Hypersaline Sea Community

Most of the species which disappeared from north-west Europe when the Zechstein 1 sea dried up did not return when the Zechstein 2 sea invaded the same areas. The fauna of the second Zechstein cycle included few species, of which molluscs were the most conspicuous. Bryozoans and brachiopods were rare and in many respects the Zechstein 2 sea biotas were comparable with those of the Bakevellia Sea during Zechstein 1 time. It is probable that hypersalinity was again the main limiting factor. However, one notable difference is the apparent absence of Bakevellia in English Zechstein 2 deposits.

Although there were few species in the Zechstein 2 sea, at some times and in some areas benthic molluscan individuals were very common. The picture shows the probable nature of a shelf sea bottom (during deposition of the Concretionary Limestone). Smith (1972), has suggested that the shelly bands in the Concretionary Limestone are turbidites, so the fauna shown probably flourished some way to the west of the present coastal outcrops where the bands are exposed. Liebea squamosa is the most common species. Its distribution in Zechstein 1 rocks and its predominance in Zechstein 3 biotas both suggest that it was the most euryhaline of Zechstein bivalves. The relative abundance of in-faunal forms (Schizodus and Phestia) indicate a soft substratum. The micro-organisms present included abundant ostracodes and nodosariid foraminifera.

Apparently the Zechstein 2 sea did not reach as far as that of Zechstein 1 and faunal remains like those shown here can be seen at outcrop only near Sunderland in north-east England.

Was this article helpful?

0 0

Post a comment