(Table 2) Color, epoch, nannofossil zone, and clay mineralogy at DSDP Site 90-591@en

Pale green laminae < 2 mm thick are common features of the Neogene and Quaternary sediment of Lord Howe Rise. We believe these laminae represent diagenetically altered volcanic ash layers from regional volcanic events. Although no consistent high abundances of volcanic glass are found within the laminae, the volcanic origin of the laminae is suggested by (1) similar temporal distribution of the laminae and the distribution of volcanic ash layers elsewhere in the southwest Pacific; (2) the high abundances of authigenic smectite in the laminae; and (3) the common occurrence of iron sulfides in proximity to most of the laminae. The resulting tephrostratigraphy is considerably more complex and detailed than was previously known.厚度小于2毫米的淡绿色纹层，是豪勋爵海隆（Lord Howe Rise）新近纪与第四纪沉积物的常见特征。我们认为，此类纹层代表区域火山事件形成的火山灰层经成岩蚀变改造后的产物。尽管纹层中未检出稳定富集的火山玻璃，但下述三点可佐证其火山成因：其一，纹层的时间分布与西南太平洋其他区域火山灰层的分布特征高度相似；其二，纹层内富集自生蒙脱石；其三，多数纹层附近普遍伴生硫化铁。据此构建的火山碎屑地层学（tephrostratigraphy）体系，其复杂度与精细度均远超此前的认知水平。