奥地利Gosau群Bibereck组Campanian早期海水变深序列的地层学和地球化学

Schmidsippl剖面位于奥地利北钙质阿尔卑斯构造带内Gosau群典型地区。剖面出露的Bibereck组记录了一个海侵和沉积区海水变深过程。Bibereck 组之下是Santonian 晚期Hochmoos 组(Sandkalkbank段),主要为砂质、粉砂质灰色生物扰动构造发育的泥灰岩,含少量双壳类碎片。Hochmoos组之上为灰色泥灰岩和泥灰质灰岩。Bibereck组下部显示变深到近滨-远滨过渡带区域;向上,泥灰岩指示细粒泥质远滨沉积,水深大致50~150 m;之上出现浮游有孔虫含量超过90%的泥灰质灰岩,代表着半深海沉积环境。生物地层数据显示采样层位整体位于浮游有孔虫asymetrica elevata 带,由Globotruncanita elevata 和Dicarinellaasymetrica 的共同出现来界定。钙质超微化石Calculites obscurus、Lucianorhabdus cayeuxii、Arkhangelsk iella cymbiformis 的出现指示属于钙质超微化石带CC17b/UC12,相当于Campanian初期。地层深度剖面上,Ca/Al比值和Catot含量显示海水来源的Ca在0~5 m地层内几近于零,向上快速增加;(Fe/Al)/碳酸盐显示两个峰值,代表更还原条件,分别位于4 m和10 m位置;K/Al比值的下降被解释为更潮湿气候条件;剖面上部Ba含量的增加显示向更低原始生产条件的变化;陆源矿物在剖面7 m以下保持稳定,之上一直到剖面顶部不断下降。生物地层

STRATIGRAPHY AND GEOCHEMISTRY OF AN EARLY CAMPANIAN DEEPENING SUCCESSION (BIBERECK FORMATION, GOSAU GROUP, AUSTRIA)

The Bibereck Formation of the Schmidsippl section in the type area of the Gosau Group (Northern Calcareous Alps, Austria) records a transgression and deepening of the depositional area from shallow neritic to bathyal depths. The Bibereck Formation overlies the sandstones of the Upper Santonian Hochmoos Formation (Sandkalkbank Member). It is characterized by sandy to silty grey bioturbated marls and marlstones, including minor amounts of mollusc debris, overlain by grey marls and marly limestones. The lower part of the Bibereck Formation indicates a deepening to nearshore-offshore transitional areas, Higher up, the marls indicate offshore deposition of fine-grained mud at palaeowater depths of about 50 to 150 m, overlain by marly limestones with more than 90% of planktonic foraminifera which point to a bathyal depositional environment. Biostratigraphic dating indicates that the whole sampled interval belongs to the asymetrica-elevata Zone of the planktonic foraminifera zonation, defined by the concurrent range of Globotruncanita elevata and Dicarinella asymetrica, and nannofossil standard zone CC17b/UC12 with the marker species Calculites obscurus, Lucianorhabdus cayeuxii (both normal and curved forms) and Arkhangelskiella cymbiformis, which can be correlated to the Early Campanian. The plot of Ca/Al and Catot over depth shows that the influence of marine derived Ca is close to zero between 0 and 5 m and increases significantly up section. (Fe/Al)/calcite display two peaks of more reducing conditions, one at 4 m and the second at 10 m. The decrease in K/Al is interpreted as a shift towards more humid conditions. Ba increases in the upper part of the profile indicating a shift towards lower primary production. Terrigenous minerals stay fairly constant above 7 m and decrease further towards the top of the profile. Biostratigraphic data indicate a duration of less than 500 000 years for the sedimentation of the Bibereck Formation, during which a deepening of the sedimentation area from a few meters water depths to about 800 to 1 500 m is recorded. Geochemistry identifies two pulses of sea level change over the profile. These data give a base for comparison with overlying oceanic red beds.