Abstract

In this paper we examine quantitative ichnological data of silty-mudstone beds from inclined heterolithic stratification (IHS) in order to understand the spatial and temporal controls affecting bioturbation in IHS. Data collected for this study include bed-scale averaged bioturbation intensity, size-diversity index, and ichnogenera abundances. These data were used to assign each bed into one of 10 clusters using K-Means clustering. The clusters were ranked according to interpreted intensity of cumulative depositional ecologic stress. Time-series, where each silty-mudstone bed represents a time-step with a corresponding ecologic stress value, were constructed from the interpreted ecologic stress cluster analysis results. To identify and interpret spatial and temporal variation in the ichnological time-series, two time-series analysis methods were employed: dynamic time-warping and continuous wavelet transforms. Dynamic time-warping is used as a descriptor of the spatial similarity between ecologic stresses, and continuous wavelet transforms are used to interpret cyclical patterns in the ichnological time-series. Spatially, the variability and cyclicity observed in the ecologic stress time-series can be linked to estuary scale stresses and more localized stresses (i.e., bar-form scale depositional stress). This is reflected by the relatively similar periodicities observed in the ecologic stress time-series. Temporally, cyclical ecologic stress patterns occur somewhat predictably in periods of approximately four, or multiples of four, which are consistent with El Nino cyclicity.

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