Gregory, K. M., and McIntosh, W. C., 1996, Paleoclimate and paleoelevation
of the Oligocene Pitch-Pinnacle flora, Sawatch Range, Colorado: GSA Bulletin,
v. 108, p. 545-561.
Abstract.-- Angiosperm leaves from the Oligocene Pitch-Pinnacle
flora, which grew between 32.9 and 29 Mya, are described for the first time.
This flora is especially interesting because it grew in a tectonically
active region around the time of the precipitous Oligocene temperature drop,
and thus provides important constraints on paleoclimate and paleoelevation.
New multiple regression models are developed from the modern vegetation
leaf physiognomy dataset of J. A. Wolfe, and when applied to the Pitch-Pinnacle
flora, suggest a mean annual temperature (MAT) of 12.7° ± 1.5
°C, with a cold month and warm month mean of 4.5° ± 2.2 °C
and 20.4° ± 2.5 °C, respectively, and a mean annual range
of temperature of 18.5 ± 3.8 °C. Growing season precipitation
is estimated to be 101 ± 16 cm with this rainfall mostly during
the non-growing season. When the MAT estimate for the Pitch-Pinnacle flora
is combined with MAT estimates for coeval floras from the coast, the implied
elevation is either 2-3 km if the flora is pre-Oligocene deterioration,
or around 1 km if post-deterioration. Paleodrainage reconstructions suggest
the former, but more data are needed to resolve this issue.