Mollusks from Wisconsinan (Pleistocene) ice-contact sediments of the Missouri Coteau in central North Dakota

This thesis here abstracted was written under the direction of Frank D. Holland, Jr. and was approved by Wilson M. Laird and George C. Wheeler as members of the examining committee, of which Dr. Holland was Chairman. Geologic and paleontologic evidence indicates that numerous mesotropic, temperate, water bodies were present while drift-covered bloacks of stagnant glacier ice, unplaced during Woodfordian (late Wisconsinan, Pleistocene) time, underlay the Missouri Coteau district (approximately 50 by 300 miles in extent) in central North Dakota. Fossil mollusks, contained in sediments deposited in contact with the stagnant ice at 40 sites, are represented by 23 species including polecypods of the families Unionidae and Sphaeriidae and gastropods of the families Valvatidae, Hydrobiidae, Physidae, Lymnaeidae, Planorbidae, Ancylidae, Succineidae, and Pupillidae. ____ shells have provided material for five radiocarbon dates in the Missouri Coteau district which indicate the melting of the stagnant ice may have required 2,100 years. The fossil mollusks, as now known, do not serve as stratigraphic indicies to the late Pleistocene deposits of the region, but the species composition of fossil Mollusca communities dominated by the branchiate genera Valvata and Amnicola is required as tentative evidence of the pre-_____ age of the Missouri Coteau sediments. The mollusks also indicate the climate of the region to have been mild and humid as early as 12,000 and as late as 8,700 radiocarbon years before the present

A Comparison of the Late Wisconsinan Molluscan Fauna of the Missouri Coteau District (North Dakota) with a Modern Alaskan Analogue

Study of forty fossiliferous sites in late Wisconsinan sediments from the Missouri Coteau district in central North Dakota has defined the molluscan fauna of the period of geologic time between 12,000 and 9,000 C14 years before the present. The fauna includes twenty-eight taxa of nonmarine gastropods and bivalves and is dominated by branchiates. The modern molluscan fauna of the Missouri Coteau district in North Dakota lacks four species which were resident in the late Wisconsinan and contains no unionids, one additional aquatic species, and is strongly dominated by pulmonate gastropods. The geology of the Missouri Coteau has been interpreted as being the sedimentary result of the stagnation of the marginal fifty to one hundred miles of the Wisconsinan ice sheet. The interpretation of the paleoecology of the late Wisconsinan molluscan fauna derives from geologic, paleoautecologic, and paleosynecologic data. It is hypothesized that at the time the late Wisconsinan continental ice sheet stagnated in central North Dakota, the climate was less extreme and more humid than at present. Ponds and streams existed on the ice-cored topography of the Missouri Coteau. They were connected by a drainage system tributary to the Missouri River and populated by an abundant, branchiate-dominated molluscan fauna. Fishes, probably of the families Percidae and Centrarchidae, lived in the ponds and rivers and unionid bivalves successfully populated many of the water bodies. Calcareous algae (Chara) and undoubtedly other species of aquatic vegetation colonized the clear, warm water of the drainage system. The ice-basined, drift-insulated lake was the most common lithotope in which fossil mollusks were preserved. The entire drainage system was supplied by greater rainfall and snowmelt than now occurs on the Missouri Coteau (probably in the order of 20 to 30 inches per year) and the precipitation - evapotranspiration ratio was positive. The humid climate changed toward the more arid climate of today before the ice core of the Coteau melted. Comparison with modern molluscan assemblages characteristic of defined habitats in Minnesota indicates that the mollusks which lived on the ice-cored Missouri Coteau, could have occupied small streams, medium-hardwater lakes, and/or hardwater prairie lakes. In consideration of the population dominance by branchiates, I believe that hard water prairie lakes are not likely to have occurred on the late Wisconsinan Missouri Coteau. In order to evaluate this hypothesis the terminus of the Martin River Glacier in south-central Alaska was studied. A molluscan fauna of ten fresh-water and thirteen terrestrial taxa was discovered on and in front of the stagnant terminus of the glacier. Twenty-three potential habitats for mollusks were studied and defined. Twelve of these were found to contain mollusks. The aquatic mollusks were found to occupy cool water (as low as 5°C) and warm water (above 10°C) and to be able to withstand very low concentrations of dissolved solids and high turbidity. Branchiate gastropods and bivalves were found to favor turbid environments next to the glacier and to populate successfully ice-basined, clear, warm lakes on the glacier. Terrestrial snails and slugs were found as much as a kilometer out on the drift-covered stagnant glacial terminus separated from the glacier ice by only 11 inches of alder-leaf-litter. Terrestrial snails were found in spruce forests only once. They were not found under willow bushes, young alder shrubs (less than 7 years in age), or on outwash gravel surfaces. Acid peat growths, and ponds developed in them, were also barren of mollusks. Edaphic conditions are assumed to account for their absence in these potential habitats. The Alaskan studies lend credence to the hypothesis erected to explain the paleoecology of the late Wisconsinan molluscan fauna of the Missouri Coteau in that they prove that mollusks are vigorous pioneers near and on stagnating glaciers, that less than a foot of super glacial drift is sufficient to insulate terrestrial molluscan habitats, and that six feet of superglacial drift is sufficient to insulate ice-basined, clear, warm lakes from their containing ice walls. The studies further emphasize that terminal glacial features such as end moraines, outwash fans, dead-ice moraines, kettles, and superglacial lakes are the result of a non-glacial climate and the inference of glacial climate from such features is a fundamental error. The employment of fossil nonmarine mollusks as indicators of past water quality was brought under serious question by the studies reported here. The fact that aquatic mollusks live successfully in Alaskan waters which contain less than 1 ppm dissolved solids brings into question the practice of employing mollusks as paleolimnologic indicators of chemical aspects of their environments. I believe the use of mollusks as indicators of past water quality of their habitats must be discontinued

Simulating a dual beam combiner at SUSI for narrow-angle astrometry

The Sydney University Stellar Interferometer (SUSI) has two beam combiners, i.e. the Precision Astronomical Visible Observations (PAVO) and the Microarcsecond University of Sydney Companion Astrometry (MUSCA). The primary beam combiner, PAVO, can be operated independently and is typically used to measure properties of binary stars of less than 50 milliarc- sec (mas) separation and the angular diameters of single stars. On the other hand, MUSCA was recently installed and must be used in tandem with the for- mer. It is dedicated for microarcsecond precision narrow-angle astrometry of close binary stars. The performance evaluation and development of the data reduction pipeline for the new setup was assisted by an in-house computer simulation tool developed for this and related purposes. This paper describes the framework of the simulation tool, simulations carried out to evaluate the performance of each beam combiner and the expected astrometric precision of the dual beam combiner setup, both at SUSI and possible future sites.Comment: 28 pages, 23 figures, accepted for publication in Experimental Astronomy. The final publication is available at http://link.springer.co

The Angular Diameter and Fundamental Parameters of Sirius A

The Sydney University Stellar Interferometer (SUSI) has been used to make a new determination of the angular diameter of Sirius A. The observations were made at an effective wavelength of 694.1 nm and the new value for the limb-darkened angular diameter is 6.048 +/- 0.040mas (+/-0.66%). This new result is compared with previous measurements and is found to be in excellent agreement with a conventionally calibrated measurement made with the European Southern Observatory's Very Large Telescope Interferometer (VLTI) at 2.176 microns (but not with a second globally calibrated VLTI measurement). A weighted mean of the SUSI and first VLTI results gives the limb-darkened angular diameter of Sirius A as 6.041 +/- 0.017mas (+/-0.28%). Combination with the Hipparcos parallax gives the radius equal to 1.713 +/- 0.009R_sun. The bolometric flux has been determined from published photometry and spectrophotometry and, combined with the angular diameter, yields the emergent flux at the stellar surface equal to (5.32+/- 0.14)x10^8 Wm^-2 and the effective temperature equal to 9845 +/- 64 K. The luminosity is 24.7 +/- 0.7 L_sun.Comment: Accepted for publication in PAS

Direct Detection of the Brown Dwarf GJ 802B with Adaptive Optics Masking Interferometry

We have used the Palomar 200" Adaptive Optics (AO) system to directly detect the astrometric brown dwarf GJ 802B reported by Pravdo et al. 2005. This observation is achieved with a novel combination of aperture masking interferometry and AO. The dynamical masses are 0.175$\pm$0.021 M$_\odot$ and 0.064$\pm$0.032 M$_\odot$ for the primary and secondary respectively. The inferred absolute H band magnitude of GJ 802B is M$_H$=12.8 resulting in a model-dependent T$_\mathrm{eff}$ of 1850 $\pm$ 50K and mass range of 0.057--0.074 M$_\odot$.Comment: 4 Pages, 5 figures, emulateapj format, submitted to ApJ