A latest Cretaceous gastropod fauna from the Jiaolai Basin of East Asia

Taphonomic and diagenetic implications of reduction spot formation in Cretaceous red beds from the Jiaolai Basin, Eastern China

“…These studies demonstrate that continuous fluvial and lacustrine deposition occurred through the K/Pg boundary interval (Xu et al, 2019;Yang et al, 2021). The Jiaozhou Formation preserves a rich biota including charophytes, ostracods, and gastropods from shallow lacustrine settings, and sporopollen assemblages derived from terrestrial floras (Du et al, 2020;Li et al 2020;Tian, et al 2021;Yu et al 2021). The charophyte flora of the Jiaozhou Formation have been analyzed biostratigraphically by Tian et al (2021), and include typical Maastrichtian species (Tolypella grambastii, Peckichara praecursoria, Microchara cristata, M. prolixa, Lamprothamnium ellipticum, Nodosochara (Turbochara) specialis, and Lychnothamnus aff.…”

“…vectensis) and Paleocene species (Lychothamnus lanpingensis), as well as species with ranges that span the boundary (Chara changzhouensis). The gastropod Hydrobia datangensis indicates a Late Cretaceous age, while the ostracod species Porpocypris sphaeroidalis indicates a Paleocene age (Yu et al, 2021).…”

“…Regarding palaeoenvironmental interpretations, Tan et al (2019) suggested that the Jiaozhou Formation in LK-1 borehole (614-0 m) consists mainly of floodplain facies purple mudstones, grey-greenish siltstones and sandstones in the lower part (614-452 m), shore-shallow lacustrine, sage-green to purple mudstone in the middle part (452-250 m), and meandering fluvial, upward-thinning sandstones and mudstones with intercalated conglomerates and marlstones in the upper part (250-0 m). Subsequently, Li et al (2020) divided the Jiaozhou Formation in the LK-1 borehole into seven intervals based primarily on lithological associations, in which the interval from 533-499 m is interpreted as shallow lake deposits, the interval from 498-426 m are channels and floodplain facies, while the interval of 425-311 m is returned to shallow lake deposits (Li et al, 2020Yu et al, 2021). The other parts of the Jiaozhou Formation in the LK-1 borehole lack charophyte flora, which was interpreted to reflect climate cooling (Li et al, 2020.…”

“…In the recently drilled JK-1 borehole, situated 1 km from the LK-1 borehole, reduction spots only occur in a 74 m thick interval at the bottom of the Jiaozhou Formation, situated between basalts of the Shijiatun Formation and green lacustrine mudstones that span the K/Pg boundary (Yu et al, 2021;Fig. 2).…”

“…2). This 74 m interval comprises an alluvial-lacustrine continental red bed sequence (Tan et al, 2019;Yu et al, 2021;Tian et al, 2021), but detailed sedimentological investigations and palaeoenvironmental interpretations of the JK-1 core, and precise correlation with the nearby LK-1 borehole, are yet to be undertaken. It is also unknown if diagenetic alteration of titanomagnetites from basalts from the Shijiatun Formation during the primary sedimentary cycle played a role in reduction spot formation as a source of vanadium in the Jiaozhou Formation.…”