Thomas H. Morris1,
Tamara L. Nix2
(1) Brigham Young University, Provo, UT
(2) Exxon Exploration Company, Houston, TX
Abstract: Structural and sedimentologic elements of an evolving growth fault system: outcrop and photomosaic analysis of the Ferron Sandstone, Utah
Detailed study and annotated photomosaics of two-dimensional outcrops of the Turonian Ferron Sandstone in Muddy Creek Canyon, Utah, illustrate twelve structural and sedimentologic elements within a growth fault system. Together, these elements indicate that the growth fault system evolved by processes of sand deposition, shale withdrawl and compaction, and basinward shale diapirism. These elements include rollover, rollover anticlines, counter-regional faulting, tilted erosional truncation surfaces, lens-shaped sandstone bodies within fault blocks, ejected diapiric shale, synthetic and antithetic faults, tension fractures associated with anticlines, and offlap, onlap, and toplap bed terminations. Many of these elements cannot be resolved seismically and may not develop in less dynamic sandbox models which validates the need for detailed outcrop studies.
The evolution of the growth fault system at Muddy Creek involved an early phase of fault growth by relatively continuous syndepositional processes. Shale movement became a more dominant process as sand accumulation and associated depth of penetration into the underlying shale increased in developing basinward fault blocks. The dynamic shale movement pushed up the basinward edge of several fault blocks to the point that the blocks experienced erosion at the seafloor. The landward edge of at least one fault block sagged due to this rotation. Bedding relationships between sandstone beds, erosional truncation surfaces, and fault planes indicate that shale movement was not always in a basinward direction. The culmination of shale movement is seen at the basinward edge of the study area where an ejected shale diapir breached the seafloor.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana