Correlation of the middle devonian formations of Australia

In the Precambrian rocks west and southwest of the Mount Isa Fault three significant fold generations are recognized. Within individual successions, units containing an early phase of deformation are juxtaposed by a late fault against a sequence that does not share these earlier events.

Many of the large‐scale structures in the Judenan Beds are first‐generation folds, whereas west of the Judenan Beds the area is dominated by second‐generation folds. These two sets of folds are tentatively correlated and are referred to as the Judenan Folds. An earlier set of pre‐Judenan folding is only found in the units west of the Judenan Beds. One phase of the Sybella Granite is also associated with the Judenan folding. Later small‐scale folds associated with a crenulation cleavage are, however, of little regional importance and are commonly found only in zones of highly deformed rocks.     

A highstand oolitic sequence and associated facies from a Late Triassic lake basin, south-west England

High energy, lake‐shoreline carbonate sequences are rarely documented in the geological record. However, one example occurs in the Upper Triassic Mercia Mudstone Group (MMG) of southern Britain. The MMG is one of a number of thick, non‐fossiliferous mudstone deposits associated with North Atlantic Mesozoic rift basins. The origin of the MMG mudstones is the subject of current debate, with marine, playa‐lacustrine and alluvial–aeolian models having been proposed. Shoreline features have been documented from the northern margin of the basin, but the rarity of such features elsewhere in the MMG has led many workers to doubt a lacustrine origin for the mudstones. Wave‐dominated, lake‐shoreline deposits have been recognized in several sections from the southern basin margin in the Clevedon area of the Bristol Channel in south‐west England. These deposits provide evidence for the development of a sizeable perennial to semi‐perennial hypersaline lake in which the MMG mudstones accumulated. Shoreline sediments overlie alluvial stream and sheet‐flood deposits, and pass from transgressive gravel–conglomerate beach units with bioclasts, influenced by shore‐normal waves (deposited under semi‐humid conditions), to lower gradient, highstand oolitic sands affected by more varied wave approach (deposited under progressively more arid conditions), which culminated in lowstand, oolitic strand‐plain deposits overlain by a playa‐mudflat unit. Shoreline deposits record a simple shallowing‐upward transgressive–highstand–lowstand sequence. However, a change from a reflective (transgressive) to dissipative (highstand) shoreline is believed to represent a climatically induced change in prevailing wind direction. Shoreline features recognized in the MMG are similar to those of recent playa‐lacustrine basins of the western United States. Ooids display a variety of size, fracture and dissolution features in addition to beachrock fabrics, suggesting that they were originally composed of radial aragonite, similar to modern ooids from the Great Salt Lake, Utah.     

Tufa Accumulations in Ephemeral Streams: Observations from The Kimberley,north-west Australia

Four types of tufa occur along creeks draining the Oscar Range in the Kimberley region of Western Australia; stream-bed tufa, tufa dams, stream-bed tufa waterfalls, and rimstone pools. Well-developed tufa dam and waterfall formations occur at significant breaks of slope within the channel long profile. This suggests that disruption of the hydraulic flow regime and increased turbulence at these points has an important role to play in determining the location of tufa deposits. However, the best-developed stream-bed tufa deposits are located immediately upstream of dam and waterfall formations, which indicates that the evaporation of water ponded behind these flow obstructions may lead to calcium carbonate precipitation during the dry season. The presence of plant and cyanobacterial communities on, and the incorporation of organic material into, the best-developed tufa formations indicates that biological activity may have an important role to play in determining both the rate of tufa deposition and the internal structure of the resulting accumulations.     

The cosmological dependence of galactic specific angular momenta

Hydrodynamical simulations of galaxy formation in spatially flat cold dark matter (CDM) cosmologies with and without a cosmological constant (Λ) are described. A simple star formation algorithm is employed and radiative cooling is allowed only after redshift z =1 so that enough hot gas is available to form large, rapidly rotating stellar discs if angular momentum is approximately conserved during collapse. The specific angular momenta of the final galaxies are found to be sensitive to the assumed background cosmology. This dependence arises from the different angular momenta contained in the haloes at the epoch when the gas begins to collapse and the inhomogeneity of the subsequent halo evolution. In the Λ-dominated cosmology, the ratio of stellar specific angular momentum to that of the dark matter halo (measured at the virial radius) has a median value of ∼0.24 at z =0. The corresponding quantity for the Λ=0 cosmology is over three times lower. It is concluded that the observed frequency and angular momenta of disc galaxies pose significant problems for spatially flat CDM models with Λ=0 but may be consistent with a Λ-dominated CDM universe.     

The ammonite faunas of the Osmington Oolite Formation (Jurassic, Middle Oxfordian) of the Dorset coast

A detailed study of the lithologies of each of the beds present in the Osmington Oolite Formation of south Dorset is used to allocate numerous loose-collected ammonites to their correct stratigraphic horizons. Much new material has been collected by the author in addition to the limited amount of material available in museum collections. The age of the faunas of the three constituent members of the Osmington Oolite Formation is each assessed and placed into the context of Middle Oxfordian ammonite sequences elsewhere in England and in Europe.     

An approach to modeling climate based on feedback relationships

Feedback occurs between many components of the climate system, and makes the study of climate very difficult. A modeling approach is presented in which feedbacks are represented specifically. Analysis of very simple models shows how feedback between two components affects their behavior; positive feedback increases persistence, and can produce climatic changes even without changes in external forcing. In any quantitative study, the magnitudes of all relevant feedbacks must be known accurately. As an example, it is shown how the effect of CO₂ on global temperature must depend greatly on the feedback between global temperature and ice extent.     

Is there a limit to bioretention effectiveness? Evaluation of stormwater bioretention treatment using a lumped urban ecohydrologic model and ecologically based design criteria

In this study, we developed the urban ecohydrology model (UEM) to investigate the role of bioretention on watershed water balance, runoff production, and streamflow variability. UEM partitions the land surface into pervious, impervious, and bioretention cell fractions. Soil moisture and vegetation dynamics are simulated in pervious areas and bioretention cells using a lumped ecohydrological approach. Bioretention cells receive runoff from a fraction of impervious areas. The model is calibrated in an urban headwater catchment near Seattle, WA, USA, using hourly weather data and streamflow observations for 3 years. The calibrated model is first used to investigate the relationship between streamflow variability and bioretention cell size that receives runoff from different values of impervious area in the watershed. Streamflow variability is quantified by 2 indices, high pulse count (HPC), which quantifies the number of flow high pulses in a water year above a threshold, and high pulse range (HPR), which defines the time over which the pulses occurred. Low values of these indices are associated with improved stream health. The effectiveness of the modelled bioretention facilities are measured by their influence on reducing HPC and HPR and on flow duration curves in comparison with modelled fully forested conditions. We used UEM to examine the effectiveness of bioretention cells under rainfall regimes that are wetter and drier than the study area in an effort to understand linkages between the degree of urbanization, climate, and design bioretention cell size to improve inferred stream health conditions. In all model simulations, limits to the reduction of HPC and HPR indicators were reached as the size of bioretention cells grew. Bioretention was more effective as the rainfall regime gets drier. Results may guide bioretention design practices and future studies to explore climate change impacts on bioretention design and management.     

Basin architecture and thermal maturation in the strike-slip Deer Lake Basin, Carboniferous of Newfoundland

Abstract The Deer Lake Basin is an entirely non-marine basin associated with the Cabot fault zone. Structural and stratigraphic evidence strongly suggest dextral strike-slip movements along the fault zone during Tournaisian-Visean time. Two elongated, end-on structural blocks (probable positive flower structures) contain fold axes and second-order faults oriented obliquely to fault traces bounding the blocks, in a manner implying dextral movements. In one part of the basin, the stratigraphic thickness of a long homoclinal section of later basin-fill sediment (Deer Lake Group) greatly exceeds the suggested depth to basement based on gravity measurements, a situation common to strike-slip basins. Formations representing basin fill can be arranged into megasequences (from oldest to youngest: Anguille Group, Wetstone Point and Wigwam Brook Formations, Deer Lake Group, Howley Formation) corresponding to lateral growth stages of the basin. Gravity, magnetic, and seismic data show that depths to basement on either side of the end-on flower structures are comparable, so that the youngest strata in the basin (Howley Formation) are not underlain by earlier basin fill. These geophysical data, therefore, corroborate the geological conclusion of onlapping stratigraphic relations. The geophysical data suggest participation of basement in Carboniferous gravity faulting and show the location of the subsurface extension of the Taylors Brook Fault in the western part of the Deer Lake Basin. Thermal maturation of the Anguille and Deer Lake Groups, as measured by vitrinite reflectance, clay mineral assemblages, illite crystallinity, and Rock-Eval pyrolysis, indicate a much higher level of maturation for the Anguille than for the Deer Lake Group. Palaeotemperatures for the Anguille and Deer Lake Groups are estimated to be around 200 and 100^oC, respectively, suggesting that Anguille Group rocks are overmature whereas Deer Lake Group strata are within the oil-generating window. Onlapping stratigraphic relations and areally homogeneous time/temperature effects, however, have created a situation in which the Deer Lake Group and Howley Formation have similar maturation levels.