The Experts below are selected from a list of 11496 Experts worldwide ranked by ideXlab platform
Romesh Palamakumbura - One of the best experts on this subject based on the ideXlab platform.
-
Table S1. Sedimentary Geochemistry used to infer the provenance of Permian–Triassic marine sandstones related to the SE Gondwana active continental margin, South Island, New Zealand
2019Co-Authors: Alastair H.f. Robertson, Romesh PalamakumburaAbstract:Point-count data for sandstones from the Murihiku Terrane (Late Permian of the Kuriwao Group, Titiroa area, Southland; Late Triassic of the Taringatura Group, Nugget Point, Southland; Late Triassic of the Richmond Group, Nelson area) (see Fig. S6)
-
Fig. S3. Sedimentary Geochemistry used to infer the provenance of Permian–Triassic marine sandstones related to the SE Gondwana active continental margin, South Island, New Zealand
2019Co-Authors: Alastair H.f. Robertson, Romesh PalamakumburaAbstract:Outline geological map of the Late Permian succession of the Murihiku Terrane exposed in the 'Mataura Island'–Titiroa area, southern Southland
-
Fig. S2. Sedimentary Geochemistry used to infer the provenance of Permian–Triassic marine sandstones related to the SE Gondwana active continental margin, South Island, New Zealand
2019Co-Authors: Alastair H.f. Robertson, Romesh PalamakumburaAbstract:Photomicrographs of sandstones. (a)–(f) From the Permian–Triassic succession exposed at Parapara Peak, Takaka Terrane, Western Province. (a) Large, rounded grain of microcrystalline quartz (translucent; central) set in smaller angular to sub-rounded quartz grains, together with some plagioclase; GPS WSG 84 E24 82605 N60 40305; viewed under plane polarized light (PPL); Parapara section, Flowers Formation; Western Province. (b) Foliated siltstone lithoclast (partially recrystallized) within detrital grains of mostly quartz and plagioclase (as in a). The brown mineral is neomorphic biotite; viewed under PPL; Flowers Formation; Parapara section. (c) Large, sub-angular grain of altered feldspar (orthoclase) within smaller mostly angular to sub-angular grains, including common polycrystalline (detrital metamorphic) quartz; viewed under crossed nicols; Flowers Formation; Parapara section. (d) Upper left: polycrystalline quartz grain; centre right: large uniform monocrystalline quartz grain, of probable plutonic rock origin; note the incipient cleavage development picked out by neomorphic biotite; viewed under crossed nicols; Flowers Formation; Parapara section. (e) Large detrital grain of monocrystalline quartz showing incipient recrystallization at the edges, together with recrystallization of finer-grained quartz and biotite; viewed under plane crossed nicols; Flowers Formation; Parapara section. (f) Rounded monocrystalline quartz which cracked prior to final deposition; note the incipient cleavage picked out by biotite; Walker Formation; Parapara section
-
chapter 10 Sedimentary Geochemistry used to infer the provenance of permian triassic marine sandstones related to the se gondwana active continental margin south island new zealand
Geological Society London Memoirs, 2019Co-Authors: Alastair H.f. Robertson, Romesh PalamakumburaAbstract:Abstract Major, trace and rare earth element data for sandstones and conglomerates from the Mid-Permian–Mid-Triassic Maitai Group are compared with other tectonostratigraphic units, using discrimination diagrams and comparisons with potential source terranes. Maitai Group sandstones reveal a mainly ophiolitic–oceanic-arc source during the Mid-Permian, followed by a mixed continental margin-arc–terrigenous source during the Late Permian. Latest Permian–Early Triassic sandstones mainly came from little-evolved continental margin-arc extrusives, tending to more evolved (but variable) during the Triassic. Source volcanism of the Murihiku Terrane sandstones was magmatically evolved relative to the Maitai Group generally (except during the Late Triassic). The Maitai Group and Murihiku Terrane are restored as proximal and more distal parts, respectively, of the SE Gondwana forearc basin. The localized Willsher Group shows some Maitai Group affinities. Sandstones in two melanges that formed in an outer forearc–subduction trench setting mainly indicate a mixed terrigenous–continental margin-arc source, similar to the Late Permian Maitai Group. The Caples Terrane, a Triassic accretionary prism, received detritus from little-evolved, to evolved continental margin-arc volcanics and terrigenous sources. Much of the arc-related material in all units is compatible with derivation from the latest Permian–Triassic Median Batholith, or a lateral equivalent along the SE Gondwana active margin.
Alastair H.f. Robertson - One of the best experts on this subject based on the ideXlab platform.
-
Table S1. Sedimentary Geochemistry used to infer the provenance of Permian–Triassic marine sandstones related to the SE Gondwana active continental margin, South Island, New Zealand
2019Co-Authors: Alastair H.f. Robertson, Romesh PalamakumburaAbstract:Point-count data for sandstones from the Murihiku Terrane (Late Permian of the Kuriwao Group, Titiroa area, Southland; Late Triassic of the Taringatura Group, Nugget Point, Southland; Late Triassic of the Richmond Group, Nelson area) (see Fig. S6)
-
Fig. S3. Sedimentary Geochemistry used to infer the provenance of Permian–Triassic marine sandstones related to the SE Gondwana active continental margin, South Island, New Zealand
2019Co-Authors: Alastair H.f. Robertson, Romesh PalamakumburaAbstract:Outline geological map of the Late Permian succession of the Murihiku Terrane exposed in the 'Mataura Island'–Titiroa area, southern Southland
-
Fig. S2. Sedimentary Geochemistry used to infer the provenance of Permian–Triassic marine sandstones related to the SE Gondwana active continental margin, South Island, New Zealand
2019Co-Authors: Alastair H.f. Robertson, Romesh PalamakumburaAbstract:Photomicrographs of sandstones. (a)–(f) From the Permian–Triassic succession exposed at Parapara Peak, Takaka Terrane, Western Province. (a) Large, rounded grain of microcrystalline quartz (translucent; central) set in smaller angular to sub-rounded quartz grains, together with some plagioclase; GPS WSG 84 E24 82605 N60 40305; viewed under plane polarized light (PPL); Parapara section, Flowers Formation; Western Province. (b) Foliated siltstone lithoclast (partially recrystallized) within detrital grains of mostly quartz and plagioclase (as in a). The brown mineral is neomorphic biotite; viewed under PPL; Flowers Formation; Parapara section. (c) Large, sub-angular grain of altered feldspar (orthoclase) within smaller mostly angular to sub-angular grains, including common polycrystalline (detrital metamorphic) quartz; viewed under crossed nicols; Flowers Formation; Parapara section. (d) Upper left: polycrystalline quartz grain; centre right: large uniform monocrystalline quartz grain, of probable plutonic rock origin; note the incipient cleavage development picked out by neomorphic biotite; viewed under crossed nicols; Flowers Formation; Parapara section. (e) Large detrital grain of monocrystalline quartz showing incipient recrystallization at the edges, together with recrystallization of finer-grained quartz and biotite; viewed under plane crossed nicols; Flowers Formation; Parapara section. (f) Rounded monocrystalline quartz which cracked prior to final deposition; note the incipient cleavage picked out by biotite; Walker Formation; Parapara section
-
chapter 10 Sedimentary Geochemistry used to infer the provenance of permian triassic marine sandstones related to the se gondwana active continental margin south island new zealand
Geological Society London Memoirs, 2019Co-Authors: Alastair H.f. Robertson, Romesh PalamakumburaAbstract:Abstract Major, trace and rare earth element data for sandstones and conglomerates from the Mid-Permian–Mid-Triassic Maitai Group are compared with other tectonostratigraphic units, using discrimination diagrams and comparisons with potential source terranes. Maitai Group sandstones reveal a mainly ophiolitic–oceanic-arc source during the Mid-Permian, followed by a mixed continental margin-arc–terrigenous source during the Late Permian. Latest Permian–Early Triassic sandstones mainly came from little-evolved continental margin-arc extrusives, tending to more evolved (but variable) during the Triassic. Source volcanism of the Murihiku Terrane sandstones was magmatically evolved relative to the Maitai Group generally (except during the Late Triassic). The Maitai Group and Murihiku Terrane are restored as proximal and more distal parts, respectively, of the SE Gondwana forearc basin. The localized Willsher Group shows some Maitai Group affinities. Sandstones in two melanges that formed in an outer forearc–subduction trench setting mainly indicate a mixed terrigenous–continental margin-arc source, similar to the Late Permian Maitai Group. The Caples Terrane, a Triassic accretionary prism, received detritus from little-evolved, to evolved continental margin-arc volcanics and terrigenous sources. Much of the arc-related material in all units is compatible with derivation from the latest Permian–Triassic Median Batholith, or a lateral equivalent along the SE Gondwana active margin.
Zhangdong Jin - One of the best experts on this subject based on the ideXlab platform.
-
lake qinghai sediment Geochemistry linked to hydroclimate variability since the last glacial
Quaternary Science Reviews, 2015Co-Authors: Zhangdong Jin, Fei ZhangAbstract:Abstract Geochemistry of basin sediments from semi-arid regions is valuable to understand past hydroclimatic changes. Here, we investigate the links of Sedimentary Geochemistry (Rb, Sr, Ca/Zr, TOC, and %CaCO 3 ), carbonate mineralogy and ostracod shell δ 18 O of Lake Qinghai, a basin proximal to major dust production centers at mid-latitudes of the Northern Hemisphere, to changes in depositional conditions and hydroclimate during the past 32 ka. Surface lacustrine sediments are characterized by low-Rb, high-Sr, low-Rb/Sr, high-%CaCO 3 and high-Ca/Zr values, in contrast to the chemical compositions of eolian loess (high-Rb, low-Sr, high-Rb/Sr, low-%CaCO 3 , and low-Ca/Zr). A direct comparison of soluble Ca and Sr in two short cores with instrumental water discharge data suggests that lacustrine precipitates in Lake Qinghai are dominated by authigenic aragonite formed under Ca 2+ -limited water conditions, and that the accumulation rate of aragonite dominantly depends on solute fluxes into the lake during the rainy seasons (late May to September). Our high-resolution down-core records show that sediments during the last glacial (∼32–19.8 ka) had high-Rb, low-Sr, low-%CaCO 3 , and low-Ca/Zr, indicating eolian dust (loess) accumulation in a desiccated basin under dry glacial conditions, further supported by grain size and pollen results. This type of sedimentation was maintained during the last deglacial (∼19.8–11.5 ka), but interrupted by episodic lacustrine precipitates with high-Sr, high-%CaCO 3 , high-Ca/Zr, and low-Rb. At ∼11.5 ka, Sedimentary Rb/Sr, Ca/Zr, %CaCO 3 and TOC show dramatic and permanent changes, implying an abrupt shift in the atmospheric circulation at the onset of the Holocene in the Lake Qinghai region. Lacustrine precipitates have persisted throughout the Holocene with a maximum during the early to mid-Holocene (∼10.5–8.0 ka). Since ∼8.0 ka, the gradual and significant decreases in aragonite and Sr accumulations in tandem with increasing dust deposit and more positive ostracod δ 18 O may be linked to a weakening of Asian summer monsoons during the mid-to-late Holocene. Overall, our records appear to show a high sensitivity of sediment development and Geochemistry in Lake Qinghai to the regional hydroclimate changes since the last glacial.
T F Pedersen - One of the best experts on this subject based on the ideXlab platform.
-
Sedimentary Geochemistry of manganese implications for the environment of formation of manganiferous black shales
Economic Geology, 1996Co-Authors: S E Calvert, T F PedersenAbstract:The Sedimentary Geochemistry of manganese is dominated by the redox control of its speciation, higher oxidation states (Mn (super 3+) and (super 4+) ) occurring as insoluble oxyhydroxides in well-oxygenated environments and the lower oxidation state (Mn (super 2+) ) being much more soluble in oxygen-deficient settings. Its geochemical behavior is therefore quite different in oxic and anoxic environments, and where oxic and anoxic conditions are juxtaposed, Mn is recycled between the two environments. In modern marine sediments, Mn is present above its crustal abundance as an oxyhydroxide in all slowly accumulating (pelagic) sediments of the deep ocean and in surficial deposits of continental margin environments. Diagenetic recycling of Mn in the latter causes surficial deposits to have larger Mn enrichments than in many pelagic sediments. Bottom sediments of permanently anoxic basins show no enrichments and have Mn concentrations that are controlled solely by the aluminosilicate fraction. Manganese carbonates (kutnohorite and calcic rhodochrosite) are found only in anoxic sediments accumulating beneath surface oxic horizons (and therefore under oxygenated bottom waters) in many nearshore environments. Such enrichments are due to delivery of Mn by burial of surface oxyhydroxides into the subsurface anoxic environment where they are dissolved. Pore-water Mn levels can reach saturation with respect to a mixed Mn-Ca carbonate phase in such sediments. The diagenetic origin for these phases is shown by their carbon isotope compositions, which typically indicate a carbon source from decomposing organic matter. The presence of Mn carbonates therefore signifies that the host sediment must have accumulated under oxygenated bottom waters.On the basis of this information it is proposed that, in contrast to several current explanations for the formation of Mn carbonates (kutnohorite and rhodochrosite) in ancient organic-rich shales, limestone, and marl sequences and in many Mn ore deposits, the occurrence of these mineral phases indicates that the sediments originally accumulated beneath oxygenated bottom waters. By analogy with the present, Mn carbonates could not have formed in the bottom waters of anoxic basins. These diagenetic phases, however, did form where Mn was supplied at a high rate, namely, by the burial of oxyhydroxide-enriched surface sediments, to a subsurface anoxic environment. This situation could only have occurred under oxygenated bottom waters. The presence of Mn carbonates in ancient black shales (and in some carbonate-rich rocks) lends strong support to the notion that these rocks did not necessarily form in anoxic basins but owe their carbon richness to a high supply of organic matter to sediments deposited under oxygenated bottom waters, probably in continental margin settings.
Fei Zhang - One of the best experts on this subject based on the ideXlab platform.
-
lake qinghai sediment Geochemistry linked to hydroclimate variability since the last glacial
Quaternary Science Reviews, 2015Co-Authors: Zhangdong Jin, Fei ZhangAbstract:Abstract Geochemistry of basin sediments from semi-arid regions is valuable to understand past hydroclimatic changes. Here, we investigate the links of Sedimentary Geochemistry (Rb, Sr, Ca/Zr, TOC, and %CaCO 3 ), carbonate mineralogy and ostracod shell δ 18 O of Lake Qinghai, a basin proximal to major dust production centers at mid-latitudes of the Northern Hemisphere, to changes in depositional conditions and hydroclimate during the past 32 ka. Surface lacustrine sediments are characterized by low-Rb, high-Sr, low-Rb/Sr, high-%CaCO 3 and high-Ca/Zr values, in contrast to the chemical compositions of eolian loess (high-Rb, low-Sr, high-Rb/Sr, low-%CaCO 3 , and low-Ca/Zr). A direct comparison of soluble Ca and Sr in two short cores with instrumental water discharge data suggests that lacustrine precipitates in Lake Qinghai are dominated by authigenic aragonite formed under Ca 2+ -limited water conditions, and that the accumulation rate of aragonite dominantly depends on solute fluxes into the lake during the rainy seasons (late May to September). Our high-resolution down-core records show that sediments during the last glacial (∼32–19.8 ka) had high-Rb, low-Sr, low-%CaCO 3 , and low-Ca/Zr, indicating eolian dust (loess) accumulation in a desiccated basin under dry glacial conditions, further supported by grain size and pollen results. This type of sedimentation was maintained during the last deglacial (∼19.8–11.5 ka), but interrupted by episodic lacustrine precipitates with high-Sr, high-%CaCO 3 , high-Ca/Zr, and low-Rb. At ∼11.5 ka, Sedimentary Rb/Sr, Ca/Zr, %CaCO 3 and TOC show dramatic and permanent changes, implying an abrupt shift in the atmospheric circulation at the onset of the Holocene in the Lake Qinghai region. Lacustrine precipitates have persisted throughout the Holocene with a maximum during the early to mid-Holocene (∼10.5–8.0 ka). Since ∼8.0 ka, the gradual and significant decreases in aragonite and Sr accumulations in tandem with increasing dust deposit and more positive ostracod δ 18 O may be linked to a weakening of Asian summer monsoons during the mid-to-late Holocene. Overall, our records appear to show a high sensitivity of sediment development and Geochemistry in Lake Qinghai to the regional hydroclimate changes since the last glacial.