Paleoceanographic and paleoclimatic interpretations of the Mancos Shale (Upper Cretaceous), Black Mesa Basin, Arizona

Paleocirculation and foraminiferal assemblages of the Cenomanian–Turonian Bridge Creek Limestone bedding couplets: Productivity vs. dilution during OAE2

“…Planktic biserial morphotypes dominate planktic foraminiferal assemblages as initiated by the widespread "Heterohelix shift" event ( Fig. 5; Leckie, 1985;Leckie et al, 1991Leckie et al, , 1998. This event had been previously recorded in a shaly interval of Bed 78 (Leckie, 1985) just a few centimeters above a chalky limestone bed known as LS5 (Elder, 1985) and had been explained in the context of the dilution model.…”

“…The S. gracile Zone coincides with a rapid incursion of a warm southern Tethyan watermass into the WIS as indicated by the sharp increase in abundance and diversity of foraminiferal and molluscan assemblages reaching far north into the seaway (Eicher and Worstell, 1970;McNeil and Caldwell, 1981;Kauffman, 1984Kauffman, , 1985Eicher and Diner, 1985;Elder, 1985;Caldwell et al, 1993;Kauffman and Caldwell, 1993). The disappearances of environmentally sensitive, thermoclinedwelling planktic morphotypes such as keeled species (Rotalipora), as well as Globigerinelloides, have been attributed to the impingement of an OMZ into the WIS from the southern end of the basin (e.g., Leckie, 1985;Leckie et al, 1991Leckie et al, , 1998. Arthur and Schlanger (1979) suggested that a strong OMZ prevailed in the proto-Gulf of Mexico during the Cenomanian-Turonian boundary interval.…”

“…These taxa among others are considered "Epicontinental Sea Fauna" (Leckie, 1987) and may have been tolerant to significant changes in seasonal productivity, salinity, and temperature . Heterohelix is an opportunistic taxon and is the most abundant planktic genus in the CeT rocks of the WIS (e.g., Eicher, 1969;Eicher and Worstell, 1970;Caldwell et al, 1978;McNeil and Caldwell, 1981;Leckie et al, 1991Leckie et al, , 1998Elderbak et al, 2014), while Guembelitria is most abundant in cooler, productive coastal waters of the western WIS and decreases towards the basin center (Leckie et al, 1991. In general, biserial (Heterohelix) and triserial (Guembelitria) planktic morphotypes tend to occupy the shallower and more proximal waters of epicontinental seas and become very rare beyond the continental shelf during mid-Cretaceous time (Leckie, 1987;Leckie et al, 1991Leckie et al, , 1998Nederbragt, 1991).…”

High precision U–Pb zircon geochronology for Cenomanian Dakota Formation floras in Utah

“…The age of the Dakota Formation has typically been determined based upon biostratigraphic methods, a practice which has served to highlight the large temporal differences between the disparate Dakota Formation sections, rather than allow for meaningful correlation. Frequent sea level fluctuations of the Western Interior Seaway are preserved in some of the sedimentary rocks of the Dakota Formation (Leckie et al, 1991;Shanley and McCabe, 1991;Shanley and McCabe, 1993;Shanley and McCabe, 1995), providing precise ammonite and inoceramid biostratigraphy that helps determine the age of the marine strata and also creates bounding ages for the adjacent terrestrial units (Cobban and Scott, 1972;Kauffman and Caldwell, 1993;Elder et al, 1994;Cobban et al, 2000). For the exclusively non-marine portions of the Dakota Formation in Utah, of particular interest to this study, the relative age continues to be determined using palynology (May and Traverse, 1973;Nichols and Sweet, 1993;Oboh-Ikuenobe et al, 2007;Currie et al, 2008;Sprinkel et al, 2012).…”

Evidence for oxic conditions during oceanic anoxic event 2 in the northern Tethyan pelagic realm

“…In the sections of Pueblo, Eastbourne and Wunstrof, peak "b" is coeval with the "Heterohelix shift" (Leckie, 1985;Leckie et al, 1991Leckie et al, , 1998Nederbragt and Fiorentino, 1999;Huber et al, 1999;Caron et al, 2006;Jarvis et al, 2006). This event follows the disappearance of complex keeled morphotypes.…”