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Records of the Australian Museum (2017) Vol. 69 
Figure 16. Stratigraphical position of Janthina fossil localities in New Zealand. Stratigraphy greatly simplified. Symbols: A Janthina 
chavani, • Janthina typica. Grey tone = stratigraphical hiatus. 
rocks in northern Hawke’s Bay and Westland. It is also 
common, although poorly preserved and somewhat crushed, 
in Opoitian mudstone forming the main cape promontory at 
Cape Kidnappers, Hawke’s Bay. It also occurs widely, but 
scattered in small numbers, in Waipipian (early Piacenzian) 
rocks in northern Hawke’s Bay, along the South Taranaki 
coast of Whanganui Basin, and in the Kaniere-Arahura 
district and on the Greenstone-Kumara Road in Westland, 
with a single record from the Chatham Islands (which lie 850 
km east of the central South Island). The Wairoa Syncline in 
northern Hawke’s Bay reveals a particularly thick succession 
of late Miocene-early Pleistocene rocks, 9 km thick, between 
the outlet of Lake Waikaremoana and the coast at Wairoa. 
The most significant succession for dating Janthina evolution 
is exposed along the Mohaka River, in a long, continuously 
exposed section through the Wairoa Syncline succession 
upstream from the Mohaka River road and rail bridges. 
Unfortunately, no complete stratigraphical column has been 
compiled for the Mohaka River Opoitian-Waipipian section 
between Willow Flat and Highway 2 (c. 25 km of continuous 
exposure along the river, 17 km in a straight line, entirely 
through gently and consistently dipping Pliocene rocks). 
Partial columns and maps of the stratigraphy in this region 
were provided by Hornibrook (1981), Scott et al. (1990), 
Cutten (1994), Bland et al. (2004) and Kamp et al. (2006), 
and the geology of the wider region was mapped by Lee et al. 
(2011). The writer collected from the Mohaka River section 
by boat with N. de B. Hornibrook and T. L. Grant-Taylor 
during February 1982. A good specimen of Janthina chavani 
was collected from the thin, richly fossiliferous Mangapanian 
brown-weathering sandstone bed 3 km upstream from the 
road bridge (GS13079, W19/f031), whereas the underlying 
thick Opoitian and Waipipian mudstone unit contains 
sparse specimens of J. typica wherever it was examined. 
Importantly, a specimen of J. typica was observed, but not 
collected, 1 m below the top of the Waipipian mudstone 
unit immediately underlying the Mangapanian sandstone 
formation. This identifies the Waipipian-Mangapanian 
Stage boundary (mid-Piacenzian, 3.0 Ma) as the date of 
replacement of J. typica by J. chavani. Janthina chavani 
occurs rarely at a few other localities in Mangapanian (late 
Piacenzian-early Gelasian) and Nukumaruan (Gelasian- 
earliest Calabrian) rocks in Hawke’s Bay and Whanganui 
Basin. Exposures of similarly young rocks further south in 
Marlborough-North Canterbury have not yielded specimens 
of Janthina. The New Zealand succession demonstrates a 
late Kapitean-Waipipian (late Messinian-early Piacenzian) 
time range for J. typica and a Mangapanian-Nukumaruan 
(late Piacenzian-early Calabrian) time range for J. chavani , 
with an age of 3.0 Ma for the extinction of J. typica and 
origination of J. chavani. 
The Pliocene-Pleistocene boundary is now placed at the 
base of the Gelasian Stage (2.59 Ma; Gibbard et al. ,2010) in 
MIS 103 (Lisiecki & Raymo, 2005: fig. 4; Pillans & Gibbard, 
2012: fig. 30.4). Based on correlations by Naish etal. (1998) 
and Carter & Naish (1998, 1999) this boundary, identified 
by the Gauss-Matuyama geomagnetic polarity reversal, 
is now recognized within the upper part of the succession 
included within the Mangapanian Stage in Whanganui Basin. 
It lies between the Parihauhau Shellbed and the overlying Te 
Rama Shellbed in Fleming’s (1953b: 125-126) description 
of Whanganui Basin stratigraphy and paleoecology. Late 
Mangapanian, Nukumaruan and younger strata are now 
all classified as Pleistocene. Therefore, Janthina chavani 
extends well into the expanded Pleistocene in New Zealand. 
The succession in Whanganui Basin (Fleming, 1953b; 
Fig. 17) is complex stratigraphically because much of it 
was deposited in less than 50 m of water during the Plio- 
