Smaller Foraminifera From Guam - USGS

14 GEOLOGY AND HYDROLOGY OF GUAM, MARIANA ISLANDS
6-1 with the other three samples, Gj 13-1, Gj 11-1,
and Gj 14-1, that are assigned to this zone. The fur­
ther circumstance that sample Hi 6-1 contains three
additional planktonic species, namely Globigerina dan-
vUlensis Howe and Wallace, G. yeguaensis Weinzierl
and Applin, and Globigerinella danvittensi-s (Howe
and Wallace), none of which are found in any of the
other three Oligocene samples and all of which have
ranges extending farther downward than upward from
the lower Oligocene, is yet another point in favor of
differentiating sample Hi 6-1 from the remaining three
Oligocene ones. The recognition in sample Hi 6-1
of forms transitional between Globigerina ampliaper-
tura Bolli and Globorotalia centralis Cushman and
Bermudez forms identical with some illustrated from
the highest Eocene zone in Trinidad is an additional
point in favor of interpreting Hi 6-1 as slightly older
than the Globigerina sellii zone.
Nevertheless, in spite of the fact that the previously
discussed points favor a pre-early Oligocene age for
sample Hi 6-1, there are some weighty reasons for in­
cluding it with the Oligocene rather than with the
Eocene, as follows: First, the presence of Cassigerinella
chipolensis (Cushman and Ponton) in abundance favors
Oligocene age because this genus has not been reported
in the Eocene. However, the question of exclusion of
Cassigerinella from the Eocene is currently under debate
owing to Tsunemasa Saito's finding (written commun.,
Jan. 10, 1964) of some small specimens of it in a deep-
sea core in the Atlantic off Florida where it was reported
in association with undoubted Eocene planktonic
Foraminifera. Second, the presence of many species
characteristic of the lower Oligocene, such as Bolivina
l>eyrichi Reuss, B. fastigia Cushman, B. olig