Seismic volcanostratigraphy of large-volume basaltic extrusive complexes on rifted margins

Large-volume extrusive basaltic constructions have distinct morphologies an d seismic properties depending on the eruption and emplacement environments . The presence and amount of water is of main importance, while local I ift basin configuration, erosion, and resedimentation determine the overall ge ometry of the volcanic constructions. We have developed the concept of seis mic volcanostratigraphy, a subset of seismic stratigraphy, to analyze volca nic deposits imaged on seismic reflection data. The method places special f ocus on identification and mapping of seismic facies units and the volcanol ogical interpretation of these units. Interpretation of seismic reflection data along the Atlantic and Western Australia rifted margins reveals six ch aracteristic volcanic seismic facies units named (1) Landward Flows, (2) La va Delta, (3) Inner Flows, (4) Inner Seaward Dipping Reflectors (Inner SDR) , (5) Outer High, and (6) Outer SDR. These units are interpreted in terms o f 3 five-stage tectonomagmatic volcanic margin evolution model comprising ( 1) explosive volcanism in 3 wet sediment, broad basin setting, (2) subaeria l effusive volcanism forming Gilbert-type lava deltas along paleoshorelines , (3) subaerial effusive volcanism infilling a fairly narrow rift basin, (3 ) shallow marine explosive volcanism as the inject-ion axis is submerged be low sea level, and finally (5) deep marine sheet flow or pillow-basalt volc anism. Further, erosion and resedimentation processes are particularly impo rtant during the shallow marine stages. Seismic volcanostratigraphy provide s important constraints on rifted-margin development, in particular, on the prevolcanic basin configuration, relative timing of tectonomagmatic events , total amount of volcanic rocks, location of paleoshorelines, and margin s ubsidence history. These parameters give key boundary conditions for unders tanding the processes forming volcanic margins and other large-volume basal tic provinces.