https://bereket-haileab.geology.sites.carleton.edu/files/original/df0566af2a96ca5d02bbde118bd27cf8.jpg 185a69452ac26ab0a6d807cf9a1f17f1 Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource Sedimentary Rocks Subject The topic of the resource This collection includes sandstones, limestones, breccias, conglomerates, dolostones, shales, oolites, and BIF. Creator An entity primarily responsible for making the resource Bereket Haileab Source A related resource from which the described resource is derived Housed in Anderson Hall, Carleton College. Format The file format, physical medium, or dimensions of the resource Thin sections, thin section scans, hand samples, hand sample images, photomicrographs. Hand sample Dublin Core The Dublin Core metadata element set is common to all Omeka records, including items, files, and collections. For more information see, http://dublincore.org/documents/dces/. Title A name given to the resource BH250-128 Subject The topic of the resource Platteville Limestone Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Sogn Valley, Minnesota, USA Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample BH250-128. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Hand sample Relation A related resource <br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1D_z--CEoK9W9iC6b1exAf_iAKbj4K_m7/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1ZAbEiaAsGWCD2_R9_FYiXirr05Egj-Wt/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1pZ-BEhQHV7QE-CTcZlXHp3qgUNGn4ug6/preview" allow="autoplay"></iframe> <iframe width="100%" height="480" src="https://drive.google.com/file/d/1ycdjgmJ7uxURHpPOnvt_0Cgj5iHVzeaW/preview" allow="autoplay"></iframe><iframe width="100%" height="480" src="https://drive.google.com/file/d/1EIjF9oH86S9_eePi2-jyELFEe6yK-21U/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Description An account of the resource Major Minerals: calcite The Platteville Limestone, deposited during the Middle Ordovician (~461–450 million years ago), formed in a shallow, tropical marine setting along the equatorial margin of ancient North America. Warm, clear waters allowed carbonate mud and abundant shell debris to accumulate on the seafloor, creating a fossil-rich limestone that reflects a vibrant marine ecosystem. Common fossils include brachiopods, bryozoans, corals, crinoids, cystoids, trilobites, gastropods, and trace fossils such as burrows and ostracods. These fossils are often densely packed in shell beds, particularly in intervals rich in echinoderms. This formation is widespread across the Upper Midwest, particularly in southeastern Minnesota and western Wisconsin. It typically measures 8–9 meters thick in the region and is underlain by the Glenwood Shale and the older St. Peter Sandstone. Despite its age, the Platteville Limestone is resistant to erosion and forms prominent ledges. Within the formation, thin layers of bentonite altered volcanic ash serve as important stratigraphic markers. These bentonite seams, only 1-5 cm thick, were originally deposited as ash falls from distant Middle Ordovician volcanic eruptions. Over time, the volcanic glass altered to smectite clay minerals, forming soft, plastic bentonites. These beds, visible in places like road cuts (Highway 14, Sogn Valley) and quarries in the Twin Cities, contain trace minerals like zircon and sanidine, which are valuable for radiometric dating. Bentonite layers not only help geologists correlate strata across southeastern Minnesota and beyond, but also offer key insights into Ordovician volcanism and diagenetic processes in marine carbonate settings. Tephra layers from the Turkana Basin have produced hundreds of tuff beds, many of which remain remarkably pristine, preserving volcanic glass that is extensively used for regional stratigraphic correlation. However, a few tephra units—such as Tuff B-10—are fully altered, with no volcanic glass preserved. In these cases, melt inclusions trapped within phenocrysts have provided a valuable proxy for reconstructing the original geochemical composition of the tuff. The chemistry preserved in these melt inclusions offers critical insight into the pre-alteration nature of Tuff B-10, allowing researchers to infer its volcanic source characteristics despite the complete loss of glass through diagenesis. Bentonite carbonate Fossiliferous Limestone limestone Melt Inclusions Middle Ordovician Ordovician Stratigraphy Platteville Limestone sedimentary Stratigraphic Marker Tephra Layers Tuff Alteration Volcanic Ash Alteration Volcanic Ash Layers Volcanic glass