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FLOODPLAIN
DEPOSITS AND PALEOSOL PROFILES OF THE LATE CARBONIFEROUS CUMBERLAND BASIN, JOGGINS, NOVA SCOTIA, CANADA
M.G. SMITH and I.P. MARTINI
Department of Land Resource Science, University of Guelph, Guelph, Ont.,
Canada กก
The 1400 m thick succession of Late Carboniferous (Westphalian A to
Early Westphalian C) Cumberland Group strata exposed near Joggins, Nova Scotia
is composed of four fluvial successions. In
ascending order they consist of: (I) a succession containing floodplain strata
composed of mudstone, lacustrine limestone deposits and thin coals; (II) a
succession dominated by gray mudstone floodplain deposits containing thick coals
and numerous standing fossilized trees (Lepidodendron and Calamites);
(III) a succession containing floodplain deposits of locally variegated, gray
and red mudstone, containing desiccation cracks and thin coally shale horizons;
and (IV) an upper fluvial succession composed of interbedded red and gray
mudstones layers with numerous, thin coal bands and abundant Stigmaria
root remains. Successions I, II,
and IV contain a number of thick channel sandstone layers, some with epsilon
cross bedding, interpreted as meandering river channel deposits.
Succession III contains channel sandstone layers indicative of
anastomosing river channel deposits. Incipient
paleosols occur throughout. Paleosol
profiles are distinguished by their organic-rich epipedons, root remains, color
mottling, various blocky and platy structures, and a variety of calcite and
siderite nodules and root casts. Some
of these later mineral inclusions may be diagenetic, but their local occurrence
is in part dictated by the presence of pre-existent pedogenic features.
Coal layers and associated underclays are thought to derive from original
polygenetic soils altered by diagenesis associated with coal formation.
Four typical paleosol profile types reinforce sedimentological and
palaeontological observations and provide new information about well-drained to
poorly-drained sites in the floodplain setting and an overall change from humid
conditions in successions I and II to more arid climatic conditions in
succession III of the exposure. |
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