Paleontology and stratigraphy of the lower Chickabally mudstone (barremian-aptian) in the Ono Quadrangle, Northern California / Палеонтология и стратиграфия аргиллита нижнего Чикабалли (барремиан-апт) в квадрангле Оно, Северная Калифорния

The lower Chickabally Mudstone Member of the Budden Canyon Formation is Ba'rfemian and probable lowermost Aptian in age. Its lower contact is gradational with the Roaring River Member 'of 'the formation, but is bounded above by an angular unconformity at the base of the Huling Member in the Mitchell Creek Area of the Ono Quadrangle. The unconformity is documented by the angular relation of beds in the two members, the thinning section in the lower Chickabally Member from southwest to northeast, and the cutting out of fossil zones in the lower Chickabally Member from south to north. 

The unconformity is bracketed by probable lowermost Aptian and middle Aptian strata. Three faunal assemblages containing elements correlateable with the European middle and upper Barremian are dominated by the genus Shasticrioceras whose species serve to subdivide the strata into three biostratigraphic zones: S. poniente, S. roddai, and S. patricki from top to base. Thirtyfive taxa have documented occurrences in the lower Chickabally Member, 33 ammonites and 2 bivalves. Ten new species of the genera lEuptychoceras, Ancyloceras, Toxoceras, Toxoceratoides, Heteroceras, IHemihoplites, and Shasticrioceras are described.  <...>