Sequence Stratigraphic Characterization of a Microbially Influenced Carbonate Ramp: Khufai Formation, Huqf Supergroup, Sultanate of Oman

The Khufai Formation is a thick, microbially-influenced carbonate ramp preserved within the Ediacaran to earliest Cambrian age Huqf Supergroup. The Khufai ramp is exposed in two major areas in Oman including the Huqf-Haushi High where inner- to outer- ramp facies are preserved, and in the Oman Mountains that feature correlative distal ramp deposits. Here we present the results of detailed sequence and litho- stratigraphic analysis of the Khufai Formation.

The Khufai Formation spans one and a half 3rd order depositional sequences and exhibits extensive cyclic depositional patterns at finer scales. A maximum flooding surface occurs in the basal Khufai Formation within outer- and mid-ramp intraclast wackestones and packstones. Much of the deposition occurs above this surface as the ramp prograded, forming a highstand system tract. A type 2 sequence boundary is located within the upper microbially-dominated peritidal facies and is marked by a systematic increase in parasequence thickness. The transition into the overlying Shuram Formation is marked by a transgressive oolite, micritic microbial bioherms, and rapid flooding of the ramp surface.

Significant facies variability is observed both laterally along a given depositional profile and through time as the ramp profile evolved. Microbially-dominated facies were particularly responsive to changes in relative accommodation and wave energy. These facies range from the deep water crinkly laminites observed in the Oman Mountains to the heavily silicified irregular laminites and domal to tufted stromatolites that comprise much of the peritidal deposits in the Huqf. Within the later facies group, higher relative accommodation corresponds to increased synoptic relief on microbial accumulations. Additional depositional variability appears to reflect the influence of syn-sedimentary faulting and influx of clastic material into particular parts of the basin. The presented sequence stratigraphic model will allow for greater understanding of the nuances of Khufai Formation deposition, along with its potential as a target for hydrocarbon exploration.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California