Palaeomagnetic and 40Ar/39Ar dating constraints on the age of the Jehol Biota and the duration of deposition of the Sihetun fossil-bearing lake sediments, northeast China

New palaeomagnetic and 40Ar/39Ar dating was carried out on the volcanic rocks and interbedded fossil-bearing lake sediments at the Sihetun section (northeast China) to determine the duration of deposition of the lacustrine sediments. The 40Ar/39Ar ages of the lower and upper volcanic rocks near the lava-sediment contacts are respectively 125.7 ± 2.6 Ma and 124.2 ± 2.5 Ma, which is in good agreement with a previously reported age of tuffs in the lake deposits. This is further supported by a normal palaeomagnetic polarity recorded by the whole lacustrine interval. With these palaeomagnetic investigations and new age controls, we conclude that the whole lacustrine interval at Sihetun was deposited within the normal polarity chron M3n (marine anomaly) during the Early Cretaceous. The possibly volcanic-associated ancient lake may have existed for a relatively short duration of less than 0.7 myr, assuming the M3n chron age to be between 124.72–124.04 Ma.