Rare earth element composition of manganese nodules and micronodules from the northwest Atlantic

The shale-normalized REE patterns of manganese nodules from the northwest Atlantic show enrichment in Sm and Eu relative to the heavier and lighter REE, excluding Ce, and are similar to the patterns previously observed in deep water (> 3000m) nodules from the Pacific. The inverse relation of this pattern to that of sea water and the high Ce anomaly (average 5.5) indicate that probably the REE in the nodules originate from sea water and the nodules are possibly hydrogenous. The patterns for micronodules are similar to those of the nodules but the concentrations of REE were substantially higher in two of them. The red clay occurring on abyssal hills where nodules and micronodules are found also shows higher REE concentrations over terrigenous gray clay. The latter is devoid of nodules and micronodules and occurs in abyssal plains. The excess REE in the red clay also show a pattern similar to those of the nodules and micronodules. Most of the micronodule samples show a lower Ce anomaly (1.7) and lower Co concentration compared to the nodules, so it is inferred that at least some micronodules were formed during post-depositional periods when the conditions were less oxidizing than average.

西北大西洋锰结核的页岩标准化稀土元素（REE）配分模式显示，相对于重稀土和轻稀土元素（不包括铈），钐（Sm）和铕（Eu）富集，且与此前在太平洋深水（>3000米）结核中观察到的配分模式相似。该配分模式与海水模式的逆相关性，以及高铈异常（平均值5.5）表明，结核中的稀土元素可能来源于海水，且结核或许为氢成成因。微结核的配分模式与结核相似，但其中两个样品的稀土元素浓度显著更高。在发现结核和微结核的深海丘陵上分布的红黏土，其稀土元素浓度也高于陆源灰色黏土。后者不含结核和微结核，分布于深海平原。红黏土中的过剩稀土元素也呈现出与结核和微结核相似的配分模式。与结核相比，大多数微结核样品显示出较低的铈异常（1.7）和较低的钴浓度，因此可推断至少部分微结核形成于沉积后期，当时的氧化条件低于平均水平。