Ar. Orpin et al., Modern and ancient Zygochlamys debicatula shellbeds in New Zealand, and their sequence stratigraphic implications, SEDIMENT GE, 122(1-4), 1998, pp. 267-284
The scallop Zygochlamys delicatula is an indicator species for a carbonate
shellground facies which occurs on the sediment-starved outer shelf and upp
er slope around southern New Zealand. The modern distribution of Z. delicat
ula is restricted to areas where sea summer surface temperatures are less t
han ca. 15 degrees C. Its occurrence in Late Pliocene and Pleistocene strat
a in North Island has, therefore, been taken to indicate a northward-expand
ed range during former glacial intervals. We describe the sequence stratigr
aphic setting of examples of the Z. delicatula assemblage from the modem ea
stern South Island shelf, and from the Plio-Pleistocene Wanganui and Mangao
pari Basins in North Island. We show that the Z. delicatula fauna occurs in
both glacial and interglacial sediments, and that its development requires
the concurrence of cold-water conditions and terrigenous sediment starvati
on. These conditions occur most commonly at the transition between the tran
sgressive and highstand systems tracts (i.e. during rapid post-glacial sea-
level rise, and probable warming temperature). However, for palaeo-location
s below the contemporaneous lowstand shoreline, Z. delicatula can also occu
r at the transition between the highstand and lowstand systems tracts (i.e.
during rapid post-interglacial sea-level fall, and probable cooling temper
ature). (C) 1998 Elsevier Science B.V. All rights reserved.