THE BOUNDARY BETWEEN THE SAUK AND TIPPECANOE SLOSS SEQUENCES

The base of the Tippecanoe Sloss Sequence is generally placed at the base of widespread transgressive sandstones, e.g. the St. Peter Sandstone, that unconformably overlie carbonate rocks of the Sauk Sequence. Accordingly, the Sauk/Tippecanoe sequence boundary correlates with the middle Whiterockian Series. Deep-marine successions deposited on the margins of Laurentia indicate, however, that this sequence boundary is appreciably lower. A thick package of quartz sandstone in the lower Vinini Formation in central Nevada composes a submarine fan complex deposited during a lowstand that corresponds to the post-Sauk, pre-Tippecanoe unconformity of the craton. It correlates with the lower Whiterockian Series, and the sand, derived from the craton and transported across the shelf, first began accumulating during very latest Ibexian to earliest Whiterockian time. The Vinini sand package is correlative with the Blakely Formation of Arkansas, the quartz sand of which was eroded from the craton and deposited off the southern, Ouachita, margin of Laurentia during the early Whiterockian. In sequence stratigraphic terminology, the Vinini and Blakely sandstones represent basin floor fans, the base of which, coincident with the base of the lowstand systems tract, is a type 1 sequence boundary. Accordingly, we consider this sequence boundary to be the boundary between the Sauk and Tippecanoe sequences. The stratigraphy of the Vinini sand package and that of other stratigraphic units deposited on the continental margin, such as the Everton Formation of northern Arkansas, indicate that the sea-level lowstand marking the sequence boundary was extended and fluctuating. Rapid transgression to highstand conditions began in mid Whiterockian time. Accordingly, the boundary between the Sauk and Tippecanoe sequences in relatively complete deep-marine settings correlates with the boundary between the Ibexian and Whiterockian series.