A Brief Overview of the Diversity and Patterns in Bioturbation Preserved in the Cambrian–Ordovician Carbonate and Siliciclastic Deposits of Laurentia
Stephen T. Hasiotis, 2012. "A Brief Overview of the Diversity and Patterns in Bioturbation Preserved in the Cambrian–Ordovician Carbonate and Siliciclastic Deposits of Laurentia", Great American Carbonate Bank: The Geology and Economic Resources of the Cambrian—Ordovician Sauk Megasequence of Laurentia, James Derby, Richard Fritz, Susan Longacre, William Morgan, Charles Sternbach
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The diversity, abundance, distribution, and depth of trace fossils in the Cambrian–Ordovician deposits in Laurentia, from California and Nevada to New York (United States) and Quebec (Canada), are a series of biozones that record the early evolution and radiation of metazoans in shallow-marine environments. The Neoproterozoic–Paleozoic transition (NPT) plays a significant part in understanding the diversity, timing, rate, circumstance of first appearances and subsequent metazoan radiations, and trends in ecospace utilization through the Cambrian–Ordovician as recorded in carbonate and mixed carbonate-siliciclastic deposits. The first burrows with spreiten and complex branching, designated as the Phycodes (Treptichnus) pedum Zone, delineate the base of the Cambrian. This zone overlies the uppermost Neoprotero-zoic Harlaniella podolica Zone and is composed of relatively simple horizontal burrows. The Rusophycus avalonensis Zone, characterized by the occurrence of more complex burrow architectures, overlies the Phycodes (Treptichnus) pedum Zone and represents the last pretrilobite biozone. As recorded by ichnofabric through the Cambrian–Ordovician, trends in the depth and extent of bioturbation illustrate the spatial and temporal change in ecospace utilization. With the onset of the substrate (media) revolution across the NPT, animals adapted, and evolved new innovations to penetrate microbial-mediated sedimentary environments. This change reflects ongoing Cambrian–Ordovician evolution and radiation of metazoans from shallow inner-shelf environments to middle-shelf environments with increasing biogenic reworking through time. Nonetheless, a mixing depth of 6 cm (2.4 in.) was not surpassed until later in the Ordovician. This pattern ismirrored by the first appearances of trace-fossil ichnotaxa in shallow-water environments that later gradually moved offshore to shelf environments. The ichnological patterns are debated, however, asevidence of deep burrowing (i.e.,>6cm[>2.4in.]) has been described from the Cambrian and the Ordovician deposits in the Mackenzie Mountains (western Canada) and the Great Basin (western United States). Evidence for the early evolution of continental ecosystems does not exist in Laurentian deposits until the Late Ordovician, although some evidence for the invasion of land in the Early Cambrian and the Early Ordovician exists.
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Great American Carbonate Bank: The Geology and Economic Resources of the Cambrian—Ordovician Sauk Megasequence of Laurentia
The Great American Carbonate Bank (GACB) comprises the carbonates (and related siliciclastics) of the Sauk megasequence, which were deposited on and around the Laurentian continent during Cambrian through earliest Middle Ordovician, forming one of the largest carbonate-dominated platforms of the Phanerozoic. The Sauk megasequence, which ranges upwards of several thousand meters thick along the Bank's margin, consists of distinctive Lithofacies and fauna that are widely recognized throughout Laurentia. A refined biostratigraphic zonation forms the chronostratigraphic framework for correlating disparate outcrops and subsurface data, providing the basis for interpreting depositional patterns and the evolution of the Bank. GACB hydrocarbon fields have produced 4 BBO and 21 TCFG, mostly from reservoirs near the Sauk-Tippecanoe unconformity. The GACB is also a source of economic minerals and construction material and, locally, serves as either an aquifer or repository for injection of waste material. This Memoir comprises works on biostratigraphy, ichnology, stratigraphy, depositional facies, diagenesis, and petroleum and mineral resources of the GACB. It is dedicated to James Lee Wilson who first conceived of this publication and who worked on many aspects of the GACB during his long and illustrious career.