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ABSTRACT: Floodplain and Paleosol Profiles of the Carboniferous Cumberland Coal Basin, Nova Scotia, Canada

M. Smith, I. P. Martini

The continuous, easily accessible, thick (1400 m) exposure of Late Carboniferous (late Westphalian A to early Westphalian C) fluviolacustrine rocks of the Cumberland Group along the south shore of the Bay of Fundy, at Joggins, allows detailed sedimentological work. The overall paleoenvironments of the rapidly subsiding, closed Cumberland basin have previously been reconstructed. This study focuses on the analyses of various types of floodplain sequences and their incipient (poorly developed) paleosol profiles. The rock exposure can be subdivided into three major parts. (1) Muddy and carbonate lacustrine conditions and coal formation frequently interrupted by

flooding events predominated in the lower part of the exposure. Gray mudstone, stigmaria rooting, local accumulations of plant material, siderite nodules, and thin coals are indicative of soils formed under poorly drained to water saturated conditions. Recurrence of sun-cracked red mudstone indicate periodic emergence of parts of the floodplain. (2) Red mudstone becomes predominant in overbank deposits of the middle portion of the exposure. Profiles showing color horizonation, mottling, and rooting are indicative of soil formation under humid to semi-arid climate (no caliche profiles have been observed). (3) More humid and flood-prone conditions were reestablished in the upper part of the rock sequence, where there are poorly developed coal seams, gray and red mudstone, stigmaria root ng, and sparse accumulation of detrital plant material. No carbonate-bearing lacustrine rocks are found in this part.

AAPG Search and Discovery Article #90998 AAPG Eastern Section Meeting, London, Ontario, Canada, September 10-12, 1990