Maps in pocket bound with piece.

This study has confirmed the existence of a distinct mineralogical component in the upper part of the Yorkville Till Member of the Wedron Formation of Wisconsinan age in northeastern Illinois. This upper till unit occurs within the area of, but is not bounded by, the older Marseilles Morainic System and the younger, overriding Minooka Moraine. The analyses of samples from 79 locations that were used to identify, compare, and differentiate the two tills were: matrix grain size, clay mineral composition, carbonate content, and color.The upper till is a grayish brown, silty clay till with 76% illite and a dolomite-calcite ratio of 2:1. The lower till is an olive gray, silty clay till with 81% illite and a dolomite-calcite ratio of4:1. Results of this study indicate that (1) the two tills are separable and mappable units with the aid of laboratory data; (2) the lower till composes the bulk of the Marseilles Morainic System; (3) the upper till is thin between the moraines and constitutes the till of the Minooka Moraine; and (4) the upper till apparently represents a minor readvance and a concurrent change in source material.Ball State UniversityMuncie, IN 47306

Over 7000 sq. km of salt and six Plio-Pleistocene biostratigraphic horizons were mapped in the East Breaks and Garden Banks areas using a 12,000 km grid of seismic data and all obtainable well data. Structure mapping of allochthonous Jurassic salt and the six horizons (Globoquadrina altispira, Lenticulina 1, Angulogerina B, Hyalinea B, Trimosina A, and Sangamon Fauna) and isopachs of the intervals between these horizons revealed notable lateral variations in the area underlain by salt, in the degree of salt deformation, and in the size and thickness of associated intraslope basins. East of 94.5° W salt structures occupy 40% of the area and exhibit complex shapes that suggest a high degree of salt deformation. West of 94.5° W salt structures occupy 11% of the area and consist mostly of structurally simple salt stocks. A zone of high-offset north-south trending faults mark the transition between these two areas. Isopach maps of the six Plio-Pleistocene intervals (from 2.9 Ma to the present) reveal major shifts in the rates and locations of sediment accumulation. From 2.9 to 1.0 Ma. sediment-accumulation rates averaged only 0.8-1.3 mm/y with a maximum rate of 2.7 mm/y. From 1.0 to 0.69 Ma. sediment-accumulation rates averaged 5.8 mm/y with a maximum rate of 11.6 mm/y. This interval correlates to sediments deposited between the extinctions of Hyalinea balthica and Trimosina denticulata and recorded a major period of sediment loading/salt withdrawal between 1.0-0.69 Ma. From the end of this time to the present, sediment -accumulation rates averaged 1.7-2.1 mm/y with a maximum rate measured at 6.2 mm/y. Increased sediment influx during 1.0-0.69 Ma coincides with a major third order sea level lowstand and was focused in central Garden Banks. The restriction of such dramatically increased accumulation rates to this area suggests that sediment influx was accompanied by large-scale salt withdrawal. The increase in accommodation space created by salt withdrawal appears to be the most important factor affecting accumulation rates. Salt structural styles found on the upper continental slope are transitional between those found on the lower slope and those on the shelf. The shelf is dominated by isolated, individual salt stocks (km²) surrounded by kilometer thick sedimentary sections. The lower slope is dominated by broad, laterally continuous, allochthonous salt sheets (10³ km²) with moderate to thin sediment cover. The upper slope contains both of these structural styles plus intermediate size (10-10² km²) salt ridges and massifs. Observations made during this study suggest that differential sediment loading is the mechanism causing the changes in structural style. A Loading/Dissection model is presented to explain the formation of the three primary salt structural styles, their genetic relationship, and their observed distribution. Differential loading has dissected large salt sheets into numerous smaller and irregularly shaped ridges and stocks (like those found on the upper slope). Salt found on the upper slope originated in the Jurassic Louann Formation, but is now surrounded by Pleistocene age sediments. To achieve this relationship, it appears that some Jurassic salt has undergone at least two cycles of sediment loading and consequent diapirism. Salt/sediment relationships suggest that virtually all of the mapped salt is allochthonous. Repetitive sediment loading and salt structural development has not been previously documented and represents a step beyond the limits of current salt structural models. / text

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No description available.

Detrital magnetite, although averaging less than I% of till volume, is a common constituent in glacial tills of eastern Indiana and western Ohio. Because of its abundance and ease of sampling, detrital magnetite was chosen to determine its potential as a tool to 1) determine provenance of the glacial tills and 2) to chemically fingerprint glacial sedimentary deposits for use in stratigraphic analysis. Two sampling programs were performed. First, glacial till samples were collected from a vertical section in western Ohio at the location of Doty's High Bank. Second, glacial tills were collected from a lateral distribution of five moraines in northeast and east central Indiana.Petrographic analysis of 946 detrital magnetite grains from eastern Indiana and western Ohio has shown that 81% of the magnetite grains are homogeneous, 15% have magnetite-ilmenite intergrowths, and 4% have exsolved phases of ulvospinel/pleonaste.Eighteen percent of all detrital magnetite grains have some level of hematite alteration. Chemical analyses were performed on 403 homogeneous detrital magnetite grains. These grains were analyzed for Fe, Ti, Mg, Mn, Cr, V, Al, and Si. The means and standard deviations of these eight elements, in weight percent oxide, are FeO (89.8087.696), TiO2 (1.58 ± 4.99), MgO ( 0.052 ± 0.200), MnO ( 0.172 ± 0.284), Cr2O3 (0.1942.256), V2O3 ( 0.241 ± 0.245), Al2O3 (0.455 ± 1.234), and SiO2 ( 0.035 ± 0.047).A Canadian source north of Lake Huron and south of James Bay is suggested based on previous studies of flow directions of the Laurentide Ice Sheet and bedrock geology in southern Canada. The bedrock in this area is primarily felsic plutonic and mafic volcanic. The petrographic and geochemical results of this study indicate this area as the source area for the detrital magnetite in eastern Indiana and western Ohio tills. Chemical fingerprints based on cluster analysis and bivariate plots were found within the vertical exposure of Doty's High Bank and the lateral moraines of eastern Indiana. Samples from the Muncie esker (unknown age) were found to correlate with the southernmost set of eastern Indiana moraines based on the chemical fingerprint analysis. / Department of Geology

Maps in pocket bound with piece.

No description available.

Five coastal sites have been studies on the Isle of Skye to investigate Late Devensian and Holocene relative sea level changes. In the field, detailed stratigraphical work, geomorphological mapping and levelling were undertaken and representatives cores were sampled. Detailed pollen and diatom analyses were undertaken in the laboratory and samples were submitted for radiocarbon assay where distinct pollen, diatom or lithostratigraphical changes were recorded. Loss on ignition analysis was also undertaken to ascertain the carbon content of the samples. The investigations have revealed that during the Late Devensian marine transgressions were experienced at two sites in southern Skye. These are thought to relate to readvances of the ice that arrested the isostatic recovery of the land, caused renewed isostatic depression and upon deglaciation, allowed marine waters to penetrate the sites. At Inver Aulavaig the transgression is thought to relate to the Wester Ross Readvance recorded in Wester Ross, Coll and Tiree and at Point of Sleat the transgression is thought to relate the Loch Lomond Readvance recorded extensively in Scotland. Relative sea level at Point of Sleat (southern Skye) then fell below an altitude of 4.13mOD at 10460+-50BP and remained low during the early Holocene until the Main Postglacial Transgression occurred. This transgression is recorded at three of the sites: at Inver Aulavaig (southern Skye) at 8850+-70BP where it had attained an altitude of at least 5.10mOD, at Peinchorran (eastern Skye) where it is thought to have been underway by 7980+-BP and attained an altitude of 4.49mOD and at Talisker Bay (western Skye) at 7790+-100BP where it had attained an altitude of -2.18mOD. At Ardmore Bay (northern Skye) it is thought that the Main Postglacial Transgression did not reach an altitude of 3.34mOD. It is possible that barrier formation at some of the sites accompanied the early states of the Mian Postglacial Transgression. It is thought that regression of the sea occurred between circa 6600 BP and circa 5400 BP and remained low until circa 4200 BP when a later rise in relative sea level took place at Peinchorran attaining a maximum altitude of 4.90mOD. A late Holocene transgression is also recorded at Point of Sleat at between circa 3800 BP and circa 2900 BP where it attained an altitude of greater than 4.13mOD and at Inver Aulavaig after circa 3200 BP where it attained an altitude of between 5.10-6.01mOD. It is unclear whether this episode of high relative sea level represents the diachronous nature of one late Holocene transgression or several fluctuations in relative sea level during the late Holocene. Following the late Holocene transgression, relative sea level fell until the present day. Comparison of the data obtained from Skye with the isobase maps and rheological models suggests that the isobases for the Main Lateglacial Shoreline (Firth et al., 1993) show a good fit in age and altitude but the rheological model of Lambeck (1993b) for 10500 BP requires modification. The isobases for the Main Postglacial Shoreline appear to lie circa 4m too high for the sites studied on Skye and the isobases produced for a late Holocene shoreline appear to be greatly in error (Firth et al., 1993). It is possible that the build up of ice during the Loch Lomond Stadial may have had a greater effect on crustal movements than previously thought and this may account for discrepancies identified in the isobase maps. The study of isolation basins and back-barrier environments has allowed an assessment of their potential in recording relative sea level changes. The use of isolation basins in areas devoid of estuarine sedimentation has been particualrly demonstrated. The vegetation reconstruction undertaken, suggests that variations do occur in coastal locations compared to sites further inland, although these are subtle. The dates obtained for the increase in taxa such as 'Corylus avellana' and 'Alnus' and the recording of anthropogenic indicators on the vegetation, agree with those previously obtained for Skye. The use of pollen analysis in verifying the radiocarbon dates obtained, particualrly for the Late Devensian, has been recognised and, combined with diatom analysis, has provided a comprehensive database from which to reconstruct past relative sea levels.

No description available.