Evidence of early bottom water current flow after the Messinian Salinity Crisis in the Gulf of Cadiz
Evidence of early bottom water current flow after the Messinian Salinity Crisis in the Gulf of Cadiz
复制标题
加的斯湾墨西拿盐度危机后早期底层水流的证据
DOI：
10.1016/j.margeo.2016.04.005
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发表时间：
2016
期刊：
影响因子：
2.9
通讯作者：
García-Gallardo, Á.
中科院分区：
文献类型：
--
作者：
van der Schee, Marlies;Sierro, F.J.;Jiménez-Espejo, F.J.;Hernández-Molina, F.J.;Flecker, R.;Flores, J.A.;Acton, G.;Gutjahr, M.;Grunert, P.;García-Gallardo, Á.
综合大洋钻探计划(IODP)考察了加的斯湾的多个地点，以研究地中海外流水(MOW)造成的等高线沉积。其中一口井U1387C的取心深度为海底以下865.85米(MBsf)，目的是恢复最新的中新世至上新世的过渡，以便在梅西尼亚盐度危机结束后立即评估世界最新钻探的历史。为了理解这段历史，需要一个准确的演替年龄模型，但构建起来很有挑战性，因为中新世-上新世的界线没有明显的大西洋生物地层事件，而且在恢复的地层记录中存在取心间隙。通过组合各种年代地层数据集来构建符合当前可用的年龄指标的年龄模型，克服了这些限制，并表明U1387C孔的取心确实恢复了中新世-上新世边界，约为826 Mbsf。这一边界与沉积环境的明显突变有关。在最近的梅西期，沉积了表现出进动引起的气候变化的半远洋沉积物。这些都是由上新世沉积以更高的沉积速率沉积的，XRF岩芯扫描的Zr/Al比比下伏沉积物高得多，变化也更大，这表明存在风选、颗粒分选和粒度增大的证据，我们解释这与MoW流量增加有关。上新世沉积旋回性在海底δ~(18)O记录和Zr/Al数据中都清晰可见，可能也是先期控制的。在上新世第三次沉积旋回之上，发现了两个玄武质复式砂层。在这些结果的基础上，我们得出结论，与地中海-大西洋弱交换有关的沉积实际上是在中新世-上新世界线或之后不久在加迪兹湾开始的。
Integrated Ocean Drilling Program (IODP) Expedition 339 cored multiple sites in the Gulf of Cadiz in order to study contourite deposition resulting from Mediterranean Outflow water (MOW). One Hole, U1387C, was cored to a depth of 865.85 m below seafloor (mbsf) with the goal of recovering the latest Miocene to Pliocene transition in order to evaluate the history of MOW immediately after the end of the Messinian Salinity Crisis. To understand this history, an accurate age model for the succession is needed, but is challenging to construct, because the Miocene–Pliocene boundary is not marked by a clear biostratigraphic event in the Atlantic and coring gaps occur within the recovered stratigraphic record. These limitations are overcome by combining a variety of chronostratigraphic datasets to construct an age-model that fits the currently available age indicators and demonstrates that coring in Hole U1387C did indeed recover the Miocene–Pliocene boundary at about 826 mbsf. This boundary is associated with a distinct and abrupt change in depositional environment. During the latest Messinian, hemipelagic sediments exhibiting precession-induced climate variability were deposited. These are overlain by Pliocene sediments deposited at a much higher sedimentation rate, with much higher and more variable XRF core scanning Zr/Al ratios than the underlying sediment, and that show evidence of winnowing, particle sorting and increasing grain size, which we interpret to be related to the increasing flow of MOW. Pliocene sedimentary cyclicity is clearly visible in both the benthic δ18O record and the Zr/Al data and is probably also precessionally controlled. Two contouritic bigradational sandy-beds are revealed above the third sedimentary cycle of the Pliocene. On the basis of these results, we conclude that sedimentation associated with weak Mediterranean–Atlantic exchange, began in the Gulf of Cadiz virtually at or shortly after the Miocene–Pliocene boundary.
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