The quantitative areal distribution of chemical, radiometric, and mineralogic variates within the Enchanted Rock batholith is examined statistically by means of least squares. The resultant partial trend surfaces and deviation maps indicate that the rocks are progressively more basic from the center of the batholith outward. The core of the batholith, however, deviates in composition from the regional trend. Alternative explanations are offered for the crystallization of the batholith and formation of the core. Hypotheses are also proposed to explain the following observations: (1) the heterogeneous distribution of thorium and uranium within the outer zones of the batholith, (2) different systematic chemical trends within the surrounding wall-rocks, and (3) the NW-SE trends and anomalies on the deviation maps. Trend surface analysis of least squares is demonstrated to be applicable to the petrogenesis of a single pluton such as the Enchanted Rock batholith.

This report defines and describes all exposed rock units in the Pahranagat Range, southeastern Nevada. The 600 square mile subject area, located in one of the most isolated regions of the United States, has not received previous detailed investigation.

The object of this investigation is to find large scale variations in thorium and uranium contents of granitic rocks and to link these variations to petrographic types and to geological characteristics of the plutons in which the rocks occur; in short, the object is to find the relation between the major petrogenesis of granitic rocks and their thorium and uranium contents. For this purpose representative granitic plutons from North America have been sampled. These samples have been examined petrographically and have been analyzed by gamma-ray spectrometry for thorium, uranium, and potassium. The study is predicated on the assumption that samples sufficiently representative of plutons could be obtained so that variation between hand specimens would not mask larger variations. The fact that large-scale relations are found justifies this assumption, at least in part. The material will be presented in four main parts: a review of the previous literature, the analytical method, presentation of data, and results.

No description available.

No description available.

Detailed mapping of over 10 kms of cliff exposure on Whidbey Island, Washington has resulted in the recognition of six major lithofacies within "Everson" age glacial-marine deposits (late-Pleistocene). These lithofacies were deposited in an isostatically depressed basin, comprise up to 25 m of section, and occur in a predictable vertical succession. Proximity to both the ice margin and sources of meltwater input played a key role in the facies distribution. Stratified and convoluted beds of diamicton exhibit sedimentary characteristics indicative of mass flow processes. An ice marginal, submarine environment is assigned to the stratified diamictons since they are interbedded with marine sediments. In most exposures stratified diamictons are directly overlain by pebbly silts, muds, and massive diamictons. Locally, small (300 m wide) delta-like sequences consist of well stratified silty sand which is interbedded with pebbly mud. Turbidity current channel infills consist of normally graded, laminated sands which fine upwards into laminated sand-silt and silt-clay. Both of these facies are overlain by pebbly mud and massive diamicton. Pebbly silt and mud grade up into massive, fossilifierous diamicton. Post depositional mass movement has locally interrupted the normal stratigraphic sequence. With regard to the ice margin, the massive "till-like" diamictons are interpreted as the most distal of the glacial-marine facies. All exposures are capped by channel lags, beach and eolian sediments which represent emergence of the basin above sea level. Erosional surfaces at the base of the sequence (glacial and/or meltwater) and above (regressive shoreline) serve to separate the isostatic glacial marine sequence from correlative nearshore, offshore, and terrestrial glacial sequences. Extensive development of meltwater and sediment flow facies suggest that the sequence was deposited in a moderate glacial climatic setting, not unlike the present Gulf of Alaska. Correlation of the central tendency of pebble fabric and sand content for glacial marine diamictons distinguish them from tills and sediment flow diamictons. Sediment flows are distinguished from tills and glacial marine diamictons by their high and variable clast abundances, textural variability, and variable bedding character. Deglaciation of central and northern Whidbey Island involved retreat of a highly irregular ice margin which was grounded

Detailed and reconnaissance field and gravity studies indicate that the Brevard zone in Alabama consists of a lithologically-distinctive, multiply-deformed polymetamorphosed sequence of Cambrian(?)-age metasedimentary and metaigneous rocks bounded on the northwest and southeast by high-angle reverse faults that flatten with depth. It is likely that this sequence underlies the Inner Piedmont at depths (LESSTHEQ) 10km, and crops out to the southeast as the parautochthonous cover overlying Grenville basement in the Pine Mountain window. Along strike, Brevard zone lithic types (i.e., the Jacksons Gap group) are dominated by mica schists and phyllites to the northeast, and by quartzites to the southwest. This probably represents a change in original lithofacies and, when coupled with relevant structural data, indicates a possible southeastern clastic source. The Jacksons Gap group and immediately adjacent rock sequences have been subjected to at least four phases of contractional deformation, and possibly one phase of minor transpressional deformation. All deformational phases are regionally similar with respect to style, orientation, and relative timing, but vary spatially in intensity. D(,1) and D(,2) were ductile events that produced tight to isoclinal folds, and amphibolite- and greenschist-facies mineral assemblages, respectively. The Inner Piedmont allochthon was probably emplaced during D(,2). D(,3) produced most map-scale folds in the Brevard and a locally well-developed axial plane foliation. D(,4) was a cross-folding event that may be related to minor strike slip, and D(,5) was a brittle thrusting event confined mainly to the northwest-bounding fault of the Brevard, the Abanda. Based on reasonable geometric assumptions (e.g., the strike change of the Brevard south of Jacksons Gap is the up-plunge expression of a southeast-dipping fault ramp), it is likely that the Abanda fault soles in the major detachment beneath the Alabama Piedmont, and that the southeast-bounding fault of the Brevard, the Katy Creek, soles southeast of the Pine Mountain window. A minimum thrust-related shortening of 18 km on the Abanda, and 47 km on the Katy Creek could produce the observed geometries. These assertions are compatible with two-dimensional modeling of both newly-collected and recently-published gravity data. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI

The mixed carbonate-siliciclastic depositional system in the Gulf of Papua (GoP) was studied by standard sequence stratigraphic method based on a large industry seismic and well datasets, in addition to gravity, multibeam bathymetry, Landsat imagery, and core data. The Cenozoic geological history of the mixed system is represented by four-phase evolutionary model, which includes (1) tectonic, (2)carbonate, (3) carbonate system demise, and (4) siliciclastic phases, defined based on the intensity of such factors as tectonics, eustasy, climate, carbonate production, and siliciclastic supply. During the Late Cretaceous - Paleocene tectonic phase, the Coral Sea spreading triggered extensional tectonics, consequent uplift, and erosion which formed a structural configuration controlling the later evolution of the system. During the Eocene and late Oligocene - middle Miocene carbonate phase, basinal scale sedimentary geometries are largely controlled by eustatic seal level fluctuations. Because the geometry pattern identified within the carbonate sequences in the GoP mimics contemporaneous sedimentary geometry pattern observed in other pure carbonate and even siliciclastic depositional systems around the world, eustasy had to be the major factor influencing the GoP mixed system during this second phase. Although partial carbonate demise was observed during the early Miocene, the demise phase per se occurred during the late middle Miocene exposure of the system and its subsequent drowning in the early late Miocene, and was probably related to a major sea level rise enhanced by fold belt loading. During the Oligocene Peninsular Orogeny, the siliciclastics did not influence the carbonate system because they were trapped in the Aure Trough, a foreland basin to the northeast of the study area. The siliciclastic phase in the GoP was initiated during the late Miocene Central Range Orogeny. At that time and in the early Pliocene, siliciclastic infill was limited to the deep troughs in northeast corner of the GoP. The major siliciclastic input and progressive burial of the GoP carbonate system only occurred in the late Pliocene, as a response to the contemporaneous renewed uplift and exhumation of Peninsular region. During this fourth phase, the siliciclastics infilled 3-4 km deep troughs and completely buried the most of the carbonate system. The northern end of the Great Barrier Reef along with several large isolated carbonate platforms located far away from the siliciclastic sources are still active today.

The history of relative sea-level rise along the northern Gulf of Mexico must be constrained in order to determine the relative effects of eustatic sea-level rise, subsidence, antecedent topography, and sediment supply variations on fluvial--bay-shoreline sedimentary systems. This study adds important additional sea-level indicators for the past 10 kyrs in addition to compiling the extensive pre-existing data from the literature. The northern Gulf of Mexico data from the modern shoreline is compared western and eastern Gulf of Mexico datasets to determine the relative difference in subsidence rates over the past 4 kyrs. Subsidence differences are negligible. Furthermore, quantification of the antecedent topography provides a means to account for its effects on sedimentary architecture and the evolution of the Sabine and Calcasieu river-bay systems. The record of eustasy potentially indicates 3 to 4 meter-scale rapid rise intervals during the early Holocene. Subsequent to 7.5 ka, the progradation and retrogradation of the sedimentary systems must be attributed to sediment supply variations (climate change). From 7.5 ka to ∼3 ka, the east Texas, west Louisiana climate oscillated between sub-humid to sub-arid to produce greater than modern sediment flux manifested as deltaic deposits in the modern estuaries. Important future applications of this study include comparison to the nature and timing of fluvial-deltaic retreat in other estuaries along the Gulf of Mexico and Atlantic coasts. The South Shetland Islands, off the western side of the Antarctic Peninsula, are separated by glacial troughs carved during glacial maxima. These glacial troughs are currently fjords which contain a glaciomarine sedimentary record. Age constraining the sediments provides a retreat history of the ice cap for the past 15 kyrs including rates and magnitude of retreat for sub-polar glacial systems. Furthermore, the timing of the migration of sub-glacial polar (cold-based) glacial conditions southward is constrained to ∼10kyr. This has important implications for Holocene glacial flow rates and ice shelf stability in the Antarctic Peninsula region.

The study of tidewater glacier systems from the Last Glacial Maximum to the Present in southern Patagonia provides a relatively continuous high-resolution sedimentary record of climate change. This record enables us to establish the style and rate of sedimentation in the basin, as well as to determine the glacial history of the fjord with respect to the surrounding regions and hemispheric climate forcing. A comprehensive marine geologic study was conducted in Marinelli Fjord (54°S), southern Chile. A major transition is sedimentation at 12.5 ka marks the retreat of Marinelli Glacier with no evidence for glacial re-advance. This is consistent with the climatic trends for southern South America where the final deglaciation of the region ended at ∼12 ka, indicating a Southern Hemisphere climatic forcing. Marinelli Glacier has undergone a modern rapid retreat that is unprecedented in the time interval we recorded and is not related to hemispheric-scale forcing mechanisms.