(Table 1) Biostratigraphic horizons of ODP Leg 133 sites

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.

对819与821站位之间的地震反射（seismic reflection）数据及岩心数据（core data）所开展的研究，揭示了由相对海平面（relative sea level）周期性波动与气候扰动（climatic perturbations）所引发的沉积作用模式。基于层序地层学（sequence stratigraphic）解释，我们识别出9套以层序界面为边界的层序；每套层序均包含岩性独特且相对较薄的单元，这些单元被定义为凝缩段（condensed sections）。由于该区域碳酸盐-硅质碎屑混合沉积速率极高，本次研究得以分辨三级、四级与五级海平面变化。每套层序内均识别出1套主要凝缩段，且与该层序的最大海泛面（maximum flooding surface）相对应。这些凝缩段的识别标志包括：石英、黏土及浅水生物碎屑（shallow-water bioclasts）丰度升高、未再沉积的纯净海绿石（glauconites）含量增加、总碳酸盐丰度降低，以及磁化率（magnetic susceptibility）升高。海绿石含量升高被间接解释为沉积速率（sedimentation rates）相对降低的反映，此时沉积物在缺氧细菌降解带（suboxic bacterial degradation zones）内的停留时间（sediment residence time）得以延长。海进体系域（transgressive systems tracts）内生物碎屑含量升高，可归因于伴随突发性海侵事件（punctuated flooding events）发育的浅水礁群落（reefal communities）快速建隆；在此期间，随着礁群落快速向上生长以跟上海平面上升的步伐，浅水碳酸盐沉积作用加速。最大海泛期石英与黏土含量升高，被认为与沉积物饥饿（sediment starvation）作用相关，即背景黏土与石英发生富集。相对高位期可容纳空间降低，促进了高位体系域（highstand systems tract）的持续进积作用（progradation），以及再沉积海绿石与陆源砂、粉砂和黏土的沉积。这些沉积阶段还伴随有生物碎屑砂（bioclastic sands）含量升高，这与进积型向海推进的沉积事件相匹配。