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Full-Text Articles in Physical Sciences and Mathematics
Chemical And Biological Trends During Lake Evolution In Recently Deglaciated Terrain, Daniel R. Engstrom, Sherilyn C. Fritz, James E. Almendinger, Stephen Juggins
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 …
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
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 …
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
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 …
Isotopic Signature Of Burial Diagenesis And Primary Lithological Contrasts In Periplatform Carbonates (Miocene, Great Bahama Bank), Tracy D. Frank, Karin Bernet
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 …
Preliminary Results Of Bitumen And Whole-Rock Elemental Analyses Of Crp-2/2a, Victoria Land Basin, Antarctica, Richard Kettler, E. Papastavros
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 …
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
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 …
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
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.
Palaeogene Calcareous Nannofossils From Crp-2/2a, Victoria Land Basin, Antarctica, David K. Watkins, G. Villa
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 …
Spaceborne Microwave Remote Sensing Of Arctic Sea Ice During Spring, Sheldon D. Drobot, Mark R. Anderson
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 …
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
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 …
Nutrients As A Link Between Ionic Concentration/Composition And Diatom Distributions In Saline Lakes, J. E. Saros, Sherilyn C. Fritz
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 …
Clay Mineral Composition Of Glacial Erratics, Mcmurdo Sound, Mary Anne Holmes
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.
Morphology And Taxonomic Position Of The Late Cretaceous Diatom Genus Pomphodiscus Barker & Meakin, Vladimir A. Nikolaev, David M. Harwood
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 …
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
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 …
Kinematic Structure Of Minipermeameter Flow, Daniel M. Tartakovsky, J. David Moulton, Vitaly A. Zlotnik
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 …
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
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 …
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
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 …