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  • Articles  (318)
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  • 1
    Publication Date: 2018-03-06
    Description: The collision of bathymetric features with modern convergent margins has been investigated with the full range of tools used in geosciences. Hence, a comprehensive picture exists of the characteristic effects of collision events on the evolution of convergent margins. In contrast, much less studies documented past collisions of bathymetric features with convergent margins, as colliding features were generally lost to subduction. The arc-trench system of southern Central America provides modern and past textbook examples of active margin interaction with incoming bathymetric reliefs. Here we propose a synthesis which combines basin and terrane analysis of the forearc of northern Costa Rica and takes up the challenge of documenting past episodes of plateau accretion to the active margin. As illustrated in modern examples, our study shows that kilometric uplift of the overriding plate and termination of the volcanic arc activity are the most profound effects of colliding/accreting oceanic plateaus. Kilometric uplift of the forearc is documented by short-lived (~ 3 m.y.) occurrences of shallow-water deposits in an overall deep-water forearc record. These shallow deposits contain material reworked from underlying sedimentary and basement lithologies. The development of spatial gaps in arc volcanism is deduced from the transition from arc-derived turbidites to pelagic sediments. Eventually, end of the collision event is evidenced by the subsidence of the whole forearc to deep-water environments. Basin subsidence is accompanied or followed by renewed volcanic arc activity and coeval arc-derived sedimentation, which may occur 1–7 m.y. after plateau collision. These past episodes of plateau accretion are archetypal for the following reasons: a) they may be studied in outcrop, whereas most of the modern collisions of plateaus largely occur underwater; b) no tectonic or metamorphic imprint has significantly complicated the forearc geological record; c) the colliding feature and the sedimentary response to its collision are both preserved in the forearc geology; d) they may be used as analogues for any setting where a bathymetric feature is suspected to have caused rapid forearc uplift and cessation of the volcanic arc activity. This article is protected by copyright. All rights reserved.
    Print ISSN: 0950-091X
    Electronic ISSN: 1365-2117
    Topics: Geosciences
    Published by Wiley-Blackwell
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  • 2
    Publication Date: 2018-03-06
    Description: Kilometre-scale geobodies of diagenetic origin have been documented for the first time in a high-resolution 3D seismic survey of the Upper Cretaceous chalks of the Danish Central Graben, North Sea Basin. Based on detailed geochemical, petrographic and petrophysical analyses it is demonstrated that the geobodies are of an open-system diagenetic origin caused by ascending basin fluids guided by faults and stratigraphic heterogeneities. Increased amounts of porosity-occluding cementation, contact cement and/or high-density/-velocity minerals caused an impedance contrast that can be mapped in seismic data, and represent a hitherto unrecognized, third type of heterogeneity in the chalk deposits in addition to the well-known sedimentological and structural features. The distribution of the diagenetic geobodies is controlled by porosity/permeability contrasts of stratigraphic origin, such as hardgrounds associated with formation tops, and the feeder fault systems. One of these, the Top Campanian Unconformity at the top of the Gorm Formation, is particularly effective, and created a basin-wide barrier separating low-porosity chalk below from high-porosity chalk above (a regional porosity marker, RPM). It is in particular in this upper high-porosity unit (Tor and Ekofisk formations) that the diagenetic geobodies occur, delineated by ‘Stratigraphy Cross-cutting Reflectors’ (SCRs) of which 8 different types have been distinguished. The geobodies have been interpreted as the result of: 1) escaping pore-fluids due to top seal failure, followed by local mechanical compaction of high-porous chalks, paired with 2) ascension of basinal diagenetic fluids along fault systems that locally triggered cementation of calcite and dolomite within the chalk, causing increased contact cements and/or reducing porosity. The migration pathway of the fluids is marked by the SCRs, which are the outlines of high-density bodies of chalk nested in highly porous chalks. This study thus provides new insights into the 3D relationship between fault systems, fluid migration and diagenesis in chalks, and has important applications for basin modeling and reservoir characterization. This article is protected by copyright. All rights reserved.
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    Electronic ISSN: 1365-2117
    Topics: Geosciences
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  • 3
    Publication Date: 2018-02-22
    Description: We used detrital zircon U/Pb geochronology and apatite (U–Th–Sm)/He thermochronology to better constrain depositional ages and sedimentation rates for the Pliocene Productive Series in Azerbaijan. U/Pb analysis of 1379 detrital zircon grains and (U–Th–Sm)/He analysis of 57 apatite grains – from Kirmaky Valley and Yasamal Valley onshore sections, Absheron Peninsula – yielded two distinct sub-populations: ‘young’ Neogene grains; and ‘old’ Mesozoic, Paleozoic and Proterozoic/Archean grains. The large numbers of Neogene age grains (around 10% of all grain ages) provided a new absolute age constraint on the maximum depositional age of the Lower Productive Series of 4.0 Myr. These ‘young’ Neogene zircon grains most likely originated from volcanic ash falls sourced from the Lesser Caucasus or Talesh Mountains. In this paper we propose a timescale scenario using the maximum depositional age of the Productive Series from detrital zircon grain U/Pb constraints. Potential consequences and limitations of using apatite (U–Th–Sm)/He dating method in estimating maximum depositional ages are also discussed. These new age constraints for the Lower Productive series gave much faster sedimentation rates than previously estimated: 1.3 km/Myr in the South Caspian Basin margin outcrops and up to 3.9 km/Myr in the basin centre. The sedimentation rates are one of the highest in comparison to other sedimentary basins and coeval to global increase in sedimentation rates 2-4Myr. The older group of detrital zircon grains constitutes the majority of grains in all sample sets (~80%). These older ages are inferred to reflect the provenance of the Productive Series sediment. This sediment is interpreted to have been derived from the Proterozoic and Archean crystalline basement rocks and Phanerozoic cover of the East European Craton, Proterozoic/Paleozoic rocks of the Ural Mountains, and Mesozoic sedimentary rocks of the Greater Caucasus. This sediment was likely supplied from northerly sourced drainage that emptied into the South Caspian Basin. This article is protected by copyright. All rights reserved.
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    Electronic ISSN: 1365-2117
    Topics: Geosciences
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  • 4
    Publication Date: 2018-02-20
    Description: The control of slide blocks on slope depositional systems is investigated in a high-quality 3D seismic volume from the Espírito Santo Basin, SE Brazil. Seismic interpretation and statistical methods were used to understand the effect of differential compaction on strata proximal to the headwall of a blocky mass-transport deposit (MTD), where blocks are large and undisturbed (remnant), and in the distal part of this same deposit. The distal part contains smaller rafted blocks that moved and deformed with the MTD. Upon their emplacement, the positive topographic relief of blocks created a rugged seafloor, confining sediment pathways and creating accommodation space for slope sediment. In parallel, competent blocks resisted compaction more than the surrounding debrite matrix during early burial. This resulted in differential compaction between competent blocks and soft flanking strata, in a process that was able to maintain a rugged seafloor for 〉5 Ma after burial. Around the largest blocks, a cluster of striations associated with a submarine channel bypassed these obstructions on the slope and, as a result, reflects important deflection by blocks and compaction-related folds that were obstructing turbidite flows. Log-log graphs were made to compare the width and height of different stratigraphic elements; blocks, depocentres, and channels. There is a strong correlation between the sizes of each element, but with each subsequent stage (block – depocentre – channel) displaying marked reductions in height. Blocky MTDs found on passive margins across the globe are likely to experience similar effects during early burial to those documented in this work. This article is protected by copyright. All rights reserved.
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    Electronic ISSN: 1365-2117
    Topics: Geosciences
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  • 5
    Publication Date: 2018-02-12
    Description: Since the last century, several geological and geophysical studies have been developed in the Santiago Basin to understand its morphology and tectonic evolution. However, some uncertainties regarding sedimentary fill properties and possible density anomalies below the sediments/basement boundary remain. Considering that this is an area densely populated with more than 6 million inhabitants in a highly active seismotectonic environment, the physical properties of the Santiago Basin are important to study the geological and structural evolution of the Andean fore-arc and to characterize its seismic response and related seismic hazard. Two and three-dimensional gravimetric models were developed, based on a database of 797 compiled and 883 newly acquired gravity stations. To produce a well-constrained basement elevation model, a review of 499 wells and 30 transient electromagnetic soundings were used, which contribute with basement depth or minimum sedimentary thickness information. For the 2-D modeling, a total of 49 gravimetric profiles were processed considering a homogeneous density contrast and independent regional trends. A strong positive gravity anomaly was observed in the center of the basin, which complicated the modeling process but was carefully addressed with the available constrains. The resulting basement elevation models show complex basement geometry with, at least, eight recognizable depocenters with maximum sedimentary infill of ~ 500 m. The 3-D density models show alignments in the basement that correlates well with important intrusive units of the Cenozoic and Mesozoic. Along with interpreted fault zones westwards and eastwards of the basin, the observations suggest a structural control of Santiago basin geometry, where recent deformation associated with the Andean contractional deformation front and old structures developed during the Cenozoic extension are superimposed to the variability of river erosion/deposition processes. This article is protected by copyright. All rights reserved.
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    Electronic ISSN: 1365-2117
    Topics: Geosciences
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  • 6
    Publication Date: 2018-01-28
    Description: When we model fluvial sedimentation and the resultant alluvial stratigraphy, we typically focus on the effects of local parameters (e.g., sediment flux, water discharge, grain size) and the effects of regional changes in boundary conditions applied in the source region (i.e., climate, tectonics) and at the shoreline (i.e., sea level). In recent years this viewpoint has been codified into the ‘source-to-sink’ paradigm, wherein major shifts in sediment flux, grain-size fining trends, channel-stacking patterns, floodplain deposition, and larger stratigraphic systems tracts are interpreted in terms of (1) tectonic and climatic signals originating in the hinterland that propagate downstream; and (2) eustatic fluctuation, which affects the position of the shoreline and dictates the generation of accommodation. Within this paradigm, eustasy represents the sole means by which downstream processes may affect terrestrial depositional systems. Here, we detail three experimental cases in which coastal rivers are strongly influenced by offshore and slope transport systems via the clinoform geometries typical of prograding sedimentary bodies. These examples illustrate an underdeveloped, but potentially important ‘sink-to-source’ influence on the evolution of fluvial-deltaic systems. The experiments illustrate the effects of (1) submarine hyperpycnal flows, (2) submarine delta front failure events, and (3) deformable substrates within prodelta and offshore settings. These submarine processes generate (1) erosional knickpoints in coastal rivers, (2) increased river channel occupancy times, (3) rapid rates of shoreline movement, and (4) localized zones of significant offshore sediment accumulation. Ramifications for coastal plain and deltaic stratigraphic patterns include changes in the hierarchy of scour surfaces, fluvial sand-body geometries, reconstruction of sea-level variability, and large-scale stratal geometries, all of which are linked to the identification and interpretation of sequences and systems tracts. This article is protected by copyright. All rights reserved.
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    Electronic ISSN: 1365-2117
    Topics: Geosciences
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  • 7
    Publication Date: 2018-01-25
    Description: This paper proposes a new methodology to improve the location of potential karstified areas by gravity inversion of a 3D geological model. A geological 3D model is built from surface observations, 2D seismic reflection profiles and well data. The reliability of this geological 3D model obtained from integration, interpretation and interpolation of such data is first tested against the structural consistency of the model. Its theoretical gravimetric response is compared to gravity field during the forward problem in order to evaluate the validity/robustness of the geological model. The coherency between the gravity field and the gravimetric response is tested. The litho-inversion modelling quantifies the distribution of rock density in a probabilistic way, taking into account the geology and physical properties of rocks, while respecting the geological structures represented in the 3D model. The result of the inversion process provides a density distribution within carbonate formations that can be discussed in term of karstification distribution. Thus, lower densities correlate with areas that are strongly karstified. Conversely, higher than mean densities are found in carbonate formations mostly located under marly and impervious formations, preserving carbonate from karstification and paleokarstification. This article is protected by copyright. All rights reserved.
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    Topics: Geosciences
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  • 8
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    Wiley-Blackwell
    Publication Date: 2018-01-16
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    Topics: Geosciences
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  • 9
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    Wiley-Blackwell
    Publication Date: 2018-01-16
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    Topics: Geosciences
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  • 10
    Publication Date: 2017-12-13
    Description: This study of Eocene carbonate succession in the Dinaric Foreland Basin of northern Dalmatia, Croatia, integrates palaeontological and sedimentological data to document a range of carbonate ramps formed intermittently during the basin tectonic development. The end-Cretaceous basal erosional unconformity records the coupling of Adria and Eurasia crustal plates, with an antiformal uplift along their suture zone. The overlying late Ypresian carbonate ramp, spanning biozones SBZ 11–12, developed on the forebulge flank of a shallow-marine early synclinal basin. Basal grainstone/packstone facies, dominated by encrusting foraminifers with alveolinids and miliolids, pass upwards into packstones dominated by miliolids and rotaliids with bryozoan and echinoid fragments, indicating an increased bathymetry of the retreating forebulge flank. Deposition of grainstone facies preceded an end-Ypresian (SBZ 12/13 transition) subaerial exposure due to post-subductional isostatic uplift. The younger, middle to late Eocene carbonate ramps (SBZ 13–19) formed episodically as perched isolated features on blind-thrust anticlines in a bathymetrically diversified wedge-top basin, where phases of clastic and skeletal biogenic sedimentation alternated due to disharmonic thrusting and relative sea-level changes. Clastic sedimentation reflects anticline crest erosion and a forced-regressive progradation of gravelly foreshore and sandy shoreface facies over heterolithic offshore-transition and muddy offshore facies on the anticline flank. Biogenic sedimentation represents inner to middle ramp environments, with the latter terminating bluntly in muddy offshore environment. An outer ramp environment, known from classic ramp models, was lacking due to bathymetric threshold. Analysis of Larger Benthic Foraminifera (LBF), as biostratigraphic age indicators and palaeobathymetric proxies, helped distinguish systems tracts and determine their time-span. A comparison of local and global sea-level changes allowed the interplay of tectonic and eustatic forcing to be deciphered for the study area. This article is protected by copyright. All rights reserved.
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    Topics: Geosciences
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