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Stratigraphic Heterogeneity of Lower Carboniferous Grainstones, Missouri
Gene Rankey
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Purposes Document facies and sequence stratigraphy of Carboniferous grainstone succession Illustrate internal complexity and heterogeneity within grainstones Provide framework for fracture and diagenetic study Rankey Mississippian, CSL Annual Review
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Major Findings Succession forms an overall progradational highstand systems tract, with facies ranging from sub-wavebase to peritidal Grainstones have diverse geometries, but heterogeneity occurs in predictable paleogeographic and sequence stratigraphic settings Internal truncation and heterogeneity – create complex compartmentalization Rankey Mississippian, CSL Annual Review
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Location Landward (N) –basinward (S) transect Flank of Illinois Basin
Low-angle ramp Rankey Mississippian, CSL Annual Review
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Stratigraphic Setting
Rankey Mississippian, CSL Annual Review
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Stratigraphic Setting
Flooding surfaces ‘Parasequence Sets’ Shallow-up: progradational facies tracts
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Facies Rankey Mississippian, CSL Annual Review
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Indiana Analogs (courtesy Brian Keith, Indiana Geol. Survey)
Facies Indiana Analogs (courtesy Brian Keith, Indiana Geol. Survey) Rankey Mississippian, CSL Annual Review
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Facies Model Rankey Mississippian, CSL Annual Review
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Parasequences Lower HST/ Downdip Upper HST
Rankey Mississippian, CSL Annual Review
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Grainstone Heterogeneity
Several Scales: Laminae Sedimentary structures Beds Parasequences Rankey Mississippian, CSL Annual Review
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Grainstone Heterogeneity
Upper HST Updip areas Rankey Mississippian, CSL Annual Review
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Grainstone Heterogeneity
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Grainstone Heterogeneity
Truncation common in upper HST
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Grainstone Heterogeneity
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Grainstone Heterogeneity
Complex Tabular Rankey Mississippian, CSL Annual Review
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Tabular Grainstone Facies: crinoid-bryozoan-skeletal grainstone
Height: up to 1m Continuity: many continuous across 300+ m outcrops Geometry: planar base and top Sequence Stratigraphic Occurrence: lower HST Geographic Occurrence: more common downdip Rankey Mississippian, CSL Annual Review
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Channeled Grainstone Facies: foram-rich skeletal grainstone; common sigmoids and muddy toes or drapes; thin mudstone layers/lenses Height: erode up to ~1.5 m of section Continuity: some greater than 50m across Geometry: concave base, planar top; multiple channels Sequence Stratigraphic Occurrence: most common in middle-upper HST of composite sequence Geographic Occurrence: more common updip Rankey Mississippian, CSL Annual Review
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Sand Waves Facies: crinoid-foram grainstone; large-scale (up to 2 m) troughs Height: up to 3m Continuity: some greater than 60+ m across Geometry: convex top, planar base Sequence Stratigraphic Occurrence: most common just above flooding surfaces of high-frequency sequences, just below grey shale Geographic Occurrence: ubiquitous
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Summary and Implications
Succession forms an overall progradational highstand sequence set, with facies ranging from sub-wavebase to peritidal Internal truncation and heterogeneity – create complex compartmentalization Grainstones have diverse geometries, but heterogeneity occurs in predictable paleogeographic and sequence stratigraphic settings Rankey Mississippian, CSL Annual Review
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