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Weilin Zhang - One of the best experts on this subject based on the ideXlab platform.

  • evaporite minerals of the lower 538 5 m sediments in a long Core from the western qaidam basin tibet
    Quaternary International, 2013
    Co-Authors: Xiaomin Fang, Weilin Zhang, Jiuyi Wang, Yougui Song, Yibo Yang, Xiaoming Liu
    Abstract:

    Abstract Qaidam Basin is a tectonically controlled Mesozoic–Cenozoic depression on the northern margin of the Tibetan Plateau. A 938.5 m-long Core was drilled in the Qahansilatu sub-basin in the western Qaidam Basin, with an average Core Recovery of 95%. It revealed alternating salt layers and carbonate clay layers. Samples were collected at 10–40 cm intervals for mineralogical analysis by XRD and chemical analysis by ICP-OES. The lower 538.5 m sediments are composed of halite, gypsum, anhydrite, gaylussite, calcite, aragonite, ankerite, dolomite, and an unnamed mineral (Mg0.92Ca0.08CO3·3H2O), with trace eugsterite. The mother brines could be Na-type, Na–Ca-type, Na–Ca–(Mg)-type, Ca–(Na)-type, Ca–(Mg)–(Na)-type, and trace Ca–Mg–(Na). Reflux and bacterial activity could be suitable for the formation of dolomite. Deep burial diagenesis could have played an active role in the formation of ankerite and anhydrate. The continuous presence of halite suggested the paleo-lake water was highly brackish or saline, with high evaporation since 2.77 Ma. Salt layers in the lower 538.5 m-long sediments were present from 2221 ka to 2052 ka, corresponding to Pleistocene salt formation in the Qaidam Basin. As hydrated carbonate minerals, both gaylussite and the unnamed mineral are deposited under high precipitation rates with microbial activity. Gaylussite was deposited from Na–Ca-enriched solutions with molar ratios of Na/Ca more than 2 from 691 m (2226 ka) to 413.6 m (1222 ka). The un-named mineral (Mg0.92Ca0.08CO3·3H2O) was found from 523.4 m (1728 ka) to 724.2 m (2308 ka). Anhydrite could be transformed from gypsum under deep burial from 657.42 m (2052 ka) to 867 m (2556 ka). Alternating salt and clay layers in the lower part of the Core recorded arid and relatively wet climatic oscillations and the evolution of brine. As a tectonic sub-basin, tectonic activities could change the local climate during episodes of uplift and subsidence. The dominant minerals in the Chahansilatu sub-basin are similar to those of the other sub-basins in the western Qaidam Basin, but have asynchronous evolutionary stages of brine.

  • magnetostratigraphy of deep drilling Core sg 1 in the western qaidam basin ne tibetan plateau and its tectonic implications
    Quaternary Research, 2012
    Co-Authors: Weilin Zhang, Erwin Appel, Xiaomin Fang, Chunhui Song, Olaf A Cirpka
    Abstract:

    Abstract The Qaidam Basin is the largest intermontane basin of the northeastern Tibetan Plateau and contains a continuous Cenozoic sequence of lacustrine sediments. A ~ 1000-m-deep drilling (SG-1) with an average Core Recovery of ~ 95% was carried out in the depocenter of the Chahansilatu playa (sub-depression) in the western Qaidam Basin, aimed to obtain a high-resolution record of the paleoenvironmental evolution and the erosion history. Stepwise alternating field and thermal demagnetization, together with rock magnetic results, revealed a stable remanent magnetization for most samples, carried by magnetite. The polarity sequence consisted of 16 normal and 15 reverse zones which can be correlated with chrons 1n to 2An of the global geomagnetic polarity time scale. Magnetostratigraphic results date the entire Core SG-1 at ~ 2.77 Ma to ~ 0.1 Ma and yielded sediment accumulation rate (SAR) ranging from 26.1 cm/ka to 51.5 cm/ka. Maximum SARs occurred within the intervals of ~ 2.6–2.2 Ma and after ~ 0.8 Ma, indicating two episodes of erosion, which we relate to pulse tectonic uplift of the NE Tibetan Plateau with subsequent global cooling.

Xiaomin Fang - One of the best experts on this subject based on the ideXlab platform.

  • evaporite minerals of the lower 538 5 m sediments in a long Core from the western qaidam basin tibet
    Quaternary International, 2013
    Co-Authors: Xiaomin Fang, Weilin Zhang, Jiuyi Wang, Yougui Song, Yibo Yang, Xiaoming Liu
    Abstract:

    Abstract Qaidam Basin is a tectonically controlled Mesozoic–Cenozoic depression on the northern margin of the Tibetan Plateau. A 938.5 m-long Core was drilled in the Qahansilatu sub-basin in the western Qaidam Basin, with an average Core Recovery of 95%. It revealed alternating salt layers and carbonate clay layers. Samples were collected at 10–40 cm intervals for mineralogical analysis by XRD and chemical analysis by ICP-OES. The lower 538.5 m sediments are composed of halite, gypsum, anhydrite, gaylussite, calcite, aragonite, ankerite, dolomite, and an unnamed mineral (Mg0.92Ca0.08CO3·3H2O), with trace eugsterite. The mother brines could be Na-type, Na–Ca-type, Na–Ca–(Mg)-type, Ca–(Na)-type, Ca–(Mg)–(Na)-type, and trace Ca–Mg–(Na). Reflux and bacterial activity could be suitable for the formation of dolomite. Deep burial diagenesis could have played an active role in the formation of ankerite and anhydrate. The continuous presence of halite suggested the paleo-lake water was highly brackish or saline, with high evaporation since 2.77 Ma. Salt layers in the lower 538.5 m-long sediments were present from 2221 ka to 2052 ka, corresponding to Pleistocene salt formation in the Qaidam Basin. As hydrated carbonate minerals, both gaylussite and the unnamed mineral are deposited under high precipitation rates with microbial activity. Gaylussite was deposited from Na–Ca-enriched solutions with molar ratios of Na/Ca more than 2 from 691 m (2226 ka) to 413.6 m (1222 ka). The un-named mineral (Mg0.92Ca0.08CO3·3H2O) was found from 523.4 m (1728 ka) to 724.2 m (2308 ka). Anhydrite could be transformed from gypsum under deep burial from 657.42 m (2052 ka) to 867 m (2556 ka). Alternating salt and clay layers in the lower part of the Core recorded arid and relatively wet climatic oscillations and the evolution of brine. As a tectonic sub-basin, tectonic activities could change the local climate during episodes of uplift and subsidence. The dominant minerals in the Chahansilatu sub-basin are similar to those of the other sub-basins in the western Qaidam Basin, but have asynchronous evolutionary stages of brine.

  • magnetostratigraphy of deep drilling Core sg 1 in the western qaidam basin ne tibetan plateau and its tectonic implications
    Quaternary Research, 2012
    Co-Authors: Weilin Zhang, Erwin Appel, Xiaomin Fang, Chunhui Song, Olaf A Cirpka
    Abstract:

    Abstract The Qaidam Basin is the largest intermontane basin of the northeastern Tibetan Plateau and contains a continuous Cenozoic sequence of lacustrine sediments. A ~ 1000-m-deep drilling (SG-1) with an average Core Recovery of ~ 95% was carried out in the depocenter of the Chahansilatu playa (sub-depression) in the western Qaidam Basin, aimed to obtain a high-resolution record of the paleoenvironmental evolution and the erosion history. Stepwise alternating field and thermal demagnetization, together with rock magnetic results, revealed a stable remanent magnetization for most samples, carried by magnetite. The polarity sequence consisted of 16 normal and 15 reverse zones which can be correlated with chrons 1n to 2An of the global geomagnetic polarity time scale. Magnetostratigraphic results date the entire Core SG-1 at ~ 2.77 Ma to ~ 0.1 Ma and yielded sediment accumulation rate (SAR) ranging from 26.1 cm/ka to 51.5 cm/ka. Maximum SARs occurred within the intervals of ~ 2.6–2.2 Ma and after ~ 0.8 Ma, indicating two episodes of erosion, which we relate to pulse tectonic uplift of the NE Tibetan Plateau with subsequent global cooling.

Debari S. M. - One of the best experts on this subject based on the ideXlab platform.

  • Expedition 350 summary
    'International Ocean Discovery Program (IODP)', 2015
    Co-Authors: Tamura Y., Busby C. J., Blum P., Guèrin G., Andrews G. D. M., Barker A. K., Berger J. L. R., Bongiolo E. M., Bordiga M., Debari S. M.
    Abstract:

    International Ocean Discovery Program (IODP) Hole U1436A (proposed Site IBM-4GT) lies in the western part of the Izu fore-arc basin, ~60 km east of the arc-front volcano Aogashima, ~170 km west of the axis of the Izu-Bonin Trench, and 1.5 km west of Ocean Drilling Program (ODP) Site 792, at 1776 meters below sea level (mbsl). It was drilled as a 150 m deep geotechnical test hole for potential future deep drilling (5500 meters below seafloor [mbsf]) at proposed Site IBM-4 using the D/V Chikyu. Core from Site U1436 yielded a rich record of Late Pleistocene explosive volcanism, including a distinctive black glassy mafic ash layer that may record a large-volume subaqueous eruption on the Izu arc front. Because of the importance of this discovery, Site U1436 was drilled in three additional holes (U1436B, U1436C, and U1436D), as part of a contingency operation, in an attempt to get better Recovery on the black glassy mafic ash layer and its enclosing sediments and to better constrain its thickness. IODP Site U1437 is located in the Izu rear arc, ~330 km west of the axis of the Izu-Bonin Trench and ~90 km west of the arc-front volcanoes Myojinsho and Myojin Knoll, at 2117 mbsl. The primary scientific objective for Site U1437 was to characterize “the missing half of the subduction factory” because numerous ODP/Integrated Ocean Drilling Program sites had been drilled in the arc-front to fore-arc region (i.e., ODP Site 782A Leg 126), but this was the first site to be drilled in the rear-arc region of the Izu arc. A complete view of the arc system is needed to understand the formation of oceanic arc crust and its evolution into continental crust. Site U1437 on the rear arc had excellent Core Recovery in Holes U1437B and U1437D, and we succeeded in hanging the longest casing ever in the history of R/V JOIDES Resolution scientific drilling (1085.6 m) in Hole U1437E and Cored to 1806.5 mbsf. The stratigraphy at Site U1437 was divided into seven lithostratigraphic units (I–VII) that were distinguished from each other based on the proportions and characteristics of tuffaceous mud/mudstone and interbedded tuff, lapilli-tuff, and tuff-breccia. The section is much more mud rich than expected, with ~60% tuffaceous mud for the section as a whole (89% in the uppermost 433 m) and high sedimentation rates of 100–260 m/My for the upper 1320 m (Units I–V). The proportion (40%) and grain size of volcaniclastics are much smaller than expected for an intra-arc basin, composed half of ash/tuff and half of lapilli-tuff of fine grain size (clasts

  • Expedition 350 Summary
    Western CEDAR, 2015
    Co-Authors: Tamura Y., Busby C. J., Blum P., Guèrin G., Andrews G. D. M., Barker A. K., Berger J. L. R., Bongiolo E. M., Bordiga M., Debari S. M.
    Abstract:

    International Ocean Discovery Program (IODP) Hole U1436A (proposed Site IBM-4GT) lies in the western part of the Izu fore-arc basin, ~60 km east of the arc-front volcano Aogashima, ~170 km west of the axis of the Izu-Bonin Trench, and 1.5 km west of Ocean Drilling Program (ODP) Site 792, at 1776 meters below sea level (mbsl). It was drilled as a 150 m deep geotechnical test hole for potential future deep drilling (5500 meters below seafloor [mbsf]) at proposed Site IBM-4 using the D/V Chikyu. Core from Site U1436 yielded a rich record of Late Pleistocene explosive volcanism, including a distinctive black glassy mafic ash layer that may record a large-volume subaqueous eruption on the Izu arc front. Because of the importance of this discovery, Site U1436 was drilled in three additional holes (U1436B, U1436C, and U1436D), as part of a contingency operation, in an attempt to get better Recovery on the black glassy mafic ash layer and its enclosing sediments and to better constrain its thickness. IODP Site U1437 is located in the Izu rear arc, ~330 km west of the axis of the Izu-Bonin Trench and ~90 km west of the arc-front volcanoes Myojinsho and Myojin Knoll, at 2117 mbsl. The primary scientific objective for Site U1437 was to characterize “the missing half of the subduction factory” because numerous ODP/Integrated Ocean Drilling Program sites had been drilled in the arc-front to fore-arc region (i.e., ODP Site 782A Leg 126), but this was the first site to be drilled in the rear-arc region of the Izu arc. A complete view of the arc system is needed to understand the formation of oceanic arc crust and its evolution into continental crust. Site U1437 on the rear arc had excellent Core Recovery in Holes U1437B and U1437D, and we succeeded in hanging the longest casing ever in the history of R/V JOIDES Resolution scientific drilling (1085.6 m) in Hole U1437E and Cored to 1806.5 mbsf. The stratigraphy at Site U1437 was divided into seven lithostratigraphic units (I–VII) that were distinguished from each other based on the proportions and characteristics of tuffaceous mud/mudstone and interbedded tuff, lapilli-tuff, and tuff-breccia. The section is much more mud rich than expected, with ~60% tuffaceous mud for the section as a whole (89% in the uppermost 433 m) and high sedimentation rates of 100–260 m/My for the upper 1320 m (Units I–V). The proportion (40%) and grain size of volcaniclastics are much smaller than expected for an intra-arc basin, composed half of ash/tuff and half of lapilli-tuff of fine grain size (clastscm). These volcaniclastics were deposited by suspension settling through water and from density currents, in relatively distal settings. Volcanic blocks are only sparsely scattered through the lowermost 25% of the section (Units VI and VII, 1320–1806.5 mbsf), which includes hyaloclastite, in situ quench-fragmented blocks, and a rhyolite peperite intrusion (i.e., proximal deposits). The transition from unconsolidated to lithified rocks occurred progressively; however, sediments were considered lithified from 427 mbsf (top of Hole U1437D) downward. Alteration resulted in destruction of fresh glass from ~750 mbsf downward, but minerals are less altered. Because of the alteration, the deepest biostratigraphic datum was at ~850 mbsf and the deepest paleomagnetic datum was at ~1300 mbsf. Additional age control deeper than ~1300 mbsf is provided by an age range of 10.97–11.85 Ma inferred from a nannofossil assemblage at ~1403 mbsf and a preliminary U-Pb zircon concordia intercept age of 13.6 +1.6/−1.7 Ma, measured postcruise on a rhyolite peperite in Unit VI at ~1390 mbsf. Based on the seismic profiles, the Miocene–Oligocene hiatus (~17–23 Ma) was predicted to lie at ~1250 mbsf, but strata at that depth (Unit V, 1120–1312 mbsf) are much younger (~9 Ma), indicating that we recovered a thicker Neogene section of volcaniclastics and associated igneous rocks than anticipated. Our preliminary interpretation of shipboard geochemistry of solids is that arc-front versus rear-arc sources can be distinguished for individual intervals in the upper, relatively distal 1320 m of the section (Units I–V), whereas data for the lower, proximal 25% of the section (Units VI–VII) overlap and exceed the compositional fields for Neogene rear-arc seamounts and Quaternary arc-front volcanoes. This suggests that the compositional divergence between arc-front and rear-arc magmas only fully developed after ~13 Ma

  • Izu-Bonin-Mariana Rear Arc - The missing half of the subduction factory, 30 March – 30 May 2014
    'International Ocean Discovery Program (IODP)', 2014
    Co-Authors: Tamura Y., Busby C. J., Blum P., Guèrin G., Andrews G. D. M., Barker A. K., Berger J. L. R., Bongiolo E. M., Bordiga M., Debari S. M.
    Abstract:

    International Ocean Discovery Program (IODP) Hole U1436A (proposed Site IBM-4GT) lies in the western part of the Izu fore-arc basin, ~60 km east of the arc-front volcano Aogashima, ~170 km west of the axis of the Izu-Bonin Trench, 1.5 km west of Ocean Drilling Program (ODP) Site 792, and at 1776 meters below sea level (mbsl). It was drilled as a 150 m deep geotechnical test hole for potential future deep drilling (5500 meters below seafloor [mbsf]) at proposed Site IBM-4 using the D/V Chikyu. Core from Site U1436 yielded a rich record of Late Pleistocene explosive volcanism, including distinctive black glassy mafic ash layers that may record large-volume eruptions on the Izu arc front. Because of the importance of this discovery, Site U1436 was drilled in three additional holes (U1436B, U1436C, and U1436D), as part of a contingency operation, in an attempt to get better Recovery on the black glassy mafic ash layers and enclosing sediments and to better constrain the thickness of the mafic ash layers. IODP Site U1437 is located in the Izu rear arc, ~330 km west of the axis of the Izu-Bonin Trench and ~90 km west of the arc-front volcanoes Myojinsho and Myojin Knoll, at 2117 mbsl. The primary scientific objective for Site U1437 was to characterize “the missing half of the subduction factory”; this was because numerous ODP/Integrated Ocean Drilling Program sites had been drilled in the arc to fore-arc region (i.e., ODP Site 782A Leg 126), but this was the first site to be drilled in the rear part of the Izu arc. A complete view of the arc system is needed to understand the formation of oceanic arc crust and its evolution into continental crust. Site U1437 on the rear arc had excellent Core Recovery in Holes U1437B and U1437D, and we succeeded in hanging the longest casing ever in the history of R/V JOIDES Resolution scientific drilling (1085.6 m) in Hole U1437E and Cored to 1806.5 mbsf. The stratigraphy at Site U1437 was divided into seven lithostratigraphic units (I–VII) that were distinguished from each other based on the proportions and characteristics of tuffaceous mud/mudstone and interbedded tuff, lapilli tuff, and tuff breccia. The section is much more mud rich than expected, with ~60% tuffaceous mud for the section as a whole (89% in the uppermost 433 m) and high sedimentation rates of 100–260 m/My for the upper 1320 m (Units I–V). The proportion (40%) and grain size of tephra are much smaller than expected for an intra-arc basin, composed half of ash/tuff and half of lapilli tuff of fine grain size (clasts < 3 cm). These were deposited by suspension settling through water and from density currents, in relatively distal settings. Volcanic blocks are only sparsely scattered through the lowermost 25% of the section (Units VI and VII, 1320–1806.5 mbsf), which includes hyaloclastite, in situ quench-fragmented blocks, and a rhyolite peperite intrusion (i.e., proximal deposits). The transition from unconsolidated to lithified rocks occurred progressively; however, sediments were considered lithified from 427 mbsf (top of Hole U1437D) downward. Alteration resulted in destruction of fresh glass from ~750 mbsf downward, but minerals are less altered. Because of the alteration, the deepest biostratigraphic datum was at ~850 mbsf and the deepest paleomagnetic datum was at ~1300 mbsf. Additional age control deeper than this depth is provided by an age range of 10.97–11.85 Ma inferred from a nannofossil assemblage at ~1403 mbsf and a preliminary U-Pb zircon concordia intercept age of 13.6 +1.6/–1.7 Ma, measured postcruise on a rhyolite peperite in Unit VI at ~1390 mbsf. Based on the seismic profiles, the Miocene–Oligocene hiatus (~17–23 Ma) was predicted to lie at ~1250 mbsf, but strata at that depth (Unit V, 1120–1312 mbsf) are much younger (~9 Ma), indicating that we recovered a thicker Neogene section of volcaniclastics and associated igneous rocks than anticipated. Our preliminary interpretation of shipboard geochemistry is that arc-front versus rear-arc sources can be distinguished in the upper, relatively distal 1320 m of section (Units I–V), whereas the lower, proximal 25% of the section (Units VI–VII) may be geochemically heterogeneous, suggesting that the rear-arc magmas only fully compositionally diverged after ~13 Ma

  • International Ocean Discovery Program\ud Expedition 350 Preliminary Report\ud Izu-Bonin-Mariana Rear Arc\ud The missing half of the subduction factory
    International Ocean Discovery Program, 2014
    Co-Authors: Tamura Y., Busby C. J., Blum P., Guèrin G., Andrews G. D. M., Barker A. K., Berger J. L. R., Bongiolo E. M., Bordiga M., Debari S. M.
    Abstract:

    International Ocean Discovery Program (IODP) Hole U1436A (proposed Site IBM-4GT) lies in the western part of the Izu fore-arc basin, ~60 km east of the arc-front volcano Aogashima, ~170 km west of the axis of the Izu-Bonin Trench, 1.5 km west of Ocean Drilling Program (ODP) Site 792, and at 1776 meters below sea level (mbsl). It was drilled as a 150 m deep geotechnical test hole for potential future deep drilling (5500 meters below seafloor [mbsf]) at proposed Site IBM-4 using the D/V Chikyu. Core from Site U1436 yielded a rich record of Late Pleistocene explosive volcanism, including distinctive black glassy mafic ash layers that may record large-volume eruptions on the Izu arc front. Because of the importance of this discovery, Site U1436 was drilled in three additional holes (U1436B, U1436C, and U1436D), as part of a contingency operation, in an attempt to get better Recovery on the black glassy mafic ash layers and enclosing sediments and to better constrain the thickness of the mafic ash layers.\ud \ud IODP Site U1437 is located in the Izu rear arc, ~330 km west of the axis of the Izu-Bonin Trench and ~90 km west of the arc-front volcanoes Myojinsho and Myojin Knoll, at 2117 mbsl. The primary scientific objective for Site U1437 was to characterize “the missing half of the subduction factory”; this was because numerous ODP/Integrated Ocean Drilling Program sites had been drilled in the arc to fore-arc region (i.e., ODP Site 782A Leg 126), but this was the first site to be drilled in the rear part of the Izu arc. A complete view of the arc system is needed to understand the formation of oceanic arc crust and its evolution into continental crust. Site U1437 on the rear arc had excellent Core Recovery in Holes U1437B and U1437D, and we succeeded in hanging the longest casing ever in the history of R/V JOIDES Resolution scientific drilling (1085.6 m) in Hole U1437E and Cored to 1806.5 mbsf.\ud \ud The stratigraphy at Site U1437 was divided into seven lithostratigraphic units (I–VII) that were distinguished from each other based on the proportions and characteristics of tuffaceous mud/mudstone and interbedded tuff, lapilli tuff, and tuff breccia. The section is much more mud rich than expected, with ~60% tuffaceous mud for the section as a whole (89% in the uppermost 433 m) and high sedimentation rates of 100–260 m/My for the upper 1320 m (Units I–V). The proportion (40%) and grain size of tephra are much smaller than expected for an intra-arc basin, composed half of ash/tuff and half of lapilli tuff of fine grain size (clasts < 3 cm). These were deposited by suspension settling through water and from density currents, in relatively distal settings. Volcanic blocks are only sparsely scattered through the lowermost 25% of the section (Units VI and VII, 1320–1806.5 mbsf), which includes hyaloclastite, in situ quench-fragmented blocks, and a rhyolite peperite intrusion (i.e., proximal deposits). The transition from unconsolidated to lithified rocks occurred progressively; however, sediments were considered lithified from 427 mbsf (top of Hole U1437D) downward. Alteration resulted in destruction of fresh glass from ~750 mbsf downward, but minerals are less altered. Because of the alteration, the deepest biostratigraphic datum was at ~850 mbsf and the deepest paleomagnetic datum was at ~1300 mbsf. Additional age control deeper than this depth is provided by an age range of 10.97–11.85 Ma inferred from a nannofossil assemblage at ~1403 mbsf and a preliminary U-Pb zircon concordia intercept age of 13.6 +1.6/–1.7 Ma, measured postcruise on a rhyolite peperite in Unit VI at ~1390 mbsf.\ud \ud Based on the seismic profiles, the Miocene–Oligocene hiatus (~17–23 Ma) was predicted to lie at ~1250 mbsf, but strata at that depth (Unit V, 1120–1312 mbsf) are much younger (~9 Ma), indicating that we recovered a thicker Neogene section of volcaniclastics and associated igneous rocks than anticipated. Our preliminary interpretation of shipboard geochemistry is that arc-front versus rear-arc sources can be distinguished in the upper, relatively distal 1320 m of section (Units I–V), whereas the lower, proximal 25% of the section (Units VI–VII) may be geochemically heterogeneous, suggesting that the rear-arc magmas only fully compositionally diverged after ~13 Ma

Peter G Brewer - One of the best experts on this subject based on the ideXlab platform.

  • in situ raman measurement of hs and h2s in sediment pore waters and use of the hs h2s ratio as an indicator of pore water ph
    Marine Chemistry, 2016
    Co-Authors: Edward T Peltzer, Xin Zhang, Peter Walz, Melissa Luna, Peter G Brewer
    Abstract:

    The smell of hydrogen sulfide upon Recovery of deep sea Cores from areas of reducing sediments is familiar to most ocean scientists and is simple testimony to the problem of dissolved gas loss during Core Recovery and processing. For this reason methods of in situ measurement of sulfide and other gases are keenly sought, and both microelectrode and spectroscopic measurements have been widely used. We report here on the use of a robust 50 cm long titanium pore water probe combined with a laser Raman sensing system for in situ measurement of the sulfide concentration and sulfide speciation status of deep sea sediment pore waters. Uniquely the Raman signal spectroscopically senses and simultaneously resolves both the H2S (v(1) 2592 Delta cm(-1)) and HS- (v(1) 2573 Delta cm(-1)) species. We have calibrated the Raman response factors as a function of pH and found that the Raman cross section for HS- is a factor of 1.563 greater than for the H2S form. We have carried out stepwise profiling of the pore water chemistry (CH4, SO42-, H2S, HS-) of highly reducing sediments in the Santa Monica Basin and from the combined sulfide species we can assess total dissolved sulfide. Since the ratio of HS-:H2S is a well-defined function of pH with the pK for this equilibrium being close to 7.0, and since the pH of many sediment pore waters is also close to 7 then the observed HS-:H2S ratio provides an elegant pH sensitive "dye". We have solved the required Raman-equilibrium relationships and show that the in situ pH of sulfide rich pore waters can be determined rapidly and directly from these observations. Several field examples are provided. (C) 2016 Elsevier B.V. All rights reserved.

  • gas hydrate measurements at hydrate ridge using raman spectroscopy
    Geochimica et Cosmochimica Acta, 2007
    Co-Authors: Keith C Hester, R M Dunk, Sheri N White, Peter G Brewer, Edward T Peltzer, E D Sloan
    Abstract:

    Abstract Oceanic gas hydrates have been measured near the seafloor for the first time using a seagoing Raman spectrometer at Hydrate Ridge, Oregon, where extensive layers of hydrates have been found to occur near the seafloor. All of the hydrates analyzed were liberated from the upper meter of the sediment column near active gas venting sites in water depths of 770–780 m. Hydrate properties, such as structure and composition, were measured with significantly less disturbance to the sample than would be realized with Core Recovery. The natural hydrates measured were sI, with methane as the predominant guest component, and minor/trace amounts of hydrogen sulfide present in three of the twelve samples measured. Methane large-to-small cage occupancy ratios of the hydrates varied from 1.01 to 1.30, in good agreement with measurements of laboratory synthesized and recovered natural hydrates. Although the samples visually appeared to be solid, varying quantities of free methane gas were detected, indicating the possible presence of occluded gas in a hydrate bubble fabric.

Olaf A Cirpka - One of the best experts on this subject based on the ideXlab platform.

  • magnetostratigraphy of deep drilling Core sg 1 in the western qaidam basin ne tibetan plateau and its tectonic implications
    Quaternary Research, 2012
    Co-Authors: Weilin Zhang, Erwin Appel, Xiaomin Fang, Chunhui Song, Olaf A Cirpka
    Abstract:

    Abstract The Qaidam Basin is the largest intermontane basin of the northeastern Tibetan Plateau and contains a continuous Cenozoic sequence of lacustrine sediments. A ~ 1000-m-deep drilling (SG-1) with an average Core Recovery of ~ 95% was carried out in the depocenter of the Chahansilatu playa (sub-depression) in the western Qaidam Basin, aimed to obtain a high-resolution record of the paleoenvironmental evolution and the erosion history. Stepwise alternating field and thermal demagnetization, together with rock magnetic results, revealed a stable remanent magnetization for most samples, carried by magnetite. The polarity sequence consisted of 16 normal and 15 reverse zones which can be correlated with chrons 1n to 2An of the global geomagnetic polarity time scale. Magnetostratigraphic results date the entire Core SG-1 at ~ 2.77 Ma to ~ 0.1 Ma and yielded sediment accumulation rate (SAR) ranging from 26.1 cm/ka to 51.5 cm/ka. Maximum SARs occurred within the intervals of ~ 2.6–2.2 Ma and after ~ 0.8 Ma, indicating two episodes of erosion, which we relate to pulse tectonic uplift of the NE Tibetan Plateau with subsequent global cooling.