The Paleocene–Eocene transition in the marginal northeastern Tethys (Kazakhstan and Uzbekistan)     

M.-P. Bolle  A. Pardo  K.-U. Hinrichs  T. Adatte  K. Von Salis  S. Burns  G. Keller  N. Muzylev 《International Journal of Earth Sciences》2000,89(2):390-414

We studied two sections that accumulated during the Paleocene–Eocene transition in shelf waters in the northeastern Tethys. Stable carbon isotopic compositions of marine and terrestrial biomarkers are consistent with a ¹³C depletion in the oceanic and atmospheric carbon dioxide pools during the Late Paleocene Thermal Maximum (LPTM; Subzone P5b). The 2–3‰ negative δ ¹³C excursion in planktic foraminifera coincides with minimum δ ¹⁸O values, an incursion of transient subtropical planktic foraminiferal fauna, and the occurrence of an organic-rich sapropelite unit in Uzbekistan, which accumulated at the onset of a transgressive event. Biomarker distributions and hydrogen indices indicate that marine algae and bacteria were the major organic matter sources. During the Late Paleocene (Subzones P4 and P5a), the marginal northeastern Tethys experienced a temperate to warm climate with wet and arid seasons. Most likely, warm and humid climate initiated during the LPTM (Subzone P5b) and subsequently extended during the Eocene (Zone P6) onto adjacent land areas of the marginal northeastern Tethys. Received: 18 May 1999 / Accepted: 2 February 2000  相似文献   

Gas flux and carbonate occurrence at a shallow seep of thermogenic natural gas   总被引：1，自引：1，他引：0  

Franklin S. Kinnaman  Justine B. Kimball  Luis Busso  Daniel Birgel  Haibing Ding  Kai-Uwe Hinrichs  David L. Valentine 《Geo-Marine Letters》2010,30(3-4):355-365

The Coal Oil Point seep field located offshore Santa Barbara, CA, consists of dozens of named seeps, including a peripheral ～200 m² area known as Brian Seep, located in 10 m water depth. A single comprehensive survey of gas flux at Brian Seep yielded a methane release rate of ～450 moles of CH₄ per day, originating from 68 persistent gas vents and 23 intermittent vents, with gas flux among persistent vents displaying a log normal frequency distribution. A subsequent series of 33 repeat surveys conducted over a period of 6 months tracked eight persistent vents, and revealed substantial temporal variability in gas venting, with flux from each individual vent varying by more than a factor of 4. During wintertime surveys sediment was largely absent from the site, and carbonate concretions were exposed at the seafloor. The presence of the carbonates was unexpected, as the thermogenic seep gas contains 6.7% CO₂, which should act to dissolve carbonates. The average δ¹³C of the carbonates was ?29.2?±?2.8‰ VPDB, compared to a range of ?1.0 to +7.8‰ for CO₂ in the seep gas, indicating that CO₂ from the seep gas is quantitatively not as important as ¹³C-depleted bicarbonate derived from methane oxidation. Methane, with a δ¹³C of approximately ?43‰, is oxidized and the resulting inorganic carbon precipitates as high-magnesium calcite and other carbonate minerals. This finding is supported by ¹³C-depleted biomarkers typically associated with anaerobic methanotrophic archaea and their bacterial syntrophic partners in the carbonates (lipid biomarker δ¹³C ranged from ?84 to ?25‰). The inconsistency in δ¹³C between the carbonates and the seeping CO₂ was resolved by discovering pockets of gas trapped near the base of the sediment column with δ¹³C-CO₂ values ranging from ?26.9 to ?11.6‰. A mechanism of carbonate formation is proposed in which carbonates form near the sediment–bedrock interface during times of sufficient sediment coverage, in which anaerobic oxidation of methane is favored. Precipitation occurs at a sufficient distance from active venting for the molecular and isotopic composition of seep gas to be masked by the generation of carbonate alkalinity from anaerobic methane oxidation.