Browsing by Subject "Southern Indiana"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Geochemical Analysis of Late Middle Pennsylvanian Cores From Southern Indiana
    (Office of the Vice Chancellor for Research, 2016-04-08) Henke, Alyssa
    During the late middle Pennsylvanian (~300 Ma) southern Indiana was a tropical inland, (epeiric) sea characterized by repeated fluctuations in sea-level. During this period, a massive glacier covered much of an ancient continent: Gondwana. When the ice area expanded during the Pennsylvanian, sea-level lowered, forming extensive peatlands along the exposed shores. The geologic record also shows there were periods when the amount of ice decreased, and the melting water raised sea-level, flooding the coastal peatlands. The coal layers formed from the compaction and lithification of the extensive peat-beds have been studied for economic value. These coals retain some record of sea-level fall and subsequent rise. Above the coal seam is a layer of organic-rich black shale, deposited during a transgression as seawater flooded the area. However, this interpretation is debated because marine fossils are not always deposited at these transitions. We are using reactive iron, pyrite concentrations, and sulfur isotopes as paleoenvironmental proxies for glaciation, atmospheric CO2, and dust and iron influx. Pyrite accumulation in shale is controlled by sulfate availability, reactive iron delivery, and quantity of organic matter. Using data from pyrite extraction, sulfur concentration can be used in conjunction with reactive iron totals as a proxy for determining freshwater or marine dominated system environments. Sequential iron extractions can determine mineral speciation of Fe, to show how much iron is locked in the sediment as sulfides, oxides, and carbonates. In addition, highly reactive iron and total iron ratios (FeHR/FeT) is an indication of oxic, anoxic, or euxinic (anoxic and sulfidic) conditions, and can be used as a representation of dust input from the erosion of ancient mountain ranges. Preservation of highly reactive iron occurs in an anoxic environment. We anticipate that the data may provide evidence for anoxic or euxinic depositional environment, with a possibility of high dust input.
  • Thumbnail Image
    Item
    Pyrite Analysis of an Ordovician Phosphate Rock Core from Southern Indiana
    (Office of the Vice Chancellor for Research, 2016-04-08) Orazi, Daniel
    Understanding the depositional environments that preserve phosphate-rich rock is becoming progressively more important in light of the increasing scarcity of phosphorus. Phosphorus is the primary constituent in one of the most common types of fertilizer, and it is also used in industries ranging from semiconductor production to flame retardant clothing. Phosphate beds are currently accumulating along select active and passive coastal margins through oceanic upwelling. Upwelling occurs when cold deep phosphorus-rich waters flow to the surface from wind-driven circulation. The nutrient-rich waters increase phytoplankton productivity creating an oxygen minimum zone (OMZ) with available dissolved iron. Southern Indiana is home to a deposit of phosphate rock that formed in a drastically different environment. Throughout much of the Ordovician (488.3-443.7 Mya), Indiana was partially submerged by a shallow (~10m-150m deep) tropical inland sea. The area was situated approximately 20o south of the equator in a position that would be similar to modern-day Brazil, as a member of the ancient landmass called Laurentia. The oxygen concentrations of the inland sea control phosphatization and the materialization of other minerals, including pyrite (FeS2). Pyrite formation is fundamental to geochemical proxies used to determine seawater and sediment traits in ancient environments. It can be formed through a variety of pathways including direct precipitation, solid monosulfide conversion, hydrogen sulfide (H2S) reaction, and iron loss preceding oxidation. The distinct mechanisms driving pyrite formation can be determined through the isotopic signature and the abundance of sulfide released through chromium reducible sulfur (CRS) methods. This study seeks to better understand the ancient water column and pore water characteristics of Ordovician Indiana. We present pyrite concentration isotope data and total phosphorous data to better understand the environmental conditions under which these sediments formed. Identifying these characteristics will add significantly to existing knowledge on phosphate accumulation independent of the oceanic upwelling model. Mentor: William P. Gilhooly III, Department of Earth Sciences, School of Science, IUPUI