New Insights on the Sequence Stratigraphic Architecture of the Dakota Formation, Ludvigson et al. i New Insights on the Sequence Stratigraphic Architecture of the Dakota Formation in Kansas–Nebraska–Iowa from a Decade of Sponsored Research Activity Greg A. Ludvigson, Kansas Geological Survey, The University of Kansas, Lawrence, KS Brian J. Witzke, Iowa Geological Survey, Iowa Department of Natural Resources, Iowa City, IA R. M. Joeckel, Nebraska Conservation and Survey Division, School of Natural Resources, The University of Nebraska-Lincoln, Lincoln, NE Robert L. Ravn, The IRF Group, Anchorage, AK Preston Lee Phillips, Department of Geology and Geography, University of North Carolina at Pembroke, Pembroke, NC Luis A. González, Department of Geology, The University of Kansas, Lawrence, KS Robert L. Brenner, Department of Geoscience, The University of Iowa, Iowa City, IA Abstract The Cretaceous Dakota Formation in the areas of Kansas, Nebraska, and Iowa contains a rich and well-preserved microfl ora of fossil palynomorphs. A comprehensive listing of these taxa is presented in this publication as part of a continuing effort to develop a refi ned biostratigraphic scheme for mid-Cretaceous terrestrial deposits in North America. The Dakota Formation in this region contains four distinctive Albian–Cenomanian palynostratigraphic zones that are used to partition the unit into successive depositional cycles, and each zone records deposition in fl uvial-estuarine environments. The late Albian Kiowa–Skull Creek depositional cycle at the base of the Dakota Formation is recognized throughout the study area, and is also recognized in other parts of the Cretaceous North American Western Interior basin. The overlying newly recognized latest Albian “Muddy–Mowry Cycle” is formally defi ned for the fi rst time in this paper and correlates with depositional cycles recognized by other workers in other parts of the Western Interior basin. The Cenomanian lower Greenhorn Cycle is already widely recognized by many other workers throughout the Western Interior basin. Laterally extensive thin zones of pervasive carbonate mineral cementation are noted in fl uvial-estuarine deposits in the Dakota Formation. They are believed to have formed as synsedimentary cements that precipitated below estuarine marine-fl ooding surfaces in settings related to discharging paleoground waters. The existence of these early diagenetic cementation zones has important implications for the recognition of diagenetic barriers and baffl es to modern fl uid fl ow in the Dakota Formation. New stable isotopic data on these authigenic cements are reported in this paper and add to a body of published data on the δ18O of mid-Cretaceous paleoprecipitation in North America. Current Research in Earth Sciences, Bulletin 258, part 2 (http://www.kgs.ku.edu/Current/2010/Ludvigson/index.html) New Insights on the Sequence Stratigraphic Architecture of the Dakota Formation, Ludvigson et al. 1 New Insights on the Sequence Stratigraphic Architecture of the Dakota Formation in Kansas–Nebraska–Iowa from a Decade of Sponsored Research Activity Greg A. Ludvigson, Kansas Geological Survey, The University of Kansas, Lawrence, KS Brian J. Witzke, Iowa Geological Survey, Iowa Department of Natural Resources, Iowa City, IA R. M. Joeckel, Nebraska Conservation and Survey Division, School of Natural Resources, The University of Nebraska-Lincoln, Lincoln, NE Robert L. Ravn, The IRF Group, Anchorage, AK Preston Lee Phillips, Department of Geology and Geography, University of North Carolina at Pembroke, Pembroke, NC Luis A. González, Department of Geology, The University of Kansas, Lawrence, KS Robert L. Brenner, Department of Geoscience, The University of Iowa, Iowa City, IA Introduction In 1994, a long-term research program to investigate the relates to the Graneros marine shale in Colorado (fi g. 2). Brenner stratigraphy of the Cretaceous Dakota Formation in Iowa and et al. (2000) partitioned the Dakota Formation into three major immediate environs (Brenner et al., 1981; Witzke and Ludvigson, sedimentary sequences bounded by correlative unconformities 1982, 1987, 1994; Witzke et al., 1983; Ravn and Witzke, 1994, (D0, D1, and D2), correlations that were based on recognition of 1995) was geographically expanded to include exposures and four palynostratigraphic zones (fi g. 3). This report presents a research drillcores in Nebraska and Kansas, under the auspices more complete discussion of the palynostratigraphy of the Dakota of NSF grant number EAR–9628128. This research program in- Formation, with updated information on the stratigraphic ranges cluded 1) systematic collection, identifi cation, and correlation of of some key palynologic taxa. palynostratigraphic samples, with the goal of improving biostrati- Published fi ndings on the stable isotope paleohydrology and graphic and chronostratigraphic resolution in the interval, and 2) paleoclimatology of the Dakota Formation have described work systematic collection of stable isotope paleoclimate proxy data on pedogenic sphaerosiderites from paleosols (Ludvigson et to address the mid-Cretaceous climate-change record contained al., 1998c; White et al., 2001; Ufnar et al., 2002, 2004a, 2004b; within the Dakota Formation. White et al., 2005). Concomitant works on other terrestrial stable Initial major fi ndings on the regional stratigraphy of the isotope proxies from the unit are just beginning to emerge in Dakota Formation were published by Brenner et al. (2000). They the peer-reviewed scientifi c literature (see Ufnar et al., 2004a; showed that strata of the Dakota Formation, as originally defi ned Phillips et al., 2007). One important facet of this emerging work by Meek and Hayden (1862) from its type region in the Missouri pertains to the fi eld recognition of early diagenetic cementation River valley (fi g. 1), include Albian units that are time-strati- of high-frequency (i.e. parasequence) boundaries in estuarine fa- graphic correlates to the marine shales of the Kiowa Formation cies of the Dakota Formation. We present previously unpublished in Kansas, and Cenomanian units that are time-stratigraphic cor- results on this topic in this report. Palynofl oras of the Dakota Formation Mid-Cretaceous sediments of the midcontinent, as in much are especially relevant. From surrounding areas, the studies of of North America, contain extraordinarily rich and well-preserved Brenner (1963), Singh (1964, 1971, 1983), Hedlund (1966), fossil palynomorphs. Through much of the region, these popula- Norris (1967), Agasie (1969), Playford (1971), Phillips and Felix tions are dominated by the spores and pollen of terrestrial plants, (1972a, 1972b), Romans (1975), Srivastava (1977), Win- refl ecting the mid-Cretaceous seaway regression that punctuated gate (1980), Nichols and Jacobson (1982), and Ravn (1995) are Albian–Cenomanian time. These microfossils record a bio- especially useful. Overall, the assemblages and succession from stratigraphic succession of great utility for correlation and age nearby areas are well documented, and a record of the palyno- interpretation. Detailed documentation of the regional Albian– stratigraphy from this area central to the Cretaceous midcontinent Cenomanian microfl oral succession is in preparation and is be- seaway is of great value in interrelating these earlier studies. yond the scope of this publication, but a number of key forms are The taxa illustrated in plates 1 and 2 are from numer- illustrated here, and some brief comments on their signifi cance ous localities in Kansas, Nebraska, Iowa, and South Dakota, are in order. and represent characteristic material from strata of late Albian Numerous comparative studies are valuable in assessing through Cenomanian age. Of particular interest for Albian-age the ages of strata examined in the region. In the immediate area, interpretation are the fern-related spore species Plicatella jansonii the publications of Pierce (1961) from Minnesota, Ward (1986) (Pocock) Dörhöfer 1977, Plicatella unica (Markova) Dörhöfer from Kansas, and Ravn and Witzke (1994, 1995) from Iowa 1977, Impardecispora marylandensis (Brenner) Venkatachala et Current Research in Earth Sciences, Bulletin 258, part 2 (http://www.kgs.ku.edu/Current/2010/Ludvigson/index.html) New Insights on the Sequence Stratigraphic Architecture of the Dakota Formation, Ludvigson et al. 2 SD Goodhue Co. Windrow Bluff RIDGE Ostrander SIOUX MN IA Iron East Hill Upper Cretaceous Bluff marine strata WS OUTCROP M IL type Dakota area Neogene on Paleozoic outcrop Cretaceous Guthrie Co. Burt Co. Des Moines DAKOTA Lower Platte type Nishnabotna area Valley Yankee Hill MO KEY: Dakota Fm. outcrop Baylis Fm. Jefferson Co. NB (and equivalents) marine strata Upper Cretaceous KS Precambrian outcrop KGS Kenyon Core Republic County Neogene (Ogallala Gp.) N KGS Jones #1 Core overlap Lincoln County Windrow-Dakota outlier Salina Type locality Paleozoic outcrop 0 50 100 200 km L. R. FIGURE 1—Generalized regional outcrop map of the Dakota Formation and equivalent strata between southern Minnesota (MN) and northern Kan- sas (KS). Blue-green-colored outcrop denotes the Dakota Formation in western Iowa (IA) and eastern Nebraska (NB), the Dakota and Kiowa Formations in Kansas, and equivalent units in Minnesota. Eastern outliers (dots) include the Dakota Formation in Iowa; the Windrow Forma- tion in Iowa, Wisconsin (WS), and Minnesota; and the Baylis Formation in western Illinois (IL). Cretaceous strata lap the margins of the Sioux Ridge, a long-lived paleotopgraphic feature composed