Planktonic foraminifera stratigraphy and datums of ODP Site 184-1143 and Hole 184-1146A, South China Sea

The biostratigraphy of Miocene-age sediment samples recovered from Ocean Drilling Program Sites 1143 and 1146, South China Sea, is presented. The preservation of the planktonic foraminifers recovered from both sites varies widely, from poor to very good. The volume of biogenic sediment in the >63-µm size fraction also varies considerably, with many samples being dominated by mud. In comparison to shipboard biostratigraphy, based on core catcher analyses with a depth resolution of ~10 m, we analyzed samples from the two stratigraphic columns every 2-3 m (~45- to 93-k.y. resolution). The placement of planktonic foraminifer zonal boundaries was made at a resolution of ~1.5 m at Site 1146 and ~3.0 m at Site 1143. The higher resolution has resulted in significant changes in biostratigraphic zonal boundary locations compared to shipboard results.
For the time interval of 5.54-10.49 Ma, the changes in zonation reveal similar age-depth models at both sites, with three segments of changing sedimentation rate through the upper Miocene, though the differences in sedimentation rates at Site 1146 are subtler than those at Site 1143. The boundary between lithologic Units II and III at Site 1146 corresponds to a sharp change in sedimentation rate (58 to 21 m/m.y.) at 15.1 Ma (the first occurrence of Orbulina suturalis). At this site, the interval from 16.4 to 15.1 Ma is characterized by very high mass accumulation rates in the noncarbonate fraction. Above this interval the carbonate fraction becomes increasingly important in the sediment flux to the South China Sea. At Site 1143, sedimentation rates increase from 8 to 99 m/m.y. at 8.6 Ma. This corresponds to a dramatic increase in both carbonate and noncarbonate mass accumulation rates at the site, but no change in lithology.

本数据集收录了取自南海大洋钻探计划（Ocean Drilling Program, ODP）1143与1146站位的中新世沉积样品的生物地层学研究结果。两处站位所获浮游有孔虫（planktonic foraminifers）的保存状态差异显著，跨度从极差至极佳。大于63微米粒级的生物成因沉积物占比同样存在显著波动，多数样品以泥质为主要组分。相较于基于岩心抓斗（core catcher）分析、深度分辨率约10米的船上生物地层学研究，本研究对两处地层柱的采样间隔为2-3米（对应约4.5万至9.3万年的时间分辨率）。1146站位的浮游有孔虫分带界线标定分辨率约为1.5米，1143站位则约为3.0米。相较于船上分析结果，更高的时间分辨率使得生物地层分带界线的位置发生了显著变动。
在5.54至10.49百万年的时间区间内，两处站位的生物地层分带变化揭示了相似的年龄-深度模型，晚中新世时期存在三段沉积速率变化阶段，但1146站位的沉积速率差异较1143站位更为平缓。1146站位岩性单元II与III的分界对应15.1 Ma时沉积速率的突变（从58米/百万年降至21米/百万年），该点为拱圈抱球虫（Orbulina suturalis）的首次出现层位。该站位16.4至15.1 Ma的区间内，非碳酸盐组分的质量堆积速率极高；该区间之上，碳酸盐组分在南海沉积物通量中的占比逐渐升高。1143站位在8.6 Ma时，沉积速率从8米/百万年升至99米/百万年，这对应站位处碳酸盐与非碳酸盐组分质量堆积速率的显著提升，但岩性未发生变化。