Early Cretaceous volcanism and its impact on fossil preservation in Western Liaoning, NE China
Abstract The so-called Jehol Biota, an excellently preserved Early Cretaceous biota consisting of both lacustrine and terrestrial organisms, is one of the most important Mesozoic fossillagerstatten. Although there have been extensive palaeontological studies, little work has been done on the volcanic settings under which the biota was preserved. The Sihetun area is the most famous fossil locality of the Jehol Biota in western Liaoning, and the volcanic succession in that area is the most representative and best studied. We use a case study of the volcanic succession of the Lower Cretaceous Yixian Formation in the Sihetun area to reconstruct the volcanic complexes and their history, to propose a depositional model of the volcanic successions, and to understand the relationship between volcanic activity and fossil preservation in western Liaoning. The volcanic succession comprises four volcanic complexes, each with distinct products; a shield volcano, an intermediate multi-vent center, a volcanic lake (in summit caldera), and finally lava domes. The presence of a caldera is postulated from exposures which suggest the presence of an inner topographic wall, bounding faults, and intra-caldera fill. Frequent volcanic activities and widespread existence of volcanic lakes during the Early Cretaceous are thought to account for the exceptional preservation of invertebrates and vertebrates of the Jehol Biota in western Liaoning.