Stratigraphic Sediments

Adapted from: The U.S. Global Change Research Information Office. 2001. Sediment sequence and composition. http://www.gcrio.org/geo/sediment.html. 1/13/01.

Lakes, wetlands, streams and other bodies of water, including ancient inland seas, commonly accumulate deposits derived from bedrocks, soils, and organic remains within the drainage basin. Fine particles can also be blown in by winds from distant sources. These aquatic deposits may preserve a record of past or on-going environmental processes and components, both natural and human-induced, including soil erosion, air-transported particulates, solute transport, and landsliding. The chemical, physical and biological composition of sediment sequences provides one of the best natural archives of recent environmental changes in terrestrial and aquatic systems.

Some of these bodies of water are dynamic and sensitive systems whose sedimentary deposits preserve in their chemical, physical and biological composition a chronologically ordered and resolvable record of physical and chemical changes through their mineralogy, structure, and geochemistry (e.g. organic C, biogenic silica, stable O isotopes in carbonates and cellulose, trace metals). Of particular value in determining long-term data on water chemistry are the remains of aquatic organisms (e.g. diatoms, chrysophytes, chironomids, and other algae and invertebrates) which can be correlated with various environmental parameters. In addition, fossil pollen, spores, and seeds reflect past terrestrial and aquatic vegetation. Sediment deposits can, thus, provide an indication of the degree and nature of impact of past events on the system, and a baseline for comparison with contemporary environmental change.

Spores and pollen grains can reveal past vegetation patterns. Diagnostic indicators of human activity found in sediments include: pollen or seeds of cultivated plants; fly-ash, charcoal, soot and oil particles from coal or oil-fired power stations and industrial and domestic sources; high concentrations of heavy metals (such as Pb from leaded fuels and paints), artificial radionuclides, and derivatives from fertilizers and pesticides; and geochemical gradients related to acidification.

Analysis of sediment sequence and composition is primarily used for paleoenvironmental reconstructions. Pollen, diatoms, spores, algae, and certain other micro- and macrofossils in water-laid sediments provide information about changes in composition and spatial pattern of Late Quaternary vegetation that can be used to infer regional paleoclimatic trends. The geochemical and physical character of the sediments can also provide a record of `baseline' changes in natural and human activities within and outside the drainage basin. This is a source of valuable data on pre-industrial environments, and on agricultural impacts on water resources, and it can provide a basis for watershed planning.

The degree of resolution of past records depends on deposition rates and sediment preservation, and on the ability to establish a detailed chronology. This can be difficult, for temporal and spatial resolution of the record are controlled by properties of the accumulating system. In some lakes, sediments are continuously deposited, whereas others, such as playas, dry out periodically and are less useful as a source of paleo-data. Fluvial sediments, particularly in estuaries, may preserve a record of environmental changes, but river systems tend to be more open than lacustrine. There are also problems with processes that affect organisms after death (taphonomy) and sediments after their initial deposition, such as bioturbation and diagenesis.

References and Resources:

Andrews, J. T., Carrara, P. E., King, F. B. and Stuckenrath, R. 1975. Holocene environmental changes in the Alpine Zone, northern San Juan Mountains, Colorado: Evidence from bog stratigraphy and palynology. Quaternary Research 5: 173-197.

Berglund, B.E. 1986. Handbook of Holocene palaeoecology and palaeohydrology. New York: John Wiley.

Charles, D.F. & J.P.Smol 1994. Long-term chemical changes in lakes: quantitative inferences from biotic remains in the sediment record. In Baker, L (ed) Environmental chemistry of lakes and reservoirs: 3-31. Advances in Chemistry Series 237, Washington DC: American Chemical Society.

Davis, O. K., Hevly, R. H. and R. D. Foust, J. 1985. A comparison of historic and prehistoric vegetation change caused by man in central Arizona. In: Jacobs, B. F., Fall, P. F. and Davis, O. K., editors. Late Quaternary vegetation and climates of the American Southwest. Contributions Series Number 16. American Association of Stratigraphic Palynologists, Houston, TX.

Fall, P. L. 1985. Holocene dynamics of the subalpine forest in central Colorado. Pp. 31-46 In: Jacobs, B. F., Fall, P. L. and Davis, O. K., editors. Late Quaternary vegetation and climates of the American Southwest. Contributions Series Number 16. American Association of Stratigraphic Palynolologists Foundation, Houston, TX.

Hall, S. A. 1983. Holocene stratigraphy and paleoecology of Chaco Canyon. Pp. 219-226 In: Wells, S. G., Love, D. W. and Gardner, T. W., editors. Chaco Canyon country: A field guide to the geomorphology, quaternary geology, paleoecology, and environmental geology of northwestern New Mexico. American Geomorphological Field Group, Albuquerque, NM.

Hall, S. A. and Ferguson, T. J. 1996. Pollen, stratigraphy, and chronology of the north edge of Zuni Pueblo. Kiva 61: 225-239.

Hereford, R. 1983. Effect of climate and a geomorphic threshold on the historic geomorphology and alluvial stratigraphy of the Paria and Little Colorado rivers, southwest Colorado Plateaus. Pp. 247 In: Wells, S. G., Love, D. W. and Gardner, T. W., editors. Chaco Canyon country. American Geomorphological Field Group, Albuquerque, NM.

Hevly, R. H. 1985. A 50,000 year record of Quaternary environments; Walker Lake, Coconino Co., Arizona. Pp. 141-154 In: Jacobs, B. F., Fall, P. F. and Davis, O. K., editors. Late Quaternary vegetation and climates of the American Southwest. Contributions Series Number 16. American Association of Stratigraphic Palynologists, Houston, TX.

Jacobs, B. F. 1985. Identification of pine pollen from the southwestern United States. Pp. 155-168 In: Jacobs, B. F., Fall, P. F. and Davis, O. K., editors. Quaternary vegetation and climates of the American Southwest. Contributions Series Number 16. American Association of Stratigraphic Palynologists, Houston, TX.

Jacobs, B. F., Fall, P. F. and Davis, O. K., editors. 1985. Late Quaternary vegetation and climates of the American Southwest. Contributions Series Number 16. American Association of Stratigraphic Palynologists, Houston, TX, 185 pp.

Martin, P. S. 1985. Introduction. Pp. 3-6 In: Jacobs, B. F., Fall, P. F. and Davis, O. K., editors. Late Quaternary vegetation and climates of the American Southwest. Contributions Series Number 16. American Association of Stratigraphic Palynologists, Houston, TX.

Petersen, K. L. 1985. Palynology in Montezuma County, southwestern Colorado: The local history of the pinyon pine (Pinus edulis). Pp. 47-62 In: Jacobs, B. F., Fall, P. F. and Davis, O. K., editors. Late Quaternary vegetation and climates in the American Southwest. Contributions Series Number 16. American Association of Stratigraphic Palynologists, Houston, TX.

Rosen, M.R. (ed) 1994. Paleoclimate and basin evolution of playa systems. Geological Society of America Special Paper 289.

Smol, J.P. 1995. Paleolimnological approaches to the evaluation and monitoring of ecosystem health: providing a history for environmental damage and recovery. In Rapport, D.J., C.L.Gaudet & P.Calow. Evaluating and monitoring the health of large-scale ecosystems: 301-318. Berlin: Springer-Verlag.

Street-Perrott, F.A. 1994. Palaeo-perspectives: changes in terrestrial ecosystems. Ambio 23:37-43.

Warner, B.J. (ed) 1990. Methods in Quaternary Ecology. St. John's, NF: Geological Association of Canada.

Paleobotany and Paleoclimate of the Southern Colorado Plateau. The biota of the Colorado Plateau during the middle (50,000-27,500 B.P.) and late (27,500-14,000 B.P.) Wisconsin time periods was dramatically different from that seen today. Differences were primarily a result of major climate changes associated with the last major glacial period. This site examines the environment of the southern plateau during this time. Adapted by R. Scott Anderson from his journal article.

Late Holocene Environmental Change in the Upper Gunnison Basin, Colorado. The Upper Gunnison Basin is a high elevation (3100 to 3600 m) region on the edge of the Colorado Plateau in southwestern Colorado. Its unusual ecological characteristics include an absence of plant and animal taxa that should occur here. Fossil and archaeological evidence indicates that many of the missing species existed in the Basin during the late Pleistocene to middle Holocene. Authored by Steve Emslie.

The Changing Physical Environment of the Hopi Indians of Arizona. This abstract from a classic 1942 paper by John T. Hack describes the geomorphology of the Hopi country, their dry-farming methods, the effects of a recent period of arroyo-cutting, the use of sand dunes as a means of deciphering climatic change, and evidence for the effect of the changing physical environment on ancient farming.