Stratigraphic analysis of the hurricane deck formation, Sierra Madre, Santa Barbara County, California

Six stratigraphic sections were measured and studied in the Hurricane Deck Formation (lower to middle Miocene) of the central Sierra Madre of northeastern Santa Barbara County, California. Seven lithosomes, or discrete lithologic entities, are recognized within the formation. These seven lithosomes can be grouped into three major types: (1) structureless sandstone that was deposited by some mass-movement process (i.e. grain creep or mass slumping, sliding, or creeping), (2) graded, bedded sandstone that was deposited by turbidity currents, and (3) pelagic and/or hemipelagic muds tone deposited by suspension. The mudstone is rare within the formation and occurs mainly in the shale units which overlie and underlie the Hurricane Deck Formation. The Hurricane Deck Formation is interpreted as a time-transgressive submarine ramp deposit. It was fed through a prograding delta from multiple points which migrated back and forth across the delta platform. The structureless sandstone, which occurs almost exclusively along the northern front of the Sierra Madre, was deposited in a proximal ramp setting. The graded, bedded sandstone, which occurs in the southwest Sierra Madre was deposited in a proximal to distal ramp setting. The mudstone was deposited on the delta slope and on the ramp during times of low terrigenous sedimentation. During Saucesian time the submarine ramp system that would become the Hurricane Deck Formation was fed from a delta to the north, with deposition of the ramp deposits to the south in the area of the present-day San Rafael Mountains. The area of the present-day Sierra Madre accumulated mainly delta slope mudstone deposits of Vaqueros shale. A transgression in the Cuyama basin during early Relizian time caused a landward and northeastward displacement of depositional environments, so that the area of the present-day Sierra Madre became the depocenter for the Hurricane Deck ramp deposits. During this time the ramp was fed from a delta to the northeast. A basin-wide regression near the beginning of the medial Miocene resulted in progradation of the shoreline and deposition of shoreface deposits of the Branch Canyon Formation throughout the area of the present-day Sierra Madre.