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Robert M Carter - One of the best experts on this subject based on the ideXlab platform.
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plio pleistocene Cyclothems from wanganui basin new zealand type locality for an astrochronologic time scale or template for recognizing ancient glacio eustacy
Philosophical transactions - Royal Society. Mathematical physical and engineering sciences, 1999Co-Authors: Robert M Carter, S T Abbott, T R NaishAbstract:Wanganui Basin is a 200 200 km 2 ovoid sedimentary basin of Plio-Pleistocene age situated in a back-arc position in western North Island, New Zealand. The eastern edge of the basin has been subjected to smooth tectonic uplift since about 350 000 years BP, resulting in the exposure onland of young sediments which elsewhere are more usually located beneath the modern continental shelf. The ll of the basin comprises several kilometres of markedly Cyclothemic sediment of Plio-Pleistocene age. Accurate environmental interpretation of the succession is greatly enhanced by the presence of abundant sedimentary structures, and fossil invertebrates whose conspecic descendants live in modern New Zealand seas. The maximum water depth attained during the deposition of most Cyclothems is less than 100 m, i.e. less than the known 100{130 m magnitude of most Late Pleistocene sea-level fluctuations. The magnetostratigraphic boundaries and abundant tephra which occur within the section allow accurate international correlation. The 47 Wanganui Cyclothems which correspond to the last 2.4 Ma (oxygen isotope stages 100{1) each correlate with the highstand part only of each glacial-interglacial isotope stage couplet, i.e. with oddnumbered isotope stages. Even-numbered glacial stages are represented by the unconformities which separate stratigraphically adjacent Cyclothems, and which mark sealevel withdrawal and subaerial exposure of the inner part of the basin. Therefore, only about half of elapsed geological time is represented by sediment within shallowwater basin lls deposited during times of high-amplitude glacio-eustatic sea-level fluctuation. Such strata, including those at Wanganui, are unsuitable for use as type sections for time-scale intervals. Nonetheless, the Cyclothemic sedimentary motifs described from Wanganui, and especially the known relationships there between shellbed type and systems tracts, provide invaluable insights for the interpretation of other Phanerozoic glacio-eustatic successions such as those of Permo-Carboniferous and Ordovician age.
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sedimentary cyclicity in the marine pliocene pleistocene of the wanganui basin new zealand sequence stratigraphic motifs characteristic of the past 2 5 m y
Geological Society of America Bulletin, 1999Co-Authors: G Saul, Tim R Naish, S T Abbott, Robert M CarterAbstract:Earth’s climatic history since 2.5 Ma has been controlled by Milankovitch variations in the planetary orbit, comprising alternate periods of glaciation and interglaciation with a dominant frequency of 41 000 yr. Concomitantly, eustatic sea level has fluctuated 70 to 130 m, causing rapid transgressions and regressions of the shoreline across the world’s continental shelves. The resulting sedimentary record is Cyclothemic, each Cyclothem corresponding to a single climate and sea-level cycle. The Wanganui basin, New Zealand, contains a 2-km-thick, almost complete, composite record since isotope stage 100 (ca. 2.5 Ma) in the form of 47 superposed Cyclothems of shelf origin. Each Cyclothem corresponds to an unconformity-bound stratigraphic sequence, and typically contains a transgressive systems tract, sometimes a mid-cycle shell bed, a highstand systems tract, and sometimes a regressive systems tract. No advantage accrues from using transgressive-regressive units rather than Cyclothems and/or sequences in description of the succession. Six basic sequence motifs represent deposition in locations between the shoreline and offshore shelf, i.e., the Hawera, Birdgrove, Turakina, Seafield, Castlecliff, and Rangitikei motifs. A seventh, the Nukumaru motif (which includes dominant coquina limestone), represents deposition in shallow-water areas of reduced terrigenous sediment on the flank of the basin. The sequence motifs represented in any section change systematically in sympathy with basin-scale changes in subsidence and sediment supply. In contrast with the 41000 year length of individual glacioeustatic sequences, these basin-wide tectonic cycles have a periodicity of many hundreds of thousands to a few million years, i.e., that of third- or fourth-order sequences of the Exxon type. This, coupled with the restriction of strongly Cyclothemic sediments to geological periods of known glacio-eustasy (PermianCarboniferous, Pliocene-Pleistocene), suggests that tectonic subsidence cycles rather than glacio-eustasy are the driving forces behind the development of the third- and fourth-order unconformity-bound sequences that are reported to occur throughout the stratigraphic record.
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a review of wanganui basin new zealand global reference section for shallow marine plio pleistocene 2 5 0 ma cyclostratigraphy
Sedimentary Geology, 1998Co-Authors: Robert M Carter, Tim R NaishAbstract:Abstract Wanganui Basin, New Zealand, contains one of the most complete late Neogene marine stratigraphic records in the world. The ca. 2 km thick basin-fill for the last ca. 2.5 Ma comprises 47 superposed Cyclothems which correspond to successive 5th (100 ka) and 6th (41 ka) order glacio-eustatic, sea-level fluctuations on the palaeo-New Zealand shelf since oxygen isotope stage 100. Stages 100 to 5 are represented by marine Cyclothems, whereas stages 17 to 3 are represented by a suite of coeval and younger uplifted marine terrace sequences. Additionally, a predominantly glacial loess stratigraphy exists for isotope stages 12–2. The presence of interbedded tephras and an established paleomagnetic stratigraphy allows the development of an integrated cyclostratigraphy for Wanganui Basin which correlates closely with the global oxygen isotope scale. In all except two cases (cycles 12 and 36), individual unconformity-bound Cyclothems (sequences) represent a single glacial/interglacial couplet of Milankovitch frequency. Lithologic and faunal variation within the Cyclothems corresponds closely to that predicted by the sequence stratigraphic model. Each Cyclothem generally contains a transgressive systems tract, a mid-cycle condensed shellbed, a highstand systems tract, and often a regressive systems tract. Six common Cyclothem motifs are inferred to represent deposition in shelf locations between the highstand and lowstand shorelines, viz. the Hawera, Maxwell, Turakina, Seafield, Castlecliff, and Rangitikei motifs. A seventh type, the Nukumaru motif, includes coquina limestone and represents deposition in shoreface and very shallow water marine environments.
David Pollard - One of the best experts on this subject based on the ideXlab platform.
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2007), Orbital and CO 2 forcing of late Paleozoic continental ice sheets, Geophys
2015Co-Authors: Daniel E Horton, Christopher J Poulsen, David PollardAbstract:[1] Contrasting views of the size, duration, and history of the Gondwanan continental ice sheets have been proposed from late Paleozoic glaciological and sedimentological evidence. To evaluate these differing views, a coupled ice sheet-climate model is used to simulate continental ice sheets under a wide range of late Paleozoic orbital and pCO2 conditions. The model experiments indicate that orbital variations at pCO2 concentrations below 2X pre-industrial atmospheric levels (PAL; 280 ppm) produce large changes in late Paleozoic ice volume (1.3 108 km3) and sea level (20 to 245 m). Between 2 and 8X PAL Gondwana continental ice is simulated only under the most extreme Southern Hemisphere cold summer orbit, but still produces significant ice volumes (8–12 107 km3). Our results highlight the important role of atmospheric CO2 in determining the distribution, volume, and stability of late Paleozoic ice sheets, factors that ultimately impacted sea level, Cyclothem deposition, and global climate, and reconcile disparate views of the Late Paleozoic Ice Age
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orbital and co2 forcing of late paleozoic continental ice sheets
Geophysical Research Letters, 2007Co-Authors: Daniel E Horton, Christopher J Poulsen, David PollardAbstract:[1] Contrasting views of the size, duration, and history of the Gondwanan continental ice sheets have been proposed from late Paleozoic glaciological and sedimentological evidence. To evaluate these differing views, a coupled ice sheet-climate model is used to simulate continental ice sheets under a wide range of late Paleozoic orbital and pCO2 conditions. The model experiments indicate that orbital variations at pCO2 concentrations below 2X pre-industrial atmospheric levels (PAL; 280 ppm) produce large changes in late Paleozoic ice volume (∼1.3 × 108 km3) and sea level (∼20 to 245 m). Between 2 and 8X PAL Gondwana continental ice is simulated only under the most extreme Southern Hemisphere cold summer orbit, but still produces significant ice volumes (∼8–12 × 107 km3). Our results highlight the important role of atmospheric CO2 in determining the distribution, volume, and stability of late Paleozoic ice sheets, factors that ultimately impacted sea level, Cyclothem deposition, and global climate, and reconcile disparate views of the Late Paleozoic Ice Age.
Yu Qi - One of the best experts on this subject based on the ideXlab platform.
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organic matter provenance and depositional environment of marine to continental mudstones and coals in eastern ordos basin china evidence from molecular geochemistry and petrology
International Journal of Coal Geology, 2020Co-Authors: Leon Bowen, Kun Yu, Yiwen Ju, Yu Qi, Cheng Huang, Weilai ZhangAbstract:Abstract Cyclothems, composed of interbedded mudstone, coal and sandstone layers, make up the Taiyuan and Shanxi Formations in the Late Carboniferous to Early Permian in North China under a marine-to-continental depositional environment. The Cyclothems act as important fossil energy hosts, such as coalbeds, hydrocarbon source rocks and unconventional natural gas reservoirs. Organic geochemistry and petrology of mudstones and coals in the Taiyuan and Shanxi Formations in the eastern Ordos Basin were studied to reveal the organic matter sources and paleoenvironments. Total organic carbon (TOC) contents vary from 1.1 wt% (mudstone) to 72.6 wt% (coal). The samples are mainly within the oil window, with the Tmax values ranging from 433 to 469 °C. Organic petrology and source biomarkers indicate that the mudstones were sourced from a mixed organic matter input, and terrigenous organic matter predominates over aquatic organic matter. The coals are mostly sourced by terrigenous organic matter inputs. High concentrations of hopanes argue for a strong bacterial input. Some m/z 217 mass chromatograms have peaks at the hopanes' retention times as a result of high hopane to sterane ratios. These hopane-derived peaks do not interfere the identification of the steranes because the hopanes and the steranes have different retention times. Maturity-dependent biomarkers demonstrate that the samples have been thermally mature, which agree with the Tmax values. Anomalously low C29 20S/(20S + 20R) and C29 ββ/(ββ + αα) sterane ratios are present in all the samples, and are interpreted as due to the terrigenous organic matter input or the coal-related depositional environment. In addition, biomarkers and iron sulfide morphology indicate that the organic matter of the mudstones deposited in a proximal setting with shallow, brackish/fresh water bodies. With consideration of preservation of organic matter, the redox conditions are dysoxic. Redox oscillations resulted in the records of oxic conditions in some samples. Finally, the coals and the mudstones mainly generate gas and have poor oil generative potential.
Tim R Naish - One of the best experts on this subject based on the ideXlab platform.
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sedimentary cyclicity in the marine pliocene pleistocene of the wanganui basin new zealand sequence stratigraphic motifs characteristic of the past 2 5 m y
Geological Society of America Bulletin, 1999Co-Authors: G Saul, Tim R Naish, S T Abbott, Robert M CarterAbstract:Earth’s climatic history since 2.5 Ma has been controlled by Milankovitch variations in the planetary orbit, comprising alternate periods of glaciation and interglaciation with a dominant frequency of 41 000 yr. Concomitantly, eustatic sea level has fluctuated 70 to 130 m, causing rapid transgressions and regressions of the shoreline across the world’s continental shelves. The resulting sedimentary record is Cyclothemic, each Cyclothem corresponding to a single climate and sea-level cycle. The Wanganui basin, New Zealand, contains a 2-km-thick, almost complete, composite record since isotope stage 100 (ca. 2.5 Ma) in the form of 47 superposed Cyclothems of shelf origin. Each Cyclothem corresponds to an unconformity-bound stratigraphic sequence, and typically contains a transgressive systems tract, sometimes a mid-cycle shell bed, a highstand systems tract, and sometimes a regressive systems tract. No advantage accrues from using transgressive-regressive units rather than Cyclothems and/or sequences in description of the succession. Six basic sequence motifs represent deposition in locations between the shoreline and offshore shelf, i.e., the Hawera, Birdgrove, Turakina, Seafield, Castlecliff, and Rangitikei motifs. A seventh, the Nukumaru motif (which includes dominant coquina limestone), represents deposition in shallow-water areas of reduced terrigenous sediment on the flank of the basin. The sequence motifs represented in any section change systematically in sympathy with basin-scale changes in subsidence and sediment supply. In contrast with the 41000 year length of individual glacioeustatic sequences, these basin-wide tectonic cycles have a periodicity of many hundreds of thousands to a few million years, i.e., that of third- or fourth-order sequences of the Exxon type. This, coupled with the restriction of strongly Cyclothemic sediments to geological periods of known glacio-eustasy (PermianCarboniferous, Pliocene-Pleistocene), suggests that tectonic subsidence cycles rather than glacio-eustasy are the driving forces behind the development of the third- and fourth-order unconformity-bound sequences that are reported to occur throughout the stratigraphic record.
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a review of wanganui basin new zealand global reference section for shallow marine plio pleistocene 2 5 0 ma cyclostratigraphy
Sedimentary Geology, 1998Co-Authors: Robert M Carter, Tim R NaishAbstract:Abstract Wanganui Basin, New Zealand, contains one of the most complete late Neogene marine stratigraphic records in the world. The ca. 2 km thick basin-fill for the last ca. 2.5 Ma comprises 47 superposed Cyclothems which correspond to successive 5th (100 ka) and 6th (41 ka) order glacio-eustatic, sea-level fluctuations on the palaeo-New Zealand shelf since oxygen isotope stage 100. Stages 100 to 5 are represented by marine Cyclothems, whereas stages 17 to 3 are represented by a suite of coeval and younger uplifted marine terrace sequences. Additionally, a predominantly glacial loess stratigraphy exists for isotope stages 12–2. The presence of interbedded tephras and an established paleomagnetic stratigraphy allows the development of an integrated cyclostratigraphy for Wanganui Basin which correlates closely with the global oxygen isotope scale. In all except two cases (cycles 12 and 36), individual unconformity-bound Cyclothems (sequences) represent a single glacial/interglacial couplet of Milankovitch frequency. Lithologic and faunal variation within the Cyclothems corresponds closely to that predicted by the sequence stratigraphic model. Each Cyclothem generally contains a transgressive systems tract, a mid-cycle condensed shellbed, a highstand systems tract, and often a regressive systems tract. Six common Cyclothem motifs are inferred to represent deposition in shelf locations between the highstand and lowstand shorelines, viz. the Hawera, Maxwell, Turakina, Seafield, Castlecliff, and Rangitikei motifs. A seventh type, the Nukumaru motif, includes coquina limestone and represents deposition in shoreface and very shallow water marine environments.
Weilai Zhang - One of the best experts on this subject based on the ideXlab platform.
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organic matter provenance and depositional environment of marine to continental mudstones and coals in eastern ordos basin china evidence from molecular geochemistry and petrology
International Journal of Coal Geology, 2020Co-Authors: Leon Bowen, Kun Yu, Yiwen Ju, Yu Qi, Cheng Huang, Weilai ZhangAbstract:Abstract Cyclothems, composed of interbedded mudstone, coal and sandstone layers, make up the Taiyuan and Shanxi Formations in the Late Carboniferous to Early Permian in North China under a marine-to-continental depositional environment. The Cyclothems act as important fossil energy hosts, such as coalbeds, hydrocarbon source rocks and unconventional natural gas reservoirs. Organic geochemistry and petrology of mudstones and coals in the Taiyuan and Shanxi Formations in the eastern Ordos Basin were studied to reveal the organic matter sources and paleoenvironments. Total organic carbon (TOC) contents vary from 1.1 wt% (mudstone) to 72.6 wt% (coal). The samples are mainly within the oil window, with the Tmax values ranging from 433 to 469 °C. Organic petrology and source biomarkers indicate that the mudstones were sourced from a mixed organic matter input, and terrigenous organic matter predominates over aquatic organic matter. The coals are mostly sourced by terrigenous organic matter inputs. High concentrations of hopanes argue for a strong bacterial input. Some m/z 217 mass chromatograms have peaks at the hopanes' retention times as a result of high hopane to sterane ratios. These hopane-derived peaks do not interfere the identification of the steranes because the hopanes and the steranes have different retention times. Maturity-dependent biomarkers demonstrate that the samples have been thermally mature, which agree with the Tmax values. Anomalously low C29 20S/(20S + 20R) and C29 ββ/(ββ + αα) sterane ratios are present in all the samples, and are interpreted as due to the terrigenous organic matter input or the coal-related depositional environment. In addition, biomarkers and iron sulfide morphology indicate that the organic matter of the mudstones deposited in a proximal setting with shallow, brackish/fresh water bodies. With consideration of preservation of organic matter, the redox conditions are dysoxic. Redox oscillations resulted in the records of oxic conditions in some samples. Finally, the coals and the mudstones mainly generate gas and have poor oil generative potential.
