Paleomagnetic and Rock Magnetic Stratigraphy of the Mid- Cretaceous

Albian Contessa剖面的古地磁研究（翁布里亚， 意大利）定义了几个反向特征区间 由高解阻塞进行的逆磁化（ChRM）- 白垩纪正极性温赤铁矿 超级时代 相反的间隔对应于2个红色区域 （piglitazone hemite）在翁布里亚发现，这可能反映了 沉积期间海底的氧化状态。 反 ChRM可能代表1800万年前获得的再磁化。后 沉积在极性相反的33 R年代（或更晚）。 如果 重新磁化，该过程是非常感兴趣的，因为它可以 产生类似于极性间隔的再磁化图案。 或者，反向ChRM可以记录反向ChRM的间隔。 地磁场极性在强烈海底期间获得 阿尔布纪中期（107-104 Ma）的氧化事件。 如果正确的话， 有几个间隔期的持续时间足够长（10万年）， 在磁性地层学研究中很有用， 白垩纪宁静带的洋壳上 如果是主要的， 间隔也表明地磁模型的修改 反转频率 最近，两个带红色，含赤铁矿沉积物， 也在Albian Breggia部分（瑞士）确定。 的 红色区域可能不仅仅具有区域意义;它们可能 标志着古海洋学条件的快速变化， (but与白垩纪全球缺氧事件相反。 古地磁数据表明， 我们可以从中排除重磁化 循环流体仅影响一部分的情况 测量的部分。 先存矿物的再活化 然而，相位是另一种再磁化机制， 目前正在考虑。 然而，资金的逆转 ChRM位于地层狭窄的间隔中，间隔良好 站点提供了进一步的支持，一个主要的磁化模型。 我们建议将我们的研究扩展到参考部分 在意大利和深海（ODP），旨在表征 通过岩石的中Albian沉积物的古气候特征， 磁性和旋回地层学（层理和地球化学） 测量. 首先，我们希望确定其性质、期限和 氧化区间的范围。 第二，我们希望利用这些 数据作为批判性地检查锁定机制的手段 在Albian（和 其他）远洋沉积物。

Paleomagnetic study of the Albian Contessa section (Umbria, Italy) has defined several intervals of reversed characteristic remanent magnetizations (ChRM) carried by high unblocking- temperature hematite within the Cretaceous Normal Polarity Superchron. The reversed intervals correspond with 2 reddish zones (pigmentary hematite) found throughout Umbria which may reflect the oxidation state of the seafloor during deposition. The reversed ChRM may represent a remagnetization acquired 18 m.y. after deposition in reversed polarity chron 33R (or later). If a remagnetization, the process is of great interest since it can produce remagnetization patterns which resemble polarity intervals. Alternatively, the reversed ChRM may record intervals of reversed geomagnetic field polarity acquired during intense seafloor oxidation episodes during the mid-Albian (107-104 Ma). If correct, several of the intervals are of sufficient duration (100 kyr) to be of use in magnetostratigraphic studies and might provide markers on oceanic crust of the Cretaceous Quiet Zone. If primary, the intervals also suggest a modification of models of geomagnetic reversal frequency. Recently, 2 zones of reddish, hematite-bearing sediments were also identified in the Albian Breggia section (Switzerland). The reddish zones may have more than a regional significance; they may mark rapid changes in paleoceanographic conditions analogous to (but opposite in oxidation) to the Cretaceous global anoxic events. Paleomagnetic data suggest the presence of reversed ChRMs from the Breggia sediments from which we can exclude a remagnetization scenario calling upon circulating fluids affecting only a portion of the measured sections. Reactivation of a preexisting mineral phase, however, is another remagnetization mechanism which is presently being considered. Nevertheless, the funding of reversed ChRMs in a stratigraphically narrow interval at well-separated sites gives further support to a primary magnetization model. We propose an extension of our studies to a reference section in Italy and the deep sea (ODP) aimed at characterizing the paleoclimate signature of the mid-Albian sediments through rock- magnetic and cyclostratigraphic (bedding and geochemical) measurements. First, we hope to determine the nature, duration and extent of the oxidized intervals. Second, we hope to use these data as a means to examine critically the lock-in mechanism of the remanent components of magnetization observed in the Albian (and other) pelagic sediments.