The White Wall-Sugar Loaf mixed volcanic-volcaniclastic-carbonate Formation in St. Eustatius: Evidence for the emergence of an island arc volcano

The uplifted volcanic-volcaniclastic-carbonate White Wall-Sugar Loaf Formation is located on the southwestern flank of the Quill volcano, in the island of St. Eustatius, Lesser Antilles. The White Wall-Sugar Loaf Formation is an excellent example of proximal volcano-sedimentary sequences. It shows seven volcano-sedimentary sequences of pyroclastic deposits interbedded with platform limestones. The pyroclastic deposits represent a change from subaerial to submarine volcanism. Volcano-sedimentary sequences are separated from upper pyroclastics by an erosional unconformity, subdividing the sequence into pre-Quill and Quill volcanism. Geochemical data suggest bimodal changes in magma composition from basaltic andesite to soda rhyolite, with some crustal contamination. In contrast, the Quill deposits above the unconformity are only andesitic in composition. The results provide a model for the early evolution of a tropical island arc volcano that can be used to interpret formation conditions of older, less well-exposed sequences, such as the Late Cretaceous of southwestern Puerto Rico.