CILIMUS: A NEW CHONDRITE FALL

Cilimus is a new Indonesian chondrite. Its mineralogy and chemistry categorize it as a veined, intermediate-to-white hypersthene or L-5 chondrite. Black veins and impact-produced glasses including maskelynite show evidence that Cilimus has been severely shocked.     

Breccias resembling melt bombs from the Roter Kamm Crater

Abstract Irregular, dark green to black, glassy-looking boulders are locally common in the northwest portion of the rim of the Roter Kamm impact crater in southern Namibia. Their smooth surfaces, flow-like textures, presence of folds, and their similarity to melt bombs have led to the interpretation that these are molten impact ejecta. However, the samples we have examined are all fine-grained breccias composed of angular fragments that show no evidence of melting. Meltlike surface textures of these rim breccias are largely a consequence of surface wind polishing of fine-grained rocks in a desert environment. These mono-mict breccias were produced by impact-related brecciation of Gariep sediments (carbonaceous, siliceous shales) previously modified by low-grade Damaran metamorphism. Secondary quartz within the breccias is attributed to fluid activity that postdates the impact.     

Subsurface flow responses of a small forested catchment in the Ouachita mountains

Despite considerable research performed on forested catchments in the Ouachita Mountains of Oklahoma and Arkansas, little information on hydrological processes in operation is available. Based on catchment physical characteristics, subsurface flow was thought to be an important hydrological process in the region. Therefore, this study was undertaken to determine the occurrence, rates, timing and volumes of subsurface flow, and to estimate the importance of subsurface flow as a streamflow generating process. Subsurface flow was collected from three hillslope sites on a 7.7 ha forested catchment. Hillslope sites drained through natural seepage faces located near stream channels. Subsurface flow was collected from three depths at each hillslope site, below the litter layer, below the a horizon, and within the B horizon (Bt21). Subsurface flow occurred and was measured during 11 of 31 rainfall events. Subsurface flow responded rapidly to the initiation of and to changes in intensity of rainfall at all depths. the rapid response was indicative of flow through soil macropores. B horizon subsurface flow commenced within 10 to 180 min of the initiation of rainfall. Multiple linear regression showed that the volume of subsurface flow generated during a given storm was directly related to rainfall depth and a 7-day antecedent precipitation index used to represent antecedent water content. About 67 per cent of the total subsurface flow collected during the study was produced in one large storm under wet antecedent conditions. the storm was equal to the 2-year, 24-hour storm for the region. Measured subsurface flow volumes were extended to the watershed scale to provide estimates of catchment-wide contributions to streamflow. It was estimated that subsurface flow contributed from 1 to 48 per cent of total quickflow measured at the catchment outlet. Based on the timing of subsurface flow, it was estimated that subsurface flow May, contribute up to 70 per cent of quickflow before and soon after peak flow.     

Little Ice Age recorded in summer temperature reconstruction from vared sediments of Donard Lake, Baffin Island, Canada

Clastic varved sediments from Donard Lake, in the Cape Dyer region of Baffin Island, provide a 1250 yr record of decadal-to-centennial scale climate variability. Donard Lake experiences strong seasonal fluctuations in runoff and sediment fluxes due to the summer melting of the Caribou Glacier, which presently dominates its catchment. The seasonal variation in sediment supply results in the annual deposition of laminae couplets. A radiocarbon date measured on moss fragments, with a calibrated age of 860 ± 80 yrs before present (BP), is in close agreement with the age based on paired-layer counts. Together with the fabric of the laminae determined from microscope analysis, the age agreement demonstrates that the laminae couplets are annually deposited varves. Comparisons of varve thickness and average summer temperature from nearby Cape Dyer show a significant positive correlation (r= 0.57 for annual records, r = 0.82 for 3-yr averages), indicating that varve thickness reflects changes in average summer temperature. Varve thickness was used to reconstruct average summer temperatures for the past 1250 yrs, and shows abrupt shifts and large amplitude decadal-to-centennial scale variability throughout the record. The most prominent feature of the record is a period of elevated summer temperatures from 1200-1375 AD, followed by cooler conditions from 1375-1820 AD, coincident with the Little Ice Age.     

Gravity in one dimension: Stability of a three particle system

The autonomous dynamical system consisting of parallel planes of constant mass density moving under their mutual gravitational attraction is of interest for testing diverse astrophysical models of gravitational relaxation. The simplest non-integrable system consists of three sheets. In this paper the dynamics and stability of this one-dimensional solar system is systematically investigated. A linear transformation of the coordinates reduces the problem to that of a falling body constrained by oblique boundaries. By constructing a Poincare surface of section, it is found that regions of stability and chaos coexist. This behavior is predicted by the KAM theorem for systems having smoother trajectories in phase space, but does not apply here because of the discontinuity in acceleration experienced by each sheet during an encounter. The results of numerical experiments indicate that chaotic regions may be associated with trajectories which contain nearly triple collisions of the three particles.