ABSTRACT

A unique 10–140 cm thick veneer of greensand and glauconite-rich deposits (10–80 wt% glauconite) presently sits atop central Chatham Rise (CR) in water depths of 200-500 m. The glauconite is dominated by chemically mature, polished ovoidal and lobate pellets, with a 10–12 Å phyllosilicate structure and K-Ar ages of 7–5 Ma, indicating that the glauconite pellets are predominantly allogenic (i.e. derived/reworked) grains, and not of in situ authigenic origin. Glauconite possibly evolved from seafloor alteration of detrital and/or volcanogenic smectitic clays, likely concentrated within organic-rich faecal pellets under unique paleoceanographic conditions (nutrient cycling, upwelling, carbon isotope gradients) within the latest Miocene Subtropical Front. The distribution of glauconite abundance suggests a ‘glauconite factory’ existed at this time about Reserve Bank on western central CR. The pellets were dispersed eastwards along the crest by intensified bottom currents within the dynamic Subtropical Frontal zone, perhaps during the numerous glacial periods of lowered sea level throughout the Plio-Quaternary. The bioturbated greensand veneer, and its mix of other reworked Neogene and Quaternary skeletal, phosphatic and siliciclastic components, rest unconformably on mainly Early Oligocene chalks, forming a highly condensed, relict/palimpsest deposit that alone embodies the last up to 30 My of sedimentation history atop central CR.

摘要

一个独特的 10-140 厘米厚的绿砂单板和富含海绿石的沉积物（10-80 wt% 海绿石）目前位于查塔姆隆起 (CR) 中央的顶部，水深为 200-500 米。海绿石以化学成熟、抛光的卵形和叶状颗粒为主，具有 10-12 Å 的页硅酸盐结构和 7-5 Ma 的 K-Ar 年龄，表明海绿石颗粒主要是同种异体（即衍生/再加工）颗粒，和不是在原地自生起源。海绿石可能是从碎屑和/或火山成因的蒙蒙石粘土的海底蚀变演化而来，在最新的中新世亚热带前缘独特的古海洋条件（养分循环、上升流、碳同位素梯度）下，可能集中在富含有机物的粪便颗粒中。海绿石丰度的分布表明，此时在 CR 中西部的储备银行附近存在一个“海绿石工厂”。在动态的亚热带锋区内，底部水流增强，颗粒沿着山顶向东分散，这可能是在整个 Plio-Quaternary 的众多海平面降低的冰川时期。生物扰动的绿沙单板，以及其他经过改造的新近纪和第四纪骨骼、磷酸盐和硅质碎屑成分的混合物，