Date of Award
Master of Arts (MA)
Dr. Lisa Boucher
Physiognomy of fossil leaves collected from Late Cretaceous floodplain sediments in present-day northwestern New Mexico was used to estimate paleoclimate. Woody dicot species were collected from this area to determine the Mean Annual Temperature (MAT) and Mean Annual Precipitation (MAP) using both uni- and multi-variate methods. From the same stratigraphic level at the contact between the upper Fruitland and lower Kirtland Formations, 188 specimens from three sites representing twenty-five morphotypes were sampled. Specimens were plotted on a collection curve to ensure species numbers approached saturation during sampling. Leaf margin analysis, a technique that compares the percentage of entire margin to non-entire margin leaves, was used to measure paleo MAT. In addition, the relationship between the mean natural logarithm of leaf areas of the species and sample (MlnA) and precipitation was used to measure the paleo MAP. These results indicate that the San Juan basin was warm and humid during this time with a MAT of 26.8 ± 2.24oC and an estimated MAP of 121.4 cm (the standard error range is 83.6 to 176.8 cm). For another estimate of paleoclimate, a multivariate approach employing the CLAMP 3B database was used. The results with this method indicate a MAT of 17.2 ± 2.50oC with a cold month mean (CMM) temperature of 9.9 ± 2.50oC and a warm month mean (WMM) temperature of 25.3 ± 2.10oC and a MAP of 115.1 ± 12 cm. These values classify the Fossil Forest area as mesothermal. These estimates are also consistent with qualitative evidence, such as the presence of palms, gingers, weakly developed to absent growth rings in wood, and crocodilian remains. Differences between the temperature estimates may be due to several factors, such as taphonomic effects, sample size, and inherent differences in the methodologies. This research contributes to our knowledge of paleoclimate during the Late Cretaceous and provides measured variables to consider when comparing paleoecological data among regions.
Vogt, Frederick, "Paleoclimate estimates from the Late Cretaceous San Juan Basin using leaf physiognomy." (2002). Student Work. 3294.
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