GSA Bulletin: Nonmarine Extinction Across the Cenomanian-Turonian

Nonmarine extinction across the Cenomanian-Turonian boundary, southwestern Utah, with a comparison to the Cretaceous-Tertiary extinction event Jeffrey G. Eaton* Department of Geosciences, Weber State University, Ogden, Utah 84408-2507 James I. Kirkland Dinamation International Society, 550 Crossroads Court, Fruita, Colorado 81521 J. Howard Hutchison Museum of Paleontology, University of California, Berkeley, California 94720 Robert Denton New Jersey State Museum, Trenton, New Jersey 08625-0530 Robert C. O’Neill } J. Michael Parrish Department of Biological Sciences, Northern Illinois University, Dekalb, Illinois 60115 ABSTRACT Cenomanian-Turonian boundary and suggests that some mechanism other than eustatic change played a significant role in the extinction. There is a marked, possibly stepwise, extinction of marine taxa across the Cenomanian-Turonian boundary. Across the boundary in south- INTRODUCTION western Utah, there is only minor species-level extinction of brackish- water taxa, and an actual increase in diversity of fully terrestrial organ- Extinction of marine taxa across the Cenomanian-Turonian boundary is isms; significant family-level extinctions are restricted to aquatic taxa well documented (e.g., Kauffman, 1984). Extinction of marine mollusks in such as fishes and turtles. the Western Interior of North America included ≈13% of genera and 51% It is not possible in the nonmarine setting to determine if this is a of species (Elder, 1987) and a global extinction of ≈30% of genera and 70% gradual, stepwise, or instantaneous extinction, or to what degree it cor- of species (Hut et al., 1987). Detailed study across this boundary reveals a relates to marine extinction events. Nonmarine faunas underwent no stepwise nature to the extinction event for marine mollusks in the Western major change during the transgressive phase of the Greenhorn cycle, Interior (Elder, 1985, 1987, 1991) and the nannoflora of Europe (Paul et al., and the loss of aquatic taxa along with displacement (but not extinc- 1994), suggesting widespread, possibly global controls resulting in the step- tion) of brackish-water vertebrates and some marsupial mammals is wise extinction pattern. first apparent in rocks deposited during regression in the Turonian. Data for nonmarine taxa (including terrestrial as well as brackish-water The loss of flood-plain habitat at maximum transgression may have taxa) were not included previously in discussions of extinction across the caused the extinction of some of the aquatic taxa. The absence but not Cenomanian-Turonian boundary. This paper provides data on the history of extinction of certain taxa on flood plains during the Greenhorn regres- nonmarine taxa across the Cenomanian-Turonian boundary and compares sion suggests that there may be some significant difference in trans- patterns to those of the better-known Cretaceous-Tertiary (K-T) extinction. gressive and regressive flood plains. Drawdown increases the gradients of rivers and results in incision along coastal margins. This restricts the Geologic Setting extent of brackish-water environments and may have had an impact on faunal compositions of riverine systems and contributed to extinction Southwestern Utah (Fig. 1) contains a relatively continuous record of within aquatic communities. deposition across the Cenomanian-Turonian boundary (Fig. 2). This bound- This pattern is quite different from that at the Cretaceous-Tertiary ary is marked biostratigraphically in marine rocks at the boundary of the (K-T) boundary. Aquatic taxa underwent relatively minor losses at that Neocardioceras juddii and the overlying Watinoceras coloradoense am- boundary, whereas terrestrial organisms underwent major extinction. monite zones (e.g., Elder, 1991). The stratigraphic sequence at the eastern It appears that much of the Late Cretaceous aquatic community was part of the study area (Kaiparowits Plateau region) contains nonmarine and restructured (mostly by exclusion of many taxa rather than extinction) brackish-water deposits of late Cenomanian age (Dakota Formation) over- and reduced in diversity during large-scale regression in the middle of lain by marine rocks of late Cenomanian through middle Turonian age the Maastrichtian before the end of the Cretaceous. This aquatic com- (Tropic Shale) (Eaton, 1991). The marine rocks represent the transgression munity was living in a rapidly expanding environment (overall regres- of the Greenhorn Sea (Kauffman, 1977a). The regression of the seaway is sion of marine waters) at the K-T boundary. The extinction of terres- recorded in the nearshore deposits of the Tibbet Canyon Member of the trial taxa at the boundary is unlike the pattern observed at the Straight Cliffs Formation of middle Turonian age and in the brackish-water and terrestrial deposits of the overlying Smoky Hollow Member of the Straight Cliffs Formation of middle or late Turonian age (Eaton, 1991). *E-mail: [email protected] The marine and marginal marine deposits thicken westward into a deep GSA Bulletin; May 1997; v. 109; no. 5; p. 560–567; 5 figures; 2 tables. 560 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/109/5/560/3382658/i0016-7606-109-5-560.pdf by guest on 27 September 2021 NONMARINE EXTINCTION ACROSS THE CENOMANIAN-TURONIAN BOUNDARY trough in the foreland of the Sevier orogenic belt (Eaton et al., 1987; Eaton and Nations, 1991) and these deposits grade westward into the predomi- Great nantly nonmarine Iron Springs Formation (Fig. 2), which represents proxi- Salt Lake UTAH mal debris shed from the Sevier orogenic belt. Brackish-water mollusks were recovered throughout the region (Fig. 2). Terrestrial and fresh-water faunas were recovered primarily from the Da- kota Formation and the Smoky Hollow Member of the Straight Cliffs For- mation in the Kaiparowits Plateau area. Terrestrial faunas of unknown age Salt Lake City (because of the lack of associated marine strata) were recovered from the Uinta Straight Cliffs Formation on the Markagunt Plateau and from the Iron Basin Springs Formation in the Pine Valleys Mountains (Fig. 2). BRACKISH WATER FAUNAS Price Book Brackish-water taxa were recovered in great abundance, including brack- Cliffs ish environments along the western margin of the study area associated with Plateau Wasatch maximum transgression (equivalent to the Tropic Shale to the east) and re- Green River gressive facies (lower part of the Straight Cliffs Formation, see Fig. 2). Brack- Swell San Rafael ish-water localities were also abundant within the transgressive facies of the STUDY AREA Dakota Formation; they are not shown in Figure 2 because they are present in ➤ an almost continuous belt across the study area, and the recovered fauna is al- Hanksville Henry most identical to that already described by Kirkland (1983, 1990, 1996) and Basin 38º Cedar Fursich and Kirkland (1986) from the upper part of the Dakota Formation at Canyon Black Mesa, Arizona. Cenomanian occurrences of brackish-water taxa are Pine Cedar Valley City Kaiparowits based on the Black Mesa fauna, our collections in the study area, and exami- Mts. Markagunt Plateau Plateau nation of collections made in the study area by Gustason (1989). Plateau Paunsaugunt The Cenomanian-Turonian boundary is well established within the ma- Kolob Gunlock Terrace rine Tropic Shale in the Kaiparowits basin (Eaton et al., 1987), and brack- Kanab ish-water faunas in this area show little change across the boundary. Of more than 33 taxa, there are only a few (possibly only 2 or 3) extinctions at 111º the species level and virtually no loss at the genus or family level. A specific Figure 1. Cretaceous outcrop map of Utah showing study area. table of taxa is not provided at this time because virtually all of the groups 02010 km 50 Markagunt Plateau Cedar Canyon Pine Valley 100 Kaiparowits m Mountains Plateau 1230 Figure 2. Schematic east-west cross section showing formations, 1222,1223 Straight Cliffs Fm. (lower part) approximate stratigraphic thick- Iron Springs Fm. 1258 nesses, and fossil localities. Fossil 1231,1232 995 996 locality numbers are those of the Museum of Northern Arizona, Flagstaff; x indicates brackish-water invertebrate localities; triangles Tropic Shale indicate nonmarine vertebrate localities. C-T is Cenomanian-Turo- 1226,1225 C-T Boundary nian boundary. 1067,1064 Dakota Formation Geological Society of America Bulletin, May 1997 561 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/109/5/560/3382658/i0016-7606-109-5-560.pdf by guest on 27 September 2021 EATON ET AL. involved are in critical need of revision, and we would like to avoid con- Even with these taxonomic restrictions, certain patterns are clear (Fig. 3). tributing further to nomenclatural problems. We can recognize whether a There is no loss at the family level among either mammals or dinosaurs, and taxon crosses the boundary; however, it will take years of systematic revi- although there is considerable turnover of mammalian species during this sion to produce meaningful taxonomic lists. 2–3 m.y. interval, there is no indication that the turnover of species would It appears that the changes in the fauna (both extinctions and originations) be above the normal background rate for mammals over this length of time. occur in either a stepwise or gradual fashion, because it was not possible to Most of the families of marsupial mammals that are common throughout identify a distinct change in the brackish-water fauna at any specific strati- the Late Cretaceous make a

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