1999 Abstract: Sanabria et al.
Climatic Control on Facies Architecture of Continental Stratigraphic Sequences in the Lower Jurassic Kayenta Formation of the Colorado Plateau
Diego
I. Sanabria
Department
of Geology and Geophysics
Rice
University
P.O.
Box 1892
Houston,
Texas 77251
John
C. Van Wagoner
Exxon
Production Research Company
Post
Office Box 2189
Houston,
Texas 77001
Peter
R. Vail
Department
of Geology and Geophysics
Rice
University
P.O.
Box 1892
Houston,
Texas 77251
Abstract
The Lower Jurassic Kayenta Formation along the Echo Cliffs of northern Arizona represents an excellent analog for arid to semi-arid continental strata. Wet/dry climatic cycles exerted a major control on the regional distribution of facies tracts during deposition of the Kayenta Formation.
Two scales of wet/dry climatic cyclicity can be recognized in the record of the Kayenta Formation. Long-term climatic cycles are represented by three sequence sets that span the Kayenta and its transition to the Navajo Sandstone. Superimposed on this long-term signal is a series of high-frequency sequences expressed by an alternation of widespread fluvial and eolian deposition.
Dry portions of the cycles are characterized by low lake levels, fluvial incision, depressed water tables, and the development of extensive deflationary surfaces. Consequently, sequence boundaries at the base of incised valleys correlate with broad deflationary surfaces in a landward direction. Incised valleys, along the lower reaches of the system, are filled with fluvial strata deposited by ephemeral streams during lowstands of the lake level.
Eolian facies of regional to sub-regional extent are preserved during rises of the water table and serve as prominent stratigraphic markers. The top of these deposits is interpreted as the transgressive surface because it represents the peak of the first significant base-level rise.
Wet portions of the cycle consist of widespread fluvial deposits that correlate with lacustrine parasequences arranged in aggradational to progradational stacking patterns. Fluvial deposits in this part of the cycle are typically represented by amalgamated sandy facies punctuated by fine-grained overbank deposition.