Abstract The Upper Albian-Coniacian section cored in the Amoco No. 1 Rebecca K. Bounds well in Greeley County western Kansas, serves as a reference section for the timing of depositional events in the Western Interior Seaway. Chronostratigraphy of this section was calibrated by a multidisciplinary study of nannofossils, dinoflagellates, spores, pollen, foraminifers, and mollusks. Range data of the biota in the Bounds core were compared by graphic correlation to a global composite standard that includes key reference sections in Europe and North Africa. The basal Upper Albian sequence boundary is overlain by transgressive facies of the Purgatoire Formation dated as 102.8 Ma. The upper Upper Albian sequence boundary between the Purgatoire and Dakota Formations marks a hiatus in deposition from 99.4 to 98.2 Ma. The Albian-Cenomanian intra-Dakota sequence boundary spans from 96.0 to 94.1 Ma. The Turonian-Coniacian sequence boundary between the Carlile and Niobrara Formations spans from 89.9 to 88.3 Ma. Maximum flooding is documented within the Purgatoire at 101.4 Ma and in the Graneros Shale at 93.7-92.8 Ma. The Albian-Cenomanian boundary defined by European ammonites and correlated by dinoflagellates is placed at the intra-Dakota unconformity. Graphic correlation is an independent method of measuring the durations of Milankovitch-scale depositional cycles and can separate climatic cycles from longer tectono-eustatic cycles. Four orders of depositional cycles are recorded by lithological changes, and their durations are constrained by graphic correlation. The longest cycles range from 2.0 to 3.4 My and are found in the sequences defined by the Purgatoire Formation, the lower part of the Dakota Formation, the upper Dakota and Graneros Formations, and the Greenhorn and Carlile Formations. The next lower order comprises transgressive-regressive subcycles of about 0.5 My long in the Purgatoire. The third-scale cycles include sandstone-mudrock cycles in the Dakota, limestone-marl cycles in the lower part of the Greenhorn, and cyclical strata in the Fort Hays Limestone Member of the Niobrara Formation that are about 100 ka long. The shortest cycles are limestone-marl couplets in the upper Greenhorn that are about 41 ka long.

Abstract Siliciclastic- and carbonate-dominated lacustrine systems are present within the Morrison Formation (Upper Jurassic), Western Interior basin, U.S.A. The siliciclastic dominated systems, common on the Colorado Plateau ,have been studied intensely in association with the extensive Lake T' 00'dichi' complex, an alkaline-salinelake in the Brushy Basin Member of the Morrison Formation(Bell, 1983, 1986; Peterson and Turner-Peterson,1987; Turner and Fishman, 1991). Conversely, the carbonate-dominated lacustrine systems prevalent in east central Colorado, New Mexico, Kansas, and Wyoming have received limited attention (Frazier et al., 1983;Sweet 1984; Lockley et al., 1986; Sweet and Donovan,1988; Johnson, 1991), with few regional-scale and even fewer detailed sediment logic and stratigraphic investigations(exceptions include West, 1978; Jackson, 1979;Dunagan et al., 1996, 1997; Dunagan, 1997, 1998). This study describes the initial results of a systematic, regional scale investigation of lacustrine carbonate deposits in the Morrison Formation focusing on the well-developed lacustrine complex in east-central Colorado, which willultimately provide important insights into one of the most poorly understood depositional environments in the Morrison paleoeco system. Detailed results are forthcoming in other publications.