Middle Pennsylvanian (Desmoinesian) strata of the Lower Desert Creek (LDC) sequence within the sub-surface Greater Aneth Field (GAF) reflect a hierarchy of 4th and 5th order carbonate-dominated cycles. The Lower Desert Creek sequence, along the studied transect are composed of eight carbonate facies deposited on an east-facing shelf. There is a lateral transition from open marine algal buildup from the southeast (cores R-19, Q-16, O-16, and J-15) to a more restricted lagoonal environment to the northwest (core K-430 and E-313). The Lower Desert Creek sequence within the GAF contains three main parasequence sets: a basal, relatively deep-water unit (LDC 1), a middle skeletal to algal unit (LDC 2-4), and a shallow, open-marine/restricted lagoon unit (LDC 5-7). The southeast cores (R-19, Q-16, O-16, and J-15) contain the dolomitized basal unit in parasequence LDC 1. The northwest cores (K-430 and E-313) also contain the dolomitized basal unit in LDC 1, but show a deeper facies succession through LDC 2-4. Parasequences LDC 2-4 are the heart of the algal buildup in the GAF particularly in the southern part of the transect. The upper few parasequences (LDC 5-7) are dominated by an open marine environment represented by robust fauna. The upper parasequences (LDC 5-7) show the same shallowing upward trends with algal facies in K-430 and restricted lagoon facies in E-313. Shoaling upward trends that characterize the Lower Desert Creek sequence terminate with an exposure surface at the 4th order (Lower Desert Creek-Upper Desert Creek) sequence boundary. Porosity and permeability is weakly correlated to facies. Diagenesis within the algal reservoir is the most important factor in porosity and permeability. Marine diagenesis is observed in the form of micritization of Ivanovia, a phylloid algae. Thin fibrous isopachous rims of cloudy cement also indicate early marine diagenesis. Ghost botryoidal cements are leached during meteoric diagenesis. Meteoric drusy dog tooth cements as well as sparry calcite fill most depositional porosity. Neomorphism of micrite and the isopachous rim cements reflect meteoric diagenesis. Burial diagenesis is represented by baroque dolomite cement, compaction, and mold-filling anhydrite cement.

The Greater Aneth Buildup (GAB) is comprised of the 3rd-order middle Pennsylvanian (Desmoinesian) Desert Creek sequence of the Paradox Formation. A hierarchy of 4th- and 5th order, carbonate-dominated cycles comprise the Upper Desert Creek (UDC) 4th-order sequence. A SE to NW trending transect line, utilizing core and petrophysical data from six oil and gas wells (from SE to NW wells R-19, Q-16, O-16, J-15, K-430, E-313), revealed deposition of seven carbonate facies within four 5th-order parasequences in the UDC. While each of the seven carbonate facies are present across the transect line, the UDC parasequences are dominated by a shallow-water oolite facies. Laterally and vertically, a general facies transition is evident in each of the four parasequences from a dominantly deeper-water succession of facies in the SE, to a more shallow-water, open marine to restricted lagoon, succession of facies to the NW. Parasequence UDC-3 contains the best representation of this facies transition with the SE wells (R-19, Q-16, and O-16) displaying the deeper-water/mixed algal facies grades into the shoaling oolite facies in the NW wells (J-15, K-430, and E-313). Within UDC strata, porosity and permeability correlate well to each other, but poorly to facies type. Porosity and permeability are predominantly controlled by diagenesis. Minor appearances of fibrous isopachus rim cements, and more common micritization (both whole grain and envelope) suggest that early-marine diagenesis occurred within the oolite facies. Meteoric diagenesis is demonstrated by abundant calcite spar, and drusy dogtooth cements within oomoldic pores, intraparticle pores, and interparticle pores, in addition to neomorphism of early marine diagenetic fabrics. Spastolithic ooids, stylolitization, and grain brecciation are representative of burial diagenesis within these strata. Dolomitization is present in each of the six studied core, but only in minor amounts. The Upper Desert Creek 3rd-order sequence has preserved laminamoldic diagenetic fabric that is the oldest known example of selective leaching in a meteoric vadose environment. Lithofacies trends along transect line A to A' demonstrate an increase in ooid-rich grainstone NSCF both vertically and laterally from the SE to the NW. Lithofacies type, combined with diagenesis, are the major drivers for porosity and permeability creation and destruction within Upper Desert Creek strata. NSCF, specifically ooid grainstones, have the greatest diagenetic potential of the seven UDC lithofacies.

The Greater Aneth Buildup (GAB) is comprised of the 3rd-order middle Pennsylvanian (Desmoinesian) Desert Creek sequence of the Paradox Formation. A hierarchy of 4th- and 5th order, carbonate-dominated cycles comprise the Upper Desert Creek (UDC) 4th-order sequence. A SE to NW trending transect line, utilizing core and petrophysical data from six oil and gas wells (from SE to NW wells R-19, Q-16, O-16, J-15, K-430, E-313), revealed deposition of seven carbonate facies within four 5th-order parasequences in the UDC. While each of the seven carbonate facies are present across the transect line, the UDC parasequences are dominated by a shallow-water oolite facies. Laterally and vertically, a general facies transition is evident in each of the four parasequences from a dominantly deeper-water succession of facies in the SE, to a more shallow-water, open marine to restricted lagoon, succession of facies to the NW. Parasequence UDC-3 contains the best representation of this facies transition with the SE wells (R-19, Q-16, and O-16) displaying the deeper-water/mixed algal facies grades into the shoaling oolite facies in the NW wells (J-15, K-430, and E-313). Within UDC strata, porosity and permeability correlate well to each other, but poorly to facies type. Porosity and permeability are predominantly controlled by diagenesis. Minor appearances of fibrous isopachus rim cements, and more common micritization (both whole grain and envelope) suggest that early-marine diagenesis occurred within the oolite facies. Meteoric diagenesis is demonstrated by abundant calcite spar, and drusy dogtooth cements within oomoldic pores, intraparticle pores, and interparticle pores, in addition to neomorphism of early marine diagenetic fabrics. Spastolithic ooids, stylolitization, and grain brecciation are representative of burial diagenesis within these strata. Dolomitization is present in each of the six studied core, but only in minor amounts. The Upper Desert Creek 3rd-order sequence has preserved laminamoldic diagenetic fabric that is the oldest known example of selective leaching in a meteoric vadose environment. Lithofacies trends along transect line A to A<&trade> demonstrate an increase in ooid-rich grainstone NSCF both vertically and laterally from the SE to the NW. Lithofacies type, combined with diagenesis, are the major drivers for porosity and permeability creation and destruction within Upper Desert Creek strata. NSCF, specifically ooid grainstones, have the greatest diagenetic potential of the seven UDC lithofacies.

THE PARADOX Basin is a northwest-southeast trending intracratonic basin that formedin southwestern Colorado, southeastern Utah and adjacent parts of Arizona and New Mexicoduring the late Paleozoic Era. During rise of the adjacent Uncompahgre Uplift (Ancestral RockyMountains) the rapidly subsiding basin was filled with over 2000 m of Permo-Pennsylvaniansediments. Stacked depositional sequences accumulated in three roughly parallel facies belts: anortheastern clastic belt (adjacent to uplift), a central salt and black shale belt, and asouthwestern carbonate belt. Over 400 million barrels of oil have been extracted from upperParadox (Desert Creek and Ismay) carbonates in the southern Blanding Subbasin (Greater AnethField) since 1956. The sedimentology and sequence stratigraphy of Paradox Shelf strata on thewalls of the San Juan River gorge and in the subsurface Aneth Buildup are well documented.Less well documented are the stratigraphy and facies architecture of basinward extensions ofupper Paradox sequences in the northern part of the Blanding Subbasin.Detailed analysis of the lower and upper Desert Creek and lower and upper Ismay 4thordersequences from three cores (Long Point, Lewis Road, Cedar Point) demonstrate theexistence of distinctive basinward depositional trends. Compared to sequences exposed on theParadox Shelf (San Juan River outcrops) and the Aneth Buildup, sequences in the more distalnorthern Blanding Subbasin are thinner, are dominated by muddy carbonate facies, displaylimited occurrences of porous phylloid-algal and oolitic carbonates, contain thicker, morecomplete occurrences of black shale, and possess distinctive suites of lowstand facies (quartzsandstone on the shelf, bedded and nodular evaporates in the basin). Vertically, the four 4th-ordersequences display 2nd-order progradation of the Paradox Shelf through Desert Creek and Ismaytime. Carbonate-starved sequences (4th order) and parasequences (5th order) comprised of muddominatedfacies are succeeded upward by thicker, more grain-rich sequences andparasequences. The implications for the petroleum system relative to established oil and gasfields is that conventional reservoir rock facies are rare, except in small, isolated buildups.Meteoric diagenesis associated with 4th-order lowstands of sea level has reduced overallpermeability. Lowstand conditions also promoted limited precipitation of pore-occludingevaporite cement. The maximum-flood Chimney Rock, Gothic and Hovenweep shales arethicker and contain a more complete succession of basinal cycles than updip occurrences of thesepetroleum source rocks. A suite of samples from the Gothic Shale from the Cedar Point coreindicate higher burial maturity (kerogen has mostly been converted to gas) compared to valuesderived from the outcrop belt and more proximal subsurface samples.

The Chimney Rock and Gothic units of the Pennsylvanian Paradox Formation have long been considered source rocks for the rich hydrocarbon fields of southeastern Utah. Fundamental questions about these units include: source and nature of the organic material, source rock character, and position of the source rocks in the existing sequence stratigraphic framework. The Chimney Rock and Gothic, historically referred to as shales, are composed of calcareous mudstone, dolomudstone, and calcareous sandstone. High total organic carbon (TOC) values are more closely linked to sequence stratigraphic position than lithology. In the Gothic, TOC values decrease upwards. Terrestrial maceral content increases upwards in both the Gothic and the Chimney Rock as determined through point-count and qualitative observation. Pyrolysis indicates that greater than anticipated terrestrial influence is present and is consistent for all wells. No distinct difference in geochemical character exists between the two units. Sequence stratigraphic boundaries appear to be as good as, or better, than traditional lithostratigraphic boundaries for determining high TOC occurrence and source rock location. Within repetitive major sea level transgressions the organic matter that fed the basin evolved from a marine-dominated signature to a terrestrial-dominated signature. / text