Abstract Detail

Campanian-Maastrichtian floras on Laramidia: vegetation trends west of the seaway

Upchurch, Jr., Garland [1], Parrott, Joan [2], Estrada-Ruiz, Emilio [3], Contreras, Dori L. [4].

Climate and vegetation of southern Laramidia: A paleobotanical reconstruction for the upper Campanian Jose Creek Member, McRae Formation, south-central New Mexico.

Leaf physiognomy of non-monocot angiosperms (“dicots”) is a long-standing source of data on Late Cretaceous terrestrial climate. Wood anatomy of non-monocot angiosperms has similar potential, but error in the relation between wood anatomy and climate leads wood anatomists to urge caution. Leaf and wood macrofossils rarely occur in sufficiently close stratigraphic/geographic proximity to permit cross checking, especially wood assemblages with high species diversity. The upper Campanian (74–76 mya) Jose Creek Member (JCM) of the McRae Formation, south-central New Mexico, USA, provides a unique opportunity to reconstruct climate for southern Laramidia through the combined analysis of leaf physiognomy, wood anatomy, and life form. The JCM preserves an abundant and diverse impression flora of >175 species, and an exceptionally-preserved permineralization flora of >50 species that comprises non-monocot angiosperm woods, conifer woods, and stems of palms and other large monocots. Leaf margin analysis estimates Mean Annual Temperature (MAT) of 21–22ºC, based on an early collection of 42 species and an expanded collection of 161 species, both from the same volcanic ash bed. Wood anatomy estimates warmer temperatures, with 30 and 38 species from the entire JCM estimating MAT of 24–27ºC and Cold Month Mean Temperature (CMMT) of 16–23ºC. Leaf and wood estimates of MAT and CMMT are congruent with the absence of annual rings in most angiosperm and conifer wood types, and the presence of diverse rosette plants, including multiple types of palm stems and leaves, thermophilic cycad leaves and cones (cf. Ceratozamia) and a large palm stem base suggestive of tree habit. These constrain MAT to >13ºC and CMMT to >10–11ºC. Estimates of Mean Annual Precipitation (MAP) are in general less certain, but year-round precipitation is indicated by abundant palms and gingers in non-swamp environments and non-calcic paleosols; wood anatomy sets an upper limit for MAP of ~3.5 m. The more southerly Olmos flora of Coahuila, Mexico provides similar climatic estimates from dicot leaf margins and wood anatomy but with possibly wetter conditions, consistent with major coal deposits. The range of estimates for the JCM and Olmos floras indicates climate most comparable to that of modern paratropical to tropical forest (sensu Wolfe, 1979) and tropical lowland to premontane moist/wet forest (sensu Holdridge, 1947). The JCM and Olmos floras, in combination with marine geochemical data, imply that lowland regions of southern Laramidia had fully tropical temperatures during the late Campanian-Maastrichtian.

1 - Texas State University, Department Of Biology, 601 University Drive, San Marcos, TX, 78666, USA
2 - Texas State University, Department of Biology, 601 University Drive, San Marcos, TX, 78666
3 - Instituto Politécnico Nacional, Departamento de Zoología, Prolongación de Carpio y Plan de Ayala s/n,, Col. Santo Tomás, Ciudad de México, MX, 11340
4 - University of California Berkeley

Keywords:
Laramidia
Paleobotany
Paleoclimate.

Presentation Type: Colloquium Presentations
Session: CO3, Campanian-Maastrichtian floras on Laramidia: vegetation trends west of the seaway
Location: Sundance 3/Omni Hotel
Date: Wednesday, June 28th, 2017
Time: 8:45 AM
Number: CO3002
Abstract ID:337
Candidate for Awards:None