New Zealand Journal of Geology and Geophysics abstracts
Bajocian (Middle Jurassic) Ammonitina of New Zealand
GERD E. G. WESTERMANN
School of Geography & Geology
McMaster University
Hamilton, Ontario
Canada L8S 4M1
NEVILLE HUDSON
JACK A. GRANT-MACKIE
Department of Geology
The University of Auckland
Private Bag 92 019
Auckland, New Zealand
Abstract A relatively rich, previously unknown fauna of
Ammonitina is described from the Bajocian of southwest Auckland. The great
majority are Sphaeroceratidae. The Chondroceras fauna has yielded
C. orbignyanum and C. (Defonticeras) cf. oblatum,
clearly indicating the Humphriesianum Chron. Also associated is the bivalve
index Retroceramus inconditus. The superjacent fauna of Waikatoceratinae
(n. subfam.) is almost exclusively endemic to New Zealand, with Waikatoceras
crassum, W. hudsoni, Opuatia circularis, O. inflata,
and O. challinori n. genn. et spp. Accessory taxa include
Chondroceras cf. orbignyanum, and Toxamblyites aff.
densicostatus, previously known only from the upper Lower Bajocian of
Europe and North Africa. However, stratigraphic evidence together with the
bivalve index Retroceramus marwicki clearly date the Waikatoceratinae
fauna as mostly post-Humphriesianum Chron (i.e., early Late Bajocian). The
presence of Toxamblyites in this fauna suggests that its range was one
chron longer in the Southwest Pacific than in Eurafrica--unless the fragmented
specimens were reworked, which is considered unlikely.
Relatively rare and often immature phylloceratids and lissoceratids are also
associated. Other single finds of Middle Jurassic Ammonitina from other New
Zealand regions are also discussed. Other stratigraphically important taxa
include the bivalve Meleagrinella n. sp. and the belemnite Hibolithes
catlinensis.
The boundary between the Middle and Upper Temaikan regional substages can be
defined by the first occurrence of either Retroceramus marwicki or of
Waikatoceratinae; both boundaries lie in the Humphriesianum Chron. The bivalve
index is widespread, permitting inter-regional correlation, whereas the
ammonite index allows reasonably precise dating.
Keywords Ammonitina; Bajocian; Sphaeroceratidae;
Waikatoceratinae n. subfam.; Waikatoceras n. gen.; Opuatia n.
gen.; new species; Retroceramus; New Zealand; Temaikan; Jurassic
New Zealand Journal of Geology & Geophysics, 2000, Vol. 43: 33-57
0028-8306/00/4301-0033 $7.00/0 (c) The Royal Society of New Zealand
2000
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