意大利亚平宁地区第三纪中新世“Calcaria Lucina”冷泉碳酸盐岩中结晶扇的沉积岩石学及地球化学特征

结晶扇是冷泉碳酸盐岩的一种标志性沉积构造,主要由文石或重晶石等矿物呈放射状聚集形成。意大利亚平宁地区的第三纪中新统广泛发育冷泉碳酸盐岩,其中"Calcari a Lucina"冷泉碳酸盐岩中发育有典型的结晶扇。结晶扇主要由放射状文石聚集形成,含少量的方解石,具有明显的生长纹层。文石纹层的δ13CPDB为-37.9‰~-53.5‰,δ18OPDB为+2.4‰~+6.0‰,相邻文石纹层之间的δ13CPDB和δ18OPDB值差别明显,可能是与碳和氧的来源及流体渗漏速度有关。全岩稀土元素总量很低,w(REE)为0.23×10-6,页岩标准化模式具有明显的Ce负异常,显示结晶扇形成于氧化环境。

Sedimentary and Geochemical Characteristics of Crystal Fan in the "Calcari a Lucina" Cold Seep Carbonate of Miocene in the Northern Apennines, Italy

Crystal fan is a marked structure of cold seep carbonates,which consists of radial mineral aggregations,e.g.,aragonite,barite.Numerous cold seep carbonates developed in the Miocene strata of the northern Apennines in Italy,and there were typical crystal fans in the "Calcari a Lucina" seep carbonate.These crystal fans consist of radial aragonite aggregations with minor calcite and clearly growth lamina.The δ13CPDB values of aragonite lamina of crystal fan are from-37.9‰ to-53.5‰,and the δ18OPDB values are from +2.4‰ to+6.0‰.The δ13CPDB and δ18OPDB values of the adjacent aragonite lamina are significant different,and it might be resulted from the sources of carbon and oxygen and the variation of seep flux.The content of rare earth elements(REE) of crystal fan carbonate is very low(0.23×10-6),and shale-normalized REE patterns show significantly negative Ce anomaly,indicating that crystal fans were deposited in oxidation environment.