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Department of Earth and Atmospheric Sciences: Faculty Publications

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Articles 481 - 510 of 673

Full-Text Articles in Earth Sciences

Depositional Environments For Strata Cored In Crp-3 (Cape Roberts Project), Victoria Land Basin, Antarctica: Palaeoglaciological And Palaeoclimatological Inferences, R. D. Powell, M. G. Laird, T. R. Naish, Christopher R. Fielding, L. A. Krissek, J.J. M. Van Der Meer Jan 2001

Depositional Environments For Strata Cored In Crp-3 (Cape Roberts Project), Victoria Land Basin, Antarctica: Palaeoglaciological And Palaeoclimatological Inferences, R. D. Powell, M. G. Laird, T. R. Naish, Christopher R. Fielding, L. A. Krissek, J.J. M. Van Der Meer

Department of Earth and Atmospheric Sciences: Faculty Publications

Cape Roberts Project drill core 3 (CRP-3) was obtained from Roberts ridge, a sea-floor high located at 77oS, 12 km offshore from Cape Roberts in western McMurdo Sound, Antarctica. The recovered core is about 939 m long and comprises strata dated as being early Oligocene (possibly latest Eocene) in age, resting unconformably on ~116 m of basement rocks consisting of Palaeozoic Beacon Supergroup sediments. The core includes ten facies commonly occurring in five major associations that are repeated in particular sequences throughout the core and which are interpreted as representing different depositional environments through time. Depositional systems inferred …

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Comparison Of Interannual Snowmelt-Onset Dates With Atmospheric Conditions, Sheldon D. Drobot, Mark R. Anderson Jan 2001

Comparison Of Interannual Snowmelt-Onset Dates With Atmospheric Conditions, Sheldon D. Drobot, Mark R. Anderson

Department of Earth and Atmospheric Sciences: Faculty Publications

The snowmelt-onset date represents an important transitional point in the Arctic surface energy balance, when albedo decreases and energy absorption increases rapidly in response to the appearance of liquid water. Interannual variations in snowmelt onset are likely related to large-scale variations in atmospheric circulation, such as described by the Arctic Oscillation (AO). This research therefore examines the relationship between monthly-averaged AO values and mean annual snowmelt-onset dates over Arctic sea ice in 13 regions, from 1979 to 1998. The objective is to statistically relate variations in mean annual regional snowmelt-onset dates to variations in the AO. Additionally, monthly-averaged 500 hPa …

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The Onset Of Arctic Sea-Ice Snowmelt As Detected With Passive- And Active-Microwave Remote Sensing, Richard R. Forster, David G. Long, Kenneth C. Jezek, Sheldon D. Drobot, Mark R. Anderson Jan 2001

The Onset Of Arctic Sea-Ice Snowmelt As Detected With Passive- And Active-Microwave Remote Sensing, Richard R. Forster, David G. Long, Kenneth C. Jezek, Sheldon D. Drobot, Mark R. Anderson

Department of Earth and Atmospheric Sciences: Faculty Publications

Daily acquisitions from satellite microwave sensors can be used to observe the spatial and temporal characteristics of the Arctic sea-ice snowmelt onset because the initial presence of liquid water in a dry snowpack causes a dramatic change in the active and passive-microwave response. A daily sequence of backscatter coefficient images from the NASA scatterometer (NSCAT) clearly shows the spatially continuous progression of decreasing backscatter associated with snowmelt onset across the Arctic Ocean during spring 1997. A time series of the active NSCAT backscatter and a scattering index from the passive Special Sensor Microwave/Imager (SSM/I) show similar trends during the time …

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Spatial And Temporal Variability In Snowmelt Onset Over Arctic Sea Ice, Mark R. Anderson, Sheldon D. Drobot Jan 2001

Spatial And Temporal Variability In Snowmelt Onset Over Arctic Sea Ice, Mark R. Anderson, Sheldon D. Drobot

Department of Earth and Atmospheric Sciences: Faculty Publications

Climate models suggest surface warming in the Arctic will be rapid and pronounced, implying substantial changes in snowmelt onset are likely. This research therefore examines spatial and temporal variability in passive-microwave derived snowmelt-onset dates over Arctic sea ice. The objectives are to understand better the regional characteristics of snowmelt and to document whether the snowmelt-onset record shows signs of climate change. Snowmelt-onset dates are derived with Scanning Multichannel Microwave Radiometer and Special Sensor Microwave/Imager brightness-temperature data, and they are subsequently stratified into 13 regions to analyze spatial and temporal variability. Results illustrate significant spatial variability in snowmelt onset, with the …

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Drawdown And Stream Depletion Produced By Pumping In The Vicinity Of A Partially Penetrating Stream, James J. Butler Jr., Vitaly A. Zlotnik, Ming-Shu Tsou Jan 2001

Drawdown And Stream Depletion Produced By Pumping In The Vicinity Of A Partially Penetrating Stream, James J. Butler Jr., Vitaly A. Zlotnik, Ming-Shu Tsou

Department of Earth and Atmospheric Sciences: Faculty Publications

Commonly used analytical approaches for estimation of pumping-induced drawdown and stream depletion are based on a series of idealistic assumptions about the stream-aquifer system. Anew solution has been developed for estimation of drawdown and stream depletion under conditions that are more representative of those in natural systems (finite width stream of shallow penetration adjoining an aquifer of limited lateral extent). This solution shows that the conventional assumption of a fully penetrating stream will lead to a significant overestimation of stream depletion (> 100%) in many practical applications. The degree of overestimation will depend on the value of the stream leakance …

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Laser-Derived Particle Size Data From Crp-3, Victoria Land Basin, Antarctica: Implications For Sequence And Seismic Stratigraphy, Christopher R. Fielding, G. B. Dunbar, S. M. Bryce Jan 2001

Laser-Derived Particle Size Data From Crp-3, Victoria Land Basin, Antarctica: Implications For Sequence And Seismic Stratigraphy, Christopher R. Fielding, G. B. Dunbar, S. M. Bryce

Department of Earth and Atmospheric Sciences: Faculty Publications

Seven hundred and nineteen samples from throughout the Cainozoic section in CRP-3 were analysed by a Malvern Mastersizer laser particle analyser, in order to derive a stratigraphic distribution of grain-size parameters downhole. Entropy analysis of these data (using the method of Woolfe & Michibayashi, 1995) allowed recognition of four groups of samples, each group characterised by a distinctive grain-size distribution. Group 1, which shows a multi-modal distribution, corresponds to mudrocks, interbedded mudrock/sandstone facies, muddy sandstones and diamictites. Group 2, with a sand-grade mode but showing wide dispersion of particle size, corresponds to muddy sandstones, a few cleaner sandstones and some …

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Chronostratigraphy Of The Crp-3 Drillhole, Victoria Land Basin, Antarctica, M J. Hannah, F Florindo, David M. Harwood, Christopher R. Fielding, Cape Roberts Science Team Jan 2001

Chronostratigraphy Of The Crp-3 Drillhole, Victoria Land Basin, Antarctica, M J. Hannah, F Florindo, David M. Harwood, Christopher R. Fielding, Cape Roberts Science Team

Department of Earth and Atmospheric Sciences: Faculty Publications

An 823 m thick glaciomarine Cenozoic section sitting unconformably on the Lower Devonian Beacon Supergroup was recovered in CRP –3. This paper reviews the chronostratigraphical constraints for the Cenozoic section. Between 3 and 480.27 mbsf 23 unconformity bounded cycles of sediment were recorded. Each unconformity is thought to represent a hiatus of uncertain duration. Four magnetozones have been recognised from the Cenozoic section. The record is complex with several “tiny wiggles” recorded throughout. Biostratigraphical or Sr ages, which could be used to link these magnetozones to the magnetic polarity time scale are restricted to the upper 190 m of sediment. …

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Chemical And Biological Trends During Lake Evolution In Recently Deglaciated Terrain, Daniel R. Engstrom, Sherilyn C. Fritz, James E. Almendinger, Stephen Juggins Nov 2000

Chemical And Biological Trends During Lake Evolution In Recently Deglaciated Terrain, Daniel R. Engstrom, Sherilyn C. Fritz, James E. Almendinger, Stephen Juggins

Department of Earth and Atmospheric Sciences: Faculty Publications

As newly formed landscapes evolve, physical and biological changes occur that are collectively known as primary succession. Although succession is a fundamental concept in ecology, it is poorly understood in the context of aquatic environments. The prevailing view is that lakes become more enriched in nutrients as they age, leading to increased biological production. Here we report the opposite pattern of lake development, observed from the water chemistry of lakes that formed at various times within the past 10,000 years during glacial retreat at Glacier Bay, Alaska. The lakes have grown more dilute and acidic with time, accumulated dissolved organic …

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Shifts In Mid- To Late-Holocene Anion Composition In Elk Lake (Grant County, Minnesota): Comparison Of Diatom And Ostracode Inferences, Jasmine E. Saros, Sherilyn C. Fritz, Alison J. Smith May 2000

Shifts In Mid- To Late-Holocene Anion Composition In Elk Lake (Grant County, Minnesota): Comparison Of Diatom And Ostracode Inferences, Jasmine E. Saros, Sherilyn C. Fritz, Alison J. Smith

Department of Earth and Atmospheric Sciences: Faculty Publications

The fossil diatom record from Elk Lake (Grant County, Minnesota) was used to reconstruct salinity and brine type between 2640 and 4645 14C yr BP. This lake was selected for a brine-type reconstruction because a previous study using fossil-ostracode assemblages indicated a shift in anion composition during the mid-Holocene (Smith et al., 1997). Salinity was reconstructed using a transfer function developed for the Northern Great Plains (NGP) of North America; the reconstruction revealed that salinity was higher (1.5–6.2 g l−1) between ~4000 and 4645 14C yr BP and dropped to 0.35–1.2 g l−1 after 4000 14C yr …

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Hydrologic Variation In The Northern Great Plains During The Last Two Millennia, Sherilyn C. Fritz, Emi Ito, Zicheng Yu, Kathleen R. Laird, Daniel R. Engstrom Mar 2000

Hydrologic Variation In The Northern Great Plains During The Last Two Millennia, Sherilyn C. Fritz, Emi Ito, Zicheng Yu, Kathleen R. Laird, Daniel R. Engstrom

Department of Earth and Atmospheric Sciences: Faculty Publications

Reconstructions of lake-water salinity at decadal resolution for the last 2,000 years are compared among three lakes in North Dakota to infer regional patterns of drought. The intersite comparisons are used to distinguish local variation in climate or hydrology from regional patterns of change. At one lake, diatom-inferred salinity and lake-water Mg/Ca inferred from ostracode shell chemistry are coherent, both in terms of direction and magnitude of change, indicating that each is a robust technique for reconstructing lake-water chemistry. The data show that the last 2,000 years have been characterized by frequent shifts between high and low salinity, suggesting shifts …

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Spaceborne Microwave Remote Sensing Of Arctic Sea Ice During Spring, Sheldon D. Drobot, Mark R. Anderson Jan 2000

Spaceborne Microwave Remote Sensing Of Arctic Sea Ice During Spring, Sheldon D. Drobot, Mark R. Anderson

Department of Earth and Atmospheric Sciences: Faculty Publications

This paper outlines the fundamental roles sea ice plays during the spring Arctic climate, and it demonstrates the use of passive microwave remote sensing in measuring climatically important sea ice variables during the spring transitional period. It discusses the theoretical concepts underlying passive microwave remote sensing of sea ice, and it summarizes the historical use of satellite microwave radiometry in the Arctic region. In addition, this paper discusses the derivation of climatically important sea ice variables, including sea ice extent, concentration, multiyear ice fraction, and snow melt onset, with additional comments on the precision and accuracy of the remote sensing …

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Facies Analysis And Sequence Stratigraphy Of Crp-2/2a, Victoria Land Basin, Antarctica, Christopher R. Fielding, T R. Naish, K J. Woolfe, M A. Lavelle Jan 2000

Facies Analysis And Sequence Stratigraphy Of Crp-2/2a, Victoria Land Basin, Antarctica, Christopher R. Fielding, T R. Naish, K J. Woolfe, M A. Lavelle

Department of Earth and Atmospheric Sciences: Faculty Publications

The Oligocene to Quaternary succession encountered in CRP-2/2A is divided into twelve recurrent lithofacies (some of which have been subdivided further), reflecting a range of marine, glacimarine and possibly subglacial environments of sediment accumulation. A cyclical vertical arrangement of lithofacies was noted throughout the core, and is used as the basis for a sequence stratigraphic analysis. Twenty-four sequences are recognised, each of which begins with a Sequence Boundary (Glacial Surface of Erosion), and each is interpreted to record a cycle of glacial advance and retreat with associated changes in relative sea-level. During at least some of these cycles, ice is …

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Chronostratigraphy Of Crp-2/2a, Victoria Land Basin, Antarctica, G S. Wilson, S. M. Bohaty, Christopher R. Fielding, F. Florindo, M. J. Hannah, David M. Harwood, W. C. Mcintosh, T. R. Naish, A. P. Roberts, L. Sagnotti, R. P. Scherer, C. P. Strong, K. L. Verosub, G. Villa, David K. Watkins, P. N. Webb, K. J. Woolfe Jan 2000

Chronostratigraphy Of Crp-2/2a, Victoria Land Basin, Antarctica, G S. Wilson, S. M. Bohaty, Christopher R. Fielding, F. Florindo, M. J. Hannah, David M. Harwood, W. C. Mcintosh, T. R. Naish, A. P. Roberts, L. Sagnotti, R. P. Scherer, C. P. Strong, K. L. Verosub, G. Villa, David K. Watkins, P. N. Webb, K. J. Woolfe

Department of Earth and Atmospheric Sciences: Faculty Publications

The 624.15 m glaciomarine sedimentary succession recovered in the CRP-2/2A drillcore comprises lower Oligocene (< c. 31 Ma) to lower Miocene (18.5 Ma) strata that are overlain by a thin succession of Pliocene and Pleistocene strata. The age model for the CRP-2/2A drillhole, as presented in this paper, is based on combined microfossil biostratigraphy, 40Ar/39Ar ages on volcanic material, 87Sr/86Sr analyses on mollusc shells, and correlation of a magnetic polarity zonation to the magnetic polarity time scale (MPTS). Between 25.92 and 109.05 metres below sea floor (mbsf), several alternative correlations to the MPTS are possible, all of which suggest that sediment accumulation rates averaged ~180 m/m.y. between unconformities, although actual sedimentation rates may have been higher. Between 109.05 and 306.65 mbsf, the age model is straightforward and average sedimentation rates were much higher …

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Variability, Petrography And Provenance Of Basement Clasts In Core From Crp-2/2a, Victoria Land Basin, Antarctica, F Talarico, S Sandroni, Christopher R. Fielding, C Atkins Jan 2000

Variability, Petrography And Provenance Of Basement Clasts In Core From Crp-2/2a, Victoria Land Basin, Antarctica, F Talarico, S Sandroni, Christopher R. Fielding, C Atkins

Department of Earth and Atmospheric Sciences: Faculty Publications

Distribution patterns, petrography, whole-rock and mineral chemistry, and shape and fabric data are described for the most representative basement lithologies occurring as clasts (granule to boulder grain-size class) from the 625 m deep CRP-2/2A drillcore. A major change in the distribution pattern of the clast types occurs at c. 310 mbsf, with granitoid-dominated clasts above and mainly dolerite clasts below; moreover, compositional and modal data suggest a further division into seven main detrital assemblages or petrofacies. In spite of this variability, most granitoid pebbles consist of either pink or grey biotite±hornblende monzogranites. Other less common and ubiquitous lithologies include …

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Chronostratigraphy Of Crp-2/2a, Victoria Land Basin, Antarctica, G S. Wilson, S. M. Bohaty, Christopher R. Fielding, F Florindo, M J. Hannah, David M. Harwood, W C. Mcintosh, T R. Naish, A. P. Roberts, L Sagnotti, R P. Scherer, C P. Strong, K L. Verosub, G Villa, David K. Watkins, P N. Webb, K J. Woolfe Jan 2000

Chronostratigraphy Of Crp-2/2a, Victoria Land Basin, Antarctica, G S. Wilson, S. M. Bohaty, Christopher R. Fielding, F Florindo, M J. Hannah, David M. Harwood, W C. Mcintosh, T R. Naish, A. P. Roberts, L Sagnotti, R P. Scherer, C P. Strong, K L. Verosub, G Villa, David K. Watkins, P N. Webb, K J. Woolfe

Department of Earth and Atmospheric Sciences: Faculty Publications

The 624.15 m glaciomarine sedimentary succession recovered in the CRP-2/2A drillcore comprises lower Oligocene (< c. 31 Ma) to lower Miocene (18.5 Ma) strata that are overlain by a thin succession of Pliocene and Pleistocene strata. The age model for the CRP-2/2A drillhole, as presented in this paper, is based on combined microfossil biostratigraphy, 40Ar/39Ar ages on volcanic material, 87Sr/86Sr analyses on mollusc shells, and correlation of a magnetic polarity zonation to the magnetic polarity time scale (MPTS). Between 25.92 and 109.05 metres below sea floor (mbsf), several alternative correlations to the MPTS are possible, all of which suggest that sediment accumulation rates averaged ~180 m/m.y. between unconformities, although actual sedimentation rates may have been higher. Between 109.05 and 306.65 mbsf, the age model is straightforward and average sedimentation rates were much higher …

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Kinematic Structure Of Minipermeameter Flow, Daniel M. Tartakovsky, J. David Moulton, Vitaly A. Zlotnik Jan 2000

Kinematic Structure Of Minipermeameter Flow, Daniel M. Tartakovsky, J. David Moulton, Vitaly A. Zlotnik

Department of Earth and Atmospheric Sciences: Faculty Publications

Minipermeameters are rapidly becoming a popular tool for collecting localized
measurements of permeability in both laboratory and field studies. While one of the main advantages of minipermeameters is their ability to collect data on various support volumes, there have been only limited attempts to analyze their size and geometry. We define the support volume of minipermeameter measurements as a region containing 90% of the total gas flow, i.e., a region bounded by the 10% streamline. Using our new semianalytical solutions for the Stokes' stream function, we demonstrate that the support volume has a shape of the semitoroid adjacent to the …

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Preliminary Results Of Bitumen And Whole-Rock Elemental Analyses Of Crp-2/2a, Victoria Land Basin, Antarctica, Richard Kettler, E. Papastavros Jan 2000

Preliminary Results Of Bitumen And Whole-Rock Elemental Analyses Of Crp-2/2a, Victoria Land Basin, Antarctica, Richard Kettler, E. Papastavros

Department of Earth and Atmospheric Sciences: Faculty Publications

Sediments and rocks recovered in CRP-2/2A coring operations contain relatively little organic matter (average TOC=0.28%) and very small amounts of solvent-soluble organic matter. Because Early Oligocene sediment included significant amounts of coal detritus, TOC values are higher in Early Oligocene rocks than in younger rocks. TOC values are highest in the fine-grained rocks deposited as part of the highstand systems tract (HST) and TOC values decrease from the bottom to the top of the HST. The TOC:TN ratios observed in the CRP-2/2A core typically exceed 10, and are strong evidence that the preserved organic matter comprises a mixture of detrital …

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Laser-Derived, Particle Size Data From Crp-2/2a: Implications For Sequence And Seismic Stratigraphy, K J. Woolfe, L K. Stewart, Christopher R. Fielding, M Lavelle Jan 2000

Laser-Derived, Particle Size Data From Crp-2/2a: Implications For Sequence And Seismic Stratigraphy, K J. Woolfe, L K. Stewart, Christopher R. Fielding, M Lavelle

Department of Earth and Atmospheric Sciences: Faculty Publications

Gravel-free, high-resolution (1-metre spacing, 32 channel) particle size data from the CRP-2/2A drill core indicate that many of the diamictites were likely deposited from floating ice. Textural dislocations occur at most sequence boundaries and provide independent corroboration of the sequence stratigraphic interpretation. Likewise the data largely support the correlation drawn (Fielding et al., this volume) between the sequence stratigraphic cycles and the regional seismic stratigraphy (an alternative correlation to Reflector ‘f’ is also suggested). The gravel-free data appear to be reflecting predominantly regional (global?) forcing with some possible local effects, and long-term trends persisting through gravelly textural dislocations.

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Morphology And Taxonomic Position Of The Late Cretaceous Diatom Genus Pomphodiscus Barker & Meakin, Vladimir A. Nikolaev, David M. Harwood Jan 2000

Morphology And Taxonomic Position Of The Late Cretaceous Diatom Genus Pomphodiscus Barker & Meakin, Vladimir A. Nikolaev, David M. Harwood

Department of Earth and Atmospheric Sciences: Faculty Publications

Results from our investigation of Upper Cretaceous diatoms from the Marca Shale Member of the Moreno Shale in California and from Ocean Drilling Program (ODP) Hole 748C on the Kerguelen Plateau ,Southern Indian Ocean enable a clarification of the taxonomic position of several diatoms. Differences in areola structure ,a primary and conservative character of the diatom valve, are used to separate diatoms recently included in the genus Benetorus. We resurrect he genus Pomphodiscusto include species with locular areolae, a central rimoportula ,and a central inflated chamber .We propose the new species Pomphodiscusk erguelensisn. sp. and new combination Pomphodiscusc …

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Oligocene And Lower Miocene Siliceous Microfossil Biostratigraphy Of Cape Roberts Project Core Crp-2/2a, Victoria Land Basin, Antarctica, R. Scherer, S. M. Bohaty, David M. Harwood Jan 2000

Oligocene And Lower Miocene Siliceous Microfossil Biostratigraphy Of Cape Roberts Project Core Crp-2/2a, Victoria Land Basin, Antarctica, R. Scherer, S. M. Bohaty, David M. Harwood

Department of Earth and Atmospheric Sciences: Faculty Publications

Marine diatoms are the primary biostratigraphical and palaeoenvironmental tool for interpreting the upper Palaeogene and lower Neogene strata recovered during the second drilling season of the Cape Roberts Project at site CRP-2 in the western Ross Sea, Antarctica. Silicoflagellates, ebridians, and a chrysophyte cyst provide supporting biostratigraphical information. More than 100 dominantly planktic diatom taxa are recognised. Of these, more than 30 are treated informally, pending SEM examination and formal description. Many other taxa are noted only to generic level. Lower Oligocene (c. 31Ma) through lower Miocene (c. 18.5 Ma) diatoms occur from 28 mbsf down to 565 …

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Nutrients As A Link Between Ionic Concentration/Composition And Diatom Distributions In Saline Lakes, J. E. Saros, Sherilyn C. Fritz Jan 2000

Nutrients As A Link Between Ionic Concentration/Composition And Diatom Distributions In Saline Lakes, J. E. Saros, Sherilyn C. Fritz

Department of Earth and Atmospheric Sciences: Faculty Publications

Diatom profiles in closed-basin lake sediments are commonly used to reconstruct climate change based on the observed correlations between salinity (ionic concentration) and modern diatom assemblages. Diatom assemblages are strongly correlated not only with salinity but also anion composition, with certain taxa characteristic of carbonate systems and others sulfate-dominated waters. Although strong correlations exist, the actual mechanisms behind these correlations are unknown. Here we briefly review the influence of salinity and ionic composition on nutrient dynamics in saline lakes and suggest that these interactions may drive shifts in diatom species composition along gradients of ionic concentration/ composition. We discuss the …

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Clay Mineral Composition Of Glacial Erratics, Mcmurdo Sound, Mary Anne Holmes Jan 2000

Clay Mineral Composition Of Glacial Erratics, Mcmurdo Sound, Mary Anne Holmes

Department of Earth and Atmospheric Sciences: Faculty Publications

Twenty-two erratics collected from coastal moraines along the shores of Mount Discovery, Brown Peninsula, Minna Bluff, on Black Island, and from the Salmon and Miers valley floors in East Antarctica were examined for their mineral composition in the <2 m fraction by x-ray diffraction to determine their provenance and the climate under which the sediment in the erratics formed. Semi-quantitative results from peak areas were subjected to principal components analysis and indicate that there are two distinct mineral compositions in the erratics (C = 0.05): A) dominant smectite group minerals, minor illite and kaolinite, and no chlorite, and B) dominant illite, subordinate smectite group, and either chlorite and R=l US clay or R=3 US clay. Group A erratics include two types: 1) Eocene age siliciclastic sediment and 2) volcaniclastics of unknown age. Group B erratics comprise three types: 1) Eocene age siliciclastic sediment dominated by illite with subordinate smectite, no chlorite, and very low levels of kaolinite and mixed-layer clays; 2) post Eocene age erratics dominated by illite with a major component of chlorite and R=l US clay, minor or no smectite and kaolinite; and 3) post Eocene age erratics dominated by illite and containing R=3 US clay. Eocene age sediment occurs in either group and so had two distinct provenances for the clay fraction: a smectite-dominant area and an illite-rich, smectite-poor area. Post Eocene age sediment also had two distinct provenances for the clay fraction and are different from the Eocene sources: a metamorphic + ancient sedimentary terrain that supplied chlorite, illite, and R=l US clay to some of the erratics, and a sedimentary terrain that supplied illite and R=3 US clay. Kaolinite levels are low, indicating the absence of intense weathering and/or any significant contribution from the Beacon Supergroup.

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Isotopic Signature Of Burial Diagenesis And Primary Lithological Contrasts In Periplatform Carbonates (Miocene, Great Bahama Bank), Tracy D. Frank, Karin Bernet Jan 2000

Isotopic Signature Of Burial Diagenesis And Primary Lithological Contrasts In Periplatform Carbonates (Miocene, Great Bahama Bank), Tracy D. Frank, Karin Bernet

Department of Earth and Atmospheric Sciences: Faculty Publications

The stable isotope geochemistry of Miocene sediments from the leeward margin of the Great Bahama Bank was examined to investigate burial diagenetic processes in periplatform carbonates. Data indicate that, in addition to differences in bulk proportions of neritic and pelagic carbonate along the slope, rhythmic variation in primary carbonate content has controlled patterns of burial diagenesis and associated geochemical signatures throughout much of the succession examined. The present study focuses on Ocean Drilling Program Sites 1006 and 1007, the most distal of five sites drilled from marginal to deep basin environments during Leg 166. These Miocene sections are characterized by …

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Palaeogene Calcareous Nannofossils From Crp-2/2a, Victoria Land Basin, Antarctica, David K. Watkins, G. Villa Jan 2000

Palaeogene Calcareous Nannofossils From Crp-2/2a, Victoria Land Basin, Antarctica, David K. Watkins, G. Villa

Department of Earth and Atmospheric Sciences: Faculty Publications

Rare calcareous nannofossils from the Cape Roberts Project drillhole CRP-2A indicate that this area was episodically invaded by marginal oceanic surface waters during the late and late early Oligocene. These depauperate assemblages lack most of the biostratigraphic index fossils for the Oligocene, but do provide two datums that aid in constraining the age of the section: the last appearance datum (LAD) of Dictyococcites bisectus (23.9 Ma) at 149.28 mbsf and the LAD of Chiasmolithus altus (26.1 Ma) at 412.25 mbsf. Calcareous nannofossil assemblages stratigraphically below c. 440 mbsf contain conspicuous evidence of reworking of older (late Eocene) specimens that renders …

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Diagenesis Of Lower Cretaceous Pelagic Carbonates, North Atlantic: Paleoceanographic Signals Obscured, Tracy D. Frank, Michael A. Arthur, Walter E. Dean Oct 1999

Diagenesis Of Lower Cretaceous Pelagic Carbonates, North Atlantic: Paleoceanographic Signals Obscured, Tracy D. Frank, Michael A. Arthur, Walter E. Dean

Department of Earth and Atmospheric Sciences: Faculty Publications

The stable isotope and minor element geochemistry of Neocomian (Lower Cretaceous) pelagic carbonates of the North Atlantic Basin (Deep Sea Drilling Project Sites 105, 367, 387, 391, and 603) was examined to develop a diagenetic model for pelagic limestones. In particular, we hoped to test the fidelity of whole-rock geochemical records as paleoceanographic indicators for pelagic deposits of pre-Aptian age, in which individual microfossils are not available for analysis. Data indicate that in addition to depth of burial, rhythmic variations in primary carbonate content have strongly controlled diagenetic patterns and associated geochemical signatures in these Neocomian sequences. Samples become increasingly …

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Interannual Variations In Snowmelt Onset And Links To 500 Hpa Atmospheric Anomalies Over The Arctic, Sheldon D. Drobot, Mark R. Anderson Jul 1999

Interannual Variations In Snowmelt Onset And Links To 500 Hpa Atmospheric Anomalies Over The Arctic, Sheldon D. Drobot, Mark R. Anderson

Department of Earth and Atmospheric Sciences: Faculty Publications

Interannual variations in the melt onset of snow provide a mechanism to observe climatic fluctuations. Timing of initial ablation is associated with certain poorly defined overlying atmospheric conditions. This paper investigates the spatial and temporal patterns in melt onset dates and associated 500 hPa height anomalies over the Arctic region from 1982 to 1992. Melt onset dates are derived from Scanning Multichannel Microwave Radiometer (SMMR) and Special Sensor Microwave Imager (SSM/I) data, while 500 hPa height anomalies are computed from the National Centers for Environmental Protection (NCEP) reanalysis models. Results indicate significant interannual variations in the spatial pattern and timing …

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Tectonic Forcings Of Maastrichtian Ocean-Climate Evolution, Tracy D. Frank, Michael A. Arthur Apr 1999

Tectonic Forcings Of Maastrichtian Ocean-Climate Evolution, Tracy D. Frank, Michael A. Arthur

Department of Earth and Atmospheric Sciences: Faculty Publications

A global compilation of deep-sea isotopic records suggests that Maastrichtian ocean-climate evolution was tectonically driven. During the early Maastrichtian the Atlantic intermediate-deep ocean was isolated from the Pacific, Indian, and Southern Oceans; deep water formed in the high-latitude North Atlantic and North Pacific. At the early/late Maastrichtian boundary a major reorganization of oceanic circulation patterns occurred, resulting in the development of a thermohaline circulation system similar to that of the modem oceans. A combination of isotopic and plate kinematic data suggests that this event was triggered by the final breaching of tectonic sills in the South Atlantic and the initiation …

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Mountain Evolution And Environmental Changes Of Huangshan (Yellow Mountain), China, Pei-Hua Huang, Robert F. Diffendal Jr., Min-Qing Yang, Patricia E. Helland Mar 1999

Mountain Evolution And Environmental Changes Of Huangshan (Yellow Mountain), China, Pei-Hua Huang, Robert F. Diffendal Jr., Min-Qing Yang, Patricia E. Helland

Department of Earth and Atmospheric Sciences: Faculty Publications

Huangshan (Yellow Mountain) is located in southern part of the lower reaches of the Yangtze River. The highest Lotus Flower peak is 1,864 m above sea level. Formative ages of the Huangshan and its granite, process of mountain geomorphic evolution from the Eocene to Quaternary, environmental changes of Quaternary, formative origin of beautiful peaks and fascinating rocks were studied and the questionable “Pleistocene glaciation” was also discussed in this paper.

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Evaluation Of Stream Depletion Considering Finite Stream Width, Shallow Penetration, And Properties Of Streambed Sediments, Vitaly A. Zlotnik, Huihua Huang, James J. Butler Jr. Jan 1999

Evaluation Of Stream Depletion Considering Finite Stream Width, Shallow Penetration, And Properties Of Streambed Sediments, Vitaly A. Zlotnik, Huihua Huang, James J. Butler Jr.

Department of Earth and Atmospheric Sciences: Faculty Publications

Commonly used methods for estimation of pumping-induced stream depletion are based on a series of idealistic assumptions about the stream-aquifer interface. In many cases, however, these assumptions are not consistent with field conditions. In order to obtain stream-depletion estimates that are based on assumptions more appropriate for conditions often faced in the field, a new analytical model is proposed. This model, which incorporates the effects of finite stream width, shallow stream penetration, and a low permeability streambed, is based on the Dupuit assumptions and a steady-state representation of flow across the streambed. A general solution for stream depletion is developed …

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Lethal Sandslides From Eolian Dunes, David B. Loope, Joseph A. Mason, Lowell Dingus Jan 1999

Lethal Sandslides From Eolian Dunes, David B. Loope, Joseph A. Mason, Lowell Dingus

Department of Earth and Atmospheric Sciences: Faculty Publications

Fossil vertebrates entombed within the Upper Cretaceous Djadokhta Formation of southern Mongolia bear testimony to a heretofore unknown geologic phenomenon: mass wasting of eolian dunes during heavy rainstorms. Evaporation of shallow-penetrating rainwater led to progressive calcite accumulation in a thin layer of sand about 0.5 m below the surface of dune lee slopes. During rare heavy rainstorms, a perched water table developed at the top of calcitic zones. Positive pore water pressure led to translational slides and fast-moving sediment gravity flows that overwhelmed animals on the lee slopes of large dunes and in interdune areas.

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