Differences in Parasequence Architecture and Stacking Patterns from Large Carbonate Platforms: Field Examples from Laurentia
Michael Pope1, Peter Isaacson2, Isabel
Montanez3, Bonny Archuleta4, Liselle Batt2,
and Kelly Dilliard1
1 Washington State University, Pullman, WA
2 University of Idaho, Moscow, ID
3 University of California, Davis, CA
4
Washington State University, Pullman
Meter-scale parasequences
of carbonates and siliciclastics and their
stacking patterns are distinctive to the climate mode in which they were
deposited. Greenhouse
parasequences
are composed predominantly of carbonate and
are easy to correlate over broad areas. As climate evolves toward icehouse
conditions the amount of siliciclastics increases in
parasequences
and regional
correlation becomes more difficult.
Upper Lower Cambrian rocks of the Sekwi Formation, Northwest Territories, Canada record deposition along a passive margin during a greenhouse time with deep to shallow ramp facies stacked in repeated patterns that are traceable over 10's to 100's of km along a dip profile.
Transitional climate modes are recorded in Upper Ordovician and Upper
Mississippian rocks. Upper Ordovician foreland basin rocks of the Cincinnati
Arch region record moderate amplitude, high-frequency parasequences
composed of
deep and shallow ramp facies. The upper part of this succession is dominated by
3rd-order
sequences
recording longer-term sea level oscillations with only
regionally correlative
parasequences
. Similarly, Upper Ordovician rocks of the
southern Laurentian passive margin preserve 3rd-order
sequences
correlative to
those in the Appalachian Basin, but their component
parasequences
are only
correlative locally. Upper Mississippian (Chesterian) foreland basin carbonates
of Montana and Idaho record thick 3rd-order
sequences
with only locally
correlative
parasequences
. The uppermost part of this succession includes more
abundant coarse siliciclastics and interfingering of deep and shallow water
facies indicative of higher amplitude fluctuations.
Upper Pennsylvanian "cyclothems" of east-central Idaho were deposited during an icehouse time. The intimate interfingering of deepwater carbonates and nearshore or terrestrial siliciclastics in this succession indicate high-amplitude, high-frequency eustatic fluctuations in the Late Pennsylvanian.
AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005