Depositional, Infiltrated and Authigenic Clays in Fluvial Sandstones of the Jurassic Sergi Formation, Recôncavo Basin, Northeastern Brazil

Moraes, Marco A. S.; Ros, Luiz Fernando De

doi:10.2110/pec.92.47.0197

Cited by 53 publications

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“…pre-depositional, syndepositional and post-depositional (e.g., Moraes and de Ros 1992;Wilson 1992;Harris 1998;Skolasińska 2006Skolasińska , 2012Kilfeather et al 2009;van der Meer and Menzies 2011). This study found 'surface grain coatings' that appear to form during deformational processes.…”

Section: Discussionmentioning

confidence: 58%

Micromorphology of modern tills in southwestern Spitsbergen – insights into depositional and post-depositional processes

Skolasińska¹,

Rachlewicz

Szczuciński³

2016

Polish Polar Research

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Textural properties and microstructures are commonly used properties in the analysis of Pleistocene and older glacial deposits. However, contemporary glacial deposits are seldom studied, particularly in the context of post-depositional changes. This paper presents the results of a micromorphological study of recently deposited tills in the marginal zones of Hansbreen and Torellbreen, glaciers in southwestern Spitsbergen. The main objectives of this study were to compare modern tills deposited in subglacial and supraglacial conditions, as well as tills that were freshly released from ice with those laid down several decades ago. The investigated tills are primarily composed of large clasts of metamorphic rocks and represent coarse-grained, matrix-supported diamictons. The tills reveal several characteristic features for ductile (e.g. turbate structures) and brittle (e.g. lineations, microshears) deformations, which have been considered to be indicative of subglacial conditions. In supraglacial tills, the same structures are common as in the subglacial deposits, which points to the preservation of the primary features, though the sediment was transferred up to the glacier surface due to basal ice layer deformation and redeposited as slumps, or to formation of similar structures due to short-distance sediment re-deposition by mass flows. This study revealed that it might not be possible to distinguish subglacial and supraglacial tills on the basis of micromorphology if the latter are derived from a subglacial position. The only noted difference was the presence of iron oxide cementation zones and carbonate dissolution features in supraglacial tills. These features were found in tills that were deposited at least a few years ago and are interpreted to be induced by early post-depositional processes involving porewater/ sediment interactions.

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Section: Discussionmentioning

confidence: 58%

Micromorphology of modern tills in southwestern Spitsbergen – insights into depositional and post-depositional processes

Skolasińska¹,

Rachlewicz

Szczuciński³

2016

Polish Polar Research

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“…The presence of mechanically infiltrated clay in this facies suggests fluctuating groundwater levels, more consistent with a terrestrially influenced fluvial or fluvio-estuarine setting than a subtidal environment (Moraes & de Ros 1992). An association with subaerial environments is further supported by the local occurrence of rootlets and coals.…”

Section: Facies 4: Barrier Sandstonesmentioning

confidence: 70%

Role of forced regression in controlling Brent Group reservoir architecture and prospectivity in the northern North Sea

Went¹,

Hamilton²,

Platt³

et al. 2013

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The Middle Jurassic Brent Group of the northern North Sea presents a mature and highly productive reservoir play fairway where a combination of effective facies analysis and depositional sequence stratigraphy offers real potential to optimize exploitation. The north of the Brent province differs from classically studied southern areas in being dominated by marginal-marine delta-front facies. A core- and log-based study of 37 wells around the Don fields was performed to establish a sequence stratigraphic framework, map facies and thereby describe facies architecture. The results demonstrate that reservoir quality and productivity are regionally and locally controlled by facies. Of particular interest are intervals of fluvio-estuarine channel to sharp-based shoreface sandstone that formed during sea-level lowstands, since it is these packages that boost well productivity but, conversely, also increase the risk of early water breakthrough on production. Analogy with the Saloum Delta of Senegal highlights the importance of rapid and continuous barrier migration and destruction in controlling the deflection and switching of fluvio-estuarine channels, explaining also the preferential preservation of channel-floor deposits over continuously eroded barrier and delta-top facies. Interpretations suggest that deposition in the study area was dominated by punctuated progradation of the Brent Delta, as periods of delta plain incision alternated with episodes of base-level rise and delta aggradation/progradation. A model of regression for the Brent Delta is presented, where the Rannoch, Etive and Ness formations are an amalgam of highstand, falling stage and lowstand systems tract deposits, and the Tarbert Formation is a transgressive systems tract deposit, with the delta responding to regional relative sea-level changes driven by uplift and deflation of the mid North Sea dome. The prograding Brent Delta is characterized as a succession of attached shorefaces formed by alternating periods of normal and forced regression. Significantly, this explains the long distance (>200 km) build out of the Brent Delta and the continued presence of coarse-sandstone packages, as well as the potential for high-quality reservoirs even in the distal reaches of the system. It also suggests that there is limited potential for lowstand fan plays beyond the northernmost tip of the delta.

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“…Most of the 'pseudomatrix' (1^25%), which consists of sericite and chlorite, formed from in situ alteration of clay minerals and lithic grains. The matrix is not post depositional, as it exceeds the maximum volume of reported in¢l-trated material of 3^9% [26] and occludes pore space instead of forming grain coatings [27] ( Fig. 2d).…”

Section: Petrology Of the Sandstonesmentioning

confidence: 99%

Geochemical and petrological evidence for subduction–accretion processes in the Archean Eastern Indian Craton

Saha

Basu

Garzione

et al. 2004

Earth and Planetary Science Letters

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The composition of sandstones often provides key evidence about the tectonic, weathering and transport processes operating on the surface at the time of deposition. Petrologic and geochemical analyses of little-metamorphosed middle^late Archean sandstones from the Eastern Indian Craton show that the sedimentary rocks were derived from dominantly 3.3-Ga-old amphibolites of the Older Metamorphic Group (OMG) and tonalites of the Older Metamorphic Tonalite Gneisses (OMTG), the two oldest lithologic units of this craton. Chondrite-normalized rare earth element (REE) patterns of the sandstones show a light REE-enriched signature with (La/Sm) N varying from 5.2 to 6.7 with no Eu anomaly, while the heavy REEs display flat patterns with (Gd/Lu) N values of 0.9^1.6. Primitive mantle-normalized incompatible and compatible trace element plots of these sandstones demonstrate an overall similarity with global Proterozoic^Archean sandstones, including strong Nb^Ta negative anomalies. In an f Sm=Nd vs. O Nd (0) diagram, the sandstones plot precisely between the regional amphibolites and tonalites. We infer from the REE abundances and the f Sm=Nd vs. O Nd (0) plot that the sandstones represent a bimodal mechanical mixture of OMG and OMTG. The low Ce/Pb ratios of these rocks of 1^4 indicate a variably Pb-enriched Archean crust and that the Ce/Pb ratio acquired the continental crustal signature, distinctly different from those of the bulk silicate earth and mantle values at least as early as mid-Archean. Strong Nb^Ta depletion relative to the primitive mantle suggests the sandstones were derived from subduction-related magmatic arc sources. This latter suggestion is strongly supported by the low Nb/Ta and high Zr/Sm ratios of these sandstones, identical to Archean tonalite^trondhjemites that require, based on recent trace-element partitioning results, their protoliths to have formed by subduction melting of lowmagnesium amphibolites or metamorphosed hydrous basalts [1,2]. The average Nd model ages of the sandstones are greater than the Sm^Nd crystallization ages of the OMG and OMTG at V3.3 Ga. The geochemical data presented here can be collectively interpreted to suggest the presence of subduction^accretion processes operational in the midArchean Eastern Indian Craton. Because the OMG and OMTG, the source rocks of the sandstones, formed in a subduction-related arc setting, the basement rocks upon which this arc was constructed must have been older. This observation and the depleted mantle Nd model ages (T DM ) of the sandstones, ranging from 3.6 to 4.0 Ga, strongly indicate the presence of continental crust in this Eastern Indian craton older than 3.3 Ga and possibly as old as 0012-821X / 04 / $^see front matter ß

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Depositional, Infiltrated and Authigenic Clays in Fluvial Sandstones of the Jurassic Sergi Formation, Recôncavo Basin, Northeastern Brazil

Cited by 53 publications

References 0 publications

Micromorphology of modern tills in southwestern Spitsbergen – insights into depositional and post-depositional processes

Micromorphology of modern tills in southwestern Spitsbergen – insights into depositional and post-depositional processes

Role of forced regression in controlling Brent Group reservoir architecture and prospectivity in the northern North Sea

Geochemical and petrological evidence for subduction–accretion processes in the Archean Eastern Indian Craton

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