https://bereket-haileab.geology.sites.carleton.edu/files/original/8cea951315868b0f9463847fc3cfc89d.jpg dec591a3f62570556498474c7705d649 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. Thin section and 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 BH250-175h Subject The topic of the resource Hakatai Shale Description An account of the resource Major Minerals: clay minerals and silt-sized particles such as quartz BH250-175h represents a fine-grained sedimentary rock from the Hakatai Shale, part of the Mesoproterozoic Unkar Group. This unit was deposited approximately 1.25 billion years ago and records a period of basin development associated with crustal extension in the early geologic evolution of the Grand Canyon region. The Hakatai Shale is well known for its distinctive red to maroon coloration in outcrop, although hand samples may range from reddish brown to dark gray depending on weathering state, oxidation, and organic content. This specimen is unusually dark gray to nearly black in hand sample, giving it a more subdued appearance than many typical Hakatai exposures, but it still preserves the fine-grained character and fissility expected of shale. In hand sample, BH250-175h is extremely fine grained and breaks along smooth, planar surfaces that reflect original bedding and fissility. The rock shows thin laminations and subtle compositional layering visible on freshly broken surfaces. Its fine grain size indicates deposition in a low-energy environment, where clay-sized particles and very fine silt could settle from suspension in quiet water. Such environments may have included tidal flats, restricted marine basins, lagoons, floodplains, or shallow offshore settings where sediment input fluctuated through time. The thin section reveals beautifully preserved fine lamination. Alternating darker and lighter bands reflect variations in grain size, mineral composition, and possible organic or iron-rich material. The lighter laminae appear to contain silt-sized grains dominated by Quartz and possibly minor feldspar, while the darker layers are composed largely of clay-rich material and opaque phases. These thin, parallel laminations are excellent examples of primary sedimentary layering preserved in fine-grained rocks. The photomicrographs also show thin secondary fractures or veins that have been filled by later minerals, likely Quartz or calcite, demonstrating that the rock experienced later fluid movement after lithification. These cross-cutting veinlets provide a useful teaching example of distinguishing primary depositional features from later diagenetic or tectonic overprints. The Hakatai Shale plays an important role in reconstructing the early history of the Grand Canyon because it records a quieter interval of sedimentation between more resistant units. It overlies the Bass Formation and underlies the Shinumo Quartzite, preserving evidence of changing depositional environments during development of the Grand Canyon Supergroup basin. This specimen is especially valuable for teaching because it demonstrates fine-grained sedimentary processes, lamination preservation, fissility, vein formation, and the remarkable preservation of Proterozoic sedimentary records over more than a billion years of Earth history. Coverage The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant Location: Mile 132 Stone Creek, Grand Canyon, Arizona, USA Nearby Geographic Feature: Grand Canyon Source A related resource from which the described resource is derived From the rock collection of Bereket Haileab. Sample 175h. Housed at Carleton College in Minnesota. Type The nature or genre of the resource Thin section and hand sample Relation A related resource <iframe width="100%" height="600" style="border: 0;" src="https://carleton.maps.arcgis.com/apps/instant/media/index.html?appid=9a9f7eb2de7c4a878b1d7306d92e3876" frameborder="0" allowfullscreen="allowfullscreen">iFrames are not supported on this page.</iframe><br />View on ArcGIS Online <a href="https://carleton.maps.arcgis.com/home/item.html?id=9a9f7eb2de7c4a878b1d7306d92e3876">here</a><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1V-hLYjOUOtbeunCSLWymZV8hGXzzKSVp/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/1vOzjqklXculn2eOFe_PHhM0lNF8edxB5/preview" allow="autoplay"></iframe><br /><br /><iframe width="100%" height="480" src="https://drive.google.com/file/d/14vegNenPRSQYlQ_B3354dMUh9EePn8sf/preview" allow="autoplay"></iframe> Creator An entity primarily responsible for making the resource Bereket Haileab Dark Shale fine-grained sedimentary rock fissility Grand Canyon stratigraphy Grand Canyon Supergroup Hakata Shale Hakatai Shale Laminated shale mudstone sedimentary Sedimentary Structures shale Unkar Group