Harry Rowe

Evidence for a diachronous Late Permian marine crisis from the Canadian Arctic region

A high-resolution chemostratigraphic study of a 24-m-thick section at West Blind Fiord on Ellesmere Island (Canadian Arctic) documents stepwise environmental deterioration in the marine Sverdrup Basin during the late Changhsingian (late Late Permian) as a result of volcanic disturbances to surrounding landmasses. A horizon within the upper Lindstrom Formation (datum A) is characterized by increased Fe-oxyhydroxide fl uxes and weathering intensity as well as modest shifts toward more reducing watermass conditions and higher marine productivity, recording an initial disturbance that washed soils into the marine environment. The contact between chert of the Lindstrom Formation and silty shale of the overlying Blind Fiord Formation, which is 1.6 m higher and ~50 k.y. younger than datum A, records a large increase in detrital sediment fl ux, more strongly enhanced marine productivity, and a regional extinction of siliceous sponges, herein termed the “Arctic extinction event.” The horizon equivalent to the latest Permian mass extinction of Tethyan shallow-marine sections is 5.6 m higher and ~100 k.y. younger than the Arctic extinction event, demonstrating the diachronous nature of the marine biotic and environmental crisis at a global scale; it is associated with intensifi ed anoxia and possible changes in phytoplankton community composition in the study section. Marine environmental deterioration in the Sverdrup Basin, probably triggered by terrestrial ecosystem deterioration and elevated detrital sediment fl uxes, was under way by the early part of the late Changhsingian, well before the onset of main-stage Siberian Traps fl ood basalt volcanism. The event sequence at West Blind Fiord may record the deleterious effects of early-stage explosive silicic eruptions that affected the Boreal region, possibly through deposition of toxic gas and ash within a restricted latitudinal band, while having little impact on marine ecosystems in the peri-equatorial Tethyan region.

Dominance of putative marine benthic Archaea in Qinghai Lake, north-western China

Recent studies have revealed important and versatile roles that Archaea play in a wide variety of environmental processes on Earth. In this study, we investigated the abundance and diversity of archaeal communities in lake water and a 5 m sediment core collected from Qinghai Lake on the Tibetan Plateau, north-western China. An integrated approach was employed including geochemistry, quantitative polymerase chain reaction (Q-PCR) and 16S rRNA gene analysis. Here, we show that Archaea dominated the prokaryotic community in the lake sediments. Members of putative marine benthic groups [Marine Benthic Group (MBG)-B, -C and -D] and Miscellaneous Crenarchaeotic Group (MCG) were dominant, many of which were previously reported to be predominantly present in deep-sea environments. These results demonstrate that these groups are not limited to marine sediments. Despite their ubiquitous presence in aquatic environments, metabolic functions of these important groups largely remain unknown. Whereas many of these groups (such as MBG-B and -D) have typically been found in methane-hydrate deposits in marine environments, our carbon isotopic and molecular results from Qinghai Lake sediments indicate a lacustrine origin.

Nuclear magnetic resonance characterization of shallow marine sediments from the Nankai Trough, Integrated Ocean Drilling Program Expedition 333

We measured nuclear magnetic resonance (NMR) relaxation times on samples from Integrated Ocean Drilling Program Expedition 333 Sites C0011, C0012, and C0018. We compared our results to permeability, grain size, and specific surface measurements, pore size distributions from mercury injection capillary pressure, and mineralogy from X-ray fluorescence. We found that permeability could be predicted from NMR measurements by including grain size and specific surface to quantify pore networks and that grain size is the most important factor in relating NMR response to permeability. Samples within zones of anomalously high porosity from Sites C0011 and C0012 were found to have different NMR-permeability relationships than samples from outside these zones, suggesting that the porosity anomaly is related to a fundamental difference in pore structure. We additionally estimated the size of paramagnetic sites that cause proton relaxation and found that in most of our samples, paramagnetic material is present mainly as discrete, clay-sized grains. This distribution of paramagnetic material may cause pronounced heterogeneity in NMR properties at the pore scale that is not accounted for in most NMR interpretation techniques. Our results provide important insight into the microstructure of marine sediments in the Nankai Trough.

High-resolution stratigraphy and facies architecture of the Upper Cretaceous (Cenomanian–Turonian) Eagle Ford Group, Central Texas

Rock-based studies of the Eagle Ford Group of Central Texas demonstrate that mudrock deposition is more complicated than previously supposed. X-ray diffraction, x-ray fluorescence, total organic carbon (TOC), and log data collected from eight cores and two outcrops demonstrate that bottom-current reworking and planktonic productivity are primary depositional controls, acting independently from eustatic forcing. Central Texas Eagle Ford facies include (1) massive argillaceous mudrock, (2) massive foraminiferal calcareous mudrock, (3) laminated calcareous foraminiferal lime mudstone, (4) laminated foraminiferal wackestone, (5) cross-laminated foraminiferal packstone–grainstone, (6) massive bentonitic claystone, and (7) nodular foraminiferal packstone–grainstone. High degrees of lateral facies variability, characterized by pinching and swelling of units, lateral facies changes, truncations, and locally restricted units, are observed even at small lateral scales (50 ft [15 m]). At 10 mi (16 km) and greater lateral spacings, core and geochemical data significantly underestimate intraformational facies variability. Approximately 73% of units can be successfully correlated across a distance of 500 ft (152 m), 35% are traceable across 1 mi (1.6 km), and only 16% of beds are correlative across 10 mi (16 km). Geochemical proxies (enrichment in molybdenum and other trace elements) indicate that maximum anoxia occurred within the Bouldin Member despite being composed of the most calcareous and high-energy facies. Comparison of total gamma ray (GR) logs to computed GR logs is requisite, because GR alone may provide misleading determination of facies, TOC content, depositional environment, and sequence stratigraphic implications.

Pore types, pore-network analysis, and pore quantification of the lacustrine shale-hydrocarbon system in the Late Triassic Yanchang Formation in the southeastern Ordos Basin, China

AbstractContinental Upper Triassic Yanchang “black shales” in the southeastern Ordos Basin have been proven to be unconventional gas reservoirs. Organic-matter-lean and organic-matter-rich argillaceous mudstones form reservoirs that were deposited in a deeper water lacustrine setting during lake highstands. In the stratified lake, the bottom waters were dysaerobic to anoxic. This low-energy and low-oxygen lake-bottom setting allowed types II and III organic matter to accumulate. Interbedded with the argillaceous mudstones are argillaceous arkosic siltstones deposited by gravity-flow processes. Rock samples from the Yanchang Chang 7–9 members are very immature mineralogically. Mineral grains are predominantly composed of relatively equal portions of quartz and feldspar. The high clay-mineral content, generally greater than 40%, has promoted extensive compaction of the sediments, permitting the ductile material to deform and occlude interparticle pores. Furthermore, this high clay-mineral content does not f...

High influx of carbon in walls of agglutinated foraminifers during the Permian-Triassic transition in global oceans

The Permian–Triassic mass extinction is postulated to be related to the rapid volcanism that produced the Siberian flood basalt (Traps). Unrelated volcanic eruptions producing several episodes of ash falls synchronous with the Siberian Traps are found in South China and Australia. Such regional eruptions could have caused wildfires, burning of coal deposits, and the dispersion of coal fly ash. These eruptions introduced a major influx of carbon into the atmosphere and oceans that can be recognized in the wall structure of foraminiferal tests present in survival populations in the boundary interval strata. Analysis of free specimens of foraminifers recovered from residues of conodont samples taken at a Permian–Triassic boundary section at Lung Cam in northern Vietnam has revealed the presence of a significant amount of elemental carbon, along with oxygen and silica, in their test wall structure, but an absence of calcium carbonate. These foraminifers, identified as Rectocornuspira kalhori, Cornuspira mahajeri, and Earlandia spp. and whose tests previously were considered to be calcareous, are confirmed to be agglutinated, and are now referred to as Ammodiscus kalhori and Hyperammina deformis. Measurement of the 207Pb/204Pb ratios in pyrite clusters attached to the foraminiferal tests confirmed that these tests inherited the Pb in their outer layer from carbon-contaminated seawater. We conclude that the source of the carbon could have been either global coal fly ash or forest fire-dispersed carbon, or a combination of both, that was dispersed into the Palaeo-Tethys Ocean immediately after the end-Permian extinction event.

Facies, rock attributes, stratigraphy, and depositional environments: Yanchang Formation, Central Ordos Basin, China

AbstractThe Late Triassic Yanchang Formation (Fm) is a major target of drilling for hydrocarbons in the Ordos Basin. Although most of the early focus on this thick succession of lacustrine rocks has been the dominant deltaic sandstones and siltstones, which act as local reservoirs of oil and gas, more recent consideration has been given to the organic-rich mudstone source rocks. We used modern chemostratigraphic analysis to define vertical facies successions in two closely spaced cores through the Chang 7 Member, the primary source rock for the Yanchang hydrocarbon system. We used integrated high-resolution X-ray fluorescence and X-ray diffraction measurements to define four dominant facies. Variations in stable carbon isotopes mimic facies stacking patterns, suggesting that terrigenous organic matter (although minor in volume) is associated with the arkoses and sandstones, whereas aquatic organic matter is dominant in the mudstones. Facies stacking patterns define three major depositional cycles and part...

Introduction to special section: Shale paleoenvironments

The processes that deposit mud, and the environmental conditions under which the mud is deposited, are the primary controls on the composition (i.e., mineralogy, organic content) and texture (laminations, bedding, etc.) of mudstones (“shales”). Together, these and other factors (e.g., diagenesis