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  • 1
    Publication Date: 2018-06-28
    Description: Publication date: 1 October 2018 Source: Sedimentary Geology, Volume 373 Author(s): Hiep Huu Nguyen, Andrew Carter, Long Van Hoang, Son Trung Vu Heavy mineral rich sands along the coastal margin of southern Vietnam often contain commercial deposits of ilmenite and zircon but their origin is unknown. A multi-method approach based on petrology, geochemistry and detrital zircon geochronology was used to define the provenance and transport history of these mainly Quaternary sands. A trend of progressive enrichment of ilmenite TiO 2 content, from north to south, was observed. This reflects increased levels of weathering attributed to a wider coastal margin and shelf in the south combined with a succession of erosion and reburial events associated with interstadial and interglacial sea-level changes. Weathering took place during lowstands. Detrital zircon U Pb age signatures collected from 25 major river outlets along the coast of Vietnam helped to locate potential sand sources. Prominent age groups spanning 90–120 Ma and 220–250 Ma with a minor group at 400–500 Ma are present in all of the detrital zircon U Pb age distributions of contemporary beach sands and Quaternary coastal dune placer deposits. Proterozoic grains are also present but constitute 〈10% of dated grains. The main source terrain for the placer sands is southern Vietnam where there are widespread outcrops of Mesozoic magmatic rocks. Detrital zircon U Pb age signatures from river sands that drain this area are identical to zircon age distributions in placer sands. River sands from northern Vietnam, the Mekong and its delta contain abundant Paleozoic and Proterozoic zircons, which are largely absent from the placer sands, and so are ruled out as primary sources.
    Print ISSN: 0037-0738
    Electronic ISSN: 1879-0968
    Topics: Geosciences
    Published by Elsevier
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  • 2
    Publication Date: 2018-06-27
    Description: Publication date: Available online 26 June 2018 Source: Sedimentary Geology Author(s): Benoit Vincent, Jen Waters, Francis Witkowski, Gautier Daniau, Norman Oxtoby, Stephen Crowley, Rob Ellam The Upper Slochteren Sandstones of the Rotliegend Formation (ROSLU) were studied in offshore Netherlands to evaluate the impact of diagenesis, and more particularly of carbonate diagenesis, on sandstone reservoirs. An integrated study applying petrography, geochemistry (SEM-EDS, XRD, C & O stable isotopes, Sr isotopes), and fluid inclusion measurements, was undertaken. Early phases consisting of silica-bearing minerals (authigenic clays, quartz overgrowths), associated with mechanical compaction plus dissolution of labile grains and/or feldspars, are rare. These are succeeded by a sequence of carbonate cements including non-ferroan dolomite cement, ferroan dolomite cement, and finally siderite. Dolomite cements are associated with fracturing and bleaching of the sandstone. The latest phases consist of another set of authigenic clays, quartz overgrowths, plus sulphate cements. Carbonate pore-filling cements dominate the authigenic phases, representing more than 50% of the total, of which 80% is dolomite and 20% siderite. Although mechanical compaction is the dominant factor influencing porosity reduction, dolomite cements also have a negative impact on porosity and permeability properties, which do not only depend on sedimentary characteristics. Non-ferroan dolomite precipitated at approximately 100°C, from highly saline brines migrating downward from the Zechstein. Conversely during the Mid Cimmerian Unconformity (MCU), faulting and fracturing allowed the upward migration of CO 2 -bearing, acidic and reducing, hotter fluids from the Carboniferous, which includes hydrocarbon source rocks. The mixing of the upward and downward migrating fluids resulted in the precipitation of ferroan dolomites. These results indicate an increased risk of encountering pore-filling dolomite cements close to fault/fractured zones in that area, where carbonate cements may not have been properly assessed. Moreover, this study emphasizes again the importance of a combined analytical approach to gain a deeper understanding of carbonate diagenesis, which should be considered with the same caution as clay diagenesis within clastic-hosted reservoirs. Graphical abstract
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    Electronic ISSN: 1879-0968
    Topics: Geosciences
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  • 3
    Publication Date: 2018-06-26
    Description: Publication date: 1 October 2018 Source: Sedimentary Geology, Volume 373 Author(s): Brian Jones, Erjun Zheng, Long Li The spectacular wave-cut notch on Cayman Brac, which is ~6 m above sea level, formed during Marine Isotope Stage 5e highstand, 128,000 to 116,000 years ago. On Cayman Brac, the notch is commonly decorated with speleothems (mostly stalactites) that are formed of calcite, aragonite and micrite. These notch speleothems are characterized by numerous growth zones that are delimited by minor and major hiatal surfaces. U/Th dating indicates that the major growth phases, which took place ~73,000 to 59,000 years ago, 46,000 to 49,000 years ago, and ~4000 to 1000 years ago, were separated by periods when erosion and minimal precipitation were the norm. The δ 18 O VPDB values range from −6.5‰ to +0.3‰ with a mode between −2 and −4‰ and an average of −3.1‰, whereas the δ 13 C VPDB values range from −10.5‰ to +1.9‰ with one mode between −2.0 and −3.0‰, a second mode between −7.0 and −8.0‰, and an overall average of −6.1‰. The δ 18 O and δ 13 C values co-vary. The δ 18 O VPDB and δ 13 C VPDB values are similar to those from the “young” (〈125,000 years old) cave speleothems but heavier than those from the “old” (>125,000 years) cave speleothems. Today, with the little evidence of active speleothem growth in the notch or caves, Cayman Brac is characterized by dry sub-tropical forest and shrubland with xeric components on the elevated eastern end of the island. Available data indicate that most of the speleothem growth took place during the transitions from Marine Isotope Stage (MIS) 5a to 4, and MIS2 to 1. These transitional periods, which define the onset and termination of glaciation in the northern latitudes, were probably characterized by higher rainfall and development of tropical rainforests. It is evident that notch speleothems, like those from Cayman Brac, are valuable archives of the paleoclimate conditions that have existed since the highstand associated with MIS5e.
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    Electronic ISSN: 1879-0968
    Topics: Geosciences
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  • 4
    Publication Date: 2018-06-25
    Description: Publication date: Available online 23 June 2018 Source: Sedimentary Geology Author(s): Sanghita Dasgupta, Parthasarathi Ghosh Spring-related carbonates are valuable repositories for information on physical and biotic environments of the past. However, for Mesozoic and earlier records, their use is limited due to their low preservation potential and difficulties in accurate identification of the carbonate type. This study aims to characterize the source of carbonate clasts preserved as thin beds of cross-bedded grainstones in Late Triassic, siliciclastic fluvial deposits, the Maleri Formation, Pranhita-Godavari rift basin, India. The microfabric and stable isotopic compositions of the grainstones and thin and discontinuous beds of impure limestones of this formation are presented here. These features help in identifying the freshwater carbonate-precipitating environments that existed in an ancient continental rift basin, though such deposits are not primarily preserved in this case. The microfabric of the carbonate grains provides evidence for carbonate precipitation in aquatic environment related to karstic springs. Taking together the microfabric, stable isotopic compositions, as well as the associated geological and palaeontological information, it could be shown that the calcium carbonate precipitation took place in palustrine pools related to tufa-like spring systems and in alluvial swamps under a pluvial climatic setting. This research, thus, demonstrates that carbonate grains derived from spring-related carbonate deposits, formed mainly near the margins of rift basins, can be incorporated into nearby siliciclastics. If interpreted correctly, they can be used in reconstructing ancient karstic carbonate environments, even when in situ primary record in not preserved – therefore making it possible to access the information stored in freshwater carbonates.
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    Electronic ISSN: 1879-0968
    Topics: Geosciences
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  • 5
    Publication Date: 2018-06-23
    Description: Publication date: Available online 21 June 2018 Source: Sedimentary Geology Author(s): Shujuan Yang, Qingfei Wang, Qizuan Zhang, Jiahao Chen, Yuanxiao Huang The terrestrial deposition process for karst bauxite is difficult to constrain due to its allochthonous origin, multiple controls and the difficulty in geodynamic reconstruction. This ambiguity has been clarified from investigation of the provenance and geologic-geographic conditions for the formation of Quaternary gibbsite nodules in the Yongjiang Basin. This karst basin, located at the southeastern propagation front of the Tibet Plateau, was affected by the SE Asia monsoon climate developed since the Late Oligocene and a later Quaternary glaciation. A thick blanket of Quaternary laterite is located on Paleozoic carbonate bedrock, and covers an area about 1000 km 2 along the east-flowing river systems in the basin. The laterite profiles are well layered, with a layer of iron-rich gibbsite nodules overlying on a basal clay zone and irregularly covered by a thin clayey topsoil. Gibbsite nodules from most localities yield detrital zircons with age peaks at ca. 1000 Ma, 450 Ma and 250 Ma, corresponding to those of the Mesozoic clastic and magmatic rocks exposed on the western and southern surrounding highlands; nevertheless, those from the Pingtianshan area produce an exclusive spike at ca. 100 Ma, consistent with the emplacement age of nearby granites. Apatite fission-track modeling for the Mesozoic clastic rocks and Darongshan granites shows a rapid cooling since the early Miocene, and that for the Pingtianshan Cretaceous granite reveals fast exhumation since the late Miocene. These data indicate differential erosion reshaped the topography and consequently a low-relief karst basin was developed, allowing a diverse material supply from the surrounding and local highlands via sheet flow and east-flowing rivers. Under a monsoon-influenced subtropical climate, aluminum and iron oxides/hydroxides were accumulated as nodules or concretions, which were cemented by and coated with Fe oxides due to alternating consolidation and swelling, while silica was leached. At greater depth, groundwater solutions preferentially removed and brought upward Fe under a reducing environment during the wet seasons, while an underlying clay layer occurred due to the reduced solubility of silica. Later, this bauxitization process was probably hindered by the Quaternary glaciation, which could have promoted the formation of the top clay layer. This terrestrial deposition process of Quaternary gibbsite nodules serves as one analogue for ancient karst bauxite, in which the following submergence would improve the quality via further precipitation of alumina hydroxide and leaching of extra Fe.
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    Electronic ISSN: 1879-0968
    Topics: Geosciences
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  • 6
    Publication Date: 2018-06-17
    Description: Publication date: Available online 15 June 2018 Source: Sedimentary Geology Author(s): Korhan Ayranci, Nicholas B. Harris, Tian Dong The application of sequence stratigraphy to deep-water mud-dominated systems is more challenging than in shallow water siliciclastic settings, largely because mudstones display subtle contrasts in grain size and lithology that make identification of facies and recognition of major stratigraphic surfaces difficult. However, the integration of sedimentology, ichnology and geochemistry and an extensive suite of cores from the Middle to Upper Devonian Horn River Group shales allow us to better understand how deep-water mud-dominated systems respond to fluctuations in the relative sea level, manifested in sequence stratigraphic relationships. The Horn River Group consists of, in ascending order, the Evie Member and Otter Park Member of the Horn River Formation and the Muskwa Formation. Four systems tracts, including highstand, transgressive, lowstand and falling stage systems tracts (HST, TST, LST, FSST, respectively) are identified and mapped. Highstand and transgressive systems tracts are both represented by dominantly massive mudstone lithofacies, sparse bioturbation, high Mo/Al ratios and high TOC values (avg. 3.1 and 3.4 wt%, respectively), as well as low Al 2 O 3 concentrations. They can be distinguished by upward increasing gamma ray values for transgressive systems tracts and upward decreasing values for highstand systems tracts. The falling stage and low stand systems tracts display more heterolithic and laminated lithofacies, sparse to intense bioturbation, lower Mo/Al ratio and lower TOC values (avg. 1.2 and 1.7 wt%, respectively) and high Al 2 O 3 , concentrations and relatively low gamma ray readings. Sequence boundaries are represented by a transition from unbioturbated units to moderately or intensely bioturbated units, suggesting increased bottom water oxygen levels, which we infer to represent shallower waters. They are gradational and clearly conformable contacts in distal parts of the basin. They are sharp in more proximal settings, but no erosional surfaces were identified that would indicate unconformable contacts. Maximum flooding surfaces are characterised by the highest TOC contents and an increased gamma ray values. Our results suggest that the Otter Park Member belongs to a long-period sea level lowstand (e.g., 2 nd order cycle), whereas the Evie Member and Muskwa Formation belong to long-period sea level highstands.
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    Topics: Geosciences
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  • 7
    Publication Date: 2018-06-16
    Description: Publication date: Available online 15 June 2018 Source: Sedimentary Geology Author(s): Björn Nyberg, William Helland-Hansen, Rob L. Gawthorpe, Pål Sandbakken, Christian Haug Eide, Tor Sømme, Frode Hadler-Jacobsen, Sture Leiknes Catchments provide water and sediment to downstream sedimentary systems, and these form individual source-to-sink systems. Source-to-sink systems comprise adjacent linked segments, commonly hinterland catchments, alluvial- and coastal plains, the continental shelf, continental slope and submarine fan. The dimensions of the catchment and how it scales to downstream segments provides insight into the sedimentary and tectonic controls that influence the morphology and sedimentation patterns in a basins evolution. In ancient sedimentary successions, where the sedimentary routing system is buried and inaccessible for study, or fragmented due to uplift and erosion, using scaling relationships can provide a powerful tool to understand the complete sedimentary system. Observational data from modern sedimentary systems provide an opportunity to create morphological and sedimentological scaling relationships of segments on the entire source-to-sink system. However, previous studies on global modern source-to-sink systems have typically been based on a limited number of examples restricted by the data available at the time and the methodology used to analyze large datasets. In the last decade, the volume and quality of remotely sensed information has significantly improved so that it is now timely to revisit scaling relationships of modern source-to-sink systems' segment morphologies, and discuss the implications of those r esults for sedimentological parameters and applicability to ancient source-to-sink systems. The results of this reanalysis show that dimensions of the catchment and submarine fan segments scale internally in terms of fan width, length and area. In addition, fan area scales to its largest hinterland catchment area in agreement with previous studies, however, it is important to consider all catchments that contribute sediment to a basin floor region. In paleogeographic settings, where individual submarine fans are difficult to tie to a single catchment, and where basin floor systems are amalgamated, the contributing sediment discharge of all catchments may be significant and likely influence the scale of its submarine fan. Accommodation versus sediment supply in relation to relative sea level change are important controls on the position of the shoreline which vary considerably from system to system over time and space, thus influencing morphological relationships between source-to-sink segments. The continental shelf should therefore be viewed as a transient geomorphic feature rather than a segment of a source-to-sink system. Furthermore, the continental slope length should not be used to scale other segments of the source-to-sink system, which contradicts previous research. The underlying tectonic and sedimentological control on the continental shelf and slope segments, in addition to the subjective interpretation of their basinward boundaries, may render those segment unsuitable for scaling the morphology of other segments. The study highlights both the temporal variability and complexity of controls that influence the morphology and scaling relationships of internal and adjacent linked source-to-sink segments, and the need to place this in a framework of both tectonic and sedimentological history.
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    Electronic ISSN: 1879-0968
    Topics: Geosciences
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  • 8
    Publication Date: 2018-06-16
    Description: Publication date: Available online 15 June 2018 Source: Sedimentary Geology Author(s): Ana M. Alonso-Zarza The Pajares calcrete in Central Spain, a modern calcrete, consists of an accumulation of powder carbonate around the roots of living trees and bushes which penetrates Miocene deposits by more than 3 m. Calcrete development is mostly vertical and oblique, but thinner horizontal calcified root mats also occur. Carbonate accumulation, up to 15 cm thick, is made up of micrite with some etched clasts, alveolar septal structures, calcified rootlets, coated grains and micrite grains. In detail many of these features are composed of needle fibre calcite and micro-rods. Accumulation of carbonate was produced both by roots through direct calcification of their cells and also by microbial activity within the rhizosphere. This case study provides a good example of how carbonate is accumulating around roots at present and may allow better understanding of ancient calcretes, especially those which formed directly around roots in direct contact with the hostrock. In addition the calcrete's setting, and its occurrence around roots belonging to various types of plants, suggest that carbonate accumulation in modern landscapes may be a relatively rapid, common process even in erosive regimes, and unrelated to specific vegetation types. Graphical abstract
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    Electronic ISSN: 1879-0968
    Topics: Geosciences
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  • 9
    Publication Date: 2018-06-15
    Description: Publication date: Available online 14 June 2018 Source: Sedimentary Geology Author(s): Luke J. Wooldridge, Richard H. Worden, Joshua Griffiths, James E.P. Utley, Anu Thompson The presence and distribution of clay minerals attached to grain surfaces as coats (also known as rims) are of great interest because they affect petroleum reservoir quality via the inhibition of the porosity-occluding quartz cement during prolonged burial and heating. Being able to predict the distribution of clay-coated sand grains in petroleum reservoirs is thus important to help find and exploit anomalously high porosity sandstones deep in sedimentary basins. The few studies focused on the distribution of clay coats in marginal marine sediments derive from surface sediment-based data sets, with limited emphasis placed on the preservation of the surface trends in sediment undergoing eodiagenesis in the near-surface environments. The post-depositional processes of bioturbation (sediment homogenization) and infiltration of clay into sand-grade sediment have been widely invoked as potential mechanisms that produce clay coats in modern sands and ancient sandstones. However, the potential for such processes to alter surface trends and govern clay-coat distribution in the subsurface remains unconstrained. In this study, we report the development of a novel, quantitative model of clay-coat coverage in order to identify the controlling mechanisms that govern clay-coat distributions. This study has focused on surface and near-surface sediments in the Saltcoats tidal flat deposits of the Ravenglass Estuary, UK. This unique bio-sedimentary study involved geomorphic mapping, core logging, a range of scanning electron microscopy techniques, and quantification of grain-size, clay fraction content, biofilm abundance (total carbohydrate and biomarker analysis), clay-coat coverage, and clay-coat mineralogy. In this study, against established convention, we demonstrate that infiltration and bioturbation do not significantly affect clay-coat grain coverage in near-surface sediments. Instead, we show that the extent, distribution, and mineralogy of clay coats in near-surface sediment are governed by the surface-based hydrological segregation of the clay mineral assemblage and biological clay-coat formation.
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    Electronic ISSN: 1879-0968
    Topics: Geosciences
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  • 10
    Publication Date: 2018-06-13
    Description: Publication date: Available online 11 June 2018 Source: Sedimentary Geology Author(s): Mario Lara, Ana M. Salazar-Franco, Juan C. Silva-Tamayo The late Oligocene-middle Miocene Amagá Formation is a continental siliciclastic succession deposited along several semi-isolated intramontane sedimentary basins in the northwestern the Andes. Despite the potential information that this sedimentary record may bear on the evolution of tropical intramontane siliciclastic successions along active Andean type convergent margins, little is known about its provenance. Here we document petrographic, heavy mineral and detrital zircon U-Pb ages data from the Amagá Formation, cropping out along the Santa Fe de Antioquia - San Jerónimo Sub-Basin, from which we investigate the evolution and controlling factors leading to changes in its provenance. Sandstones from the late Oligocene Lower Member of the Amagá Formation display compositional modes and U-Pb detrital zircon ages which suggest sediment sources exclusively associated to the continental South American Plate. The compositional modes and detrital zircon U-Pb ages of sandstones from the early - middle Miocene Upper Member suggest, instead, sediment sources associated to both, the South American Plate and the allochthonous Panamá-Chocó Block. In particular, the Upper Member documents the arrival of detrital zircons younger than 50 Ma (18.7, 21.0, 25.3, 31.9, 40.7, 45.1 Ma), which are not present in the South American Plate. This change in provenance parallels a change in sedimentary environments, from meandering (Lower Member) to braided (Upper Member) rivers, which have been interpreted as a major decrease in sediment accommodation space along the northern Andes. This decrease in accommodation space is associated to a regional accelerated uplift in the northern Andes resulting from the early Miocene accretion of the Panamá-Chocó Block to northern South America.
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    Electronic ISSN: 1879-0968
    Topics: Geosciences
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