ANATOMY OF LOWSTAND DEPOSITS IN THE SAUK III SUPERSEQUENCE, HOUSE RANGE-IBEX AREA, WESTERN UTAH

The upper members of the Orr Formation and the Notch Peak, House, and basal Fillmore formations comprise 825 m of strata that are divided into 14 sequences with 7 distinct lowstand intervals. Each sequence is different, but many have thin microbialites that are truncated by sequence boundaries. Several boundaries are karst surfaces with 1-10 cm of relief. The lowest and highest sequence boundaries are the most significant ones in Utah. Typical lithologies include flat-pebble conglomerate and skeletal and intraclast grainstones with high siliciclastic content and low-angle cross-bedding.

The Corset Spring Lowstand has a karst surface at the Sauk II-III boundary within shaly lowstand deposits. It is overlain by thick, clean carbonates of the Sauk III Transgression and Hellnmaria Highstand, which lack typical lowstand strata and comprise Sequences 1-3 (S1-S3). The base of S4 is a widespread karst surface that is also found in Texas. The base of the Red Tops Lowstand in S5 truncates microbialites and typically has a middle microbialite in its most regressive part, near the level of the HERB carbon-isotope excursion. A thin lowstand deposit is at the base of S6. The Lange Ranch Lowstand (S7) has three cycles, each bounded by a truncation surface; the shallowest, upper cycle is capped by a karst surface truncating microbialites and is recognized in Texas and North China. No lowstand strata occur in S8 and S9, although both include truncated microbialites. The Basal House Lowstand is part of S10 and has abundant quartz sand recrystallized to nodular and bedded chert. The base of S11 is the Drum Mountains Lowstand, which often begins with an unconformity at the base of the Cordylodus lindstromi s.l. Zone. The overlying Iapetognathus Zone is in the lower part of S11, and the base of the Rossodus manitouensis Zone is in the upper part. At the base of S12 is the Burnout Canyon Lowstand; its lower part is regressive, its upper part is transgressive, and both parts have abundant quartz sand recrystallized to chert. S13 is the thin Tule Valley Lowstand, which spans the House-Fillmore contact; three boundaries with influxes of quartz sand delineate two cycles. The regressive pinning point at the top, ca. 3 m in the Fillmore, coincides with the top of the Rossodus manitouensis Zone. Overlying strata are assigned to S14 and to the Low Diversity Interval.