Representatives of Early Aalenian inoceramids of the western Priokhotie (Far East)
Abstract
Inoceramids (retroceramids) are widespread in the Middle Jurassic sediments of the eastern USSR. They are the dominant and often the only fossil remains in rocks of this age. Unfortunately, ammonite finds are extremely rare in layers with inoceramids, which makes it difficult to determine the age range of representatives of this most important group of Jurassic bivalves. Usually, their age is determined either conditionally or within very wide limits, whereas more precise dating from inoceramids will undoubtedly make it possible to develop a sufficiently detailed stratigraphy of Middle Jurassic deposits. Therefore, each joint find of retroceramids and ammonites is of great interest. Such finds were made by the author in western Priokhotie – on the coast of Tugur Bay of the Sea of Okhotsk. Here, rocks of the lower part of the Middle Jurassic – Aalenian and Bajocian stages, containing rich complexes of inoceramids, are exposed in coastal cliffs. The Aalenian deposits in this area are characterized by numerous ammonites, which make it possible to identify local zones and correlate them with the standard scale. The accompanying retroceramids are dated accordingly.
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