Late quaternary insects of Rancho La Brea and McKittrick,California

Asphalt-impregnated sediments at Rancho La Brea (Los Angeles County) and McKittrick (Kern County) in California provide a rich Quaternary insect record. Ages of various sites at Rancho La Brea range from more than 40,000 ¹⁴C yr B.P. to modern. McKittrick insects studied by W. D. Pierce are not contemporaneous with the late Pleistocene vertebrate fauna, but are only about 7000 ¹⁴C yr old. The major paleoecological groupings are: (1) ground dwellers, (2) aquatics. (3) scavengers, and (4) miscellaneous. Contrary to conclusions of earlier authors, most specimens represent modern species. Only two apparent terminal Pleistocene extinctions are recognized. both dung beetles (Scarabaeidae).     

The Role of CaCO<Subscript>3</Subscript> Reactions in the Contemporary Oceanic CO<Subscript>2</Subscript> Cycle

The present analysis adjusts previous estimates of global ocean CaCO₃ production rates substantially upward, to 133 × 10¹² mol yr^?1 plankton production and 42 × 10¹² mol yr^?1 shelf benthos production. The plankton adjustment is consistent with recent satellite-based estimates; the benthos adjustment includes primarily an upward adjustment of CaCO₃ production on so-called carbonate-poor sedimentary shelves and secondarily pays greater attention to high CaCO₃ mass (calcimass) and turnover of shelf communities on temperate and polar shelves. Estimated CaCO₃ sediment accumulation rates remain about the same as they have been for some years: ~20 × 10¹² mol yr^?1 on shelves and 11 × 10¹² mol yr^?1 in the deep ocean. The differences between production and accumulation of calcareous materials call for dissolution of ~22 × 10¹² mol yr^?1 (~50 %) of shelf benthonic carbonate production and 122 × 10¹² mol yr^?1 (>90 %) of planktonic production. Most CaCO₃ production, whether planktonic or benthonic, is assumed to take place in water depths of <100 m, while most dissolution is assumed to occur below this depth. The molar ratio of CO₂ release to CaCO₃ precipitation (CO₂↑/CaCO₃↓) is <1.0 and varies with depth. This ratio, Ψ, is presently about 0.66 in surface seawater and 0.85 in ocean waters deeper than about 1000 m. The net flux of CO₂ associated with CaCO₃ reactions in the global ocean in late preindustrial time is estimated to be an apparent influx from the atmosphere to the ocean, of +7 × 10¹² mol C yr^?1, at a time scale of 10²–10³ years. The CaCO₃-mediated influx of CO₂ is approximately offset by CO₂ release from organic C oxidation in the water column. Continuing ocean acidification will have effects on CaCO₃ and organic C metabolic responses to the oceanic inorganic C cycle, although those responses remain poorly quantified.     

Pore water fluoride in Peru continental margin sediments: Uptake from seawater

Fluoride analyses display downward decreasing pore water gradients in Peru shelf phosphatic muds that require diffusion from the overlying seawater into the sediment column and removal by reaction within the upper few tens of centimeters, presumably by incorporation into carbonate fluorapatite. The profiles can be modeled as first-order F-removal with rate constants of ~3 yr^?1 and asymptotic F-concentrations deep in the cores of 35–45 μM, almost one-half the seawater value. The integrated flux of fluoride from seawater into organic-rich shelf sediments in coastal-upwelling zones (phosphatic muds) yields a contemporaneous global F-burial of 0.54 × 10¹⁰ mol-F yr^?1, about one-fifth the burial in other sinks (mostly carbonates and opal). The associated burial flux of phosphorus in shelf phosphorites is about 1.6 × 10¹⁰ mol-P yr^?1, comparable to P-burial in the deep sea with organic matter (~1.4 × 10¹⁰ mol yr^?1) and biogenic carbonates (~1.4 × 10¹⁰ mol yr^?1). Thus phosphorite formation on the Peru shelf is a significant contemporaneous process.     

GPS rotation and strain rates in the Baikal–Mongolia region

Current deformation in Pribaikalia, Western and Central Mongolia, and Tuva has been studied from measured horizontal GPS velocities and respective computed strain and rotation rates using 1994–2007 data of the Baikal–Mongolian GPS triangulation network.The GPS velocity field shows two main trends: an NE trend within Jonggaria, the Mongolian Altay, and the Great Lakes Valley and an SE trend in the Hangayn and eastern Gobi Altay mountains, and in the Transbaikalian block of the Amur plate. The velocity magnitudes and vectors are consistent with an SE motion of the Amur plate at a rate of ～2 mm/year.The derived strain pattern includes domains of crustal contraction and extension recognized from the magnitudes of relative strains. Shortening predominates in the Gobi and Mongolian Altay and in the Khamar-Daban Range, where it is at ?₂ = (19.2 ± 6.0)×10^?9 yr^?1 being directed northeastward. Extension domains exist in the Baikal rift and in the Busiyngol–West Hangayn area, where the crust is stretching along NW axes at ?₁ = (22.2 ± 3.1) × 10^–9 yr^–1. The eastern Hangayn dome and the Gobi peneplain on its eastern border show low and unstable strain rates. In central and northern Mongolia (Orhon–Selenge basin), shortening and extension are at similar rates: ?₂ = (15.4 ± 5.4)×10^?9 yr^?1 and ?₁ = (18.1 ± 3.1)×10^?9 yr^?1. The strain pattern changes notably in the area of the Mogod earthquake of 1967.Most of rotation throughout Central Asia is clockwise at a low rate of about Ω = 6×10^?9 deg·yr^?1. High rates of clockwise rotation are observed in the Hangayn domain (18.1 ± 5.2)×10^?9 deg·yr^?1, in the Gobi Altay (10.4 ± 7.5)×10^?9 deg·yr^?1, and in the Orhon–Selenge domain (11.9 ± 5.2)×10^?9 deg·yr^?1. Counterclockwise rotation is restricted to several domains. One is in western Tuva and northwestern Great Lakes Valley of Mongolia (Ω = 3.7×10^?9 deg·yr^?1). Two more counterclockwise rotation regions occur on both flanks of the Baikal rift: along the craton edge and in basins of Transbaikalia on the rift eastern border, where rotation rates are as high as (13.0 ± 3.9)×10^?9 deg·yr^?1, while rotation within the Baikal basin does not exceed the measurement error. Another such domain extends from the eastern Hövsgöl area to the Hangayn northern foothills, with the counterclockwise rotation at a highest rate of (16.3 ± 2.8)×10^?9 deg·yr^?1.     

Amino acid racemization in mammalian bones and teeth from La Chaise-de-Vouthon (Charente), France

A controlled test of the amino acid dating method as it is currently being applied to bones and teeth was attempted for the time range 100-250 ka, beyond that of ¹⁴C, at the archeological site of La Chaise-de-Vouthon (Charente, France). In Bourgeois-Delaunay, mammal fossils associated with Paleolithic artifacts were collected from layers dated at 101 ± 12 to 114 ± 7 ka by ²³⁰Th/²³⁰ dating of the over- and underlying stalagmitic floors. Racemization ratios for most amino acids were significantly lower than for comparably aged materials from other European sites. Regardless of the rate constants used, most amino acid dates were incorrect. Large associated errors spanned the late Pleistocene, making the dates useless for discriminating archaeological or geological events. Stratigraphic correlations using any tissue were also problematic. Relative interacid ratios varied with age, indicating that diagenetic alteration had affected racemization. Therefore, amino acid relative and absolute dating cannot be accurately applied to mid-Pleistocene bones or teeth.     

Geochronology and sedimentology of the lower Passaic River,New Jersey

In an attempt to characterize localized rates of sediment accretion, 10 sediment cores were collected from the lower reach of the Passaic River, a major tributary of Newark Bay, New Jersey. Sediments were assayed for ²¹⁰Pb activity at predetermined depths and the rate of sediment accretion (cm yr^?1) was estimated from the least squares regression of the log of unsupported activity versus depth. Sediment accretion rates, derived from ²¹⁰Pb measurements (R_Pb) were used to predict the depth interval within the core containing sediments deposited around 1954; subsequent ¹³⁷Cs analyses were focused on this depth interval. Sediment accretion rates derived from ¹³⁷Cs measurements (R_Cs) were extrapolated from the depth of the 1954 horizon. Lead-210 derived sediment accretion rates in cores collected from a sediment bench extending along the inside bend on the southern shore of a meander in the river, ranged from 4.1 cm yr^?1 to 10.2 cm yr^?1 and averaged 6.8 cm yr^?1. The R_Cs estimates for cores from this area ranged from 3.8 cm yr^?1 to 8.9 cm yr^?1 and averaged 6.6 cm yr^?1. The R_Cs for cores collected in a more hydrologically dynamic reach of the river upstream of the sediment bench, were only 0.41 cm yr^?1 and 0.66 cm yr^?1. The results of this investigation indicate that this reach of the lower Passaic River is an area of high sediment accumulation, retaining much of the sediment load deposited from upstream and downstream sources. The rates of sediment accretion in the lower Passaic River are among the highest reported anywhere in the Newark Bay estuary.     

Conservative behaviour of riverine dissolved organic carbon in the Severn Estuary: chemical and geochemical implications

The distribution, variability and chemical behaviour of dissolved organic carbon (DOC) was investigated over 2$\text{1}\text{2}$ years in the Severn Estuary and Bristol Channel, UK. The concentrations of riverine DOC (3.1–7.8 mg C l^?1) covaried with river flow and were invariably conservative in this turbid slowly flushing (~200 days) estuary, indicating that any microbial degradation, chemical flocculation or adsorption processes do not affect the flux of riverine DOC through the estuary. The DOC inputs from the Severn (1.7–2.7 × 10¹⁰ g Cyr^?1) and other rivers (2.6–3.4 × 10¹⁰ g Cyr^?1) are the principal sources of DOC in the estuary and correspond to an export of 0.7–1.1% of the terrestrial productivity from the river catchment to the ocean. This export rate is in accord with recent predictions derived from global compilations of organic inputs from rivers and would imply that the global flux of riverine DOC could be as high as 7.8 × 10¹⁴ g Cyr^?1 which is 5 times greater than some previous estimates.The geochemical significance of a conservative delivery of riverine DOC to the ocean is that irrespective of which flux estimate is considered, such river inputs would make a significant contribution (~SO%) to oceanic DOC, and that the steady-state oceanic DOC flux would have to be significantly greater than present estimates (2.9 × 10¹⁴ g Cyr^?1) which are based on a mean radio carbon age of 3400 yr.An alternative, more realistic DOC flux model, which assumes a polydisperse age distribution about the mean age, is shown to yield the higher oceanic DOC fluxes required. Flocculation and adsorption processes would remove less than 10% and 0.2% respectively of riverine DOC in estuaries.     

Estimating secondary production and benthic consumption in monitoring studies: A case study of the impacts of dredged material disposal in Galveston Bay, Texas

We examined the effects of dredged material disposal on benthic macroinvertebrates in Galveston Bay, Texas, USA, while investigating the utility of estimating secondary production with estimation methods that have less rigorous data requirements than most classical techniques. Production estimates were compared to estimates of benthic consumption by blue crabs, shrimp, and epibenthic fish. There was no evidence that dredged material disposal had a detrimental impact on benthic production; however, production was low throughout the entire bay the year following dredged material disposal, which may have obscured an assessment of the impact of disposal. In fact, disposal sites yielded both the highest production estimates and species richness in both the upper and lower bay areas 2 yr after disposal. Of the five estimation methods used, two that incorporated environmental parameters (temperature and depth) yielded similar and moderate results, ranging from 1.1 g ash-free dry weight m² yr¹ to 26.9 g ash-free dry weight (AFDW) m^?2 yr^?1 over the 4 yr studied. Daily food ration estimates applied to fishery-independent trawl-survey data yielded overall benthic consumption estimates ranging from 1.1 g AFDW m^?2 to 1.7 g AFDW m^?2. A second method of estimating consumption, which used transfer efficiency estimates and annual fisheries statistics produced slightly lower benthic consumption estimates (0.72–1.13 g AFDW m^?2). The average consumption estimate exceeded benthic production in the upper bay in one of the 4 yr for which benthic production was estimated. In years with high benthic production, the estimated benthic food requirement of epibenthic predators was roughly 10–15% of benthic production. Variation in annual benthic production estimates was two to three times greater than the variation in consumption estimates.     

Sediment accumulation rates in Conowingo reservoir as determined by man-made and natural radionuclides

The Susquehanna River is the major contributor to sediment loadings in the Chesapeake Bay. Because many environmental contaminants are associated with suspended particulates, the degree of particle retention within the reservoirs of the lower Susquehanna River is an important consideration in evaluating contaminant loadings to the Chesapeake Bay. Profiles of weapons-test Cs-137, nuclear power plant-related Cs-134 and Cs-137, and naturally-derived Pb-120 were used to estimate rates of sediment accretion in the conowingo Reservioir, an impoundment of the Susquehanna River along the Maryland-Pennsylvania border. Net accretion rates ranged from about 2 cm yr^?1 downstream of a nuclear power plant cooling discharge to a high of about 7 cm yr^?1 at the mount of an incoming creek. Slight, but consistent, increases in the annual rate of accretion since the creation of the reservoir in 1928 are apparent. The current net average annual sediment load reatined by the reservoir is estimated to be 0.4×10⁶ to 1.5 × 10⁶ metric tons yr^?1. The retained sediment load represents about 8–23% of the long-time average sediment input to the reservoir.     

Fluctuation in proteinaceous labile organic matter verified with degradation rate constants of terrestrial biochemical indicators

Biogenic amino acids, taken as representative of organic matter, were analyzed to determine the apparent degradation rate constant in boreal terrestrial sediment. Age determination using ¹⁴C dating gave two rate constants: the initial degradation rate constant for glycine (k_{GLY 1}), the simplest amino acid, was 1.5 × 10⁻³ yr⁻¹ (r = 0.97) until about 2200 yr BP. After the inflection point, the rate constant k_{GLY 2} was 9.1 × 10⁻⁵ yr⁻¹ (r = 0.73). The degradation of amino acids in the labile organic matter in the sediment was markedly affected by rapid processes. After the inflection point, the rate constant profiles for sub-surface amino acids were shown to have discontinuous relationships with sediment age. One pattern which emerged in the vertical distribution is that the biogenic amino acid degradation rate constant k was far greater in the labile organic matter phase than that in the refractory organic matter over the past 10,000 years.     

Sedimentation rates in Fayetteville Green Lake, New York, U.S.A.

In Fayetteville Green Lake, past sedimentation rates can be accurately and precisely estimated by separating annual couplets or varves in dried sediment samples. Two measures were used, which serve as upper and lower limits on estimated sedimentation rate. They agree within 5 % with average annual sedimentation rate in couplets for recent years. Between 3 and 5 replicate samples are needed to reduce the half-width of 95 % confidence intervals on individual couplet sedimentation rates to 30 g m^?2 yr^?1 about 5 % of average recent rates. In the late 1800s sedimentation rate averaged 392 g m^?2 yr^?1 and ranged between 324 and 466 g m^?2 yr^?1, while in the 1970s the rate averaged 581 g m^?2 yr^?1 by the same measure, and ranged between 384 and 646 g m^?2 yr^?1. Sedimentation rate averaged for 13 years does not vary over short distances in the profundal zone, but lateral variation in sedimentation rate can be detected for individual years over the same distance. Not all this variation was associated with the non-uniform distribution of dark sublaminae and thin turbidites which cannot be separated from the annual layers. This indicates that although precise estimates of sedimentation rates can be made at different points in the lake, estimates will have to be made at numerous points before annual sedimentation rates for the lake as a whole can be accurately assessed.     

Estimating hydraulic conductivity using grain-size analyses, aquifer tests, and numerical modeling in a riverside alluvial system in South Korea

Hydraulic conductivity (K) for an alluvial system in a riverbank filtration area in Changwon City, South Korea, has been studied using grain-size distribution, pumping and slug tests, and numerical modeling. The alluvial system is composed of layers: upper fine sand, medium sand, lower fine sand, and a highly conductive sand/gravel layer at the base. The geometric mean of K for the sand/gravel layer (9.89?×?10^?4 m s^?1), as determined by grain-size analyses, was 3.33 times greater than the geometric mean obtained from pumping tests (2.97?×?10^?4 m s^?1). The geometric mean of K estimates obtained from slug tests (3.08?×?10^?6 m s^?1) was one to two orders of magnitude lower than that from pumping tests and grain-size analyses. K estimates derived from a numerical model were compared to those derived from the grain-size methods, slug tests and pumping tests in order to determine the degree of deviation from the numerical model. It is considered that the K estimates determined by the slug tests resemble the uppermost part of the alluvial deposit, whereas the K estimates obtained by grain-size analyses and pumping tests are similar to those from the numerical model for the sand/gravel layer of the riverside alluvial system.     

A 2,500-year history of anoxia and eutrophication in Chesapeake Bay

Ongoing monitoring programs and historical data are not sufficient to establish anthropogenic effects on the ecology of Chesapeake Bay. However, stratigraphic records preserved in the sediments can be used to reconstruct both prehistoric and historic sedimentation and water conditions of the bay, including anoxia and eutrophication. Pollen, diatoms, total organic carbon (TOC), nitrogen, total sulfur, and an estimate of the degree of pyritization of iron (DOP) are being used as paleoecological indicators in dated sediment cores for the purpose of reconstructing a long-term environmental history of the bay. Analysis of the data indicates that sedimentation rates, anoxic conditions, and eutrophication have increased in the Chesapeake Bay since the time of European settlement. For example, since initial land clearance around 1760, sedimentation rates have increased from as low as 0.02 cm yr^?1 to an average 0.22 cm yr^?1, and TOC from 0.14 mg cm^?2 yr^?1 to a high 4.96 mg cm^?2 yr^?1. Diatom community structure shows a steady decrease in overall diversity since 1760 and the centric:pennate ratio has increased significantly since 1940.     

Spatial and temporal distribution of methane in an extensive shallow estuary, South India

Sedimentary methane (CH₄) fluxes and oxidation rates were determined over the wet and dry seasons (four measurement campaigns) in Pulicat lake, an extensive shallow estuary in south India. Dissolved CH₄ concentrations were measured at 52 locations in December 2000. The annual mean net CH₄ flux from Pulicat lake sediments was 3.7 × 10⁹ g yr^-1 based on static chamber measurements. A further 1.7 × 10⁹g yr_-1 was estimated to be oxidized at the sediment-water interface. The mean dissolved concentration of CH₄ was 242nmol |^-1 (ranging between 94 and 501 nmol |^-1) and the spatial distribution could be explained by tidal dynamics and freshwater input. Sea-air exchange estimates using models, account only for ∼13% (0.5 × 10⁹ g yr-1) of the total CH₄ produced in sediments, whereas ebullition appeared to be the major route for loss to the atmosphere (∼ 63% of the net sediment flux). We estimated the total atmospheric source of CH₄ from Pulicat lake to be 0.5 to 4.0 × 10⁹g yr^-1.     

Chemical weathering rates in the Alaknanda–Bhagirathi river basins in Himalayas,India

The Alaknanda and Bhagirathi rivers flow through the Higher and Lesser Himalayas and confluence at Devprayag, which represents the origin of the Ganga (or Ganges) river. In the present study, a vast number of temporal and spatial samples of the river waters were collected and analyzed for major cations and anions. In addition, more recent and time series water flow data have been obtained and based on these inputs, a more refined dissolved flux rates have been estimated. The Alaknanda and Bhagirathi rivers show significant variations in chemical compositions during different seasons. Carbonate rock weathering is responsible for more than 70% of the chemical compositions in the river waters. The chemical weathering rates show seasonal variations and are much higher during non-monsoon season. The dissolved flux of Alaknanda river is much higher (1.80 × 10⁶ tons yr^?1) as compared to the Bhagirathi river (0.34 × 10⁶ tons yr^?1). The chemical weathering rates in the basin vary between 85 and 155 tons km^?2 yr^?1, which is significantly higher compared to the global average of ～24 tons km^?2 yr^?1.     

Petrogenesis and Dating of Two Types of Granite from North Qilian, China

1 IntroductionThree E-W-trending lithologic belts of the Paleozoic ageoccur in the eastern part of north Qilian. From north tosouth they are (a) the Huangyanghe-Gulang-Dajing-Beidengzi belt (the northern lithologic belt), (b) theLeigongshan-Maomaoshan-Laohushan belt (the middlelithologic belt) and (c) the Mayaxieshan-Shihuigou-Beiyinbelt (the southern lithologic belt) (Fig. 1). The rocks inthese belts are mainly Paleozoic volcanics and sandysiltstone. There are some Mesozoic and Cenozo…     

Do seismic slip deficits indicate an underestimated earthquake potential along the Vienna Basin Transfer Fault System?

Seismic slip rates of about 0.2 mm yr^?1 calculated from cumulative seismic moments of earthquakes along the Vienna Basin Transfer Fault (VBTF) between the Alps and the Carpathians are very low compared to geologically and geodetically determined slip rates of 1–2 mm yr^?1, proving a significant seismic slip deficit. Additional seismic slip calculations for arbitrarily selected fault sectors reveal large differences along strike ranging from c. 0.02 to 0.5 mm slip yr^?1. As the earthquake frequency distribution suggests seismically coupled deformation, these variations might indicate locked fault segments. Results suggest that (1) the seismic cycle of the VBTF exceeds the length of available seismological observation, and (2) larger earthquakes than those recorded may occur along the fault. Thus, current local seismic hazard estimates, which are solely based on this historical database, probably underestimate the earthquake potential of the fault system.     

The age of the Stillwater complex—a comparison of U-Pb zircon and Sm-Nd isochron systematics

A zircon U-Pb age of 2713 ± 3 Myr confirms the less precise age of about 2710 Myr (corrected for new decay constants of Jaffeyet al., 1971) obtained from the same sample of zircon from the Stillwater complex chill zone (Nunes and Tilton, 1971). This age compares with Sm-Nd mineral and whole-rock isochron ages of 2701 ± 8 Myr (Depaolo and Wasserburg, 1979); or 2706 ± 8 Myr if the Lugmairet al. (1975) normalization procedure is used. The agreement of these ages to within about 0.4% indicates that the λ₁₄₇ = 0.00654 × 10^?9yr^?1 value is less than 0.8% too large relative to the U decay constants determined by Jaffeyet al. (1971) and enables more correct geological syntheses to be made when working out detailed absolute age stratigraphies using precise data from both systems.     

Distribution and abundance of tidal marshes along the coast of maine

Planimetry studies of coastal geology maps prepared by the Maine Geological Survey show that there is more than an order of magnitude more tidal marsh area in the state of Maine than documented in previously published estimates. The highly convoluted coast of Maine, which is approximately 5,970 km long, contains almost 79 km² of salt marsh, far more than any other New England state, New York, or the Bay of Fundy region. Reasonable estimates for the per-unit primary productivity of salt marshes lead to projections of total marsh productivity on the order of 10¹⁰ g dry weight yr^?1 for the Maine coast and 10¹¹ g dry weight yr^?1 for the Gulf of Maine as a whole. Distribution of tidal marsh area is strongly controlled by coastal geomorphology, which varies considerably along the coast of Maine. The salt marsh area is concentrated in the southwestern coastal region of arcuate bays, where marshes have developed behind sandy beaches. A series of long islands and bedrock peninsulas in the south-central portion of the coast also provides sheltered areas where large marshes occur. Northeast of Penobscot Bay salt marshes become more numerous and smaller in average areal extent. A lack of protection from waves, along with limited sources of glacio-fluvial and glacio-marine sediments, restricts the occurrence of salt marshes in that region to the frignes of coves and tidal rivers.