Late paleozoic and early mesozoic plant fossils from the Cordillera Oriental of Colombia and correlation of the Giron Formation

Abstract

Fossil plants from a few localities in the Girón Formation and associated rocks in Santander and Boyacá provide additional information regarding the age of the Girón Formation. Despite poor preservation that precludes specific identification of many specimens, the plant assemblages provide a good indication of general age. The Mesocalamites of the Bocas Formation indicate that the Girón Formation rests on Lower Pennsylvanian rocks in the Lebrija Gorge. The assemblage of Pecopteridia, Rhodea, Calanites, and others, from the middle Girón Formation in the Lebrija Gorge, suggest an Upper Pennsylvanian age. No fossil plants were found in the upper Girón Formation, in the Lebrija Gorge, or in the Pujamanes section. The Floridablanca fossils (stratigraphically immediately below the Mesa de Ritoque section) are not related to the Middle Girón Formation in the Lebrija Gorge. However, the abundance of Ptilophyllum specimens seems to indicate Jurassic age. The plant assemblage of the Middle Clay Member of the Arcabuco section (formerly considered Girón Formation by R. L. LANGENHEIM 1959) may be Rhaetian or Jurassic. Although he believes they may be younger, these plants are accompanied by stheridia assigned by W. Bock (1953) to the Rhaetian. The assemblage of plants, which includes Sagenopter-is cf. nilssoniana, Elatocladus, Ptilophyllum, and Podozamites, generally indicates Jurassic rather than Rhaetian age. Thus, the correlation of the middle member of the Arcabuco section and the middle member of the Lebrija Gorge section is not feasible in terms of the evidence derived from the fossil plant assemblages because the Lebrija assemblage is Upper Pennsylvanian and cannot be younger than Permian. Therefore, the layers of the Arcabuco Range that were previously considered as the eastern facies of the Girón Formation are now assigned to the Montebel Formation.