Time Scale Controversy: accurate orbital calibration of the late Miocene

该项目的目的是研究岩石时钟在放射性同位素和天文测年技术之间同步的潜在内在问题。我们假设中新世晚期地中海剖面（Sorbas, Faneromeni， Messadit等）的灰层调整位于C3An磁时纪。2 n, C3。用于同步的Ar和c3b)有2-3个岁差周期（40-60 kyr）的误差。为了验证这个假设，我们正在开发一个非常精确的，天文校准的中新世晚期磁极年表C3An。1n （6ma）至C4n。1n (7.5 Ma)（含C3An）2 n, C3。Ar和c30)，使用地中海以外的三个ODP/IODP站点（926,U1337, U1338）。在项目的第一阶段，对U1337站点获得的新磁地层数据进行了初步解释，确定了14个地磁反转，其中8个反转位置的定位具有很高的置信度。其余6个逆转头寸（包括Chron c30亿）仍需进一步分析。到目前为止，稳定同位素地层学分析的样品中含有足够的底栖有孔虫，可以产生适合天文校正的同位素记录。该扩展方案的主要目标是精确定位6个关键反转的位置，扩展U1337站点的高分辨率底栖生物稳定同位素记录，并填补ODP站点982和1264同位素记录的空白。所有记录将被整合，生成5.2-8.2 Ma之间的高分辨率、天文校正的底栖稳定氧同位素叠加，为晚托尔顿期和迈西尼亚期提供全球地层参考剖面。基于设想的底栖生物稳定氧和碳同位素记录的高分辨率古海洋学重建将使解决突出的晚中新世古气候问题成为可能。在新数据的基础上进行古海洋重建时，还需要对底栖生物同位素信号如何受到次生成岩蚀变的影响以及分析和自然样本变异进行研究。

The objective of the project is to investigate potential intrinsic problems with the rock clock synchronization between radio-isotopic and astronomic dating techniques. We hypothesize that the tuning of ash layers in the late Miocene Mediterranean sections (Sorbas, Faneromeni, Messadit, etc.; located in magnetochrons C3An.2n, C3.Ar and C3Bn) used for the synchronization is incorrect by 2-3 precession cycles (40-60 kyr). To test this hypothesis, we are developing a very accurate, astronomically calibrated late Miocene time scale for magnetic polarity Chrons C3An.1n (6 Ma) to C4n.1n (7.5 Ma) (including C3An.2n, C3.Ar and C3Bn) using three ODP/IODP sites outside the Mediterranean (926, U1337, U1338). During the first phase of the project, preliminary interpretation of new magnetostratigraphic data acquired at Site U1337 allowed identification of fourteen geomagnetic reversals, of which eight reversal positions have been located with very high confidence. The remaining six reversal positions, including Chron C3Bn, still need further analyses. The samples for the stable isotope stratigraphy analyzed so far contain sufficient benthic foraminifera to generate an isotopic record suitable for astronomical tuning. The main goal of this extension proposal is to exactly pinpoint the position of six key reversals and extend the high-resolution benthic stable isotope record at Site U1337, and fill gaps located in isotope records from ODP Sites 982 and 1264. All records will be integrated to generate a high-resolution, astronomically tuned benthic stable oxygen isotope stack between 5.2-8.2 Ma to provide a global stratigraphic reference section for the late Tortonian and Messinian. High-resolution paleoceanographical reconstructions based on the envisaged benthic stable oxygen and carbon isotope records will allow resolving of outstanding late Miocene paleoclimate questions. The paleoceanographic reconstructions based on our new data need to be accompanied by investigations evaluating how the primary benthic isotope signal is affected by secondary diagenetic alterations, and analytical and natural sample variability.