Effect of iron type on kinetics and carbon isotopic enrichment of chlorinated ethylenes during abiotic reduction on Fe(0)     

VanStone NA  Focht RM  Mabury SA  Lollar BS 《Ground water》2004,42(2):268-276

Four samples of two commercially available iron brands used as substrate for iron permeable reactive barriers (PRBs) were tested for suitability for remediation of perchloroethylene (PCE), trichloroethylene (TCE), cis-dichloroethylene (cDCE) and vinyl chloride (VC). Kinetic studies indicate that rates of reaction are enhanced for cDCE and VC on Connelly iron (2.8 x 10(-4) to 6.9 x 10(-4) L/m2/hr and 2.0 x 10(-4) to 9.0 x 10(-4) L/m2/hr, for cDCE and VC, respectively) vs. Peerless iron (3.1 x 10(-5) to 4.6 x 10(-5) L/m2/hr and 2.4 x 10(-5) to 4.1 x 10(-5) L/m2/hr, for cDCE and VC, respectively). Carbon isotopic analyses of the residual chlorinated ethylene (CE) during degradation indicate significant fractionation occurs during reductive dechlorination, with, for example, up to 70% enrichment in carbon isotopic values observed when VC is more than 99% degraded. Comparison of fractionation factors (epsilon) indicates significant differences in carbon isotopic fractionation for different iron types and for different CEs. For the lower CEs (cDCE and VC) in particular, both slower reaction rates and larger fractionation are observed for degradation on Peerless vs. Connelly iron. This is the first study to establish a correlation between the rate of abiotic degradation on Fe(0) and the extent of isotopic fractionation, and the first to confirm consistent differences in these two parameters as a function of iron type. The possibility that these differences in kinetics and carbon isotopic fractionation for cDCE and VC are related to differences in branching ratios between competing hydrogenolysis and beta-elimination reactions during reductive dechlorination on the iron surfaces is discussed.  相似文献   

Petrology of a suite of sedimentary rocks associated with some cole-bearing basins in northwestern Thailand     

N.R. Sherwood  A.C. Cook  M. Gibling  C. Tantisukrit 《International Journal of Coal Geology》1984,4(1):45-71

A number of basins in northwestern Thailand contain thick sequences of Cenozoic sedimentary rocks. Oil shales and coals are prominent lithologies within these sequences and occur together in some basins. Most of the sequences are, however, dominated by either oil shales or coals. The major oil shale deposit is in the Mae Sot Basin but oil shales also occur in the Ban Huay Dua, Mae Moh, Ban Pa Ka Li, Mae Teep, Ban Na Hong and Jae Hom Basins.Drilling and detailed mapping, in the Mae Sot Basin indicate thick sequences of oil shales and organic petrological studies show that they contain abundant lamalginite. Trace amounts of telalginite, liptodetrinite, bitumen/resinite and huminite/inertinite are also present in some of the rocks. The parts of the sequences rich in authigenic minerals are, in general, petrographically similar to Green River Formation lamosites. Where clay/silt-sized epiclastics are more abundant, similarities exist to Australian Tertiary lamosites. Vitrinite reflectance date from the oil shales and associated coals indicate a low level of maturity.Oil shales from the other basins are, petrographically similar to the Mae Sot lamosites, however some differences do exist. The Mae Sot and other lamosites were deposited in lacustrine environments that probably had highly variable water depths.  相似文献   

Origins and maturity of organic matter in mid-Cretaceous black shales from ODP Site 1138 on the Kerguelen Plateau     

Philip A. Meyers  Jong-Gwon Yum  Sherwood W. Wise 《Marine and Petroleum Geology》2009

We have conducted elemental, isotopic, and Rock-Eval analyses of Cenomanian–Santonian sediment samples from ODP Site 1138 in the southern Indian Ocean to assess the origin and thermal maturity of organic matter in mid-Cretaceous black shales found at this high-latitude location. Total organic carbon (TOC) concentrations range between 1 and 20 wt% in black to medium-gray sediments deposited around the Cenomanian–Turonian boundary. Results of Rock-Eval pyrolysis indicate that the organic matter is algal Type II material that has experienced modest alteration. Important contributions of nitrogen-fixing bacteria to the amplified production of organic matter implied by the high TOC concentrations is recorded in δ¹⁵N values between −5 and 1‰, and the existence of a near-surface intensified oxygen minimum zone that favored organic carbon preservation is implied by TOC/TN ratios between 20 and 40. In contrast to the marine nature of the organic matter in the Cenomanian–Turonian boundary section, deeper sediments at Site 1138 contain evidence of contributions land-derived organic matter that implies the former presence of forests on the Kerguelen Plateau until the earliest Cenomanian.  相似文献   

Evaluation of TCE and MTBE in situ Biodegradation: Integrating Stable Isotope, Metabolic Intermediate, and Microbial Lines of Evidence     

Jennifer R. McKelvie  Sarah K. Hirschorn  Georges Lacrampe-Couloume  Jon Lindstrom  Joan Braddock  Kevin Finneran  Don Trego  Barbara Sherwood Lollar 《Ground Water Monitoring & Remediation》2007,27(4):63-73

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Clionid sponge surveys on the Florida Reef Tract suggest land-based nutrient inputs   总被引：1，自引：0，他引：1  

Ward-Paige CA  Risk MJ  Sherwood OA  Jaap WC 《Marine pollution bulletin》2005,51(5-7):570-579

Bioerosion by Cliona delitrix and Cliona lampa was assessed at 43 sites along the Florida Reef Tract, USA, in the summer of 2001. Sponge abundances were estimated using rapid visual assessment. Tissue samples of sponges were taken for analysis of delta15N. Comparison samples were taken from Belize. Annual trends in sponge abundance were estimated from archived videos covering the period from 1996 to 2001. Sites with the greatest boring sponge size and cover were in the Backcountry and Lower Keys, where total nitrogen, ammonium, and delta15N levels were highest. The sites with the largest relative increase of C. delitrix and C. lampa over the 5 year period were in the Upper Keys, where the greatest relative decline in stony coral cover has occurred. Florida sponge delta15N values were 5.2(+/-0.1)%, suggesting the influence of human waste; in comparison, offshore Belize samples were 2.1(+/-0.1)%. These results suggest sewage contamination of the Florida Reef Tract, shifting the carbonate balance from construction to destruction.  相似文献   

Late Holocene radiocarbon and aspartic acid racemization dating of deep-sea octocorals   总被引：1，自引：0，他引：1  

Owen A. Sherwood  David B. Scott 《Geochimica et cosmochimica acta》2006,70(11):2806-2814

Primnoa resedaeformis is a deep-sea gorgonian coral with a two-part skeleton of calcite and gorgonin (a fibrillar protein), potentially containing long-term records of valuable paleo-environmental information. For various reasons, both radiocarbon and U/Th dating of these corals is problematic over the last few centuries. This paper explores aspartic acid racemization dating of the gorgonin fraction in modern and fossil specimens collected from the NW Atlantic Ocean. Radiocarbon dating of the fossil specimen indicates a lifespan of 700 ± 100 years, the longest yet documented for any octocoral. Gorgonin amino acid compositions were identical in the fossil and modern specimens, indicating resistance to organic diagenesis. Similar to bone collagen, the fibrillar protein of gorgonin may impose conformational constraints on the racemization of Asp at low temperatures. The rate of racemization of aspartic acid (d/l-Asp) was similar to previously published results from an 1800 year old anemone (Gerardia). The age equation was: age (years BP 2000 AD) = [(d/l − 0.020 (±.002))/.0011 (±.0001)]² (r² = 0.97, p < .001). The error in an age estimate calculated by d/l-Asp was marginally better than that for ¹⁴C dating over the most recent 50-200 years, although the dating error may be improved by inclusion of more samples over a broader time range. These results suggest that d/l-Asp dating may be useful in augmenting ¹⁴C dating in cases where ¹⁴C calibrations yield two or more intercept ages, or in screening samples for further ¹⁴C or U/Th dating.  相似文献   

Probing the Deepest Limits of the Earth’s Biosphere     

Thomas L. Kieft  T.C. Onstott  Maggie C. Y. Lau  Barbara Sherwood Lollar 《《地质学报》英文版》2018,92(Z1):195-195

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Calcareous nannofossil changes linked to climate deterioration during the Paleocene-Eocene thermal maximum in Tarim Basin,NW China     

Wenxin Cao  Dangpeng Xi  Mihaela C.Melinte-Dobrinescu  Tian Jiang  Sherwood W.Wise Jr.  Xiaoqiao Wan 《地学前缘(英文版)》2018,9(5):1465-1478

The Paleocene-Eocene Thermal Maximum(PETM) event was a dramatic global warming w55.93 Ma ago that resulted in biological extinction events, lithological changes, and major deviations in σ13 C and σ18 O.The southwestern Tarim Basin of China exposes successive Paleogene strata as a result of Tethys evolution and is considered an ideal region for PETM research.Based on calcareous nannoplankton biostratigraphy, we also used stable isotopes and XRD to analyse the Paleocene-Eocene transition in the Tarim Basin. At the Bashibulake Section, the PETM interval is characterized by(1) an abrupt negative shifts in σ13 C_(org), σ13 C_(carb) and σ18 O(-3%, -4.5% and -3%respectively);(2) an obvious negative correlation between the K-mode(Discoaster, Fasciculithus, Ericsonia, Sphenolithus and Rhomboaster) and r-mode(Biscutum, Chiasmolithus, Toweius) nannofossil taxa coincident with a robust Rhomboaster-Discoaster assemblage; and(3) a significant increase in the percentage of detrital input along with an increase in gypsum content. In the upper part of the Qimugen Formation Micrantholithus and Braarudosphaera are commonly found right up to the top where most of the nannofloras suffer a sharp decrease. In the overlying Gaijitage Formation, calcareous nannofossils disappear completely. These events indicate that the southwestern Tarim Basin was a warm shallow continental shelf during the deposition of the Qimugen Formation. From the early Eocene, the environment changed conspicuously. Evaporation increased and sea level fell, which led to an acid climate.This climate mode continued within the youngest unit studied, the Gaijitage Formation, characterized by the deposition of thick evaporates. Consequently, most of the marine plankton, i.e. calcareous nannoplankton, became disappear, because of the significant climate shift.  相似文献   

Evidence for Holocene Aeolian Activity at the Close of the Middle Bronze Age in the Eastern Carpathian Basin: Geoarchaeological Results from the Mureş River Valley,Romania     

Sarah C. Sherwood  Jason D. Windingstad  Alex W. Barker  John M. O'Shea  W. Cullen Sherwood 《Geoarchaeology》2013,28(2):131-146

While extensive Pleistocene loess deposits have been identified across Eurasia, Holocene age loess (typically nonglaciogenic) is rarely recognized. We explore possible loess deposits in the Mureş River Valley of western Romania, providing a regional signal of increased aridity during the mid‐late Holocene. This proposed aridity may be responsible for the abandonment of Middle Bronze Age tell settlements along the major drainages of the eastern Carpathian Basin (Pannonian plain). This hypothesis centers on a proposed aeolian deposit (the “Pecica deposit”), a ca. 50–80 cm thick, relatively homogeneous, gray layer blanketing the top of the Bronze Age tell of Pecica—Şanţul Mare. Comparing the morphological, geochemical, and physical characteristics of this specific tell deposit with two representative profiles near the site containing glaciogenic calcareous loess and potential Holocene loess deposits developed in Chernozems, we find significant similarities to support this hypothesis. We then review various forms of proxy data published from elsewhere in Central and Eastern Europe suggesting a warming trend during this period. The temporal placement of the Pecica deposit is bracketed using diagnostic artifacts, radiocarbon dates, and the degree of soil development, suggesting a period of increased aridity likely occurring soon after the 17th century B.C.  相似文献   

Calcareous nannofossil biostratigraphy of the Paleocene at the Misheiti section,East Central Sinai,Egypt     

Atef Masoud Kasem  Sherwood WiseJr  Mahmoud Faris  Sherif Farouk  Esam Zahran 《Arabian Journal of Geosciences》2017,10(20):455

Integration of calcareous nannofossil data, δ¹³C and δ¹⁸O values, and carbonate contents of the lower Paleocene–upper Paleocene sequence that crops out at the Misheiti section, East Central Sinai, Egypt, were used to denote the Danian/Selandian (D/S) and Selandian/Thanetian (S/T) stage boundaries. The study interval belongs to the Dakhla and Tarawan formations. Four calcareous nannofossil zones (NP4, NP5, NP6, and NP7/8) were recognized. The base of the Selandian Stage is tentatively placed at the lowest occurrences (LOs) of taxa ascribable to the second radiation of fasciculiths (i.e., Lithoptychius janii). This level is marked by a sudden drop of δ¹³C and δ¹⁸O values and carbonate content. No distinctive lithological changes were observed across the D/S boundary at the study section. A hiatus at the NP5/NP6 zonal boundary is indicated by the condensation of zones NP5 and NP6.The base of the Thanetian is placed at the base of Zone NP7/8 at the lithological change observed in correspondence to the boundary between the Dakhla and Tarawan formations. The δ¹³C and δ¹⁸O values abruptly decrease slightly above the base of Zone NP7/8. No consistent variations in the carbonate contents were recorded within Zone NP6 or across the NP6/NP7/8 zonal boundary.  相似文献