tonstein

plural tonsteins

1. countableuncountablegeographyA hard, compact, kaolinite-rich claystone formed by the diagenetic alteration of volcanic ash, usually occurring as thin, laterally persistent layers interbedded with coal seams.

   Tonsteins, which are altered volcanic ash, mark instantaneous events over large areas and thus are excellent time markers for basin analysis.

   1990, W.F. Outerbridge, P.C. Lyons, D.M. Triplehorn, “New Tonstein Beds in the Middle Pennsylvanian of the Central Appalachian Basin-Time Lines for Basin Analysis”, in USGS Research on Energy Resources—1990 Program and Abstracts: Sinth V.E. McKelbey Forum on Mineral and Energy Resources (U.S. Geological Survey circular; 1060), Houston, TX, page 61

   1 more example

   Because the zircons of the Upper Banner and Hitchins tonsteins (as well as other sampled Pennsylvanian tonsteins) lack radiogenic inheritance, the may derive from the magmatic arc of Sinha and Zietz, which was farther east and outboard of the North American continent at that time.

   1994, Charles L. Rice, editor, Elements of Pennsylvanian Stratigraphy, Central Appalachian Basin, Geological Society of America, page 102

2. countableuncountablegeographyAny indurated argillaceous rock that stands out within coal measures as a distinctive marker horizon.

   In Figure 13, all data points of the tonstein samples fall within the CHARAC range.

   2025 June 27, Ahmed E. Radwan, Hu Li, Peng Tan, editors, Differences in shale oil and gas reservoirs across various sedimentary environments: theories and applications, volume II, page 74