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Hansel, Ardith K., and W. Hilton Johnson, 1996, Wedron and Mason Groups: Lithostratigraphic Reclassification of Deposits of the Wisconsin Episode, Lake Michigan Lobe Area: Illinois State Geological Survey Bulletin 104, 116 p.

Ardith K. Hansel and W. Hilton Johnson

Robein Silt (Willman and Frye 1970; a direct replacement name for Farmdale silt, Frye and Willman 1960).

Robein, a village in Tazewell County.

===History&#47;background=== Frye and Willman (1960, p. 6) defined the Farmdale silt as "... massive silt, noncalcareous, light brown to pale purple, that commonly contains wood fragments and locally is replaced by peat." They interpreted it to be primarily silt that was derived from the Roxana Silt and reworked by sheetwash and colluvial processes. The unit was renamed Robein Silt in 1970 by Willman and Frye to avoid confusion because the name Farmdale also had been applied to other sediment (Leighton 1960). They indicated the Robein Silt accumulated primarily during the Farmdalian Subage. Because the Robein Silt is leached and commonly contains organic remains, it is a distinctive stratigraphic marker unit and the most widely radiocarbon-dated unit in Illinois. Although distinct and traceable in the subsurface, the Robein Silt is thin (usually less than 2 m thick). In this report, it is reduced in rank to a member within the Roxana Silt. <center> <gallery widths=250px heights=250px perrow=4> File:104-Figure_9.jpg|alt=Stratigraphic diagram showing relationship of Robein Member within Roxana Silt and overlying and underlying glacial units.|{{File:104-Figure_9.jpg}} </gallery> </center> ==Type section== ===Type location=== Farm Creek Section, along the south side of Farm Creek, 2 kilometers south of Sunnyland, Illinois. ===Type status=== Still exposed, but the Robein Member is only locally present along the exposure. ==Reference section== ===Reference location=== Athens Quarry North, Danvers, and Charleston Quarry Sections; all good for lithology and contacts. ===Reference author&#40;s&#41;=== ===Reference status=== ==Stratigraphic relationships== The Robein Member consists of stratified to massive silt, sandy silt, humic material, and peat. Where present, it occurs as the uppermost member of the Roxana Silt. It is overlain by the Peoria Silt, the Henry and Equality Formations, or the Wedron Group. The Farmdale Geosol is developed in it, and pedogenesis commonly obscures stratification within the unit. <center> <gallery widths=250px heights=250px perrow=4> File:104-Figure_32.jpg|alt=Diagram showing stratigraphic position of Robein Member with associated soil development and overlying units.|{{File:104-Figure_32.jpg}} </gallery> </center> The Robein Member is differentiated within the Roxana Silt by its stratification, darker color, organic content, and position at the top of the formation. It is distinct from organic silt in the overlying Peoria Silt because it is leached of carbonate minerals and displays pedogenic features. ==Extent and thickness== The Robein Member is discontinuous in the subsurface across Illinois. It commonly is less than 2 meters thick but may locally exceed 4 meters. ==Lithology== Light to dark brown to black, noncalcareous, stratified to massive silt loam that commonly contains organic debris. The uppermost layer may locally be peat or muck. ==Core&#40;s&#41;== ==Photograph&#40;s&#41;== ==Contacts== Lower boundary: contact with Roxana Silt or older units. Upper boundary: contact with Peoria Silt, Henry and Equality Formations, or the Wedron Group. ==Well log characteristics== ==Fossils== ==Age and correlation== Deposited from before 50,000 to about 20,000 radiocarbon years ago during the Athens Subepisode. Correlates with similar stratigraphic units in surrounding states. <center> <gallery widths=250px heights=250px perrow=4> File:104-Figure_10.jpg|alt=Diagram showing timing of glacial phases and associated stratigraphic units during late Wisconsin time.|{{File:104-Figure_10.jpg}} </gallery> </center> ==Environments of deposition== Represents accumulation of silt and organic material in poorly drained, low-lying landscapes prior to glacial advance. ==Economic importance== ==Remarks== ''Revised unit.'' Reduced in rank to member of the Roxana Silt. ==References== CURRY, B. B., and L. R. FOLLMER, 1992...<br> CURRY, B. B., and J. P. KEMPTON, 1985...<br> FRYE, J. C, and H. B. WILLMAN, 1960...<br> HORBERG, C. L., 1953...<br> KEMPTON, J. P., et al., 1991...<br> LEIGHTON, M. M., 1960...<br> WILLMAN, H. B., and J. C. FRYE, 1970...<br> {{Codes |membercode=0600 |geo_unit=r-r }}

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