NOAA/WDS Paleoclimatology - Keweenaw Peninsula, Michigan 11,000 Year Lake Sediment Metals Data

The Old Copper Complex (OCC) refers to the production of heavy copper-tool technology by Archaic Native American societies in the Lake Superior region. To better define the timing of the OCC, we evaluated 53 (eight new and 45 published) radiocarbon (14C) dates associated with copper artifacts and mines. We compared these dates to six lake sediment-based chronologies of copper mining and annealing in the Michigan Copper District. 14C dates grouped by archaeological context show that cremation remains, and wood and cordage embedded in copper artifacts have ages that overlap with the timing of high lead (Pb) concentrations in lake sediment. In contrast, dates in stratigraphic association and from mines are younger than those from embedded and cremation materials, suggesting that the former groups reflect the timing of processes that occurred post-abandonment. The comparatively young dates obtained from copper mines therefore likely reflect abandonment and infill of the mines rather than active use. Excluding three anomalously young samples, the ages of embedded organic material associated with 15 OCC copper artifacts range from 8500 to 3580 cal BP, confirming that the OCC is among the oldest known metalworking societies in the world.

古铜器复合体（Old Copper Complex, OCC）指代苏必利尔湖地区古印第安社会所形成的重型铜器制造技术体系。为更精准地划定古铜器复合体的年代框架，本研究对53组与铜器遗存及矿址相关的放射性碳（14C）测年数据展开了评估，其中包括8组新测数据与45组已发表测数据。我们将这些测年数据与密歇根铜矿区基于湖泊沉积物的6项铜矿开采与铜退火工艺年代序列进行了对比。按考古背景分组的14C测年结果显示，嵌入铜器遗存的火葬遗骸、木材及绳类遗存的年代，与湖泊沉积物中高铅（Pb）浓度的出现时段高度重合。与之形成鲜明对比的是，地层关联样本与矿址样本的测年结果均晚于嵌入遗存及火葬遗骸样本的测年结果，这表明前者所反映的是矿址废弃后发生的过程的年代。因此，从铜矿遗址中获得的相对年轻的测年数据，其所反映的大概率是矿址废弃后的填埋过程，而非铜矿的实际开采使用时段。在剔除3个异常年轻的样本后，与15件古铜器复合体铜器遗存相关的嵌入有机质遗存的年代区间为8500至3580校准年前（cal BP），这证实古铜器复合体是目前已知的全球最早的金属加工社会之一。