Stratigraphic Heterogeneity of Lower Carboniferous Grainstones, Missouri

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
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