23 - Sedimentation of palynomorphs in rocks of pre-Devonian age

Summary

Introduction

Paleopalynology is the study of microscopic structurally preserved organic matter which can be extracted from siliciclastic rocks by acid maceration. Traditionally, paleopalynology includes the study of various algal remains, microscopic parts of some protists and animals, spores of cryptogamic plants and fungi, and the pollen grains of seed-bearing plants, all of which are thought to possess a resistant organic outer wall composed of sporopollenin, chitin, or a similar derivative. This definition restricts the palynological record prior to the evolution of the terrestrial embryophytic plants to the resistant remains of algal phytoplankton, chitinous scolecodonts, and possible zooplankton such as chitinozoans. However, in this chapter I expand the view of paleopalynology to include some other structurally intact, microscopic organic remains which are thought to be of planktonic origin. This means that phytoplankton preserved in both siliciclastic (Acritarcha) and in cherty carbonate facies (Cryptarcha, sensu Diver & Peat, 1979)) is included.

In broadest terms, the study of palynomorphs as sedimentary particles concerns the distribution and dynamics of biological carbon through geologic time. The stratigraphic record of microplankton is of great importance in modeling the dynamics of former marine and terrestrial ecosystems. The changes in the flux of carbon brought about by the rise of a standing biomass in terrestrial habitats represents a fundamental shift in the distribution of biogenic carbon on the earth. This shift occurred during the Silurian Period and is marked by the fossil record of the cryptospores, which represent the palynological evidence of a transition to an embryophytedominated terrestrial ecosystem (Strother, 1991).