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1	Understanding the history of a volcanic arc: linking geochemistry of Cenozoic volcanic cobbles from the Wrangell arc, Alaska, to upper plate and subducting slab tectonic processes Morter, Bethany Kathleen January 1900 (has links) Master of Science / Department of Geology / Matthew E. Brueseke / The Wrangell arc (WA) is a ~29 Ma magmatic belt, extending from south-central Alaska into the Yukon Territory, that lies above the edges and leading front of the Yakutat microplate, a buoyant oceanic plateau that is causing shallow subduction (11-16º) in the region. The WA occurs in a transition zone between “normal” Aleutian subduction to the west and dextral strike-slip tectonics to the east, accomplished by the Totschunda, Denali, and Duke River faults. This geologic setting offers a chance to study the interrelations between subduction, strike-slip motion, and slab-edge magmatic processes in a relatively well-exposed arc. We implemented a novel technique of applying geochemical and geochronologic analyses on volcanic cobbles collected from glacio-fluvial systems (rivers, streams, and glaciers) encircling/draining the WA. Our primary objective is to integrate our cobble datasets with the existing bedrock and detrital sand records to develop a comprehensive understanding of WA magmatism through time and space. Our secondary objective is to test the validity of this novel technique for reproducing what is documented from bedrock samples and its potential for utilization in other locations. This study provides new major element data from 215 samples and trace element data from 236 samples collected from 17 major rivers that drain from the modern western and central WA (this study excludes the eastern WA). This study also provides new age data from a total of 119 samples from 10 major rivers. New geochronology of modern detrital volcanic cobbles and sand/zircons reveal that the WA initiated at ~29 Ma and that magmatism migrated northwestward through time. Cobble ages and locations across the arc agree with the northwestward progression of magmatism previously identified by Richter et al. (1990). Forty-seven cobbles are dated <~1 Ma and only nine cobbles are dated 29 – ~20 Ma, whereas there are no cobbles from 17 – ~13 Ma. Geochemical data reveal similarities between our data and that of the <~5 Ma WA defined by Preece and Hart (2004): Trend 1 (transitional-tholeiitic), Trend 2a (calc-alkaline), Trend 2b (calc-alkaline, adakite-like). Therefore, we use the geochemical framework defined in Preece and Hart (2004) to contextualize spatio-temporal trends of magmatism and tectonic implications in the WA during its ~29 m.y. history. Trend 2a and 2b cobbles are spatially and temporally ubiquitous in the WA, indicating that subduction and partial slab melting have been the dominant tectonic processes throughout WA history. Trend 1 cobbles are not found in southwestern WA rivers and are temporally restricted to ~11 – ~6 Ma and <1 Ma, suggesting intra-arc extension has occurred in discrete periods during WA history. These conclusions are confirmed by the existing (Richter et al., 1990; Skulski et al., 1991; 1992; Preece and Hart, 2004; Trop et al., 2012) and new (Berkelhammer, 2017; Weber et al., 2017) bedrock records. Finally, this study shows that the sampled cobble lithologies largely reproduce the known bedrock record in geochemical, temporal, and spatial contexts, which suggests the novel methodology applied here can be used in other locations where field conditions limit access to bedrock. Wrangell arc Cobble Geochemistry
2	The Diversity of Macroinvertebrate Grazers in Streams: Relationships With the Productivity and Composition of Benthic Algae McKenny, Claire, n/a January 2005 (has links) There has been much interest in the last decade concerning the factors that influence diversity, especially how diversity and ecosystem processes may be linked. This study was based in small, cobble streams in South East Queensland. Its aim was to determine how the diversity and composition of consumers (the grazer guild) is influenced by both the production and composition of benthic algae, at different spatial scales. It also aimed to ascertain whether this response differs among grazer sub guilds with different dispersal capabilities. Ten sites in the Upper Brisbane and Mary catchments were sampled. The sites were selected to provide a range of productivity and composition. Grazers from these sites included snails and elmids, and larval mayflies, moths, and caddisflies. Grazer diversity and composition appeared to be structured by catchment scale influences, but environmental variables also affected which animals colonised patches and microhabitats (cobbles) within catchments. Primary productivity and algal composition could not be separated, with highly productive reaches also having a high cover of filamentous algal taxa. Grazer diversity displayed strongly positive, linear relationships with algal variables at the reach scale. It had a negative relationship with filamentous algae at the cobble scale, and a non-significant hump-shaped relationship with primary productivity. Survey data alone could not separate whether grazers were responding to habitat or food-related drivers, or to variations in productivity. Experimental manipulation of algal variables at the patch scale, using light and nutrients, also could not clearly uncouple the relationship between primary productivity and filamentous algal cover. Once reach scale variation was removed, grazer diversity displayed hump-shaped relationships with algal variables, including algal diversity. Much of this variation was due to patterns in mobile grazers, as sedentary grazers did not respond to algal variation at this scale. The density of the more mobile taxa showed similar patterns to those at the cobble scale (hump-shaped). A second field experiment was carried out in order to further investigate the responses of invertebrates to algal community composition at the cobble scale. Data from all three chapters suggested that as sites shifted to a dominance of filamentous algae, often with an associated increase in GPP, there was also a shift in the grazer community towards more sedentary grazers and away from the more mobile taxa. This also occurred at the cobble scale in the second experiment. The gut analysis and diet studies in the third chapter indicated that while many grazers consumed filamentous algae, it was not assimilated. This suggests that the preferences for sedentary taxa for cobbles and reaches dominated by filamentous algae are likely to be due to some other, possibly habitat-related, factor such as flow or predation refuge. The study provides a rare examination of relationships between primary productivity and consumer diversity in freshwater streams, and finds support for the pattern found in other systems of monotonic relationships of these two variables at large scales and hump-shaped relationships at smaller scales. It emphasises the importance of understanding other, potentially confounding, aspects of communities of producers, and investigates the possible roles of the most important of these (community composition) in structuring consumer communities in the small cobble streams of South-East Queensland. Macroinvertebrate grazers benthic algae cobble streams (Queensland) stream ecology Upper Brisbane River Mary River
3	Stone tools employed in prehistoric metal mining. A functional study of cobblestone tools from prehistoric metalliferous mines in England and Wales in relation to mining strategies by use-wear analysis and cobble morphometry Gale, David January 1995 (has links) This is a study of cobblestone tools from metalliferous mine sites in England and Wales dated to the Bronze Age which were most probably used to extract copper ore. The site assemblages studied are from the Great Orme, Copa Hill in Cwmystwyth, Nantyreira, Parys Mountain and Alderley Edge. The majority of the tools are hammerstones used to mine and beneficiate metal ore. Some of these have been modified to facilitate hafting. The functional uses of these tools have been identified by the form and position of use- wear on a macroscopic level. The recording procedure encompasses cobble morphology, the degree, type and direction of use, breakage patterns, the reuse of tools and tool fragments and the classification of hafting modification. The possibility of tool specialization within tool types has been examined by the analysis of use-wear and cobble shape and size. The analysis of stone hammer size suggests that the Great Orme material is related to specific working techniques employed to extract ore from the different types of ore deposits. Ore comminution has been demonstrated to have been generally achieved by ‘block-on-block’ crushing with flat-sided hammers. Conclusions are draw on the overall efficiency of ore extraction in the Bronze Age and theories on the organization of mining are presented. The sedimentary form of the cobblestone tools has also been examined, including the identification of natural abrasion marks and features. At Cwmystwyth and the Great Orme possible sources of cobblestones have been studied in order to assess the nature of cobble selection. / SERC studentship / The additional content files which accompanied the thesis are not available on Bradford Scholars, but are available from the British Library Ethos Service. Prehistoric Britain Stone tools Metal mining Function Use-wear Cobble morphology Bronze Age Hammerstones
4	The Origin Of The Lion's Head Peninsula Beach Davidson, Ian Ritchie 04 1900 (has links) <p> The beach deposits at the head of the Lion's Head Peninsula are described and categorized according to the type, size and morphology of the rocks making up the deposit and their origins. This categorization emerges as a pattern of four zones along the l ength of the beach. </p> <p> The points at each end of the beach, which used to be in a much more defined bay, have been glacially eroded by re-entrants and undercut by postglacial lakes. Shales and dolomite from the escarpment make up this zone's deposits. </p> <p> Zone two is a dolomite cobble beach supplied by the escarpment's erosion from a blockaded late-glacial ice margin and the undercutting of postglacial lakes. </p> <p> Zone three is a mixture of the dolomite from the escarpment, lacustrine sand deposits, and glacial erratics. </p> <p> Zone four is made up of a distinct band of erratics deposited by the ice of the Georgian Bay lobe of the Late Wisconsin Glaciation. The Lion's Head promontory stood resistant to the flow of ice and caused it to deposit these large erratics which are still visible today. </p> / Thesis / Bachelor of Arts (BA)
5	Cobble Beaches Along The Coastlines Of The Georgian Bay Islands Grosset, Cathy Ann 04 1900 (has links) <p> This report is the only detailed study concerning the fresh water cobble beaches of the Georgian Bay Islands. It includes extensive studies on the morphological characteristics, especially the platform development and profile configuration, and the sedimentary provenance of the cobbles. </p> <p> It was found that the platform configuration (step topography) acts as a substrate control for the cobble beaches. The presence of two cobble generations, angular and well-rounded, indicate that t he shore platform is the source for these cobble beaches. </p> <p> The roundness values of these cobble generations depends on t heir mode of transport. Evidence indicates that longshore movement of cobbles increases their roundness values, but their angular shape i s indicative of their lack of transport. </p> <p> Very little proof was found within this study to correlate relict cobble beaches with any specific stage of the Lake Huron Basin, although it was possible to generalize and state that the relict cobble beaches were generated by high-energy wave events during the transition from the Algoma stage to Lake Huron. </p> <p> Clast analysis determines the relationship between the length of the wave fetch and its related energy environment. It was found that high-energy coastal environments have oblate cobbles with a high roundness and low sphericity. In each case, the samples were associated with a large fetch. Those cobbles of a low-energy coastal environment have a high sphericity, low roundness, and are associated with smaller fetches. </p> <p> The steepness of the beach profile results from the increase in wave height, generated by an increase in shallowness. It also depends upon the volume of backwash. The backwash is reduced by the increased percolation rates through the cobbles, thus reducing the combing down effect of the backwash. </p> <p> This study also provides a discussion on the minor morphological features such as sinkholes and imbrication. </p> / Thesis / Bachelor of Arts (BA)
6	低攪乱な礫床河川に優占する造網型トビケラの固体群動態とそれに伴う河床固化に関する解析田代, 喬, TASHIRO, Takashi, 渡邉, 慎多郎, WATANABE, Shintaro, 辻本, 哲郎, TSUJIMOTO, Tetsuro 02 1900 (has links) No description available. Net-spinning caddis larvae population dynamic modeling substratum adhension bed-load transport cobble river with fewer disturbances
7	Geology of the Phil Pico Mountain Quadrangle, Daggett County, Utah, and Sweetwater County, Wyoming Anderson, Alvin D. 25 April 2008 (has links) (PDF) Geologic mapping in the Phil Pico Mountain quadrangle and analysis of the Carter Oil Company Carson Peak Unit 1 well have provided additional constraints on the erosional and uplift history of this section of the north flank of the Uinta Mountains. Phil Pico Mountain is largely composed of the conglomeratic facies of the early Eocene Wasatch and middle to late Eocene Bridger Formations. These formations are separated by the Henrys Fork fault which has thrust Wasatch Formation next to Bridger Formation. The Wasatch Formation is clearly synorogenic and contains an unroofing succession from the adjacent Uinta Mountains. On Phil Pico Mountain, the Wasatch Formation contains clasts eroded sequentially from the Permian Park City Formation, Permian Pennsylvanian Weber Sandstone, Pennsylvanian Morgan Formation, and the Pennsylvanian Round Valley and Mississippian Madison Limestones. Renewed uplift in the middle and late Eocene led to the erosion of Wasatch Formation and its redeposition as Bridger Formation on the down-thrown footwall of the Henrys Fork fault. Field observations and analysis of the cuttings and lithology log from Carson Peak Unit 1 well suggest that initial uplift along the Henrys Fork Fault occurred in the late early or early middle Eocene with the most active periods of uplift in the middle and late Eocene (Figure 8, Figure 24, Appendix 1). The approximate post-Paleocene throw of the Henrys Fork fault at Phil Pico Mountain is 2070 m (6800 ft). The Carson Peak Unit 1 well also reveals that just north of the Henrys Fork fault at Phil Pico Mountain the Bridger Formation (middle to late Eocene) is 520 m (1710 ft) thick; an additional 460 m (1500 ft) of Bridger Formation lies above the well on Phil Pico Mountain. Beneath the Bridger Formation are 400 m (1180 ft) of Green River Formation (early to middle Eocene), 1520 m (5010 ft) of Wasatch Formation (early Eocene), and 850 m (2800 ft) of the Fort Union Formation (Paleocene). Stratigraphic data from three sections located east to west across the Phil Pico Mountain quadrangle show that the Protero-zoic Red Pine Shale has substantially more sandstone and less shale in the eastern section of the quadrangle. Field observations suggest that the Red Pine Shale undergoes a facies change across the quadrangle. However, due to the lack of continuous stratigraphic exposures, the cause of this change is not known. Eocene Red Pine Shale Uinta Mountains Bridger Formation Wasatch Formation Henrys Fork Fault Uplift uplift history anticline syncline Laramide Green River Formation Bishop Conglomerate inverted cobble stratigraphy unroofing unroofing sequence conglomerate Phil Pico Mountain Flaming Gorge Utah Wyoming Paleocene clast erosional history north flank facies change strike-slip fault Madison Limestone Weber Sandstone Vr VrTwo VrOne geologic mapping geology glacial deposits Smiths Fork Uinta thrust cuttings lithology log erosion Carson Peak well geologic map cross-section stratigaphy stratigraphic column unit descriptions tectonic history Tertiary depositional deposition Proterozoic Precambrian Geology

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