Paleoenvironmental insights from the deposition and diagenesis of Aptian pre-salt magnesium silicates from the Lula Field, Santos Basin, Brazil

2022 ◽  
Vol 92 (1) ◽  
pp. 12-31
Author(s):  
Nívea G. Carramal ◽  
Daniel M. Oliveira ◽  
Alessandra S.M. Cacela ◽  
Matheus A.A. Cuglieri ◽  
Natasha P. Rocha ◽  
...  
Keyword(s):  
Homogeneous Nucleation ◽  
Scientific Community ◽  
Intermediate Energy ◽  
Energy Conditions ◽  
Fine Grained ◽  
Rock Fragments ◽  
Diagenetic Alteration ◽  
Current Action ◽  
Magnesium Silicates ◽  
Silicate Deposits

ABSTRACT Since the discovery of giant Aptian pre-salt reservoirs in Brazilian margin basins, the study of lacustrine carbonates has drawn great attention from the scientific community. Comparatively, minor attention was given to the characterization and genesis of the Mg-silicates (e.g., stevensite, kerolite) which are commonly associated with these carbonates. A systematic petrological study was performed in the Aptian Barra Velha Formation (BVF) within distinct structural compartments of the giant Lula Field in the Santos Basin, in order to recognize the patterns of primary formation and diagenetic alteration of these Mg-silicates. Mg-silicates occur as peloids, ooids, intraclasts, and fine-grained laminated deposits, either mixed in variable proportions with other particles, such as carbonate bioclasts and volcanic rock fragments, or constituting specific intrabasinal deposits. In the BVF interval, clay peloids and laminated deposits are associated with spherulitic and fascicular calcite aggregates, as substrate and hosts for these precipitates. Ooids are interpreted as formed at the sediment–water interface by the nucleation of concentric envelopes on the surface of particles (heterogeneous nucleation), through repeated rolling under gentle wave and current action. Laminated deposits, interpreted as precipitated directly from the water column (homogeneous nucleation) in highly supersaturated and low-hydrodynamic-energy environments, constitute extensive deposits in the BVF. Peloids were probably formed in intermediate energy conditions. Some ooidal arenites show porosity from the dehydration and contraction, and/or the dissolution of ooids. In some rocks, these pores are filled with fibrous calcite, while the remaining Mg-silicates are replaced by dolomite, calcite, or silica. A similar diagenetic pattern occurs in the laminated deposits, where magnesite and dolomite fill shrinkage pores formed along their characteristic wavy laminae. Owing to their elevated solubility, most of the Mg-silicates were dissolved, or intensely replaced by calcite, dolomite, or silica. The detailed petrologic analysis indicates that the original volumes of Mg-silicates were substantially larger, and that their deposition was widespread in the basin, including on structurally high areas. The types and intensity of diagenetic alteration of the Mg-silicate deposits are distinct for each structural compartment, being more intense towards the highs and closer to the overlying evaporites, which imposed a strong influence on reservoir quality.

Amorphous silica coating on α-alumina particles

1995 ◽  
Vol 53 ◽  
pp. 210-211
Author(s):  
J. W. Mellowes ◽  
C. M. Chun ◽  
I. A. Aksay
Keyword(s):  
Amorphous Silica ◽  
Heterogeneous Nucleation ◽  
Homogeneous Nucleation ◽  
Silica Coating ◽  
Full Density ◽  
Optimal Conditions ◽  
Fine Grained ◽  
Alumina Particles ◽  
Complete Mullitization ◽  
Powder Compacts

Mullite (3Al2O32SiO2) can be fabricated by transient viscous sintering using composite particles which consist of inner cores of a-alumina and outer coatings of amorphous silica. Powder compacts prepared with these particles are sintered to almost full density at relatively low temperatures (~1300°C) and converted to dense, fine-grained mullite at higher temperatures (>1500°C) by reaction between the alumina core and the silica coating. In order to achieve complete mullitization, optimal conditions for coating alumina particles with amorphous silica must be achieved. Formation of amorphous silica can occur in solution (homogeneous nucleation) or on the surface of alumina (heterogeneous nucleation) depending on the degree of supersaturation of the solvent in which the particles are immersed. Successful coating of silica on alumina occurs when heterogeneous nucleation is promoted and homogeneous nucleation is suppressed. Therefore, one key to successful coating is an understanding of the factors such as pH and concentration that control silica nucleation in aqueous solutions. In the current work, we use TEM to determine the optimal conditions of this processing.

Evidence for pyroclastic emplacement of the Crowsnest Formation, Alberta

1996 ◽  
Vol 33 (5) ◽  
pp. 715-728 ◽  
Author(s):  
R.N. Adair ◽  
R.A. Burwash
Keyword(s):  
Elevated Temperatures ◽  
Pyroclastic Flows ◽  
Coarse Grained ◽  
Rock Fragment ◽  
Fine Grained ◽  
Rock Fragments ◽  
Explosive Phase ◽  
Graded Structures ◽  
Textural Evidence ◽  
Charred Wood

The middle Cretaceous Crowsnest Formation west of Coleman, Alberta, is composed of bedded alkaline volcanic deposits containing heterolithic volcanic rock fragments and crystal clasts. Comparison with modern examples of subaerial pyroclastic rocks suggests that pyroclastic flows, surges, fallout of material from vertical eruption columns, and minor mud flows emplaced the deposits. Textural evidence in the form of plastically deformed volcanic fragments, chilled deposit margins, baked rock fragment margins, recrystallization, and the presence of charred wood and charred wood molds indicate emplacement at elevated temperature. Massive deposits containing a fine-grained basal zone are interpreted as the product of pyroclastic flows, whereas deposits characterized by a block-rich base overlain by a thin layer of block-depleted stratified material are interpreted as the product of density-stratified surges. Deposits exhibiting pronounced stratification were emplaced by ash-cloud surges. Thickly bedded breccias exhibiting rheomorphic textures were emplaced as vent-proximal pyroclastic flows. Deposits characterized by parallel beds and graded structures are interpreted as fallout tephra deposits, and deposition by lahars is indicated by coarse-grained beds that lack evidence for emplacement at elevated temperatures. The eruptions of the Crowsnest Formation were cyclical. An initial explosive phase generated deposits by pyroclastic flows, surges, fallout, and lahars. As an eruption progressed, it evolved into a poorly gas-charged effusive stage that emplaced coarsely porphyritic domes, plugs, spines, and vent-proximal lava flows. Subsequent eruptions destroyed the effusive vent facies deposits and produced abundant heterolithic clasts typical of the formation.

scholarly journals Characterization of glacial silt and clay using automated mineralogy

2019 ◽  
Vol 60 (80) ◽  
pp. 49-65
Author(s):  
Jeff W. Crompton ◽  
Gwenn E. Flowers ◽  
Brendan Dyck
Keyword(s):  
Grain Size ◽  
Size Composition ◽  
Rock Properties ◽  
Fine Grained ◽  
Rock Fragments ◽  
Grain Sizes ◽  
Automated Mineralogy ◽  
Log Normal ◽  
Discrete Populations

AbstractGlacial erosion produces vast quantities of fine-grained sediment that has a far-reaching impact on Earth surface processes. To gain a better understanding of the production of glacial silt and clay, we use automated mineralogy to quantify the microstructure and mineralogy of rock and sediment samples from 20 basins in the St. Elias Mountains, Yukon, Canada. Sediments were collected from proglacial streams, while rock samples were collected from ice marginal outcrops and fragmented using electrical pulse disaggregation. For both rock fragments and sediments, we observe a log-normal distribution of grain sizes and a sub-micrometer terminal grain size. We find that the abrasion of silt and clay results in both rounding and the exploitation of through-going fractures. The abundance of inter- versus intragranular fractures depends on mineralogy and size. Unlike the relatively larger grains, where crushing and abrasion are thought to exploit and produce discrete populations of grain sizes, the comminution of fines leads to a grain size, composition and rounding that is continuously distributed across size, and highly dependent on source-rock properties.

scholarly journals Sea-floor and sea-ice conditions in the western Weddell Sea, Antarctica, around the wreck of Sir Ernest Shackleton's Endurance

2020 ◽  
Vol 32 (4) ◽  
pp. 301-313 ◽  
Author(s):  
Julian A. Dowdeswell ◽  
Christine L. Batchelor ◽  
Boris Dorschel ◽  
Toby J. Benham ◽  
Frazer D.W. Christie ◽  
...  
Keyword(s):  
Sea Ice ◽  
Autonomous Underwater Vehicles ◽  
Underwater Vehicles ◽  
Weddell Sea ◽  
Energy Conditions ◽  
Mass Wasting ◽  
Sea Floor ◽  
Fine Grained ◽  
Ice Conditions ◽  
Sedimentary System

AbstractMarine-geophysical evidence on sea-floor morphology and shallow acoustic stratigraphy are used to examine the substrate around the location at which Sir Ernest Shackleton's ship Endurance sank in 1915 and on the continental slope-shelf sedimentary system above this site in the western Weddell Sea. Few signs of turbidity-current and mass-wasting activity are found near or upslope of the wreck site, and any such activity was probably linked to full-glacial higher-energy conditions when ice last advanced across the continental shelf. The wreck is well below the maximum depth of iceberg keels and will not have been damaged by ice-keel ploughing. The wreck has probably been draped by only a few centimetres of fine-grained sediment since it sank in 1915. Severe modern sea-ice conditions hamper access to the wreck site. Accessing and investigating the wreck of Endurance in the Weddell Sea therefore represents a significant challenge. An ice-breaking research vessel is required, and even this would not guarantee that the site could be reached. Heavy sea-ice cover at the wreck site, similar to that encountered by Agulhus II during the Weddell Sea Expedition 2019, would also make the launch and recovery of autonomous underwater vehicles and remotely operated vehicles deployed to investigate the Endurance wreck problematic.

scholarly journals Grain size statistics and depositional pattern of the Ecca Group sandstones, Karoo Supergroup in the Eastern Cape Province, South Africa

2017 ◽  
Vol 9 (1) ◽  
Author(s):  
Christopher Baiyegunhi ◽  
Kuiwu Liu ◽  
Oswald Gwavava
Keyword(s):  
South Africa ◽  
Grain Size ◽  
Depositional Environments ◽  
Energy Conditions ◽  
Grain Size Analysis ◽  
Size Analysis ◽  
Equal Proportion ◽  
Eastern Cape Province ◽  
Eastern Cape ◽  
Fine Grained

AbstractGrain size analysis is a vital sedimentological tool used to unravel the hydrodynamic conditions, mode of transportation and deposition of detrital sediments. In this study, detailed grain-size analysis was carried out on thirty-five sandstone samples from the Ecca Group in the Eastern Cape Province of South Africa. Grain-size statistical parameters, bivariate analysis, linear discriminate functions, Passega diagrams and log-probability curves were used to reveal the depositional processes, sedimentation mechanisms, hydrodynamic energy conditions and to discriminate different depositional environments. The grain-size parameters show that most of the sandstones are very fine to fine grained, moderately well sorted, mostly near-symmetrical and mesokurtic in nature. The abundance of very fine to fine grained sandstones indicate the dominance of low energy environment. The bivariate plots show that the samples are mostly grouped, except for the Prince Albert samples that show scattered trend, which is due to the either mixture of two modes in equal proportion in bimodal sediments or good sorting in unimodal sediments. The linear discriminant function analysis is dominantly indicative of turbidity current deposits under shallow marine environments for samples from the Prince Albert, Collingham and Ripon Formations, while those samples from the Fort Brown Formation are lacustrine or deltaic deposits. The C-M plots indicated that the sediments were deposited mainly by suspension and saltation, and graded suspension. Visher diagrams show that saltation is the major process of transportation, followed by suspension.

scholarly journals The ceramic artifacts in archaeological black earth (terra preta) from lower Amazon region, Brazil: mineralogy

2004 ◽  
Vol 34 (2) ◽  
pp. 165-178 ◽  
Author(s):  
Marcondes Lima da Costa ◽  
Dirse Clara Kern ◽  
Alice Helena Eleotério Pinto ◽  
Jorge Raimundo da Trindade Souza
Keyword(s):  
Sedimentary Rocks ◽  
Mineralogical Composition ◽  
Chemical Study ◽  
Amazon Region ◽  
Equivalent Material ◽  
Fine Grained ◽  
Rock Fragments ◽  
Clayey Material ◽  
Terra Preta ◽  
Low Crystalline

Several archaeological black earth (ABE) sites occur in the Amazon region. They contain fragments of ceramic artifacts, which are very important for the archaeological purpose. In order to improve the archaeological study in the region we carried out a detailed mineralogical and chemical study of the fragments of ceramic artifacts found in the two ABE sites of Cachoeira-Porteira, in the Lower Amazon Region. Their ceramics comprise the following tempers: cauixi, cariapé, sand, sand +feldspars, crushed ceramic and so on and are composed of quartz, clay equivalent material (mainly burned kaolinite), feldspars, hematite, goethite, maghemite, phosphates, anatase, and minerals of Mn and Ba. Cauixi and cariapé, siliceous organic compounds, were found too. The mineralogical composition and the morphology of their grains indicate a saprolite (clayey material rich on quartz) derived from fine-grained felsic igneous rocks or sedimentary rocks as source material for ceramic artifacts, where silica-rich components such cauixi, cariapé and/or sand (feldspar and rock fragments) were intentionally added to them. The high content of (Al,Fe)-phosphates, amorphous to low crystalline, must be product of the contact between the clayey matrix of pottery wall and the hot aqueous solution formed during the daily cooking of animal foods (main source of phosphor). The phosphate crystallization took place during the discharge of the potteries put together with waste of organic material from animal and vegetal origin, and leaving to the formation of the ABE-soil profile.

scholarly journals Multiscale Erosion Surfaces of the Organic-Rich Barnett Shale, Fort Worth Basin, USA

2013 ◽  
Vol 2013 ◽  
pp. 1-16 ◽  
Author(s):  
Mohamed O. Abouelresh
Keyword(s):  
Sediment Supply ◽  
Energy Conditions ◽  
Barnett Shale ◽  
Sequence Stratigraphic ◽  
Fort Worth Basin ◽  
Fine Grained ◽  
Base Level ◽  
Genetic Types ◽  
Sea Level Fluctuation ◽  
Associated Surfaces

The high frequency and diversity of erosion surfaces throughout the Barnett Shale give a unique view into the short-duration stratigraphic intervals that were previously much more difficult to detect in such fine-grained rocks. The erosion surfaces in Barnett Shale exhibit variable relief (5.08–61 mm) which commonly consists of shelly laminae, shale rip-up clasts, reworked mud intraclasts, phosphatic pellets, and/or diagenetic minerals (dolomite and pyrite) mostly with clay-rich mudstone groundmass. Several factors control this lithological variation, including the energy conditions, rate of relative sea-level fluctuation, rate of sedimentation, sediment influx, and the lithofacies type of the underlying as well as the overlying beds. The erosional features and their associated surfaces make them serve at least in part as boundaries between different genetic types of deposits but with different scales according to their dependence on base level and/or sediment supply. Accordingly, the studied erosion surfaces of the Barnett Shale can be grouped into three different scales of sequence stratigraphic surfaces: sequence-scale surfaces, parasequence-scale surfaces, and within trend-scale surfaces.

Submarine-fan characteristics and dual sediment provenance, Lower Carboniferous Bragdon Formation, eastern Klamath terrane, California

1989 ◽  
Vol 26 (5) ◽  
pp. 927-940 ◽  
Author(s):  
M. Meghan Miller ◽  
Bingquan Cui
Keyword(s):  
Early Carboniferous ◽  
Sediment Provenance ◽  
Dispersal Pattern ◽  
Submarine Fan ◽  
Lower Carboniferous ◽  
Sediment Dispersal ◽  
Fine Grained ◽  
Rock Fragments ◽  
Western Cordillera ◽  
Volcaniclastic Rocks

The Carboniferous Bragdon Formation comprises sandstone, argillite, and conglomerate, which were deposited in a hybrid submarine-fan setting. The Bragdon Formation contains a crudely progradational succession of sand-rich turbidites and intercalated channel fill and debris flows. Apparent paucity of fine-grained rocks and relatively high sedimentation rates may suggest deposition within a small, rapidly subsiding, ponded basin. Three end-member petrologic sandstone types include (i) quartz-rich, chert-rich, and sedimentary-lithic-rich sandstone, (ii) volcanic-lithic- and feldspar-rich sandstone, and (iii) crystal-rich sandstone and tuffaceous argillite. The compositions reflect basement uplift, arc dissection, and the persistence of volcanism, respectively. Interbedded strata of differing provenance, together with little or no provenance mixing within beds, indicate multicomponent source terranes, line-source sediment dispersal pattern, and limited transport distances.Facies associations and provenance together suggest extension or transtension within an arc-related basinal setting during the Late Devonian and Early Carboniferous, resulting in deposition of epiclastic sediments that were rich in sedimentary rock fragments in a Paleozoic succession otherwise dominated by volcaniclastic rocks or fringing carbonates. Mid-Paleozoic chert-rich epiclastic strata are widespread within the western Cordillera in a variety of tectonic regimes that may be broadly related to the same oblique plate margin.

Provenance of post-Wapiabi sandstones and its implications for Campanian to Paleocene tectonic history of the southern Canadian Cordillera

1989 ◽  
Vol 26 (4) ◽  
pp. 665-676 ◽  
Author(s):  
Greg H. Mack ◽  
T. Jerzykiewicz
Keyword(s):  
Drainage Basin ◽  
Relative Proportion ◽  
Volcanic Rocks ◽  
Rocky Mountain ◽  
Potassium Feldspar ◽  
Low Grade ◽  
Late Mesozoic ◽  
Fine Grained ◽  
Rock Fragments ◽  
Early Paleocene

Late Campanian to Early Paleocene sandstones of the Alberta Foothills were derived from three types of rocks: (i) andesitic–dacitic volcanic rocks that were presumably comagmatic with middle to late Mesozoic plutons in the Omineca Crystalline Belt; (ii) low-grade metamorphic rocks in the suprastructure of the Omineca Crystalline Belt; and (iii) sedimentary rocks in die Rocky Mountain Thrust Belt, principally pelitic rocks in the western Main Ranges and carbonates and chert-arenites in the eastern Main and Front ranges. A paucity of quartzo-feldspathic rocks fragments and potassium feldspar indicates that the core of the Omineca Crystalline Belt was not extensively exposed at that time.Vertical trends in composition of the sandstones reveal five petrographic stages. Stage I is dominated by volcanic rock fragments and plagioclase, suggesting that initial progradation of the sediment was largely a response to coeval volcanism or tectonic emplacement of older volcanic rocks. Stages III and V are characterized by a significant decrease in the relative proportion of metamorphic detritus and an increase in the proportion of carbonate and chert detritus. These stages may represent periods of thrusting in the eastern Main Ranges or Front Ranges. In contrast, stages II and IV display increases in metamorphic detritus and stage II shows a concomitant decrease in carbonate and chert detritus, trends that indicate wearing down of the eastern Main Ranges or Front Ranges thrust sheet(s) and reintegration of the Omineca Crystalline belt and the western Main Ranges into the drainage basin. The compositional stages indicative of thrust events are associated with coarse facies, including the Entrance and High Divide Ridge conglomerates, whereas those stages indicative of tectonic quiescence are associated with fine-grained facies including coal.

Tectonic, stratigraphic, and sedimentologic significance of a regional discontinuity in the upper Judith River Group (Belly River wedge) of southern Alberta, Saskatchewan, and northern Montana

1993 ◽  
Vol 30 (1) ◽  
pp. 174-200 ◽  
Author(s):  
David A. Eberth ◽  
Anthony P. Hamblin
Keyword(s):  
Volcanic Rock ◽  
Gamma Ray ◽  
Coarse Grained ◽  
Fine Grained ◽  
Rock Fragments ◽  
Isostatic Rebound ◽  
Accommodation Space ◽  
Lithostratigraphic Units ◽  
Alberta Basin ◽  
Dinosaur Park Formation

The lithostratigraphic interval between the Taber and Lethbridge coal zones in the upper portion of the nonmarine Judith River Group of southeastern Alberta is divisible into two lithostratigraphic units separated by a regionally extensive and diachronous discontinuity. The lower unit, referred to here as the Oldman Formation, is characterized by very fine grained to fine-grained sandstones that contain fewer than 2% volcanic rock fragments; sandstone bodies with numerous sets of horizontally stratified sandstone, showing little or no evidence of lateral accretion; siliceous paleosols (ganisters); and a relatively high gamma-ray signal in the upper half of the formation. The Oldman Formation comprises deposits of a low-sinuosity, perhaps ephemeral fluvial system that originated in the southern Cordillera of Canada and northern Montana and flowed northeastward, perpendicular to the axis of the Alberta Basin.The upper unit is assigned to a new formation, the Dinosaur Park Formation, and is characterized by fine- to medium-grained sandstones with up to 10% volcanic rock fragments; sandstone bodies that exhibit lateral-accretion surfaces in the form of inclined heterolithic stratification; numerous articulated dinosaurs and dinosaur bone beds; and a relatively low gamma-ray signal in the lower half of the formation. The Dinosaur Park Formation comprises deposits of a high-sinuosity, fluvial-to-estuarine system that originated in the north and central Cordillera and flowed southeastward, subparallel to the axis of the Alberta Basin.40Ar/39Ar and K–Ar dating of Judith River Group bentonites shows that the contact between the Oldman and Dinosaur Park formations becomes younger toward the south and southeast. These data also demonstrate that the Dinosaur Park Formation clastics migrated southeastward at a rate of approximately 130–140 km/Ma, gradually overstepping the Oldman Formation elastics.The widely recognized north-to-south increase in intensity of overthrust loading along the western margin of the Alberta Basin during the Late Cretaceous is thought to be responsible for (i) differences in accommodation space for the proximal portions of the Oldman and Dinosaur Park formations, and (ii) the establishment of a southerly tilt in the Alberta Basin leading to the southeastward migration of the Dinosaur Park Formation elastics. In the northern portion of the basin, relatively lower rates of subsidence, combined with periods of isostatic rebound in the foredeep, resulted in the southeastward migration of Dinosaur Park Formation elastics as sediment input exceeded accommodation space. In the southern portion of the basin, relatively higher rates of subsidence and little isostatic rebound acted to trap coarse-grained Oldman Formation elastics in the foredeep and may have led to periods of sediment starvation in more distal portions of the basin. An inferred lower depositional slope associated with the Dinosaur Park Formation (relative to the Oldman Formation) is thought to have resulted from gradual loading of the basin as Dinosaur Park Formation elastics migrated southeastward or some form of tectonically induced subsidence.

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