Showing papers by "Philip A. Meyers published in 1981"

Sedimentary processes in the Great Lakes

Abstract: Sediments in the Great Lakes are subject to four general categories of processes: input, transport, deposition, and postdepositional alteration. Sedimentary input is from coastal erosion (64%), riverine input (26%), atmospheric transport (3%), and several lesser sources (7%). Once in the lake, sediments are transported to their place of deposition along the bottom and/or in suspension depending upon grain size and density. The rate of deposition in the Great Lakes is variable and ranges from zero in some areas to over 6000 g m/sup -2/yr /sup -1/ in the eastern basin of Lake Erie. After deposition, sediments undergo bioturbation, dissolution of carbonate and opal, remobilization of many metals followed by reprecipitation within the surficial oxidized layer, and degradation of organic compounds.

Environmental changes in Saginaw Bay, Lake Huron recorded by geolipid contents of sediments deposited since 1800

Abstract: Changes in organic materials preserved within sediments of Saginaw Bay deposited over the past two centuries record corresponding periods in the environmental history of this part of Lake Huron and its watershed. Sediments deposited since 1940 show an increasingly greater input of aquatic organic matter in response to accelerating cultural eutrophication of Saginaw Bay. Concentrations of fatty acids, sterols, fatty alcohols, and aliphatic hydrocarbons are higher in these modern sediments than in deeper ones. Molecular distributions of these geolipids reflect less aquatic material deeper in the sediments. Prior to 1875, sediment organic matter appears to be diluted by mineral matter from enhanced erosion caused by clearing of the watershed for farming and settlement. During this period there is better preservation of carbonate minerals due to quicker burial. Since 1875, petroleum components comprise over 90% of the total aliphatic hydrocarbon content of these sediments, reflecting the advent and continued existence of chronic, low-level petroleum contamination of this part of the Great Lakes.

Cretaceous Black Shales in Angola Basin of South Atlantic Ocean: ABSTRACT

Abstract: Conditions favorable to deposition of black shales in the deep ocean occurred several times during the Cretaceous. Anoxic sediments were laid down in the South Atlantic during two distinct periods, the Aptian-early Albian and the late Albian-Coniacian. At site 530 of DSDP Leg 75 in the Angola Basin, black shales averaging 5.1% and containing up to 16.5% organic carbon were found in a late Albian-Coniacian turbidite sequence. Shipboard analysis shows most of the organic matter to be of marine origin, although several layers contain some terrigenous material. Based upon Rock Eval pyrolysis and the absence of significant amounts of light hydrocarbons, all of this organic matter is classified as immature. Thicknesses of the black shale layers are generally several centimeters or less, and they are separated by fine-grained turbidites containing less than 0.3% organic carbon. These Aptian-Coniacian shales seem to be the result of downslope density flows of shelf-edge sediments rich in organic matter. Preservation of organic matter was a result of rapid burial, not by stagnant basin waters. Furthermore, this mode of preservation appears to be responsible for the Cretaceous black shales throughout the South Atlantic. End_of_Article - Last_Page 958------------

Sources, Preservation, Maturation, and Migration of Organic Matter in Neogene Sediments from the Continental Margin off California and Baja California: A Synthesis of Organic Geochemical Studies from Deep Sea Drilling Project Leg 63

Abstract: This synthesis of organic geochemical studies from Leg 63 was designed to answer fundamental questions about the source, deposition, preservation, and alteration of organic matter off California and Baja California. The answers to these questions help to determine the extent and degree of influence of paleoenvironmental factors, the understanding of which was among the main objectives of drilling on this leg. The organic matter is mostly marine, and was deposited as pelagic sediment. Terrigenous components are abundant in the deep sea fan at Site 471, and in the upper Pliocene and Quaternary rocks and sediments of the California Borderland. Total organic matter (TOC) is highest in the upper Miocene to lower Pliocene rocks and sediments at Site 467, and in the middle Miocene rocks and sediments at Site 468, probably as a response to increased upwelling and high productivity, accompanied by depletion of oxygen in the oxygen minimum zone. Deeper water sites contain little organic matter, and do not exhibit a record of changes in surface circulation. All of the drilled sections are thermally immature, but light hydrocarbons are being generated in small amounts deep at Site 467. Light hydrocarbons that were probably generated in the vicinity of a sill at the bottom of Hole 471 have migrated in substantial amounts into the overlying section.