SEA LEVEL SIGNATURES AND REGIONAL CORRELATIONS ELUCIDATED BY CARBONATE CYCLE ARCHITECTURE: MIDDLE CAMBRIAN HIGHLAND PEAK FORMATION, EASTERN NEVADA

Detailed analysis of the internal architecture of shallowing-upward carbonate cycles (1) provides a rapid and easy approach to assess trends and relative rates of sea level change, (2) validates Fischer Plots, and (3) clearly delineates sequence systems tracts. Cycle architecture is the arrangement and thickness of facies within an individual cycle controlled by eustasy. Facies within a cycle records response to changes in sedimentation rate and amount of available accommodation space (Soreghan and Dickinson, 1994). Analysis of cycle architectures within systems tracts provides for better understanding of high-frequency sea-level changes, including relative rates of change. This method also refines and corroborates the Fischer Plot method by providing a clearer and more precise history and definition of the character of sea level change. Combining cycle architecture and Fischer Plots with sequence stratigraphy helps to delineate systems tracts and their correlative conformities. Therefore, cycle architecture analysis is an essential tool for temporal regional correlation of carbonate successions.

Using the methods above, we analyzed the Middle to lower Upper Cambrian Highland Peak Formation (HPF) in eastern Nevada. The HPF contains over 1000 m of shallow-water cyclic carbonates representing deposition on a broad carbonate platform along the passive margin of western Laurentia. Limited biostratigraphy across the platform allowed only broad regional correlations. Cycle stacking patterns and lithofacies analysis resulted in delineation of 7 sequences, 2 correlative across North America and 4 correlative across the local platform. Cycle architectural analysis resolved the high-frequency signals and corroborated Fischer Plots and sequence stratigraphic interpretations. The type of cycle architecture and the clustering of particular types within a systems tract reflect the relative rate of sea level rise or fall under uniform subsidence. Consequently, recognition of this clustering pattern may provide us with an enhanced tool for understanding the complex interplay between orbital events, the sea level fluctuations they are said to cause, and the resultant stratigraphic record.