The ammonites of the Middle Jurassic Cranocephalites beds of East Greenland

Authors

  • John H. Callomon (Deceased) University College London, Gower Street, WC1E 6BT, London, UK
  • Peter Alsen Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen, Denmark
  • Finn Surlyk Department of Geosciences and Natural Resource Management, University of Copenhagen, Øster Voldgade 10, DK- 1350 Copenhagen K, Denmark

DOI:

https://doi.org/10.34194/geusb.v34.4488

Keywords:

Greenland

Abstract

Thick successions of marine Middle Jurassic deposits rich in ammonites occur in the Jameson Land Basin in central East Greenland. The fauna of the so-called Cranocephalites beds of this basin, comprising the Borealis–Pompeckji Standard Zones, was until now largely represented by a single collection. This was made by T.M. Harris during a 1927 excursion up the valley of Ugleelv to Katedralen, the type area of Cranocephalites pompeckji, which is the oldest named species of this genus. Revisits to this area in 1994 and 1996 by JHC resulted in a large bed-by-bed collection of Cranocephalites. The number of faunal horizons that could be distinguished grew from the nine previously recognised to thirty-four today. The zonal stratigraphy of the Cranocephalites beds encompasses the Borealis, Indistinctus and Pompeckji Standard Zones. The Pompeckji Zone is subdivided into four new subzones, reflecting four successive basic morphologies of Cranocephalites that should be recognisable more widely and are thus useful for subzonal correlations. The detailed zonation that serves as the secondary standard zonation for the Boreal Province in the Middle Jurassic is thus highly improved. The biostratigraphic resolution obtained here is near the achievable limits. It allows a high-resolution study of the evolution of the ammonites which on this timescale appears to be continuous. Three new species are described: Cranocephalites carolae sp. nov., Cranocephalites intermissus sp. nov. and Cranocephalites episcopalis sp. nov. An additional new species, Cranocephalites tvaerdalensis sp. nov., is described in the appendix by P. Alsen based on collections from Tværdal on Geographical Society Ø, North-East Greenland. This species is also recorded in Jameson Land.

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Published

2015-12-28

How to Cite

Callomon, J. H., Alsen, P., & Surlyk, F. . (2015). The ammonites of the Middle Jurassic Cranocephalites beds of East Greenland. GEUS Bulletin, 34, 1–86. https://doi.org/10.34194/geusb.v34.4488

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