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

PDF file of entire paper: medium quality (5800K); (scanned from paper original: notes about this process)

---

This year's abstracts | Journal home page | All abstracts | Publishing home page