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Bulk Chemistry Analysis to Delineate the Subtle J-1 Unconformity, Utah’s Colorado Plateau

Phillips, Stephen P.1; Morris, Thomas H.*1
(1) Geology, Brigham Young University, Provo, UT.

The Navajo Sandstone and the White Throne Member of the Temple Cap Formation have been extremely productive reservoirs in the Covenant Oil Field of central Utah’s Overthrust Belt. The Sinawava Member of the Temple Cap Formation was deposited between the Navajo Sandstone and the White Throne Member. It acts as a barrier to fluid flow. The regional J-1 Unconformity rests above the Navajo Sandstone. The geographic extent, of the Navajo Sandstone is well understood, but the Sinawava and White Throne Members of the Temple Cap Formation may have a larger geographic extent than previously recognized. Recent dates have shown that the White Throne Member of the Temple Cap Formation is time-equivalent to the lower Page Sandstone in eastern Utah. In some locations the contact between the Navajo Sandstone and the Temple Cap Formation/Page Sandstone is extremely hard to locate due to similar lithology and facies. It may be that some parts of these formations have been misinterpreted as part of the underlying Navajo Sandstone.

Analysis of the bulk chemistry of the above formations using a portable XRF has the potential to delineate the J-1 Unconformity. Indeed, preliminary results are promising in this regard. Analysis at field locations where the position of the J-1 Unconformity is well known has resulted in recognizable chemical trends that differ between the Navajo Sandstone and the Temple Cap Formation/Page Sandstone. These differences in chemistry may be due to secondary diagenesis, provenance, or marine influence during Temple Cap/Page time versus non-marine influence during Navajo time.

Well logs, core from the Covenant Oil Field, and outcrop on the Colorado Plateau will aid us in producing a surface to subsurface correlation of the J-1 Unconformity, the Navajo Sandstone, and the Temple Cap Formation/Page Sandstone.

The use of a portable XRF as a tool for delineation of an unconformity is of great importance to stratigraphers, sedimentologists, and the petroleum industry. The portable XRF is a new tool that can detect small differences across an unconformity. Detection and interpretation of these small differences will increase our understanding of reservoir features such as areal extent and reservoir partitioning (J-1). It will improve our understanding of the depositional history of the Early and Middle Jurassic reservoir quality erg sands in Utah.

 

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