ABSTRACT

Analysis of planktonic microfossils and benthic foraminifera indicates one deep-water depositional cycle in the Upper Cretaceous of northern Colombia and two major deep-water sequences in the Cenozoic of both northern Colombia and eastern Panama. Only slight evidence of an Upper Cretaceous deep-water cycle was found in eastern Panama. The Upper Cretaceous deep-water cycle in the radiolarian-rich Campanian sequence of northern Colombia is characterized by a Dictyomitra multicostata radiolarian assemblage. Deep-water or abyssal depths of the next younger cycle (Upper Paleocene-Lower Eocene) are suggested by a Pleurostomella-Nuttallides fauna in combination with a rich radiolarian assemblage. A third abyssal sequence or cycle, in Middle Oligocene-to-Lower Miocene strata, is indicated by a Melonis pompilioides fauna together with a rich radiolarian assemblage.

The shallowest-water facies, separating the deep-water cycles, represent mostly neritic or upper-bathyal depths. These are characteristic of the basal Paleocene, the Upper Eocene-Lower Oligocene, and the Upper Miocene through Quaternary sequences of eastern Panama and northern Colombia. Locally, unconformities and/or nonmarine beds may represent these geologic ages.

In contrast to the deep-water cycles of eastern Panama, the sections of the Gatun Lake area, to the west of the Rio Limon fault, show relatively shallow-water marine facies (neritic to upper-bathyal depths at the most). These shallow marine facies occur in the Eocene, in the Upper Oligocene, and in the Upper Miocene-Pliocene sections. They are separated by either paralic beds or unconformities. Faults such as the Rio Limon fault separate tectonic blocks that have contrasting stratigraphic and depositional records throughout most of the Cenozic.

In eastern Panama and northern Colombia, the shallowest-water horizons of each paleobathymetric cycle may represent times conducive to the migration of land faunas. These times are: latest Cretaceous-earliest Paleocene; late Eocene-early Oligocene; Pliocene and Quaternary.