BH250-128e
Title
BH250-128e
Subject
Shakopee Dolostone (Upper part of the Prairie du Chien Group)
Description
Major Minerals: Quartz, dolomite
BH250-128e is a sample of the Shakopee Dolostone collected from the Cannon River Wilderness Park area in Rice County, Minnesota. The Shakopee Dolostone forms the upper part of the Lower Ordovician Prairie du Chien Group and consists primarily of dolostone interbedded with varying amounts of sandstone, siltstone, shale, and chert.
The Shakopee Dolostone overlies the Oneota Dolostone and records deposition in a warm, shallow-marine carbonate environment. Sandy and silty intervals indicate periodic influxes of siliciclastic sediment into the carbonate system. Later dolomitization altered much of the original limestone and may have obscured some primary sedimentary textures.
Some exposures preserve stromatolites and other laminated structures formed by microbial mats. These features provide evidence of biological activity in shallow, commonly restricted marine environments during the Early Ordovician.
Near the site where BH250-128e was collected, groundwater emerges as springs along or near the contact between the Shakopee Dolostone and the overlying St. Peter Sandstone. These springs support microbial communities associated with the oxidation of dissolved ferrous iron (Fe²⁺) to ferric iron (Fe³⁺). The resulting iron oxyhydroxide minerals form conspicuous reddish-orange coatings on the exposed Shakopee Dolostone. This modern process illustrates the close relationship among groundwater flow, microorganisms, oxidation–reduction reactions, and mineral precipitation.
Related sample: BH250-128b — Oneota Dolostone
BH250-128e is a sample of the Shakopee Dolostone collected from the Cannon River Wilderness Park area in Rice County, Minnesota. The Shakopee Dolostone forms the upper part of the Lower Ordovician Prairie du Chien Group and consists primarily of dolostone interbedded with varying amounts of sandstone, siltstone, shale, and chert.
The Shakopee Dolostone overlies the Oneota Dolostone and records deposition in a warm, shallow-marine carbonate environment. Sandy and silty intervals indicate periodic influxes of siliciclastic sediment into the carbonate system. Later dolomitization altered much of the original limestone and may have obscured some primary sedimentary textures.
Some exposures preserve stromatolites and other laminated structures formed by microbial mats. These features provide evidence of biological activity in shallow, commonly restricted marine environments during the Early Ordovician.
Near the site where BH250-128e was collected, groundwater emerges as springs along or near the contact between the Shakopee Dolostone and the overlying St. Peter Sandstone. These springs support microbial communities associated with the oxidation of dissolved ferrous iron (Fe²⁺) to ferric iron (Fe³⁺). The resulting iron oxyhydroxide minerals form conspicuous reddish-orange coatings on the exposed Shakopee Dolostone. This modern process illustrates the close relationship among groundwater flow, microorganisms, oxidation–reduction reactions, and mineral precipitation.
Related sample: BH250-128b — Oneota Dolostone
Coverage
Cannon River Wilderness Park
GPS coordinates: 44°23'11.15"N, 93°12'4.06"W
GPS coordinates: 44°23'11.15"N, 93°12'4.06"W
Creator
Bereket Haileab
Source
From the rock collection of Bereket Haileab. Sample BH250-128e. Housed at Carleton College in Minnesota.
Type
Thin section and hand sample
Relation
Collection
Citation
Bereket Haileab, “BH250-128e,” BH250 Mineralogy Teaching Collection, accessed October 22, 2026, https://bereket-haileab.geology.sites.carleton.edu/items/show/387.