Some approaches for location of centroids of quartz grain outlines to increase homology between Fourier amplitude spectra

The ability to test for similarities and differences among families of shapes by closed-form Fourier expansion is greatly enhanced by the concept of homology. Underlying this concept is the assumption that each term of a Fourier series, when compared to the same term in another series, represents the same thing. A method that ensures homology is one which minimizes the centering error, as reflected in the first harmonic term of the Fourier expansion. The problem is to chose a set of edge points derived from a much larger, but variable, number of edge points such that a valid homologous Fourier series can be calculated. Methods are reviewed and criteria given to define a proper solution. An algorithm is presented which takes advantage of the fact that minimization of the error term can be accomplished by minimizing the distance between the origin of the polar coordinate system in the calculation of the Fourier series and the shape centroid. The use of this algorithm has produced higher quality solutions for quartz grain provenance studies.     

Modern sedimentology and hydrology of Lake Manitoba,Canada

Lake Manitoba, North America's thirteenth largest lake, occupies a glacier-scoured basin in south-central Manitoba. Despite its large size, the lake is extremely shallow with a mean depth of 4.5 m. The lake can be subdivided into two connected but distinctly different basins: a small, irregular-shaped North Basin and a much larger and smoother South Basin. Most of the water inflow is from the Waterhen River (42% of the inflow) and from precipitation directly on the lake's surface (40%), while nearly 60% of the outflow is by evaporation. Lake Manitoba water is alkaline and brackish with the salinity dominated by sodium and chloride ions. The surficial offshore deposits of the main South Basin of the lake consist mainly of silt and clay-sized sediments composed of detrital components (clay minerals, quartz, carbonates, and feldspars) and endogenic/authigenic components (carbonates, sulfides, and organic matter). In addition to these modern sediments, several areas of relict fluvial-shoreline sand and till deposits occur in the South Basin. The lacustrine processes presently operating in Lake Manitoba reflect the influence of (1) the extreme shallow depth of the lake, (2) the basin morphology, and (3) the water chemistry. In addition, land clearing and increased watershed drainage have resulted in substantially increased sedimentation rates in the South Basin during the past century.     

The present day formation of apatite in Mexican continental margin sediments

Results of pore water and sediment analyses from the western Mexican continental margin strongly suggest the present day formation of apatite. The interstitial water phosphate and fluoride profiles indicate chemical removal at a depth which corresponds to a large maximum in the phosphorus content of the sediments. Apatite is identified within this maximum via X-ray diffraction but is elsewhere undetectable in the core. Radioisotopic thorium, uranium, and radium data support the conclusion that this deposit is modern. The present day depositional environment is consistent with those reported by other workers for phosphorite formation with the exception that pore water magnesium is not depleted below its seawater value.     

Multistage evolution of the European lithospheric mantle: new evidence from Sardinian peridotite xenoliths

Peridotite xenoliths entrained in Plio-Pleistocene alkali basalts from Sardinia represent fragments of the uppermost lithospheric mantle, and are characterised by an anhydrous four-phase mineral assemblage. They range in bulk rock composition from fertile spinel-lherzolites to residual spinel-harzburgites. The Sr-Nd isotope and trace element composition of clinopyroxene mineral separates varies between LREE-depleted samples with ⁸⁷Sr/⁸⁶Sr as low as 0.70262 and ¹⁴³Nd/¹⁴⁴Nd up to 0.51323 and LREE-enriched samples with ⁸⁷Sr/⁸⁶Sr up to 0.70461 and ¹⁴³Nd/¹⁴⁴Nd down to 0.51252. The available data suggest that all the studied peridotite samples suffered variable degrees of partial melting during Pre-Mesozoic times (based on Nd model ages relative to CHUR and DMM). The overprinted enrichment is related to a subsequent metasomatism, induced by fluids rising through the lithosphere that preferentially percolated the originally most depleted domains. Despite the occurrence of orogenic volcanism in the area, preferential enrichment in elements typically associated with slab derived fluids/melts (K, Rb, Sr, Th) relative to LREE has not been detected, and metasomatism seems to be more likely related to the infiltration of highly alkaline basic melts characterised by an EM-like Sr-Nd isotopic composition. Similar ⁸⁷Sr/⁸⁶Sr-¹⁴³Nd/¹⁴⁴Nd compositions, characterised by an EM signature, are observed in anorogenic mafic lavas and peridotite xenoliths from widespread localities within the "European" plate, whereas they have not previously been recorded in peridotite xenoliths and associated alkaline mafic lavas from the stable "African" lithospheric domain.     

Seasonal variation in stable oxygen and carbon isotope values recovered from modern lacustrine freshwater mollusks: paleoclimatological implications for sub-weekly temperature records

A fingernail clam (Sphaerium simile, Sphaeriidae) from Science Lake, a small watershed located in Allegany State Park, New York, USA and a zebra mussel (Dreissena polymorpha, Dreissenidae) from Keuka Lake, New York, the third largest Finger Lake of central New York, were selected to evaluate the applicability of using ¹⁸O_(CaCO3) and ¹³O_(CaCO3) values for sub-weekly climate records. Seasonal variation in ¹⁸O_(CaCO3) values was compared with predicted equilibrium values to test the hypothesis that lacustrine molluscs produce shell aragonite according to environmental variables. For the purpose of comparison, aragonite temperature-fractionation equations determined by Grossman& Ku (1986) and Patterson et al. (1993) were used. Sphaerium simile appears to produce ¹⁸O_(CaCO3) values predicted by Patterson et al. (1993), while Dreissena polymorpha produces ¹⁸O_(CaCO3) values in agreement with Grossman & Ku (1986). We attribute the difference to family-specific temperature-fractionation relationships. Because both types of mollusc record climate variables with a high degree of integrity, they should each serve as excellent paleoclimate proxies.The fingernail clam collected from a small watershed exhibits higher variation about the seasonal pattern than did the zebra mussel collected from a large watershed. This is attributed to the increased sensitivity of the small watershed to storm perturbation. Analysis of fossil molluscs from such watersheds might be useful in discerning paleo-storminess.