A Deep-Tow Magnetometer, SEABEAM, and Airgun Study of the Pacific Jurassic Quiet Zone

在过去三十年的地球科学研究中，冻结在洋壳中的磁性反转模式的“磁带录音机”模拟一直是重大发现之一。尽管海洋磁性线条已被发现追溯到M38，但太平洋中没有一条比M25更早的地磁线条被确凿地证明是场反转的结果。评估这些最古老的异常的部分困难是因为它们具有典型的低幅度和明显的短周期。约翰逊和他的同事们提议建造一台磁力计，将其拖到海底附近，比起传统的船载或机载仪器，该设备更接近线条的来源，因此将探测到特别细微的特征。在为期22天的调查中，约翰逊和他的同事们还将分别使用地震反射剖面和SEABEAM条带地图收集洋壳和海底的地形测量数据。将在西太平洋的三个地区进行调查，从以前的研究中得知M25之后的磁性线条。这些新数据将使建模研究能够比较三个研究领域的细节。如果在波长和幅度上发现相似之处，它们将有力地支持这样的解释，即它们是磁场逆转的真实记录。如果未来的大洋钻探恢复，并确定这些岩层上的沉积物的年代，那么海洋磁性逆转的时间尺度可能会延长到侏罗纪的数百万年。

The "tape recorder" analogy of magnetic reversal patterns frozen into oceanic crust has been one of the major discoveries in the last three decades of earth science research. Though marine magnetic lineations have been identified back to M38, none in the Pacific that are older than M25 have yet been proven conclusively to result from field reversals. Part of the difficulty in evaluating these oldest anomalies results from their characteristically low amplitudes and apparently short periods. Johnson and his colleagues propose to construct a magnetometer that will be towed near the seafloor, and being closer to the source of the lineations than conventional shipboard or airborne instruments, this device will detect especially subtle features. During 22 days of surveying, Johnson and his colleagues will also gather topographic measurements of the oceanic crust and the seafloor with seismic reflection profiles and SEABEAM swath maps, respectively. Three regions will be surveyed in the western Pacific where post-M25 magnetic lineations are known from previous studies. These new data will allow modelling studies to compare details among the three study areas. If similarities in wavelength and amplitude are found, they will strongly support the interpretation that they are true records of magnetic field reversals. If future ocean drilling recovers and dates the sediments resting on these lineations, the marine magnetic reversal time scale could be extended several millions of years further back into the Jurassic.