The pre-volcanic Cenozoic stratigraphy near the study area can be characterized by a series of non marine and marine clastic sediments (Youngson and Craw, 1996) deposited on an early Cretaceous erosional surface (LeMasurier and Landis, 1996) of a schist

The pyroclastic rocks of "The Crater", South Island, New Zealand belong to the Miocene, alkaline basaltic Dunedin Volcanic Group and represent an individual eruptive center with possible multiple vents. Three pyroclastic units have been separated at the study area based on textural and compositional features as well as their stratigraphic positions. The central part of The Crater comprises basal accidental lithic rich tuff breccias and unsorted, weakly bedded lapilli tuffs inferred to have been deposited by "en masse" deposition of fall back tephra and/or high concentration pyroclastic density currents from vent opening phreatomagmatic explosions, near vent. The unit subsequently subsided into the conduit. Above this unit, is a juvenile rich lapilli tuff deposited near vent by high-concentration pyroclastic density currents. These pyroclastic density currents were generated by phreatomagmatic explosions occurring at shallow levels, which did not excavate significant amounts of subsurface strata. In the western side of the area a large and complex crater rim sequence has collapsed into the vent. The rim exhibits a pyroclastic sequence developed by phreatomagmatic explosion generated pyroclastic density currents of decreasing energy and efficiency followed by magmatic explosion generated fall-out. Accidental lithic fragments in the pyroclastic beds are derived from pre-volcanic strata that are not now preserved in the vicinity of The Crater but which are inferred to have been present at the site at the time of eruption. be existing in the area during the volcanism. Calculating the total erosion since the volcanism an average of 30 m/My erosion rate is implied. Introduction/geological setting "The Crater", named for its circular tuff ramparts surrounded by schist, is an approximately 1 km long and 700 m wide depression, partially filled with pyroclastic rocks and cross-cutting dykes and/or sills, on the Otago Schist peneplain. The pre-volcanic Cenozoic stratigraphy near the study area can be characterized by a series of non marine and marine clastic sediments (Youngson and Craw, 1996) deposited on an early Cretaceous erosional surface (LeMasurier and Landis, 1996) of a schist basement ( Otago Schist ). The oldest terrestrial clastic sediments deposited on the schist surface form the Hogburn Formation . Widespread marine transgression followed Late Cretaceous extension and separation of New Zealand from Gondwana (Carter, 1988) causing widespread marine clastic sedimentation in the area ( Oligocene marine sequence ). The area probably reemerged in the early Miocene in response to transpressional tectonics with the inception of the Alpine Fault (Cooper et al., 1987), with renewed terrestrial clastic deposition (fluvio-lacustrine) taking place ( Dunstan Formation ). Most of the Cenozoic sedimentary sequence has eroded away especially in uplifted areas (LeMasurier and Landis, 1996). Volcanic eruptions took place in late Miocene time (Dunedin Volcanic Group: Coombs et al., 1986) along hydrologically active zones producing widespread phreatomagmatic maar/diatreme volcanism with extensive Strombolian scoria cone and lava flow forming eruptions. Most of the eruptive centers are strongly eroded to their root zones where downdropped sequences of pre-volcanic and former crater rim rocks can be identified. These entrapped blocks of pre-volcanic rocks in the conduits of eruptive centers provide important indications of the former lateral distribution of the pre-volcanic sedimentary units. The lack of any Cenozoic sedimentary rocks cropping out around The Crater, together with the presence of Cenozoic sedimentary rocks as fragments in the pyroclastic rocks, suggests that 1) the Cenozoic cover either exists beneath the volcanics or 2) the fragments represent slide blocks and clasts from the former conduit wall of The Crater vent(s). Field observations presented in this paper eliminate the first possibility, since there is no reason for a small, sediment-filled, Cenozoic basin to exist on the surface of the schist basement. Support for the