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Anicet Beauvais - One of the best experts on this subject based on the ideXlab platform.
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Ferricrete biochemical degradation on the rainforest–savannas boundary of Central African Republic
Geoderma, 2009Co-Authors: Anicet BeauvaisAbstract:In southeastern Central African Republic the lateritic weathering mantles are capped by 2 to 5 m thick Ferricretes, which previously formed under a seasonal tropical climate. The actual humid tropical climatic conditions result in the biophysical disaggregation of the Ferricretes everywhere the forest develop that lead to a soil formation composed of Ferricrete relicts and ferruginous nodules embedded in a soft bioturbated micro-aggregated clay-ferruginous matrix. The potential effect of the biological activity (e.g., termites) on the soil and vegetation dynamics and therefore on the evolution of the previous consolidated Ferricrete is discussed. Following its mechanical disaggregation by the forest tree roots, the Ferricrete underwent a chemical degradation under the combined effect of hydration and redox conditions, which result from the biodegradation and oxidation of the organic matter. The transformation of the Ferricrete into a soft bioturbated micro-aggregated clay-ferruginous soil matrix implies the hematite dissolution, and the kaolinite transformation into gibbsite, which may characterize a late "bauxitization" (secondary gibbsitization of kaolinite) of previous Ferricrete profiles linked to a late Quaternary environmental (climate and vegetation) change. However, the geochemical and mineralogical patterns of the matrix not only reflect the geochemistry of the parental Ferricrete but also depend on the physical transfers of quartz and heavy minerals from the lower horizons of the profile. Hence, the use of geochemical indexes such as Ti and/or Zr for mass balance calculations in the lateritic weathering profiles is precluded because these supposedly inert chemical elements are not simply accumulated by in situ chemical weathering process.
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Ferricrete biochemical degradation on the rainforest-savannas boundary of Central African Repiublic
Geoderma, 2009Co-Authors: Anicet BeauvaisAbstract:In southeastern Central African Republic the lateritic weathering mantles are capped by 2 to 5 m thick Ferricretes, which previously formed under a seasonal tropical climate. The actual humid tropical climatic conditions result in the biophysical disaggregation of the Ferricretes everywhere the forest develop that lead to a soil formation composed of Ferricrete relicts and ferruginous nodules embedded in a soft bioturbated micro-aggregated clay-ferruginous matrix. The potential effect of the biological activity (e.g., termites) on the soil and vegetation dynamics and therefore on the evolution of the previous consolidated Ferricrete is discussed. Following its mechanical disaggregation by the forest tree roots, the Ferricrete underwent a chemical degradation under the combined effect of hydration and redox conditions, which result from the biodegradation and oxidation of the organic matter. The transformation of the Ferricrete into a soft bioturbated micro-aggregated clay-ferruginous soil matrix implies the hematite dissolution, and the kaolinite transformation into gibbsite, which may characterize a late "bauxitization" (secondary gibbsitization of kaolinite) of previous Ferricrete profiles linked to a late Quaternary environmental (climate and vegetation) change. However, the geochemical and mineralogical patterns of the matrix not only reflect the geochemistry of the parental Ferricrete but also depend on the physical transfers of quartz and heavy minerals from the lower horizons of the profile. Hence, the use of geochemical indexes such as Ti and/or Zr for mass balance calculations in the lateritic weathering profiles is precluded because these supposedly inert chemical elements are not simply accumulated by in situ chemical weathering process.
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Ferricrete biochemical degradation on the rainforest–savannas boundary of Central African Republic
Geoderma, 2009Co-Authors: Anicet BeauvaisAbstract:International audienceIn southeastern Central African Republic the lateritic weathering mantles are capped by 2 to 5 m thick Ferricretes, which previously formed under a seasonal tropical climate. The actual humid tropical climatic conditions result in the biophysical disaggregation of the Ferricretes everywhere the forest develop that lead to a soil formation composed of Ferricrete relicts and ferruginous nodules embedded in a soft bioturbated micro-aggregated clay-ferruginous matrix. The potential effect of the biological activity (e.g., termites) on the soil and vegetation dynamics and therefore on the evolution of the previous consolidated Ferricrete is discussed. Following its mechanical disaggregation by the forest tree roots, the Ferricrete underwent a chemical degradation under the combined effect of hydration and redox conditions, which result from the biodegradation and oxidation of the organic matter. The transformation of the Ferricrete into a soft bioturbated micro-aggregated clay-ferruginous soil matrix implies the hematite dissolution, and the kaolinite transformation into gibbsite, which may characterize a late "bauxitization" (secondary gibbsitization of kaolinite) of previous Ferricrete profiles linked to a late Quaternary environmental (climate and vegetation) change. However, the geochemical and mineralogical patterns of the matrix not only reflect the geochemistry of the parental Ferricrete but also depend on the physical transfers of quartz and heavy minerals from the lower horizons of the profile. Hence, the use of geochemical indexes such as Ti and/or Zr for mass balance calculations in the lateritic weathering profiles is precluded because these supposedly inert chemical elements are not simply accumulated by in situ chemical weathering process
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Ultramafic rock weathering and slope erosion processes in a South West Pacific tropical environment
Geomorphology, 2007Co-Authors: Anicet Beauvais, Jean-claude Parisot, Cécile SavinAbstract:Abstract Weathering and erosion processes are investigated using electrical resistivity tomography (ERT) imaging and the quantification of geomorphic patterns at the edges of a lateritic plateau overlying ultramafic rocks in the north western region of the main island of New Caledonia (Southwest Pacific). The obtained ERT images document the structure and long-term evolution of the regolith, while source area parameters such as area (A) local slope above channel head (tanθ) and longitudinal river profiles allow the characterization of contrasting geomorphic patterns around the plateau. The geo-electrical profiles show a succession of hard rock protrusions and weathering troughs, whose depth varies greatly. The area–slope relationship allows the distinction between saprolite- and Ferricrete-mantled source areas. The former could result from a regolith erosion process by shallow landslides; the latter from a secondary ferruginization process of reworked lateritic debris. The deepest troughs underlie saprolite-mantled source areas above channel heads, which are characterized by a low permeability saprolite, relatively high slope gradient, and lower area/slope ratios. Such source areas generate fairly high runoff, sustaining rivers and creeks with relatively high erosion power. The Ferricrete-mantled source areas are characterized by higher permeability and area/slope ratios, leading to lower runoff and less erosion but further chemical rock weathering. The Ferricrete of those source areas acts as a protective hardcover against mechanical erosion of the underlying regolith. This Ferricrete reworks, at least partly, allochtonous lateritic materials inherited from a previous disaggregated Ferricrete that suggests past erosion processes driven by hydro-climatic condition changes.
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Ferricrete genesis and supergene gold behaviour in Burkina Faso,West Africa
Geochemistry: Exploration Environment Analysis, 2002Co-Authors: Ousmane Bamba, Jean-claude Parisot, Georges Grandin, Anicet BeauvaisAbstract:The lateritic weathering process of Precambrian albitite formations containing gold sulphide mineralization has been studied at Larafella, southern Burkina Faso. The regional landscape consists of three land surface units with respective altitudes of 300 m, 280 m and 265–250 m. Plateaus on a barren schist formation form the first two upper units; there are remnants of two old planation surfaces capped by Ferricretes. The third unit is a large recent pediment covered by a soft Ferricrete. Within the weathering profile of this lower surface, preservation of the parent rock structures, Au and As content, Au particle morphology and the Ag content indicate the inheritance of the parent mineralized rock. The preservation of unweathered sulphides within the soft Ferricrete and their absence in the underlying saprolite indicate that the Ferricrete formed on a stripped surface at the expense of a slightly weathered rock, and preceded the formation of the clay horizons and the deepening of the weathering profile. Some sulphide grains and Au particles affected by transportation marks are also present within the Ferricrete of the upper units. Transported bauxitic and ferruginous debris of previous lateritic formations have also been described. The upper units are accumulation surfaces, each with 8–10 m of reworked material on the bedrock. The results provided here improve our knowledge of the geomorphic dynamics that can be useful for Au exploration in lateritic environments.
David M. Price - One of the best experts on this subject based on the ideXlab platform.
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Ferricretes at Burringurrah (Mount Augustus), Western Australia: Proof of lateral derivation
Geomorphology, 2020Co-Authors: Robert P. Bourman, Solomon Buckman, Allan R. Chivas, Clifford Ollier, David M. PriceAbstract:Abstract Surficial iron-rich deposits (Ferricretes) occur on and around Burringurrah (Mount Augustus), a huge, remote inselberg in the Gascoyne district of Western Australia. Oriented NW-SE, Burringurrah is approximately 14 km long, 5 km wide, rises to 1105 m above sea level and stands some 700 m above the surrounding plain. The majority of the Ferricretes occupy bedrock valley bottom floors on the southern side of the inselberg at Edney Springs, Flintstone Creek, and on the Edney Trail where they have formed on unweathered quartzose Mount Augustus Sandstone, which only contains a few percent Fe2O3. At ‘The Pound’, a boulder Ferricrete overlies deeply weathered igneous bedrock, unroofed by erosion of the overlying Mount Augustus Sandstone, exposing the unconformity between the weathered granitic bedrock and the Mount Augustus Sandstone in the core of a broad, asymmetrical and doubly plunging anticline. On the northern, steeper, side of the mountain, vermiform and conglomeratic Ferricretes are sparsely exposed in drainage lines. Ferricrete mineralogy is dominated by goethite with only small amounts of hematite. Oxygen isotope inferred ages of weathered monzogranite produced a top-down weathering front extending up to the Neogene at an elevation coincident with the Ferricretes within bedrock valley bottoms. Beyond the mountain, the age of Ferricreted sandy alluvium was established by thermoluminescence polymineral fine grain dating. These produced a minimum depositional age of >37.6 ± 2.6 ka and a second finite age of 139 ± 44 ka, suggesting Ferricrete formation here may have begun during the last interglacial period and continued throughout the late Pleistocene. Formation of Ferricretes on top of iron-poor quartzites is unusual. It reflects not only the absolute accumulation of iron oxides derived from the Mount Augustus Sandstone but possibly the additional contributions of iron-bearing aeolian dust from the surrounding plains subsequently washed down drainage lines to accumulate in swampy depressions at the foot of the inselberg. Ferricrete formation was initially simple, with iron in solution impregnating sandy sediment and organic host materials, sporadically impacted by bioturbation by termites. Thin-section petrography reveals an interesting form of in-situ, self-brecciation of quartz and feldspar clasts, which are fractured and infilled with iron oxides and newly precipitated clay which further promotes fragmentation. The mode of Ferricrete formation described from Burringurrah is relevant to the laterite-Ferricrete debate, for here it is most unlikely that the zones of iron enrichment developed in situ and vertically above the iron-poor quartzite basement as in the sense of the regional ‘classic laterite profile’.
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Quaternary inheritance of coastal landforms, Cobourg Peninsula, northern territory
Australian Geographer, 1992Co-Authors: Colin D. Woodroffe, David M. Price, Edward A Bryant, Stephen A. ShortAbstract:SUMMARY In contrast to the abundant evidence of former shorelines on the sea floor of the Sahul Shelf in northern Australia, little evidence has been reported for late Pleistocene coastal landforms along the modern coast of north Australia. Using radiocarbon, thermoluminescence and uranium/thorium dating techniques, however, it can be shown that the present coastal morphology on the Cobourg Peninsula is partly inherited from features both deposited and eroded during the late Quaternary. Shore platforms, in particular, are veneered with Ferricretes, some of which can be U/Th dated. In places bedforms are preserved within the Ferricrete, suggesting that the platform existed at, and was modified during, the Last Interglacial, and probably formed during earlier interglacials. TL dating indicates that sands around Cape Don were deposited when sea level was lower, but may have been reworked during a Holocene high stand. A sequence of beach ridges at Smith Point indicates Holocene progradation over an earlier pl...
Robert P. Bourman - One of the best experts on this subject based on the ideXlab platform.
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Ferricretes at Burringurrah (Mount Augustus), Western Australia: Proof of lateral derivation
Geomorphology, 2020Co-Authors: Robert P. Bourman, Solomon Buckman, Allan R. Chivas, Clifford Ollier, David M. PriceAbstract:Abstract Surficial iron-rich deposits (Ferricretes) occur on and around Burringurrah (Mount Augustus), a huge, remote inselberg in the Gascoyne district of Western Australia. Oriented NW-SE, Burringurrah is approximately 14 km long, 5 km wide, rises to 1105 m above sea level and stands some 700 m above the surrounding plain. The majority of the Ferricretes occupy bedrock valley bottom floors on the southern side of the inselberg at Edney Springs, Flintstone Creek, and on the Edney Trail where they have formed on unweathered quartzose Mount Augustus Sandstone, which only contains a few percent Fe2O3. At ‘The Pound’, a boulder Ferricrete overlies deeply weathered igneous bedrock, unroofed by erosion of the overlying Mount Augustus Sandstone, exposing the unconformity between the weathered granitic bedrock and the Mount Augustus Sandstone in the core of a broad, asymmetrical and doubly plunging anticline. On the northern, steeper, side of the mountain, vermiform and conglomeratic Ferricretes are sparsely exposed in drainage lines. Ferricrete mineralogy is dominated by goethite with only small amounts of hematite. Oxygen isotope inferred ages of weathered monzogranite produced a top-down weathering front extending up to the Neogene at an elevation coincident with the Ferricretes within bedrock valley bottoms. Beyond the mountain, the age of Ferricreted sandy alluvium was established by thermoluminescence polymineral fine grain dating. These produced a minimum depositional age of >37.6 ± 2.6 ka and a second finite age of 139 ± 44 ka, suggesting Ferricrete formation here may have begun during the last interglacial period and continued throughout the late Pleistocene. Formation of Ferricretes on top of iron-poor quartzites is unusual. It reflects not only the absolute accumulation of iron oxides derived from the Mount Augustus Sandstone but possibly the additional contributions of iron-bearing aeolian dust from the surrounding plains subsequently washed down drainage lines to accumulate in swampy depressions at the foot of the inselberg. Ferricrete formation was initially simple, with iron in solution impregnating sandy sediment and organic host materials, sporadically impacted by bioturbation by termites. Thin-section petrography reveals an interesting form of in-situ, self-brecciation of quartz and feldspar clasts, which are fractured and infilled with iron oxides and newly precipitated clay which further promotes fragmentation. The mode of Ferricrete formation described from Burringurrah is relevant to the laterite-Ferricrete debate, for here it is most unlikely that the zones of iron enrichment developed in situ and vertically above the iron-poor quartzite basement as in the sense of the regional ‘classic laterite profile’.
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Traces from the past: The Cenozoic regolith and intraplate neotectonic history of the Gun Emplacement, a Ferricreted bench on the western margin of the Mt Lofty ranges, South Australia
Australian Journal of Earth Sciences, 2010Co-Authors: Robert P. Bourman, Solomon Buckman, Brad Pillans, Martin Williams, Frances M. WilliamsAbstract:The Gun Emplacement is a small but distinctive bench on the Eden–Burnside Fault Escarpment near Anstey Hill, in the northeastern suburbs of Adelaide, South Australia, occurring at an elevation of ∼210–220 m asl. It is underlain by Middle Eocene North Maslin Sand and is capped by resistant, Ferricreted colluvium. Paleomagnetic dating of hematitic mottles in the Ferricreted colluvium, immediately underlying the emplacement, returned a Pliocene/Early Pleistocene age. This age is equivalent to that obtained for summit surface weathering. Fault scarps and exposures, including slickensides and fault gouge material, suggest that the Eden–Burnside Fault at this location has a strong en echelon pattern developed in response to reverse-sinistral oblique-slip faulting, reflecting continental stress fields. Remnants of Ferricrete cappings forming stranded benches on the Eden–Burnside Fault Escarpment at elevations up to 25 m above the Gun Emplacement demonstrate recurrent tectonism of the South Mt Lofty Ranges relate...
Torsten Schwarz - One of the best experts on this subject based on the ideXlab platform.
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Distribution and genesis of bauxite on the Mambilla Plateau. SE Nigeria
Applied Geochemistry, 1997Co-Authors: Torsten SchwarzAbstract:Abstract Only small, low grade occurrences of bauxite are known in Nigeria, associated with Ferricretes on the Jos Plateau. Widespread bauxite has been discovered on the Mambilla Plateau. Laterite is developed on gneisses and basalt, while on trachytic parent rocks low-silica bauxite occurs with a thickness of more than 5 m and covering an area of at least 1 km2. This bauxite consists of gibbsite and goethite. In contrast to the Ferricretes of the Jos Plateau, weathering on the Mambilla Plateau led to the formation of stone line profiles. Ferricretes were developed on the Upper Jurassic Gondwana surface under contrasting climate and are preserved as relicts in the southern part of the Mambilla Plateau where weathered Precambrian basement occurs in a highly uplifted position. Dismantling of these Ferricretes is attributed to a gradual change of paleoclimate towards more humid conditions. After the extrusion of volcanic rocks in the northern part of the plateau, presumably during Lower to Mid Miocene, these volcanics underwent intense chemical weathering. Bauxite and laterite formed depending on the type of parent rock. Weathering profiles are mostly truncated and overlain by reworked material. Allochthonous components occur both within and also below the stone-line. This is shown by mineralogical indicators such as ilmenite or quartz and by a shift in the Zr/Ti-ratio. Similar profiles are missing further north on the Jos plateau, where Ferricretes formed instead. This is attributed to regional differences in paleoclimatic conditions which were more humid at Mambilla while Jos was under the influence of dryer conditions. The widespread formation of laterite on different parent rocks on the Mambilla Plateau could be related to a global Mid-Miocene climatic optimum, which led to a general intensification of chemical weathering processes.
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Ferricrete formation and relief inversion: an example from Central Sudan
CATENA, 1994Co-Authors: Torsten SchwarzAbstract:Abstract The development of a Ferricrete in relationship to the structural and morphological evolution is demonstrated by the example of Jebel Howag (Kordofan, Sudan). Products of deep lateritic weathering have been reworked by mass wasting processes. In this material a Ferricrete developed in a low landscape position by lateral migration and absolute enrichment of iron. Subsequently, relief inversion brought the hard Ferricrete into its present high position. During the Miocene this Ferricrete plateau was disrupted by faulting, which has been used to indicate the minimum age of the Ferricrete. The composition and structure of the Jebel Howag Ferricrete are identical with those of Ferricretes formed on deep lateritic weathering profiles. Compositional differences such as Al-goethite and high V-contents distinguish such Ferricretes from ferruginized sediments.
Solomon Buckman - One of the best experts on this subject based on the ideXlab platform.
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Ferricretes at Burringurrah (Mount Augustus), Western Australia: Proof of lateral derivation
Geomorphology, 2020Co-Authors: Robert P. Bourman, Solomon Buckman, Allan R. Chivas, Clifford Ollier, David M. PriceAbstract:Abstract Surficial iron-rich deposits (Ferricretes) occur on and around Burringurrah (Mount Augustus), a huge, remote inselberg in the Gascoyne district of Western Australia. Oriented NW-SE, Burringurrah is approximately 14 km long, 5 km wide, rises to 1105 m above sea level and stands some 700 m above the surrounding plain. The majority of the Ferricretes occupy bedrock valley bottom floors on the southern side of the inselberg at Edney Springs, Flintstone Creek, and on the Edney Trail where they have formed on unweathered quartzose Mount Augustus Sandstone, which only contains a few percent Fe2O3. At ‘The Pound’, a boulder Ferricrete overlies deeply weathered igneous bedrock, unroofed by erosion of the overlying Mount Augustus Sandstone, exposing the unconformity between the weathered granitic bedrock and the Mount Augustus Sandstone in the core of a broad, asymmetrical and doubly plunging anticline. On the northern, steeper, side of the mountain, vermiform and conglomeratic Ferricretes are sparsely exposed in drainage lines. Ferricrete mineralogy is dominated by goethite with only small amounts of hematite. Oxygen isotope inferred ages of weathered monzogranite produced a top-down weathering front extending up to the Neogene at an elevation coincident with the Ferricretes within bedrock valley bottoms. Beyond the mountain, the age of Ferricreted sandy alluvium was established by thermoluminescence polymineral fine grain dating. These produced a minimum depositional age of >37.6 ± 2.6 ka and a second finite age of 139 ± 44 ka, suggesting Ferricrete formation here may have begun during the last interglacial period and continued throughout the late Pleistocene. Formation of Ferricretes on top of iron-poor quartzites is unusual. It reflects not only the absolute accumulation of iron oxides derived from the Mount Augustus Sandstone but possibly the additional contributions of iron-bearing aeolian dust from the surrounding plains subsequently washed down drainage lines to accumulate in swampy depressions at the foot of the inselberg. Ferricrete formation was initially simple, with iron in solution impregnating sandy sediment and organic host materials, sporadically impacted by bioturbation by termites. Thin-section petrography reveals an interesting form of in-situ, self-brecciation of quartz and feldspar clasts, which are fractured and infilled with iron oxides and newly precipitated clay which further promotes fragmentation. The mode of Ferricrete formation described from Burringurrah is relevant to the laterite-Ferricrete debate, for here it is most unlikely that the zones of iron enrichment developed in situ and vertically above the iron-poor quartzite basement as in the sense of the regional ‘classic laterite profile’.
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Traces from the past: The Cenozoic regolith and intraplate neotectonic history of the Gun Emplacement, a Ferricreted bench on the western margin of the Mt Lofty ranges, South Australia
Australian Journal of Earth Sciences, 2010Co-Authors: Robert P. Bourman, Solomon Buckman, Brad Pillans, Martin Williams, Frances M. WilliamsAbstract:The Gun Emplacement is a small but distinctive bench on the Eden–Burnside Fault Escarpment near Anstey Hill, in the northeastern suburbs of Adelaide, South Australia, occurring at an elevation of ∼210–220 m asl. It is underlain by Middle Eocene North Maslin Sand and is capped by resistant, Ferricreted colluvium. Paleomagnetic dating of hematitic mottles in the Ferricreted colluvium, immediately underlying the emplacement, returned a Pliocene/Early Pleistocene age. This age is equivalent to that obtained for summit surface weathering. Fault scarps and exposures, including slickensides and fault gouge material, suggest that the Eden–Burnside Fault at this location has a strong en echelon pattern developed in response to reverse-sinistral oblique-slip faulting, reflecting continental stress fields. Remnants of Ferricrete cappings forming stranded benches on the Eden–Burnside Fault Escarpment at elevations up to 25 m above the Gun Emplacement demonstrate recurrent tectonism of the South Mt Lofty Ranges relate...