1. Stratigraphic Heterogeneity of Lower Carboniferous Grainstones, Missouri
Gene Rankey

2. 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

3. 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

4. Location Landward (N) –basinward (S) transect Flank of Illinois Basin
Low-angle ramp
Rankey Mississippian, CSL Annual Review

5. Stratigraphic Setting
Rankey Mississippian, CSL Annual Review

6. Stratigraphic Setting
Flooding surfaces
‘Parasequence Sets’
Shallow-up:
progradational
facies tracts

7. Facies
Rankey Mississippian, CSL Annual Review

8. Indiana Analogs (courtesy Brian Keith, Indiana Geol. Survey)
Facies
Indiana
Analogs
(courtesy Brian Keith, Indiana Geol. Survey)
Rankey Mississippian, CSL Annual Review

9. Facies Model
Rankey Mississippian, CSL Annual Review

10. Parasequences Lower HST/ Downdip Upper HST
Rankey Mississippian, CSL Annual Review

11. Grainstone Heterogeneity
Several Scales:
Laminae
Sedimentary structures
Beds
Parasequences
Rankey Mississippian, CSL Annual Review

12. Grainstone Heterogeneity
Upper HST
Updip areas
Rankey Mississippian, CSL Annual Review

13. Grainstone Heterogeneity

14. Grainstone Heterogeneity
Truncation common in upper HST

15. Grainstone Heterogeneity

16. Grainstone Heterogeneity
Complex
Tabular
Rankey Mississippian, CSL Annual Review

17. 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

18. 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

19. 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

20. 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