Evaluating the tephra input into Pacific Ocean sediments: distribution in space and time

We studied the volcanic contribution to the global sediment budget in the P acific Ocean basin. It is the world's oldest (174 m.y.) and largest (approx imate to 49% of Earth's surface area) ocean basin and has had a high and co ntinuous tephra influx from intraplate and convergent margin volcanoes thro ugh time. Computerized shipboard data from 65 legs of the Deep Sea Drilling Project (DSDP) and the Ocean Drilling Program (ODP) were screened for the presence of volcaniclastic components. Tephra-bearing and tephra-free core sections (standard 1.5- and 0.30-m core catcher sections) were separated, r egardless of the mass fraction of tephra present. The percentage of tephra- bearing core sections ("tephra frequency") per site and time span ("age uni t") was calculated. The age units were the Quater nary, the subepochs of th e Tertiary, and the stages of the Cretaceous. A total of 424 drill sites yi elded 1433 usable stratigraphic units. Fifty percent are younger than 13 m. y., corresponding to only approximately 10% of the total interval studied ( 124.5 m.y.). The percentage of tephra-bearing age units is high throughout (83+/-6%) and correlates linearly with the total number of age units (R-2=0 .998; n=17). The average tephra frequency (30-50%) fluctuates, because the abundance of age units of different tephra frequency classes (0, 1-33, 34-6 7, 68-100% tephra frequency) varies with time. This indicates that the Ceno zoic increase in tephra production results from increase in volcanicity and not spatial extension of volcanic source areas. The Cenozoic sediments tha t were recovered are dominated by distal tephra from explosive are volcanis m. Pulses of are volcanism occurred in the Pliocene-Quaternary (since appro ximate to 5 m.y.) and mid-Miocene (approximate to 12-15 m.y.). However, the record of explosive are volcanism in Paleogene and Cretaceous sediments wa s either not drilled or has been destroyed by subduction. Except for the Cr etaceous (approximate to 70-110 m.y.) volcanic pulse, intraplate volcanism is poorly represented in the tephra record because the drill sites are outs ide the proximal range (>500-1000 km) of the sources. Thus, the tephra reco rd drilled contains significant gaps that bias the estimate of tephra volum e towards the less voluminous distal deposits. Most of the volcaniclastic v olume accumulated by mass wasting as volcaniclastic aprons surrounding ocea n island volcanoes. Volcaniclastic production rates range from 10,000 to 41 ,800 km(3)/m.y, for large intraplate volcanoes and approximately 10-13 km(3 )/km are length per million years for oceanic island arcs. Extrapolation ov er the lifetime of major Pacific arcs and hotspot chains, combined with a v olume estimate of the distal tephra component, indicates a minimum of 9.3x1 0(6) km(3) of tephra, corresponding to 23 vol.% of the existing Pacific oce anic sediments. At least two thirds of the tephra volume was deposited in t he proximal range and at least half of it is derived from intraplate source s. The large proportion of tephra, its composition, and its localized accum ulation causes significant spatial and temporal variation in Pacific oceani c sediments that should have a perceptible impact on the elemental fluxes b etween ocean, crust, and mantle.