Index map to study area. A, Large-scale Pennsylvanian tectonic structures (after Spoelhof, 1976) and location of study area. N = area of Needle Mountains. B, Locality map and key geographic features. Paradox and San Juan basins from Cole and Moore (1996). Localities are identified in Appendix A. (Note: Forest Route 591 is the Lime Creek Road.)
Tamarron Member at stratotype (locality A [Bakers Bridge]). G = granite. The dashed line identifies the nonconformity between the basement and the Ignacio Quartzite. The section is composed chiefly of estuarine sand-flat deposits.
Amalgamated sedimentation units of mostly SW-dipping cross-beds in the Tamarron Member near Tamarron (locality A [Bakers Bridge]). Bleached zones cut across bedding and are selective to coarser layers.
Stratigraphic sections of the rocks studied showing the distribution of the members and facies. Sections are projected onto a north–south transect. Spacing is not to scale. Localities are identified in Appendix A.
Quartz-feldspar-rock fragment (QFR) plots of sandstone composition (A) including clay rip-up clasts and (B) ignoring clay rip-up clasts as rock fragments. Lines encompass most samples of each facies or member.
Heterolithic tidal couplets in upper part of Tamarron Member at locality B (Shalona Lake railroad cut). Iron oxide in clay drapes survived the bleaching event. Clay accumulated at high tides during the tide turnaround.
Probable paleocaliche nodules in basal Mill Creek facies at its contact with the Tamarron Member at locality A (Bakers Bridge). A = outcrop view; B = plain-light photomicrograph of thin section; brown = microsparry dolomite.
Spud Hill Member (red beds, SH) abruptly overlies slightly bleached beds of the Tamarron Member (T) at locality Q (Canyon Creek). Complete thicknesses of the two stratigraphic units exposed at this locality are not shown in the figure.
Basal heterolithic beds of Spud Hill Member at type area of locality I (Mill Creek road cut). Starved megaripples display bi-directional cross-beds. Most non-resistant beds are sandstones composed of >40% mashed red clay rip-up clasts.
Mill Creek facies at its reference section at locality I (Mill Creek road cut). Iron and manganese oxides coat many fracture surfaces and obscure bedding. Man points to a meter-thick layer with probable hummocky cross-stratification (HCS) that developed irregular fractures.
Well-rounded, subspherical (“billiard-ball”) quartz grains visible by ghost “dustlines.” The latter are minute pores where iron-oxide grain coats were removed by diagenetic reducing fluids. Sultan Creek facies of the McCracken Member. View in transmitted light.
Weathering pits, stained by MnO2, in Mill Creek facies at locality I (Mill Creek road cut). Near-surface dissolution of concretionary calcite cement permitted removal of quartz sand grains during weathering.
N–S cross-section showing remarkable thinning over a distance of only 2.5 km of both members of the Ignacio Quartzite and of the Mill Creek facies of the McCracken Sandstone. After Block (1986). His section 1 = my locality I (Mill Creek road cut); his section 9 is my locality K (Coal Bank Pass north).
Cyclic dolostones of the Sultan Creek facies at locality M (Sultan Creek south). Cycles begin at a shale parting and end at a quartzarenite cap (at hammer head). Arrows identify two complete cycles. The uppermost beds of the Sultan Creek facies are not shown in this photo.
Close-up of a dolostone cycle in the Sultan Creek facies. Stromatolites near the top are overlain by a quartzarenite layer that was destroyed locally by bioturbation. Resistant patches in the upper half of the bed are quartzarenite layers disrupted through bioturbation.
Location of the main age provinces in central and southern North America that may have provided sediment to the Ignacio and McCracken sandstones based on zircon ages (after Gehrels et al., 2011, their fig. 7, with permission). Map details: Hearne, Wyoming, and Superior cratons; Yavapai and Mazatzal provinces; Amarillo-Wichita Uplift; Grenville, Appalachian, Ouachita and Oaxaca orogens; Suwanee terrane; Yucatán-Campeche block.