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Jeremy K Hourigan - One of the best experts on this subject based on the ideXlab platform.
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cenozoic multiple phase tectonic evolution of the northern tibetan plateau constraints from sedimentary records from qaidam basin hexi corridor and subei basin northwest china
American Journal of Science, 2011Co-Authors: Guangsheng Zhuang, Bradley D. Ritts, Jeremy K Hourigan, Malinda Louise KentcorsonAbstract:An integrated research of sedimentology, stratigraphy, and provenance analysis on eleven sedimentary sections from the Qaidam basin, Hexi Corridor, and Subei basin representing ∼36 km Cenozoic strata provides a detailed record of the northern Tibetan Plateau growth since the early Eocene. Sections are divided into three groups based on age, geological similarities, and geographical locations. Group One includes three early Eocene–late Miocene sections from the northern Qaidam basin; Group Two contains four sections along the Altyn Tagh fault (ATF) which preserve a complete stratigraphic record from the Oligocene to late Miocene; Group Three contains the four youngest sections investigated from the northeastern Qaidam basin and Hexi Corridor which preserve a record since the middle Miocene to Quaternary. Together, the sections reveal a multiple-phase tectonic history of the northern Tibetan Plateau. The punctuated history can be divided into four phases. (1) The Eocene Lulehe Formation from the northern Qaidam basin is interpreted as a synorogenic conglomerate deposited by high-gradient depositional systems. Strong unimodal Paleocurrent towards the southwest, coarse lithology and distinct, recognizable clast types constrain the sediment source within the North Qaidam and South Qilian terranes, indicating activity on inferred thrust faults within the North Qaidam and South Qilian terranes in response to the initial India-Eurasia collision. The activity on these thrust faults continued through the late Eocene. (2) The early Oligocene conglomerate from Group Two formed in response to the sinistral transpression related to motion on the ATF, suggesting inception of substantial slip on the ATF in the early Oligocene in order to accommodate the continuing indentation of India into Eurasia. (3) Oligocene–early Miocene fine-grained fluvio-lacustrine sediments from Groups One and Two formed as the result of development of internal drainage systems in the Qaidam basin in response to the large-amplitude slip motion on the ATF. Paleocurrents collected from the Oligocene–early Miocene strata of Group One are northwest-directed, pointing towards the ATF, consistent with the pre-existing subsurface data showing the shift of depocenter from along North Qaidam and South Qilian terranes toward the ATF. (4) All eleven sections preserve a post-early Miocene upward-coarsening sequence, consistent with the extensive crustal shortening and topographic growth across the northern Tibetan Plateau.
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evidence of miocene crustal shortening in the north qilian shan from cenozoic stratigraphy of the western hexi corridor gansu province china
American Journal of Science, 2009Co-Authors: Paul M Bovet, A O Abbink, Brian J. Darby, Bradley D. Ritts, George E. Gehrels, Jeremy K HouriganAbstract:New sedimentologic, stratigraphie, and compositional data from the Paleogene-Neogene stratigraphie succession exposed in the northwest Hexi Corridor and within the North Qilian Shan, provide evidence to suggest that crustal shortening in the North Qilian Shan fold-thrust belt initiated during die Miocene. The section is composed of four lithostratigraphic units: Oligocene-Miocene fine- to coarse-grained Unit 1, Miocene conglomeratic Unit 2, and Pliocene-Pleistocene conglomeratic Units 3 and 4. Unit 3 lies in angular unconformity over both Units 1 and 2, and Unit 4 contains a progressive unconformity. The onset of conglomerate deposition at the base of Unit 2 suggests an increase in depositional energy, which we interpret as me result of proximal orogenesis in the North Qilian Shan fold and tiirust belt. Supporting evidence includes the appearance of strongly northeast-trending Paleocurrents, indicat-ing paleoflow away from the Qilian Shan, clast lidiologies that match sources in the North Qilian Shan, and sandstone with detrital framework modes that indicate a recycled orogen source. In contrast, Unit 1 contains Paleocurrent indicators that are variable but generally trend northward and sandstone and clast compositions which are more diagnostic of a continental block source. Detrital zircon age determinations from Unit 1 are also not consistent with a source in the North Qilian Shan; rather, they suggest a provenance in hinterland regions within the South Qilian Shan and North Qaidam terranes. In sum, these results are all consistent with initiation of proximal uplift of the North Qilian Shan during deposition of the gradational transition from Unit 1 to Unit 2, demonstrating shortening in the Qilian Shan before die late Miocene. This comprehensive study tightens our understanding of when far-field stress related to the India-Eurasia continent-continent collision reached the northeastern edge of the Tibetan Plateau.
Toshitsugu Yamazaki - One of the best experts on this subject based on the ideXlab platform.
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Paleocurrent patterns of the sedimentary sequence of the taitao ophiolite constrained by anisotropy of magnetic susceptibility and paleomagnetic analyses
Sedimentary Geology, 2007Co-Authors: Eugenio E Veloso, Ryo Anma, Tsutomu Ota, Tsuyoshi Komiya, Shin Ichi Kagashima, Toshitsugu YamazakiAbstract:Abstract Determination of Paleocurrent directions is a robust approach to establish the mechanism of sediment transport and of deposition. However, in tectonically controlled (or affected) basins where rotations are suspected, it is of critical importance to correct previously calculated Paleocurrent directions to establish the original (pre-tectonic) transport and deposition patterns. In order to illustrate this, we determined the orientations of the anisotropy of magnetic susceptibility (AMS) fabrics from 14 sites distributed along the sedimentary deposits interbedded within the Late Miocene Main Volcanic Unit (MVU) of the Taitao ophiolite, Southern Chile. Data were used to estimate characteristics (directions and relative velocities) of the sediment transporting Paleocurrents and orientations of the depositional slope. Sedimentary deposits consist of a rhythmic sequence of conglomerate (base), sandstone and mudstone (top) beds that present a systematic decrease in grain size up-sequence as a whole, and within individual beds. Sedimentary deposits of the MVU, as well as overlaying effusive volcanic products, are disrupted by small and discrete dextral/normal brittle faults. The distribution of fault planes and their kinematic characteristics suggest the development of a dextral negative flower-like fault zone in the area. Previously reported NW-ward Paleocurrent directions obtained from the orientations of sedimentary structures roughly agree with our calculations based on the orientations of AMS fabrics. Calculated Paleocurrent directions are sub-parallel to the NW-SE trend of Estero Cono channel, the main lineament in the area. The spatial distribution of AMS axes between and within sites suggest that coarse grain deposits were transported by relatively high velocity flows whereas fine grained deposits were by low to nearly null velocity flows. Previously reported paleomagnetic analyses indicate that counterclockwise rotations affected the whole Taitao ophiolite, including the MVU. By applying the necessary corrections we obtained Paleocurrent directions yielding mostly NNW-ward directions. Restoration of the orientations of beddings indicates that the depositional surface dipped steeply at its easternmost edge and shallowly at the westernmost end. We propose here that sediments were transported by turbidite flows generated by slope instabilities in the innermost part of the Estero Cono. These turbidites followed the Estero Cono lineament while they filled the channel and transported sedimentary material (eroded from the upper portions of the ophiolite and nearby units) towards the Pacific Ocean. Sediments were deposited on a NW- to W-facing slope and sorted in decreasing grain size along the channel. The instability of the slope was most probably triggered by the activity of a transtensional fault zone developed along the mid-axis of the Estero Cono channel.
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Paleocurrent analysis for the late pleistocene holocene incised valley fill of the yangtze delta china by using anisotropy of magnetic susceptibility data
Marine Geology, 2001Co-Authors: Baozhu Liu, Toshitsugu Yamazaki, Yoshiki Saito, A L Abdeldayem, Hirokuni Oda, Kazuaki Hori, Quanhong ZhaoAbstract:Abstract Anisotropy of magnetic susceptibility (AMS) analysis has been conducted on samples from borehole core CM-97 from the Yangtze River (Changjiang) incised-valley fill, China, to determine the Paleocurrent directions to help in reconstructing sedimentary paleoenvironments. Borehole CM-97 consists of fluvial (Unit 1), estuarine (Units 2–6), and deltaic (Units 7–9) sediments after the Last Glacial Maximum in ascending order. The AMS results show that the Paleocurrent directions for the tide-dominated estuarine and deltaic sediments were westerly or northwesterly directed (flood-tide dominated), but give no definite trend for the fluvial sediments. Comparison between the Paleocurrent directions inferred from primary sedimentary structures and in situ AMS data shows that they are in good agreement, confirming the applicability of AMS as a good Paleocurrent indicator for sediments deposited in coastal tide-dominated environments. Considering that these sediments were strongly tide-influenced and the tidal pattern since 12 kyr bp has not changed significantly, we think that the westerly or northwesterly current direction most probably resulted from flood-tidal currents, and the sedimentary paleoenvironment was a flood-tide dominated estuary or delta. Additionally, it has been found that downhole changes of some AMS parameters, including the mean magnetic susceptibility ( K ), the corrected anisotropy degree ( P j ) and the magnetic foliation ( F ), clearly mark the defined stratigraphic boundaries in the borehole. This further extends the validity of AMS as a good stratigraphic marker in addition to its long known credibility as a sensible Paleocurrent recorder.
Malinda Louise Kentcorson - One of the best experts on this subject based on the ideXlab platform.
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cenozoic multiple phase tectonic evolution of the northern tibetan plateau constraints from sedimentary records from qaidam basin hexi corridor and subei basin northwest china
American Journal of Science, 2011Co-Authors: Guangsheng Zhuang, Bradley D. Ritts, Jeremy K Hourigan, Malinda Louise KentcorsonAbstract:An integrated research of sedimentology, stratigraphy, and provenance analysis on eleven sedimentary sections from the Qaidam basin, Hexi Corridor, and Subei basin representing ∼36 km Cenozoic strata provides a detailed record of the northern Tibetan Plateau growth since the early Eocene. Sections are divided into three groups based on age, geological similarities, and geographical locations. Group One includes three early Eocene–late Miocene sections from the northern Qaidam basin; Group Two contains four sections along the Altyn Tagh fault (ATF) which preserve a complete stratigraphic record from the Oligocene to late Miocene; Group Three contains the four youngest sections investigated from the northeastern Qaidam basin and Hexi Corridor which preserve a record since the middle Miocene to Quaternary. Together, the sections reveal a multiple-phase tectonic history of the northern Tibetan Plateau. The punctuated history can be divided into four phases. (1) The Eocene Lulehe Formation from the northern Qaidam basin is interpreted as a synorogenic conglomerate deposited by high-gradient depositional systems. Strong unimodal Paleocurrent towards the southwest, coarse lithology and distinct, recognizable clast types constrain the sediment source within the North Qaidam and South Qilian terranes, indicating activity on inferred thrust faults within the North Qaidam and South Qilian terranes in response to the initial India-Eurasia collision. The activity on these thrust faults continued through the late Eocene. (2) The early Oligocene conglomerate from Group Two formed in response to the sinistral transpression related to motion on the ATF, suggesting inception of substantial slip on the ATF in the early Oligocene in order to accommodate the continuing indentation of India into Eurasia. (3) Oligocene–early Miocene fine-grained fluvio-lacustrine sediments from Groups One and Two formed as the result of development of internal drainage systems in the Qaidam basin in response to the large-amplitude slip motion on the ATF. Paleocurrents collected from the Oligocene–early Miocene strata of Group One are northwest-directed, pointing towards the ATF, consistent with the pre-existing subsurface data showing the shift of depocenter from along North Qaidam and South Qilian terranes toward the ATF. (4) All eleven sections preserve a post-early Miocene upward-coarsening sequence, consistent with the extensive crustal shortening and topographic growth across the northern Tibetan Plateau.
Bradley D. Ritts - One of the best experts on this subject based on the ideXlab platform.
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cenozoic multiple phase tectonic evolution of the northern tibetan plateau constraints from sedimentary records from qaidam basin hexi corridor and subei basin northwest china
American Journal of Science, 2011Co-Authors: Guangsheng Zhuang, Bradley D. Ritts, Jeremy K Hourigan, Malinda Louise KentcorsonAbstract:An integrated research of sedimentology, stratigraphy, and provenance analysis on eleven sedimentary sections from the Qaidam basin, Hexi Corridor, and Subei basin representing ∼36 km Cenozoic strata provides a detailed record of the northern Tibetan Plateau growth since the early Eocene. Sections are divided into three groups based on age, geological similarities, and geographical locations. Group One includes three early Eocene–late Miocene sections from the northern Qaidam basin; Group Two contains four sections along the Altyn Tagh fault (ATF) which preserve a complete stratigraphic record from the Oligocene to late Miocene; Group Three contains the four youngest sections investigated from the northeastern Qaidam basin and Hexi Corridor which preserve a record since the middle Miocene to Quaternary. Together, the sections reveal a multiple-phase tectonic history of the northern Tibetan Plateau. The punctuated history can be divided into four phases. (1) The Eocene Lulehe Formation from the northern Qaidam basin is interpreted as a synorogenic conglomerate deposited by high-gradient depositional systems. Strong unimodal Paleocurrent towards the southwest, coarse lithology and distinct, recognizable clast types constrain the sediment source within the North Qaidam and South Qilian terranes, indicating activity on inferred thrust faults within the North Qaidam and South Qilian terranes in response to the initial India-Eurasia collision. The activity on these thrust faults continued through the late Eocene. (2) The early Oligocene conglomerate from Group Two formed in response to the sinistral transpression related to motion on the ATF, suggesting inception of substantial slip on the ATF in the early Oligocene in order to accommodate the continuing indentation of India into Eurasia. (3) Oligocene–early Miocene fine-grained fluvio-lacustrine sediments from Groups One and Two formed as the result of development of internal drainage systems in the Qaidam basin in response to the large-amplitude slip motion on the ATF. Paleocurrents collected from the Oligocene–early Miocene strata of Group One are northwest-directed, pointing towards the ATF, consistent with the pre-existing subsurface data showing the shift of depocenter from along North Qaidam and South Qilian terranes toward the ATF. (4) All eleven sections preserve a post-early Miocene upward-coarsening sequence, consistent with the extensive crustal shortening and topographic growth across the northern Tibetan Plateau.
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evidence of miocene crustal shortening in the north qilian shan from cenozoic stratigraphy of the western hexi corridor gansu province china
American Journal of Science, 2009Co-Authors: Paul M Bovet, A O Abbink, Brian J. Darby, Bradley D. Ritts, George E. Gehrels, Jeremy K HouriganAbstract:New sedimentologic, stratigraphie, and compositional data from the Paleogene-Neogene stratigraphie succession exposed in the northwest Hexi Corridor and within the North Qilian Shan, provide evidence to suggest that crustal shortening in the North Qilian Shan fold-thrust belt initiated during die Miocene. The section is composed of four lithostratigraphic units: Oligocene-Miocene fine- to coarse-grained Unit 1, Miocene conglomeratic Unit 2, and Pliocene-Pleistocene conglomeratic Units 3 and 4. Unit 3 lies in angular unconformity over both Units 1 and 2, and Unit 4 contains a progressive unconformity. The onset of conglomerate deposition at the base of Unit 2 suggests an increase in depositional energy, which we interpret as me result of proximal orogenesis in the North Qilian Shan fold and tiirust belt. Supporting evidence includes the appearance of strongly northeast-trending Paleocurrents, indicat-ing paleoflow away from the Qilian Shan, clast lidiologies that match sources in the North Qilian Shan, and sandstone with detrital framework modes that indicate a recycled orogen source. In contrast, Unit 1 contains Paleocurrent indicators that are variable but generally trend northward and sandstone and clast compositions which are more diagnostic of a continental block source. Detrital zircon age determinations from Unit 1 are also not consistent with a source in the North Qilian Shan; rather, they suggest a provenance in hinterland regions within the South Qilian Shan and North Qaidam terranes. In sum, these results are all consistent with initiation of proximal uplift of the North Qilian Shan during deposition of the gradational transition from Unit 1 to Unit 2, demonstrating shortening in the Qilian Shan before die late Miocene. This comprehensive study tightens our understanding of when far-field stress related to the India-Eurasia continent-continent collision reached the northeastern edge of the Tibetan Plateau.
J Le P Roux - One of the best experts on this subject based on the ideXlab platform.
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estimation of channel sinuosity from Paleocurrent data a method using fractal geometry discussion
Journal of Sedimentary Research, 2001Co-Authors: J Le P RouxAbstract:The use of fractals to solve geological problems is an exciting new development in the Earth Sciences, and Ghosh (2000) is to be congratulated for his application of fractal geometry to estimate channel sinuosities from Paleocurrent data. In spite of the skepticism voiced by Miall (1996) as to the validity of methods based on Paleocurrent dispersal patterns, any progress in this field is to be welcomed. In fact, although the technique proposed by Ghosh (2000) represents an entirely new angle to solving the problem, the results closely approximate those produced by the method of Le Roux (1992) as modified in 1994 (Fig. 1). Surely, the good correlation between two independent techniques that are based purely on theoretical principles, must indicate that there is some merit in the Paleocurrent approach. Figure 1 Comparison of sinuosity values for different consistency ratios using the methods of Le Roux (1994) and Ghosh (2000). Ghosh used a theoretical model considering the shape of a single meander, but the method …
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determining the channel sinuosity of ancient fluvial systems from Paleocurrent data
Journal of Sedimentary Research, 1992Co-Authors: J Le P RouxAbstract:ABSTRACT The classification of modern river channels is based primarily on their sinuosity values, which can be determined directly from aerial photographs. Ancient channel systems are seldom sufficiently exposed to allow direct measurement of thalweg and valley lengths, but Paleocurrent directions can be used to calculate fairly accurate sinuosity values. Aerial photographs of four modern meander-belts were studied to determine the relationship between local current directions within the meander-belts and the actual sinuosity of the active river channels. A value of 3.2 times the standard deviation gave the best approximation of the operational channel range, resulting in a close correspondence between calculated and actual sinuosity values. This method can therefore be used to estimate the s nuosity of ancient fluvial systems.
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Paleocurrent analysis using lotus 1 2 3
Computers & Geosciences, 1991Co-Authors: J Le P RouxAbstract:Abstract The analysis of Paleocurrent data is performed easily on spreadsheets such as Lotus 1-2-3. Paleocurrent directions in strata dipping up to 90° can be entered directly from field notebooks, as tilt corrections are followed by sorting according to 10° sectors. A vector analysis determines the vector mean azimuth, vector magnitude, and true standard deviation around the vector mean. In fluvial environments, the true standard deviation also can be used to compute a sinuosity value for the paleoriver channel.