Distinct Facies Research Articles

Microfacies analysis and depositional environment of the Upper Devonian Dankovo-Lebedyansky sediments, Tatarstan, Volga-Ural Basin, Russia

The Upper Devonian, Middle Famennian Dankovo-Lebedyansky sediments in Southeast Tatarstan territory are a carbonate sequence composed of limestone and dolomite, which is important hydrocarbon reservoir units, therefore, it is necessary to conduct in-depth study on its microfacies and depositional environment. In this study, a multidisciplinary approach that combines core observation with thin section examination is used. The limestone contains abundant skeletal grains (echinoderms, foraminifera, algae, gastropods, and calcispheres), as well as non-skeletal grains (intraclasts and peloids). On the basis of detailed petrographic investigations, six sedimentary microfacies can be identified, including (i) peloidal grainstone (MF 1), (ii) cemented bioclastic peloidal grainstone (MF 2), (iii) echinoderm-concentrated packstone (MF 3), (iv) algae packstone (MF 4), (v) bioclastic wackestone (MF 5), (vi) whole-fossil wackestone (MF 6), as well as dolomite or dolostone as diagenetic facies (MF 7). Based on microfacies analysis, the Dankovo-Lebedyansky sediments were deposited in three distinct sedimentary facies belts (shoal, lagoon and open marine environment). In order to reflect dispositional energy condition, the microfacies were grouped into facies associations: (i) low-energy microfacies associations including MF 5 and MF 6, (ii) moderate energy microfacies associations including MF 1, MF 2, MF 3, and MF 4. The dolomite, or diagenetic facies (MF 7), is the result of slightly to extensively dolomitization of limestone in the Dankovo-Lebedyansky sediments. Most of frequent dolostone types are euhedral planar-e and subhedral planar-s. According to petrographic characteristic of the dolostone, a seepage reflux model can be used to explain the dolomitization process of Dankovo-Lebedyansky sediments.

The dynamic floor of Yellowstone Lake, Wyoming, USA: The last 14 k.y. of hydrothermal explosions, venting, doming, and faulting

AbstractHydrothermal explosions are significant potential hazards in Yellowstone National Park, Wyoming, USA. The northern Yellowstone Lake area hosts the three largest hydrothermal explosion craters known on Earth empowered by the highest heat flow values in Yellowstone and active seismicity and deformation. Geological and geochemical studies of eighteen sublacustrine cores provide the first detailed synthesis of the age, sedimentary facies, and origin of multiple hydrothermal explosion deposits. New tephrochronology and radiocarbon results provide a four-dimensional view of recent geologic activity since recession at ca. 15–14.5 ka of the >1-km-thick Pinedale ice sheet.The sedimentary record in Yellowstone Lake contains multiple hydrothermal explosion deposits ranging in age from ca. 13 ka to ~1860 CE. Hydrothermal explosions require a sudden drop in pressure resulting in rapid expansion of high-temperature fluids causing fragmentation, ejection, and crater formation; explosions may be initiated by seismicity, faulting, deformation, or rapid lake-level changes. Fallout and transport of ejecta produces distinct facies of subaqueous hydrothermal explosion deposits. Yellowstone hydrothermal systems are characterized by alkaline-Cl and/or vapor-dominated fluids that, respectively, produce alteration dominated by silica-smectite-chlorite or by kaolinite. Alkaline-Cl liquids flash to steam during hydrothermal explosions, producing much more energetic events than simple vapor expansion in vapor-dominated systems. Two enormous explosion events in Yellowstone Lake were triggered quite differently: Elliott’s Crater explosion resulted from a major seismic event (8 ka) that ruptured an impervious hydrothermal dome, whereas the Mary Bay explosion (13 ka) was triggered by a sudden drop in lake level stimulated by a seismic event, tsunami, and outlet channel erosion.

Palaeostrait tectonosedimentary facies during late Cenozoic microplate rifting and dispersal in the western Mediterranean

Abstract Palaeostraits are common features formed during the extension and fragmentation of active continental margins, when back-arc basins are formed and microplates develop through upper-plate extension. In this contribution, we focus on narrow seaways and straits associated with successive pulses of late Cenozoic rifting along the southwestern Eurasian continental margin, and the ensuing formation and dispersal of microplates. The incomplete and largely non-cylindrical Africa–Eurasia continental collision in the Mediterranean region provides snapshots of the various phases of microplate fragmentation and dispersal, punctuated by the presence of narrow seaways/straits. These peculiar physiographical conditions induced current amplification, and led to the accumulation of characteristic large-scale, cross-stratified deposits and tidal facies in an otherwise generally microtidal setting. Although not univocally related to rifting, the identification of such distinctive sedimentary facies within deformed orogenic belts may ultimately help in terrane analysis and in the discrimination of individual microplates, which were then amalgamated. Recognition and dating of palaeostrait tectonosedimentary facies can thus constrain the presence and the onset of extension in the geological record.

The development of the eastern Orpheus rift basin, offshore eastern Canada: A case study of the interplay between rift-related faulting and salt deposition and flow

The salt-rich Orpheus rift basin, part of the eastern North American (ENAM) rift system, formed during the Late Triassic to Early Jurassic prior to opening of the Atlantic Ocean. Using a dense grid of 2D seismic-reflection lines, data from nearby wells, and information from adjacent ENAM rift basins, we have established a tectonostratigraphic framework, identified key structural elements, and reconstructed the deformation history for the eastern part of the basin. Our work shows that a series of E-striking, S-dipping faults with normal separation bound the basin on the north. Deformation within the basin is complex with forced folds above deep-seated intrabasin faults, detachment folds, detached thrust faults, and salt diapirs. The synrift evaporite sequence consists of an older massive salt unit that underlies a younger unit with two distinct interfingering facies. Facies A, consisting of salt and interbedded sedimentary rocks (likely shales), developed near the border-fault system and its relay ramps. Facies B, consisting of massive salt with few interbedded sedimentary rocks, developed toward the basin center. The youngest synrift unit accumulated exclusively within minibasins near the northern border-fault system. Based on location, this youngest synrift unit likely consists of coarse-grained and poorly sorted alluvial-fan or talus-slope deposits shed from the footwall. All synrift units are intruded by igneous sheets likely associated with the Central Atlantic Magmatic Province and, thus, are mostly Late Triassic in age (or possibly older). The border-fault system profoundly affected deposition within the eastern Orpheus rift basin by providing pathways for clastic sediment input into the salt-rich basin. These depositional patterns subsequently influenced deformation associated with lateral salt flow during minibasin formation. In regions with interbedded salt, detachment folds and thrust faults developed, whereas salt walls and stocks developed in regions with more massive salt.

Zn-clays in the Kihabe and Nxuu prospects (Aha Hills, Botswana): A XRD and TEM study

Abstract Zinc clays are commonly found in oxidized Zn deposits and, even though they rarely represent the main target of the ore exploitation, they can be used as a proxy to restore the genetic conditions during ore-forming processes. This work sheds light on the micro- to nano-mineralogy and on the genesis of Zn-clays in the Kihabe and Nxuu prospects (located in the Aha Hills district, Northern Botswana), through an integrated XRD and TEM study of the mineralized facies occurring in the ore system. The Kihabe and Nxuu ores are hosted in a Neoproterozoic metamorphozed quartzwacke unconformably covered by the recent sedimentary rocks, also containing calcretes, of the Kalahari Group. In the analyzed samples, four distinct mineralogical facies have been recognized: (1) vanadate-calcrete facies, poor of Zn-clays; (2) low Zn-clay facies, characterized mostly by clays showing low Zn concentrations; (3) Zn-clay facies, containing proper Zn clay minerals; and (4) sulfide facies, devoid of Zn-clays. In all the facies detrital dioctahedral mica (muscovite and illite) is interstratified with smectite in the form of random (R0) to short-range ordered (R1) I/S, which locally shows significant Zn concentrations. In the sulfide facies kaolinite overgrowing onto mica packets has been detected. The low Zn-clay facies is dominated by Zn-bearing beidellite, with minor kaolinite and fraipontite. The Zn-clay facies consists mostly of a random (R0) interstratified clay between a 7 Å phase corresponding to fraipontite, and a 2:1 swelling clay component identifiable with the dioctahedral smectite, with minor sauconite. The micro- to nano-scale paragenetic study performed by TEM indicates that the above-mentioned clays formed through a multistage process, eventually ending with the genesis of Zn-bearing phyllosilicates assemblages. The main steps were: (1) alteration of detrital mica and dissolution of feldspar clasts, which led to the formation of epitaxial kaolinite and replacive beidellite; (2) fertilization of barren clays and formation of replacive to epitaxial fraipontite/smectite and of Zn-bearing mica, through input of Zn2+ deriving from sphalerite or willemite dissolution by mixed meteoric-hydrothermal fluids; (3) formation of low tetrahedral charge sauconite, either in pores or as replacement of K-feldspars under surficial hypersaline conditions, possibly also linked to the establishment of the arid climate in region. These processes provide insights into genesis of Zn-Pb-V ore deposits in northwest Botswana. Furthermore, the identification of a Zn-smectite species having a stevensite-like stoichiometry is valuable for future studies dealing with the systematics of clay minerals.

Benthic foraminifera as indicators of recent mixed turbidite-contourite sediment transport system in the Eastern Mediterranean upper continental slope, offshore Israel

Nile derived siliciclastic sediments are the main source of sedimentation along the Levant continental margins of the Mediterranean Sea. These sediments are transported along the southeastern Mediterranean coast via well-documented longshore currents, mainly operating along the shelf. However, the cross shelf component of sediment transport, responsible for conveying sediments toward the upper slope, is less known. To better understand the cross-shelf vs. the longshore component of sediment transport we studied a ~6 m long piston core (DOR280) sampled on the upper continental slope (280 m water depth) and analyzed benthic foraminiferal assemblages and their shell taphonomy alongside the particle size distribution and mineralogy of bulk sediments, to document both the source and the transport mechanism of those upper continental-slope sediments. The radiocarbon dating at the core-base is ~650 Cal. Yrs BP, indicating an exceptionally high average sedimentation rate of ~800 cm/kyr.DOR280 consists of two alternating distinct sedimentary facies: (1) laminated (L) intervals up to ~40 cm thick each and showing a high ratio of allochthonous vs. autochthonous (allo/auto) benthic foraminiferal species and a high percentage of broken shells, indicating contribution of transported sediments originating from mid-shelf habitats; (2) non-laminated (NL) intervals up to ~200 cm thick each and showing a low allo/auto ratio and low percentages of broken shells, indicating mostly in-situ hemipelagic deposition. The L intervals are interpreted here as turbidites. The sedimentation rates calculated only for the NL intervals are still exceptionally high, thus excluding hemipelagic sedimentation as the sole mechanism for the NL deposition. Therefore, a contour bottom current transported component is suggested here as a source of the NL sedimentation.We conclude that a mixed contourite-turbidite system actively prevails along the upper continental slope of the Levant coast, offshore Israel. The mid-shelf to upper slope sediment transport is nearly continuous and presents occasional turbidite events of average decadal reoccurrence time.

Morphological and textural analysis of basaltic pyroclasts (Atexcac maar, central Mexico): Implications for fragmentation and conduit processes

Atexcac is a maar volcano, which forms part of the monogenetic volcanic field of the Serdán-Oriental Basin, in the eastern sector of the Mexican Volcanic Belt. This volcanic landform was originated by a combination of phreatic, magmatic and phreatomagmatic explosive eruptions. During the formation of the distinct depositional facies, fluctuations in the water availability of the local aquifer, as well as in the magma flux, were probably responsible for the different mechanisms of magmatic and phreatomagmatic fragmentation and the production of the two main populations of fragments (breccia and cross-bedded deposits particles), whose morphological features, allow us to infer the dominant regime (brittle or ductile), fragmentation mechanism (magmatic or phreatomagmatic) and conditions of bubble growth dynamics and fragmentation processes during the ascent of magma through the conduit. We conclude that the breccia particles were derived from dominant magmatic explosions while the cross-bedded deposits particles are thought to be generated from explosive phreatomagmatic events. 3D imaging based on high-precision X-ray microtomography was used to determine the vesicularity of juvenile fragments of the Atexcac maar. Calculated vesicularity index, vesicle number density (VND) and vesicle morphology indicate important processes of coalescence of gas bubbles, during the ascent of the magma. VND's Atexcac clasts suggests vesicle mechanisms similar to medium-intensity eruptions, reported in the literature. The elongated and polylobular vesicle morphology of the Atexcac clasts reveals early acceleration of magma and subsequent coalescence events at most stages of gas bubble growth.

Paradoxical Cerebral Air Embolism after Cardiac Ablation in Williams-Beuren Syndrome: A Clinico-Pathological Correlation

Non-traumatic neurological deterioration is a medical emergency that may arise from diverse causes, to include cerebral infarction or intracranial hemorrhage, meningoencephalitis, seizure, hypoxic-ischemic or toxic/metabolic encephalopathy, poisoning, or drug intoxication. We describe the abrupt onset of neurological deterioration in a 53-year-old man with Williams-Beuren syndrome, a sporadically occurring genetic disorder caused by chromosomal microdeletion at 7q11.23. The clinical phenotype of Williams-Beuren syndrome is suggested by distinctive elfin facies, limited intellect, unique personality features, growth abnormalities, and endocrinopathies. The causative microdeletion of chromosomal material will frequently involve loss of the elastin gene, ELN, with resulting arteriopathy, supravalvular aortic stenosis, non-ischemic cardiopathy, and atrial fibrillation. Our patient sustained acute neurological decline within one month after undergoing a cardiac ablative procedure to convert atrial fibrillation to sinus rhythm. We present our findings in the setting of a clinico-pathological correlation, in which we reveal the cause of the abrupt neurological deterioration and discuss how our patient was affected by an uncommon stroke disorder.

Quantifying occurrence of deformation bands in sandstone as a function of structural and petrophysical factors and their impact on reservoir quality: an example from outcrop analog of Productive Series (Pliocene), South Caspian Basin

Deformation bands (DB) are known to influence porosity and permeability in sandstones. This study aims to predict the occurrence of DB and to quantify their impact on reservoir properties based on field measurements in the steeply dipping limb of a kilometer-scale fold in Yasamal Valley, western South Caspian Basin. An integrated approach of characterizing bands and their effect on reservoir properties included measurements of natural gamma radioactivity and permeability using portable tools, along with bed dip and the count of DB across distinct facies. A set of core analyses was performed on outcrop plugs with and without bands to estimate the alteration of rock properties at the pore scale. Interpretation of outcrop gamma-ray data indicates the absence of bands in Balakhany sandstones containing shale volume greater than 18% for unconsolidated and 32% for calcite-rich facies. A high amount of calcite cement appears to increase the number of DB. A poor, positive trend between bed dip and DB concentration was identified. We show that net to gross, defined as the thickness fraction of sandstone bound by mudstones, is among the parameters controlling the occurrence of bands. Samples containing a single DB show a 33% and 3% decrease in permeability and porosity, respectively, relative to the host rock. We reveal a new set of lithological and petrophysical factors influencing DB occurrence. This study offers a direct tool that can be applied in subsurface reservoir analogs to predict the occurrence and concentration of DB and estimate their influence on rock properties.

Mapping subaerial sand-gravel-cobble fluvial sediment facies using airborne lidar and machine learning

Substrate facies monitoring is critical for the understanding of fluvial geomorphologic and ecohydraulic patterns and processes. However, direct substrate measurement is time-consuming and subjected to data sparsity because of small sample, size, and limited data collections within an area of interest, which make it difficult to capture facies patterns. Most new experimental studies focus on mapping substrate based on median grain size of a specific grain size class using automatic or semiautomatic photosieving techniques. This study aimed to develop and apply a method to accurately predict size-mixture facies patterns on exposed riverbeds with minimal ground truth plots (100) using airborne lidar and machine learning. The selected testbed river was a 37.5-km stretch of the regulated lower Yuba River in California, USA, mapped at sub-meter resolution in 2017. First, we designed a grid-by-point grain size sampling method and binned grain sizes into representative mixtures, such as fine or large gravel, to assign subaerial facies labels. Second, we classified facies based on a multivariate cluster analysis. Third, we generated 15 lidar-derived topographic and spectral predictors. Six distinct size-mixture facies were identified from field data and a seventh, pure sand facies, from UAV data. A random forest predictive model with an 86% 10-fold cross-validation accuracy was applied to produce a facies map at the 1.54 m pixel scale. The detrended elevation was identified as the most important variable for predicting facies spatial patterning, followed by baseflow, wetted area proximity, and green lidar intensity. We conclude that machine learning combined with intensity lidar data is highly effective for distinguishing mixed classes of substrates. Ultimately, the new substrate mixture-binning approach also provides novel insights into the arrangement of river sediment facies patterns.

Gamma-ray log derivative and volatility attributes assist facies characterization in clastic sedimentary sequences for formulaic and machine learning analysis

Rate of change, second derivative and volatility of gamma-ray (GR) well-log curves provide useful indicators with which to characterize lithofacies in clastic sedimentary sequences. Rolling averages of these variables, as they change with depth, are also able to distinguish certain lithofacies features. These attributes make it possible to accurately distinguish key facies by using only gamma-ray data, both with formulaic calculations and employing machine-learning (ML) algorithms. This is useful in the many wellbores for which only basic logging suites are available. As well as enhancing lithofacies classification more generally using well-log variables, these GR attributes can be used to forecast facies in real time based on logging-while-drilling data. The application is demonstrated with simple formula using synthetic GR logs featuring common clastic lithofacies and their transitions. Seven widely used ML methods are each trained and validated with a synthetic GR curve (1450 data points) displaying six distinct facies. The ability of the ML model to distinguish those facies using seven GR attributes is compared and further tested with an independent GR data set (800 data points). The random forest algorithm outperforms the other ML models in this facies prediction task, achieving a mean absolute error of 0.25 (on a facies class range of 1 to 6) for the independent testing dataset. The results highlight the benefit of this technique in providing reliable facies analysis based only on GR data. Random forest, support vector classification and eXtreme Gradient Boost are the ML models that provide the most reliable facies classification from the GR attributes defined. Annotated confusion matrices assist in revealing the details of facies class prediction accuracy and precision achieved by the ML and models and classification formulas. Cited as: Wood, D.A. Gamma-ray log derivative and volatility attributes assist facies characterization in clastic sedimentary sequences for formulaic and machine learning analysis. Advances in Geo-Energy Research, 2022, 6(1): 69-85. https://doi.org/10.46690/ager.2022.01.06

Autogenic and allogenic controls on the temporal palaeographic evolution of the Himalayan foreland basin: Insights from facies analysis of the lower Siwalik succession, Kumaun Himalaya, India

AbstractThe lower Siwalik succession in the south‐central Kumaun Himalaya records Middle Miocene fluvial sedimentation in the Himalayan foreland basin, the largest foreland basin of the world. Detailed facies analysis reveals three distinct facies associations, one of which is sand dominated channel deposits, and the other two are mudstone‐sandstone, and mudstone dominated overbank deposits. The initial sedimentation in the region was in channels and frequently/extensively flooded overbank areas of a meandering/anastomosing river system. Activities along basement structures sometimes caused upheaval of the basin so that the streams got incised, and overbank areas rose up beyond the reach of flood waters. As a result, the fluvial sedimentation in these upland areas ceased, the sediments that had already deposited there were subjected to extensive pedogenesis, and occasionally reworked and redistributed by sheet flows and shallow channels. The channel pattern in the region gradually changed to braided type due to channel adjustments in response to rejuvenated tectonic activities and monsoon intensification in the hinterland. These factors caused increased influx of coarser sediments in the channels, which led to gradual steepening of the channel, and once the steepening crossed the threshold, the channel changed from meandering to braided type. Interpretation of our results is contrary to the general belief that Siwalik fluvial system changed from meandering streams to braided streams during the Middle Siwalik times, and the fluvial system in the studied part of the Siwalik basin underwent this change much earlier, during the sedimentation of Lower Siwalik.

Chemical and Isotopic Tracers for Characterization of the Groundwater in the Heterogeneous System: Case from Chichaoua-Imin’tanout (Morocco)

The geological and hydrogeological approach of the structure of the basin OuladBouSbaâ led to the definition of the geometry of the main aquifers. In general, the profiles show the complexity of the geological configuration. The filling of the depression of OuladBouSbaâ is from the Eo-Cretacian. At this level, the aquifer is recharged by direct water infiltration. The quaternary, Eocene, and Cenomanian-Turonian formations constitute the main aquifers. Horizontal as well as vertical heterogeneity lead to a higher diversification of aquifer characteristics. To define the origins and understand the groundwater flows in this complex zone, we used a multi-tracer approach with the analysis of major elements and the isotopes of δ2H and δ18O. The chemical composition is mainly governed by the interaction with the rock with low electrical conductivity except in areas around domestic landfills. Geochemical results analyzing groundwater in the Piper diagram show two distinct chemical facies: the sulfated calcium and magnesium, and the hyper-chloride calcium. The levels of δ18O range from −7.60 to −4.25 while those of δ2H vary between −53.07 and −27.03. Analyses of signature isotopes differentiate two groups. The first contains high levels of heavy isotopes (highest levels of δ2H and δ18O) having therefore been submitted to evaporation. The second with lower levels of δ2H and δ18O did not undergo evaporation. The first one belongs to the unconfined free aquifer while the second corresponds to the captive aquifer.

The Medial Offshore Record of Explosive Volcanism Along the Central to Eastern Aegean Volcanic Arc: 2. Tephra Ages and Volumes, Eruption Magnitudes and Marine Sedimentation Rate Variations

AbstractWe use the tephrostratigraphic framework along the Aegean Volcanic Arc established in Part 1 of this contribution to determine hemipelagic sedimentation rates, calculate new tephra ages, and constrain the minimum magnitudes of (sub)plinian eruptions of the last 200 kyrs. Hemipelagic sedimentation rates range from ∼0.5 cm/kyr up to ∼40 cm/kyr and vary laterally as well as over time. Interpolation between dated tephras yields an eruption age of ∼37 ka for the Firiplaka tephra, showing that explosive volcanism on Milos is ∼24 kyrs younger than previously thought. The four marine Nisyros tephras (N1 to N4) identified in Part 1 (including the Upper (N1) and Lower (N4) Pumice) have ages of ∼57 ka, ∼63 ka, ∼69 ka, and ∼76 ka, respectively. Eruption ages for the Yali‐1 and Yali‐2 tephras are ∼55 ka and ∼34 ka, respectively. The Yali‐2 tephra comprises two geochemically and laterally distinct marine facies. The southern facies is identical to the Yali‐2 fall deposit on land but the western facies has slightly less evolved glass compositions. Overall, erupted plinian and co‐ignimbrite fall tephra volumes range from <1 to 56 km3 (excluding possible caldera fillings and ignimbrite volumes), and 80% of the eruptions had magnitude 5.5 < M ≤ 7.2 (M = log(m)‐7; m = erupted magma mass in kg). Twenty percent of the tephras represent 3.2 < M < 5.5 eruptions. The long‐term average tephra magma mass flux through highly explosive eruptions of Santorini is estimated at ∼40 kg/s. The analogous data for the Kos‐Yali‐Nisyros volcanic complex is less‐well constrained but similar to Santorini.

The initiation of the Mesoproterozoic Bylot basins (Nunavut, Arctic Canada) as recorded in the Nyeboe Formation, Fury and Hecla Group

ABSTRACT Reconstructing Precambrian sedimentary environments over broad cratonic regions often relies on a combination of facies, structural, and provenance analyses. The Mesoproterozoic (ca. 1270–1090 Ma) Fury and Hecla Group, exposed on the Melville Peninsula and northern Baffin Island (Nunavut, Canada), is considered broadly correlative with strata of the Borden, Hunting–Aston, and Thule basins (together referred to as the Bylot basins). We present the results of updated mapping and the first high-resolution sedimentologic and stratigraphic analysis of the lowermost unit in the Fury and Hecla Group, the Nyeboe Formation. The Nyeboe Formation comprises five distinct facies associations: alluvial to fluvial, eolian-backshore, marine-intertidal, marine foreshore to shoreface, and marine-offshore. Thin mafic units are interbedded within the marine shoreface facies and are interpreted to represent volcanic flows. Lateral relationships between facies associations are complex, but generally, facies associations transition from a terrestrial environment at the base to a nearshore marine environment at the top, indicating a transgression. Considering both the along-strike and -dip thickness trends, the presence of mafic volcanic rock units, and possible syndepositional fault orientations crosscutting the deposits, we infer that the Fury and Hecla Group was deposited in a regime of crustal thinning in a half-graben setting. Our results from the Nyeboe Formation suggest a lithostratigraphic correlation to the Nauyat and Adams Sound formations of the Borden Basin. Therefore, this study establishes a geodynamic link between the opening of the Fury and Hecla Basin to the other Bylot basins and contributes to the understanding of a large late Mesoproterozoic intracontinental-basin system.

Multiproxy characterization of sedimentary facies in a submarine sulphide mine tailings dumping site and their environmental significance: The study case of Portmán Bay (SE Spain)

Mining activities are essential to our society, but ore extraction and treatment produce waste that must be stored in safe places without harm to the environment. For a long time, seafloor disposal has been viewed as a cheap option with barely visible impacts. In Portmán Bay, SE of Spain, large amounts of tailings from open pit sulphide mining were discharged directly into the coastal sea over 33 years, thus forming a massive deposit that completely infilled the bay and expanded seawards over the inner continental shelf. Here we present the first multiproxy physicochemical characterization of the submarine tailings in Portmán Bay, mostly by using non-destructive techniques, also including pre-dumping and post-dumping sediments. Eight distinct sedimentary facies, grouped in four stratigraphic units, have been thus identified in a set of up to 4.3 m long gravity cores totalling more than 60 m. Geogenic and anthropogenic geochemical proxies consistently allow differentiating pre-dumping sediments from tailings. Potentially toxic metals if made bioavailable can reach high concentrations in units including or formed exclusively by tailings (i.e. up to 3455, 2755 and 1007 mg kg−1 for Pb, As, and Zn, respectively). Some physical properties, such as magnetic susceptibility, are particularly useful as the tailings are rich in Fe-bearing minerals (>30% Fe in some layers). Estimated sedimentation rates show a strong gradient from proximal to distal locations, with rates in excess of 50 cm yr−1 to less than 1 cm yr−1. We ultimately document the history of the transformation of Portmán Bay from an almost natural state to a new condition after a long period of massive dumping of mine tailings. Our study provides guidance to further assessments in a context where the diversity of marine environments impacted by the disposal of mine waste is expected to grow in the near future.

Facies Analysis and Sedimentary Architecture of Hybrid Event Beds in Submarine Lobes: Insights from the Crocker Fan, NW Borneo, Malaysia

Hybrid event beds represent the combined effect of multiple geological processes, which result in complex depositional geometries and distinct facies distribution in marine environments. Previous work on hybrid event beds highlights the classification, origin, and types of hybrid facies. However, in the present study, we discuss the development of hybrid event beds in submarine lobes with an emphasis on the analysis of proximal to distal, frontal to lateral relationships and evolution during lobe progradation. Detailed geological fieldwork was carried out in the classical deep-marine Late Paleogene Crocker Fan to understand the relationship between the character of hybrid bed facies and lobe architecture. The results indicate that hybrid facies of massive or structureless sandstone with mud clasts, clean to muddy sand, and chaotic muddy sand with oversized sand patch alternations (H1–H3) are well developed in proximal to medial lobes, while distal lobes mainly contain parallel to cross-laminated clean to muddy hybrid facies (H3–H5). Furthermore, lateral lobes have less vertical thickness of hybrid beds than frontal lobes. The development of hybrid beds takes place in the lower part of the thickening upward sequence of lobe progradation, while lobe retrogradation contains hybrid facies intervals in the upper part of stratigraphy. Hence, the development of hybrid beds in submarine lobe systems has a significant impact on the characterization of heterogeneities in deep-marine petroleum reservoirs at sub-seismic levels.

Depositional Heterogeneities and Brittleness of Mudstone Lithofacies in the Marcellus Subgroup, Appalachian Basin, New York, U.S.A.

Organic-rich rocks of the Marcellus subgroup in the study area consist of a diverse suite of mudstone lithofacies that were deposited in distinct facies belts. Lithofacies in the succession range in composition from argillaceous to siliceous, calcareous, and carbonaceous mudstone. Heterogeneities in the succession occurs in the form of varying mineralogical composition, slightly bioturbated to highly bioturbated chaotic matrix, organic-rich and organic-lean laminae, scattered fossil shells in the matrix, and fossils acting as lamination planes. Lithofacies were deposited in three facies belts from the proximal to the distal zone of the depositional system. Bedded siliceous mudstone (BSM) facies occur in the proximal facies belt and consists of a high quartz content in addition to clay minerals and pyrite. In the medial part of the facies belt lies the laminated argillaceous mudstone (LAM), bedded calcareous mudstone (BCaM), and bedded carbonaceous mudstone (BCM). The size of detrital mineral grains in the lithofacies of the medial facies belt is larger than bedded argillaceous mudstone (BAM) of the distal facies belt, characterized by clay-rich matrix with occasional fossil shells and horizontally aligned fossils. Two types of horizontal traces and one type of fecal string characterize the proximal mud-stone facies, whereas only single horizontal trace fossil is found in the mudstones of the medial and distal facies belt. Parallel alignment of fossil shells and fossil lags in lithofacies indicate that bed-load transport was active periodically from the proximal source of the depositional system. Bioturbation has heavily affected all of the lithofacies and presence of mottled burrows as well as Devonian fauna indicate that oxic to dysoxic conditions prevailed during deposition. The deposition of this organic-rich mudstone succession through dynamic processes in an overall oxic to dysoxic environment is different from conventional anoxic depositional models interpreted for most of the organic rich black shales worldwide. Total organic content (TOC) varies from top to bottom in the succession and is highest in BCM facies. The brittleness index, calculated on the basis of mineralogy, allowed classification of the lithofacies into three distinct zones, i.e., a brittle zone, a less brittle zone, and a ductile zone with a general proximal to distal decrease in the brittle behavior due to a decrease in the size of the sediments.

Provenance of organic matter in an intracratonic rift basin: Insights from biomarker distribution in Palaeogene crude oils of Cambay Basin, western India

The biomarker distributions of crude oils are a valuable and complementary tool for understanding the provenance of source organic matter (OM) in intracratonic rift basins such as the Cambay Basin, India, which has five tectonic blocks from north to south. Distinctive biomarkers recorded in Cambay oils included tetrapolyprenoids, C29 28-nor-spergulane, diaryl isoprenoids and methylated chromans. Other diagnostic markers including oleanane, A-ring degraded hexanortriterpanes, bicadinanes and aromatic oleanoid/ursanoid triterpenoids, suggest substantial inputs to the OM from tropical angiosperm families. The biomarker distributions and various plots of the data, including a principal component analysis, indicate two distinct OM facies present in the basin. The depositional environment of the source OM that prevailed in the north blocks (NB) and south blocks (SB) of the basin are different, despite similar ages and geography. The results suggest that the NB oils were generated from mixed algal/microbial and higher plant-derived organic biomasses, deposited in suboxic to anoxic conditions, probably in a restricted marine or lacustrine environment. Contrarily, the oils of SB were generated from OM substantially derived from tropical lowland angiosperm rainforest trees, which were deposited under a fluvio-deltaic environment with a suboxic to oxic setting. The various maturity parameters reveal that northern oils are marginally less mature than the southern oils.

Ichnology of the Pliocene Casa Cruz Member (Moruga Formation), Trinidad, West Indies: Delineating depositional environments and environmental stresses

Integrated sedimentologic and ichnologic analysis of outcrops of the Casa Cruz Member (Moruga Formation, early to mid-Pliocene) yields distinct facies associations representing river- and wave-dominated deltaic deposits, and non-deltaic shoreface successions. This study demonstrates how river and wave processes interacted and their products were preserved across a small geographic area. It also shows evidence of the impact of these processes on infauna and epifauna. Wave-dominated delta front deposits comprise hummocky and swaley cross-stratified tempestites and wave-rippled sandstone beds. Event sedimentation and heightened water turbidity associated with frequent or intense storm events generated low intensity, sporadically distributed, reduced diversity trace fossil suites of the Rosselia ichnofacies. Wave-dominated prodelta deposits display diminutive structures ascribable to the Phycosiphon ichnofacies. Wave-dominated deposits transition into non-deltaic shoreface successions that contain densely bioturbated sediment with high diversity trace fossil suites belonging to the Cruziana ichnofacies. Common traces are Scolicia, Macaronichnus, Ophiomorpha, Thalassinoides, Planolites, Palaeophycus, and Skolithos. In contrast, river-dominated delta front and prodelta deposits are characterised by sandstone, siltstone and mudstone beds devoid of bioturbation. Syn-sedimentary deformational, current-generated structures, and organic particulates are abundant. Hyperpycnal discharge and concomitant increased sedimentation rates, freshets, and phytodetrital pulses linked to seasonal floods are possibly due to the presence of the Intertropical Convergence Zone at that time. This discharge generated extreme physical and chemical stress that inhibited benthic colonisation.