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A fossil lycopsid forest succession in the classic Joggins section of Nova Scotia: Paleoecology of a disturbance-prone Pennsylvanian wetland

By
John H. Calder
John H. Calder
Nova Scotia Department of Natural Resources, P.O. Box 698, Halifax, Nova Scotia B3J 2T9, Canada
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Martin R. Gibling
Martin R. Gibling
Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia B3H 3J5, Canada
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Andrew C. Scott
Andrew C. Scott
Department of Geology, Royal Holloway (University of London), Egham, Surrey TW20 0EX, UK
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Sarah J. Davies
Sarah J. Davies
Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, UK
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Brian L. Hebert
Brian L. Hebert
RR 1, Joggins, Nova Scotia B0L 1A0, Canada
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Published:
January 01, 2006

Standing lycopsid trees occur at 60 or more horizons within the 1425-m-thick coal-bearing interval of the classic Carboniferous section at Joggins, with one of the most consistently productive intervals occurring between Coals 29 (Fundy seam) and 32 of Logan (1845). Erect lepidodendrid trees, invariably rooted within an organic-rich substrate, are best preserved when entombed by heterolithic sandstone/mudstone units on the order of 3–4 m thick, inferred to represent the recurring overtopping of distributary channels of similar thickness. The setting of these forests and associated sediments is interpreted as a disturbance-prone interdistributary wetland system. The heterogeneity and disturbance inherent to this dynamic sedimentary environment are in accord with the floral record of the fossil forests and interpretation of the peat-forming wetlands as topogenous, rheotrophic forest swamps.

Candidates for the erect, Stigmaria-bearing trees, which range in diameter (dbh) from 25 to 50 cm, are found in prostrate compressions and represent a broad range of ecological preferences amongst the Lycopsida. This record, which is not significantly time averaged, closely parallels the megaspore record from thin peaty soils in which they are rooted, but differs significantly from the miospore record in studies of other, thicker coals. Dominant megaspores are Tuberculatisporites mamillarus and Cystosporites diabolicus, derived from Sigillaria and Diaphorodendron/Lepidodendron respectively. Intervening beds preserve a record of an extra-mire flora composed in the main of seed-bearing pteridosperms and gymnosperms (and ?progymnosperms). Reproductive adaptation to disturbance appears to have played a key role in ecological partitioning of plant communities within these wetlands. Burial of lycopsid trees by onset of heterolithic deposition resulted in the demise of entire forest stands. Disturbancetolerant Calamites regenerated in the episodically accruing sediment around the dead and dying lycopsid stands, a succession identified here as typical of Euramerican fossil forests. Rapid, ongoing subsidence of the basin accommodated the submergence of the fossil forests, and abiotic disturbance inherent to the seasonal climate facilitated their episodic entombment. Disturbance is inferred to have been mediated by short-term (?seasonal) precipitation flux as suggested by the heterolithic strata and in the record of charred lycopsid trees, recording wildfire most probably ignited by lightning. Within this fossil forest interval is found a glimpse of animal life within the wetland ecosystem beyond the confines of the tree hollows, whence the bulk of the terrestrial faunal record of Joggins historically derives.

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Contents

GSA Special Papers

Wetlands through Time

Stephen F. Greb
Stephen F. Greb
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William A. DiMichele
William A. DiMichele
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Geological Society of America
Volume
399
ISBN print:
9780813723990
Publication date:
January 01, 2006

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