Abstract

This paper deals with analytical investigations of pollen from the Late Cretaceous to the Lower Tertiary of the Eastern Cordillera of Colombia. The aim is to demonstrate that the lower and middle part of the Guaduas paludal formation of the Cordillera Oriental and the upper part of the Umir marine and paludal formation (lower Magdalena valley) are of Maastrichtian age. In contrast, the upper part of the Guaduas formation and the Lisama formation (lower Magdalena valley) correspond to the Lower Tertiary, probably to the Paleocene (lower Eocene).

Based on analytical pollen differences, the Maastrichtian is divided into three zones and eight subzones that are constant over considerably large distances and therefore stratigraphically useful (Tables I and II). With the aid of these palynological data, it was possible to demonstrate the gradual recession of the sea from south to north within this region and with respect to Maaestrichtian time (Table VI).

The studied section is the product of continuous sedimentation and allows the recognition of the change of flora in the Lower Tertiary. The Lower Maastrichtian (zone A) contains a relatively primitive flora but already includes a considerable number of angiosperms. In the middle part (zone B), we recognize a change in the numerical composition of the flora, apparently due to a change in the climatic conditions, in the sense of the predominance of certain palms (Monocolpites minutus, Monocolpiles huerlasi, Monocolpites medius). Then some new species of a more highly developed character appear. More new species occur in the Upper Maa strichtian (zone C); the percentage of spore plants is quite high in the Lower Maastrichtian and in the upper part of the Middle Maastrichtian, is reduced in the uppermost Maastrichtian and represents only a few percent of the pollen flora.

In the Lower Tertiary, probably during the Paleocene, another important change of flora takes place. Almost all the primitive species that are still present in the Maastrichtian, disappear and many new species are formed that coexist with certain species of the Upper Maastrichtian. Somewhat later, the flora already presents a definite "modern" character, to a certain extent typically South American.

In the systematic section, the most important species are described. Most of them belong to the Maastrichtian. Tertiary forms are marked with the sign (L) after the name. Our system is not a natural type, but of a practical nature, and the generic names are based on the names of pollen types in relation to the number and shape of the openings proposed by Iversen and Troels Smith (1950). According to this concept, pollen grains of the tricolpatae type belong to the genus Tricolpites. A pollen grain of uncertain type is classified under the genus Pollenites. Similarly, a trilete spore belongs to the genus Triletes. For certain spores that may belong to the Fungi the term -sporites (i.e., Monoporisporites) is used.

In this work, we generally and definitively use such a system of fossil pollen and spore nomenclature for pollen and spores of Cretaceous and Tertiary age. If the relationship of a fossil grain or a spore to recent plants is known or can be assumed, this relationship is indicated separately at the end of the description of the corresponding fossil flora.