Pyroclastic deposition in the Cretaceous Shahezi Formation (Well SK‐2) Songliao Basin, China: Implications for tectonics and volcanism.

Well SK‐2 is located in the Songliao Basin. Core samples from this well indicate that the Early Cretaceous Shahezi Formation has a length of 2,359.01 m and is in direct contact with the basin basement of the Middle Triassic, missing the Huoshiling Formation. This paper is focused on the lowest sequence 1 (S1, at the bottom of the Shahezi Formation, interval of 5,450.72–5,695.00 m, a length of 244.28 m) of the Cretaceous basin fills. It was found that the volcanic components contributed important parts in the sequence of basin fills, and the start of the rifting resulted from the combination of regional extensional tectonics and volcanism. Based on the centimetre‐scale description of the continuous core samples, we propose a model to delineate the interaction between tectonics, volcanism, and pyroclastic deposition. The study shows the tectonic‐volcanism in the earliest rifting stages and its control on sedimentary filling. These results also have common sense for the initial rifting process of a continental half‐graben basin. Sequence 1 of the Shahezi Formation in well SK‐2 shows a typical volcanic‐ sedimentary sequence. During the lowstand stage, the weathering‐depositional system was controlled by extension; during the transgressive and highstand stages, the transitional weathering‐depositional system and the mixed volcanic and weathering depositional system were controlled by transtension. [ABSTRACT FROM AUTHOR]