Magnetostratigraphy of ODP sites 114-701 and 114-702@en

During Leg 114 of the Ocean Drilling Program 12 holes were drilled at seven sites in the subantarctic South Atlantic Ocean. A major objective of this cruise was to document the development of the deep-water passageway that formed as the Meteor and Islas Orcadas rises rifted and spread apart. We report here the results of a magnetostratigraphic study of the sediments recovered at Site 701, a deep-water site located within the gateway, and Site 702, a shallow-water site located near the crest of the Islas Orcadas Rise. The sequence of Pliocene-Pleistocene reversals observed at Site 701 is readily correlated with the Brunhes Chron through Chron C3A. Although correlation is more difficult in the older sections at Site 701 because of coring gaps and the lack of tight biostratigraphic control, it is possible to correlate the late Miocene sequence of reversals with Chrons C4A and C5. The polarity sequence observed in the very weakly magnetized middle to upper Eocene nannofossil chalks recovered from Hole 702B is correlated with Chrons C18 through C21. The correlation of the polarity sequences at these two sites provides a temporal framework for these sediments and makes it possible to calibrate southern high-latitude biostratigraphic datums to the geomagnetic polarity time scale.在大洋钻探计划（Ocean Drilling Program）第114航次中，科研团队于南大西洋亚南极海域的7个站位共布设了12个钻孔。本次航次的核心目标之一是阐明梅特罗海岭（Meteor Rise）与伊斯拉斯·奥达斯海岭（Islas Orcadas Rise）张裂扩张所形成的深水通道的演化过程。本研究报道了对站位701（位于该深水通道内部的深水站位）与站位702（位于伊斯拉斯·奥达斯海岭峰顶附近的浅水站位）所获取沉积物的磁性地层学研究结果。在站位701观测到的上新世-更新世极性反转序列，可直接与布容正向极性时（Brunhes Chron）至C3A极性亚时（Chron C3A）的地层序列进行对比。尽管由于取芯缺失以及缺乏精确的生物地层约束，站位701的较老地层段的对比难度更高，但仍可将晚中新世的极性反转序列与C4A、C5极性亚时进行对应。从702B钻孔获取的弱磁化始新世中-上部颗石藻灰岩中观测到的极性序列，可与C18至C21极性亚时进行对比。对这两个站位的极性序列进行对比，可为上述沉积物提供可靠的年代框架，并可将南极高纬度地区的生物地层基准面校准至地磁极性年表中。