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ABSTRACT: Analysis of Ichnofossil Associations in the Subsurface Bluesky Formation (Albian, Alberta, Canada)

Michael J. Ranger, S. George Pemberton

The quantitative analysis of ichnological associations is in an early stage of development. Several studies of spatial distributions of ichnofossils using ecological methodology have provided insight into spatial ecological interactions in modern and ancient environments.

This study examines another dimension, the vertical development of paleoecological and paleoenvironmental conditions through time.

Ichnological data from diamond drill cores of 22 wells that penetrated the Bluesky Formation of northwestern Alberta were digitized. Q-mode cluster analysis distinguished eight biofacies based on associations of ichnofossil forms and a few diagnostic physical structures. R-mode cluster analysis of these ichnofossil associations distinguished three major groups. The control provided by an existing differentiation of the sediment cores into facies intervals allowed an examination of the efficacy of several different clustering functions. Ward's method using Euclidian distance for the similarity coefficients and the error sum of squares for the fusion transformation function appeared to be the optimum technique for this study. Using eight biofacies as the transition states, two methods o Markov analysis were employed. These methods were the Gingerich-Read row-scaling method using Harper's binomial probabilities as a test of significance, and the Goodman iterative proportional fitting method to obtain expected transition frequencies, using the x2 statistic and Turk's normalized residuals as a test of significance. The iterative proportional fitting technique showed significant deviation from independence at the 95% confidence limit. Both methods distinguished similar significant biofacies transitions. The local biofacies model for the Bluesky Formation in the study area suggests a nearshore-to-marginal marine regressive sequence following a sudden transgression over a coastal plain or salt marsh environment.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990