The Middle Cambrian Langston and Ute formations were studied in the northern portion of the Bear River Range and the south-central part of the Portneuf Range in southeastern Idaho. The rocks of the Langston and Ute formations were divided into 17 different rock types. The 17 rock types were formed within four recognizable lithofacies: I) Shoal - or Coastal -Peritidal Carbonate Complex; 2) Agitated Shoal; 3) Inner Marine Shelf; and 4) Outer Marine Shelf. Clastic sediments belonging to the Spence Shale Member of the Langston Formation (outer marine shelf) were deposited over the carbonate complex . A transgressive sequence marks the base of both formations. Paleomagnetic evidence suggests that during the time of the deposition of the two formations, the study area was located near the outer reaches of an equatorial epeiric sea. Clay mineralogy of insoluble residues suggests a warm, humid, tropical climate. Eogenetic diagenetic features include compaction, cementation, aggrading, and degrading neomorphism, birdseye structures, and initiation of dolomitization . Mesogenetic diagenetic features include dolomitization and pressure solution. Telogenetic diagenetic features are confined to fracturing and subsequent calcite infilling, and the oxidation of pyrite. Massive dolomitization in the northernmost section is believed to be the result of a downward flux of fluids originating as hypersaline brines. The nonconformable lower contact, conformable upper contact, the vertical and lateral extent of dolomitization, and the general association with coastal-peritidal facies have led to this conclusion. Two other subordinate types of dolomite are believed to be the result of: 1) the release of magnesium caused by the decomposition of magnesium-rich organic matter; and 2) the formation of a secondary ferroan dolomite as Fe/Mg ratios in the precipitating fluids increased under reducing conditions.

The Middle Cambrian Spence Shale Member contains meter-scale, shallowing-up cycles (parasequences) and record approximately 360 ky of deposition. These meter-scale cycles are nested within transgressive systems tracts (TST) and highstand systems tracts (HST) which reflect different stages of a lower-order, higher-magnitude sea-level excursion. Fossil assemblages are located in stratigraphic positions within the Spence Shale Member that can be predicted on the basis of sequence architecture. The cycle architecture, taphonomy, and geochemistry of the Spence parasequences confirm synthetic sections and theoretical models of meter-scale cycles developed in other studies. Delineation of meterscale cycles, based on taphonomic and sedimentologic criteria, allows high-resolution (100-500 ky) correlation. This study also documented the Cambrian existence of the Tooele and Arco Arches and aided in further understanding paleoenvironmental conditions within the Spence Shale Member.

An interbasinal study of Late Cambrian cyclic carbonate successions in the Appalachian and Cordilleran passive margins, the Texas cratonic embayment and the southern Oklahoma aulacogen has provided controls on the simultaneous development of peritidal to subtidal meter-scale cycles and the larger scale depositional sequences on which they are superimposed. Fining-upward peritidal cycles grade seaward into coarsening-upward, shallow to deep subtidal cycles that form a continuum across the carbonate platforms and are genetically linked to one another by shared lithofacies. Eustacy appears to exert the dominant control on the simultaneous development of peritidal and subtidal cycles on different carbonate platforms. Based on the recognition of dominant periodicities on power spectra derived from time series of subtidal cycles, high frequency eustatic oscillations may be controlled by Milankovitch astronomical rhythms. Interbasinal correlation of Late Cambrian depositional sequences was performed by graphic correlation and the time-equivalent intervals were correlated lithostratigraphically using isochronous biomere boundaries as time datums. Fischer plots of meter-scale cycles define changes in relative sea level based on the amount of extra accommodation space produced by eustacy beyond that provided by subsidence. Residual eustatic curves derived from subsidence analysis are useful for correlating the longer-term Late Cambrian sea level events and changes in the rate of sea level rise and fall can be used to define shorter-term events. Combining the sea level curves defined by Fischer plots and subsidence analysis with paleobathymetric curves of Late Cambrian cyclic strata suggests that the curves may approximate the form of the eustatic sea level curve. A composite "eustatic” sea level curve for the Late Cambrian was created by qualitatively combining the sea level curves defined by the different techniques for each of the four localities. “Eustatic" sea level curves defined by Fischer plots and subsidence analysis may be used to apply sequence stratigraphic concepts to onedimensional outcrop sections. Combined with systematic changes in the stacking patterns of meter-scale cycles, they can be used to define the internal composition of systems tracts, sequence boundaries, and flooding surfaces of third-order depositional sequences. One- and two-dimensional models of peritidal and subtidal cycle development indicate that peritidal cycle thickness is primarily controlled by accommodation space and deeper subtidal cycle thickness is primarily controlled by sedimentation rate. Whereas lithofacies within peritidal cycles alternate in response to fluctuations in sea level, subtidal cycle development may be related to fluctuations in fairweather and storm wave base that oscillate in harmony with sea level fluctuations. / Ph. D.

The Elbrook-Conococheage Formations (Middle to Upper Cambrian) are a kilometer-thick sequence of cyclic, peritidal carbonates that formed an aggraded, rimmed shelf on a mature, passive continental margin. Sedimentation rates for peri tidal carbonate environments far exceeded long term subsidence of the platform (3 to 5 cm/1000 yrs.); thus, the shelf stayed filled to sea level (i.e., was aggraded). Relative sea level rise did exceed sedimentation for brief periods, causing cyclic transgressions (max. 3 m initial submergence). Average cycle duration was 60,000 years. Cycles (1-7 m thick) are composed of basal subtidal/intertidal limestone consisting of bioherms, grainstone and ribbon carbonate; and dolomitic laminite caps containing minor quartz arenite, shale and breccia. Cycle development was controlled by initial submergence increment and position relative to shelf edge. Large initial submergence produced thick subtidal-based cycles representing shelf lagoon and shoal conditions. Small events resulted in submergence within the intertidal zone, which deposited thick, mudcracked intertidal limestones in outerplatform settings, and thick sequences of laminite in inner platform settings. Slopes on the platform were low (less than 3 cm/km); thus, subtidal facies developed in a mosaic pattern of lagoons and shoals, rather than in shore-parallel belts. When low areas filled, tidal flat laminites prograded seaward over subtidal units. Cyclicity may reflect spasmodic subsidence of the shelf, or uniform subsidence overprinted by small-scale glacio-eustatic sea level changes related to shifting patterns of mountain glaciation. Interior areas of Quaternary carbonate shelves are characterized by incipiently drowned facies and are punctuated by soil/caliche horizons and karst surfaces, that reflect 100 rn glacio-eustatic sea 'level fluctuations. In contrast, many ancient shelves, including the Cambre-Ordovician shelf of the Appalachians, were dominated by cyclic peritidal sequences lacking evidence of major sea level events. Aggraded shelves may represent the typical state of mature carbonate continental shelves in the absence of large-scale sea level fluctuations. / M.S.

A morphometric analysis of Cambrian trilobites shows that extinction events sharply reduced the morphological diversity of ptychopariid trilobites living on the shelf at the lower boundaries of the Marjumiid, Pterocephaltid, and Ptychaspid biomeres (Middle to Upper Cambrian). These extinction events not only separate the trilobite assemblages that characterize each biomere, but they also separate similar sequences of morphological diversification. During the initial deposition of each biomere, the shelf was repopulated by a limited number of ptychopariid species that had similar morphologies of very limited range and type. These initial faunas then underwent a morphological diversification evolving similar morphologies during the deposition of the remainder of each biomere. This pattern of repeating episodes that begin with similar morphologies of trilobites which then undergo similar morphological diversifications suggests that the extinction events at the base of each biomere limited the range of morphologies from which new taxa could evolve. Each new biomere assemblage was unable to build upon the adaptations of the specialized taxa of the previous biomere. Only the limited range of similar morphologies of the initial repopulating trilobites was the source from which new taxa could evolve. As a result, new taxa “reevolved the wheel” each time they became adapted to the vacated habitats that were previously occupied in the underlying biomere. In contrast, near the Cambrian-Ordovician boundary, the extinction event at the base of the Lower Ordovician Symphysurinid biomere did not reduce the range of morphologies as drastically as the previous biomere extinctions in the Cambrian. A more diverse initial fauna occurs in the Symphysurinid biomere. This fauna did not undergo a morphological diversification during deposition of the biomere and some regions of morphospace previously occupied in the Cambrian were not reoccupied in this biomere. Taxa of the lower Ordovician were relatively canalized in their morphology. In the Marjumiid biomere (Middle to lower Upper Cambrian), the morphological diversification of ptychoparid trilobites was not significantly influenced by either paleogeography, depositional settings, or migration of taxa from outside North America. The morphological diversification of the ptychopariid assemblage is also seen in a subset of ptychopariids that consists of the Superfamilies Raymondinacea, Asaphiscacea, and Marjumiacea. These superfamilies are the numerically abundant and most diverse taxonomic groups in the Marjumiuid biomere. The patterns of morphological diversification in both the Order Ptychopariida and the combined assemblages of the Superfamilies Raymondinacea, Asaphiscacea, and Marjumiacea were relatively consistent among different paleogeographic regions and were not influenced by general lithofacies. The consistency of the regional patterns and the lack of influence of general lithofacies on these patterns indicate that the overall pattern of morphological diversification is the result of in situ evolution of taxa within the North American Craton and not the result of shifting biofacies or the migration of taxa from outside North America. The morphological diversification of ptychoparids in the Marjumiid Biomere is composed of two distinct phases. The morphological expansion of the Superfamily Ptychopariacea (the ehmaniellids) in the Ehmaniella Biozone is an early phase of diversification. The morphological expansion of the Superfamilies Norwoodiacea, Solenopleuracea (exclusive of the Family Solenopleuracea), Asaphiscacea, Raymondinacea, and Marjumiacea in the Bolaspidella to Crepicephalus biozones represent the later phase of diversification. This second phase is also composed of two morphological expansions, an early expansion in the Superfamilies Norwoodiacea and Solenopleuracea in the Bolaspidella and Cedaria biozones, and a later expansion in the Superfamilies Asaphiscacea, Raymondinacea, and Marjumiacea in the Cedaria and Crepicephalus biozones. The ptychopariid assemblages of the younger Ptychaspid biomere (Upper Cambrian) also display a two-phase morphological diversification. / Ph. D.

Bibliography: leaves [206]-244.

Bibliography: leaves [206]-244. / xxviii, 244 leaves, [31] leaves of plates : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Geology and Geophysics, 2001

Bibliography: leaves [206]-244. / xxviii, 244 leaves, [31] leaves of plates : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Geology and Geophysics, 2001

No description available.

<p>Arthropods have a rich fossil record spanning the Phanerozoic. Biomineralized forms such as the extinct trilobites are particularly common and are proven index fossils for biostratigraphy. Forms with an unmineralized cuticle are more rare, preserved only in so called <i>konservat lagerstätten</i>. Cambrian strata of Greenland have yielded rich trilobite faunas with potential for intercontinental correlation of Cambrian strata, but also an exceptionally preserved fauna, the Sirius Passet Lagerstätte. The first part of this thesis is concerned with trilobite biotratigraphy of the provisional Cambrian Series 2 in Greenland. The second part is concerned with exceptionally preserved arthropods from the Sirius Passet Lagerstätte, but also from 'Orsten' deposits from the Cambrian of Sweden.</p><p><i>Perissopyge phenax occurs</i> in the Henson Gletscher and Paralleldal formations spanning the Series 2 and 3 boundary interval in North Greenland. It also occurs in the Sekwi Formation of Yukon Territory, demonstrating that the species may hold potential for correlation within Laurentia. An indeterminate species of <i>Perissopyge</i> is shown to occur in the Ella Island Formation of North-East Greenland together with <i>Olenellus</i> cf. <i>hanseni</i>, which is similar to <i>Olenellus</i> cf. <i>truemani</i> described from the Henson Gletscher Formation. If this correlation is further corroborated it would offer a first tie-point for the An t'Sron Formation of North-West Scotland which yields <i>Fritzolenellus</i> <i>lapworthi</i>, herein reported for the first time from the Bastion Formation which underlies the Ella Island Formation.</p><p><i>Oelandocaris</i> <i>oelandica</i> from ‘Orsten’ deposits in the Cambrian series 3 and 4 boundary interval in Sweden is an early representative of the Crustacean stem lineage. <i>Kiisortoqia</i> <i>avannaarsuensis</i> is a new arthropod from the Sirius Passet Lagerstätte with robust antennulae strikingly similar to the 'raptorial' limb of the problematic anomalocaridids. The ventral morphology of the 'bivalved' <i>Isoxys</i> <i>volucris</i> is described for the first time and compared with other species assigned to <i>Isoxys</i> from Cambrian lagerstätten around the world. Finally, <i>Siriocaris</i> <i>trolla</i>, is a new arthropod that similarities with trilobites and certain ‘trilobitomorphs’ but seems to lack important synapomorphies of these taxa, though this may be due to preservational limitations in the material at hand.</p>