Magnetostratigraphic, biostratigraphic, and stable isotope stratigraphy of an Upper Miocene drill core from the Salé Briqueterie (northwestern Morocco): A high‐resolution chronology for the Messinian stage
Magnetostratigraphic, biostratigraphic, and stable isotope stratigraphy of an Upper Miocene drill core from the Salé Briqueterie (northwestern Morocco): A high‐resolution chronology for the Messinian stage
复制标题
Salé Briqueterie（摩洛哥西北部）上中新统钻芯的磁性地层学、生物地层学和稳定同位素地层学：麦西尼亚阶段的高分辨率年代学
DOI：
10.1029/94pa01838
复制
发表时间：
1994
期刊：
影响因子：
--
通讯作者：
K. R. Bied
中科院分区：
文献类型：
--
作者：
D. Hodell;R. H. Benson;D. Kent;A. Boersma;K. R. Bied
我们报告了来自摩洛哥西北部Bou regg剖面的Sale Briqueterie 175米岩心的高分辨率稳定同位素、碳酸盐、磁地层和生物地层记录。Sale岩心跨越了古地磁期C4n ~ C3r（最早的吉尔伯特期），代表了地中海的隔离和干燥（即墨西尼亚盐危机）之前和包括这段时间。在C3An和C3Ar （6.935 ~ 5.894 Ma）时期，同位素和碳酸盐信号呈现准周期变化，估计周期分别为40和100 kyr。我们将40 kyr的δ18O变化解释为反映了由倾角引起的极地太阳日照变化（41 kyr）引起的全球冰量变化。100 kyr的碳酸盐变化可能代表岁差周期振幅的长期调制（~ 21 kyr），这不是我们的采样频率所能解决的。氧同位素信号的循环性质允许我们将Shackleton et al. （1994a）的同位素命名法从C3r期TG24期（最早的Gilbert期）扩展到C3Ar.δ18O期。18在Chron C3Ar （6.935 Ma）的底部。在托尔顿-墨西尼亚边界上记录了一个主要的古海洋条件变化，我们将其与c30亿年的7.04 Ma联系起来。底栖有孔虫δ18O值在7.17 Ma和6.8 Ma两个阶段平均上升0.4‰，δ13C值在7.1 ~ 6.8 Ma期间平均下降0.7 ~ 0.8‰，反映了晚中新世的碳转移。δ18O值的第一步与推断出的通过里夫走廊的深水环流反转相吻合，第二步与的黎波里组的底部和地中海“危机条件”的开始相关。我们认为，δ18O值的增加至少在一定程度上代表了全球冰量的增加，这降低了海平面，并促成了地中海负水收支的建立。平均δ18O值在C3Ar和C3An的大部分时间保持较高，在C3r（最早的Gilbert）的TG20和22同位素阶段达到最大值。与这些事件相关的冰川-涨落可能导致地中海与世界海洋完全隔绝（Shackleton等人，1994年a）。在Sale记录的TG12阶段之后，δ18O值有逐渐降低的趋势，这可能代表了一系列海侵最终重新淹没地中海，结束了盐度危机。
We report a high-resolution stable isotope, carbonate, magnetostratigraphic, and biostratigraphic record from a 175-m drill core from the Sale Briqueterie, which is part of the Bou Regreg section in northwestern Morocco. The Sale drill core spans the interval from paleomagnetic Chron C4n partim to C3r (earliest Gilbert), which represents the time leading up to and including the isolation and desiccation of the Mediterranean (i.e., the Messinian salinity crisis). During Chrons C3An and C3Ar (6.935 to 5.894 Ma) the isotope and carbonate signals display quasi-periodic variations with estimated periods of 40 and 100 kyr, respectively. We interpret the 40-kyr δ18O variations as reflecting changes in global ice volume caused by obliquity-induced changes (41 kyr) in solar insolation in polar regions. The 100-kyr carbonate variations probably represent long-term modulation of the amplitude of the precessional cycle (∼21 kyr), which is not resolved by our sampling frequency. The cyclic nature of the oxygen isotope signal permits us to extend the isotope nomenclature of Shackleton et al. (1994a) from stage TG24 in Chron C3r (earliest Gilbert) to stage C3Ar.δ18O.18 at the base of Chron C3Ar (6.935 Ma). A major change in paleoceanographic conditions is recorded across the Tortonian/Messinian boundary, which we correlate to Chron C3Bn at 7.04 Ma. Benthic foraminiferal δ18O values increased by an average of 0.4‰ in two steps at 7.17 Ma and 6.8 Ma and δ13C values decreased by 0.7–0.8‰ between 7.1 and 6.8 Ma, representing the late Miocene carbon shift. The first step in δ18O values coincides with an inferred reversal in deep water circulation through the Rifian Corridor, and the second correlates with the base of the Tripoli Formation and onset of “crisis conditions” in the Mediterranean. We suggest that the increase in δ18O values represents, at least in part, an increase in global ice volume that lowered sea level and contributed to the establishment of a negative water budget in the Mediterranean. Average δ18O values remained high throughout most of Chrons C3Ar and C3An, reaching maximum δ18O values during isotope stages TG20 and 22 in Chron C3r (earliest Gilbert). The glacio-eustatic falls associated with these events may have resulted in the complete isolation of the Mediterranean from the world ocean (Shackleton et al., 1994a). Following stage TG12 in the Sale record, there exists a trend toward progressively lower δ18O values that may represent a series of marine transgressions that eventually reflooded the Mediterranean and ended the Salinity Crisis.