Context and environment in taphonomic analysis: Examples from Alaska's Porcupine River Caves

Field investigations of caves along Alaska's Porcupine River document three major mechanisms which modify bone in patterns similar to alterations produced by man: (1) carnivore fracture; (2) rodent gnawing; and (3) rock fall and rubble scarring. A late Wisconsin faunal assemblage composed of Equus sp., Rangifer tarandus, Ovis dalli, Bison sp., proboscidean, numerous small mammal species, birds, and fish is well documented. This faunal assemblage suggests a mosaic environment of grassland-tundra-forest in the immediate vicinity of these caves and implies that the late Wisconsin environment in north-central Alaska may have been characterized by a number of microenvironments and colder, dryer, steppe conditions. Taphonomic data which have historically been interpreted to support human occupation of eastern Beringia during the Pleistocene are critically examined and the context of these discoveries (not the specimens themselves) provides the test essential to document the antiquity of man in North America prior to 12,000 yr ago.     

Late Quaternary sapropel sediments in the eastern Mediterranean Sea: Faunal variations and chronology

Distinctive planktonic foraminiferal assemblages which characterize particular late Quaternary sapropel layers in deep basin sediments from the eastern Mediterranean Sea have been identified using cluster analysis. Three distinct clusters allow for identification and intercore correlation of the nine sapropels deposited during the last 250,000 yr. Cluster 1, representing sapropel layers S1 and S9, exhibits low abundances of Neogloboquadrina dutertrei and high abundances of Globigerinoides ruber; Cluster 2, which groups S3, S5, and S7, contains high abundances of G. ruber, N. dutertrei, and Globigerina bulloides, and Cluster 3, which includes samples from S4, S6, and S8, is marked by extremely abundant N. dutertrei and G. bulloides, and rare G. ruber. Analysis of sedimentation rates in 14 cores reveals the following approximate ages for the sapropel layers: S2 = 52,000 yr B.P.; S3 = 81,000–78,000 yr B.P.; S4 = 100,000–98,000 yr B.P.; and S5 = 125,000–116,000 yr B.P. As previously suggested, sedimentation rates on the Mediterranean Ridge were determined to be relatively constant during the last 127,000 yr. In contrast, basin sedimentation rates have fluctuated markedly from lower rates during interglacial stage 5 to higher rates during the last glacial episode. These glacial/interglacial differences are most pronounced in the northern Ionian Basin, because of increased terrigenous sediment deposition during glacial episodes. Unusually high biogenic sedimentation rates occurred in an arc south of Crete during the deposition of sapropel S5, probably due to higher productivity in this region.     

Characteristics of vertical turbulent velocities in the urban convective boundary layer

Turbulence measurements of the vertical velocity component were obtained by an instrumented aircraft under fair weather conditions in the St. Louis, Missouri, metropolitan area. Time series of vertical velocity fluctuations from horizontal flight segments made in the lower part of and near the middle of the convective boundary layer (CBL) over the urban area and surrounding region were subjected to various statistical and objective analyses. Higher order vertical velocity moments, and positive and negative velocity statistics, were computed. The horizontal dimensions of updrafts and downdrafts, and related properties of these turbulent eddies were derived by conditional sampling analysis. Emphasis is on a comparison of the results from urban and selected rural measurements from the lower part of the CBL.The vertical velocity probability density distribution for each segment was positively skewed and the mode was negative. The means and standard deviations of positive and negative velocity fluctuations were greater over the urban area. The urban vertical velocity variance was 50% greater than rural values, and power spectra revealed greater production of vertical turbulent energy in the urban area over a wide frequency range.The mean and maximum widths of downdrafts were generally larger than the corresponding values for updrafts. Differences between urban and rural eddy sizes were not statistically significant. The widths of the largest updraft and downdraft are comparable to the boundary-layer depth, Z _i, and the mean value of the ratio of spectral peak wavelength to Z _iwas about 1.3 and 1.1 for urban and rural areas, respectively. Convective similarity scaling parameters appeared to order both the urban and rural measurements.On assignment from the National Oceanic and Atmospheric Administration, U.S. Dept. of Commerce.     

Effect of discharge on the chlorophylla distribution in the tidally-influenced Potomac River

In the tidal Potomac River, high river discharges during the spring are associated with high chlorophylla concentrations in the following in the following summer, assuming that summertime light and temperature conditions are favorable. Spring floods deliver large loads of particulate N and P to the tidal river. This particulate N and P could be mineralized by bacteria to inorganic N and P and released to the water column where it is available for phytoplankton use during summertime. However, during the study period relatively low concentrations of chlorophylla (less than 50 μg l^?1 occurred in the tidal river if average monthly discharge during July or August exceeded 200 m³s^?1. Discharge and other conditions combined to produce conditions favorable for nuisance levels of chlorophylla (greater than 100 μg l^?1 approximately one year out of four. Chlorophylla maxima occurred in the Potomac River transition zone and estuary during late winter (dinoflagellates) and spring (diatoms). Typical seasonal peak concentrations were achieved at discharges as high as 970 m³ s^?1, but sustained discharges greater than 1,100 m³ s^?1 retarded development. Optimum growth conditions occurred following runoff events of 10 to 15 d duration which produced transit times to the transition zone of 7 to 10 d. Wet years with numerous moderate-sized runoff events, such as 1980, tend to produce greater biomass in the transition zone and estuary than do dry years such as 1981.     

The Cold Bay Volcanic Center,Aleutian Volcanic arc

The widespread abundance of Hi-Alumina Basalt (HAB) lavas in most volcanic arcs has been suggested by some as evidence for a primary, parental HAB magma generated by the high pressure melting of subducted oceanic crust (quartz eclogite). Others suggest a parental, mantle-derived olivine tholeiite magma which produces HAB magmas through fractionation of olivine, clinopyroxene, chrome-spinel +/– plagioclase. The petrology and geochemistry of seven HAB lavas from the Aleutian Cold Bay Volcanic Center have been studied in order to specifically address these two possibilities. All lavas show mineralogical and compositional features typical of most Aleutian HAB lavas. Coexisting opx and cpx in a closely associated basaltic-andesite indicate a minimum pre-eruption temperature of 1,110° C. A comparison of the observed (plag-tmag-olivcpx) and experimentally determined crystallization sequences yields a minimum pre-eruption pressure estimate of 7 kb and estimated H₂O contents of 0.7 wt.%. Maximum pre-eruption f _{o 2} values have been estimated at NNO+0.6 log units.Mass balance calculations demonstrate that the HAB compositions are satisfied by the fractionation of olivine, clinopyroxene +/– plagioclase from a primitive (Mg-# > 65) parental tholeiite. Plagioclase accumulation does not play a significant role in their origin. Many of the same compositional characteristics are also satisfied by high pressure melting of altered ocean ridge tholeiite +5 v.% pelagic sediment (quartz eclogite). The available HAB phase equilibria data do not support a fractionation origin but do support an origin involving high pressure melting of quartz eclogite. The lack of compositional zonation in the HAB phenocrysts, and the complete absence of disequilibrium MgO-rich mafic phenocrysts further argue against a tholeiite fractionation origin.Consideration of all these features indicates that the geochemical data are permissive in their interpretation. A process involving tholeiite fractionation successfully predicts the compositions of the HAB lavas but is at odds with the mineralogical and phase equilibria evidence. With some exceptions (notably Ni, Cr and Sr abundances), a process of high pressure quartz eclogite melting is consistent with the compositional, mineralogical and phase equilibria characteristics of these HAB lavas. When the relative merits of both origins are weighed it is apparent that a quartz eclogite source satisfies more of important features of these HAB lavas.Extrusive rocks have been grouped on a basis of SiO₂ content into basalt (<52 wt.%), basaltic-andesite (52–56 wt.%) and andesite (>56 wt.%) after Ewart (1982)     

Pressure dependence of melt viscosities on the join diopside-albite

The pressure dependence of melt viscosities on the join diopside-albite has been studied using falling-sphere viscometry. The five melt compositions investigated are: diopside, Ab₂₅Di₇₅, Ab₅₀Di₅₀, Ab₇₅Di₂₅ and albite. Experiments were performed at 1500° and 1600°C and at pressures of 5, 10, 15, 20 and 25 kbar. The positive and negative pressure dependence of the viscosity of diopside and albite, respectively, were confirmed. All intermediate compositions show an initial decrease in viscosity with increasing pressure; however, melt of Ab₂₅Di₇₅ composition passes through a minimum viscosity at approximately 12 kbar and 1600°C. This behavior is analogous to the variation in the viscosity of water with pressure at low temperature.

It is suggested that the three-dimensional, fully polymerized, albite structure dominates flow at low pressures. With increasing pressure, disruption of this structure and decrease in the average size of the flow units leads to domination by the diopside structure. The variation in viscosity with composition along the join at one atmosphere can be adequately modelled using the and (1965) configurational entropy model with an additional two-lattice configurational entropy of mixing term. The pressure dependence of viscosity in the diopside-albite system, however, cannot be predicted by the model, because there is an absence of information on the pressure dependence of the model parameters.

It is probable that relatively polymerized magmas (e.g. rhyolites to SiO₂-saturated basalts) show a negative pressure dependence of viscosity to depths where they originate in the lower crust or upper mantle. In contrast, the most depolymerized, naturally-occurring melts, such as strongly SiO₂-undersaturated basalts and picrites, may exhibit a viscosity minimum. The viscosity of these melts may be sufficiently high at depths within the upper mantle to inhibit their segregation, rise and eventual eruption at the surface.     

High latitude river runoff in a doubled CO2 climate

A global atmospheric model is used to calculate the monthly river flow for nine of the world's major high latitude rivers for the present climate and for a doubled CO₂ climate. The model has a horizontal resolution of 4° × 5°, but the model's runoff from each grid box is quartered and added to the appropriate river drainage basin on a 2° × 2.5° resolution. A routing scheme is used to move runoff from a grid box to its neighboring downstream grid box and ultimately to the mouth of the river. In a model simulation in which atmospheric carbon dioxide is doubled, mean annual precipitation and river flow increase for all of these rivers, increased outflow at the river mouths begins earlier in the spring, and the maximum outflow occurs approximately one month sooner due to an earlier snow melt season. In the doubled CO₂ climate, snow mass decreases for the Yukon and Mackenzie rivers in North America and for rivers in northwestern Asia, but snow mass increases for rivers in northeastern Asia.     

Radiocarbon and δ13C Values Related to Ground-Water Recharge and Mixing

Ground-water levels in the Upper Floridan aquifer beneath the southeastern coast of South Carolina have undergone pumpage-induced declines approaching 20 ft below sea level at the southern end of Hilton Head Island. This scenario suggests the potential exists for the inducement of recharge to the Upper Floridan aquifer across the island, which could affect the quality of water being pumped by wells. However, low radiocarbon concentrations in ground-water samples (0.5 to 1.4 ± 0.1 PMC) indicate that most of the water is relict ground water reflecting prepumpage ground-water flow conditions in the Upper Floridan aquifer. The isotopic data indicate long residence times and water-chemistry evolution more characteristic of ground-water recharge occurring farther inland prior to the commencement of pumpage in the late 1800s. Radiocarbon concentrations (as Percent Modern Carbon) and stable carbon isotope ratios (as δ¹³C in dissolved inorganic carbon) determined during this study and reported in other studies on and around Hilton Head Island varied in a systematic manner. Heavier δ¹³C values (–2.8 to –1.6 per mil) in ground water beneath southern Hilton Head Island reflect ground-water discharge from prepumpage flowpaths originating over 100 miles away, hence a depletion in radiocarbon concentration with corrected ground-water ages no younger than 16,000 yrs BP. In contrast, lighter δ¹³C values (–13.9 to –8.67 per mil) beneath the northern part of the island indicate recent recharge as a result of water-level declines, and recharge in areas off the island that have not changed as a result of pumpage (evidenced by enrichment in radiocarbon with corrected ground-water ages no older than 4,000 yrs BP). This suggests that the δ¹³C composition of ground water in the Upper Floridan aquifer is a useful indicator of mixing between ground waters from different sources, and can be used to delineate recharge-discharge patterns. This approach may be applicable to other aquifers of highly evolved ground-water chemistry in regional carbonate aquifer systems that may be receiving recent recharge. Moreover, this approach could prove useful in delineating the contribution of recent water being captured by pumped wells as part of wellhead protection programs designed to assess aquifer vulnerability from surficial contaminant sources.     

A Sophisticated Ground Water Analytical Tool

Stiff diagrams arc a multivariate method of analysis used to describe the chemical state of ground water. The use of Stiff diagrams to describe multiconstituent contamination sites, such as landfills, has distinct advantages over single constituent analyses. Problems associated with traditional Stiff diagram analyses, such as diagram attentuation, can be addressed by allowing the scale of the diagram to vary with the ionic strength of the analyzed sample. The use of these sliding scale Stiff diagrams reveals the chemical slate of the ground water over wide ranges of constituent concentrations and thus allows for sensitive and sophisticated depictions of complicated contamination sites in a fashion that is extremely difficult to replicate with single constituent analyses. This approach has possible applications for understanding and tracing the mixing and chemical changes in uncontaminated settings.