Palynology

Palynology is the study of fossil pollen (and sometimes plant spores) extracted from lake sediment, peat bog, or other matrices. The most common goal of palynological research is to reconstruct the probable character of historical plant communities, inferred from the abundance of species in dated portions of the fossil pollen record. Pollen analysis is an extremely useful tool for understanding the character of ancient vegetation and its response to changes in environmental conditions, particularly in climate. Pollen analysis also has an economically important modern industrial use in the exploration for resources of fossil fuels. Palynology is also used to help reconstruct the probable habitats and foods of ancient humans and of wild animals.

Pollen consists of microscopic grains containing the male gametophyte of coniferous (cone-bearing) and angiosperm plants. Pollen of most species of plants undergoes a long-distance dispersal from the parent plant, so that fertilization can occur among individuals (instead of self-fertilization). A plant spore is a kind of reproductive grain capable of developing as a new individual, either directly or after fusion with another germinated spore, such as the kind produced by ferns, horsetails, and club-mosses. Spores with simpler functions are produced by mosses, liverworts, algae, fungi, and other less complex organisms.

The pollen of many plants can be classified by genus, and sometimes by species, on the basis of such characteristics as size, shape, and surface texture. In contrast, most spores can only be classified by higher taxonomic levels, such as family or order. Both pollen and spores are well preserved in lake sediment, peat bog, and many archaeological sites. Fossil pollen has even been identified from the bodies of extinct animals, such as mammoths discovered frozen in arctic permafrost (permanently frozen subsoil).

Plant species in the pollen record of lake sediment and peat are not represented in the same relative abundance they are in the nearby vegetation. Wind-pollinated plant species are most abundant, because these plants release huge amounts of pollen into the environment. For example, many species of pines, which are wind pollinated, are so prolific that during their flowering season a yellow froth of pollen may occur along the edges of lakes and ponds. Insect-pollinated plant species are more rare. The great differences in pollen production among plant species must be taken into account when interpreting the likely character of local vegetation on the basis of the fossil-pollen record.

Palynologists need to understand the historical context of their samples. The common method used to determine the age of samples of mud and peat is radiocarbon dating. This technique is based on the fact that after an organism dies, it no longer absorbs carbon-14 from the atmosphere. Because carbon-14 is a rare, radioactive isotope of carbon (that is, it “decays” into simpler isotopes or elements), its amount in dead biomass decreases progressively with time. This change can be used to estimate the age of organic material by calculating the ratio of carbon-14 to stable, non-radioactive carbon-12. Radiocarbon dating is effective for samples aged between 150 and 40-50 thousand years. Younger samples may be dated on the basis of their content of lead-210, and older samples using elemental isotopes with longer half-lives.

A typical palynological study might involve the collection of one or more cores of sediment or peat from a site. The layers occurring at various depths would be dated, and samples of the pollen grains contained in the layers would be extracted, classified, and enumerated. From the dated fossil pollen of various species or genera, the palynologist would develop inferences about the nature of the forests and other plant communities that may have occurred in the local environment at the time.

In the northern hemisphere, many palynological studies have been made of changes in vegetation occurring since the continental-scale glaciers melted back, beginning about 12-15 thousand years ago. A commonly observed pattern from the pollen record is that the oldest samples, representing recently deglaciated times, indicate plant species that are now typical of northern tundra, while somewhat younger samples suggest a boreal forest of spruces, fir, and birch. The pollen assemblage of younger, more recent samples is generally dominated by temperate trees such as oaks, maples, basswood, chestnut, hickory, and other species that now have a relatively southern distribution. There may also, however, be indications in the pollen record of occasional climatic reversals, such as periods of cooling that interrupt longer, warm intervals. The most recent of these cool periods was the “Little Ice Age” that occurred between about 1550 and 1850. However, palynology has also detected more severe climatic deteriorations in the past, such as the “Younger Dryas” event that began about 11,000 years ago, causing a re-development of glaciers in many areas and temporarily reversing post-glacial vegetation development.

Palynology

Palynology is the science of fossil and modern pollen, spores , algal cysts, and other microscopic plant bodies. It is a multi-disciplinary field with applications in forensic science , geology , geography, botany , entomology , zoology, archaeology , immunology, and environmental sciences. The term palynology is derived from the Greek terms paluno, meaning to strew, or to sprinkle, and suggestive of palé, meaning fine meal, or the Latin pollen, meaning also fine flour or dust.

The study of palynology has, by necessity, been closely associated with the development and later improvements of microscopes . Because pollen grains are microscopic, mankind had to wait until the invention of the compound microscope in the mid 1600s before pollen grains could be seen in any detail. During the next two centuries following the invention of the microscope, botanists studied the morphological features of pollen grains, their form and structure, and began to develop taxonomic keys for their identification .

Pollen carries the male gametes of flowering and cone-bearing plants, and spores are the asexual reproductive bodies of ferns, mosses, and fungi. Plants produce vast quantities of microscopic pollen and spores, which they disperse with the help of animals, wind, or water. Although individual pollen grains are invisible to the naked eye, they occur on almost every surface in nature. They are also highly resistant to decay, being found in rocks many millions of years old, and also persisting on or in soil, dirt, and other materials for many years. Pollen and spores come in an infinite variety of shapes and have complex surface ornamentation. Each plant type has distinctive pollen that can be distinguished from the pollen of other plants. For this reason pollen and spores are often called nature's fingerprints for plants.

The major commercial application of palynology is in geology, where it is used to date sediments to assist in petroleum, mining, and underground water exploration. Aeroallergy is the branch of medicine concerned with the seasonal occurrence, abundance, and allerogenic effect of spores and pollen. The study of extant palynomorphs, which are either living, still retain their cell contents, or whose cell contents have been removed by maceration, is called actuopalynology. It includes the disciplines mellisopalynology (study of pollen in honey or other bee products), pollination ecology (distribution of pollen by wind or animals and its efficacy in fertilization and seed set), aeroallergy, and criminology (i.e., forensic palynology). In the discipline of archaeological palynology pollen, spores, and other palynomorphs from archeological sites are employed to reconstruct prehistoric diet, funeral practices, artifact function and source, archaeological feature use, cultivation and domestication of plants, and human impact on vegetation.

The term forensic palynology refers to the use of pollen and spore evidence in legal cases. It is often possible to be very specific about where a person or thing has been from the pollen types that occur together in a sample. Pollen and spore production and dispersion are important considerations. The expected production and dispersal patterns of spores and pollen (called pollen rain) for the plants in a given region will yield the type of "pollen fingerprint" to expect in samples that come from that area. Therefore, the first task of the forensic palynologist is to try to find a match between the pollen in a known geographical region with the pollen in a forensic sample. Knowledge of pollen dispersal and productivity often plays a major role in solving such problems.

Pollen can help destroy or prove alibis, link a suspect to the scene of a crime, or link something left at the crime scene to a suspect. It can also help to determine what country or state drugs, food, merchandise, and antiques among other things, have come from. In its broader application, the field of forensic palynology also includes legal information derived from the analysis of a broad range of microscopic organisms such as dinoflagellates, acritarchs, and chitinozoans that can be found in both fresh and marine environments. One of the earliest successful cases where forensic palynology was used pertained to a criminal case in Austria in 1959.

Soil, dirt, and dust are common elements at almost every crime scene. Woven cloth, woolen blankets, ropes, clothing, and fur all make excellent traps for pollen and spores. Woven materials and fur are made of tiny interwoven fibers . When air comes in contact with woven materials, the fibers become filters that retain solid particles, such as pollen and spores. Woolen garments, including blankets, skirts, suits, ties, and sweaters, make the best pollen and spore traps.

If working on a case, pollen is extracted from exhibits (washed or scraped from items, or taken off with tape lifts); control samples are collected; and if possible, the crime scene attended. The samples are then taken through various preparation procedures so that the detail of the pollen can be examined with microscopes. Some cases are quite easy and require only the comparison of assemblages in the control and forensic sample; others require much research in the laboratory with other scientists, the public, and police.

see also Botany; Crime scene investigation; Entomology; Fingerprint; Forensic science; Geology; Identification; Microscopes; Pollen and pollen rain; Reference sample; Soils; Spores.

Palynology

Palynology is the study of fossil pollen (and sometimes plant spores) extracted from lake sediment, peat bog, or other matrices. The most common goal of palynological research is to reconstruct the probable character of historical plant communities, inferred from the abundance of species in dated portions of the fossil pollen record. Pollen analysis is an extremely useful tool for understanding the character of ancient vegetation and its response to changes in environmental conditions, particularly in climate. Pollen analysis also has an economically important modern industrial use in the exploration for resources of fossil fuels . Palynology is also used to help reconstruct the probable habitats and foods of ancient humans and of wild animals.

Pollen consists of microscopic grains containing the male gametophyte of coniferous (cone-bearing) and angiosperm plants. Pollen of most species of plants undergoes a long-distance dispersal from the parent plant, so that fertilization can occur among individuals (instead of self-fertilization). A plant spore is a kind of reproductive grain capable of developing as a new individual , either directly or after fusion with another germinated spore, such as the kind produced by ferns , horsetails , and club-mosses. Spores with simpler functions are produced by mosses, liverworts, algae , fungi , and other less complex organisms.

The pollen of many plants can be classified by genus, and sometimes by species, on the basis of such characteristics as size, shape, and surface texture. In contrast, most spores can only be classified by higher taxonomic levels, such as family or order. Both pollen and spores are well preserved in lake sediment, peat bog, and many archaeological sites. Fossil pollen has even been identified from the bodies of extinct animals, such as mammoths discovered frozen in arctic permafrost (permanently frozen subsoil).

Plant species in the pollen record of lake sediment and peat are not represented in the same relative abundance they are in the nearby vegetation. Wind-pollinated plant species are most abundant, because these plants release huge amounts of pollen into the environment. For example, many species of pines , which are wind pollinated, are so prolific that during their flowering season a yellow froth of pollen may occur along the edges of lakes and ponds. Insect-pollinated plant species are more rare. The great differences in pollen production among plant species must be taken into account when interpreting the likely character of local vegetation on the basis of the fossil-pollen record.

Palynologists need to understand the historical context of their samples. The common method used to determine the age of samples of mud and peat is radiocarbon dating. This technique is based on the fact that after an organism dies, it no longer absorbs carbon-14 from the atmosphere. Because carbon-14 is a rare, radioactive isotope of carbon (that is, it "decays" into simpler isotopes or elements), its amount in dead biomass decreases progressively with time . This change can be used to estimate the age of organic material by calculating the ratio of carbon-14 to stable, non-radioactive carbon-12. Radiocarbon dating is effective for samples aged between 150 and 40-50 thousand years. Younger samples may be dated on the basis of their content of lead-210, and older samples using elemental isotopes with longer half-lives.

A typical palynological study might involve the collection of one or more cores of sediment or peat from a site. The layers occurring at various depths would be dated, and samples of the pollen grains contained in the layers would be extracted, classified, and enumerated. From the dated fossil pollen of various species or genera, the palynologist would develop inferences about the nature of the forests and other plant communities that may have occurred in the local environment at the time.

In the northern hemisphere, many palynological studies have been made of changes in vegetation occurring since the continental-scale glaciers melted back, beginning about 12-15 thousand years ago. A commonly observed pattern from the pollen record is that the oldest samples, representing recently deglaciated times, indicate plant species that are now typical of northern tundra , while somewhat younger samples suggest a boreal forest of spruces, fir, and birch. The pollen assemblage of younger, more recent samples is generally dominated by temperate trees such as oaks , maples , basswood , chestnut , hickory, and other species that now have a relatively southern distribution. There may also, however, be indications in the pollen record of occasional climatic reversals, such as periods of cooling that interrupt longer, warm intervals. The most recent of these cool periods was the "Little Ice Age" that occurred between about 1550 and 1850. However, palynology has also detected more severe climatic deteriorations in the past, such as the "Younger Dryas" event that began about 11,000 years ago, causing a re-development of glaciers in many areas and temporarily reversing post-glacial vegetation development.

Limestone

Limestone is a sedimentary rock composed almost entirely of the mineral calcite (calcium carbonate, CaCO₃). The precursor calcium-carbonate sediment that existed prior to lithification of limestone can be of several types. These sediment types include carbonate mud, carbonate fossil fragments, carbonate pellets and rip-up clasts, and ooids. Carbonate mud is made of microcrystalline calcite crystals (crystals of a few microns in size) that form directly from seawater and from the disintegration of some calcareous marine algae. Carbonate fossil fragments include all shelly organic debris originally composed of CaCO₃ (in the form of calcite or a denser phase, aragonite). Carbonate pellets and rip-up clasts are small lumps of carbonate mud (a few millimeters in size) that have been consolidated either by being eaten and excreted (pellets), or by settling and then being ripped-up by wave energy (rip-up clasts). Ooids are sand-sized, concentrically layered grains that form by inorganic precipitation of calcium carbonate during agitation of seawater (usually by rolling on a shallow shoal area of the ocean).

The sediment precursor to limestone forms in the shallow marine realm or, less commonly, within carbonate-rich lakes . A special kind of marine limestone, composed entirely of the remains of marine micro-plankton, is called chalk. There is also a special kind of limestone, travertine, which forms from fresh-water deposition of dissolved carbonate within cave and cavern systems.

The original sediment determines limestone texture (i.e., the size and nature of grains in the rock). Micritic limestone is made of microcrystalline calcite like the original carbonate mud. Fossiliferous limestone is made of a large proportion of fossil fragments and the balance of the rock is either carbonate

mud, carbonate cement (sparry calcite crystals between grains), or a mixture of both. Pelletal limestone and limestone with ripup clasts is much like fossiliferous limestone regarding the balance of the rock (mud, spar, or both). Ooid limestone has a high proportion of ooid grains in it. Limestone that is made of sediment formed within or near organic reefs is sometimes referred to as reef rock or boundstone.

Limestones contain extensive fossil records spanning much geologic time , including microfossils, megafossils, and trace fossils (or ichnofossils). Limestones are particularly common sedimentary rocks , representing times in Earth history when globally warm conditions prevailed along with particularly high sea levels. High sea levels during these times promoted development of extensive, shallow seas (i.e., epicontinental seas) across much of Earth's continental space . Epicontinental seas with extensive limestone deposits characterize the geological time intervals such as Late Cambrian-Ordovician, Mississippian, and Cretaceous.

Limestones are particularly susceptible to dissolution by acidic groundwater , and for this reason, extensive subterranean cave and cavern systems are known from within many limestone formations. The calcite in limestones is also susceptible to replacement by dolomite where the limestone meets magnesium-rich, briny groundwaters. Where this replacement is extensive, limestone formations are changed to dolostones by this process. Considerable porosity (approximately seven percent by volume) is created within the former limestone (now dolostone), and this pore space can host important hydrocarbon and mineral deposits. Limestone is also commonly replaced by chert in places where silica has been transported into the limestone by groundwaters.

Limestone is economically important as a source of quicklime (CaO), which can be produced by heating calcite to drive off carbon dioxide (CO₂). In addition to agricultural uses, limestone is used in cement making and as a flux in the smelting of iron . Limestone can be used also for road construction and as ornamental building stone.

Palynology

Palynology is the study of plant pollen, spores, and certain microscopic planktonic organisms (collectively termed palynomorphs) in both living and fossil form. Botanists use living pollen and spores (actuopalynology) in the study of plant relationships and evolution, while geologists may use fossil pollen and spores (paleopalynology) to study past environments, stratigraphy , historical geology, and paleontology.

The oil industry is credited with demonstrating the usefulness of palynomorphs in the study of stratigraphic sequences of rocks and the potential for oil and gas exploration. Because palynomorphs are resistant to decomposition and are produced in great abundance, their recovery from rocks and sediments via special and careful chemical treatments is possible and provides scientists with information needed to describe plant life of past ages. By describing the sequence of selected palynomorphs through the rock layers of Earth, stratigraphers (scientists who study the rock layers of Earth) are able to correlate rocks of the same age and may therefore locate and correlate layers that contain oil or natural gas.

Palynomorphs found in the gut of early humans, and those found with artifacts found at their grave sites have been used to understand the diets and hunting or farming practices of these early people. For instance, the pollen and spores found in the feces of humans living seven thousand years ago allowed scientists to describe the changes in the diets through several generations of native people in northern Chile.

Melissopalynology is the study of pollen in honey, with the purpose of identifying the source plants used by bees in the production of honey. This is important to honey producers because honey produced by pollen and nectar from certain plants as mesquite, buckwheat, or citrus trees demand a higher price on the market than that produced by other plant sources. Some plants may produce nectar and pollen that is harmful to human health. A careful examination of the pollen types found in honey may identify these toxic plants, and the honey produced may be kept out of the commercial market.

Palynology is a useful tool in many applications, including a survey of atmospheric pollen and spore production and dispersal (aerobiology), in the study of human allergies, the archaeological excavation of shipwrecks, and detailed analysis of animal diets. Entomopalynology is the study of pollen found on the body or in the gut of insects. It is useful for determining insect feeding and migratory habits, especially as it involves economically important insects (e.g., the boll weevil). Forensic palynology, or the use of pollen analysis in the solving of crimes, is used by law enforcement agencies around the world.

see also Dendrochronology; Forensic Botany; Pollination Biology.

David M. Jarzen

Bibliography

Bryant, V. M., Jr., and S. A. Hall. "Archaeological Palynology in the United States:A Critique." American Antiquity 58 (1993): 416-21.

Hoen, P. "Glossary of Pollen and Spore Terminology." [Online] 1999. Available at http://www.biol.ruu.nl/~palaeo/glossary/glos-tin.htm.

Jarzen, D. M., and D. J. Nichols. "Pollen." In Palynology: Principles and Applications, Vol. 1, eds. J. Jansonius and D. C. McGregor. American Association of Strati-graphic Palynologists Foundation, 1996.

Traverse, Alfred. Paleopalynology. Boston: Unwin Hyman, 1988.