Electron spin resonance dating of the fossil deposits in the Naracoorte Caves,South Australia

The caves near Naracoorte, South Australia, contain one of the richest and most diverse fossil faunal assemblages on the Australian continent. Three sites were selected for electron spin resonance (ESR) dating because clastic, fossiliferous sediments were sandwiched between speleothem layers. This allows independent age control by highly precise thermal ionization mass‐spectrometry (TIMS) U‐series dating. We find that all ESR results agree within the constraints given by the U‐series dates, and allow further refinement of the age of the fauna analysed, indicating that most of the fauna in the large Victoria Cave Fossil Chamber is twice as old as reported previously. Our dating results, spanning from 280 to 500 ka for the Fossil Chamber, Victoria Cave, to about 125 ka for the Grant Hall, Victoria Cave, and 170 to 280 ka for the Fossil Chamber, Cathedral Cave, indicate little change, if any, in the megafaunal assemblage from the early Middle to the early Late Pleistocene. This changed dramatically after the last interglacial, when a large proportion of the megafauna suddenly disappeared. Copyright © 2001 John Wiley & Sons, Ltd.     

Investigating potential future changes in surface water flooding hazard and impact

Surface water flooding (SWF) is a recurrent hazard that affects lives and livelihoods. Climate change is projected to change the frequency of extreme rainfall events that can lead to SWF. Increasingly, data from Regional Climate Models (RCMs) are being used to investigate the potential water-related impacts of climate change; such assessments often focus on broad-scale fluvial flooding and the use of coarse resolution (>12 km) RCMs. However, high-resolution (<4 km) convection-permitting RCMs are now becoming available that allow impact assessments of more localised SWF to be made. At the same time, there has been an increasing demand for more robust and timely real-time forecast and alert information on SWF. In the UK, a real-time SWF Hazard Impact Model framework has been developed. The system uses 1-km gridded surface runoff estimates from a hydrological model to simulate the SWF hazard. These are linked to detailed inundation model outputs through an Impact Library to assess impacts on property, people, transport, and infrastructure for four severity levels. Here, a set of high-resolution (1.5 km and 12 km) RCM data has been used as input to a grid-based hydrological model over southern Britain to simulate Current (1996–2009) and Future (~2100s; RCP8.5) surface runoff. Counts of threshold-exceedance for surface runoff and precipitation (at 1-, 3- and 6-hr durations) are analysed. Results show that the percentage increases in surface runoff extremes, are less than those of precipitation extremes. The higher-resolution RCM simulates the largest percentage increases, which occur in winter, and the winter exceedance counts are greater than summer exceedance counts. For property impacts, the largest percentage increases are also in winter; however, it is the 12-km RCM output that leads to the largest percentage increase in impacts. The added-value of high-resolution climate model data for hydrological modelling is from capturing the more intense convective storms in surface runoff estimates.     

Ten Years of Studies on Maryland's Inner Continental Margin and Coastal Bays

During the past ten years of the Association of American State Geologists-Mineral Management Service Continental Margins Program, the Maryland Geological Sur vey investigated the sedimentological, paleontological, stratigraphical and geophysi cal character of Maryland's inner continental shelf. Based on seismic records and sedimentological analyses completed during the first four years, a late Quaternary stratigraphic model was developed. Five distinct stratigraphic units were identified and described on the Maryland inner shelf. These units represent late Pleistocene interglacial deposits, the oldest of which corresponds to pre-Illinoian (oxygen-isotope stages 7 and or 9) transgressive shelf sands. Overlying the Q1 unit, the Q2 unit is a 6-meter thick mud sequence of oxygen-isotope stage 5 (128-75 ka) age. Units Q3 and Q4 representing fluvial and leading edge estuarine deposits (oxygen-isotope stages 4, 3 and 2) filled numerous paleochannels that were incised into units Q2 and Q1. Modern trailing-edge transgressive shelf shoals (Unit Q5) discontinuously cap the sequence. The 5th and 6th years studies reported on the economic minerals of surficial and cored sediments. Vibracores collected off the Maryland's shelf during previous studies were analyzed for mineral types and abundances, weight percent of general size fractions, and heavy mineral (HM) content. Mineralogic maturity indices were compiled to correlate the THM and economic heavy minerals (EHM) abundances with position offshore, sediment type, and the indices themselves. For the 7th year, the Maryland Geological Survey re-examined geophysical records and lithological data originally collected by the Army Corps of Engineers to locate and assess beach fill borrow areas for the Ocean City Beach Replenishment Project. Data from 163 vibracores and over 300 kilometers of high-resolution seismic profile records collected off Ocean City, Maryland, supported the strati graphic model developed by MGS during the first four years of the AASG-MMS program. The Maryland coastal bays became the focus of study during the 8th and 9th years during which seismic records, cores and surficial sediment were collected in Isle of Wight and Assawoman Bays. Shallow pretransgression surface was mapped, relating the existing streams to offshore paleochannels. The tenth year study focused on developing a repository for vibracores collected on Maryland's inner continental shelf.     

Stability of Kerogen Classification with Regard to Image Segmentation

This paper investigates the stability of an automatic system for classifying kerogen material from images of sieved rock samples. The system comprises four stages: image acquisition, background removal, segmentation, and classification of the segmented kerogen pieces as either inertinite or vitrinite. Depending upon a segmentation parameter d, called “overlap”, touching pieces of kerogen may be split differently. The aim of this study is to establish how robust the classification result is to variations of the segmentation parameter. There are two issues that pose difficulties in carrying out an experiment. First, even a trained professional may be uncertain when distinguishing between isolated pieces of inertinite and vitrinite, extracted from transmitted-light microscope images. Second, because manual labelling of large amount of data for training the system is an arduous task, we acquired the true labels (ground truth) only for the pieces obtained at overlap d=0.5. To construct ground truth for various values of d we propose here label-inheritance trees. With thus estimated ground truth, an experiment was carried out to evaluate the robustness of the system to changes in the segmentation through varying the overlap value d. The average system accuracy across values of d spanning the range from 0 to 1 was 86.5%, which is only slightly lower than the accuracy of the system at the design value of d=0.5 (89.07%).     

Two-dimensional density currents in a confined basin

We present new experimental results on the mechanisms through which steady two-dimensional density currents lead to the formation of a stratification in a closed basin. A motivation for this work is to test the underlying assumptions in a diffusive “filling box” model that describes the oceanic thermohaline circulation (Hughes, G.O. and Griffiths, R.W., A simple convective model of the global overturning circulation, including effects of entrainment into sinking regions, Ocean Modeling, 2005, submitted.). In particular, they hypothesized that a non-uniform upwelling velocity is due to weak along-slope entrainment in density currents associated with a large horizontal entrainment ratio of E _eq ?～?0.1. We experimentally measure the relationship between the along-slope entrainment ratio, E, of a density current to the horizontal entrainment ratio, E _eq, of an equivalent vertical plume. The along-slope entrainment ratios show the same quantitative decrease with slope as observed by Ellison and Turner (, 6, 423–448.), whereas the horizontal entrainment ratio E _eq appears to asymptote to a value of E eq?=?0.08 at low slopes. Using the measured values of E _eq we show that two-dimensional density currents drive circulations that are in good agreement with the two-dimensional filling box model of Baines and Turner (Baines, W.D. and Turner, J.S., Turbulent buoyant convection from a source in a confined region, J. Fluid. Mech., 1969, 37, 51–80.). We find that the vertical velocities of density fronts collapse onto their theoretical prediction that U =-2^?2/3 B ^1/3 E _eq ^2/3 (H/R) ζ, where U is the velocity, H the depth, B the buoyancy flux, R the basin width, E _eq the horizontal entrainment ratio and?ζ?= z/H the dimensionless depth. The density profiles are well fitted with?Δ?= 2^?1/3 B ^2/3 E _eq ^?2/3 H _-1 [ln(ζ )?+?τ ], where?τ?is the dimensionless time. Finally, we provide a simple example of a diffusive filling box model, where we show how the density stratification of the deep Caribbean waters (below 1850?m depth) can be described by a balance between a steady two-dimensional entraining density current and vertical diffusion in a triangular basin.     

Mean sea level trends around the English Channel over the 20th century and their wider context

This paper provides estimates of rates of change in mean sea level around the English Channel, based on an extensive new hourly sea level data set for the south coast of the UK, derived from data archaeology. Mean sea level trends are found to vary by between 0.8 and 2.3 mm/yr around the Channel. The rates of mean sea level change are calculated by removing the coherent part of the sea level variability from the time series of annual mean sea level before fitting linear trends. The improvement in accuracy gained by using this approach is assessed by comparing trends with those calculated using the more traditional method, in which linear trends are fitted directly to the original records. Removal of the coherent part of the sea level variability allows more precise trends to be calculated from records spanning 30 years. With the traditional approach 50 years is required to obtain the same level of accuracy. Rates of vertical land movement are approximated by subtracting the mean sea level trends from the most recent regional estimate of change in sea level due to oceanographic processes only. These estimated rates are compared to measurements from geological data and advanced geodetic techniques. There is good agreement around most of the UK. However, the rates estimated from the sea level records imply that the geological data suggest too much submergence along the western and central parts of the UK south coast. Lastly, the paper evaluates whether the high rates of mean sea level rise of the last decade are unusual compared to trends observed at other periods in the historical record and finds that they are not.     

Nearshore suspended sediment variations,central Surinam coast

Nearshore suspended sediment concentration along the muddy Surinam coast is highly variable; maximum values are many times greater than on other muddy coasts. Water samples taken at four field stations during various stages of the tide range in concentration from 15 to 3,700 mg/l near the surface and from 100 to 30,000 mg/l near the bottom. Highest overall concentrations and greatest variability in concentration occur in water over large banks of fluid mud (thixotropic gel) that extend 2–3 km offshore and 5–10 km along-shore. On both the intertidal and subaqueous portions of these mudbanks highest concentrations are found at low tide. Results provide evidence that an exchange between fluid mud and suspended sediment takes place during each tidal cycle.     

Age trends in garnet-hosted monazite inclusions from upper amphibolite facies schist in the northern Grouse Creek Mountains, Utah

We performed in situ Th-Pb dating of monazite in upper amphibolite facies pelitic schist from the Grouse Creek Mountains in northwest Utah. Sixty-six ages from inclusions in four garnet grains range from 37 to 72 Ma and decrease with radial distance from garnet cores. The age range of 30 matrix monazite grains overlaps and extends to younger ages than inclusions (25-58 Ma). The monazite grains are not intersected by cracks in the garnets, through which dissolution, reprecipitation or Pb loss might occur, and are generally too small (<20 μm) to allow for more than one age determination on any one grain. Processes that might explain inclusion ages that decrease with radial distance from garnet cores include: (1) Pb diffusion in monazite, (2) dissolution and reprecipitation of monazite, and (3) co-crystallization of monazite and garnet. After consideration of these possibilities, it is concluded that the co-crystallization of monazite and garnet is the most plausible, with monazite neoblasts deriving REEs from the breakdown of muscovite. Garnet ages derived by regression of the inclusion ages and assuming a constant rate of volume increase during garnet growth yield model ages with a maximum difference between core and rim of 22 m.y.     

Identification and quantification of carbonyl-containing α-pinene ozonolysis products using <Emphasis Type="Italic">O</Emphasis>-<Emphasis Type="Italic">tert</Emphasis>-butylhydroxylamine hydrochloride

The yields of carbonyl-containing reaction products from the ozonolysis of α-pinene have been investigated using concentrations of ozone found in the indoor environment ([O₃] ≤ 100 ppb). An impinger was used to collect gas-phase oxidation products in water, where the derivatization agent O-tert-butylhydroxylamine hydrochloride (TBOX) and gas chromatography-mass spectrometry were used to identify carbonyl-containing species. Seven carbonyl-containing products were observed. The yield of the primary product, pinonaldehyde was measured to be 76 %. Using cyclohexane as a hydroxyl radical (?OH) scavenger, the yield of pinonaldehyde decreased to 46 %, indicating the influence secondary OH radicals have on α-pinene ozonolysis products. Furthermore, the use of TBOX, a small molecular weight derivatization agent, allowed for the acquisition of the first mass spectral data of oxopinonaldehyde, a tricarbonyl reaction product of α-pinene ozonolysis. The techniques described herein allow for an effective method for the collection and identification of terpene oxidation products in the indoor environment.     

The relationship between beam transmission and concentration of suspended particulate material in the Neuse River estuary,North Carolina

Monthly measurements made at 15 stations along the axis of the upper Neuse River estuary show a highly variable degree of correlation between concentration of suspended particulate material (SPM) and attenuation of light (c) as measured by transmissometer. Coefficients of determination along transect lines ranged from 0.12 to 0.93 and calibration slopes ranged from 0.50 to 5.63. When examined on a station-by-station basis, coefficients of determination ranged from 0.21 to 0.96 and calibration slopes ranged from 1.04 to 4.94. Surface calibrations made at individual stations over the full 13-month period were the most consistent of all observations and were considerably better than calibrations made using all of the stations on a given day. Organic content, which can dominate the suspended sediment load during some months, does not appear to explain the variations in reliability of the calibrations. However, an abundance of large aggregates with time-varying size and shape distributions may be partly responsible for variations in optical properties of the sediments, and thus may confound the relationship between SPM and c in the Neuse River estuary. Time-varying calibrations to account for non-negligible changes in optical properties may not suffice in complex estuarine environments where the in situ particle dynamics are poorly understood.