Acta Geologica Polonica, Vol. 50 (2000), No. 1, pp. 1-20 Heteromorph ammonites from the Upper Campanian (Upper Cretaceous) Baculites cuneatus and Baculites reesidei zones of the Pierre Shale in Colorado, USA W. JAMES KENNEDY1, WILLIAM A. COBBAN2 & GLENN R. SCOTT3 1 Geological Collections, Oxford University Museum of Natural History, Oxford OX1 3PW, United Kingdom 2 U.S. Geological Survey, Denver, Colorado 80225,USA 3 60, Estes Street, Denver, Colorado 80226, USA ABSTRACT: KENNEDY, W.J., COBBAN, W.A. & SCOTT, G.R. Heteromorph ammonites from the Upper Campanian (Upper Cretaceous) Baculites cuneatus and Baculites reesidei zones of the Pierre Shale in Colorado, USA. Acta Geologica Polonica, 50 (1), 1-20. Warszawa. Calcareous sandstone concretions in the Upper Cretaceous Pierre Shale in Middle Park and in the Fort Collins area of Colorado in the U.S. Western Interior contain heteromorph ammonites of the families Nostoceratidae HYATT, 1894, and Diplomoceratidae SPATH, 1926. The following species are described: Nostoceras cf. N. approximans (CONRAD, 1855), Nostoceras cf. N. obtusum HOWARTH, 1965, N. larimerense sp. nov., Nostoceras cf. N. splendidum (SHUMARD, 1861), Didymoceras aurarium sp. nov., D. draconis (STEPHENSON, 1941), Cirroceras conradi (MORTON, 1841), Anaklinoceras minutum sp.nov., Solenoceras texanum (SHUMARD, 1861), Solenoceras cf. S. reesidei STEPHENSON, 1941, Lewyites oronensis (LEWY, 1969), and Lewyites? sp. All these species are migrants from the Gulf coastal region. Didymoceras draconis and Cirroceras conradi are also known from the Delaware-New Jersey area, and these two species, together with Solenoceras texanum are known from as far away as Israel. Key words: Ammonites, Cretaceous, Campanian, U.S.A. INTRODUCTION found in relatively shallow-water sandy sediments mostly in two areas in Colorado, Middle Park in Heteromorph ammonites, other than baculites north-central Colorado (Text-fig. 1) and the Fort and scaphites, are scarce in rocks of latest Collins area farther east in north-central Colorado Campanian age in the US Western Interior and are (Text-fig. 2). In both areas, the heteromorph species restricted to sediments deposited in certain shallow- are either migrants from the Gulf coastal region, or water, sandy environments. Other heteromorph have evolved from such migrant taxa. Species in ammonites, notably members of the families Middle Park are associated with the Western Interior Baculitidae and Scaphitidae are abundant and wide- endemic species Baculites cuneatus COBBAN, 1962, ly distributed over much of the Western Interior in and those from the Fort Collins area are found with offshore shales as well as in nearshore sandstones. the slightly younger endemic species B. reesidei The present account treats the Campanian hetero- ELIAS, 1933, which places them in the standard zonal morph species of the families Nostoceratidae framework developed for the Western Interior HYATT, 1894, and Diplomoceratidae SPATH, 1926, (Text-fig. 3). 2 W. JAMES KENNEDY & al. Fig. 1. Map showing localities where heteromorph ammonites were collected from the Pierre Shale in Middle Park, Colorado STRATIGRAPHY OF THE HETEROMORPH concretions contain inoceramids, Placenticeras, FAUNAS Baculites cuneatus, Jeletzykites nodosus (OWEN, 1852), and other molluscs including an occasional Middle Park heteromorph characteristic of the Gulf coast region. This Gulf coast heteromorph fauna consists of In Middle Park, about 1,524 meters (m) of Pierre Didymoceras draconis (STEPHENSON, 1941), Shale are preserved beneath the Cretaceous- Cirroceras conradi (MORTON, 1841), Lewyites oro- Paleocene unconformity. Here the Pierre Shale has nensis (LEWY, 1969), and Solenoceras texanum been subdivided by IZETT & al. (1971) into five for- (SHUMARD, 1861). Gray limestone concretions and mal members separated by unnamed shale units silty limestone beds 12-52 m above the brown sand- (Text-fig. 3). The formal members, from oldest to stone concretion level contain Baculites reesidei youngest, are: Sharon Springs Member, Kremmling and J. nodosus but no other heteromorphs. Sandstone Member, Muddy Buttes Sandstone Limestone concretions about 12 m below the B. Member, Hygiene Sandstone Member, Carter cuneatus concretions contain Placenticeras meeki Sandstone Member, and Gunsight Pass Member. BÖHM, 1898, P. intercalare MEEK & HAYDEN, The lower part of the Sharon Springs Member is 1860, Axonoceras compressum STEPHENSON, 1941, typical of the Gammon Member of the Pierre Shale Anaklinoceras reflexum STEPHENSON, 1941, A. gor- in Wyoming, and the name Gammon Member is diale COBBAN, KENNEDY & SCOTT, 1993, extended herein into the Middle Park area. The two Solenoceras reesidei STEPHENSON, 1941, Baculites youngest members, Carter Sandstone Member and compressus SAY, 1820, B. undatus STEPHENSON, Gunsight Pass Member, are separated by 275 m of 1941, Jeletzkyites nodosus (OWEN, 1852), and dominantly shaly beds. A little below the middle of Hoploscaphites cf. H. landesi RICCARDI, 1983. The this unnamed shaly member, is a sandy unit about general stratigraphic positions of these faunas are 10 m thick that contains brown-weathering, fossilif- shown by IZETT & al. (1971, Fig. 2) and by IZETT & erous, sandstone concretions (Text-fig. 4). These BARCLAY (1973). AMMONITES FROM THE BACULITES CUNEATUS AND BACULITES REESIDEI ZONES OF COLORADO, USA 3 Fort Collins area The entire Pierre Shale (2,070 m) is present in the Fort Collins area, where eight named members and eight unnamed members are recognized (SCOTT & COBBAN 1986). Three closely spaced sandstone members in the middle of the Pierre Shale are, from oldest to youngest: Rocky Ridge, Larimer, and Richard. The Rocky Ridge and Larimer Sandstone Members lie in the zone of Baculites reesidei, and the Richard Sandstone Member lies in the zone of B. jenseni of latest Campanian age. A 131-m-thick unnamed shale member that underlies the Rocky Ridge Sandstone Member contains B. cuneatus and Jeletzkytes nodosus just below the middle, but other heteromorph ammonites have not been found. The Rocky Ridge Sandstone Member contains a large molluscan fauna, but J. nodosus and Baculites cf. B. reesidei are the only known heteromorphs. The Larimer Sandstone Member contains a still larger molluscan fauna (listed in SCOTT & COBBAN 1986) that includes B. reesidei, J. nodosus, Rhaeboceras subglobosum (WHITEAVES, 1885) (p. 52, Pl. 7, Fig. 3; Pl. 8, Fig. 1, 1a (not 2, 2a) (COBBAN, 1987, p. 11), and several heteromorphs of Gulf coast affinities. The latter include the following species: Nostoceras cf. N. approximans (CONRAD, 1855), Nostoceras cf. N. obtusum HOWARTH, 1965, N. larimerense sp. nov., Nostoceras cf. N. splendidum (SHUMARD, 1861), Didymoceras aurarium sp. nov., Cirroceras conradi (MORTON, 1841), Anaklinoceras minutum sp. nov., Solenoceras texanum (SHUMARD, 1861), Solenoceras cf. S. reesidei STEPHENSON, 1941, Lewyites oronensis (LEWY, 1969), and Lewyites? sp. LOCALITIES OF COLLECTIONS Localities in Colorado at which the heteromorph ammonites were collected are shown in Text-figs 1 and 2. The U.S. Geological Survey Mesozoic locali- ty number, names of collectors, year of collection, locality, and stratigraphic assignment are as follows (prefix D indicates Denver Mesozoic locality num- bers; the others are Washington, D.C., Mesozoic locality numbers): D301. G.R. SCOTT & W.A. COBBAN, 1955. South of Fossil Creek in the SW1/4SW1/4 sec. 1, T. 6 N., R. 69 W., Larimer County. Pierre Fig. 2. Map showing localities where heteromorph ammonites Shale, from uppermost ledge of Larimer were collected from the Pierre Shale in the Fort Collins area, Sandstone Member. Colorado D370. G.R. SCOTT, 1955. Round Butte in the 4 W. JAMES KENNEDY & al. SE1/4NW1/4 sec. 19, T. 11 N., R. 68 W., Grand County. Pierre Shale, from very Larimer County. Pierre Shale, from a sand- large brown-weathering sandstone concre- stone bed. tions. D371. G.R. SCOTT, 1955. Round Butte in the D1353. G.R. SCOTT and W.A. COBBAN, 1957. Same NW1/4SW1/4 sec. 19, T. 11 N., R. 68 W., locality as D1352. Pierre Shale, from cal- Larimer County. Pierre Shale, from equiva- careous, sandstone concretions 4-6 m lent of Larimer Sandstone Member. above D1352. D1284. D. ARNOLD and W.A. GILLESPIE, 1956. D1566. G.R. SCOTT, 1957. SW1/4NW1/4 sec. 1, T. SW1/4 sec. 7, T. 3 N., R. 80 W., Grand 6 N., R. 69 W., Larimer County. Pierre County. Pierre Shale. Shale, Larimer Sandstone Member. D1352. G.R. SCOTT and W.A. COBBAN, 1957. D1567. G.R. SCOTT, 1957. SW1/4NW1/4 sec. 7, T. NW1/4SW1/4 sec. 17, T. 3 N., R. 80 W., 9 N., R. 68 W., Larimer County. Pierre Fig. 3. Campanian and Maastrichtian ammonite zones and formations in Middle Park and in the Fort Collins area, Colorado AMMONITES FROM THE BACULITES CUNEATUS AND BACULITES REESIDEI ZONES OF COLORADO, USA 5 Shale, from calcareous, sandstone concre- D2825. G.R. SCOTT, 1960. SW1/4NE1/4 sec. 2, T. tions. 10 N., R. 69 W., Larimer County. Pierre D2599. G.R. SCOTT, 1960. SW1/4 sec. 24, T. 8 N., Shale, Larimer Sandstone Member. R. 69 W., Larimer County. Pierre Shale. D2846. G.R. SCOTT, 1960. SE1/4NW1/4 sec. 29, T. D2654. W.R. BROWN, 1957. Sec. 25, T. 3 N., R. 77 4 N., R 69 W., Larimer County. Pierre W., Grand County. Pierre Shale. Shale, Larimer Sandstone Member. D2701. W.A. COBBAN, 1961. SW1/4SE1/4 sec. 2, 758. T.W. STANTON, 1890. Fossil Creek south of T. 10 N., R. 69 W., Larimer County. Pierre Fort Collins. Pierre Shale, Larimer Shale, Larimer Sandstone Member. Sandstone Member. D2824. G.R. SCOTT, 1960. SE1/4NE1/4 sec. 11, T. 16213. R.G. COFFIN, 1932. Sec. 7, T. 9 N., R. 68 10 N., R. 69 W., Larimer County. Pierre W., Larimer County. Pierre Shale, 3 m Shale, Larimer Sandstone Member. below Richard Sandstone Member. 16217. R.G. COFFIN, 1932. Round Butte, sec. 19, T. 11 N., R. 68 W., Larimer County. Pierre Shale. 22922. R.G. COFFIN, 1950. Reservoir No. 3 in the SE1/4 sec. 19, T. 9 N., R. 68 W., Larimer County. Pierre Shale. 22925. J.B. REESIDE, Jr., H.R.