The integrated application of chemostratigraphy and biostratigraphy to the North Slope, Alaska

Abstract

The objective of this study is to establish a comprehensive stratigraphic framework for Brookian sequences from the Eastern Beaufort Sea from the North Slope of Alaska. This area is under explored with few wells, but recent drilling has led to number of number discoveries reinforcing the area as emerging petroleum province on the North Slope. Few studies have focused on the region and stratigraphic correlation remains challenging in part influenced by poor biostratigraphic control. The aim of this study is to establish a new integrated stratigraphic framework for the Brookian succession based on the acquisition of new quantitative biostratigraphic data, high resolution chemostratigraphy (ICP-OES+ICP-MS) and C-O isotope curve. The biostratigraphic workflow includes palynological, micropalaeontology and a limited number of nannofossils to address the variety of depositional environments. Chemostratigraphy involves the characterisation and correlation of strata based on inorganic geochemical data that relate to variations in the mineralogy, linked changes in sediment provenance, diagenesis and paleoclimate. The C-O isotope data when integrated with global reference data provides an independent chronostratigraphy. The multidisciplinary approach provides a chronostratigraphic framework that can cope with the facies diversity associated with the Brookian progradation cycles and provide a framework for subsequent provenance and reservoir quality studies. The study focuses on 10 wells and DSDP 302 4A. Data are presented on Aurora-1 to highlight the workflow. Aurora was drilled to a total depth of 18,325 ft, and penetrates clastics sequences mainly shales, claystone’s and a few interbedded sandstone and siltstone. The chemostratigraphy of the Aurora-1 well subdivides the stratigraphy into three chemostratigraphic sequences, and 15 packages which can be correlated with other Beaufort Sea wells in the study. This zonation is matched by new biostratigraphic data but differs dramatically from the published interpretations for Aurora-1. The conflict between the two schemes arises over the Eocene and Cretaceous intervals, and the new data suggest thicker Cretaceous succession with the top Cretaceous boundary being coincident with a major change in sediment provenance detected chemostratigraphically. Other dramatic changes in the stratigraphy are apparent in the study and overall, this workflow will revolutionise the stratigraphy of the Eastern Beaufort Sea.

AAPG Datapages/Search and Discovery Article #90339 ©2019 AAPG Pacific Section Convention 2019, Long Beach, California, April 1-3, 2019