Palaeontology and biostratigraphy of the Lower Cretaceous Qihulin Formation in eastern Heilongjiang, northeastern China
The purpose of the study was to provide conclusive evidence for a chronostratigraphical assignment of the Qihulin Formation of the Longzhaogou Group exposed in Mishan and Hulin counties of eastern Heilongjiang, northeastern China. To develop an integrated view of the formation, all collected fossil groups, i.e. the macrofossils (ammonites and bivalves) and microfossils (agglutinated foraminifers and radiolarians) have been studied. The low-diversity ammonite fauna consists of Pseudohaploceras Hyatt, 1900, and Eogaudryceras Spath, 1927, which indicate a Barremian-Aptian age. The bivalve fauna consists of eight genera and 16 species. The occurrence of Thracia rotundata (J. de C: Sowerby) suggests an Aptian age. The agglutinated foraminifers comprise ten genera and 16 species, including common Lower Cretaceous species such as Ammodiscus rotalarius Loeblich & Tappan, 1949, Cribrostomoides? nonioninoides (Reuss, 1836), Haplophragmoides concavus (Chapman, 1892), Trochommina depressa Lozo, 1944. The radiolarians comprise ten genera and 17 species, where Novixitus sp., Xitus cf. spicularius (Aliev, 1965), Archaeodictyomitra cf. vulgaris Pessagno, 1977, Stichomitra cf. tosaensis Nakaseko & Nishimura, 1981 all indicate an Early Cretaceous age. Thus the Qihulin Formation is assigned to the Barremian-Aptian.
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