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Coring Plan

Based on the conclusions outlined above, the preliminary coring plan is guided by four nested strategic approaches. The first is identification of a succession of stratigraphic intervals separated by laterally extensive key horizons or stratal packages representing regional unconformities, sequence boundaries, and/or major lithologic transitions without unduly prejudging their nature. Interpretations of these will be led by the coring results. Second, sufficient stratal overlap between pairs of cores is necessary to span facies changes and stratal incisions at the key horizons or within the key stratal packages. This can be done by transecting key horizons/packages multiple times and thereby enhancing prospects of understanding their importance. Third, each section cored will be sited to acquire the thickest section possible that is least impacted by stratal omission or excision, to minimize diastems or hiatuses at paleosols and scour. Fourth, thick eolianite successions should be avoided while key limestone and eolianite tongues must be intersected for age control by lateral correlation to outcrop. (more)

Section
Generalized Colorado Plateau section (Glen Canyon/Kaiparowits Plateau, based on <a style="color: rgb(255, 153, 119);"href="http://jan.ucc.nau.edu/%7Ercb7/Glen_Can.jpg">http://jan.ucc.nau.edu/~rcb7/Glen_Can.jpg</a>) with the cored sections recommended by the CPCP workshop participants, a generalized evaporation &ndash; precipitation (E-P) curve loosely based on climate sensitive facies, and some major geolofical and biological events (* actual boundary may or may not be present in rock section). See Figure 1 for core area abbreviations. Note that the relative thicknesses of various units are in general different than what is shown in the color section and not the same between different coring areas.

Using these approaches the three areas identified for long (~1 km) cores are, from the top down (above): 1) East side of San Rafael Swell (SRS), UT near Dry Mesa), ~1400 m from basal Cretaceous Cedar Mountain Formation to the Permian Kaibab Formation; 2) St. George (SG - west of the Hurricane fault), ~1100 m from locally basal Navajo Formation to Permian Kaibab Formation; and 3) Ward Terrace (WT), south of Tuba City: ~700 m from basal Navajo Formation to Kaibab Formation. [Although these appear to span the same overall section, the St. Geogre and Tuba City sections are critical complements because the Moenkopi and latest (?) Triassic-Early Jurassic Moenave formations are well developed, cyclical, and probably relatively complete in the St. George area, yet the Chinle Group is very thin and erosionally truncated. In the Tuba City area, the Chinle is very well developed but the Moenkopi is very thin and erosionally truncated.] Also, the Moenave lacks the well-developed, cyclical lacustrine strata present around St. George.

The two medium depth sections are targeted for the "Rock Point" (RP) area (north of Round Rock, Utah), ~600 m from basal Wingate Formation to Permian Kiabab Formation, and the Petrified Forest area (within Petrified Forest National Park, AZ), ~400 m from Sonsela (mid-Chinle) to Permian. The Rock Point area is a critical target because it exposes the Triassic-Jurassic boundary section in the largely eolian Wingate Formation, based on both vertebrate paleontology and magnetostratigraphy, and is a natural complement to the lacustrine-dominated Moenave Formation near St. George. The Petrified Forest area (PF) has produced the bulk of the Chinle fauna and flora, as well as dated ash beds, and is a natural complement to the Chinle section in the Tuba City area (WT).

Several shorter cores can complement and enhance understanding of the five principal targets of the CPCP. Examples include the Paria Amphitheater area to cover the basal San Rafael Group, from the lower Entrada into the top of theNavajo formations, where the middle Carmel Formation is thickest; the Triassic section in the Tucumcari basin (NM, TX) which is on the craton and is richly fossiliferous; and the Chama Basin section, which contains the famous Ghost Ranch fauna that remains relatively unconstrained in age. The workshop concluded that the geophysical logs of the core holes and cores will be critical in tying cores to outcrop (e.g., Szurlies and Bachmann, 2003).