COOPER, ERIN E.* AND JEFF MYERS. Department Earth and Physical Sciences, Western Oregon University, 345 North Monmouth Ave, Monmouth OR 97361. - Physiognomic Paleoclimate Anaylsis of the John Day Gulch Flora, Eocene Clarno Formation.
Leaf physiognomic data from the 44-45 Ma John Day Gulch Flora of the
Clarno Formation indicate that central Oregon experienced a
frost-free, warm subtropical climate with high non- seasonal rainfall
during the middle Eocene. This data was used to analyze the two
hypothesis for the pattern of cooling approaching the Eocene/Oligocene
boundary. One possibility is a series of smaller drops in temperature
approaching the boundary. Another model, proposed by Dr. Jack Wolfe
(1972, 1992), shows a drop in temperature and then a rise just before
the boundary.
Because climatic variables effect the physiognomic
characteristics of leaves, it is possible to take the characteristics
of modern day foliages and the climate they grow in and create a
reference point to which paleoflora can be compared. This can give
some idea of the climate that the paleoflora grew in. Two methods for
doing this, Dr. Jack Wolfe's CLAMP analysis and Dr. David Greenwood's
Leaf Litter analysis, were used to estimate the paleoclimate of the
middle to late Eocene at John Day Gulch, OR. The goal of these tests
was to test Dr. Wolfe's hypothesis for a rise in temperature before
the Eocene/Oligocene boundary. The leaf physigonomic data from the
John Day Gulch assemblage indicates that it grew under climate
conditions similar to those estimated from other assemblages of the
Clarno Flora, and refute the hypothesis that John Day Gulch assemblage
grew during an Eocene cool interval.
Key words: CLAMP, John Day Gulch, leaf-litter