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Welcome to the Lithic Raw Material Assemblage web page. We have created an electronic version of our in-house lithic raw material assemblage, which is the primary resource for lithic identification and analysis. This assemblage is based on macroscopic identification elements including geological references, physical samples, mapped source locations, and a visual basic script program, all combined to form a GIS based system for comprehensive state-wide lithic identification and analysis. Portions of this site are still under construction but we hope you will investigate what is posted and return often for updates and improvements. Geologic sourcing of chipped stone artifacts and lithic debitage is a routine part of archaeological analysis and report writing. In order to do this task, a comparative collection is obviously necessary, one with solid geologic associations and an expansive geographic selection. Iowa is well supplied with a variety of quality, knappable lithic raw materials from both primary and secondary sources. Identification of archaeological specimens with a specific raw material is primarily accomplished by macroscopic analysis techniques geared toward achieving a “best fit” results. Microscopic viewing is sometimes applied in order to take a close-in look at surficial characteristics however, this is still a macroscopic technique. The University of Iowa’s Office of the State Archaeologist (OSA) has an expansive lithic raw material assemblage, from within the state and 7 surrounding states, as well as 14 additional states. The assemblage has a 20+ year compilation history primarily operating on an “ad hoc” basis. Recent lithic raw material identification excursions have lead to the realization that the OSA collection was in need of revision and reorganization, on a structural level, in order to provide a more systematic and consistent approach to lithic source identification. Presently, in-state samples number almost 318 while out of state samples number approximately 230.
The Iowa Geological Survey Bureau, a division of the Iowa Department
of Natural Resources, provides the following resources. They have been
integral in assisting our efforts to make this assemblage geologically
structured. Special thanks to Raymond Anderson, Brian Witzke, and Jean
Prior. The following selections have individual web page addresses at
the end of each section. The Iowa Geological Survey Bureau home page
is: The following is a brief summary of the bedrock history and development of the present surface. At the close of the Cretaceous Period the area which is now Iowa was a land surface. The soft Cretaceous deposits and older rocks were subjected to erosion. During the long Tertiary Period all the land was eroded to a surface with gentle slopes and a relief of about 200 feet. Before the end of the Tertiary time, change in the relative elevations of land and sea caused the streams to be rejuvenated and they developed new valleys. At the new grade, the streams widened their valley floor and weathering reduced the wall slopes to form a more rugged topography than before but still one with moderate slopes and with flat-topped divides at the level of the older surface. The new level is about 200 feet lower; this relief, added to that on the older surface, gives a total relief of about 400 feet. Over such a surface came the first ice sheet of the Pleistocene. The melting of the ice and dropping of the glacial debris left a new surface – a drift surface – superimposed over the bedrock surface. New drainage was inaugurated. This was modified by succeeding ice sheet invasions that buried the new valleys and more deeply covered the preglacial surface. Today, Iowa is a prairie state having a generally moderate relief and gentle slopes. In some places there are broad uplands, in other places the valley floodplain is conspicuous. In general, the state is well drained by tributaries of the Mississippi and Missouri Rivers at its borders. Some parts of the state show extensive erosion, whereas other parts show little erosion and have distinctive constructional features. It is difficult to say which is the more important in development of the topography – erosion or deposition. However, the origin of the present surface is related very closely to the glacial history of Iowa. Several kinds of topography can be differentiated. The Mankato and Cary drift in northcentral Iowa are depositional terrain. So are the alluvial bottoms of the Mississippi and Missouri Rivers and the loess deposit bordering the Missouri River flatland. The Mankato and Cary surfaces have some of the characteristics of extreme youth of the erosion cycle of glaciated area with valleys just being formed and relatively poor drainage. The surface of the Kansan drift area is much more rolling and approaches the stage of maturity. The Iowan and Tazewell surfaces are intermediate in development but probably more erosional than depositional. In the “driftless area” of northeast Iowa the surface is even more mature. http://www.igsb.uiowa.edu/gsbpubs/pdf/EM-02.pdf Iowa’s Stratigraphic Column http://www.igsb.uiowa.edu/gsbpubs/Stratigraphy/iastratcolumn4.asp Stratigraphic Column of Iowa, 2004 http://www.igsb.uiowa.edu/gsbpubs/pdf/EM-40.pdf Bedrock Geology map of Iowa, 1998 http://www.igsb.uiowa.edu/gsbpubs/pdf/EM-19.pdf
Iowa is composed of a variety of landscapes or landforms. These are the surficial expressions of geologic processes included in the study know as geomorphology. Please see the web page on this site entitled Geoarchaeology in Iowa. http://www.uiowa.edu/~osa/geo/geo.htm
Bedrock geology of northwest Iowa, Digital geologic map of Iowa, Phase 1: Northwest Iowa, B. J. Witzke, G. A. Ludvigson, R. R. Anderson, B. J. Bunker, M. K. Slaughter, J. D. Giglierano, J. P. Pope, T. M. Whitsett, and M. J. Bounk, 1997, scale 1:250,000; contract completion report to U.S. Geological Survey for Assistance Award No. 1434-HQ-96-AG-01486, August 1997.
Map: http://www.igsb.uiowa.edu/gsbpubs/pdf/OFM-1997-1.pdf Bedrock geology of northeast Iowa, Digital geologic map of Iowa, Phase 2: Northeast Iowa, B.J. Witzke, G. A. Ludvigson, R. M. McKay, R. R. Anderson, B. J. Bunker, J. D. Giglierano, J. P. Pope, A. E. Goettemoeller, and M. K. Slaughter, 1998, scale 1:250,000; contract completion report to U.S. Geological Survey for Assistance Award No. 1434-HQ-97-AG-01719, August 1998.
Map: http://www.igsb.uiowa.edu/gsbpubs/pdf/OFM-1998-7.pdf Bedrock geology of north-central Iowa, Digital geologic map of Iowa, Phase 3: North-Central Iowa, B. J. Witzke, R. R. Anderson, B. J. Bunker, G. A. Ludvigson, and S. Greeney, 2001, scale 1:250,000, supported by Cooperative Agreement 00-HQAG-0075, May 2001.
Map: http://www.igsb.uiowa.edu/gsbpubs/pdf/OFM-2001-3.pdf Bedrock geology of south-central Iowa, Digital geologic map of Iowa, Phase 4: South-Central Iowa, J. P. Pope, B. J. Witzke, R. R. Anderson, G. A. Ludvigson, B. J. Bunker, and S. Greeney, 2001, scale 1:250,000, supported by Cooperative Agreement 010-HQAG-0091, July 2002.
Map: http://www.igsb.uiowa.edu/gsbpubs/pdf/OFM-2002-1.pdf Bedrock geology of southwest Iowa, Digital geologic map of Iowa, Phase 5: Southwest Iowa, B. J. Witzke, R. R. Anderson, B. J. Bunker, and G. A. Ludvigson, 2003, scale 1:250,000, supported by Cooperative Agreement 02-HQAG-0034, September 2003.
Map: http://www.igsb.uiowa.edu/gsbpubs/pdf/OFM-2003-1.pdf Bedrock geology of east-central Iowa, Digital geologic map of Iowa, Phase 6: East-Central Iowa, B. J. Witzke, R. R. Anderson, B. J. Bunker, and G. A. Ludvigson, 2003, scale 1:250,000, supported by Cooperative Agreement 02-HQAG-0034, September 2003. Map: http://www.igsb.uiowa.edu/gsbpubs/pdf/OFM-2003-2.pdf Bedrock geology of southeast Iowa, Digital geologic map of Iowa, Phase 7: Southeast Iowa, B. J. Witzke, R. Anderson, and B. J. Bunker, 2004, scale 1:250,000, supported by Cooperative Agreement 03-HQAG-0087, September 2004. Map: http://www.igsb.uiowa.edu/gsbpubs/pdf/ofm-2004-1.pdf
We are focusing on four main methods for future directions: geologic thin sectioning, ultraviolet florence, cathode-ray luminescence, and use of the University of Iowa’s scanning electron microscope (UI-SEM). Thin sections and the UI-SEM would establish opportunities for basic microscopic analysis. All four of these methods are productive, relatively accessible, and very time and cost effective. Macroscopic lithic analysis is a given in archaeological research and a collection of physical samples, geologically organized, and geographically well documented is a must. It is our belief that this assemblage will provide that resource. Since prehistoric artifact assemblages are so often dominated by lithic materials, a well-developed comparative assemblage could afford researchers the opportunity to address a myriad of issues including but not limited to trade, the movement of people, and social interactions. The physical, geological, and geographical revision/reorganization of this assemblage are complete and housed at the OSA lab. The web-based manifestation makes the OSA Lithic Raw Material Assemblage accessible from any place, throughout the Midwest, or even worldwide.
Mary De La Garza, Web Master November 2008
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