Studies in Neotropical Paleobotany. III. The Tertiary Communities of Panama-Geology of the Pollen-Bearing Deposits

Abstract

Samples containing fossil pollen and spores were collected from six sites representing five Tertiary formations in Panama. The Gatuncillo Formation is middle(?) to late Eocene, based on foraminifera and mollusk fossils. The formation is exposed around Madden Basin and samples were collected in the vicinity of Alcalde Diaz (Pefioncito). Material from the early Miocene Culebra Formation was obtained from a well drilled in the Contractor's Hill locality at the base of Gold Hill. The Cucaracha Formation overlies the Culebra and is also early Miocene in age. The Cucaracha material was collected from exposures along the Gaillard Cut section of the Canal. The early Miocene La Boca Formation outcrops in the same area. Although these three formations are similar in age (early Miocene), field evidence demonstrates that they are sequential from the Culebra (oldest), through the Cucaracha, to the La Boca (youngest). The Gatun Formation is late Miocene and early Pliocene in age and core samples were taken from a series of wells drilled in Gatun Lake. The location, stratigraphy, lithology, and depositional environments are summarized for these five formations. In subsequent publications the paleocommunities, paleoenvironments, and biogeographic implications will be considered for each of the microfloras. The present studies on the Cenozoic history of neotropical vegetation began in 1964 with a collection of pollen-bearing samples from Tertiary deposits in central Panama. Subsequently, other samples were obtained from the Oligocene of Puerto Rico and the Miocene of Veracruz, Mexico. At that time the vegetation of Central America was poorly known, but research by staff of the Missouri Botanical Garden, the Field Museum, and various institutions in Central America was rapidly providing new information on the composition of the flora, and on the range, ecology, and biogeographic relationships of its components. By comparison, the vegetation of more restricted areas to the north, such as Puerto Rico and Veracruz, was somewhat better known (Howard, 1973; Gomez-Pompa, 1973), and it seemed logical to begin paleofloristic studies on geologically younger deposits in these areas where modem analogs were more clearly defined. Consequently, our first studies were on the middle Oligocene San Sebastian palynoflora from Puerto Rico (Graham & Jarzen, 1969), followed by the late Miocene Paraje Solo palynoflora from Veracruz, Mexico (Graham, 1976). The decision to defer consideration of the material was fortunate for several reasons. The older Gatuncillo assemblage from proved the most difficult of our neotropical studies, and recently accumulated information on the modem vegetation was most helpful in making paleoenvironmental reconstructions. The completion of the Flora of Panama (1980) and Croat's (1978) Flora of Barro Colorado Island, initiation of Burger's Flora Costaricensis, and the Flora Mesoamerica, coordinated through the Missouri Botanical Garden and Kew, are making both specimens and information available to our studies on vegetational history. Recent biogeographic summaries are also valuable for interpreting the paleofloristic data (e.g., Gentry, 1982). Also, the pollen and spore reference collection, used for identification of the fossil palynomorphs, has increased from 10,000 slides in 1964 to nearly 22,000. From the standpoint of geology, the recently revised Geologic Map of the Canal and Vicinity, Republic of Panama (Stewart et al., 1 980) and modem plate tectonic summaries (e.g., Coney, 1982; Raven & Axelrod, 1974) are important for placing the paleobotanical data in a sound geologic context. Pollen-bearing samples from five Tertiary formations were collected in within or adjacent to the former Canal Zone (Figs. 1-3). These I Supported by NSF grants DEB-8205926, DEB-8007312, and GB-1 1862. 2 Department of Biological Sciences, Kent State University, Kent, Ohio 44242. 3Chief Geologists (retired), Canal Commission. Present address: 204 Tampa Downs Blvd., Lutz, Florida 33549. ANNm. MISSOURI BOT. GARD. 72: 485-503. 1985. This content downloaded from 157.55.39.104 on Mon, 20 Jun 2016 06:29:04 UTC All use subject to http://about.jstor.org/terms 486 ANNALS OF THE MISSOURI BOTANICAL GARDEN [VOL. 72