Boss Point Research Articles

Sedimentary Facies and Palaeocurrents in the Boss Point Formation, Southeastern New Brunswick: ABSTRACT

The Pennsylvanian Boss Point Formation was examined in gently folded coast sections on the Bay of Fundy and Petitcodiac estuary, including the type section north of Joggins, Nova Scotia, more than 3,130 feet thick. Two main intergrading facies are present. At Hopewall, Dorchester, and Aulac, cross-bedded sandstones and quartz-pebble conglomerates are greatly dominant; to the south and southwest, mainly cross-bedded sandstones alternate with siltstone and thin sandstone sequences. The coarser beds are interpreted as river channel and levee deposits, and the interbedded siltstone sequences, with root beds, represent flood-plain deposits. Mud-pellet conglomerates and marl-nodule conglomerates are common in the sandstones, the latter usually filling channels near the base of each sequence; probably these are the result of redistribution of the more tenacious flood-plain deposits during major changes of river course. Bituminous shales with nonmarine pelecypods (Carbonicola and others) and nodular arg llaceous limestones occur sparingly. Plant fragments, including transported Calamites and Lepidodendron logs, are abundant, especially in lenses of irregularly bedded sandstone thought to represent crevasse fillings in levees. Quicksand slump structures were identified in conglomeratic sandstones. No marine beds were found. End_Page 361------------------------------ Lenticularity of both major and minor sedimentary units makes correlation between sections difficult, though siltstone sequences may be traced for several miles. The Boss Point Formation is underlain conformably by Hopewell Group redbeds, and the lowest siltstone sequence in most places is red, with kunkar nodules indicating semi-arid conditions. Higher siltstones are predominantly gray, with a partial return to oxidizing conditions near the top. The gray color probably results from increased or more constant river flow rather than a climatic change, being associated with greater thicknesses of coarse clastics. Palaeocurrents indicated by cross-bedding and plant fragments show that the coarser northern sediments were deposited by currents flowing south and east, while elsewhere the flow was north and east. In conglomeratic beds plant fragments tend to be oriented parallel with the current direction, but they are perpendicular in finer-grained rocks. The palaeogeography indicated is a delta forming between northeast-southwest-trending metamorphic ridges. A large northeasterly flowing river on the site of the Bay of Fundy supplied most of the detritus, and streams flowing off the Caledonia Mountains deposited the conglomeratic beds, probably mixing with detritus from a south-flowing river entering the delta near Dorchester, which may have flowed into the adjacent Moncton basin from the southwest. End_of_Article - Last_Page 362------------