Abstract Detail

The Miocene vegetation and environment of Western North America

DUNN, MICHAEL [1], Buechler, Walter [2], Rember, William [3].

The Late Miocene Pickett Creek Flora of Owyhee County, Idaho.

A late Miocene (8.5-10.5 m.y.) fossil flora from Pickett Creek in southwestern Idaho has been recently described. The strata are tentatively placed in the Chalk Hills Formation and provide the oldest evidence of a Neogene Snake River Plain lake-system. The fossil beds consist of 3 m of fossiliferous lacustrine sediments, topped by 3 cm of volcanic ash, 3.7 m of pure diatomite, and 15 m of coarsening upward lacustrine to fluvial sediments with a second leaf assemblage. Leaves, seeds, fruits, inflorescences, diatoms, palynomorphs, insects and fish have been recovered.  The leaf flora consists of more than 45 species, and fruits recovered include those of Acer, Ostrya, Salix, Fraxinus, Quercus, Pterocarya and Fabaceae species. In addition to random collections, a stratigraphic megafossil count was done on a controlled  60 x 100 cm column, 293 cm deep. The most abundant megafossil taxa are Quercus prelobata (50%), Q. columbiana (9%), five Salix species (8%) and five Fabaceae species (5.7%). White oaks are clearly dominant. And that fact, plus the presence of several live oaks and dryland species of Pinus (pollen), small leafed Fabaceae (leaves and fruits), Amaranthaceae, and Chenopodiaceae (pollen), and numerous evergreen species (Quercus hannibali, Q. simulata, Mahonia macginitiei, Lyonothamnus cf. parvifolius, possibly Quercus oberlii and some unassignable specimens), suggest that the broad-leaved forest of the Californian foothill woodlands is the most ecologically and climatologically similar modern forest type. Additionally, a relatively high proportion (about 6.5% of the collection) of xeric leaf forms (Quercus simulata, Quercus hannibali, Quercus oberlii, Robinia species) suggest drier habitats, and perhaps the presence of a second community, possibly on slopes above the lake.

1 - CAMERON UNIVERSITY, 2800 Gore Blvd, LAWTON, OK, 73505, USA
2 - 1192 E. Braemere Rd., Boise, ID, 83702, USA
3 - University of Idaho, Geology, Moscow, ID, 83844, USA

Keywords:
Chalk Hills Formation
Late Miocene flora
Snake River Plain.

Presentation Type: Symposium or Colloquium Presentation
Session: C2
Location: Salmon/Boise Centre
Date: Tuesday, July 29th, 2014
Time: 4:30 PM
Number: C2013
Abstract ID:77
Candidate for Awards:None