Page 6 - i1052-5173-29-3-4
P. 6

A                     Depth CSF (m)
                    0       10      20      30       40      50
                  600 1
                 Magnetic susceptibility (10 -6  SI)  400 1  2  2  3  3  4  4  5  5  6  Figure 2. The tops and bottoms of cores are usually disturbed and

                                                                    there are often coring gaps between cores. To remedy this and cre-
                                                                    ate a complete stratigraphic sequence, a “composite” ideal core is
                                                                    created by splicing together data from different holes to so that
                  200
                                                                    coring gaps in one hole are filled with core intervals from an adja-
                                                                    erate a composite core depth below seafloor (CCSF-A) at least two
                   0    1      2         3       4        5         cent hole, trying not to use the tops and bottoms of cores. To gen-
                                                                    or more holes are drilled at each site and each hole is slightly offset
                                                                    by depth from the other (Fig. S3 [see text footnote 1]). Hole core
                                     Depth CCSF-A (m)               measurements, such as magnetic susceptibility and natural
                B   0       10      20      30       40      50     gamma ray, and/or split core images and lithologic changes from
                                                                    the different holes are aligned using distinguishing features, such
                  600 1                                             as a sharp peak or a color change. (See Figs. S3–S5 for additional
                 Magnetic susceptibility (10 -6  SI)  400 1  2  2  3  3  4  4  5  5  6  measurements from different holes are aligned by depth; Hole
                                                                    examples.) (A) Example from Site U1333, central Pacific, showing
                                                                    construction of a CCSF-A. In this example, magnetic susceptibility
                                                                    U1333A (red), Hole U1333B (blue), Hole U1333C (green). Numbers
                                                                    indicate the order of cores taken in the hole. (B) Depth-shifted
                                                                    cores on composite depth scale (CCSF-A [m]) aligning distinguish-
                  200
                                                                    ing features. (C) The magnetic susceptibility records the different
                                                                    the bottom. Along the top, core breaks (triangles) and hole desig-
                   0    1      2         3       4        5         holes that are part of the splice are shown by the hole color along
                                                                    nations are shown (from Pälike et al., 2010).
                C                    Depth CCSF-A (m)
                    0  B  A  10  B  C  20  B  C  30  B  C  40  B  C  50         Revolution #1: Plate Tectonics
                 Magnetic susceptibility (10 -6  SI)  400                       has come from geophysical studies,
                  600
                                                                                  In the ocean, plate tectonic knowledge
                  200
                                                                                submersible observations, and samples,
                                                                                drill cores, and instrumented boreholes to
                   0
                                                                                monitor in situ processes. As information
                                                                                leading to the wide acceptance of plate
          inaccessible. Without a riser system, with   integrated approach is laid out in the pres-  tectonics accumulated, one of the most
          its casing and the ability to circulate mud   ent science plan: Illuminating Earth’s Past,   convincing data sets came from DSDP
          and prevent blowouts, many thickly sedi-  Present, and Future (IODP, 2011).  Leg 3. “The most interesting finding from
          mented continental margins and subduc-                                the paleontological studies is the correla-
          tion zones were out of reach. Locations at   SOME SOD HIGHLIGHTS      tion of paleontologic ages of sediments
          some high latitudes with ice and in very   SOD has been an engine for understand-  immediately overlying the basalt base-
          shallow water could not be explored. To   ing Earth processes. Tens of thousands of   ment with ages of basement predicted by
          meet these scientific needs, a new era of   papers have been published, some among   the sea-floor spreading hypothesis”
          SOD began in October 2003. The riser-  the most highly cited in Earth science.   (Maxwell et al., 1970, p. 445).
          equipped, Japanese-built Chikyu, capable   Thousands of scientists from around the   Below, briefly summarized, are some
          of drilling deep into heavily sedimented   world, from undergraduates to emeritus,   of the major results learned since Leg 3.
          margins, and the mission-specific drilling   have been involved in the research, form-
          platforms (MSPs) operated though the   ing international collaborations extending   Rifted Margins (Also Called Passive
          European Consortium for Ocean Research   beyond SOD.                  Margins)
          Drilling were added.                 Describing the results in a short paper is   Continental rifting and ocean basin
                                             challenging and necessarily incomplete.   formation are central processes of plate
          International Ocean Discovery Program   Here, three areas where SOD contributed   tectonics and continue to be an important
          (IODP, 2013–2023)                  to major revolutions in our understanding   focus of SOD. This is an iterative process,
            Today, there is a much broader under-  of Earth are described: plate tectonics,   with geophysical surveys identifying
          standing of the interconnections among   paleoceanography, and the deep marine   prime drilling targets and SOD providing
          Earth’s spheres, and new fields of research   biosphere. These topics are intertwined.   the cores to determine the age and compo-
          have developed. Much has been learned   Clearly, plate tectonics impacts ocean and   sition of specific reflectors. Primary influ-
          about how Earth operates. But, the details   climate history, which in turn affects the   ences on rift development are related to
          necessary to reach the next level of under-  deep biosphere; all are connected through   mantle composition, thermal structure, and
          standing require interdisciplinary exper-  carbon and water cycling. Future drilling   tectonic stresses. This results in two end-
          tise, atmospheric scientists, computer   will continue to enhance geoscientists’   member classifications, magma-rich and
          modelers, and biologists. Achieving deeper   understanding of interconnected Earth    magma-poor (non-volcanic) margins.
          knowledge has become more complex and   processes from both a planetary and a   Magma-rich margins were drilled dur-
          requires a new approach. This broadly   human impact perspective.     ing multiple expeditions (Legs 38, 81, 104,

       6  GSA Today  |  March-April 2019
   1   2   3   4   5   6   7   8   9   10   11