Palynology has also been extensively used as a method of characterizing past depositional systems (paleoenvironments) (Farley and Traverse, 1990). Here palynomorphs play an important role in defining, for example, the extent of a marine or terrestrial environment. In other instances, certain types of palynomorphs may provide valuable information about water depth, temperature, salinity, and nutrient levels where the organisms once lived. In a few cases where vertebrates and invertebrates are found with palynomorphs and plant megafossils, an even greater degree of paleoecological resolution can be obtained (Westgate and Gee, 1990). Other detailed ecological studies are possible based on the frequency and types of pollen present both geographically and stratigraphically within a confined area (Graham, 1990). The use of pollen data in association with megafossil information has had a profound influence on the interpretation of paleophytogeographic patterns throughout the world (see, e.g., Graham, 2000, 2003, on plant distribution in the Caribbean). Such studies are especially valuable when they incorporate both extant and fossil data and are founded on well-defined geographic regions of the world (Graham, 1972; 1973). Other investigations have utilized paleoecological data to show that the early flowering plants were herbs or small trees living in unstable habitats during the Cretaceous (Wing and Boucher, 1998).
Certain climatic parameters can also be defined by the occurrence of certain palynomorphs, since various plants respond to minor environmental fluctuations (Pocknall, 1990). Tracing the appearance and disappearance of various palynomorphs vertically in the geologic column provides a method of tracking certain types of climatic shifts. Pollen analysis is a branch of palynology in which the relative proportions of pollen and spores are mapped vertically and horizontally; these proportions are then used to reconstruct the paleoenvironment by comparison with modern proportions of the same or closely related taxa. Although primarily applied to Quaternary deposits, similar techniques have been used in older sediments. Recovery of DNA from Holocene pollen (Bennett and Parducci, 2006) has potential for more accurate identification of certain pollen types, as well as tracking populations of plants through time.
Using modern pollen and spores, Traverse (1990) determined the palynomorph load in various types of bodies of water in the Trinity River of Texas. Understanding the dynamics of a modern model system such as this is important in the interpretation of past vegetation. Pollen extracted from marine sediments, together with stable isotopes and radiolar-ian microfossils extracted from ocean sediment cores, were used to provide data about ocean variability on millennial timescales (Pisias et al., 2001). This information can then be used to directly compare the climate responses of continental and oceanic systems, and incorporated into broader scale climate models. Palynomorphs or microfossils are preserved from every time period of geologic history and in many types of depositional environments, so they are a valuable source
FiguRe 1.75 Elaterocolpites castelaini (Cretaceous). Bar = 20 |im. (From Jardiné and Magloire, 1965; courtesy M. S. Zavada.)
of information with which to characterize changes in pale-oecosystems at different scales (Taggart and Cross, 1990). Although several books have been written on various aspects of palynology, the three-volume set, Palynology, Principles and Applications, edited by Jansonius and McGregor (1996) and the volume by Traverse (2007), Paleopalynology, provide very comprehensive and up-to-date surveys of the discipline. The recent volume edited by Van Geel (2006) focuses on the importance of various microfossils in the interpretation and reconstruction of Quaternary environments and the Glossary of Pollen and Spore Terminology (Punt et al., 2007) will be helpful in understanding the complex terminology used to described pollen and spores.
Even with our current extensive knowledge of pollen and spores, some palynological preparations occasionally contain structures which cannot be identified (FIGS. 1.74,
1.75). Graham et al. (2000) described sinuous to coiled filaments similar to the elaters of Equisetum spores (Chapter 10), secondary wall thickenings of conducting elements, or germinating fungal spores. They showed that these filaments actually represent artifacts. Termed petrofilaments (FIG.
1.76), they form when hydrocarbons (asphaltenes) react with solvents in the mounting medium.
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