Palynology of tertiary sediments from tropical areas

Abstract

This article deals with the most important aspects of nearly twenty years of intensive study of the pollen-and-spore content of Tertiary sediments in some parts of tropical South America, Africa and Asia. For a proper evaluation, the character of the data, including the selection and preparation of the samples, the diversity of previous recording and the statistically achieved uniformity in presentation of these basic data needs a full exposition, given in the introduction. This is directly followed by an explanation of the process of elimination of all stratigraphically unimportant species. The resulting interpretation of climatic and topographical influences on the dispersal of pollen and spores is illustrated with examples from the fossil record. The disturbing effect of redeposition forms a problem, which in some cases can be solved. Now that the main ways of dispersal of pollen and spores are understood, the characteristics of the three major depositional environments can be distinguished by purely statistical analysis, without necessarily having any botanical information from probably related Recent plant species. Additionally botany and palaeontology may bring supporting evidence. This many-sided approach leads to the discrimination between local and regional features of environmental or time-stratigraphical significance which is needed for the evaluation of long-distance correlation. As a result the marker species can be classified into: (1) a restricted number of pantropical marker species; (2) a larger number of marker species which occurred in both the South American and west African regions, tropical today (transatlantic distribution); and (3) a still greater quantity of species which are of significance only within a single botanical province (intracontinental distribution). Thus a broad stratigraphical framework on a pantropical scale is established, which may be further subdivided regionally. These three systems of subzonation are compared with independent zoopalaeontological time-stratigraphical correlation and discussed in great detail, with special emphasis on the Carribean data. The major palynological changes marking the boundaries of the pantropical subzonation are thought to reflect the evolution of new groups of plants. They are mostly marked by a gradual incoming of pollen types. Extinction of plants is stratigraphically of less value, since they may have survived longer in one area than in another. Climatic boundaries are next in importance, but in general they are more restricted to specific regions. Similarly the immigration of plants, although producing sharp and useful boundaries, is only of regional value. Of least significance for regional correlation are the locally restricted boundaries which are caused by changes in habitat or dispersal. They may still be valuable for studies within one basin. An intriguing aspect of the palynological studies is formed by the possible affinity of the fossil type with Recent botanical species. Such affinities are obviously present in many fossil types. Whereas most are restricted to the level of family relationship, some interesting cases of much closer affinity are recorded here. In exceptional cases the morphogenetic development and migration of a restricted group of related pollen types can be traced. In the final section of this paper the species selected for this study have been formally described and illustrated; they include several new ones. The study is further documented by distribution charts and sections showing the stratigraphical significance of the marker types, as discussed in detail in the stratigraphical section.