Illustrations of manganese nodules dredged from the Upper Jarvis Inlet

Manganese-iron oxide concretions are presently forming on Patrick Sill in upper Jervis Inlet. The marine geology of Patrick Sill and the adjoining basins (Queen's Reach and Princess Royal Reach) was studied to define the environment in which the concretions form. The river at the inlet head is the principal source of sediment to the upper basin. The average grain size of surficial bottom sediments within this basin decreases uniformly with distance from the source. Patrick Sill separates the upper from the lower basin. The sediment distribution pattern within the lower basin differs markedly from the upper basin as there is no dominant source of material but rather many localized sources. Abundant shallow marine faunal remains recovered in deep water sediment samples indicate that sediments deposited as deltas off river and stream mouths periodically slump to the basin floors. Geologic and optical turbidity information for the upper basin can best be explained by slumping from the delta at the inlet head with the initiation of turbidity or density currents. Patrick Sill appears to create a downstream barrier to this flow. The mineralogy of the bottom sediments indicates derivation from a granitic terrain. If this is so, the sediments presently being deposited in both basins are reworked glacial materials initially derived by glacial action outside the present watershed. Upper Jervis Inlet is mapped as lying within a roof pendant of pre-batholithic rocks, principally slates. Patrick Sill is thought to be a bedrock feature mantled with Pleistocene glacial material. The accumulation rate of recent sediments on the sill is low especially in the V-notch or medial depression. The manganese-iron oxide concretions are forming within the depression and apparently nowhere else in the study area. Also forming within the depression are crusts of iron oxide and what are tentatively identified as glauconite-montmorillonoid pellets. The concretions are thought to form by precipitation of manganese-iron oxides on pebbles and cobbles lying at the sediment water interface. The oxide materials are mobile in the reducing environment of the underlying clayey-sand sediment but precipitate on contact with the oxygenating environment of the surficial sediments. The iron crusts are thought to be forming on extensive rocky surfaces above the sediment water interface. […]

目前在杰维斯湾上游的帕特里克海岭（Patrick Sill）上正在形成锰铁氧化物结核（Manganese-iron oxide concretions）。为明确该类结核的形成环境，研究团队对帕特里克海岭及其毗邻盆地（女王航道与皇家公主航道（Queen's Reach and Princess Royal Reach））的海洋地质特征开展了系统调研。河口处的河流是上游盆地沉积物的主要物源。该盆地内的表层海底沉积物平均粒径随距物源的距离均匀递减。帕特里克海岭将上游盆地与下游盆地分隔开来。下游盆地的沉积物分布格局与上游盆地存在显著差异：其并无单一主导物源，而是存在多处局地物源。深水沉积物样品中采获的大量浅海动物化石遗存表明，河口及溪流口处形成的三角洲沉积物会周期性滑塌至盆地底部。针对上游盆地的地质与光学浊流数据，可通过河口三角洲滑塌引发浊流或密度流得到最佳解释。帕特里克海岭似乎对该类流体形成了下游阻隔。海底沉积物的矿物学特征显示其物质源自花岗岩地貌。若此推论成立，则两个盆地当前沉积的沉积物均为经再改造的冰川成因物质，其最初由当前流域之外的冰川作用形成。杰维斯湾上游区域被划归为岩基前岩石（主要为板岩）的顶板悬垂体（roof pendant）分布区。学界普遍认为帕特里克海岭是一种被更新世（Pleistocene）冰川物质覆盖的基岩地貌。海岭上近期沉积物的堆积速率较低，尤以V形缺口或中部凹陷区域为甚。锰铁氧化物结核正是在该凹陷区域形成，研究区内其余区域暂未发现此类结核。同样在该凹陷区域形成的还有氧化铁壳，以及暂定为海绿石-蒙皂石类球粒（glauconite-montmorillonoid pellets）的物质。研究认为，结核是由沉积物-水界面处的砾石与卵石表面析出锰铁氧化物而形成。该氧化物在下方黏土质砂质沉积物的还原环境中具有迁移性，但在接触表层沉积物的氧化环境后发生析出。氧化铁壳则被认为形成于沉积物-水界面之上的大面积裸露岩面。[…]