Large Lakes Observatory

Sedimentary Processes

• Sediment chronology, accumulation rates, and age modeling
• Sediment-sequence Profiling
• Lake-floor Imaging
• Tropical Weathering

Sediment chronology, accumulation rates, and age modeling

All sedimentary records of environmental change depend to a critical extent on the chronology of sediment accumulation. In addition to providing the timing of changes in various environmental proxies, the chronologies and age models for cores determine calculated rates of accumulation of the sediment and its components. These accumulation rates, or fluxes, to the sea or lake floor, are themselves important measures of environmental change. We conduct sediment dating studies for many lakes, and have developed chronologies, age models, and flux calculations for a variety of environments.

Publications:

Colman, S.M., Kaufman, D.S., Bright, J., Heil, C., King, J.W., Dean, W.E., Rosenbaum, J.R., Forester, R.M., Bischoff, J.L., Perkins, M., and McGeehin, J.P., 2006, Age models for a long Quaternary lacustrine record from Bear Lake, Utah-Idaho: Quaternary Science Reviews, v. 26, p. 2281-2300.

Colman, S.M., Bradbury, J.P., McGeehin, J.P., Holmes, C.W., Edginton, D., and Sarna-Wojcicki, A.M., 2004, Chronology of sediment deposition in Upper Klamath Lake, Oregon: Journal of Paleolimnology, v. 31, p. 139-149.

Colman, S.M., Baucom, P.C., Bratton, J., Cronin, T.M., McGeehin, J.P., Willard, D., Zimmerman, A., and Vogt, P., 2002, Radiocarbon Dating, Chronologic Framework, and Changes in Accumulation Rates of Holocene Estuarine Sediments from Chesapeake Bay: Quaternary Research, v. 57, p. 58-70.

Colman, S.M., King, J.W., Jones, G.A., Reynolds, R.L., and Bothner, M.H., 2000, Holocene and recent rates of sediment accumulation in southern Lake Michigan: Quaternary Science Reviews, v. 19, p. 1563-1580.

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Sediment-sequence Profiling

Seismic-reflection methods can be used to produce high-resolution, acoustic cross sections of sedimentary sequences deposited in lakes. The distribution, sequence, character, and configuration of each unit can then be used to reconstruct many things about the history of the lake. Deposition features related to lake level, such as beaches and deltas (see first figure), are especially useful for deciphering hydrological history, and we have used them extensively in the East African Rift Lakes and other lakes that experience large fluctuations in level. Changes in lake level can also be inferred from features such as erosional unconformities and onlap-offlap of strata. Rhythmic vertical changes in the internal character of seismic sequence can also be related to cyclical climate changes.

Large scale sedimentation patterns in lakes, such as the transition from delta front to subaqueous fan to abyssal turbidite basins in Lake Baikal, can be derived from seismic-reflection profiles. Such sedimentation pattern yield a variety of information about the relationship between sedimentation and deformation in tectonically active lake basins. In many cases, actual fault-displacement history can be observed in tectonic lake basins.

As mountain glaciers or continental ice sheets advance into and retreat from lake basins, they leave behind characteristic assemblages of sediments. These sediments are often preserved in lake basins and can be imaged using seismic-reflection methods. The sequence and distribution of such deposits provide a great deal of information on the glacial history of a region.

Publications:

Scholz, C.A., Johnson, T.C., Cohen, A.S., et al., 2007, East African megadroughts between 135 and 75 thousand years ago and bearing on early-modern human origins: Proceedings of the National Academy of Sciences, v. 104, p. 16416-16421.

Colman, S.M., 2006, Acoustic stratigraphy of Bear Lake, Utah-Idaho-Late Quaternary sedimentation patterns in a simple half-graben: Sedimentary Geology, v. 185, p. 113-125.

Colman, S.M., Karabanov, E.B., and Nelson, C.H., 2003, Quaternary sedimentation and subsidence history of Lake Baikal, Siberia, based on seismic stratigraphy and coring: Journal of Sedimentary Research, v. 73, p. 941-956.

Colman, S.M., Kelts, K., and Dinter, D., 2002, Depositional history and neotectonics in Great Salt Lake, Utah, from high-resolution seismic stratigraphy: Sedimentary Geology, v. 148, p. 61-78.

Johnson, T.C., Wells, J.D., and Scholz, C.A., 1995, Deltaic sedimentation in a modern rift lake: Geological Society of America Bulletin, v. 107, p. 812-829.

Johnson, T.C., Halfman, J.D., Rosendahl, B.R., and Lister, G.S., 1987, Climatic and tectonic effects on sedimentation in a rift-valley lake--Evidence from high-resolution seismic profiles, Lake Turkana, Kenya: Geological Society of America Bulletin, v. 98, p. 439-447.

Landmesser, C.W., Johnson, T.C., and Wold, R.S., 1982, Seismic reflection study of recessional moraines beneath Lake Superior and their relationship to regional deglaciation: Quaternary Research, v. 17, p. 173-190.

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Lake-floor Imaging

Multibeam swath-bathymetry and sidescan-sonar methods can produce detailed images and configurations of features on the floors of lakes. Such features range greatly in scale from small sand waves in shallow water to large-scale glacial troughs in deep water, and include relict features such as drowned river channels. Erosional and depositional features seen on lake floors provide much information for inferring the importance and scale of processes operating in lakes. Acoustic images of the lake floor commonly provide constraints or aids in the interpretation of geological events from seismic-reflection profiles.

Lake Superior contains an unusual system of polygonal depressions that have been discovered and mapped using multibeam bathymetric and sidescan-sonar methods. The polygons are associated with other features such as pockmarks and syn-depositional faulting. These features together appear to be related to very rapid deposition of fine-grained, water-rich, lake sediments in front of a retreating glacier, along with concurrent and later de-watering and compaction.

In addition to geological interpretations, acoustic imagery is useful in applied studies, such as the search for man-made objects or effects (e.g. anchor drag marks) on the lake floor. Also, because the lake floor is the home for a host of biological creatures, acoustic-imaging methods are a significant help in characterizing and mapping the habitats of lake biota.

Publications:

Colman, S.M., 2006, Acoustic stratigraphy of Bear Lake, Utah-Idaho-Late Quaternary sedimentation patterns in a simple half-graben: Sedimentary Geology, v. 185, p. 113-125.

Cartwright, J., Wattrus, N., Rausch, D., and Bolton, A., 2004, Recognition of an early Holocene polygonal fault system in Lake Superior: implications for the compaction of fine-grained sediments, Geology, 32, 253-256.

Wattrus, N.J. and Rausch, D.E., 2001, A preliminary survey of relict shoreface attached sand ridges in western Lake Superior, Marine Geology, 179, 163-177.

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Tropical Weathering

A wide range of weathering and sediment transport processes may be evaluated using in situ-produced cosmogenic nuclides. Although these nuclides have received attention for their power as geochronometers of surface exposure, it may be argued that they are more broadly suited for study of surface processes. In many environments they may be used to evaluate collapse, erosion, burial, bioturbation, and creep, as well as providing a qualitative basis for distinguishing allochthonous from autochthonous materials. In addition, these nuclides can provide quantitative information on rates of erosion on scales of landforms and drainage basins.

Publications:

E.T. Brown, D.L. Bourlès and F. Colin, 2003. Quantitative evaluation of denudation and soil movement using in situ-produced cosmogenic nuclides. Comptes Rendus de l'Académie des Sciences Géosciences, 335, 1161-1171.

R. Braucher, D.L. Bourlès, E.T. Brown, F. Colin, J.-P. Muller, J.-J. Braun, M. Delaune, A. Edou Minko, C. Lescouet, G.M. Raisbeck, and F. Yiou, 2000. Application of in situ-produced cosmogenic 10 Be and 26 Al to the study of lateritic soil development in tropical forest: theory and examples from Cameroon and Gabon. Chemical Geology, 170, 95-111.

E.T. Brown, R.F. Stallard, M.C. Larsen, D.L. Bourlès, G.M. Raisbeck, and F. Yiou, 1998. Determination of predevelopment denudation rates of an agricultural watershed (Cayaguás River, Puerto Rico) using in situ-produced 10 Be in river-borne quartz. Earth and Planetary Science Letters, 160, 723-728.

R. Braucher, D.L. Bourlès, E.T. Brown, F. Colin, and B. Boulangé, 1998. Brazilian laterite dynamics using in situ-produced 10 Be. Earth and Planetary Science Letters, 163, 197-205.

R. Braucher, F. Colin, E.T. Brown, D.L. Bourlès, O. Bamba, G.M. Raisbeck, F. Yiou, and J.M. Koud, 1998. African laterite dynamics using in situ-produced 10 Be. Geochimica et Cosmochimica Acta, 62, 1501-1507.

J.M. Edmond, M.R. Palmer, C.I. Measures, E.T. Brown, and Y. Huh, 1996. Fluvial geochemistry of the eastern slope of the northeastern Andes and its foredeep in the drainage of the Orinoco in Colombia and Venezuela. Geochimica et Cosmochimica Acta 60, 2949-2976.

E.T. Brown, R.F. Stallard, M.C. Larsen, G.M. Raisbeck, and F. Yiou, 1995. Denudation rates determined from the accumulation of in situ produced 10 Be in the Luquillo Experimental Forest, Puerto Rico. Earth and Planetary Science Letters 129, 193-202.

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