Thursday, September 18, 2014
Dr. Neil J. Tabor, Professor at Southern Methodist University
Title: Adventures through the Continental Permian-Triassic Boundary
Host: Erik Gulbranson
This presentation will explore work that has been done in Upper Permian and Lower Triassic strata in the southwestern United States, South Africa and China. Much of the work is focused on lithostratigraphy and geochemistry as a mean of evaluating paleoenvironments and climatic change including estimates of rainfall, temperature and atmospheric PCO2 across one of the most important biological crises of the Phanerozoic; the Permian-Triassic boundary.
Thursday, October 16, 2014
Grad Students: GSA Practice
Thursday, October 23, 2014
GSA Conference: No Colloquium
Thursday, October 30, 2014
Dr. Tina R. Hill, Department of Geosciences Lecturer, University of Wisconsin Milwaukee
Title: TEM Investigation of Nano-scale Precipitates in Ultrahigh-Pressure Clinopyroxenes
Silica and silica-rich minerals are observed in cores of ultrahigh-pressure (UHP) clinopyroxenes from multiple UHP metamorphic terranes. Precise identification of these minerals is important as they are often used as indicators for the existence of previous UHP metamorphism, particularly when other mineralogic evidence has been destroyed through exhumation. These minerals are typically too small to obtain exact polymorphic identification, so atomic-scale methods must be employed. This investigation details the Transmission Electron Microscope (TEM) characterization of epitaxially-exsolved nano-scale siliceous minerals in cores of UHP clinopyroxenes from eclogites of the Bohemian Massif and Western Gneiss Region, and a
Kokchetav Massif garnet pyroxenite. Few atomic-scale investigations have been carried out, and prior to this study, these siliceous minerals were always identified as the higher density silica polymorphs, quartz or coesite. High Resolution TEM and Scanning TEM (HRTEM/STEM) images and Selected Area Electron Diffraction now reveal the identification of each phase and the close structural and orientation relationships of these siliceous phases with their host pyroxenes.
We consider a complex combination of factors in investigating the reasons for the surprising presence of the lower pressure, low density siliceous phases of keatite, α-cristobalite, tridymite, siliceous glasses, and albite. Calculated vacancy contents in pyroxenes, interface matching between phases, localized OH contents, and nano-scale size effects likely all play a role in determining what siliceous phase exsolves from the host mineral.
High tensile strength and low thermal expansivity/compressibility of clinopyroxenes compared to the observed siliceous phases indicates exsolved phases may not affect the rheology of the exhuming rock, but may ultimately affect the interpretation of the P-T path.
Thursday, November 6, 2014
Dr. William DiMichele, Research Paleontologist and Curator at National Museum of Natural History, Smithsonian Institution
Title: The links between climate and biology in the Pennsylvanian ice-age tropics
Host: John Isbell, Erik Gulbranson
The Pennsylvanian coal age has for two hundred years been envisioned as a time of uninterrupted humid climates and steaming jungles. Recent changes in understanding have led to realization that physical and biological dynamics of that time were not, however, all that different from those of the Pleistocene. The similarities must be considered within the framework of a very different continental configuration and a much lower diversity world in the late Paleozoic. Fossil floras from the late Paleozoic track glacial-interglacial oscillations, and can be separated into the iconic wetland biome and several seasonally-dry biomes. The evolutionary dynamics of wetland and seasonally dry assemblages are different and reflect the differences in the effects glacial-interglacial periodicity on each, a consequence of the strong ties of plants to climate, and of the effect of climate fluctuations on habitat continuity.
Thursday, November 13, 2014
Elmo Rawling, Wisconsin Geological and Natural History Survey
Title: Geology of Dunes and Sandy Bay Barriers along Lake Michigan’s Door Peninsula: The Importance of Increased Sediment Supply Following High Lake Level Phases
Host: John Isbell
This presentation focuses on the geologic formation of dunes and sandy barrier beaches in Wisconsin’s Door Peninsula to document sedimentary responses to natural lake-level fluctuations. Dunes are not very common along the Lake Michigan shoreline in Wisconsin, but the three bay barriers studied were buried by wind-blown sand including dunes that have relief of up to ~60 feet. The purpose of this study was to document when the barriers formed and when the subsequent dune activity occurred. The chronology presented here for barrier emplacement and dune development is based on 65 optical ages that were collected from littoral sediment in the barriers (n = 17) and the overlying wind-blown sand (n = 48). The barriers initially formed during the Nipissing high lake phase (~6.0-4.5 thousand years ago), and were modified during the subsequent Algoma high (~3.4-2.3 thousand years ago). The majority of the dune ages fall into two primary groups that overlap with or are slightly younger than the ages acquired from the barriers. Dune development occurred rapidly when the sand supply increased as lake levels receded. In addition, some preliminary thoughts on research about Holocene sedimentary budgets in the Door Peninsula, and understanding the climatic controls of lake-level variability with tree rings, will be presented.
Thursday, November 20, 2014
Jay Zambito, Assistant Professor at Wisconsin Geological and Natural History Survey, University of Wisconsin – Extension
Title: Frac Sand and Related Natural Resources
Host: John Isbell
Wisconsin has some of the best frac sand in the world, and since 2011 the state has seen a large increase in frac sand mines, processing plants, and rail loading facilities. This talk will provide information on what frac sand is, how it is used, why and how it is being mined in Wisconsin, its connection to other natural resources, and research being undertaken at the WGNHS related to frac sand.
Thursday, December 4, 2014
Dr. Lixia Wang, Postdoctoral Researcher at University of Wisconsin – Milwaukee
Title: Transport of bacteria in saturated quartz sand: The effect of chemical and biological factors.
Host: Dr. Shangping Xu
Groundwater is an important source for drinking water supply. Microbial contaminants have been implicated in two-third of the waterborne disease outbreak. Understanding the fundamental processes, the governing factors and the interfacial interactions that contribute to the deposition of microbial contaminants to porous media is highly needed for bioremediation in the environment as well as water purification industry. In my talk, I will share my findings on the effects of (1) chemical factors including ionic strength, pH and concentration of phosphate, (2) biological factors including lipopolysaccharide (LPS), biofilm and biofilm extracellular polysaccharide (EPS), and strain type on bacterial transport and deposition in saturated sand columns. The behind mechanisms involving surface charge, hydrophobicity and steric force to bacterial attachment will be analyzed for their contributions by applying them into extend DLVO theory plus steric interaction.