Where to look for palynomorphs?
Koraljka Bakrač
Hrvatski geološki institut - Croatian Geological Survey, Sachsova 2, 10000 Zagreb, Croatia
E-mail address: kbakrac@hgi-cgs.hr
Palynomorphs are broadly defined as organic-walled microfossils between 5 and 500
micrometers in size. Palynomorphs may be composed of organic material such as chitin,
pseudochitin, sporopollenin and dinosporin. Typically, palynomorphs are dinoflagellate cysts,
acritarchs, spores, pollen, fungi, scolecodonts (scleroprotein teeth, jaws and associated features of
polychaete annelid worms), arthropod organs (such as insect-mouth parts), chitinozoans and
microforams. Palynomorph microscopic structures that are abundant in most sediments are resistant
to routine pollen extraction including strong acids and bases, and acetolysis, or density separation.
Palynomorphs are important in determining the type of prehistoric life that existed at the
time the sedimentary formation was laid down. As a result, these microfossils give important clues to
the prevailing climatic conditions of the time. Their paleontological utility derives from an abundance
numbering in millions of cells per gram in organic marine deposits, even when such deposits are
generally not fossiliferous. Palynomorphs, however, generally have been destroyed in metamorphic
or recrystallized rocks.
Beginning with Precambrian acritarchs up to 1.4 billion years old, palynomorphs occur in
sedimentary rocks of all ages and from many different sedimentary and biological environments.
They originate both on land (spores/pollen = sporomorphs) and in fresh water (Botryococcus and
other algae, some dinoflagellates and a few sporomorphs) and salt water (most dinoflagellates,
acritarchs, and other algal microscopic remains, the extinct chitinozoans, scolecodonts, foraminiferal
test linings, a few sporomorphs) (Traverse, 2007).
The whole subject of the various processes that affect palynomorphs from their shedding by
the producing organism to their incorporation in sediment and on through lithification of the
enclosing sediment, and even its later thermal history in the rock so formed, is all part of taphonomy
(Traverse, 2007).
The propensity of spores/pollen to be preserved in sediments depends largely on the amount
of sporopollenin in the exine, which is partly a function of the thickness of the exine, and of the
division of the exine between endexine and ektexine (the more ektexine, the more sporopollenin),
and partly due to other factors. Hopkins and McCarthy (2002) have shown by experimental oxidation
of dinoflagellate cysts that peridinioid (proximate) cysts were destroyed more readily than chorate
forms (those with processes), which would thereby be enriched in sediments subject to oxidation.
They also observed that pollen was more resistant to experimental oxidation than dinocysts and that
bisaccate conifer pollen was the most resistant of all forms studied. This sort of “taphonomic effect”
can obviously affect relative abundances and can even cause absence of some palynomorphs that
were originally present. Sedimentary situation into which palynomorphs are deposited also has very
great control over the likelihood of preservation: acid environments preserve better than alkaline,
reducing environments better than oxidizing and quiet sedimentary situations better than very
energetic ones. The exclusion of oxygen is especially important. However, even some seemingly
unlikely sites of deposition such as soils can preserve pollen, though preservation in soils is erratic
and usually poor, and thus the records are probably biased toward resistant types. Furthermore, in
soils, downwashing and redistribution by vectors such as earthworms must be allowed for.
Spores/pollen spectra of soils often permit drawing of conclusions about vegetational history during
soil genesis (Dimbleby, 1961). However, Cushing (1966) has shown that preservability of
spores/pollen in sediment is the result of complex factors, not just sporopollenin content alone.
Furthermore, the destruction of exines follows various pathways in various situations: degraded
exines in which the structure is generally altered are common in silty sediments, whereas superficial
corrosion (pitting, etc.) is more likely to be encountered in peat, and crumpling is characteristic of
copropels (caused by processing in animal guts).
Spores/pollen exines (and other palynomorphs such as dinoflagellate cysts and fungal spores)
when occurring in water are technically, from their size, silt or very fine sand particles, which behave
in water according to the same principles as govern other clasts(Traverse, 2007). The low specific
gravity (about 1.4) of palynomorphs, the fact that they contain internal space, their tendency after
initial stages of preservation to be tiny disks rather than spheres, and other factors give them
somewhat different settling characteristics from mineral particles (specific gravity equal to or greater
than 2.4) of the same maximum size. Stanley (1965) observed that palynomorphs usually sort out in a
mineral silt fraction one class smaller than would be expected from the palynomorph size, which is
another way of saying that they do not settle as fast as mineral particles of the same maximum
dimension. The relative proportion of various classes of palynomorphs (spores/pollen,
dinoflagellates, acritarchs) in sediments is a function of distance from shore and depth of water.
Pollen grains preserved in lake and bog sediment provide a record of past vegetation that has
been an important source of information about climate and land cover during the Quaternary Period.
The study of pollen grains in soil samples from an archaeological site provides information on
ancient human use of plants and plant resources (Kipfer, 2000). The pollen grains of trees, shrubs,
grasses, and flowers are preserved in either anaerobic conditions or in acid soils. Samples can be
taken from the deposits by means of a core or from individual layers at frequent intervals in a section
face on an archaeological site. As a dating technique, pollen has been used to identify different zones
of arboreal vegetation which often correspond to climatic changes. The sediments most frequently
investigated are peat and lake deposits, but the more acid soils, such as podsols, are also analyzed.
Radiocarbon dates may be taken at intervals in the sequence, and it is possible to reconstruct the
history of vegetation in the area around the site where the samples were taken.
Coprolite analysis can provide a great deal of information on prehistoric diet and subsistence.
This includes both the analysis of macrobotanical and palynological remains. While palynology can
contribute to studies of diet, it can also inform on the types of economic and background pollen,
seasonality of site occupation, and paleoenvironmental conditions (Bryant and Holloway 1983;
Pearsall 2000; Reinhard and Bryant 1992).
There have been many studies that attempt to determine the function of artefacts. These
involve studies of botanical remains associated with artefacts, including pollen. An often used and
potentially very important is artefact washes that involve the recovery and analysis of pollen directly
from the surface of artefacts, such as complete ceramic containers and lithic artefacts, especially,
grinding tools. These analyses can provide information both on the plants used at the site where the
artefacts are found and on the uses of the artefacts themselves (Bryant and Holloway 1983; Pearsall
2000; Shafer 1979).
Abundant pollen has been found associated with copper artefacts and deeply buried tree
bark. Pollen was preserved around copper, apparently due to dissolved copper salts which act as a
fungicide. Tree bark, an excellent collection surface for air-borne pollen, can yield abundant pollen
when preserved (King et al, 1975).
So, look everywhere for palynomorphs, take samples and palynologist will try to find the best
method to extract them and analyse.
References:
Bryant, V. M., and Holloway, R. G. (1985): A late-Quaternary paleoenvironmental record of Texas: an overview
of the pollen evidence, in: Pollen Records of Late-Quaternary North American Sediments (V. M. Bryant, Jr. and
R. G. Holloway, eds.), Am. Assoc Strat. Palynol. Found., pp. 39–70.
Cushing, E. J. (1966): Evidence for differential pollen preservation in Late Quaternary sediments in Minnesota,
Rev. Palaeobot. Palynol. 4:87–101.
Dean, G. (1993): Use of pollen concentrations in coprolite analysis: an archaeobotanical viewpoint with a
comment to Reinhard et al. (1991). Journal of Ethnobiology 13:102-114.
Dimbleby, G. W. (1961): Soil pollen analysis, J. Soil Sci. 12(1):1–11.
Dimbleby, G. W. (1985): The Palynology of Archaeological Sites, Academic Press, London. A rather brief
summary of the methods of, problems encountered in, and potential application of, palynology in archeology.
Hopkins, J. A. and McCarthy, F. M. G. (2002): Oxidation and the palynological record, Palynol. 26:266–267.
King, J. E., W. E. Klippel, and R. Duffield (1975): Pollen Preservation and Archaeology in Eastern North America.
America Antiquity 40: 180-190.
Kipfer, B.A. (2000): Encyclopedic Dictionary of Archaeology, Kluwer Academic, 724 p.
Pearsall, D. M. (2000) Paleoethnobotany: a Handbook of Procedures. 2nd ed. Academic Press, San Diego,
California.
Reinhard, K. J., and V. M. Bryant (1992): Coprolite Analysis: a Biological Perspective on Archaeology. In
Archaeological Method and Theory vol. 4, edited by M. B. Schiffer, pp. 245-288. University of Arizona Press,
Tucson.
Shafer, H. J. (1979): Organic Residue Analysis in Determining Stone Tool Function. In Lithic Use-Wear Analysis,
edited by B. Hayden, pp. 385-399. Academic Press, New York.
Sobolik, K. D. (1996): Pollen as a guide to prehistoric diet reconstruction, in: Palynology: Principles and
Applications, vol 3 (J. Jansonius and D. C. McGregor, eds.), Dallas, Am. Assoc. Strat. Palynol. Found., pp. 927–
931.
Stanley, E. A. (1965): Abundance of pollen and spores off the eastern coast of the U.S., Southeastern Geol.
7:25–33.
Traverse, A. (2007): Paleopalynology, Second Edition (Topics in Geobiology 28). Springer, Dordrecht, Netherlands, 813.