三水盆地古近系下部湖相沉积的稀土元素地球化学特征及其古气候意义

通过分析三水盆地古近系下部岩心的稀土元素丰度和分布模式，并结合其它地球化学指标(Fe/Mn, Mg/Ca)，重建了古近纪早期的古气候条件。岩心中稀土元素总量（∑REE）变化于7.06~230.01 μg /g之间，平均值为142.32 μg/g。接近全球平均大陆上地壳成分（UCC），略低于北美页岩。沉积物显示轻稀土相对富集、右倾斜型、Eu中度亏损以及Ce异常不明显的稀土元素分布模式。岩心各深度处稀土元素分布模式非常相似，且与UCC的稀土元素分布模式基本一致。表明沉积物具有较为一致的物质来源和形成机理，而且源区具有大陆上地壳性质。岩心沉积时期古气候变化经历了较为干燥—温湿—温湿与干旱气候交替出现—以温湿气候条件为主的四个阶段。总体上显示明显的变湿趋势。

Rare Earth Element Records of the Lower Paleogene Sediments in the Sanshui Basin and Their Paleoclimate Implications

The concentration of rare earth elements ( REE) was determined in the Lower Paleogene core sedimentary rock from the Sanshui Basin. The ∑REE contents range from 7.06 to 230.01μg/g, with an average value of 142.32μg/g, close to that of Upper Continental Crust (UCC) and slightly depleted relative to North American Shale. Chondrite-normalized REE patterns show little variation throughout the core and are consistent with the composition of UCC, with light REE enrichment, negative slopes, moderate Eu depletion and unobvious Ce anomaly. This indicates a relatively consistent sediment source and formation mechanism during the deposition of Lower Paleogene sediments in the Sanshui Basin. The REE records, combining with other geochemical proxies ( Fe/Mn, Mg/Ca) , suggest a general trend of getting more humidity during the core deposition and allow the recognition of four paleoclimate stages: stage I (89～72. 7 m) with drier condition, stage Ⅱ(72.7～51.8m) with dominantly humid condition, stageⅢ (51.8 (30.6 m) with fluctuation of humid and dry condition and stage Ⅳ (30. 6～0 m) with prevailing humid climate with intermittent dry condition.