Intracaldera volcanism and sedimentation- Creede Caldera, Colorado

Within the 26.7 Ma Creede caldera, Colorado, the evidence for interpreting its postcaldera volcanic and sedimentary history lies within the sequence of tuffaceous clastic sedimentary rocks and tuffs known as the Creede Formation. The intracaldera lacustrine sediments and interbedded ash deposits of the Creede Formation were sampled by research core holes Creede 1 and 2, drilled during the fall of 1991. An earlier study of the Creede Formation, based on surface outcrops and shallow mining company core holes, concluded that the process of caldera structural resurgence was rapid and that a caldera lake had developed in an annulus (moat) located between the resurgent dome and caldera wall. A picture has been developed of intracaldera activity consisting of intermittent hydrovolcanic eruptions within the caldera lake representing the lower third of the Creede Formation, and both magmatic and hydrovolcanic ash eruptions throughout the top two-thirds. Most of the ash deposits interbedded with the moat sedimentary rocks are extremely fine grained. Fallout into the moat lake and unconsolidated ash eroded from caldera walls and slopes of the resurgent dome were deposited by stream delta distributaries within relatively shallow water in the northwestern moat, and in deeper waters of the northern moat, where the caldera is intersected by a graben. Interbedded with ash beds and tuffaceous siltstones are coarse-grained turbidites from adjacent slopes and distal travertine beds from fissure ridges adjacent to the moat. Sedimentation rates and provenance for clastic sediments are linked to the frequent volcanic activity in and near the caldera; almost all of the Creede Formation sedimentary rocks are tuffaceous.