High-Resolution Sequence Stratigraphy, Condensed Sections, and Flooding Events off the Great Barrier Reef: 0-1.5 Ma

Abstract

Examination of seismic reflection and core data between Sites 819 and 821 provides information about patterns of sedimentation that result from repetitive fluctuations in relative sea level and climatic perturbations. On the basis of sequencestratigraphic interpretations, we identify nine sequences bounded by sequence boundaries; each sequence contains lithologically distinct and relatively thin units that have been interpreted as condensed sections. Because of very high mixed carbonate-siliciclastic sedimentation rates in this region, resolution of third-, fourth-, and fifth-order changes of sea level is recognized. One predominant condensed section is identified within each sequence and is associated with the maximum flooding surface of that sequence. These condensed sections are marked by increases in abundance of quartz, clay, and shallow-water bioclasts; increases in nonreworked pristine glauconites; decreases in total carbonate abundance; and increases in magnetic susceptibility. Increases in glauconite have been interpreted to indirectly reflect relative decreases in sedimentation rates, whereby sediment residence time is prolonged within suboxic bacterial degradation zones. Increases in bioclasts within transgressive systems tracts are attributed to relatively rapid buildups of shallow-water reefal communities that accompanied punctuated flooding events; during these times shallow-water carbonate growth accelerated as reefal communities built upward rapidly to keep up with rising sea level. Increases in quartz and clay contents during maximum flooding are thought to be tied to sediment starvation, whereby background clays and quartz contents are concentrated. Decreased accommodation potential during relative highstand phases promoted progressive highstand systems tract progradation and sedimentation of reworked glauconites and terrigenous sands, silts, and clays. These depositional phases also are marked by increases in bioclastic sands that accompanied the progradational, seaward building events.

Tropical view of Quaternary sequence stratigraphy: Siliciclastic accumulation on slopes east of the Great Barrier Reef since the Last Glacial Maximum

“…Although recognizing that siliciclastic-rich intervals coincide with late transgression, Glenn et al (1993) and Kronen and Glenn (2000) suggested that they represent sequence condensation. Their primary argument was that at ODP Site 821 these intervals contain ''pristine'' verdine, a mineral formed near the seafloor when sediment slowly accumulates in shallow, tropical waters (Odin and Sen Gupta, 1988).…”

“…(e.g., Davies and McKenzie, 1993;ICGBRD, 2001), rivers have discharged large masses of clay, quartz, and other weathered residue into a region with an extensive network of carbonate reefs on the outer shelf, the Great Barrier Reef. East of the Great Barrier Reef, cores from the slope and basin as well as interpretations of seismic profiles show alternating siliciclastic-rich and carbonate-rich horizons in upper Quaternary sediment (Harris et al, 1990;Davies and McKenzie, 1993;Glenn et al, 1993;Dunbar et al, 2000;Dunbar and Dickens, 2003). Following conventional models (Fig.…”

The problem of glaucony from the Shannon Sandstone (Campanian, Wyoming)

“…, 2001). Green minerals found at the Great Barrier Reef, Australia, were originally described as glauconite (Glenn et al , 1993). Following careful mineralogical investigations, however, these grains were revealed to belong to the verdine facies (Kronen and Glenn, 2000).…”

Sponge Spicules, Silicification, and Sequence Stratigraphy

“…Another example stems from the Carboniferous of the Paradox Basin, USA, where siliceous-sponge facies, bedded chert, and glauconite are associated with maximum-flooding intervals (van Buchem et al 2000). All these examples identify stratigraphic condensation by mineral authigenesis, caused by sediment starvation during flooding events (Glenn et al 1993) and inducing low-flow conditions or fluid stagnation in the shallow burial environment.…”

“…Stratigraphic condensation has multiple causes (low sediment production, oceanic currents and winnowing, sediment bypassing; Glenn et al 1993) and the conventional stratigraphic position of the condensed section (Fig. 7) may not always apply (Pomar and Ward 1994;Page et al 2003).…”