Sequence Stratigraphy in Proterozoic Successions

Sedimentological logging and facies mapping have been used to identify depositional sequences bounded by subtle but regionally persistent unconformities in rocks of Proterozoic age in the western United States, South Australia, and northwestern Canada. We conclude from these studies that the sequence stratigraphic approach is of considerable importance for intrabasinal time correlation in the Proterozoic and for facies interpretation and basin analysis in Proterozoic rocks

Testing the Extensional Detachment Paradigm: A Borehole Observatory in the Sevier Desert Basin

Low-angle normal faults or detachments are widely regarded as playing an important role in crustal extension and the development of rifted continental margins (Manatschal et al., 2007). However, no consensus exists on how to resolve the mechanical paradox implied by the gentle dips of these faults and by the general absence of evidence for associated seismicity (Sibson, 1985; Wernicke, 1995; Axen, 2004). As part of a new initiative to rationalize geological and geophysical evidence and our theoretical understanding of how rocks deform, a group of forty-seven scientists and drilling experts from five countries met for four days on 15–18 July 2008 to discuss the present status of the paradox and a borehole-based strategy for resolving it. The workshop was held at two venues in Utah (the Utah Department of Natural Resources in Salt Lake City, and Solitude Mountain Resort in the adjacent Wasatch Range), with a one-day field trip to the Sevier Desert basin of west-central Utah to examine the general setting of potential drill sites and the footwall geology of the Sevier Desert detachment (Canyon Range)

Sequence Stratigraphy and Evolution of a Basin-Slope Succession: The Late Proterozoic Wonoka Formation, Flinders Ranges, South Australia

A shelf to basin‐slope transition is vertically and laterally exposed within the Late Proterozoic Wonoka Formation in the northern Flinders Ranges of South Australia. The shelf to basin‐slope transition can be divided into four units (C to F) which are defined on the basis of facies, sedimentary structures, contacts, stratal geometry, and the type and abundance of down‐slope mass movement. The lowest unit (C) is mudstone dominated and parallel laminated with rare synsedimentary slides. Unit D, a thin, resedimented siliciclastic‐carbonate unit deposited on a sequence boundary at the end of unit C progradation, displays a lateral facies change from well bedded ‘outer shelf deposits in the east to basin‐slope debris flows in the west. Unit E forms a shallowing and coarsening upward succession from ‘outer shelf siltstone to ‘inner shelf storm wave influenced sandstone deposits. The unit thickens westwards, in the interpreted down‐slope direction, where it becomes finer grained and thinner bedded and displays an increasing abundance of synsedimentary slides. Unit F, deposited on an inferred shelf to basin‐slope transition, coarsens and shallows upward, thickens to the west and contains the highest percentage of sandstone and synsedimentary slides. Unit G, deposited at shelf depths, also shallows and coarsens upward from a thin, basal carbonate‐siliciclastic member, with sandstone increasing upsection to a gradational contact with the Pound Subgroup. Three sequences can be defined within this transition on the basis of facies, stratal terminations, and facies discontinuities at inferred sequence boundaries. Each sequence is marked by a transgressive base, overlain by a shallowing‐upward succession. On the inferred shelf and near the shelfbreak, toward the top of the succession, facies discontinuities at sequence boundaries are more obvious, with distinct contrasts in lithology and inferred palaeoenvironments; farther down‐slope and stratigraphically lower in the succession, the boundaries are cryptic, and only lateral tracing of the contacts from the shelf to the slope or the observation of stratal terminations permits them to be recognized

Working Hypotheses for the Origin of the Wonoka Canyons (Neoproterozoic), South Australia

Recent attempts to apply concepts of sequence stratigraphy to the Neoproterozoic Wilpena Group of the Adelaide "geosyncline" in South Australia have provided an important new method for improving the resolution of intrabasinal correlation in sparsely fossiliferous and unfossiliferous strata. Eight regional unconformities are now recognized within or bounding the Wilpena Group. The most prominent of these, at or near the base of the Wonoka Formation, is expressed by a series of spectacular incised valleys or canyons, some more than 1 km deep and dated as approx 630 to 580 Ma. The canyons developed following an interval of continental rifting that took place between about 800 and 700 Ma and prior to a second phase of accelerated subsidence of uncertain origin in Early Cambrian time (after about 560 Ma). Subsidence during the intervening span of more than 140 my was in part of thermal origin and in part due to the withdrawal of buried salt at depth, but it may also have involved additional extension for which little direct structural evidence is preserved. The canyons are incised into a succession of shallow marine mainly terrigenous strata that accumulated in a broad north- and east-facing ramp. They are exposed in two distinct belts within and east of the Flinders Ranges, in an area that is about 275 km in a north-south direction and about 175 km east-west. The canyons are inferred to have been filled by shallow marine sediments primarily on the basis of sedimentary structures interpreted as combined flow and oscillation ripples and hummocky cross-stratification. If this is correct, development of the canyons was related to regional lowering of depositional base level by more than 1 km. Recent work also indicates a second phase of valley incision at an unconformity immediately above the main canyons and involving a relative sealevel fall of at least 200 m. Two working hypotheses are advanced to account for the origin of the Wonoka canyons: regional uplift and an evaporitic lowering of sealevel in an isolated basin, analogous to the Messinian event in the Mediterranean. Any regional uplift would likely have been of tectonic origin. Diapirism associated with buried salt cannot account for the wide distribution of erosion or for pronounced uplift in an extensional setting lacking evidence for basin inversion or compressional deformation coeval with sedimentation. One possible mechanism for tectonic uplift involves inhomogeneous extension of the lithosphere, with the amount of extension balanced at all levels on a regional scale possibly by means of detachment faults. Possible difficulties with this hypothesis are the requirement of relatively uniform uplift over distances of hundreds of kilometers and the fact that repeated large-scale lowering of base level implies oscillatory vertical motions that are not readily explained. An evaporitic drawdown accounts for the wide distribution and scale of the canyons and for repeated lowering of base level. Possible difficulties in this case are the presence within the canyon fill of facies that have been interpreted to be of tidal origin; the fact that unlike the Messinian crisis in the Mediterranean, the Wonoka canyons do not appear to have been drowned rapidly; and the lack of direct evidence for evaporities of appropriate age. Neither hypothesis accounts for the apparent absence of appreciable meteoric diagenesis in areas far removea from sites of canyon incision. Two additional conclusions are as follows. First, neither of the hypotheses precludes eustasy as an important control on sedimentation. Sequence stratigraphic comparisons with other basins of the same general age should focus primarily on the time of formation of sequence boundaries not on the geometry of the boundaries or the facies involved. Second, a drawdown in excess of 1 km implies that the adjacent basin was originally at least this deep and hence likely underlain at least locally by highly attenuated continental crust or oceanic crust. Either hypothesis therefore has important implications for the tectonic development of the Adelaide geosyncline

Exploring views on satisfaction with life in young children with chronic illness: an innovative approach to the collection of self-report data from children under 11

The objective of this study was to explore young children’s views on the impact of chronic illness on their life in order to inform future development of a patient-based self-report health outcome measure. We describe an approach to facilitating self-report views from young children with chronic illness. A board game was designed in order to obtain qualitative data from 39 children with a range of chronic illness conditions and 38 healthy controls ranging in age from 3 to 11 years. The format was effective in engaging young children in a self-report process of determining satisfaction with life and identified nine domains. The board game enabled children aged 5–11 years with chronic illness to describe the effects of living with illness on home, family, friends, school and life in general. It generated direct, non-interpreted material from children who, because of their age, may have been considered unable or limited their ability to discuss and describe how they feel. Obtaining this information for children aged 4 and under continues to be a challenge

Late Proterozoic Patsy Springs Canyon, Adelaide Geosyncline: Submarine or Subaerial Origin?

A significant aspect of Late Proterozoic sedimentation in the Adelaide Geosyncline, South Australia, is the presence of kilometre-deep erosional incisions which have been termed canyons. These structures were formerly described to be of submarine origin, cut and filled in an inferred basin-slope setting by subaqueous processes. Subsequent detailed research, particularly on a specific incision known as Patsy Springs Canyon, indicates that sedimentary structures within some of the canyon-filling sediments are indicative of deposition above fair weather wave base. In addition, an unusual carbonate unit, which is observed to veneer upper portions of canyon shoulders and to contribute to carbonate breccias interbedded with canyon-fill, has a stable isotope signature which may imply a non-marine origin. The presence of the carbonate veneer, where it is in situ, suggests that at least upper portions of the canyons could have been emergent during the canyon-filling phase. Considering these observations, and combining them with regional stratigraphical relationships, an alternative model for canyon genesis is proposed involving subaerial erosion and subsequent filling by coastal onlap. Such a model requires base-level changes of the order of 1 km, in order to account for observed canyon cutting and filling. Vertical movements associated with halokinesis, or thermally-induced uplift of the order of 1 km, could have resulted in the observed erosional events. Alternatively, a Messinian-style evaporitic lowering of base-level is currently receiving serious attention. With present knowledge this mechanism most satisfactorily explains all observations

Detrital Zircon Provenance of Mesoproterozoic to Cambrian Arenites in the Western United States and Northwestern Mexico

U-Pb isotopic dating of detrital zircon from supracrustal Proterozoic and Cambrian arenites from the western United States and northern Mexico reveal three main age groups, 1.90 to 1.62 Ga, 1.45 to 1.40 Ga, and 1.2 to 1.0 Ga. Small amounts of zircons with ages of 3.1 to 2.5 Ga, 1.57 Ga, 1.32 Ga, 1.26 Ga, 0.7 Ga, and 0.5 Ga are also present. Detrital zircons ranging in age from 1.90 to 1.62 Ga and from 1.45 to 1.40 Ga are considered to have been derived from Proterozoic crystalline basement rocks of these known ages, and probably in part from reworked Proterozoic supracrustal sedimentary rocks, of the western United States. The 1.2 to 1.0 Ga detrital zircon ages from California, Arizona, and Sonora are characterized by distinct spikes (1.11 Ga, in particular) in the age-probability plots. These spikes are interpreted to indicate the influx of zircon from major silicic volcanic fields. Igneous rocks such as the Pikes Peak Granite (1.093 Ga) of Colorado, and the Aibo Granite (1.110 Ga) of Sonora, Mexico, may represent the deeply eroded roots of such volcanic fields. Samples from farther north along the Cordilleran margin that contain abundant 1.2–1.0 Ga detrital zircons do not show spikes in the age distribution, but rather ages spread out across the entire 1.2–1.0 Ga range. These age spectra resemble those for detrital zircons from the Grenville province, which is considered their source. Less common detrital zircons had a variety of sources. Zircons ranging in age from 3.36 to 2.31 Ga were apparently derived from inland parts of the North American continent from Wyoming to Canada. Zircons of about 1.577 Ga are highly unusual and may have had an exotic source; they may have come from Australia and been deposited in North America when Australia and North America were juxtaposed as part of the hypothetical Rodinian supercontinent. Detrital zircon of ∼1.320 Ga apparently had the same source as that for tuff (1.320 Ga) in the Pioneer Shale of the Apache Group in Arizona. Detrital zircons of about 1.26 Ga in the Apache Group and Troy Quartzite appear to be related to local, approximately coeval volcanic fields. Zircons of about 0.7 Ga may have had a source in igneous rocks related to rifting of the Proterozoic supercontinent of Rodinia, and 0.5 Ga zircons a source in relatively small areas of granitic rocks of this known, or inferred, age in Oklahoma, Texas, New Mexico, and Colorado

Human Escherichia coli O157:H7 Genetic Marker in Isolates of Bovine Origin

The antiterminator Q gene of bacteriophage 933W (Q933) was identified upstream of the stx2 gene in 90% of human disease–origin Escherichia coli O157:H7 isolates and in 44.5% of bovine isolates. Shiga toxin production was higher in Q933-positive isolates than Q933-negative isolates. This genetic marker may provide a useful molecular tool for epidemiologic studies

Ultrastructural changes of the intracellular surfactant pool in a rat model of lung transplantation-related events

<p>Abstract</p> <p>Background</p> <p>Ischemia/reperfusion (I/R) injury, involved in primary graft dysfunction following lung transplantation, leads to inactivation of intra-alveolar surfactant which facilitates injury of the blood-air barrier. The alveolar epithelial type II cells (AE2 cells) synthesize, store and secrete surfactant; thus, an intracellular surfactant pool stored in lamellar bodies (Lb) can be distinguished from the intra-alveolar surfactant pool. The aim of this study was to investigate ultrastructural alterations of the intracellular surfactant pool in a model, mimicking transplantation-related procedures including flush perfusion, cold ischemia and reperfusion combined with mechanical ventilation.</p> <p>Methods</p> <p>Using design-based stereology at the light and electron microscopic level, number, surface area and mean volume of AE2 cells as well as number, size and total volume of Lb were determined in a group subjected to transplantation-related procedures including both I/R injury and mechanical ventilation (I/R group) and a control group.</p> <p>Results</p> <p>After I/R injury, the mean number of Lb per AE2 cell was significantly reduced compared to the control group, accompanied by a significant increase in the luminal surface area per AE2 cell in the I/R group. This increase in the luminal surface area correlated with the decrease in surface area of Lb per AE2. The number-weighted mean volume of Lb in the I/R group showed a tendency to increase.</p> <p>Conclusion</p> <p>We suggest that in this animal model the reduction of the number of Lb per AE2 cell is most likely due to stimulated exocytosis of Lb into the alveolar space. The loss of Lb is partly compensated by an increased size of Lb thus maintaining total volume of Lb per AE2 cell and lung. This mechanism counteracts at least in part the inactivation of the intra-alveolar surfactant.</p