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the Culebra model will be rejected and the La Boca model supported. Alternatively, if
the La Boca Formation is found to be older than the Cucaracha Formation, then the La
Boca model will be rejected and the Culebra model supported.
Figure 5.
The two alternative stratigraphic models for the formations exposed along the Gaillard Cut
portion of the Panama Canal: (1) the Culebra model (Escalante, 1990; Woodring and Thompson,
1949; Van den Bold, 1972) and (2) the La Boca model (Graham et al., 1985; Stewart et al., 1980;
Woodring, 1964).
MATERIALS AND METHODS
Field work was conducted in February 2003, July 2003 to December 2004, and March
2005. This study benefited greatly from many newly exposed surface sections made
by recent widening of the Panama Canal by the Panama Canal Authority (ACP) and
the construction of a second bridge across the canal (Centennial Bridge). We measured
eight stratigraphic sections between the towns of Pedro Miguel and Gamboa along
the Gaillard Cut portion of the Panama Canal (Figure 6). These outcrop sections were
measured with a Jacob Staff and Brunton compass or with a tape and Brunton com-
pass (methods described in Compton (Compton, 1985)). We collected rock and fossil
samples, recording their stratigraphic position and deposited them at the Center for
Tropical Paleoecology and Archaeology, Smithsonian Tropical Research Institute, and
at the Florida Museum of Natural History. Well logs derived from drill cores from the
archives at the ACP were also examined in order to aid correlation of surface sections
and to fill in missing intervals (ECB-3, ECB-5, and GH-10 well logs at the ACP; Fig-
ure 6). We used the biochronology of the land mammals from the Gaillard Cut local
fauna, as modified by MacFaddden (2006). The land-mammal chronology and North
American Land Mammal Age subdivsions follow Tedford et al. (2004).
