EJECTA STRATA OF RECENT ORIGIN HAVE BEEN IDENTIFIED IN CENTRAL WISCONSIN AT GLOVER BLUFF IMPACT SITE
Based on the 1930 study, the WISCAH evaluation noted that the three main non-contiguous Ordovician fault blocks at Glover Bluff were once a contiguous Magnesian outlier, similar to Bald Bluff just 2 miles to the southwest. This former outlier was ruptured into distinct fault blocks which were subsided by as much as 200 feet in vertical elevation into the underlying Cambrian formations. Two abutted fault blocks were steeply tilted from 65-80 and 45-100 degrees, respectively. The WISCAH evaluation concluded that the fault blocks record a central impact ring and the outlier was ruptured by a continental airburst.
The 1930 study interpreted geological float at Glover Bluff as drift. In contrast to the expected undifferentiated clastics, however, float are exclusively native, random, angular, Ordovician dolomite. Clast sizes vary from two feet in maximum length to pebble size, suspended in a sandy matrix. No glacial erratics are noted. Fluvial and outwash stratification are absent. In matrix organic detritus are exhibiting. Three distinct observable strata are: A light lower stratum (5 feet); a black mat stratum (3 inches); and a dark upper stratum (4 feet). The WISCAH evaluation reinterpreted float as ejecta and concluded that the loose assemblages were deposited recently, less than ~15.0 ka ybp, after Late Wisconsinan ablation of the outlier.
The WISCAH evaluation presents evidence that the black mat stratum at Glover Bluff is the depositional result of an ET event due to its clear association with ejecta strata. Additional geological analysis is recommended at Glover Bluff to establish the exact timing, and to determine the relationship, if any, to known phenomena.