Degree Of Bioturbation Research Articles

Benthic response to event deposition and environmental disturbance in a shoreface to subaqueous delta system: Ichnology of the Silurian-Devonian Furada Formation of Asturias, Spain

The Furada Formation of Asturias, Spain, represents a clastic shallow-marine unit deposited during the middle Silurian to the Early Devonian. This formation contains abundant evidence of event deposition and non-uniform distribution of bioturbation structures representing a benthic response to multiple stressors. The 170-m-thick succession was measured and described, and the ichnotaxa were recorded and associated with five sedimentary facies. Most shallow-marine environments are characterized by periodic events of environmental disturbance, mainly by episodic deposition, which may be recorded by a change in both the degree of bioturbation and ichnodiversity. The general depositional setting for this formation has been previously interpreted as a wave-dominated and storm-influenced shallow-marine environment. However, sedimentologic features described in this study, such as anomalous heterolithic and mudstone units, representing fluid mud layers, hyperpycnal flow deposits and plume collapse accumulations, suggest the influence of fluvial discharge, making it a more complex depositional setting. The proposed model comprises an inner sandy shoreface belt flanked seawards by a muddy subaqueous delta platform. The trace-fossil assemblages of this formation reflect environmental stress factors introduced by the interplay of storms and fluvial input (e.g., high sedimentation rate, fluctuating hydrodynamic energy, decreased substrate consolidation), resulting in reduced ichnodiversity and low abundance. From an ichnofacies perspective, the shoreface complex is characterized by the Cruziana Ichnofacies, whereas the subaqueous delta platform is represented by the Phycosiphon Ichnofacies. Integration of sedimentologic and ichnologic datasets allows for a refined depositional interpretation of the formation and greater understanding of the environmental diversity of wave-and river-influenced shallow-marine clastic systems, including the responses of the middle Paleozoic shallow-marine benthos to event sedimentation and environmental disturbance. This study is one of the first detailed documentations of the ichnology of subaqueous deltas.

SEDIMENTARY ENVIRONMENT AND REDOX CONDITIONS OF THE LOWER TRIASSIC OSAWA FORMATION IN THE SOUTHERN KITAKAMI TERRANE, JAPAN: INSIGHTS INTO OCEAN REDOX STRATIFICATION AND FAUNAL RECOVERY

ABSTRACT The sedimentary environments and redox conditions of the Lower Triassic Osawa Formation in the Southern Kitakami Terrane were reconstructed based on lithofacies, trace fossils, and other paleontological content. The muddy and sandy lithofacies of the Osawa Formation lack evidence of storm waves despite the presence of storm-induced turbidites, suggesting that the oldest deposits of the Osawa Formation were deposited in the proximal part of the outer shelf. In turn, water depth increased from the lower to upper part of the formation, ultimately recording the distal part of the outer shelf. In addition to sandy lithofacies caused by turbidity and traction currents, multiple sandy layers within the muddy lithofacies would have originated via supply into the prodelta setting from a fan delta system. Collapses of the delta front or river system floods could have generated hyperpycnal flows, resulting in abundant supplies of mud and organic matter. Trace fossil analyses revealed that the degree of bioturbation (ichnofabric indices) dramatically decreased as water-depth increased, indicating a steep oxic-dysoxic gradient along the onshore-offshore transect. Diagenetic pyrite framboids indicative of dysoxic/anoxic benthic conditions are abundant at greater water depths. Abundant pyrite framboids less than 6 μm in diameter suggest intermittent euxinicity. With an increase in global weathering, abundant sediment supply including organic matter from the fan delta system could have contributed to the development of ocean redox stratification, which appears to have impacted on the adaptation of both nektic and benthic animals of this area during the Early Triassic.

Marine bioturbation collapse during Early Jurassic deoxygenation: implications for post-extinction marine ecosystem functioning

Abstract Climate change is undermining the health and integrity of seafloor ecosystems, with declines in bioturbation expected to impact future ecosystem functioning. We explored changes in the nature and degree of bioturbation during Early Jurassic global warming and ocean deoxygenation. Understanding how these communities responded can help anticipate how bioturbation and ecosystem functioning might change over large spatial and temporal scales. Trace and body fossils from outcrop and core in the Cleveland Basin, UK show how healthy seafloor communities deteriorated through the Pliensbachian spinatum Zone, and macroinfaunal behaviour fluctuated across the Pliensbachian–Toarcian boundary coincident with mass extinction. Deoxygenation began above the stage boundary, and conditions deteriorated until bioturbation ceased completely (upper tenuicostatum Zone) for 0.6–2.5 Ma, longer than anywhere else in NW Tethys. The macroinfaunal record revealed new details on the progression and timing of deoxygenation, benthic recovery and fluctuations in the palaeoredox boundary. After the oceanic anoxic event infauna were fewer, smaller and did not mix sediments to depth, and while the depth and diversity of bioturbation had increased by the fibulatum Subzone ( bifrons Zone), the benthos had not recovered to late Pliensbachian pre-oceanic anoxic event state. Bioturbation collapse over large parts of the Northern Hemisphere probably contributed to regional-scale changes in ecosystem functioning.

BIOTURBATORS AS ECOSYSTEM ENGINEERS: ASSESSING CURRENT MODELS

ABSTRACT Bioturbating organisms can dramatically alter the physical, chemical, and hydrological properties of the sediment and promote or hinder microbial growth. They are a classic example of “ecosystem engineers” as they alter the availability of resources to other species. Multiple evolutionary hypotheses evoke bioturbation as a possible driver for historical ecological change. To test these hypotheses, researchers need reliable and reproducible methods for estimating the impact of bioturbation in ancient environments. Early efforts to record and compare this impact through geologic time focused on the degree of bioturbation (e.g., bioturbation indices), the depth of bioturbation (e.g., bioturbation depth), or the structure of the infaunal community (e.g., tiering, ecospace utilization). Models which combine several parameters (e.g., functional groups, tier, motility, sediment interaction style) have been proposed and applied across the geological timescale in recent years. Here, we review all models that characterize the impact of bioturbators on the sedimentary environment (i.e., ‘ecosystem engineering'), in both modern and fossil sediments, and propose several questions. What are the assumptions of each approach? Are the current models appropriate for the metrics they wish to measure? Are they robust and reproducible? Our review highlights the nature of the sedimentary environment as an important parameter when characterizing ecosystem engineering intensity and outlines considerations for a best-practice model to measure the impact of bioturbation in geological datasets.

Биогенные структуры терригенных отложений пограничного пермо-триасового интервала Южного Верхоянья, Республика Саха (Якутия)

The article describes biogenic structures (trace fossils and bioturbation) of clastic rocks within the Permian-Triassic boundary interval in the Tiryakh-Kobyumeh section (Southern Verkhoyanye). The section is built by interbedding marine sandstones and siltstones, and is associated with the Late Permian mass extinction event. Most of the strata contain a variety of biogenic structures. Different taxonomic compositions of trace fossils and high bioturbation of Permian rocks indicate dense habitation of the basin bottom. In the Lower Triassic deposits, diversity of trace fossils sharply decreases as well as the degree of bioturbation. In the lower part of the Nekuchan suite's Triassic deposits, an interval of horizontally stratified rocks without bioturbation interbedded with rocks bioturbated by stratum has been identified. The interval is overlaid with highly bioturbated deposits, which indicates a rapid recovery of biodiversity after the Permian mass extinction.

Foraminiferal stratigraphy and palaeoenvironment of a storm-influenced marine shelf: Upper Aptian – lower Albian, Svalbard, Arctic Norway

This study presents the first record of foraminifera from the Lower Cretaceous Carolinefjellet Formation on the Svalbard archipelago, Arctic Norway. The Svalbard foraminiferal assemblages are dominated by agglutinated forms with a subordinate calcareous component. Several stratigraphically important species are recognised, and four assemblage zones are established: 1) Serovaina loetterlei Zone of middle Aptian or lower, 2) Ammobaculites wenonahae Zone of the middle Aptian, 3) Gaudryina tailleuri Zone of the upper Aptian, 4) Verneuilinoides borealis Zone of the lower Albian. The assemblages exhibit characteristic Boreal features, previously reported from the North Slope of Alaska, Arctic Canada, Western Siberia, and older Mesozoic strata in Svalbard. The study therefore allows for Circum-Arctic correlations and the extensions of stratigraphic ranges of several Boreal species.The investigated succession exhibits a large-scale fining-upwards trend. The lower part (the Dalkjegla Member) is characterised by abundant hummocky cross-stratified and wave-ripple cross-laminated sandstone beds, indicating deposition on a storm-dominated shelf. The upper part (the Innkjegla Member) is dominated by mudstones containing strata-bound siderite concretions and carbonate-cemented sandstone beds, suggesting deposition under more quiescent, middle to outer shelf conditions. An upwards increase in trace fossil diversity and degree of bioturbation, in concert with expanding foraminiferal diversity and morphogroup variability, reflects a long-term deepening of the shelf with fluctuating oxygen conditions. In combination with XRF data, diversity statistics, and morphogroup application, the present study thus sheds a new light on higher frequency palaeoenvironmental changes in upper part of the Carolinefjellet Formation.

Recent Vertebrate and Invertebrate Burrows in Lowland and Mountain Fluvial Environments (SE Poland)

Over geological time, fauna inhabiting alluvial environment developed numerous traces of life, called bioturbation structures. However, present literature rarely offers comprehensive and comparative analyses of recent bioturbation structures between different types of environments. In this paper, the distribution of recent animal life traces in two different fluvial environments (lowland and mountain watercourse) was examined. An analysis of a set of vertical cross-sections of river bank enabled to determine physical and environmental features of the burrows, as well as degree of bioturbation in individual sections. Most of the burrows were assigned to their tracemakers and compared between two studied reaches in relation to the geomorphic zones of a stream channel. A mesocosm was conducted using glass terraria filled with river bank sediment and specimens of Lumbricus terrestris. The experiment confirmed field observations on the ability of earthworms to migrate into deep sediment layers along plant roots. The impact of floods on fauna survival was assessed on the basis of observations of large floods in 2016, 2018 and 2019. The abundance, distribution and activity of fauna in the sediment are mainly controlled by the occurrence of high and low flows (droughts and floods), which was particularly visible in lowland river reach.

Ichnofabrics and their roles in the modification of petrophysical properties: A case study of the Ordovician Majiagou Formation, northwest Henan Province, China

The carbonate rocks of the Ordovician Majiagou Formation from the northwestern part of Henan Province and their diverse trace fossils provide an outcrop analogue for bioturbated, low porosity and low permeability carbonate reservoirs. Three ichnofabrics can be defined based on the ichnotaxonomy, ichnodiversities, individual abundances and overall bioturbation indices. The Balanoglossites ichnofabric represented medium to relatively high-energy sedimentary environments such as intertidal zone and subtidal shoals in the carbonate platform. The Planolites ichnofabric suggested relatively low-energy, protected sedimentary environments such as lagoons in a restricted carbonate platform, but also occurs in the deeper-water depressions in the open carbonate platform. The Chondrites ichnofabric characterized low-energy and reduced oxygen conditions, with burrows penetrating below a shallow redox interface in deeper-water settings that include the distal slope as well as local depressions in the open carbonate platform. Our analysis suggests that the modifications of petrophysical parameters are controlled or influenced by the ichnofabric characteristics (burrow architecture, burrow cross-cutting relationship, degree of bioturbation and burrow connectivity), the permeability contrast between burrow-fills and matrix, and the dolomitization of burrow-fills. The micritic host sediments have negligible porosity and permeability. The bioturbated sediments have significant differences in fabric, texture, porosity and permeability. The burrow-fills are very commonly dolomitised. Each of the burrow-types can enhance reservoir properties, but the greatest differences are associated with the Balanoglossites ichnofabric, in which porosity and permeability can reach over 2% and 70 mD. Preliminary stratigraphic studies indicate that reservoir potential in the subsurface will be linked to an understanding of the distribution of shoal and intertidal facies as well as their associated Balanoglossites ichnofabrics.

Trace-fossil suites and composite ichnofabrics from meandering fluvial systems: The Oligocene Lower Freshwater Molasse of Switzerland

The Oligocene Lower Freshwater Molasse of Switzerland is host to spectacular outcrops of fluvial deposits. In distal areas of the Swiss Molasse Basin, deposits of a north-eastward draining meandering system are exposed. Combined sedimentologic and ichnologic observations in the Chli Sunnhalde and Roggwil quarries allow an improved understanding of animal-substrate interactions in deposits of meandering fluvial systems. Strata include meander-belt sandstone, levee sandstone and mudstone, crevasse-channel and splay sandstone, floodplain mudstone and sandstone, and paleosols. While the meander belt and the more proximal crevasse-channel deposits are typically unbioturbated, the more distal deposits show a clear biogenic overprint, with distal crevasse-channel, crevasse-splay, and floodplain deposits being intensely bioturbated.Simple grazing and locomotion trails (included in the Cochlichnus anguineus-Helminthoidichnites tenuis suite) were formed subaqueously in ponded areas of the floodplain. Meniscate burrows (Taenidium isp. suite) and root trace fossils occur along the margin of these floodplain water-bodies and at the top of crevasse-splay deposits. Some of the floodplain, crevasse-splay, and crevasse-channel deposits are pervasively bioturbated by crayfish burrows (Camborygma litonomos suite). Crevasse-splay deposits locally host escape trace fossils.Where cross-cutting relationships are apparent, a colonization sequence can be established as follows: the Cochlichnus anguineus-Helminthoidichnites tenuis suite is cross-cut by the Taenidium isp. suite, which in turn is cross-cut by the Camborygma litonomos suite and root trace fossils. Composite ichnofabrics are common in these meandering river deposits, recording progressive lowering of the water table in overbank subenvironments. Frequency of depositional events was a first-order control on degree of bioturbation. Position of the water table and degree of substrate consolidation exerted considerable influence over the types of trace fossils produced. Distinct bioturbation phases may result in the formation of different trace-fossil suites - representative of disparate ichnofacies - preserved on a single bedding plane. This study further supports the notion that meandering fluvial systems are characterized by trace-fossil suites belonging to the Scoyenia, Camborygma and/or Mermia ichnofacies.

Facies analysis and paleoenvironment of deposition of Cretaceous Jessu Formation, Yola Sub-basin, Northern Benue Trough, Nigeria

The Jessu Formation is one of the marine Cretaceous sediments in the Yola Sub-basin of the Northern Benue Trough, NE Nigeria. Lithofacies studies was carried out on the Jessu Formation exposed at Dukul and Cham streams outcrops, in order to identify facies, establish facies association and re-construct the paleodepositional environment. Ten (10) facies were identified on the bases of lithology, grain size, sedimentary structures and degree of bioturbation. These facies form four (4) facies associations, namely: the FA-1 (offshore marine), FA-2 (lower shoreface), FA-3 (middle shoreface) and FA-4 (upper shoreface). These facies associations form coarsening upward units from offshore marine to shoreface which suggests a shoreface deposit for the Jessu Formation. The coarsening upward facies succession indicated storm and wave influenced coastal system.

The effect of oil emplacement on quartz cementation in a deeply buried sandstone reservoir

Quartz is an important, porosity-occluding cement in sandstone reservoirs that have been subjected to elevated temperature (>80°C to 100°C) for a substantial period of time. The effect of oil emplacement on quartz cementation in reservoir sandstones is controversial; some studies have concluded that early oil emplacement can inhibit quartz cementation, leading to the preservation of porosity, whereas other studies have concluded that quartz cementation appears largely unaffected by oil emplacement. Here we have studied shallow marine, Upper Jurassic sandstones from Ula field, Norwegian North Sea, with reservoir temperatures of approximately 150°C, to determine whether oil emplacement had a significant impact on diagenesis with particular attention to quartz cementation. Following sedimentological description of cores, samples above and below the oil–water contact have been collected, adjacent to core-analysis plug points. These samples then underwent a series of studies, including petrographic point counting with a transmitted light microscope, scanning electron microscopy (SEM), backscattered electron microscopy, SEM-cathodoluminescence microscopy, and fluid-inclusion studies. These data were integrated with routine core-analysis and petrophysical log data. Density and resistivity log data have been used to determine the precise oil saturation of each sample studied. The distributions of all potential controls on porosity and permeability, such as grain size, sorting, matrix clay content, and degree of bioturbation, the presence of grain coatings and dolomite cement, and the amount of quartz cement, have been assessed. The presence of primary oil inclusions within quartz cement shows that oil ingress into the Ula reservoir commenced prior to the onset of quartz cementation. Very fine–grained, matrix-rich, bioturbated, microquartz-cemented sandstones have uniformly low quartz-cement contents irrespective of oil saturation. Medium-grained, graded, matrix-poor, microquartz-poor sandstones have quartz cement ranging from 1% to greater than 17%, associated with core porosities of approximately 22% and 7%, respectively. Higher oil saturations equate to higher porosities and permeabilities in the medium-grained, graded, matrix-poor, microquartz-poor sandstones, which cannot be explained by any control other than the amount of quartz cement as a function of pore fluid type. Oil emplacement therefore appears to have inhibited quartz cementation at high oil saturations and can be viewed as an important control on reservoir quality. The significance of this study is that the presence of oil in a sandstone reservoir at the time that quartz cement was growing can have a considerable impact on reservoir quality. Models that seek to predict quartz cement and reservoir quality in sandstones need to account for the timing of oil emplacement compared with other diagenetic processes.

ICHNOLOGICAL EVIDENCE FOR ENDOBENTHIC RESPONSE TO THE K–PG EVENT, NEW JERSEY, U.S.A.

Degree of bioturbation, Thalassinoides isp. morphology, and diameters were compared across the Cretaceous–Paleogene (K–Pg) boundary interval at three localities along the New Jersey coastal plain. Within this regionally extensive ichnoassemblage, mean burrow diameters decrease abruptly by 26–29% (n = 1767) at the base of the Main Fossiliferous Layer (MFL) or laterally equivalent horizons. The base of the MFL has been previously interpreted as the K–Pg boundary based on the last occurrence of Cretaceous marine reptiles, birds, and ammonites, as well as iridium anomalies and associated shocked quartz. Along with the mean, the maximum and minimum burrow diameters exhibit a negative shift, which indicates that the changes are the result of a directional reduction in diameter, rather than an artifact of decreased variance. As a proxy for the size of the tracemaker, a change in burrow diameter indicates a decrease in thalassinid crustacean body size. We interpret this shift as dwarfing within the endobenthic community as detrital food sources became scarce following the mass extinction. Despite the difference in size, there is no change in framework geometry. Ichnofabric indices generally increase up-section at each site across the K–Pg chronostratigraphic boundary, indicating a regional reduction in sedimentation rate, which is supported by a gradual increase in glauconite maturity. Overall, the ichnological evidence at these localities suggests that a prolonged period of negative feedback followed a short-term positive endobenthic response across the K–Pg boundary.

A Re-evaluation of the Depositional Environments and Sedimentary Facies of Middle Miocene Paralic Deposits (Agbada Formation), Ewan and Oloye Fields, Northwestern Niger Delta

This study analyses depositional environments and facies of the middle Miocene (Agbada Formation), northwestern Niger delta, based on cores and well log data, and incorporating ichonological data, that has led to a revision and re-evaluation of the facies within the study area. Log motif analysis, calibrated by lithology descriptions based on core photos, was used to define log facies associations and to identify stacking patterns and key surfaces. Six main wireline log facies associations have been recognized using gamma ray log motifs calibrated with core. Within the cored interval two lithofacies associations have also been identified, based on composition, colour, sedimentary structures, and ichnofabric. They are: slope channel sand and shoreface sequences. The interpreted depositional facies model suggests an extensive development of marine dominated slope channel fill and shoreface deposits in the northwestern part of the delta. This suggests that in the studied area, the coastal barrier complex contains a large amount of sand that was originally deposited in river mouth bars, but was laterally removed by longshore current and re-deposited on the shoreline margin and basin ward through developed of canyons on the slope which serves as feeders and conducts for slope and basin fans. The descriptive framework for the ichnofabrics analysis is based on bioturbation index (degree of bioturbation), burrow size, burrow frequency and ichonological diversity. Six ichnofabrics are recognized within the core namely: Planolites-Teichnichnus, Planolites-Phoebichnus, Planolites, Planolites-Thalassinoides, Teichichnus-PhoebichnusPlanolites and Palaeophycus-Planolites ichnofabrics. Observed tiering patterns are both simple and complex, which may reflect gradual aggradation or degradation of the substrate leading to overprinting as a stable ichnofauna structure develops. This type of tiering arrangement indicates a stable environment. The ichnofabrics are named after the dominant trace observed. Sedimentological analyses indicated that the depositional environments range from inner shelf to offshore.

Stratigraphic variation in ichnofabrics at the “Shackleton Site” (IODP Site U1385) on the Iberian Margin: Paleoenvironmental implications

Ichnofabric analysis was conducted on cores from Site U1385 (IODP Expedition 339) to interpret paleoenvironmental conditions at the southwest margin of the Iberian Peninsula during the Pleistocene. Site U1385 provides an important record for the study of orbital and suborbital-scale climate variability, changes related to ocean/atmosphere dynamics, and affected environmental parameters. A detailed study of the ichnofabric characterization is presented, focusing on the types of ichnofabrics, relative abundance, amount of bioturbation, grouping, ichnofabric succession/transitions and vertical distribution. Seven ichnofabrics were differentiated; green mottled ichnofabric, Planolites ichnofabric, Taenidium &Planolites ichnofabric, Thalassinoides-like &Palaeophycus ichnofabric, Planolites &Thalassinoides/Thalassinoides-like ichnofabric, Zoophycos ichnofabric, and Chondrites ichnofabric. They exhibit significant differences in terms of ichnofabric features as well as in their stratigraphic distribution. The most abundant ichnofabrics are Planolites &Thalassinoides/Thalassinoides-like ichnofabric and green mottled ichnofabrics, with a dominance of the middle tier ichnofabrics. The degree of bioturbation is moderate, with a mean BI around 3, but showing a clear bimodal distribution: one group of intervals is characterized by high bioturbation (BI=6), while another displays low-moderate BI values (BI=1–2). In general, ichnofabric features confirm generally good environmental conditions (oxic environment and high food availability) for the macrobenthic tracemaker community, especially favorable in the uppermost part of the sediment. A complete ichnofabric succession, from deep to shallow tier ichnofabrics, is commonly registered (i.e., Zoophycos ichnofabric or Chondrites ichnofabric to Planolites &Thalassinoides/Thalassinoides-like ichnofabric, and then either to green mottled ichnofabric, or to Planolites ichnofabric and then green mottled ichnofabric). However, there are some intervals where an incomplete succession between deep and shallow ichnofabrics is observed (i.e., Chondrites ichnofabric to green mottled ichnofabric or Zoophycos ichnofabric to green mottled ichnofabric), indicating relevant modifications of environmental parameters such as oxygen or food supply. Types of ichnofabrics and the Bioturbation Index show significant short-term changes through the studied core. Such variations are probably correlated to millennial-scale climatic perturbations, such as glacial terminations and related phenomena (Heinrich events, ice-rafting events, etc.), or long-term cyclic patterns related to orbital climate variability. The patterns could be tied to a significant change in the climate system, such as the one associated with the middle Pleistocene transition.

Carbon dioxide sealing capacity: Textural or compositional controls? A case study from the Oklahoma Panhandle

One of the challenges confronting carbon dioxide capture and sequestration (CCS) in geologic media over extended periods of time is determining the caprock sealing capacity. If the pressure of supercritical carbon dioxide injected in the repository overcomes the caprock sealing capacity, leaking of may enter other porous formations, compromising the storage formation, or even may go back to the atmosphere, and thus the process of sequestration becomes futile. Carbon dioxide sealing capacity is controlled by two groups of parameters: (1) texture (e.g., the pore-throat size, distribution, geometry, and sorting; median grain size, porosity, degree of bioturbation, specific surface area, preferred orientation of matrix clay minerals, orientation, and aspect of ratio of organic particles) and (2) composition (mineralogical content, proportion of soft, deformable mineral grains to rigid grains, organic matter content, carbonate content, silt content, cementation, ductility, compaction, and ash content). The primary goal of this study was to investigate several parameters listed above and to estimate their respective contributions to sealing capacity to better understand its role in shale and carbonates. To assess the effect of textural and compositional properties on maximum retention column height, we collected 30 representative core samples from caprock formations in three counties (Cimarron, Texas, and Beaver) in the Oklahoma Panhandle. The study area was chosen because it hosts three depleted gas fields with a storage capacity of more than 35 million bbl and is situated at a crossroad leading to some significant stationary sources from North Texas, South Kansas, and northern Oklahoma. We used mercury injection porosimetry, scanning electron microscopy (SEM), Sedigraph energy dispersive spectra (EDS), x-ray diffraction (XRD), Brunauer–Emmett–Teller-specific surface area, and total organic carbon (TOC) measurements to assess textural and compositional properties of collected samples. The range of column height for the samples used in this study is between 0.2 and 1358 m (0.66 and 4455 ft). The average column height is 351 m (1152 ft). The depth interval approximately 1400 m (4593 ft) could reach relatively high values of column height, up to 1200 m (3937 ft). The above-mentioned interval is composed of mainly Cherokee and Morrowan Formations (shale seals). Principal component analysis (PCA) was carried out to infer the possible relationships between textural and compositional parameters. Generally, composition of our samples (shales vs. carbonates and sandstones) indicates a relatively stronger control on caprock sealing capacity, although individual mineral makeup of shale samples seems not correlated with retention column heights. In the same time, many textural parameters play a significant role in determining the sealing capacity of carbonate caprocks.

Unbioturbated sediments on a muddy shelf: Hypoxia or simply reduced oxygen saturation?

Abstract X-radiographs of sediment box cores acquired from the western Gulf of Mexico reveal limited bioturbation in sediment deposited in bathymetries greater than 35 m. Between 15 and 35 m, sediments are thoroughly bioturbated with averaged bioturbation indices (for all beds in a core) between 2.1 and 5.6, and trace diversities between 2 and 9 distinct burrow forms. Below 35 m water depth, box cores exhibit trace diversities of 1–3, and core-averaged bioturbation indices range between 0.3 and 3.6. There is an overall decrease in trace diversity and bioturbation indices in the offshore direction. Cross-shore ichnological trends are compared to dissolved oxygen contents of bottom waters. Above 35 m, dissolved oxygen (DO) contents show pronounced variability, ranging from 100% DO saturation through to hypoxia ( The data reveal a direct correlation between: a) the density of infauna and the diversity and density of burrows, and b) DO of bottom water. The degree of bioturbation is significantly reduced in waters that are oxic, but below 80% DO saturation. Based on these observations, we suggest that it is inappropriate to link low bioturbation intensities and diversities to hypoxia (

Water Distribution in the Montney Tight Gas Play of the Western Canadian Sedimentary Basin: Significance for Resource Evaluation

SummaryWater distribution in unconventional gas reservoirs is a key parameter that influences many aspects of resource exploitation including selecting geographic areas for multiwell development programs, identifying target zones for horizontal wells, calculating reserves, estimating permeability, and understanding variability in gas and water production. Insights on water distribution in the Montney tight gas play of northeast British Columbia and northwest Alberta were gained by integrating reliable water-saturation measurements from full-diameter core samples with other core, well-log, and geologic data. Water distribution in the studied Montney section was found to be related to stratigraphic architecture and rock fabric (defined by degree of bioturbation), and is interpreted to have been influenced by the displacement efficiency of mobile formation water updip through tight Montney siltstones during hydrocarbon charging. Low-gradient clinoform units with few shaly zones in the Lower Montney section enabled efficient water displacement and led to water contents at or close to irreducible water saturation. Higher-gradient clinoform units with greater facies variation and common shaly zones in the Upper Montney allowed less-efficient water displacement, and significant volumes of mobile water were retained in parts of the section. Water saturation varies widely and directly influences gas effective permeability. A simple method for determining gas effective permeability from well logs was developed on the basis of empirical relationships derived from the core and log data set. Gas-effective permeability logs generated by this method help to identify target zones with superior reservoir quality for exploitation by use of horizontal multistage-fracturing technology. A Pickett plot with gas-effective-permeability lines was found to be a useful tool for a log-based comparison of Montney rock quality by stratigraphic zone or geographic area. This work shows that understanding water distribution and its influence on gas effective permeability leads to the improved delineation of "sweet spots" for resource development in unconventional gas plays.

Sedimentology and ichnology of Bathonian (Middle Jurassic) ore-bearing clays at Gnaszyn, Kraków- Silesia Homocline, Poland

ABSTRACT Leonowicz, P. 2012. Sedimentology and ichnology of Bathonian (Middle Jurassic) ore-bearing clays at Gnaszyn, Krakow-Silesia Homocline, Poland. Acta Geologica Polonica, 62 (3), 281-296. Warszawa. The lithology, sedimentary structures and trace fossil association from the Bathonian organic-rich mudstones from Krakow-Silesia Homocline (SW Poland) are described and a preliminary interpretation of the palaeoenvironment is presented. The ore-bearing clays exposed in the Gnaszyn clay-pit are developed as dark grey claysilt deposits with a few horizons of sideritic concretions. Sedimentological analysis has revealed that these deposits originated in the offshore part of a marine basin, below the fair weather wave base. Relict parallel lamination suggests that the predominant mechanism of deposition was quiet settling from suspension. However, locally preserved storm deposits indicate that the sea bottom was affected by offshore flows, deriving coarser material from the nearshore area. The degree of bioturbation is high but the diversity of the trace-fossil association is low. It consists mainly of Chondrites, Trichichnus, pyritized burrows and less common Palaeophycus. Other traces, including Thalassinoides, Planolites, Taenidium and some undetermined burrows, occur mainly in the lower part of the succession. This ichnoassociation combines features of distal Cruziana and Zoophycos ichnofacies, suggesting poor oxygenation of the bottom sediment. Temporary improvements in bottom oxygenation, linked with more intense mixing of water during major storms, resulted in the more diverse trace fossil suite that is found in some intervals of the succession.

El Niño–Southern Oscillation variability from the Late Cretaceous Marca Shale of California

Changes in the possible behavior of El Nino–Southern Oscillation (ENSO) with global warming have provoked interest in records of ENSO from past “greenhouse” climate states. The latest Cretaceous laminated Marca Shale of California permits a seasonal-scale reconstruction of water column flux events and hence interannual paleoclimate variability. The annual flux cycle resembles that of the modern Gulf of California with diatoms characteristic of spring upwelling blooms followed by silt and clay, and is consistent with the existence of a paleo–North American Monsoon that brought input of terrigenous sediment during summer storms and precipitation runoff. Variation is also indicated in the extent of water column oxygenation by differences in lamina preservation. Time series analysis of interannual variability in terrigenous sediment and diatom flux and in the degree of bioturbation indicates strong periodicities in the quasi-biennial (2.1–2.8 yr) and low-frequency (4.1–6.3 yr) bands both characteristic of ENSO forcing, as well as decadal frequencies. This evidence for robust Late Cretaceous ENSO variability does not support the theory of a “permanent El Nino,” in the sense of a continual El Nino–like state, in periods of warmer climate.

Mudrock sequence stratigraphy: A multi-proxy (sedimentological, paleobiological and geochemical) approach, Devonian Appalachian Basin

Delineation of stratigraphic sequences and their component systems tracts in mudrock-dominated facies is generally difficult due to the relatively homogenous, fine-grained nature of the strata. In this study, we apply a multi-proxy analytical approach to a thick Devonian mudrock-dominated succession through detailed analysis of sedimentologic, paleobiologic, and geochemical data through 600 m of mudrock-rich facies. Varied combinations of proxies prove to be most useful in delineating sequence development in anoxic-, dysoxic-, and oxic-dominated mudrock settings, and in mixed mudrock–carbonate and mixed mudrock–sandstone successions. These interpretations are tested against an established sequence stratigraphic framework for 11 Middle to Upper Devonian (mid-Eifelian to lower Famennian) sequences in the Appalachian Basin. The sequences presented here further detail and refine global Devonian T–R cycles Id to IIe of the well known Johnson, Sandberg and Klapper sea-level curve. The usefulness of proxies in delineating depositional sequences and systems tracts varies dependent on depositional, paleoceanographic, paleoecologic, and early diagenetic conditions. Those proxies that show a range of variations in specific settings, such as grain size, degree of bioturbation, and concentrations of TOC and elements/elemental ratios (e.g., CaCO 3, Al, Ti, Mg, Sc, Si, Mo, Ni, V; Si/Al and Ti/Al) may help delineate depositional dynamics related to redox conditions, condensation, dilution, and clastic, biologic, and/or authigenic sediment sources. In fine-grained, anoxic-dominated facies, interpreted to represent basinal settings, sequences and systems tracts are best delineated by anoxic-related proxies TOC and Mo. In intermediate, dysoxic-dominated settings, TOC, Mo, bioturbation, and Al remain effective indicators of sequence development. In relatively oxygenated, mudrock-rich and carbonate poor sequences, bioturbation may function as the most effective proxy for recognizing systems tracts. For mixed fine-grained siliciclastic–carbonate successions, concentration and type of CaCO 3 (e.g., benthic macroskeletal, pelagic styliolinid/dacryoconarid, and micritic/calcisilt) are useful in identifying position within cycles. In more proximal, carbonate-poor successions, fine- and coarse-grained fractions become increasingly differentiated; these can be distinguished by relatively high Si/Al ratios (Si/Al ≥ ca. 5). Elemental ratios indicative of coarser clastic input (e.g., Si/Al, Zr/Al and Ti/Al) are applicable to identifying position with a sequence, but they may also be affected by input from eolian, volcanogenic, or biogenic sources. In addition, fluxes of siliciclastic, carbonate, and TOC sediment types may dilute the concentration of the others. Multiple lines of evidence should be examined in interpreting relative depth and position within a sequence.