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Three-dimensional to two-dimensional cross-strata transition in the lower Pleistocene Catanzaro tidal strait transgressive succession (southern Italy)
No full textSandstone tidal cross-strata are the predominant sedimentary feature of strait-fill stratigraphic successions. However, although widely described in numerous studies, tidal strait-fill two-dimensional and three-dimensional cross-strata have
rarely been reported to occur in discrete intervals which are laterally adjacent or vertically stacked, and the meaning of this stratigraphic architecture has not yet been fully investigated. Understanding of the processes responsible for changes
in the internal features of modern and ancient tidal bedforms is essential in order to predict lateral and vertical heterogeneities in analogous reservoir strata.
This facies-based study aims to interpret the three-dimensional to two-dimensional cross-strata transition observed in the lower Pleistocene mixed siliciclastic/bioclastic sandstone filling the Catanzaro Strait, in southern Italy, during a continuous phase of tectonically driven marine transgression. Tidal cross-strata
disappear in the uppermost interval of the studied succession, where mudstone strata prevail. This stratigraphic trend is interpreted as the evidence of an important change in the tidal strait hydrodynamics due to a phase of relative sea-level rise. At the beginning of the transgression, three-dimensional tidal dunes migrated throughout the ca 3 to 4 km wide and ca 30 km long, WNW–ESE-oriented Catanzaro Strait, due to strong tidal currents amplified through the seaway and flowing in semi-diurnal phase opposition. As the intermediate phase of transgression enlarged the seaway width, the tidal current strength decreased as tidal water exchange occurred over a larger cross-sectional area.
The progressive reduction of the bed shear stress modified three-dimensional tidal dunes into an extensive two-dimensional bedform field. At the end of the transgression, the further widening of the Catanzaro Strait into a ca 10 to 12 km
wide marine passageway changed the tidally dominated strait into a non-tidal open shelf. The results of this research suggest the presence of a ‘critical cross-sectional area’ in the narrowest strait-centre zone which controls the activation and deactivation of tidal current amplification along a marine seaway
Hierarchies of stratigraphic discontinuity surfaces in siliciclastic, carbonate and mixed siliciclastic‐bioclastic tidalites: Implications for fluid migration in reservoir quality assessment
No full textThe hierarchies of the stratigraphic discontinuity surfaces observed in ancient tidalites are qualitatively assessed, aiming to evaluate their role as possible preferential conduits for fluid migration. Three outcrop examples are presented from microtidal settings of southern Italy: (i) siliciclastic tidalites consisting of quartz-rich cross-stratified sandstones generated by strong two-directional tidal currents flowing along a tidal strait; (ii) carbonate tidalites, which accumulated in a Cretaceous lagoon and tidal flat where peritidal cycles formed vertically-stacked sequences of biopeloidal and fenestral packstones, wackestones and bindstones during repeated phases of Milankovitch-scale sea-level changes; (iii) mixed, siliciclastic-bioclastic tidalites, deposited in a bay and recording offshore-transition, to shoreface wave-dominated and tide-influenced environments. Observations made during this study suggest that fluid movement can be controlled by the presence of main bounding surfaces that occur at different dimensions, from large (hectometre)-scale, to medium (decametre)-scale, to smaller (metre)-scales. These surfaces produced either by depositional or erosional processes, are characterised by different features and geometries in siliciclastic, carbonate and mixed siliciclastic-bioclastic tidalites arguably revealing complex internal pathways for fluid flows. These results suggest that fluids propagating along the main discontinuities follow a dominant sub-horizontal direction of propagation, associated with minor sub-vertical movements, due to local internal surface geometries and interconnections and a general lack of fractures. This surface-based approach to the study of fluid-flow transmission within stratified rocks represents a conceptual attempt to predict fluid mobility and reservoir potential in tidalite-bearing siliciclastic, carbonate and mixed reservoir rocks.The hierarchies of the stratigraphic discontinuity surfaces observed in ancient tidalites are qualitatively assessed, aiming to evaluate their role as possible preferential conduits for fluid migration. Three outcrop examples are presented from microtidal settings of southern Italy: (i) siliciclastic tidalites accumulated in a strait; (ii) carbonate tidalites, accumulated in a lagoon and tidal flat; and (iii) mixed siliciclastic-bioclastic tidalites deposited in a bay.imag
An introduction for non-experts on using X-ray micro computed tomography as a tool for pore scale digital subsurface characterisation of siliciclastic materials
Full text linkThis paper presents an overview of using X-ray micro computed tomography (μCT) as a valuable tool for micro scale investigation of siliciclastic materials. When processed using digital image analysis (DIA), valuable quantitative data can be extracted from μCT 3D images. Subsurface reservoirs are of great importance to society as fluid-bearing formations, but also as storage reservoirs for carbon dioxide. μCT imaging has the capability to perform preliminary, highly detailed investigations of potential reservoirs. This approach has a range of benefits when compared to traditional 2D techniques, such as optical and scanning electron microscopy (SEM). Key advantages include the technique being non-destructive and capable of 3D and 4D visualisation. This facilitates rapid repeated digital measurements and experiments on microstructures. Digital samples can also be readily shared within the scientific community to replicate results and quickly launch new investigations. However, limitations still exist, posing challenges to the wider application of such a methodology. Such limitations include the identification of a representative elementary volume (REV), computational cost, and suitable processing of the output image data. Here, we highlight the value of using μCT and DIA, from our first experiences, to facilitate pore scale siliciclastic reservoir characterisation, but also highlight our perceived limitations and barriers to its much wider application. This paper introduces the key processing stages, opportunities and limitations of these techniques
Continental hydroclimate during the late Paleocene-early Eocene in the central Rockies: insights from sedimentological and geochemical records preserved in the greater Green River Basin, southwestern Wyoming, U.S.A.
No full textThe late Paleocene to early Eocene (LPEE, ∼59–50 Ma) greenhouse condition is the most recent geologic analogue for future climate change induced by increased atmospheric CO2 partial pressure (pCO2). Recognition of the hyperthermals and reconstruction of the continental hydroclimate and atmospheric pCO2 during this warm period are fundamental to the understanding of Earth’s surface responses to high atmospheric pCO2. Here we study paleosol morphology, bulk organic matter δ13Corg, leaf wax n-alkanes δ13Cn-alk and δDn-alk, and reconstruct mean annual precipitation (MAP) and atmospheric pCO2 from the fine-grained floodplain deposits in the greater Green River Basin, western U.S.A., to examine the hydroclimate evolution in the continental interior during the LPEE. The Paleocene-Eocene Thermal Maximum (PETM) was identified as a ∼4‰–5‰ negative carbon isotope excursion (CIE) in the bulk organic δ13Corg record and leaf wax n-alkanes δ13Cn-alk record, and a 30‰–50‰ increase in leaf wax n-alkanes δDn-alk record. Well-drained green paleosols and water-logged histosols dominated the floodplain deposition during the LPEE, and poorly drained red paleosols and carbonate-rich calcisols characterized the hyperthermal. Our reconstructed MAP is generally high (800–1,500 mm) during the LPEE and does not show significant change during the PETM. Our estimated atmospheric pCO2, by integrating bulk organic δ13Corg and paleosol carbonate δ13Cc values, is generally in the range of 600–900 ppm during the early Eocene, 1–2 times higher than the preindustrial level. These records suggest that the continental hydroclimate was generally humid and warm during the LPEE, and transient drying likely happened during the PETM
Miocene sedimentary sequences of the Sardinian Graben System as possible analogue for the Upper Jurassic Rogn Formation of the Norwegian Continental Shelf
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The city of Matera and its ‘Sassi’ (Italy): an opportunity to broadcast geology in the European Capital of Culture 2019
No full textMatera is an ancient city located at the top of Italy's high heel that has been anointed the European Capital of Culture 2019 and which, since 1993, has been included in the UNESCO World Heritage list. The close relationship between the urban development of the old town and its geology offers the unique opportunity to discover, in one shot, the cultural and geological history of a wonderful city that is often left out of the spotlight. As a corollary to this, the rupestrian old town of Matera and nearby areas are known also for having been the location of several movies (e.g. Bond 25 ‘No time to die’). Accordingly, media and tourists alike are showing a growing interest in Matera
Characterisation of submarine depression trails driven by upslope migrating cyclic steps: Insights from the Ceará Basin (Brazil). Marine and Petroleum Geology
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