivided into the Kangiusiap and Umiammakku members. The Kangiusiap member is dominated by mafic, scoria-rich breccias, has sulfide mineralization, and is bound at the bottom and top by the Nûkavsak Formation. This member has subalkaline, transitional to tholeiitic, mid-ocean ridge basalt (MORB) to back arc basin basalt (BABB) signatures with a Nd-isotope value similar to the depleted mantle at 1.88 Ga. The Umiammakku member is dominated by pillow lavas, with subordinate amounts of massive lavas and volcaniclastic rocks, overlies the Qeqertarssuaq Complex and is overlain by, and interleaved with, the Nûkavsak Formation. It is alkaline with characteristics similar to modern ocean island basalts and Nd-isotopic values slightly lower than the depleted mantle at 1.88 Ga.The rocks of the Kangilleq Formation represent non-arc suites or suites that have only minor subduction zone or crustal input, and display geochemical signatures similar to basalts found in modern intracontinental back arc settings. Lithofacies, bedforms, internal stratigraphy, and the identification of synvolcanic faults, suggest it is the product of volcanic eruptions during incipient rifting within a back arc setting, and seafloor mass wasting events at fault scarps related to rifting. Based on the geological characteristics and its petrogenetic and tectonic history, the Kangilleq Formation is interpreted to be correlative with the Bravo Lake Formation of the Piling Group of northeastern Canada and records incipient rifting of the southern margin of the Rae craton in the Paleoproterozoic.

Analysing of palaeoenvironment and organic matter enrichment: A case study from the Triassic Yanchang Formation in the southern Ordos Basin, China

The organic‐rich shale of the seventh Oil Member (Chang 7 Member for short) of the Middle‐Late Triassic Yanchang Formation is extensively distributed in the southern margin of the Ordos Basin. Understanding the palaeoenvironmental conditions during the sedimentary period of the Chang 7 Member is crucial to exploring the main factors that control the enrichment of organic matter in high‐quality source rocks. In this study, lithofacies analysis was conducted, and samples were collected from the N36 well located in the southern part of the Ordos Basin. Subsequently, element geochemical analysis was performed to reconstruct the palaeoenvironment, and total organic carbon (TOC) tests were conducted to analyse the characteristics of organic matter enrichment. The findings indicate that the sedimentary period of the Chang 7 Member was characterized by a relatively warm and humid palaeo‐climate and a brackish water environment with oxygen‐poor or sub‐oxygen‐rich conditions, and a gradual decrease in palaeo‐water depth. The parent rock types were mainly felsic igneous rock and intermediate igneous rock, which provide limited nutritional elements for primary producers. The enrichment of organic matter in the Chang 7 Member is influenced by several factors, mainly including palaeo‐salinity, palaeo‐water depth, palaeo‐redox conditions, terrestrial inputs, and palaeo‐climate. The warm and humid palaeo‐climate, higher palaeo‐productivity, relatively higher palaeo‐salinity, lower terrigenous input, deeper palaeo‐water depth, and better preservation conditions are conducive to the development of high‐quality source rock in the Chang 7 Member.

Devonian diamond reservoir of the Urals

Research subject. The Takata formation of the Emsian tier of the Lower Devonian (D1tk) in the Urals is a reservoir of Devonian diamonds. Aim. Confirmation and determination of the diamond-bearing conditions of the reservoir. Materials and Methods. Generalization of primary and interpreted geological information. Lithofacial analysis. Historical and geological reconstruction. Cartographic analysis and geological and cartographic modeling in the ArcMapESRY GIS environment using the ModelBuilder module. Results. The Takata formation is part of the Emsian tier of the Lower Devonian. Tectonically, the Takata formation is located in the West Ural Folded Zone. The diamond content in the Urals is spatially related to the outputs of the Takata formation. The industrial diamond-bearing capacity and the highest density of diamond placers are located in the Vishersky, Chykmansky and Chusovskoy diamond-bearing regions of the Northern and Middle Urals within the Perm Krai. In the early Devonian, the Takata Sea existed in the Vishera diamond-bearing area; a large river with a delta flowed in the direction from northwest to southeast. The sediments of the formation comprise the facies cycle: flood-plain - channel alluvium - delta sediments - underwater-delta - marine sediments. Diamonds are concentrated in the thickness of coarse-grained alluvium, small-pebble basal conglomerates that formed on the land-sea boundary of the paleocontinent of the Russian Plate. Three facies types of the Takata formation section are distinguished: continental, coastal-marine and marine. Its diamond-bearing capacity is associated with the continental and coastal-marine sediments of the formation within the Perm Region. To the north and south of the diamond-bearing areas of the Perm Krai, the Takata formation is represented by marine sediments. According to the geodynamic model based on the geological section of the Northern Urals, the alluvial and coastal-marine Takata diamond placers were formed in the early Devonian as a result of the demolition of material from the Russian Plate. The sources of destruction were rocks of the Precambrian, Ordovician and Silurian. The main spatial-geomorphological criterion for searching for diamond-bearing conglomerates of the Takata formation is the maximum distance of demolition from these conglomerations to placers, equal to 500 m.

Palaeoenvironments and palaeoclimate of the uppermost Cuyo Group and lowermost Lotena Group at Quebrada Álvarez, Picún Leufú Sub-basin, Patagonia, Argentina: a preliminary study based on palynology

The palynological (palynostratigraphical/palynofacies) analysis of samples from the Middle Jurassic outcrop at the Quebrada Álvarez section located in the Neuquén Basin, Patagonia, Argentina, allowed us to begin to evaluate the palaeoecological significance of the recovered palynofloras and their importance in the evolution of these ecosystems, during the transition between the uppermost Cuyo Group and the lowermost Lotena Group. The Lajas Formation, characterised by the palynofacies type A, could be interpreted as a tide-modified delta front environment. The high abundance and diversity of the palynomorphs identified in the studied samples, contribute to improve the palynological knowledge of the Challacó Formation (palynofacies type B − F). Considering the palaeoecological requirements of the recognised plant families, relatively humid and warm climate conditions could be inferred during the deposition of this unit. Also, the ‘seasonally dry (winterwet)’ biome was interpreted for the first time in the Neuquén Basin. Based on selected key taxa a late Bathonian–early Callovian age is proposed for the Challacó Formation at the Quebrada Álvarez section. The palynological material recorded in this unit suggests the development of a lacustrine environment with cycles of relative contraction and expansion of the water body due to fluctuations between relatively dry and wet conditions. The dominance of phytoclasts, mainly opaque particles, and freshwater algae (Botryococcus) in the Bosque Petrificado Formation (palynofacies type G − I) could suggest the development of a freshwater to brackish lacustrine environment. Based on the dominance of the same group of palynomorphs (chlorophyte algae) in the Challacó and Bosque Petrificado formations, similar palaeoenvironmental conditions would be inferred for these units. From a lithofacies analysis point of view, the Challacó and Bosque Petrificado formations show isopic facies associations in the study locality.

Volcanology and facies analysis of the youngest phreatomagmatic deposits on O'ahu, Hawai'i

The area known as the Lānaʻi Lookout has Oʻahu's youngest and best exposures of deposits from pyroclastic density currents (PDCs), generated by explosions involving magma-water interaction. This work presents the first detailed facies analysis of the deposits at the Lānaʻi Lookout, fundamental to understanding the explosion dynamics, post-fragmentation transport and depositional processes, and to unravel the eruptive history. The lithofacies identified include planar-bedded, low-angle, and megaripple, cross-bedded ash to lapilli, accretionary lapilli-rich falls and isolated ballistic blocks and bombs. These features are interpreted as generated by mostly dilute PDCs, co-PDC fall and sedimentation from eruptive clouds and ballistic-charged jets. Overall, at least four eruptive stages formed the pyroclastic succession: (i) frequent, brief explosions from Kahauloa and Koko craters, producing fallout deposits and ballistics; (ii) a dominant stage of sustained passing to short-lived production of PDCs from Kahauloa crater, followed by a short break in volcanic activity; (iii) return of explosive activity dominated by fallout deposits likely sourced at Kahauloa; (iv) intermittent PDCs from Kahauloa alternating with debris flows coming down Koko Crater flanks. This stage is followed by lava flow emplacement that marked the end of the explosive eruptions at the Koko Rift system. In summary, the lithofacies analysis and stratigraphic relations of this complex multi-vent system informs on the dynamics, eruptive style, and frequency of eruptions of the late-stage volcanism on Oʻahu.

Eruption, transport mechanisms and deposition of Paleogene ignimbrites, southwestern North Patagonian Massif, Argentina

The Paleocene-Eocene Catán Lil Ignimbrite (CLI) is one of the few occurrences within the explosive acid volcanism of this age in the extra-Andean region of the North Patagonian Massif. It represents a small-scale explosive eruption covering an area of 214 km2, with an estimated volume of 1.27 km3 and consisting of three weakly-to densely welded cooling units. The maximum thickness of this sequence is 90 m. Its basal unit is the best preserved, and has allowed a lithofacial analysis that reveals different aspects of the eruption and the emplacement mode of the Catán Lil pyroclastic flows. The CLI ignimbrites are generally massive, poorly sorted, matrix-supported deposits (tuff and lapilli tuff) resulting from dense pyroclastic currents (PDCs). They are composed mainly of juvenile fragments, scarce lithoclasts and crystalloclasts, being a product of a purely magmatic fragmentation occurred at a shallow level. A pyroclastic fountaining eruptive model is interpreted, resulting from the collapse of a low eruptive column, and a rapid and high-temperature emplacement. The CLI PDCs generally respond to slow moving pyroclastic flows with low erosive energy. The morphology and stratigraphy indicate radial emissions with thicknesses decreasing towards the periphery that become evident in Central-South ignimbrites. These PDCs flowed over a planar terrain, giving rise to most of the CLI deposits (South-Central area and North- East). The Northwestern ignimbrites are deposits in the interior (south and middle part) of the Catán Lil creek, forming thick deposits within the latter valley and thin, veneer-like deposits over the flanking Lipetrén granitoids. In the North- East region, the ignimbrites show stratigraphic relationships that suggest that the PDCs would slightly postdate those of the South-Central area. The Catán Lil Ignimbrites represent the most eastern exposures of the Paleocene-Eocene Pilcaniyeu Belt, differing from the latter in that it lacks a conspicuous lava facies, and by the unimodal character and the tectonic signature of the Catán Lil sequence.

3D geological modelling of the Bologna urban area (Italy)

Urban geological modelling plays a crucial role in facilitating the sustainable utilization of the urban subsurface and the development of effective strategies for geohazard mitigation. Traditionally, geological models of urban areas rely on lithological correlations of boreholes and well data. However, in complex depositional settings such as alluvial environments, where the standard concepts of superposition and lateral continuity of strata are often violated, lithostratigraphic correlation can be challenging even over short distances, leading to considerable uncertainty in the final geological model. Therefore, in such cases, lithofacies analysis can provide a more robust categorisation of subsurface geological units as lithofacies mainly reflect the depositional process, while their associations provide a reliable picture of sedimentary bodies and their geometries. In this work, we used the lithofacies correlation approach to develop a 3D geological model of the urban area of Bologna (Italy) where a complex, thick alluvial succession makes lithological correlations very difficult. To minimize subjectivity, we re-interpreted 940 existing borehole logs in terms of depositional facies and combined stratigraphic data with geophysical HSVR (Horizontal to Vertical Spectral Ratio) measurements and surface analysis (morphology and river network) based on a DTM (Digital Terrain Model). This led to the detailed reconstruction of the subsurface depositional architecture, forming the basis for the 3D geological model. The model revealed the presence of three distinct depositional domains with different stratigraphic architectures. From west to east: Domain A (Reno River) corresponds to the gravel-dominated fill of a river valley abruptly passing to Domain B (Bologna urban area) that represents a morphological and stratigraphical divide, topographically elevated with respect to the surrounding areas and characterised by fine-grained deposits with frequent paleosols. Lastly, Domain C (Savena River) exhibits the typical alluvial fan pattern, marked by a gentle convex-up surface morphology with gravelly-sandy deposits with a low degree of lateral amalgamation. The geological model effectively explains the distribution of ground subsidence in Bologna since the 1960s, which is attributable to significant groundwater pumping. This is evident from the comparison of the model with both the ground displacement contours resulting from the 1983–1987 topographic levelling campaign and the subsidence rate map derived from the 2006–2011 Radarsat interferometric survey. Subsidence shows strong variations at the domains' boundaries, especially at the limit between Domain A (Reno River) where high values prevail, and Domain B (Bologna city centre) characterised by the lowest values.

An integrated workflow for seismic interpretation, petrophysical and petrographical characterization for the clastic Mangahewa reservoir in Pohokura gas field, Taranaki Basin, New Zealand

This research aims at delineating the main structural elements controlling the geologic setting of Taranaki Basin in New Zealand which in turn control the hydrocarbon potential of this basin and in particular of Pohokura Field which is considered one of the main gas-producing fields in the basin. This can be achieved utilizing the seismic data including three different marine seismic data sets covering 514.6 km2 with 12.5 m horizontal resolution. A synthetic seismogram and a set of seismic attributes were created to achieve this target. In addition, an integrated reservoir characterization study is applied to the Mangahewa reservoir in the Pohokura Field. This integrated characterization includes a detailed petrographical lithofacies analysis, well logging, and core analysis studies. Based on the petrographical study, eight lithofacies are described in Pohokura Field: 1) Laminated sandstone; 2) Massive sandstones; 3) Granular laminated sandstones; 4) Bioturbated sandstones; 5) Sand dominated and mud rich bioturbated sandstones; 6) Muddy bioturbated sandstone; 7) Laminated and rippled laminated mud rocks, and 8) Coal lithofacies which have been deposited in high energy shoreface setting. On the other side, the available well logging data includes caliper, GR (gamma-ray), sonic, neutron, density, and resistivity (shallow and deep resistivities). Logging interpretation enabled the estimation of the effective porosity (av. ∅ = 11.4%), hydrocarbon saturation (av. Shc = 62.87%), and the shale volume (av. VSh = 18.02%) with a total net pay thickness of all wells = 196 m. The available core data includes porosity, density, and permeability which are used to estimate the reservoir quality ranks; the effective pore radius (R35); the flow zone indicator, the discrete rock type (DRT), and the reservoir quality index (RQI). Considering the porosity, permeability, and the DRT values, the available core data are grouped into five reservoir rock types (RRTs) with the best reservoir quality assigned for the RRT1 (bioturbated, laminated and massive sandstones), while RRT5 has the lowest reservoir quality (muddy bioturbated sandstone, Granulated laminated sandstone, and laminated and rippled mudstone). This integrated study is applicable and extendable to the other basins in New Zealand and the southwestern Pacific. The proposed workflow is also applicable to the other analogs in the various basins elsewhere.

Determination of the conditions of sedimentation of the Jurassic deposits of the Karaton field based on a comparison of electrofacies and sedimentological description of the core

This paper presents the results of lithofacies analysis of log curves and sedimentological description of the core material of wells from the Karaton field to determine the environmental condition and determine the similarity of the behavior of log curves. The field is located in the Karaton-Tengiz zone of uplifts, which are characterized by a rather complicated environmental conditions. Based on typical models of facies groups and a description of the core material of the Jurassic deposits, it was possible to identify zones of development of sandy deposits and determine the main environmental condition. Keywords: lithology; sedimentology; facies; electrofacies; generic model; depositional environment.

Three-dimensional seismic architecture of an Upper Cretaceous volcanic complex and associated carbonate systems; Taylor Group, Elaine field, South Texas, USA

The seismic architecture of a tuff-dominated volcanic complex and the associated carbonate systems in the Upper Cretaceous Taylor Group (Anacacho Limestone) Elaine field in South Texas was examined using a three-dimensional seismic dataset. The investigation demonstrates that the combination of traditional seismic lithofacies analysis and seismic sedimentology allows the visualization and interpretation of volcanic elements and penecontemporaneous carbonate lithofacies at the scale of tens of meters. A wireline-log based, rock-physics model was analyzed and calibrated using core samples, which link volcanic and carbonate lithofacies to 90°-phase seismic amplitude events. Seismic-velocity effects permit the identification of subtle volcanic lithofacies changes such as low-velocity tuff bodies or high-velocity basalt intrusions. Also, frequency fusion expands seismic visualization of thick lithofacies bodies (e.g., basaltic dykes) to the 100-m range and seismic facies analysis helps understand interrelationships between the components in and adjacent to the volcanic body. Horizontal seismic slices reveal seismic geomorphology at multiple stages of volcanic activity. This investigation reveals three major seismic facies systems (1) a magma-feeder (i.e., plumbing) intrusive system beneath the volcano, including deep faults, dykes and sills, and remnant radial/concentric fault systems; (2) a large (4000–5000 m diameter) volcanic complex consisting of a deep crater (300-m negative feature below the paleo-sea floor), a large mound (200-m positive feature above the paleo-sea floor), multiple secondary craters filled predominantly with tuffs and less common lava flows; and (3) penecontemporaneous carbonate systems including fringing and mound-top shoals and reefs, lagoon and debris fan aprons at the base of the volcanic mounds. The fringing and mound top carbonate systems were probably in water depths less than 20 m whereas for the fan-apron carbonates, water depths are estimated to be about 140–200 m. These carbonate bodies can form hydrocarbon reservoirs.

THE KUYTUN VALLEY AS AN EXOGEODYNAMIC TEST SITE FOR PRACTICING THE APPLICATION OF METHODOLOGY FOR INTERDISCIPLINARY RESEARCH IN THE SEDIMENTATION SETTINGS OF LOESS-LIKE COVER DEPOSITS IN THE LATE PLEISTOCENE TRANSBAIKALIA

An interdisciplinary research in the Late Quaternary loess-like cover deposits in the valley of the Kuytunka River (Western Transbaikalia) was aimed at reconstructing the conditions and dynamics of regional sedimentation. Particular attention is paid to assessing the information capacity of the methods involved therein: lithofacies analysis, grain-size analysis, and petromagnetic and lithochemical analyses. It is shown that the results of each method independently provide additional information on the processes of sedimentation, are not duplicated, and make it possible to obtain a full characterization of the factors and features of sedimentogenesis. It was found that the valley sedimentation was of cyclic character: warm (soil formation) periods changed to the periods of cooling-(accumulation of sandy-loamy strata); all processes occurred predominantly in semi-arid climate with slight fluctuations in humidity. The mode of the normal formation of a blanket of sedimentary material manifests itself in the structure and properties of deposits exposed on the southern slope of the valley (Kuytun-1 section). Intensive slope processes, and reworking and remixing of sediments on the gentle valley north-exposure slope by catastrophic flows (slope mudflows) and cryogenesis are reflected in the structure and properties of the deposits exposed in the Kuytun-2 section. There are shown the advantages of an integrated approach for detailing the structure of the sections, explaining the genesis of sediments, determining the most probable source areas for the sediment and modes of sediment transport, and reconstructing sedimentary environments.

Turbidite system controlled by fault interaction and linkage on a slope belt of rift basin: Zhanhua depression, Bohai Bay Basin, China

Although the relationship between faulting and sedimentation has been extensively studied and discussed over the past decades using a variety of examples and surface and subsurface data. However, limited information is available regarding the evolutions within the interaction zones in sedimentary processes, depositional architecture and sand bodies dispersal, which are crucial for hydrocarbon exploration, specifically in deep-water sedimentary system. To investigate the effects of fault interaction and linkage on the sedimentary processes and architecture of deep-water turbidite systems and explore the impact of fault linkage patterns on the dispersal of sand bodies, 3D seismic data, cores and logging data were collected from the southern slope zone of the Zhanhua Depression, Bohai Bay Basin. The Kenxi area exhibits two typical fault-reworked geomorphologies (i.e. slope geomorphology with weak reworking and fault-trough geomorphology with strong reworking), which control the development of fan depositional architecture dominated by turbidity current and fault-confined channel depositional architecture dominated by mixed traction current and turbidity current, respectively. These turbidite systems indicate that they are connected to flood occurrence based on systematic lithofacies analysis. Nevertheless, two distinct sediment grain sizes and drainages have been formed and may be related to fault confinement and slope gradients. Additionally, we propose conceptual fault linkage models that regulate drainage and the dispersion of sand bodies, highlighting the effects of fault evolution stages and separation distance on local geomorphology. First, the region with relatively unconfined geomorphology, dominated by non-separated faults in the soft linkage stage, is where lobe deposits are more likely to have formed. The relay ramps, shaped by separated faults in the soft linkage stage, control the direction of the transportation of sediments in the proximal area. Second, the distribution of fault-confined channels is laterally confined by long extended fault-trough geomorphology formed following hard linkage by non-separated faults. The local footwall hump (i.e. local topographic high) formed in an overlapped zone by separated faults provides frontal confinement for sand bodies in the hard linkage stage. This study reveals that in addition to onshore river systems, the architecture and distribution of deep-water turbidite systems are significantly influenced by fault interaction and linkage patterns. Meanwhile, it provides a new model for facilitating the prediction of the reservoir distribution of turbidite systems in the slope zone of rift basins.

Lithofacies and depositional settings of Mesoproterozoic shales: Insights from the ∼1.65 Ga Chuanlinggou Formation, Yanliao Basin, North China Craton

Precambrian black shale has become a significant trend in petroleum exploration, and the Chuanlinggou Formation is the oldest potential hydrocarbon source rock deposit in the North China Craton. The Mesoproterozoic was a unique transitional stage in the evolution of the environment and life in Earth's history. Research on lithofacies and depositional settings in this stage has important scientific and oil and gas exploration significance. Outcrop observations, thin sections, and elemental and organic geochemical analyses were used to study the mineralogy, sedimentary structures, lithofacies assemblages and their relationships with the depositional environment. Three endmembers (silicate, carbonate and clay minerals) based on X-ray fluorescence were employed to establish the lithofacies classification suitable for the Chuanlinggou Formation in the Yanliao Basin. The lithofacies of the Chuanlinggou Formation were classified into six types, including calcareous mudstone, siliceous/calcareous mixed mudstone, argillaceous/siliceous mixed mudstone, silicate-rich argillaceous mudstone, clay-rich siliceous mudstone and siliceous mudstone. Four lithofacies assemblages (LAs) were identified according to the integrated lithofacies analysis from the bottom to the top of the section. Lithofacies assemblages 1 and 2 (LA1 and LA2), which were deposited in deep subtidal to shelf environments, have high petroleum potentials and are advantageous lithofacies assemblages for organic matter accumulation. The black shale developed early rift may not be as favorable as in the late rift, while the siliceous shale developed in the continental shelf-slope is a favorable lithofacies. A comprehensive cognition of the LA and depositional settings of the Chuanlinggou Formation might provide guidance for further petroleum exploration and sedimentary environments in the Mesoproterozoic.

Characterization of a complex sand-rich gas hydrate reservoir system in the Indian marine continental margin with downhole log and seismic data

Logging-while-drilling (LWD) and coring data were acquired in Areas A, B, C and E during the National Gas Hydrate Program Expedition 02 (NGHP-02). At Sites NGHP-02-16, −17, −20, −23 and −24 of Area B in the Indian Krishna-Godavari Basin, the gas hydrate-bearing sand-rich reservoirs directly in contact with an underlying water-saturated sediment were revealed near the seismic-inferred bottom simulating reflector (BSR) along a large anticlinal structure. Lithofacies analysis of cores show that the lower gas hydrate-bearing reservoir section at these sites is an interbedded unit with thin fine-sand layers alternating with clay-rich layers. We reanalyzed the LWD data including resistivity, compressional-wave and shear-wave acoustic velocities to assess and compare the spatial variation of sand-hosted gas hydrate and possible related free-gas accumulations. The presence of free gas-bearing sediments in direct contact with gas hydrate-bearing sediments was confirmed at Sites NGHP-02-20 and −24 along the northeastern flank of the anticline. The sand-rich reservoirs associated with the Area B anticlinal feature reveal different pore-filling constituents and variable boundary conditions, including gas hydrate/water contacts and gas hydrate/free gas contacts. We infer that the sedimentary depositional history at Sites NGHP-02-20 and −24, may have resulted in an upward shift of the base of gas hydrate stability zone, that could have led to in situ gas hydrate dissociation and the accumulation of free gas and coexistence interval below the log-inferred gas hydrate-bearing reservoir sections. This study demonstrates that reservoir heterogeneity and fluid migration were major factors affecting the distribution of gas hydrate and free gas in the identified sand-rich reservoirs.

THE KUYALNYKIAN REGIONAL STAGE OF THE EUXINIAN AREA OF THE EASTERN PARATETHYS AND THE POSSIBILITY OF DETERMINING THE NEOGENE-QUATERNARY BOUNDARY (PIACENZIAN-GELASIAN) IN THE SOUTHERN UKRAINIAN DEPOSITS

The Kuyalnykian regional stage is a stage of evolution of the Euxine Basin of the Eastern Paratethys with its own conditions for the existence of biota. During that time, the estuarine-marine conditions in southern Ukraine prevailed, leading to the development of various geological formations. However, to date, the Kuyalnykian does not have the official status of a regional stratigraphic unit, either in the Neogene stratigraphic scheme of the Eastern Paratethys or in the Neogene stratigraphic scheme of southern Ukraine, also there is no generalised (formal) description of it as a separate regional stratigraphic unit. The lowering of the Neogene–Quaternary boundary from 1.8 to 2.595 Ma led to a discussion about tracing it in the middle of the Kuyalnykian deposits. This study provides a comprehensive analysis of lithofacies, biostratigraphy (molluscs, ostracods, nannofossils, small mammals), palaeomagnetic and paleogeographic data to obtain a holistic view of the stratigraphy of the Kuyalnykian deposits in southern Ukraine. As a result, we acquired a generalized description and regional stratigraphic scheme of the Kuyalnykian, introduced new local stratigraphic units, obtained criteria for tracing the Neogene-Quaternary boundary, and clarified which part of the Kuyalnykian deposits are of Pliocene age and remain on the pre-Quaternary geological maps, and which of them are already of Pleistocene age and should be transferred to the Quaternary geological maps. The Euxine Basin of the Eastern Paratethys during Kuyalnykian was characterised by euryhaline brackish water, freshwater mollusc assemblages, brackish water and freshwater ostracods assemblages that existed in estuarine-marine environments. The Kuyalnykian deposits are divided into two regional substages and be determinated in the Northern Peri-Black Sea Region, Northern Azov Region, the northern part of the Crimean Peninsula and the Kerch Peninsula. We established the following lithostratigraphic units of the Kuyalnykian for southern Ukraine: the Zamorske Formation in the central and eastern part of the Kerch Peninsula; The Mysove Formation in the northwestern part of the Kerch Peninsula and the eastern part of the Crimean Peninsula is partly Kuyalnykian; the upper part of the Bekhtery Formation on the Left Bank of the Lower Dnieper in the Skadovsk and Holoprystan districts belongs to the lower regional substage of the Kuyalnykian; the Kuyalnyk Formation in the Northern Peri-Black Sea region and Northern Azov region, in the north of the Crimean Peninsula belongs to the upper regional substage of the Kuyalnykian. The age of the Kuyalnykian deposits has been determined based on palaeomagnetic and faunal data. The lower boundary of the Kuyalnykian regional stage is 3.6 Ma which coincides with the boundary of the Hilbert-Gauss palaeomagnetic epochs. The boundary between the Lower and Upper substages is 2.59 Ma (the Gauss-Matuyama boundary). The upper boundary of the Kuyalnykian is set at different stratigraphic levels; it dates 1.780 Ma (the upper boundary of the Olduvai Subchron) in the Indol structural facies zone and also ~1.500 Ma (perhaps above the Gils Subchron, based on small mammal data) or ~0.990 Ma (above the Jaramillo Subchron, based on palaeomagnetic data) in the Western and Eastern structural facies zones of the Northern Black Sea Region, the Northern Azov Region, and the Sivash structural facies zone. This diachrony of the upper Kuyalnykian boundary is explained by environmental difference: while in more marine and “deep water” conditions (Indol structural facies zone) the Kuyalnykian molluscs have already changed to “Gurian (sensu lato)”, in relatively remote estuaries (the Northern Black Sea Region, Northern Azov Region) the Kuyalnykian fauna still “survived”. In addition, it should be noted that the palaeomagnetic dates obtained from studied sections of the Northern Black Sea region are not “absolute” and therefore may be reinterpreted in the future.

Application of Seismic Stratigraphic Slice Continuous Browsing Technology to Delicately Characterize River Sedimentary Microfacies

On the basis of understanding the regional tectonics characteristics and stratigraphic sedimentary characteristics of the study area, the sequence stratigraphic framework within the region is gradually studied by applying the principle of high-resolution sequence stratigraphy, and G4 oil formation is divided into three sets of sand formations, namely, G4 upper, G4 middle, and G4 lower sand formations, and divided into small layers in detail. Through comprehensive analysis of lithofacies, logging facies, and seismic facies, the sedimentary facies of the G4 oil formation are comprehensively analyzed. The main sedimentary facies type of the G4 oil formation is the delta front facies belt, and the most important sedimentary microfacies in the delta front facies belt are underwater distributary channel sedimentary microfacies. Using seismic sedimentology methods, make stratigraphic slices of each sub layer of the G4 oil formation, and use the rapid browsing method of stratigraphic slices to trace river sand in detail.

Experimental Study on the Damage and Crack Evolution Characteristics of TS-RCR Structural Bodies under Cyclic Loading and Unloading

Four representative TS-RCR (three-soft rock-coal-rock) structural bodies were selected according to the lithofacies analysis of coal measures in the Xiangshui Coal Mine, Guizhou, China, to analyze the mechanical properties, internal structure damage characteristics, and crack evolution law of the TS-RCR structural body composed of a soft roof, a soft floor, and soft coal seams. The mechanical model of the TS-RCR structural body was proposed. (1) The stress-strain curves of TS-RCR structures with different lithologies under cyclic loading and unloading show a change rule of sparsity, density, and sparsity with the increased cycles. The deformation of TS-RCR structures under cyclic loading and unloading can be divided into four stages. When the height ratio of the TS-RCR structural body was the same, the higher the strength of the upper and lower rocks, the more cycles the TS-RCR structural body had, and the denser the cyclic loading and unloading curve. On the contrary, the fewer cycles the TS-RCR structural body had, the sparser the cyclic loading and unloading curve. (2) The T2 (transverse relaxation time) spectrum curves of the structural bodies were monitored at about 1 and 10 ms, and two obvious peaks were detected, indicating micropores and mesopores with a large volume in the structural body. Signal intensity increased at the relaxation time of 1 ms, decreased at 10–100 ms, and increased slightly at 100–1000 ms. The pore structure of the structural body with different lithologies changed significantly with the increased cycle number. (3) The damage and failure process of the structural body was roughly divided into three periods according to the time-history analysis of acoustic-emission AF (the ratio of acoustic-emission ringing count to duration) of the structural body: the active period with a relatively low AF value (AF &lt; 60 kHz) in the 1st-2nd cycles; the rising period with a relatively stable increase of the AF value in the 3rd-4th cycles; and the explosive period with a relatively high AF value (AF ≥ 60 kHz) in the 5th cycles. According to the relationship between the RA (the ratio of the rise time to the amplitude of the acoustic-emission-detection wave) value and time, the evolution law of the RA value and AF value of structures with different lithologies is similar in different periods under cyclic loading and unloading.