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132 8 Continental Invertebrates and Trace Fossils from the Campanian Kaiparowits Formation, Utah Leif Tapanila and Eric M. Roberts A survey of over 50 localities for invertebrate fossils and their traces in the mudstones and sandstones of the Kaiparowits Formation, which spans 1.8 million years of Late Cretaceous (Campanian) time, demonstrates that it is one of the most prolific units in the Western Interior. Pulmonates , caenogastropods, and freshwater bivalves dominate the invertebrate fossil record both in number and diversity, and these are accompanied by ostracodes and a unique occurrence of bryozoan. Trace fossils such as the type specimens of Socialites nests and Osteocallis bone scrapings strongly suggest the activity of insects despite their absence in the body fossil record. At least 35 different aquatic and terrestrial gastropod and 13 freshwater bivalve morphotypes described from the formation support other independent evidence that the Campanian of southern Utah had a warm, humid climate with perennial aquatic environments. The highest-quality autochthonous preservation, including primary aragonite shell, occurs in facies interpreted as overbank ponds, lakes, and marshes. The greatest local diversity of 20 aquatic mollusk and one brackish-water bryozoan taxa is reported from a thick shell conglomerate that is interpreted as a mass-mortality storm deposit. Maximum diversity of mollusks in the middle of the formation appears to coincide with an increase in facies recording wetter fluvial environments, but future collecting efforts are required to isolate this relationship from taphonomic or sampling biases that may contribute to this preliminary signal. Introduction The Kaiparowits Formation in southern Utah (Fig. 8.1) is a major center for new discoveries in Cretaceous vertebrate paleontology, driven largely by prospecting and excavation efforts for archosaurs (Sampson et al., 2004; Wiersma, Hutchison, and Gates, 2004; Titus et al., 2005; Zanno and Sampson, 2006; Gates and Sampson, 2007). Although they have received scant attention by comparison, the invertebrate and trace fossil records are also proving to be exceptionally abundant, well preserved, and diverse throughout the formation . Gregory and Moore (1931), and later Gregory (1950, 1951) recorded a total of 11 gastropod and six bivalve taxa from the Kaiparowits Formation as a basis for biostratigraphic comparisons , and they concluded that the Kaiparowits Formation molluscan fauna resembled that of the Fruitland Formation of New Mexico in both age and general composition. Nearly 70 years later, the partial temporal correlation of the Fruitland and Kaiparowits formations was independently confirmed by radiometric dating of bentonites by Fassett and Steiner (1997) and by Roberts, Deino, and Chan (2005) and Roberts et al. (this volume, Chapter 6), respectively. The focus of our research is describing the total preserved biodiversity of the Kaiparowits Formation and identifying the interplay between environment and taphonomy in the preservation of continental fossils. This chapter furthers this goal by providing a summary of known invertebrate and trace fossil diversity, along with the first systematic descriptions of continental mollusks for the Kaiparowits Formation. Geologic Setting The Kaiparowits Formation (Fig. 8.2) represents the thickest unit (860 m) of a >2000-m-thick package of Upper Cretaceous strata deposited within the southern Cordilleran foreland basin, as a result of the combined influences of loading to the west and southwest in the Sevier Fold and Thrust Belt and Mogollon Highlands, respectively. Sediment of the Kaiparowits Formation was shed off each of these uplifts and deposited within the foredeep depocenter as the Western Interior Seaway retreated from Utah. A wet, humid continental setting is inferred (Roberts et al., this volume, Chapter 6), dominated by large, slow-moving channel systems with stable banks and abundant overbank pond and wetland environments (Fig. 8.3). The Kaiparowits Formation is subdivided into three informal members, termed the lower, middle, and upper units, which reflect major changes in alluvial architecture through the succession. The lower and upper units represent channel-dominated successions, whereas the middle unit is dominated by overbank pond and lake mudstones. Maximum transgression of the Bearpaw Sea into Utah is recorded within the lower part of the middle unit, and recognized by an increase in tidally influenced facies, brackish-marine trace fossils (e.g., Teredolites), and Continental Invertebrates and Trace Fossils 133 a unique occurrence of the brackish-water bryozoan Conopeum (Roberts, 2007; Roberts, Tapanila, and Mijal, 2008). Above this interval (~300-m level), no tidally influenced facies or brackish-water fauna are known in the formation. The Kaiparowits Formation contains a wealth of vertebrate fossils, plant macrofossils, and invertebrate body and trace fossils. Over one dozen ash beds have also been identified in the Kaiparowits...

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