STRATIGRAPHY AND GENESIS OF EARLY PROTEROZOIC DIAMICTITES: NORTH AMERICA
KURTZ, DENNIS DARL
Doctor of Philosophy
Glaciogenic rocks are present throughout the world, in strata of all ages. Where thought to represent glacial marine or glacial aquatic deposition their interpretation has been hampered by the lack of a sedimentary model based upon modern glacial marine processes. A model constructed from the study of Antarctic marine sediments and Pleistocene marine sequences exposed in the Puget Lowlands is used in this thesis to interpret Early Proterozoic (middle Pre-cambrian) glaciogenic rocks. Possible tillites were studied in the Gowganda Formation, Ontario, the Headquarters Formation, Wyoming, and in the Black Hills. Antarctic glacial marine sediments reflect the interaction and relative importance of glacial, marine, and gravity-driven sedimentary agents. Subglacial deposits on the continental shelf exhibit no indication of marine current action. Glacial marine tills on the continental shelf and slope display both glacial and marine characteristics. Marine current deposits are also present on the continental slope. Sediment gravity flow deposition of several kinds occurs, principally on the continental slope, and these sediments are interbedded with glacial and marine sediments. Sediment texture, the kinds of sedimentary structures, pebble characteristics, and sedimentary associations are the major criteria used for distinguishing these sediments types. The Gowganda Formation in northern Ontario is a thick, widespread unit that has long been thought to represent glacial deposition. A sequence of rocks representing pre-glacial and periglacial sedimentation, subglacial and glacial aquatic conditions, and post-glacial deposition is typically present. The glacial unit contains both basal and floating ice deposits. This formation is interpreted as representing one major advance and retreat of a large grounded and floating ice sheet. Local fluctuations of the grounding line, and of the retreating ice margin probably occurred but there is no need to invoke more than one glaciation to explain these deposits. The Headquarters Formation in southeastern Wyoming contains tillites that are interbedded with a variety of nonglacial sediments (fluvial-deltaic deposits, turbidites, etc.). This unit probably represents deposition in a nearshore setting under frigid climatic conditions. There is no evidence for the presence of a nearby large ice mass. Metaconglomerates in the Black Hills are of unknown origin. The presence of lonestones in argillites and gradational contacts between units suggests glacial aquatic deposition. There is no evidence in the deposits studied which indicates that a continental ice sheet covered North America at that time; though a large ice sheet was present in northern Ontario.