Carboniferous palaeogeography of the Yarrol and New England Orogens,eastern Australia

During the Carboniferous Period the Yarrol and New England Orogens comprised an active depositional margin east of cratonised parts of Australia. Patterns of deposition within the orogens were probably controlled by dextral shear systems believed responsible for tectonism and the positions of the various depositional elements (volcanic chain, shelf, slope and basin, pull‐apart troughs and graben), and global changes in sea level. These patterns are illustrated by a series of non‐palin‐spastic palaeogeographic reconstructions.

In the Early Carboniferous, similar patterns of deposition existed within the western volcanic chain, marine shelf, and eastern slope and basin provinces of both orogens. Sediments were deposited in two cycles. They range from volcanic fluvial and marine sandstone to siltstone, mudstone and turbidites. Complex depositional patterns within shelfal regions are shown in detailed palaeogeographic reconstructions.

This uniform pattern changed during the latest Visean and Namurian, with the uplift of the New England Arch, subsidence of a non‐marine graben (Werrie Trough) to the west, and development of a new shelf in the east. The Werrie Trough received volcanics as well as fluvial and glacigene sediments, and the shelf marine sandstone and siltstone. The Yarrol Orogen was unaffected by tectonism but there was a change in provenance.

Late in the Carboniferous the Yarrol Orogen was restructured by the intrusion of granitoids into the former volcanic chain, and development of the Yarrol and North D'Aguilar Troughs as probable pull‐apart basins. In the New England Arch, deformation and metamorphism were followed by intrusion of S‐type granitoids. A comparable episode of deformation and metamorphism affected the southeastern part of the Yarrol Orogen at the end of the Carboniferous Period. This partial cratonisation of the mobile zone was a prelude to widespread basin formation during the Permian Period.     

The Amazon River headstream area in the Cordillera Chila,Peru: hydrographic,hydrological and glaciological conditions

Abstract

The source of the world's largest river has fascinated scientists and adventurers for a long time. Extensive studies have been undertaken in the unexplored Llogueta River valley, Cordillera Chila, to identify the main stream of the Amazon River. Analysis of the Lloqueta River network and measurements of its hydrographic and hydrometric characteristics are presented in this study. On the basis of the acquired data, the northern hillside of the Cordillera Chila massif, concretely the basins of four mountainous courses—the Carhuasanta, Apacheta, Ccaccansa and Sillanque rivers—should be regarded as the headwaters territory of the Amazon River. Factors influencing the river system—glaciers and soils—were examined for each catchment. Glacier retreat in the last 50 years has left perennial snowfields only in the highest part of the study area, resulting in modification of the headwater runoff regimes. Preliminary results are afforded by the continual automatic water-level monitoring of the Lloqueta River since June 2008. Our investigations have determined that all types of soil in the area could be classified into two main categories: hydromorphic soils or poorly developed cryic soils.

Citation Janský, B., Engel, Z., Kocum, J., ?efrna, L. & ?esák, J. (2011) The Amazon River headstream area in the Cordillera Chila, Peru: hydrographical, hydrological and glaciological conditions. Hydrol. Sci. J. 56(1), 138–151.     

IMPACTS OF URBANIZATION ON SURFACE HYDROLOGY,LITTLE EAGLE CREEK,INDIANA, AND ANALYSIS OF LTHIA MODEL SENSITIVITY TO DATA RESOLUTION

Land-use change in urbanizing areas can significantly alter the hydrology of a watershed and can have serious impacts on wetland water balances, downstream flooding, and groundwater recharge. Most currently available models used in determining the hydrologic impacts of urbanization are not well suited to long-term hydrologic analysis or are too complex and data intensive for widespread practical application. The Long-Term Hydrologic Impact Assessment (LTHIA) model run on a Geographic Information System (GIS) is a relatively simple, user-friendly model that uses the Curve Number method to estimate changes in surface runoff between different stages of development. Application of the model to a large, rapidly urbanizing watershed near Indianapolis, Indiana, suggests that average annual runoff depths increased by more than 60% from 1973 to 1991, with even greater increases for some individual sub-basins. These results are consistent with runoff changes estimated from historical stream flow data in the watershed. A sensitivity analysis to determine minimum data requirements shows that a precipitation record length of 15 years or more is required to produce consistent results with LTHIA and that the highest possible resolution land-use and soils data should be used. The LTHIA model is now available on the Internet at http://www.ecn.purdue.edu/runoff. [Key words: hydrology, urbanization, modeling, GIS.]     

Structural and mineralogical study of active and inactive hydrothermal fluid discharges in Panarea,Italy

The isle of Panarea (Aeolian Arc, Italy) is an active hydrothermal system, characterized by different types of fluid emissions, which cause various types of unique hydrothermal structures that are typical for hydrothermal fluid discharges. Such fluid discharge structures at shallow depths of less than 30 m have not been described in marine hydrothermal systems until now to the authors’ knowledge. The focus of the investigations was set on morphological, mineralogical, geochemical, and structural analyses. A broad variety of analytical methods was applied to gain as much information as possible. In addition to geological and sedimentological documentation and standard methods like making and analyzing thin and polished sections, optical microscopy or X-ray fluorescence analysis, the samples were investigated by X-ray computer tomography and scanning electron microscopy, including energy-dispersive X-ray spectroscopy. Because discharge features occur in various settings, a general classification of the features in the hydrothermal system was performed with special focus on their preservability in geological archives. In total, nine different facies types were distinguished based on genetic and/or morphological differences. All samples show laminated structures from µm to cm scale. The single laminae vary in shape and material witnessing various chemical compositions.     

Measurements of methane absorption by the descent imager/spectral radiometer (DISR) during its descent through Titan's atmosphere

New low-temperature methane absorption coefficients pertinent to the Titan environment are presented as derived from the Huygens DISR spectral measurements combined with the in-situ measurements of the methane gas abundance profile measured by the Huygens Gas Chromatograph/Mass Spectrometer (GCMS). The visible and near-infrared spectrometers of the descent imager/spectral radiometer (DISR) instrument on the Huygens probe looked upward and downward covering wavelengths from 480 to 1620 nm at altitudes from 150 km to the surface during the descent to Titan's surface. The measurements at continuum wavelengths were used to determine the vertical distribution, single-scattering albedos, and phase functions of the aerosols. The gas chromatograph/mass spectrometer (GCMS) instrument on the probe measured the methane mixing ratio throughout the descent. The DISR measurements are the first direct measurements of the absorbing properties of methane gas made in the atmosphere of Titan at the pathlengths, pressures, and temperatures that occur there. Here we use the DISR spectral measurements to determine the relative methane absorptions at different wavelengths along the path from the probe to the sun throughout the descent. These transmissions as functions of methane path length are fit by exponential sums and used in a haze radiative transfer model to compare the results to the spectra measured by DISR. We also compare the recent laboratory measurements of methane absorption at low temperatures [Irwin et al., 2006. Improved near-infrared methane band models and k-distribution parameters from 2000 to 9500 cm⁻¹ and implications for interpretation of outer planet spectra. Icarus 181, 309-319] with the DISR measurements. We find that the strong bands formed at low pressures on Titan act as if they have roughly half the absorption predicted by the laboratory measurements, while the weak absorption regions absorb considerably more than suggested by some extrapolations of warm measurements to the cold Titan temperatures. We give factors as a function of wavelength that can be used with the published methane coefficients between 830 and 1620 nm to give agreement with the DISR measurements. We also give exponential sum coefficients for methane absorptions that fit the DISR observations. We find the DISR observations of the weaker methane bands shortward of 830 nm agree with the methane coefficients given by Karkoschka [1994. Spectrophotometry of the jovian planets and Titan at 300- to 1000-nm wavelength: the methane spectrum. Icarus 111, 174-192]. Finally, we discuss the implications of our results for computations of methane absorption in the atmospheres of the outer planets.     

GHOST – A Novel Airborne Gas Chromatograph for In Situ Measurements of Long-Lived Tracers in the Lower Stratosphere: Method and Applications

A novel fully-automated airborne gas chromatograph for in situmeasurements of long-lived stratospheric tracers hasbeen developed, combining the high selectivity of a megabore PLOTcapillary column with recently developed sampling and separationtechniques. The Gas cHromatograph for theObservation of Stratospheric Tracers (GHOST)has been successfully operated during three STREAM campaigns(Stratosphere TRoposphere Experiment byAirborne Measurement) onboard a Cessna Citation IIaircraft in two different modes: Either N₂O andCF₂Cl₂(CFC-12) or CFC-12 and CFCl₃ (CFC-11) have been measuredsimultaneously, with a time resolution of 2 min for both modes.Under flight conditions the instrument precision (1) forthese species is better than 0.9%, and the accuracy(1) is better than 2.0% of the tropospheric values ofall measured compounds. The detection limits (3) arebelow 28 ppb for N₂O, 14 ppt for CFC-12, and 8 ppt forCFC-11, respectively, i.e., well below 10 % of the troposphericvalues of all measured compounds. Post-mission optimization of thechromatographic separation showed a possible enhancement of thetime resolution by up to a factor of 2, associated with acomparable increase in precision and detection limit. As test ofactual performance of GHOST results from an in-flight N₂Ointercomparison with a tunable diode laser absorptionspectrometer (TDLAS) are presented. They yield an excellentagreement between both instruments. Furthermore, on the basis ofthe hitherto most extensive set of upper tropospheric and lowerstratospheric data, the relative stratospheric N₂2O lifetime isre-assessed. When referenced to the WMO reference CFC-11 lifetimeof 45 ± 7 years an N₂O lifetime of 91 ± 15 yearsis derived, a value substantially smaller than the WMO referencelifetime of 120 years. Moreover, this value implies astratospheric N₂O sink strength of 16.3 ± 2.7 Tg (N)yr^–1 which is 30% larger than previous estimates.     

Simulated diagenesis and catagenesis of marine kerogen precursors: Melanoidins as model systems for light hydrocarbon generation

Amino acids and sugars are principal constituents of marine organisms. The condensation of amino acids and sugars is one possible nonenzymatic, early diagenetic pathway for the incorporation of these compounds into more complex geopolymers. In this study, aqueous solutions consisting of l-lysine, l-histidine, l-arginine and d-(+)-glucose were heated (100°C) for up to 288 h. Portions of the melanoidin polymer isolated after heating were reheated in the presence of water (hydrous pyrolysis) for 72 h at 325°C. Reaction products were identified by GC and GC/MS. Stable isotopic (δ¹³C) and elemental analyses were used to follow thermal evolution.While the initial melanoidin was synthesized from a simple, four component system, the products generated during hydrous pyrolysis are of considerable complexity, and include straightchain and branched alkanes, alkadienes, alkynes, indole, dimethyl indane, ethyl phenol, quinoline, and xylenes, in addition to a multitude of as yet, unidentified components. Stable carbon isotopic values for the reactants and products correspond to trends observed for naturally generated geopolymers and light gases. Elemental analyses of the melanoidin prior and subsequent to hydrous pyrolysis indicate a kerogen evolution pathway similar to that observed for natural samples. Considering the intractable nature of kerogen, laboratory simulation studies of simple systems can provide an alternative approach for elucidating the origins of geopolymers and their potential for hydrocarbon generation.     

Traces of historical tropical cyclones and tsunamis in the Ashburton Delta (north‐west Australia)

Although the north‐western coast of Western Australia is highly vulnerable to tropical cyclones and tsunamis, little is known about the geological imprint of historic and prehistoric extreme wave events in this particular area. Despite a number of site‐specific difficulties such as post‐depositional changes and the preservation potential of event deposits, both tropical cyclones and tsunamis may be inferred from the geomorphology and the stratigraphy of beach ridge sequences, washover fans and coastal lagoons or marshes. A further challenge is the differentiation between tsunami and storm deposits in the geological record, particularly where modern deposits and/or historical reports on the event are not available. This study presents a high‐resolution sedimentary record of washover events from the Ashburton River delta (Western Australia) spanning approximately the last 150 years. A detailed characterization of event deposits is provided, and a robust chronostratigraphy for the investigated washover sequence is established based on multi‐proxy sediment analyses and optically stimulated luminescence dating. Combining sedimentological, geochemical and high‐resolution optically stimulated luminescence data, event layers are assigned to known historical events and tropical cyclone deposits are separated from tsunami deposits. For the first time, the 1883 Krakatoa and 1977 Sumba tsunamis are inferred from sedimentary records of the north‐western part of Western Australia. It is demonstrated that optically stimulated luminescence applied in coastal sedimentary archives with favourable luminescence characteristics can provide accurate chronostratigraphies even on a decadal timescale. The results contribute to the data pool of tropical cyclone and tsunami deposits in Holocene stratigraphies; however, they also demonstrate how short‐lived sediment archives may be in dynamic sedimentary environments.     

New Sediment Cores Reveal Environmental Changes Driven by Tectonic Processes at Ancient Helike,Greece

According to various historical sources an earthquake and an associated tsunami wiped out the Greek city of Helike on the Gulf of Corinth in 373 B.C. This study combines stratigraphical data from a new series of sediment cores with archaeological findings of the Helike Project to better assess the fate of Helike. Abrupt lithological changes, for example, from coarse‐grained littoral facies at the base to fine‐grained lagoonal deposits, in three of the new cores suggest sudden formation of lagoonal or lacustrine conditions in the central delta during tectonic events of subsidence due to fault‐slip. These events date before c. 2550 B.C., before 348 cal. B.C.–64 cal. A.D. (probably 373 B.C.), and before 1437–1634 cal. A.D. (probably A.D. 1402). Vertically displaced isochronic surfaces between two neighboring cores may be related to active faulting of the fan‐delta north of the Western Helike Fault Zone in 373 B.C. and A.D. 1402. Although the Helike Project reported possible tsunami evidence in earlier cores and trenches, no unequivocal sedimentary traces of a tsunami were identified in the Classical horizons of the new cores.     

Representation of agricultural conservation practices with SWAT

Results of modelling studies for the evaluation of water quality impacts of agricultural conservation practices depend heavily on the numerical procedure used to represent the practices. Herein, a method for the representation of several agricultural conservation practices with the Soil and Water Assessment Tool (SWAT) is developed and evaluated. The representation procedure entails identifying hydrologic and water quality processes that are affected by practice implementation, selecting SWAT parameters that represent the affected processes, performing a sensitivity analysis to ascertain the sensitivity of model outputs to selected parameters, adjusting the selected parameters based on the function of conservation practices, and verifying the reasonableness of the SWAT results. This representation procedure is demonstrated for a case study of a small agricultural watershed in Indiana in the Midwestern USA. The methods developed in the present work can be applied with other watershed models that employ similar underlying equations to represent hydrologic and water quality processes. Copyright © 2007 John Wiley & Sons, Ltd.