ABSTRACT: Quantitative stratigraphic techniques and sequence boundary detection

Cooper, Roger A., and James S. Crampton , Institute of Geological and Nuclear Sciences, Lower Hutt, New Zealand

A variety of methods for quantitative stratigraphic analysis are now available and enable improved precision in zonation, correlation and sequence boundary detection. We test two methods, with contrasting approaches, on a Paleocene to Miocene succession in the Taranaki Basin, New Zealand. The database comprises 493 microfossil taxa in cuttings samples from 8 wells. The position and order of taxon range-end events varies widely from well to well, making the task of correlation difficult.

Ranking and scaling (a probabilistic method) uses only the order of events in the well sections, and enables derivation of the most probable order of events and a probabilistic zonation scheme, both of which should be useful in future exploration of the basin. Constrained optimisation (a deterministic method) is a multidimensional graphic correlation technique that produces a high resolution correlation of sections. Both methods provide measures of event variance, enabling the identification of the most, and least, useful, taxa for intra-basinal correlation and zonation. Both techniques treat all sections and events simultaneously, and process large data bases quickly.

In an extension of the graphical method, the composite section was calibrated against the chronometric time scale, and enabled measurement of the depositional rates in the wells. Previously recognised depositional hiatuses or condensed intervals were detected and many new ones revealed. This 'time-scaled composite' is a powerful tool for sequence boundary detection in well sections.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia