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deposition of the Cucaracha Formation, we think it likely that once a peninsula had
formed, it would be more probable for its continued existence as a peninsula than for
its reversion back to an archipelago. Based on all the above evidence, we think it un-
likely that southern Central America existed as a complex island-arc archipelago after
the early Miocene, as suggested by Coates et al. (1992), Coates and Obando (1996),
and Collins et al. (1996). The evidence presented here indicates that the main axis of
the volcanic arc in southern Central America had coalesced into a subaerial peninsula
connected to North America by 19 Ma (Figure 8).
Figure 8.
Composite stratigraphic section of the formations along the Gaillard Cut, Panama Canal
Basin, showing lithostratigraphy and palaeoenvironmental interpretations, based on stratigraphic
relationships illustrated in Figure 6.“Data Source” indicates the stratigraphic sections used to compile
the composite section. L.C.F. = Las Cascadas Formation. E.L. = Emperador Limestone. P.M.F. =
Pedro Miguel Formation. Abbreviations at the base of the section represent grain size (C = Clay; S =
Silt; Sd = S; and G = Gravel).
