HICKEY, LEO J.* AND TIMOTHY B. ARMSTRONG. Department of Geology and Geophysics, Yale University, P.O. Box 208109, New Haven, CT 06520-8109. - A mid-Cretaceous (Cenomanian) flora from the interior of the Canadian Shield in western Labrador.
In 1958, Erling Dorf collected a small impression flora of
approximately 100 specimens from a lens of hematitic argillite in the
Redmond Formation, in extreme western Labrador, 16 km south-southeast
of Schefferville, Quebec. The unusual occurrence of this flora and an
accomapanying insect fauna results from their deposition in apparently
synorogenic, graben-filling sediments generated during Cretaceous
reactivation of the late Pre-Cambrian Labrador trough, a 50 km-wide
geosyncline that runs approximately 1,100 km north-south through the
Labrador Peninsula. During the Cenomanian, Schefferville lay well
inland at a paleolatitude of 50o North. The flora consists
of at least 39 species and is dominated by angiosperms (28 species),
with gymnosperms (5 species) and ferns (6 species) each making up 10%
or less of the specimens collected. The dominant species are
"Platanus" shirleyensis (15%),
"Magnolia" speciosa (9%), Liriodendropsis
simplex (7%), Cissites platanoidea (7%), and
"Ficus" berthoudii (5%). The angiosperms are members
of the Platanaceae, Magnoliales, Lauraceae, Menispermaceae,
Chloranthaceae, and the basal Rosidae, whereas the small conifer
component is formed by modern taxa such as the Taxodiaceae and
"archaic" taxa like Abietites, Lariopsis, and
Widdringtonites. Dating of the flora is based entirely on the
ranges of the fossil plant species. Of the 25 previously described
species, 22 occur in the Cenomanian Stage, with 10 ranging into
earlier stages and 12 to later ones. The majority of angiosperm
species fall into the notophyllous and microphyllous size classes and
26% of them are entire-margined. Although climatic interpretations
based on an angiosperm flora of such an early date must be evaluated
with caution, our preliminary findings indicate a temperate climate
with an MAT of 9-10o C and the likelihood of regular
frosts.
Key words: Cenomanian, fossil flora, Labrador, Late Cretaceous, paleoclimate