Modern and ancient Zygochlamys delicatula shellbeds in New Zealand, and their sequence stratigraphic implications
نویسنده
چکیده
The scallop Zygochlamys delicatula is an indicator species for a carbonate shellground facies which occurs on the sediment-starved outer shelf and upper slope around southern New Zealand. The modern distribution of Z. delicatula is restricted to areas where sea summer surface temperatures are less than ca. 15oC. Its occurrence in Late Pliocene and Pleistocene strata in North Island has, therefore, been taken to indicate a northward-expanded range during former glacial intervals. We describe the sequence stratigraphic setting of examples of the Z. delicatula assemblage from the modern eastern South Island shelf, and from the Plio–Pleistocene Wanganui and Mangaopari 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 starvation. These conditions occur most commonly at the transition between the transgressive and highstand systems tracts (i.e. during rapid post-glacial sea-level rise, and probable warming temperature). However, for palaeo-locations below the contemporaneous lowstand shoreline, Z. delicatula can also occur at the transition between the highstand and lowstand systems tracts (i.e. during rapid post-interglacial sea-level fall, and probable cooling temperature). 1998 Elsevier Science B.V. All rights reserved.
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