About This Item
- Full text of this item is not available.
- Abstract PDFAbstract PDF(no subscription required)
Share This Item
The AAPG/Datapages Combined Publications Database
Meridionally ornamented hedbergellids have been described from the upper Albian-Cenomanian of Lybia (Hedbergella lybica Barr 1972), the Cenomanian of Lebanon (H. costellata Saint-Marc 1973), and from the middle and upper Albian of the southeastern Atlantic, Deep Sea Drilling Project, Leg 40, Sites 363 and 364 (H. costellata, H. angolae Caron 1978). From Site 363 Caron reported meridional ornamentation of Hedbergella bornholmensis Douglas 1969 and Whitenella baltica Douglas 1969, for which there was no indication in the definition of these species from the Turonian-Coniacian of Bornholm Island in the Baltic Sea.
Meridionally ornamented hedbergellids were encountered in samples from the upper Albian-lower Cenomanian of the western Atlantic, Deep Sea Drilling Project Leg 43, Site 386 (Bermuda basin). The most common ornaments are blunt spines which join to form costellae that become meridionally oriented. Such orientation and costellation are common but apparently random and gradational from spinosity alone. Apertural flaps are unusually long, often cross the umbilicus, and frequently join to restrict or close the umbilicus, producing umbilical character that is not really satisfactorily hedbergellid, ticinellid, or margiontruncanid. Other properties of specific level show considerable variation.
Despite reports of somewhat earlier and considerably later occurrences, meridionally costate hedbergellids appear to be most common in upper Albian to lower Cenomanian rocks and have promise of biostratigraphic utility. Several species have been described on essentially the same properties and taxonomic utility has suffered. It is suggested that the distinctions are subspecific in many examples, arising from phenotypic response to ecologic factors, and that the species could be treated as "forma" of Hedbergella lybica Barr, the first of the kind to be defined.
End_of_Article - Last_Page 1608------------