Stable carbon and oxygen isotopes of foraminifera fand carbon content of ODP Leg 107 holes

High-resolution bio- and chemostratigraphy of an earliest Pliocene section from ODP Site 652 indicates that postflood paleoceanographic conditions in the Tyrrhenian Sea can be sub-divided into two discrete intervals. The first is manifested by an acme of Sphaeroidinellopsis spp., increasing carbonate contents, and a progressive decrease upsection in both the d13C and dl8O values of the planktonic foraminifera. The lower part of the acme interval contains unusual surface-to-bottom water isotope gradients suggesting a stratification of two water masses. Normal gradients in the upper part of the acme interval suggest a well-mixed water body. Between the end of the acme interval and the MP11/MP12 boundary, denoted by the first occurrence (F.O.) of Globorotalia margaritae, a migrational first appearance, there was a catastrophic collapse of the gradient marking an onset of the second post-flood interval. The disintegration of habitable conditions is suggested by a sharp decrease in carbonate content and the disappearance of the benthonic assemblage, which is subsequently replaced predominantly by Uvigerinapygmea, indicative of cold, low-oxygenated bottom waters. The introduction of benthonic species denoting well-oxygenated bottom conditions occurs within the lower MP12 zone. Superimposed on these overall trends are shorter term, warm-cold cycles, which are interpreted as orbitally induced, climatic fluctuations. Correlative studies of the less complete earliest Pliocene sections from ODP Holes 653B and 654A confirm these interpretations. A scenario derived from an integration of all the stratigraphic data indicates that normal paleoceanographic conditions were operating in the Tyrrhenian Sea only approximately 250,000 yr after the cessation of Messinian evaporative conditions at the Miocene/Pliocene boundary. The post-flood interval is marked by an initial period of gradual infilling, the Sphaeroidinellopsis spp. acme interval, followed by a disintegration of oceanographic conditions and a second recovery period. A sudden influx of cold, deep Atlantic waters into the Tyrrhenian Sea, resulting from a major tectonic break in the Gibraltar sill, may have caused this catastrophic reversal in the orderly recovery of normal paleoceanographic conditions in the post-flood period.对大洋钻探计划（Ocean Drilling Program, ODP）652站位最早上新统剖面的高分辨率生物地层与化学地层研究表明，第勒尼安海的洪灾后古海洋环境可划分为两个独立的阶段。第一阶段以球室孔虫属（*Sphaeroidinellopsis* spp.）的繁盛、碳酸盐含量升高，以及浮游有孔虫的δ¹³C与δ¹⁸O值随剖面向上逐渐降低为特征。繁盛阶段的下部出现异常的表层-底层水同位素梯度，指示存在两个水团的分层结构；繁盛阶段上部的正常同位素梯度则指示水体混合均匀。在繁盛阶段结束至MP11/MP12生物地层带边界之间（该边界以迁徙性物种玛格丽特抱球虫（*Globorotalia margaritae*）的首现（F.O.）为标志），同位素梯度发生灾难性崩溃，标志着第二洪灾后阶段的启动。可栖息环境的瓦解可通过碳酸盐含量骤降与底栖生物组合消失得以体现，随后底栖生物组合主要被矮型靴泡虫（*Uvigerina pygmea*）取代，指示此时底层水体寒冷且溶解氧含量较低。指示底层水体溶解氧充足的底栖物种首次出现于MP12带下部。在这些整体趋势之上还叠加有短期的冷暖旋回，这些旋回被认为是轨道驱动的气候波动。对ODP 653B与654A钻孔中保存相对不完整的最早上新统剖面的对比研究，证实了上述解释。 整合所有地层数据得出的演化模式表明，在中新世/上新世边界的墨西拿盐度事件（Messinian evaporative conditions）结束后约25万年，第勒尼安海才恢复正常的古海洋环境。洪灾后阶段以初始的缓慢充填过程（即球室孔虫属繁盛阶段）为标志，随后发生海洋环境瓦解，并进入第二个恢复阶段。直布罗陀海槛（Gibraltar sill）发生大规模构造断裂后，寒冷的大西洋深层水突然涌入第勒尼安海，这一过程可能引发了洪灾后阶段正常古海洋环境有序恢复过程中的灾难性逆转。