Stratigraphy and ammonite fauna of the Graneros Shale and Greenhorn Limestone near Pueblo, Colorado

Abstract

Ammonites are moderately common in most of the Graneros Shale and Greenhorn Limestone, and 30 genera and 54 species were recognized. Almost all specimens occur as internal molds, and many are somewhat distorted. Ammonites from the Thatcher Limestone Member of the Graneros Shale are assigned to four genera. Conlinoceras is described as a new subgenus of Calycoceras, and Calycoceras (Conlinoceras) gilberti n. sp. is named as the type. Ammonites in the upper fossiliferous unit of the Graneros Shale are arranged in four zones, and there is some overlap in the vertical range of the species. In ascending order these zones are Calycoceras (Conlinoceras) gilberti, Acanthoceras granerosense n. sp., A. muldoonense n. sp., and A. amphibolmn Morrow. The unit also contains species of Stomohamites, Anisoceras, Idiohamites, Desmoceras (Pseudouhligella), Euomphaloceras, Tarrantoceras, Epengonoceras, Borissiakoceras, and the new subspecies Turrilites (Turrilites) acutus Passy subsp. americanus. Only four genera of ammonites (Turrilites, Acanthoceras, Calycocerasl and Metoicoceras) were found in the Lincoln Limestone Member of the Greenhorn Limestone. The Zone of Acanthoceras amphibolum ranges upward into the basal part of the member, and the Zone of Calycoceras! canitaurinum characterizes the upper part. STRATIGRAPHY AND AMMONITE FAUNA NEAR PUEBLO, COLORADO The thin calcarenite beds in the Hartland Shale Member contain bits of ammonites which represent at least four genera (Stomohamites, Calycocerasl, Tarrantocerasl, and Metoicoceras). Metoicoceras seems to be the commonest genus. Fresh exposures of the shale reveal small impressions of juvenile ammonites that may represent an undescribed genus related to Tarrantoceras. Ammonites of the Bridge Creek Limestone Member can be assigned to four zones from oldest to youngest Sciponoceras gracile, Watinoceras coloradoense, Mammites nodosoides, and Collignoniceras woollgari; some overlapping occurs in the upper two zones. At least 23 genera are present. Puebloites is described as a new genus whose type is P. corrugatus (Stanton); Greenhornoceras is described as a new subgenus of Vascoceras, and Vascoceras (Greenhornoceras) birchbyi n. sp. is the type. Other new species described from the Bridge Creek Limestone Member are Hemiptychoceras reesidei, Ampakabites collignoni, and Kanabiceras puebloense. In terms of the standard stages of the Cretaceous, a late Cenomanian age is assigned to the upper part of the Graneros Shale and to the Lincoln Limestone Member and Hartland Shale Member of the Greenhorn Limestone. The basal part (Sciponoceras gracile Zone) of the Bridge Creek Limestone Member, formerly assigned to the lower Turonian, is herein considered of latest Cenomanian age. The rest of the member is of early Turonian age. 150 I 1.1. OKLAHOMA 200 MILES _| ._i FIGURE 1. Map of Colorado and parts of adjoining States showing places of outcrop of the Greenhorn Limestone and Graneros Shale discussed in report.

Upper Cretaceous subsurface stratigraphy and structure of coastal Georgia and South Carolina

“…Similar stratigraphic relations have been reported in northern France and in the Hainaut region of Belgium and France (Robaszynski, 1971(Robaszynski, , 1976 and also in southeastern France (Porthault and others, 1967). The Rotalipora extinction datum has also been delineated in the United States Western Interior (Eicher and Worstell, 1970); a comparison of the range of Rotalipora and the ranges of ammonites and bivalves from the same sections in Colorado and Kansas (Cobban and Scott, 1972;Hattin, 1975;Smith, 1975) shows that Rotalipora became extinct in the Sdponoceras gratile zone. This relation also appears to exist in Oklahoma (Kauffman and others, 1977).…”

“…Early studies of the European type areas reported a lack of ammonite faunas in this interval, but subsequent collecting has revealed the presence of a distinctive assemblage representative of the Sciponoceras gracile zone that was recognized first in the Western Interior of the United States (Cobban and Reeside, 1952;Cobban and Scott, 1972) and is now known also in northern France and southern England (Kennedy and Hancock, 1976 Kennedy and Juignet, 1973;Kennedy and Hancock, 1976). In the Turonian type area, elements of the Sciponoceras gracile assemblage have been reported from the Craie marneuse at the base of the Turonian in the Fretevou section (Rawson and others, 1978).…”

“…In the Western Interior United States, Cobban and Scott (1972) tentatively recognized the CenomanianTuronian boundary at the same position, between the Sdponoceras gracile zone below and the Inoceramus labiatus zone above, and subsequent studies have drawn the boundary at that level others, 1976, 1977).…”

“…In the Western Interior United States, the Sdponoceras gracile zone is in the lower part of the Bridge Creek Limestone Member of the Greenhorn Limestone in Pueblo County, Colo., and . Hamilton County, western Kansas (Cobban and Scott, 1972), and in the lower part of the Hartland Shale Member of the same formation in Russell County, central Kansas (Hattin, 1975). The S. gracile assemblage is, therefore, distinctive and widespread geographically; it is commonly confined to a few feet of section between recognized Cenomanian and Turonian rocks, and it represents an interval of time during which ammonites and other fossil groups underwent a remarkable evolutionary change.…”

The global bio-events at the Cenomanian-Turonian transition in the reduced Bahloul Formation of Bou Ghanem (central Tunisia)

“…A tentative correlation was tried with two sections belonging to the Boreal realm: the Eastbourne site in England (Paul et al, 1999;Keller et al, 2001), and the Pueblo site in USA (Cobban and Scott, 1972;Caron et al, 2006) the latter being the Global boundary Stratotype, Section and Point (GSSP) of the base of the Turonian stage. The d 13 C geochemical events are very good markers for correlation but, in addition, several bio-events are common between sections occurring in three distant continents such as: FO Metoicoceras geslinianum, LO R. cushmani, LO Th.…”