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No description available.

The Lower Jurassic stratigraphy of seven contrasting areas in western Europe is compared in order to seek evidence for a pan-Western European stratigraphic forcing mechanism. Sequencestratigraphic models are discussed and emphasis is placed upon the differing response of sedimentary systems in "accommodation space-dominated" and "supply-dominated" settings. Spectral gamma-ray data from clastic successions in the Wessex and Cleveland basins (England) are used to elucidate vertical trends. A proximal-distal model for control of Th/K ratios is advanced. Stage-frequency regressive-transgressive cycles in the two areas are shown to be closely correlative. Sedimentolgical logs and spectral gamma-ray data are presented for the carbonate ramp into turbidite sequence of Peniche (Portugal) and for a new exposure of the Pliensbachian-Toarcian in southern Germany. Systematic variation in clay mineralogy across Europe is suggested. Cycles in the Lower Jurassic of the North Viking Graben (Norwegian North Sea) are examined using wireline log correlation and the stratigraphic evolution of the Tethyan Rift in the Western and Southern Alps is reviewed. X-ray diffraction studies of the Pliensbachian-Toarcian interval in the Southern Alps are presented in order to elucidate sediment supply to the pelagic realm. The cycles observed in the English sections appear to be manifest widely across western Europe in a variety of tectonic and sedimentary settings. Sharp basinward facies shifts (candidate sequence boundaries) do not appear to be synchronous between basins. ⁸⁷SR/⁸⁶SR analysis of belemnites from the Portuguese and German sections confirms the regional applicability of the results of Jones (1992) and the utility of this technique in long range correlation. Carbon and oxygen analysis of the same material supplements the data of other workers and a direct relationship is suggested between relative sea level and organic carbon burial in the Early Jurassic.

The salt flats of west Texas are large ephemeral lakes, Pleistocene to Holocene in age. The evaporite material in these lakes represents the sedimentary history of the lake and the surrounding area. Recently, a fossil assemblage was found in the sediments of this deposit. This assemblage includes four species of ostracoda (Limnocvthere staplini, Candona rawsoni, Candona thomasi, and Cvprideis salbrosa), two species of gastropoda, (Amnicola decepta, and Amnicola pilsbrvi), and discovery is significant because this assemblage has not been previously reported, and it provides an opportunity to reconstruct part of the physical and chemical environment of the salt flats during a portion of its history. Autecological comparison of these species indicate that they lived in a shallow, alkaline, brackish water environment. The known paleoclimate of the area, and the sedimentology support this interpretation. / Department of Geology

The Middle Devonian formations to be studied in this paper are the Jeffersonville and North Vernon Limestones. Together these formations make up the Muscatatuck Group in the Illinois Basin portion of Indiana. In the area of study, the Jeffersonville Limestone consists from the base upwards of the Geneva Dolomite Member, Vernon Fork Member, and Paraspirifer acuminatus Zone. The North Vernon Limestone consists of the Speed Member overlain by the Beechwood Member.In the study area, the subsurface Muscatatuck Group dips to the southwest at a rate of 20 to 50 feet per mile. These rocks thicken to the southwest, and range in thickness from 136 to 170 feet. Closed-structural highs are present on the top of the Muscatatuck Group over Silurian pinnacle-like reefs.Resistivity log - sonic log cross plots were constructed to analyze the subsurface carbonate facies in the study area. A total of 13 cross plots were constructed with over 1,490 points plotted.From this study five conclusions can be drawn about the application and usefulness of the cross plot method in analyzing the the surface distribution of carbonate facies. As explained in the text, these conclusions remain valid only when applied to the area of study.The conclusions are as follows:1. The positioning of the point groups on the cross plots is controlled by the amount and type of porosity present in the rocks.2. Due to the diagenetic alteration of the primary porosity in the rocks, the point groups can not be divided into depositional textures or facies.3. In this case, because of the uncomplex nature of the stratigraphy and the ease of correlation of the lithologic units on the logs, the cross plots were not useful in analyzing the subsurface distribution of the carbonate facies in the area.4. The cross plots were useful in checking the accuracy of the log correlations.5. The cross plots may be used to infer lateral porosity changes in the rock units, and possibly variations in the diagenetic alteration within these units.

The upland soils of Randolph County, Indiana were studied for the following purposes: to provide an additional characterization of these soils, to identify a set of soil parameters that could delineate the extent of Late Wisconsinan glaciation in that county and to determine if there were any geographic trends in silt cap thickness. The study was prompted from observations by the recent Randolph County Soil Survey team that high clay content soils commonly associated with the county's Late Wisconsinan till (Lagro Formation) were found south of its previously mapped boundary.The only soil parameters that were effective in mapping the extent of Late Wisconsinan glaciation were: particle size analyses and some combinations of particle size analysis data with other soil parameters. The data support the previously mapped boundary of the Late Wisconsinan sediments in Randolph County, Indiana.Silt cap thickness was identified to be greatest in three areas of the county. However, the source(s) of these silts could not be determined. / Department of Geology

The purpose of this study was to define the lithofacies and areal extent of the Fort Atkinson Formation (Maquoketa Group, Upper Ordovician) in the subsurface in Indiana. Two distinct lithologic facies (Members) of the Fort Atkinson Formation can be distinguished in the subsurface. The upper Shoaling Member consists of coarse grained crinoid-bryzoan grainstone deposited in a high energy depositional environment. Beneath the Shoaling Member is the Transition Member of the Fort Atkinson. This Member consists of alternating beds of shale and limestone which were deposited in depositional environments that varied from high to low energy. The Fort Atkinson is an important stratigraphic marker used to define four depositional provinces within the Maquoketa Group in Indiana. The four depositional provinces include the Maquoketa Shelf, the Overlap Ramp. the Cincinnati Shelf, and Michigan Shelf. / Department of Geology

The collection and analysis of a large number of belemnites and oysters with excellent biostratigraphic and diagenetic control has resulted in a highly detailed determination of the seawater Sr-isotope curve through the Jurassic and Early Cretaceous. The new data confirm the broad trends established by previous work, but the much sharper resolution of the new data allows the application of Sr-isotope stratigraphy with an optimal stratigraphic resolution of ± 1 to 4 ammonite subzones (± 0.5 to 2 Ma). The data show a general decline from the Hettangian (Early Jurassic) to a minimum in the Callovian and Oxfordian (Middle/Late Jurassic). This is followed by an increase through the Kimmeridgian (Late Jurassic) to a plateau reached in the Barremian (Early Cretaceous). In addition, there are major negative excursions in the Pliensbachian/Toarcian (Early Jurassic) and Aptian/Albian (Early Cretaceous). Stable isotope data collected from belemnites and oysters have resulted in the most extensive Jurassic δ¹³C and δ¹⁸O database to date. While both the carbon and oxygen data appear to give reasonable marine signals, the scatter in the data suggests that future research must document possible biological fractionation effects and develop better indicators for the diagenetic alteration of 613C and 6i 8O. The final chapter documents an unexpected correlation between sudden shifts in the Sr-isotope curve, the occurrence of positive 513C excursions, and the eruption of flood basalts. In the Jurassic and Cretaceous there is a correlation in time between sudden downward shifts in the Sr-isotope curve (Pliensbachian, Aptian, Cenomanian/Turonian), the occurance of positive 613C excursions, and the eruption of flood basalts. Each of these major downward shifts in the Sr-isotope curve is followed by a sudden upward shift, which although associated with a positive 613C excursion is not associated with an episode of flood basalt volcanism. In the Cenozoic the Sr-isotope curve no longer displays downward shifts, but the correlation continues between the occurrence of flood basalts and positive 513C excursions. Several lines of evidence suggest that the eruption of flood basalts is associated with pulses of hydrothermal activity, and that this hydrothermal activity brings about the conditions necessary for the genesis of carbon-burial events.

The Upper Triassic, Penarth Group has been examined, throughout Britain, both at outcrop and in boreholes. It is divided, lithostratigraphically into a lower, Westbury Formation and an upper, Lilstock Formation. Within these units a number of regionally-and locally-applicable members are distinguished. The Penarth Group is a predominantly marine, sedimentary sequence transitionally situated between arid or semi-arid lacustrine and fluviatile sediments (Mercia Mudstone Group and New Red Sandstone) and more fully marine strata (Lias). Early stages of the "Rhaetic" marine incursion, principally represented by the Westbury Member, document the establishment of semi-isolated, brackish basins which were superseded by a less restricted marine environment. This transgressional advance is linked to nutrient supply and thence to phytoplankton productivity in order to explain organic carbon profiles through the Westbury Member, Offshore and nearshore zones of this sea are recognised, the latter including sediments assigned to barrier-inlet, lagoon and tidal=flat environments. Clay mineral studies reveal an enrichment of smectite in offshore areas which is ascribed to differential sedimentation processes. Transgression was interrupted by a regressional phase marked by the lagoonal sediments of the Gotham Member. A shift in the zone of smectite deposition can be related to this regression. The inferred shelf-lagoon carbonates of the Langport Member reflect a renewal of transgression. A local influx of sediment-laden fresh- water is believed to have been responsible for the local change to the Watchet Member Facies. Deeper-water intermittently oxygen-deficient, marine environments are envisaged for the Pre-planorbis Beds. These spread across the Langport Member shelf-lagoon, as a result of continuing transgression, culminating in the widespread establishment of deeper-water conditions in the Lower Jurassic. An increase in kaolinite relative to smectite in these younger strata, reflects increasingly humid climatic conditions. A regional correlation of the lithostratigraphica.1 subdivisions is attempted leading to a series of palaeogeographical reconstructions.