--> Abstract: Parasequence Stacking Patterns and the Delineation of Long-Term Sea Level History, Bonanza King Formation (Middle Cambrian), Southern Great Basin, by I. P. Montanez and D. A. Osleger; #91012 (1992).

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ABSTRACT: Parasequence Stacking Patterns and the Delineation of Long-Term Sea Level History, Bonanza King Formation (Middle Cambrian), Southern Great Basin

MONTANEZ, ISABEL P., and DAVID A. OSLEGER, University of California, Riverside, CA

The Bonanza King Formation of the southern Great Basin (California, Nevada) is composed of hundreds of meter-scale carbonate parasequences that provide an excellent strip record of Middle Cambrian third-order sea level oscillations. Detailed logging of several well-exposed sections (350-1200 m thick) has permitted the construction of a detailed cross-section from the craton (Frenchman Mountain) to the distally steepened ramp edge (Last Chance Range). The component peritidal and subtidal parasequences exhibit systematic vertical trends that can be used to identify the various components of depositional sequences. Stacks of progressively thickening subtidal parasequences appear to characterize the transgressive systems tract whereas stacks of progressively thinning peritidal parasequenc s seem to characterize the highstand systems tract.

Individual surfaces suspected of marking sequence boundaries and maximum flooding horizons can often be traced for kilometers along mountain fronts but are virtually impossible to trace between mountain ranges tens to hundreds of kilometers apart. The highest resolution of sequence boundaries and maximum flooding surfaces is usually restricted to transitional zones a few tens of meters thick that separate distinctly different intervals of parasequence sets. The transitional nature of these critical zones is believed to reflect the composite sea level history of high frequency eustatic oscillations superimposed upon a long-term third-order eustatic signal.

Confidence in the identification of systems tracts and bounding transitional zones in individual logged sections is supported by the excellent correlations of similar stacking patterns across the broad (hundreds of kilometers) passive margin. Correlation of similar stacking patterns of parasequences between isolated outcrop localities is aided by the use of Fischer plots that simply illustrate deviations from average cycle thickness. Eustatic control on Middle Cambrian sequence development is strongly suggested by the excellent degree of correlation between Fischer plots from different localities across the platform. Third-order sea level history determined from stacking patterns of meter-scale carbonate parasequences in the Bonanza King Formation may shed light on the current debate bout conflicting interpretations of accommodation history recognized in the Cordillera of Utah and the southern Canadian Rockies.

 

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)