A detailed paleomagnetic and rock-magnetic investigation around Cretaceous-Paleogene boundary: the Autlan (Western Mexico) volcanic sequence revisited     

Miguel Cervantes-Solano  Lisa Kapper  Avto Goguitchaichvili  Vicente Carlos Ruiz-Martínez  José Rosas-Elguera  Juan Morales  Rafael Maciel-Peña  Rubén Cejudo-Ruiz 《Studia Geophysica et Geodaetica》2017,61(2):233-248

We present a detailed rock-magnetic and paleomagnetic survey from Autlan volcanic succession in western Mexico. The principal aim of this study is to extend paleomagnetic data from Autlan lavas in order to confirm vertical-axis rotation observed in reconnaissance study and to evaluate long-term variation of the geomagnetic field strength based on existing and global data. The mean inclination (44.7°) is in agreement with the expected inclination for 60 and 70 Ma, as derived from available reference poles for the North American craton. The declination (333.6°), however, is significantly different from those expected, which suggests a statistically significant counterclockwise tectonic rotation ranging between 10° ± 6° and 14° ± 7°. As a measure of paleosecular variation (PSV), we obtained a geomagnetic field dispersion of 9.6° (upper and lower limits: 7.2°–11.9°) in perfect agreement with the previously published PSV compilation of selected Cretaceous data from lavas. The mean virtual dipole moments available for Autlan lavas are about 65% of the present geomagnetic axial dipole but are in reasonably good agreement with other comparable quality determinations between 5 and 90 Ma. This reinforces the hypothesis that low geomagnetic field strengths persisted for the entire Jurassic extending into the Upper Cretaceous.  相似文献   

Assessing Methane in Shallow Groundwater in Unconventional Oil and Gas Play Areas,Eastern Kentucky          下载免费PDF全文

Junfeng Zhu  Thomas M. Parris  Charles J. Taylor  Steven E. Webb  Bart Davidson  Richard Smath  Stephen D. Richardson  Lisa J. Molofsky  Jenna S. Kromann  Ann P. Smith 《Ground water》2018,56(3):413-424

The expanding use of horizontal drilling and hydraulic fracturing technology to produce oil and gas from tight rock formations has increased public concern about potential impacts on the environment, especially on shallow drinking water aquifers. In eastern Kentucky, horizontal drilling and hydraulic fracturing have been used to develop the Berea Sandstone and the Rogersville Shale. To assess baseline groundwater chemistry and evaluate methane detected in groundwater overlying the Berea and Rogersville plays, we sampled 51 water wells and analyzed the samples for concentrations of major cations and anions, metals, dissolved methane, and other light hydrocarbon gases. In addition, the stable carbon and hydrogen isotopic composition of methane (δ¹³C‐CH₄ and δ²H‐CH₄) was analyzed for samples with methane concentration exceeding 1 mg/L. Our study indicates that methane is a relatively common constituent in shallow groundwater in eastern Kentucky, where methane was detected in 78% of the sampled wells (40 of 51 wells) with 51% of wells (26 of 51 wells) exhibiting methane concentrations above 1 mg/L. The δ¹³C‐CH₄ and δ²H‐CH₄ ranged from ?84.0‰ to ?58.3‰ and from ?246.5‰ to ?146.0‰, respectively. Isotopic analysis indicated that dissolved methane was primarily microbial in origin formed through CO₂ reduction pathway. Results from this study provide a first assessment of methane in the shallow aquifers in the Berea and Rogersville play areas and can be used as a reference to evaluate potential impacts of future horizontal drilling and hydraulic fracturing activities on groundwater quality in the region.  相似文献   

Straight from the source's mouth: Controls on field-constrained sediment export across the entire active Corinth Rift,central Greece     

Stephen E. Watkins  Alexander C. Whittaker  Rebecca E. Bell  Sam A. S. Brooke  Vamsi Ganti  Robert L. Gawthorpe  Lisa C. McNeill  Casey W. Nixon 《Basin Research》2020,32(6):1600-1625

The volume and grain-size of sediment supplied from catchments fundamentally control basin stratigraphy. Despite their importance, few studies have constrained sediment budgets and grain-size exported into an active rift at the basin scale. Here, we used the Corinth Rift as a natural laboratory to quantify the controls on sediment export within an active rift. In the field, we measured the hydraulic geometries, surface grain-sizes of channel bars and full-weighted grain-size distributions of river sediment at the mouths of 47 catchments draining the rift (constituting 83% of the areal extent). Results show that the sediment grain-size increases westward along the southern coast of the Gulf of Corinth, with the coarse-fraction grain-sizes (84^th percentile of weighted grain-size distribution) ranging from approximately 19 to 91 mm. We find that the median and coarse-fraction of the sieved grain-size distribution are primarily controlled by bedrock lithology, with late Quaternary uplift rates exerting a secondary control. Our results indicate that grain-size export is primarily controlled by the input grain-size within the catchment and subsequent abrasion during fluvial transport, both quantities that are sensitive to catchment lithology. We also demonstrate that the median and coarse-fraction of the grain-size distribution are predominantly transported in bedload; however, typical sand-grade particles are transported as suspended load at bankfull conditions, suggesting disparate source-to-sink transit timescales for sand and gravel. Finally, we derive both a full Holocene sediment budget and a grain-size-specific bedload discharged into the Gulf of Corinth using the grain-size measurements and previously published estimates of sediment fluxes and volumes. Results show that the bedload sediment budget is primarily comprised (~79%) of pebble to cobble grade (0.475–16 cm). Our results suggest that the grain-size of sediment export at the rift scale is particularly sensitive to catchment lithology and fluvial mophodynamics, which complicates our ability to make direct inferences of tectonic and palaeoenvironmental forcing from local stratigraphic characteristics.  相似文献   

Marine Metapopulations     

Celeste Benham  Alison M. Cawood  Geoffrey S. Cook  Ange Darnell  Peter C. Davison  Miriam C. Goldstein  Ayana Elizabeth Johnson  Talina Konotchick  Elisa M. Maldonado  Alexis L. Pasulka  Jennifer C. Prairie  Serena M. Moseman  Vera Tai  Christina A. Tanner  Tali Vardi  Tara S. Whitty  & Lisa A. Levin 《Marine Ecology》2008,29(2):319-320

  相似文献   

Diversity of bathyal macrofauna on the northeastern Pacific margin: the influence of methane seeps and oxygen minimum zones     

Lisa A. Levin  Guillermo F. Mendoza  Jennifer P. Gonzalez  rew R. Thurber  & Erik E. Cordes 《Marine Ecology》2010,31(1):94-110

  相似文献   

Habitat heterogeneity and its influence on benthic biodiversity in oxygen minimum zones     

Andrew J. Gooday  Brian J. Bett  Elva Escobar  Baban Ingole  Lisa A. Levin  Carlos Neira  Akkur V. Raman  & Javier Sellanes 《Marine Ecology》2010,31(1):125-147

  相似文献   

Modeling and interpreting the seismic-reflection expression of sandstone in an ancient mass-transport deposit dominated deep-water slope environment     

Dominic A. Armitage  Lisa Stright 《Marine and Petroleum Geology》2010

Subsurface mass-transport deposits (MTDs) commonly have a chaotic seismic-reflection response. Synthetic seismic-reflection profiles, created from a precise lithological model, are used to interpret reflection character and depositional geometries at multiple frequencies. The lithological model was created from an outcrop of deep-water lithofacies where sandstone deposition was influenced by mass-transport deposit topography. The influence of MTD topography on sandstone distribution should be considered in reservoir characterization and modeling when MTDs underlie the reservoir, especially if the reservoir is thin relative to the scale of the topography. MTD topography up to several tens of meters in both the horizontal and vertical dimensions (relative to local elevation) compartmentalizes significant quantities of sandstone and is not resolved at lower seismic-reflection frequencies. The resolvability of thick (up to 70 m) sandstone packages is hindered when they are encased in MTDs of at least equivalent thickness. Lateral and vertical changes in seismic-reflection character (e.g., amplitude, polarity, geometry) of sandstone packages in the synthetic profiles are due to lithology changes, tuning effects, resolution limits, and depositional geometries, which are corroborated by the lithological model. Similar reflection-character changes are observed in an actual seismic-reflection profile, of comparable scale to the synthetic profiles, from the Gulf of Mexico, which demonstrates similar lithofacies distributions. Synthetic profiles, when constrained by a precise lithological model, are particularly useful analogues for interpretation of lithofacies relationships, and depositional geometries, in complicated depositional environments, such as deep-water slope deposits.  相似文献   

The 20th-century development and expansion of Louisiana shelf hypoxia,Gulf of Mexico     

Lisa E. Osterman  Richard Z. Poore  Peter W. Swarzenski  David B. Senn  Steven F. DiMarco 《Geo-Marine Letters》2009,29(6):405-414

Since systematic measurements of Louisiana continental-shelf waters were initiated in 1985, hypoxia (oxygen content <2 mg L⁻¹) has increased considerably in an area termed the dead zone. Monitoring and modeling studies have concluded that the expansion of the Louisiana shelf dead zone is related to increased anthropogenically derived nutrient delivery from the Mississippi River drainage basin, physical and hydrographical changes of the Louisiana Shelf, and possibly coastal erosion of wetlands in southern Louisiana. In order to track the development and expansion of seasonal low-oxygen conditions on the Louisiana shelf prior to 1985, we used a specific low-oxygen foraminiferal faunal proxy, the PEB index, which has been shown statistically to represent the modern Louisiana hypoxia zone. We constructed a network of 13 PEB records with excess ²¹⁰Pb-derived chronologies to establish the development of low-oxygen and hypoxic conditions over a large portion of the modern dead zone for the last 100 years. The PEB index record indicates that areas of low-oxygen bottom water began to appear in the early 1910s in isolated hotspots near the Mississippi Delta and rapidly expanded across the entire Louisiana shelf beginning in the 1950s. Since ~1950, the percentage of PEB species has steadily increased over a large portion of the modern dead zone. By 1960, subsurface low-oxygen conditions were occurring seasonally over a large part of the geographic area now known as the dead zone. The long-term trends in the PEB index are consistent with the 20th-century observational and proxy data for low oxygen and hypoxia.  相似文献   

Holocene evolution of Apalachicola Bay,Florida     

Lisa E. Osterman  David C. Twichell  Richard Z. Poore 《Geo-Marine Letters》2009,29(6):395-404

A program of geophysical mapping and vibracoring was conducted to better understand the geologic evolution of Apalachicola Bay. Analyses of the geophysical data and sediment cores along with age control provided by 34 AMS ¹⁴C dates on marine shells and wood reveal the following history. As sea level rose in the early Holocene, fluvial deposits filled the Apalachicola River paleochannel, which extended southward under the central part of the bay and seaward across the continental shelf. Sediments to either side of the paleochannel contain abundant wood fragments, with dates documenting that those areas were forested at 8,000 ¹⁴C years b.p. As sea level continued to rise, spits formed of headland prodelta deposits. Between ∼6,400 and ∼2,500 ¹⁴C years b.p., an Apalachicola prodelta prograded and receded several times across the inner shelf that underlies the western part of the bay. An eastern deltaic lobe was active for a shorter time, between ∼5,800 and 5,100 ¹⁴C years b.p. Estuarine benthic foraminiferal assemblages occurred in the western bay as early as 6,400 ¹⁴C years b.p., and indicate that there was some physical barrier to open-ocean circulation and shelf species established by that time. It is considered that shoals formed in the region of the present barrier islands as the rising sea flooded an interstream divide. Estuarine conditions were established very early in the post-glacial flooding of the bay.  相似文献   

Metal-catalyzed degradation and racemization of amino acids in iron sulfate brines under simulated martian surface conditions     

Adam P. Johnson  Lisa M. Pratt 《Icarus》2010,207(1):124-603

Recent lines of evidence indicate that Mars may have been substantially warmer and wetter, raising questions about whether the planet’s surface was once more conducive to the possibility of life. To better constrain the extent of preservation of ancient amino acid biosignatures, the effects of metal ions and UV radiation were investigated with respect to the rates of diagenesis of amino acids in metal-rich sulfate brines. Individual experimental results indicate that the oxidation rates of amino acids loosely followed trends characteristic of a radiolytic oxidation mechanism that is dependent on variations in side-chain constituents. Relative rates of racemization only show a limited dependence on the presence of metals; overall, rates of racemization in the presence of metals in solution are an order of magnitude slower than oxidation and both are several orders of magnitude faster than previously reported. This increase in rate constant is indicative of an extremely efficient catalytic enhancement of this destructive diagenetic pathway. These findings imply that chiral life-detection strategies should focus on specific geochemical environments that exhibit relatively slow rates of both degradation and racemization. Episodic liquid water during periods of increased water activity on the martian surface may have significant implications for the oxidation of organic matter through secondary diagenetic reactions and may act as a leveling mechanism for organic compounds.  相似文献