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 Dilliard^1
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