--> Abstract: First-Order Foreland Cycles: Interplay of Flexural Tectonics, Dynamic Loading and Sedimentation, by Octavian Catuneanu; #90039 (2005)

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First-Order Foreland Cycles: Interplay of Flexural Tectonics, Dynamic Loading and Sedimentation

Octavian Catuneanu
University of Alberta, Edmonton, AB

Retroarc foreland systems form through the flexural deflection of the lithosphere in response to a combination of supra- and sublithospheric subsidence mechanisms. Supracrustal loading by orogens leads to the flexural partitioning of foreland systems into foredeep, forebulge and backbulge depozones. Coupled with flexural tectonics, additional accommodation may be created by long-wavelength dynamic subsidence, whose magnitude depends on the pattern of subduction beneath the basin.

The interplay of base level shifts and sediment supply controls the degree to which accommodation is consumed by sedimentation. This defines the underfilled, filled, and overfilled stages in the evolution of a foreland system, in which depositional processes relate to sedimentation in deep marine, shallow marine, and fluvial environments respectively. Predictable shifts in the balance between flexural tectonics and dynamic loading allow subdivision of the first-order foreland cycle into early and late phases of evolution dominated by flexural tectonics, and a middle phase dominated by system-wide dynamic subsidence. The early phase dominated by flexural tectonics corresponds to an early underfilled foredeep and a forebulge elevated above base level, whose erosion and rapid progradation results in the formation of the forebulge (basal) unconformity. The middle phase dominated by dynamic subsidence corresponds to a stage of system-wide sedimentation, when the forebulge subsides below the base level and the foredeep evolves from a late underfilled to a filled state. The late stage dominated by flexural tectonics corresponds to the first-order overfilled stage of foreland evolution, when fluvial sedimentation is out of phase between the foredeep and the forebulge depozones.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005