ABSTRACT

Results from a combined paleomagnetic and petrographic study of the Peerless Formation in central Colorado indicates that the unit contains two Chemical Remanent Magnetizations (CRMs). The oldest magnetization is a CRM residing in maghemite or magnetite and is Cambrian to Ordovician in age. A younger CRM resides in hematite and is Carboniferous.

The Peerless Formation has undergone a complex diagenetic history. Several forms of authigenic hematite are present. Authigenic hematite is present in association with other authigenic phases such as dolomite, euhedral quartz overgrowths, and calcite cement. The hematite is intergrown with both dolomite (as distinct from dedolomite) rhombs and quartz overgrowths. Hematite growths are contemporaneous with or paragenetically later than these other authigenic phases. Because the hematite paleomagnetic ages are Carboniferous, the other authigenic phases must be Carboniferous or older.