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between North and Central America were much better connected in the early to mid-
Neogene than previously thought and (4) ocean circulation and biogeographic connec-
tion between the Pacifi c and Caribbean had to have been much more constricted in the
early Neogene than previously thought.
RESULTS
Results from our lithostratigraphic, biostratigraphic and Sr chemostratigraphic analy-
ses of the formations exposed along the Gaillard Cut allow us to reject the La Boca
model. Instead, all data sets support the Culebra model as being the correct interpreta-
tion for the stratigraphy of the formations along the Gaillard Cut (Figures 6, 9, and
10). We found no evidence for interfingering relationships between the Cucaracha and
L.C.Fs., or between the La Boca and P.M.Fs., as proposed by Stewart et al. (1980) and
Graham et al. (1985). We did find that what has been called the La Boca Formation
(i.e., lower Culebra Formation), conformably overlies the L.C.F. and that the upper
Culebra Formation underlies the Cucaracha Formation, which in turn is overlain by
the P.M.F. (Figure 6).
Figure 9. Geologic history of the Panama Canal Basin, showing geologic time, stratigraphy, and
paleogeography. Vertical lines represent a hiatus. Question marks under stratigraphy represent
uncertainty in age. Time scale from Gradstein et al. (2004). Oligo. = Oligocene. Pleis. = Pleistocene.
 
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