PALEOENVIRONMENT AND SULFUR BORON CONTENTS OF THE MANNVILLE (LOWER CRETACEOUS) COALS OF SOUTHERN ALBERTA, CANADA

Sulfur (S) and boron (B) contents were determined for use as paleoenvironmental indicators in 28 samples of coal from the coal-bearing sequence occupying the upper part of the Lower Cretaceous Mannville Group located in the subsurface of southern Alberta, Canada. Sulfur for these coals range from 0.56 to 23.46% daf (wt. dry-ash-free) and boron between 18 and 1144 ppm. Twenty-three samples show S values > 1 wt.% and B > 100 ppm, indicating a strong brackish to marine influence in most of these coals. A S vs. B plot of these coal samples reveals two distinct suites: (1) with high B (256-1144 ppm) and low to moderate S (0.58-2.71% daf), and (2) with moderate B (18-247 ppm) and low to high S (0.56-23.46% daf). These two suites characterize coals from two different locations with differing stratigraphic-sedimentological settings. Coals in suite 1 occur at the tops of 8-10 m thick, regressive sequences stacked one above the other. Each coal bed is overlain by a marine transgressive surface. Inundation of the underlying peat by seawater may have produced conditions which caused the anomalously high (> 500 ppm) B content of nine samples in the suite. Coals in suite 2 on the other hand, lie on top of a single, thick (20-30 m) prograding shoreline sequence not followed by transgression. Their highly variable S content probably is a reflection of their origin in a coastal swamp characterized by a long period of bacterial activity during slow progradation. © 1990.