High-energy Environment Research Articles

Exploring geophysical and palynological proxies for paleoenvironmental reconstructions in the Miocene of western Amazonia (Solimões Formation, Brazil)

Western Amazonia underwent important landscape changes during the Miocene due to the Andean uplift. Vast wetlands developed during this period and prevailed until the late Miocene. The evolution of this environment has been studied on the basis of sedimentology and paleontology. Here, we explore geophysical proxies (Gamma Ray, Electric Resistivity and Spontaneous Potential) from cores of the Solimões Formation (Brazil) to support paleoenvironmental reconstructions and potentially validate pollen taxa as environmental indicators. We show a general tendency from geophysical profiles to increasing energies in the depositional settings in agreement with lithologies during the accumulation history of the Solimões Formation. Moreover, ACME zone of the fossil palm Mauritia (Mauritiidites franciscoi) is associated with low energy environments, ACME of the extinct palm Grimsdalea magnaclavata is associated with similar environments but of a transitional nature, oscillating between high and low energies, and ACMEs of fossil Poaceae (Monoporopollenites annulatus) are mostly associated with high-energy environments of more active fluvial dynamics. These three phases appear in order from early, early/middle and middle/late Miocene in the cores, which we believe reflects the climax development and subsequent demise of the wetland system. Additionally, marine surfaces are detectable in the geophysical logging what could help sampling strategies for future studies on cores aiming to detecte these marine events.

Do intraspecific life history patterns follow interspecific predictions? A test using latitudinal variation in ringed seals

AbstractMammals adapted to unpredictable and low‐energy environments often evolve a “bet‐hedging” life history strategy characterized by less costly reproductive outputs over a longer and slower‐growing life. In contrast, species adapted to more predictable (i.e., low variation) and higher energy environments may evolve greater fecundity over a shorter and faster‐growing life. We tested whether this known interspecific pattern also occurs within a species. We compared life history traits of the ringed seal (Pusa hispida) in the Canadian High Arctic to those closer to the southern limit of the species' circumpolar distribution. We found that northern seals grew slower than southern seals (Brody growth coefficient), achieved a greater asymptotic body weight (82 and 69 kg vs. 74 and 54 kg female and male, respectively), reached sexual maturity later (6.1 years vs. 4.5 years), had lower fecundity (1.8 years vs. 1.3 years interbirth interval), longer average lifespan (5 years vs. 3 years median age), and greater movements (1,269 vs. 681 km). Mating systems also likely differed with northern seals showing morphological evidence of a promiscuous mating system with potential sperm competition as indicated by greater relative testes size. The northern region was also characterized by more unpredictable environmental timing of seasonal events, such as spring sea ice breakup. Life history variation between the intraspecific groups of seals appears to agree with interspecific patterns and provides a better understanding of how species' life history parameters shift in concert with environmental conditions.

Depositional Environment and Diagenesis processes impact on the carbonate rock quality: a case study, southeastern of Iraq

Deposition environment and diagenesis processes are very important factors which affect and control the reservoir properties. The carbonate Mishrif Formation has been selected as a carbonate reservoir in selected wells from southeastern Iraq to understand the influence of the Deposition environment and diagenesis processes on the carbonate reservoir. A core examination of thin sections, shows that Mishrif Formation comprises of six depositional environments, these are: deep marine, lagoon, rudist biostrome, back shoal, and shallow open marine. These environments have effect by many diagenetic processes, including dolomitization, dissolution, micritization, cementation, recrystallization and Stylolite, some of these processes have improved the reservoir properties of the Mishrif reservoir, these are: dissolution, dolomitization and the stylolization. The others diagenetic processes have negative influence on the Petrophysical properties, such as cementation, compaction, and recrystallization processes, which damage the porosity and decrease the pore size. The reservoir properties are controlled by deposition environment, where lagoon environment is mostly compact with low porosity, shoal environment reflects a high energy and grain-supported environment and has good reservoir potential, deep-marine environments consist of mudstone to wackestone, which represents low energy level with low porosity and represents the non-reservoir environment.

Drag and inertia forces on a branched coral colony of Acropora palmata

Some branched corals are capable of surviving in wave/current exposed areas with moderate to high energy environments, where their branches, their geometry and the global and rigid structure of their colonies play an important role for wave damping due to bottom friction and wave energy dissipation due to turbulence. Constant frictional coefficients are commonly used within wave propagation models to consider reef roughness but without accounting for the type of coral species, its topological characteristics, form and distribution over the reef surface. In this sense, this study aims to improve the understanding of near-bed hydrodynamics in coral reefs by examining the drag and inertia coefficients of branched coral colonies of Acropora palmata. Laboratory tests were carried out considering steady and oscillatory flow conditions. In-line forces, flow velocities and water surface elevations over 3-D models of Acropora palmata were recorded for both a single coral colony and a group of corals. Additionally, the validated open source CFD (Computational Fluid Dynamics) toolbox OpenFOAM® was used to simulate the hydrodynamic performance over the coral structures for a wide range of wave heights and periods. The results show that under steady flow conditions, the drag coefficient (CD) can be well represented as a function of the Reynolds number (Re) by means of a power law equation as CD= aReb+c. Also, under oscillatory flow conditions, it was found that the inertia force (FM) dominates over the drag component (FD), explaining more than 84% of the total force exerted on the coral structure. Prediction formulas were developed and validated with the laboratory test to predict the resistance coefficients (drag and inertia) as function of Keulegan and Carpenter number (KC) for the CD (R2=0.89) and CM (R2=0.92). The CFD modeling showed to be an alternative for the modeling of the hydrodynamic forces exerted over complex coral shapes and to analyze the fluid–structure interaction around natural structures.

Evaluating the effects of morphology and orientation on feeding in atrypide brachiopods using 3-D printed models

The brachiopod order Atrypida was one of the most diverse and abundant clades of marine organisms across North America during the Silurian and Devonian. Atrypide brachiopods were active sessile suspension feeders that used their lophophores to capture food particles from the water. Within the subfamily Variatrypinae, there are two end-member morphotypes associated with either high or low energy environments. It has further been suggested shape played an important role in enhancing feeding efficiency. The first morphotype is shield-shaped, weakly convex, and associated with low-energy systems. The second morphotype is globose and associated with high-energy systems. Furthermore, both pedicle-attached and liberosessile life orientations have been suggested for atrypides, based on both fossil material and biomechanical experiments. Any change in orientation could radically affect feeding efficiency. Our study uses biomechanical experiments on morphologically accurate 3-D printed atrypide models to evaluate the effects of shape and orientation on feeding current strength in the shield-shaped and globose morphotypes. We used 3-D scanning and printing to construct two morphologically accurate gaping models of the end-member shapes. The models included simulated body tissue, a flexible scale lophophore and valves of accurate thickness. A recirculating flume tank and dye streams were used to visualize ambient flow within the models in multiple pedicle-attached and pedicle-absent orientations to flow. During the trials the shield shape produced better ambient flow than the globose shape in pedicle-attached orientations. Further, pedicle-attached orientations produced better ambient flow than pedicle-absent orientations. Our results suggest that, shield-shaped atrypides benefited from enhanced ambient flow, while globose atrypides would have relied more on active pumping when in a pedicle attached orientation. As well, the results suggest a pedicle was required to orient atrypides for efficient feeding.

Determination of the Depositional Environment of Outcrop Section at Odoro Ikpe South Eastern Nigeria Using Pebble Morphometry

The depositional Environment of Odoro -Ikpe, South East Nigeria was interpreted using pebble morphometry and sieve analysis. A field observation, sieve analysis and pebble morphometric analysis was carried out on the area which comprises of conglomerate, pebbles, sand stone and intercalation of shale's and clay. The lithofacies observed are lateralitic layer, pebbly sand, alternating layers of sand and conglomerates and layers of massive sand stone. The graphic mean and skewness of the grain size analysis shows that the sediments are very coarse which indicates a high energy environment. Graphic standard deviation gives a clue that the sediment were very poorly sorted, which is indicative of a fluvial deposit with high energy , while kurtosis result revealed very coarse sediment deposits. This implies that the particles were not transported very far. Pebble analysis shows the geometric forms and this was deduced from the plot on shape measurement triangle. The shape is compact bladed which is common with river deposits. The bivarate plot of mean diameter against standard deviation also indicated a fluvial environment as well as bivarate plots of co-efficient of flatness against sphericity and maximum projection sphericity against oblate, prolate index which comprises of river and beach environment. All results showed or indicated that the environment of deposition was of river.

Sedimentary and diagenetic controls on reservoir quality of low-porosity and low-permeability sandstone reservoirs in Chang101, upper triassic Yanchang Formation in the Shanbei area, Ordos Basin, China

There are many reservoirs with low porosity and low permeability in the world, and many large oilfields have been found in these reservoirs. Unlike conventional reservoirs, the genesis of low-porosity and low-permeability reservoirs and the controls of relatively high-porosity and high-permeability zones are still unclear. This study takes the Chang101 reservoir sandstones of the Shanbei area in the Ordos Basin, China, a typical low-porosity and low-permeability, as an example. Chang101 sandstones are fine-grained to medium-grained, moderately to well sorted arkose and lithic arkose deposited in a delta plain environment. It is a typical low porosity and low permeability reservoir with an average porosity of 10.21% and an average permeability of 2.88 mD. Pore types mainly include primary intergranular pores and secondary dissolved pores. The main controls on the reservoirs are the sedimentary environment and diagenesis. The sedimentary environment determines the initial properties of the reservoir sandstones, including the material composition and texture that determine the primary porosity and permeability. Diagenesis further transforms the reservoir quality to develop heterogeneity in the porosity and permeability. The reservoir sandstones have undergone complex diagenetic processes and are currently in stage A of mesodiagenesis. Compaction accounts for the major reduction of the primary porosity of the sandstones. Different types of cementation have both positive and negative influences on reservoir quality. Carbonate cementation, quartz overgrowths and some authigenic clay cementation(i.e., I/S and illite) are major pore-filling components, that reduce the reservoir quality. An appropriate amount of chlorite resists compaction and prevents quartz overgrowth, but excessive chlorite coatings fill the pores and block the pore throats. The laumontite cement is not only resistant to compaction but also easily dissolved to form a large number of effective secondary pores. The dissolution of feldspar and rock fragments plays a role in contributing to connecting the isolated intergranular pores and increasing the secondary pores. Relatively high porosity and high permeability zones are deposited in high-energy environment, mainly delta plain distributary channel sandstones with more detrital quartz, fewer rock fragments and coarser grains than other sandstones, were deposited in high-energy environment. There is weaker compaction and less or no carbonate cement, with the preservation of the primary pores by chlorite coatings and an increase in the pores by the dissolution of laumontite cement.

Rapid Change of Foraminiferal Communities and Assemblages in the Setiu Estuary, Terengganu, Malaysia: Anthropogenic Drivers

AbstractIn November 2013, an artificial inlet was opened in the barrier island that separates the waters of the Setiu estuary-lagoon system of Terengganu, Malaysia, from the South China Sea. The inlet was opened to stabilize salinity and improve tidal flushing so that fish-farming could be expanded but, as a result, another inlet that was open in 2009 closed naturally by November 2015. These geomorphic changes caused salinity in the Setiu estuary to undergo significant increase from November 2013 to November 2015.To investigate the foraminiferal response to these salinity changes, 24 of 56 foraminiferal sampling stations occupied in 2009 were resampled in 2016. Salinity increased throughout the estuary from 2009 (mean 6.6, range 0–28.7) to 2016 (mean 33.3, range 23.3–34.8) and foraminiferal live communities and dead assemblages changed. Diversity of dead assemblages increased significantly (mean number of species/sample in 2009 = 10.9 versus 2016 = 25.8) as the result of transport of specimens of nearshore, neritic species into the estuary through the new inlet. Diversity of live populations increased slightly (2008 = 4.6 versus 2016 = 6.2). Dead assemblages and live populations dominated by agglutinated foraminifera in 2009 were co-dominated by calcareous hyaline foraminifera in 2016. Live calcareous porcelaneous foraminifera were rare in 2009 and 2016, but dead miliolids were more common and more widespread in 2016. Stations in higher energy environments immediately adjacent to the two different inlets of 2009 and 2016 were characterized by few live or dead foraminiferal tests. Changes in foraminiferal diversity, abundance, and distribution between the two sampling times of early June 2009 and late May 2016 were significant and took place within the 30-month interval between November 2013 (when the artificial inlet was opened) and May 2016 when samples were collected, but they most likely occurred over a shorter interval of time.

The catalytic activity of manganese dioxide supported on graphene promoting the electrochemical performance of lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have become a research hotspot due to their high energy density, environment friendliness and low-cost. But commercial applications are hampered by rapid capacity fading and low sulfur content. Herein, the composite of integrating manganese oxide on graphene was prepared by a facile redox reaction between potassium permanganate (KMnO4) and graphene in acidic aqueous solution to solve the problems of the Li-S batteries. X-ray Diffraction (XRD), Scanning Electron Microscope (SEM) and transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analysis show that sulfur was uniformity coated on G/MnO2 composite. TG indicated that the G/MnO2/S composites contained 76.56wt% active sulfur. The prepared cathode of G/MnO2/S composites exhibited excellent rate performance and cycle stability. At a high rate of 1C, its maximum discharge capacity reached 908mAhg−1 and its average capacity decreasing rate was only 0.105%/cycle when running over 500cycles. The interaction mechanism of MnO2 with polysulfides was investigated by adsorption tests and XPS analysis. The excellent electrochemical performance might be due to a combination of adsorption or catalytic properties of MnO2, and the conductivity network of graphene.

Dissecting the paleocontinental and paleoenvironmental dynamics of the great Ordovician biodiversification

AbstractThe Ordovician was a time of drastic biological and geological change. Previous work has suggested that there was a dramatic increase in global diversity during this time, but also has indicated that regional dynamics and dynamics in specific environments might have been different. Here, we contrast two paleocontinents that have different geological histories through the Ordovician, namely Laurentia and Baltica. The first was situated close to the equator throughout the whole Ordovician, while the latter has traversed tens of latitudes during the same time. We predict that Baltica, which was under long-term environmental change, would show greater average and interval-to-interval origination and extinction rates than Laurentia. In addition, we are interested in the role of the environment in which taxa originated, specifically, the patterns of onshore–offshore dynamics of diversification, where onshore and offshore areas represent high-energy and low-energy environments, respectively. Here, we predict that high-energy environments might be more conducive for originations.Our new analyses show that the global Ordovician spike in genus richness from the Dapingian to the Darriwilian Stage resulted from a very high origination rate at the Dapingian/Darriwilian boundary, while the extinction rate remained low. We found substantial interval-to-interval variation in the origination and extinction rates in Baltica and Laurentia, but the probabilities of origination and extinction are somewhat higher in Baltica than Laurentia. Onshore and offshore areas have largely indistinguishable origination and extinction rates, in contradiction to our predictions. The global spike in origination rates at the Dapingian/Darriwilian boundary is apparent in Baltica, Laurentia, and onshore and offshore areas, and abundant variability in diversification rates is apparent over other time intervals for these paleocontinents and paleoenvironments. This observation hints at global mechanisms for the spike in origination rates at the Dapingian/Darriwilian boundary but a domination of more regional and local mechanisms over other time intervals in the Ordovician.

Physical degradation and early diagenesis in foraminiferal tests after subaerial exposure in terrigenous-depleted beaches of Yucatan, Mexico

Degradation, diagenesis, and mineralogical changes in foraminiferal tests are recognized as mechanisms that control their preservation and destruction under the subaquatic/aerial conditions, commonly influenced by processes such as dissolution, abrasion, breakage, and mineralogical replacement. In this paper, we discuss test degradation and early diagenesis on the large benthic foraminifera Archaias angulatus from the Yucatan Peninsula beach sands, a region absent in surficial rivers and terrigenous input seawards. Two main sites of Yucatan beach were selected: the high-energy environment of the Gulf of Mexico coast (GOMC) and the low-wave-energy environment of the Mexican Caribbean coast (MCC). Test degradation in the GOMC and MCC is affected by chemical dissolution, bioerosion, and physical abrasion. Among other factors, we found the effects of the bacterial microboring and dissolution by lowering pH in seawater (i.e., nearshore springs discharging seaward), as well as longshore currents and waves, depending on the prevailing conditions before transport and resuspension of the tests landwards. The observed degradation features in the tests are wall loss, chamberlet exposure, surface pits, and highly abraded edges. However, we explain the presence of pristine A. angulatus tests in the MCC beach through its association with Thalassia seagrass patches. Very low Mg/Ca ratios were found, which suggest the early diagenesis in the foraminiferal tests and the absence of recrystallized processes. Rare-earth element analyses suggest reduced authigenic precipitation of Mn–Fe coatings in the tests, and the absence of freshwater discharges or terrigenous inputs in the beach sands.

Intraspecific Variation through Ontogeny in Late Cretaceous Ammonites

This project assesses intraspecific variation through the ontogeny of the ammonite Scaphites whitfieldiCobban, 1951, from the Upper Cretaceous of the U.S. Western Interior. Our sample consists of 103 dorsoventral cross sections from nine localities that represent two lithofacies (shale and siltstone). We measured four shell parameters (ww/dm, ww/wh, uw/ dm, and WER) to describe the ontogenetic changes in shell morphology. We investigated the variation at three growth stages: immediately after hatching (dm = 1 mm), the neanoconch (dm = 4 mm), and the submature stage (defined as at or near the base of the mature hooklike body chamber). In general, the shell becomes more discoidal through ontogeny with a narrower umbilicus and a more compressed whorl section. The results of the univariate analysis indicate that the variation is statistically significantly higher in the neanoconch than in either the hatchling or submature stage. This pattern is also apparent in the multivariate analysis in which the disparity increases markedly from the hatchling to the neanoconch and then decreases again at the submature stage. These results are consistent with the hypothesis that the neanoconch represents a transition in the life history of the animal to a more demersal mode of life followed by a canalization of morphology toward maturity. However, because the neanic transition occurs over a range of sizes, it is possible that some individuals may have already undergone these changes at dm = 4 mm, whereas others may not have, thus inflating the degree of variation. To resolve this issue in the future, it is critical to examine each ontogenetic trajectory individually to pinpoint the exact size at which the morphological changes occur. We also compared the values of ww/dm, ww/wh, uw/dm, and WER of the three growth stages for the sample from siltstone versus the sample from shale. The comparison reveals that the specimens from siltstone occupy lower regions of the morphospace, implying that these specimens are generally more compressed than those from shale. This difference may be related to selection pressures for improved hydrodynamic efficiency in the higher energy environment represented by siltstone.

Coral-like reduced graphene oxide/tungsten sulfide hybrid as a cathode host of high performance lithium-sulfur battery

Lithium-sulfur battery is one of the most promising next-generation energy storage devices owing to its high energy density and environment friendliness. However, the low electronic conductivity of sulfur and the high solubility of intermediates in electrolyte are the challenges for its wide applications. To address these issues, we report a novel architecture, a coral-like reduced graphene oxide/tungsten sulfide hybrid, as host for sulfur cathode. This hybrid is fabricated by in-situ growing tungsten sulfide nanoflakes on a reduced graphene oxide aerogel, providing not only a 3D network for electronic conductivity, but also a large surface area to entrap chemically the intermediates. As expected, the sulfur cathode based on this hybrid support exhibits a high discharge capacity of 1531 mAh g−1 at 0.05 C and a high sulfur utilization of 91.6%. Even at a high rate of 1 C, an initial specific capacity of 883 mAh g−1 and an extremely low capacity-decay rate of 0.086% per cycle are still achieved. The ability of the resulting hybrid to entrap the intermediates is confirmed by combining physical characterization and theoretical calculations.

Organic matter content and type variation in the sequence stratigraphic context of the Upper Devonian New Albany Shale, Illinois Basin

Organic matter quantity and type are important parameters in conventional source rock evaluation and unconventional shale oil/gas reservoir characterization. Understanding the stratigraphic distribution of organic matter content and type in black shale successions is critical for identifying potentially productive intervals, because organic matter can adsorb large amounts of oil and gas. Detailed examination of total organic carbon content, organic petrographic composition, and high-resolution (8 cm spacing) geochemical proxies in a sequence stratigraphic framework were conducted on an early mature (0.55% Ro) New Albany Shale core of the Illinois Basin to study the influence of relative sea-level fluctuations on paleoproductivity, clastic supply, bottom-water redox conditions, and their combined control on total organic carbon distribution pattern and organic maceral variation.Marine organic matter including amorphous organic matter and alginite (mainly derived from Tasmanites cysts) is the dominant organic matter in the New Albany Shale. Terrestrial organic matter accounts for <10% of total organic matter. Within a sequence stratigraphic context, total organic carbon content increases in transgressive systems tracts, reaches a maximum before the maximum flooding surface, and shows relatively low values in highstand systems tracts. Comparatively, low total organic carbon contents at maximum flooding surfaces reflect a combination of low sedimentation rates, elevated bottom-water oxygenation, and high biogenic silica dilution.Stratigraphically, amorphous organic matter content increases in transgressive systems tracts, reaches a maximum near the maximum flooding surface, and decreases in highstand systems tracts. Enrichment of broken Tasmanites cysts and their detrital infills are an indicator of high-energy environments and could possibly indicate lowstand systems tracts. The stratigraphic distribution of organic matter content and type may result in cyclic stratigraphic variations of hydrocarbon generation potential and oil saturation, and influence the development of secondary organic pores when the New Albany Shale is within the oil and gas windows.

Granulometric and Sedimentologic Study of Beach Sediments, Lagos, Southwestern Nigeria

Grain size analysis and sedimentology of beach sediments in Lagos, southwestern Nigeria have been studied. Ten fresh beach sediment samples were randomly collected at a depth of 25 cm - 40 cm along Lagos and Badagry axis. The sediments were analyzed by wet sieving method. Ternary diagrams indicate that the beach sediment is silty. The graphic mean ranges from 1.02ф (medium grained) to 2.21ф (fine grained) with an average of 1.61ф (medium grained). The preponderance of medium grained sediments and lack of coarse sands suggest moderate to high energy conditions of deposition. Graphic standard deviation ranges from 0.01ф - 0.81ф (very well sorted to moderately well sorted), with an average of 0.52ф (moderately well sorted). This is probably due to rapid back and forth flow of the depositing medium. Inclusive graphic skewness ranges from -0.38 to 1.41 (strongly coarse skewed to strongly fine skewed), with an average of 0.41 (strongly fine skewed). The graphic kurtosis values are between 0.44 and 1.37, which indicates very platykurtic to leptokurtic; with an average of 0.78 (platykurtic). This variation suggests that part of the sediment achieved its sorting elsewhere in high-energy environment. Histograms of the sediments exhibit both unimodal and bimodal trends. The arrangement is dominantly asymmetrical with varying modal class, which could be attributed to variation in the energy of the transporting medium. Bivariate plots (simple skewness vs. standard deviation and mean size vs. standard deviation) show the samples plotting mainly in the river sand zone, which suggests that the sediments were initially river sediments before reworking to the present site; other parameters that discriminate between river channel deposits, overbank deposits and overbank-pool deposits show the beach sediments plotting in the river channel zone. Linear discriminant functions analysis indicates a shallow marine beach environment in agitated water, with inputs from aeolian source. The Passega C-M diagram suggests suspension and rolling as the mode of deposition.

Diatoms in the Early Valdai (Weichselian) sediments in Lake Ladoga basin

The pioneer diatom study of the Early Weichselian (Valdai) sediments in Lake Ladoga basin was performed. The specifics of the diatom assemblages (co-occurrence of ecologically incompatible taxa, poor species diversity, low diatom concentration and selective preservation) suggest that during the Early Weichselian time intense erosion of previously deposited marine Eemian (Mikulino) sediments prevailed, which resulted in re-deposition of marine diatoms. The sedimentation took place in high-energy environments unfavorable for diatom accumulation and preservation.

COASTAL WAVE MODELING FOR JETTY REHABILITATION AT COOS BAY, OREGON

Coos Bay Inlet, located on the Pacific coast of southwestern Oregon, is protected by dual jetties constructed in 1928. Because the inlet is exposing to high energy environment, both north and south jetties have deteriorated since the initial construction. Aging, erosion of foundation, lack of effective maintenance, and channel dredging in the past have accelerated the jetty deterioration. To ensure navigation safety, the U.S. Army Corps of Engineers is presently investigating the rehabilitation and redesign of jetties. This paper is focused on numerical storm wave modeling of the existing jetties to provide input forcing information to physical model and redesign of jetties.

Fosildiagénesis del anélido Rotularia spirulaea (Lamarck, 1818) (Polychaeta, Serpulidae) en el Eoceno del dominio pirenaico occidental

The presence of the fossil polychaete Rotularia spirulaea (Lamarck, 1818) in Eocene deposits (middle Lutecian – upper Bartonian and (?) Priabonian) belonging to the western Pyrenean Domain is verified. In this paper, a fossildiagenetic study has been carried out. Fossils from three areas, corresponding to diff erent depositional settings, have been analysed. In area 1, sediments of the Ardanatz Sandstone and Ilundain Marls formations [Pamplona Basin and adjoining areas (Navarre)], were sampled. Here, the specimens of R. spirulaea were not substantially affected by taphonomic reworking and the original microstructure of the carbonate tube is preserved. The test consists of a thick external shell layer, composed of three zones in succession, and another extremely thin inner shell layer. The lumen of the tube is filled in by fine-grained sediment and/or calcitic cement. In area 2 , which includes the town of Anderatz and several outcrops of the Urbasa mountain range (Navarre), Urbasa-Andia Formation and overlying deposits, as well as in area 3 , located on the upper part of the calciclastic fl ysch of Punta Galea (Biscay), fossils are included in sediments deposited in high-energy environments. In this case, the microstructure of R. spirulaea tube is not completely recognized due to intense, early diagenetic silicifi cation aff ecting the tests. The lumen is filled in with fragments of foraminifera and calcareous algae, quartz-feldespathic sediment and cemented by calcite. Therefore, in zones 2 and 3 the fossildiagenetic processes are substantially different from those recognized in zone 1.

Relação entre biofábrica e porosidade, coquinas da Formação Morro do Chaves (Barremiano/Aptiano), Bacia de Sergipe-Alagoas, NE-Brasil

As coquinas da Formação Morro do Chaves são consideradas rochas análogas aos reservatórios da fase rifte do pré-sal nas bacias de Campos e Santos, são compostas principalmente por conchas e fragmentos de bivalves revelando uma grande variedade da biofábrica e do sistema poroso que possibilita o uso da tafonomia para relacionar o ambiente deposicional dessas rochas com as características de porosidade. Os principais atributos tafonômicos abordados nesse trabalho são: orientação das valvas; empacotamento das conchas; granulometria e seleção; e grau de fragmentação, abrasão e arredondamento. A interpretação dos dados teve como objetivo agrupar as amostras com relação às diferentes características tafonômicas e a porosidade, tendo como ferramenta auxiliar o método de redes neurais artificias (Self-Organization Map — SOM). A análise dos dados resultou em três agrupamentos: A1 com altos valores de porosidade (entre 11 e 23%), cujas características tafonômicas revelam ambientes de alta energia; A2 com valores intermediários de porosidade (entre 7 e 15%), cujas características tafonômicas indicam um ambiente de transição entre alta e baixa energia; por fim, o grupo A3 com menores valores de porosidade (entre 0 e 7%), cuja tafonomia indica ambientes de baixa energia. Como resultado final, as características tafonômicas revelam a energia do ambiente deposicional e é possível associar ambientes de alta energia com as altas porosidades para as coquinas da Formação Morro do Chaves.

Composition and diagenesis of Neoproterozoic Guaritas Group sandstones in the Minas do Camaquã fault zone, Camaquã Basin

Geological structures influence the formation and evolution of sedimentary rocks. The Minas do Camaquã fault zone is a primary structure of the Camaquã Basin, controlling the uplift of the ore-bearing units of the Santa Bárbara Group. To the south of the Camaquã River, the fault zone deforms alluvial and eolian sequences attributed either to the Santa Bárbara or Guaritas groups. In this study, a facies and petrographic composition and diagenetic analysis are presented to understand the evolution of the fault zone. Facies analysis was accomplished using high-resolution orthophoto mosaics and field surveys. Seven sedimentary facies were defined, grouped into three facies associations. Facies associations correspond to a succession of climate-influenced depositional environments. The transition from humid to dry conditions occurs from a fluvial (facies association 1) to eolian environments (facies association 2). These deposits are overlaid at the top by a high energy environment deposits characterized by amalgamated gravelly and sandy bodies, corresponding to an alluvial environment (facies association 3). Despite a small compositional variation, sandstones present a continental block provenance which may be related to mixed anorogenic or orogenic provenance. Diagenetic features are similar in the three facies associations, suggesting the same burial history for the sedimentary deposits separated by the fault zone. The Minas do Camaquã fault zone in the study area is an intraformational structure, as analyzed sequences are attributed to the Guaritas Group, implying a relatively high degree of deformation late after its deposition.