| Description |
x, 78 leaves : illustrations, photographs ; 29 cm |
| Summary |
"Based on the analysis of thirty-one cores obtained from the Missouri Department of Natural Resources in Rolla, the upper Cambrian Lamotte Sandstone in South Central Missouri has been divided into six sedimentary facies ranging from alluvial fan and braided stream to open marine. The Lamotte Sandstone is the basal Cambrian sandstone found throughout most of the state of Missouri. It directly overlies late Precambrian (1.4 to 1.5 billion year old) granites and metasediments. The Lamotte and overlying Bonneterre Formations are generally considered to have been deposited by a transgression which occurred during the Late Cambrian Period (Croixian Epoch). The Lamotte Sandstone varies in thickness between 132 and 306 feet in south central Missouri. Overall, it is a fining-upward sequence ranging from a feldspathic conglomerate at the base to a mature, well sorted quartz sandstone and shale at the top. Isopach maps of the six facies indicate that individual facies are variable in thickness and in some cases are totally missing. The lower four facies are interpreted to have been deposited in alluvial fan and braided stream environments. Facies #1 is the most variable in thickness and character. It contains a great deal of feldspar and is interpreted to have been deposited by local alluvial fans that occurred immediately adjacent to late Precambrian topographically high areas. Sediments were derived from the topographic highs, and filled in adjacent low areas. The topography was probably caused by earlier and possibly syndepositional block faulting. Facies #2, #3, and #4 contain very little feldspar with thicknesses somewhat less variable. They are interpreted to have been deposited by more regional fans and braided streams. Sediments found in facies #2, #3 and #4 are considered to have been derived from the Canadian Shield to the north rather than locally. Facies #5 is a marine shale wedge which occurs only in the western third of the area. It thickens to the west and is interpreted to have been deposited below wave base in a differentially downwarped area. Facies #6 is a quartz sandstone which contains glauconite, brachiopods, and some dolomite. It is interpreted to have been deposited by barrier island and shallow marine conditions"--Abstract, leaves ii-iii. |
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