Mineralogy and geochemistry of latest Miocene deposits in the Tyrrhenian Sea

Late Miocene sediments from ODP Sites 652 and 654, drilled on the Sardinian margin in the Western Tyrrhenian Sea, are investigated through mineralogical, micromorphological, geochemical, and microgeochemical analyses. Clay associations appear to be little controlled by conditions of deposition, and largely depend on pre- and post-depositional conditions. The sedimentary series from Central Mediterranean gives very different geodynamic information, according to the sector considered. While relatively stable conditions, like those encountered in Caltanissetta Basin, Sicily, favor the mineralogical expression of warm-temperate and subarid Messinian climate, the Eastern Sardinia margin (Site 654) clay suites mainly reflect the transition from tectonically active to relaxed conditions. The series deposited at the foot of the same margin above a thinner crust (Site 652) experienced the effects of burial diagenesis, enhanced by strong geothermal gradient.针对第勒尼安海西部撒丁岛陆缘钻取的大洋钻探计划（Ocean Drilling Program，ODP）652井与654井的晚中新世沉积物，本研究通过矿物学、微形态学、地球化学及微地球化学分析手段对其开展了系统研究。黏土组合的形成受沉积条件的制约作用有限，且在很大程度上取决于沉积前后的地质环境条件。地中海中部的沉积序列依据所处构造区域的不同，所反映的地球动力学信息存在显著差异：如西西里岛卡尔塔尼塞塔盆地所记录的相对稳定沉积环境，更利于暖温带亚干旱墨西拿期气候的矿物学特征得以显现；而撒丁岛东部陆缘（ODP 654井）的黏土组合则主要反映了从构造活跃期至构造松弛期的环境转变。沉积于同一陆缘坡脚、地壳厚度较薄的序列（ODP 652井）则经历了埋藏成岩作用的改造，强烈的地温梯度进一步强化了这一成岩过程。