IDENTIFICATION AND INTERPRETATION OF SEDIMENTARY HIATUS USING EVOLUTIVE HARMONIC ANALYSIS

Cyclostratigraphy has become an important tool for the refinement of pre-Pleistocene geochronologies. When statistically significant bedding cycles are accurately converted from the spatial (cycles/m) to the temporal (cycles/kyr) domain, they provide a level of geochronologic resolution that far exceeds any other method for pre-Pleistocene sedimentary deposits. However, one of the most notable hazards to the development of an accurate orbital time-scale is the presence of significant hiatus, especially when the temporal gap is not clearly reflected in the biostratigraphic and/or sedimentologic character of the strata. The danger of such pitfalls can be exacerbated in cyclic units that preserve multiple orbital components. In such cases, clear stratigraphic expression of the temporal discontinuity, such as disruption of the ~5:1 precession-eccentricity syndrome, may be masked by complex bedding patterns reflecting the combined influence of multiple orbital signals (eccentricity, obliquity, precession). In this talk we present a new method for the quantitative detection of hiatus and the assessment of its temporal duration. In addition to the refinement of sedimentary time scales, the identification of hiatus has important implications for understanding the response of the depositional system to climatic change and evolving basinal character (sediment supply vs. accommodation space). By elucidating hiatuses, their duration, the frequency of their reoccurrence, and their spatial continuity within a sedimentary basin, this method provides an enhanced level of hypothesis testing for the dominant controls on sedimentation. As an example of the utility of this methodology, we apply it to the Bridge Creek Limestone Member of the Greenhorn Formation (Western Interior, U.S.A.), a classic Mesozoic section of rhythmically bedded strata.