【作者】 张静；

【导师】 万晓樵；

【作者基本信息】 中国地质大学（北京） ， 古生物学与地层学， 2007， 硕士

【摘要】 富钴结壳由于其巨大的潜在经济价值及广阔的综合利用前景，加上其商业开采时间可能早于多金属结核，而成为新一轮“蓝色圈地”的重点。本次工作对采自西北太平洋麦哲伦海山区的富钴结壳MHD56和M17D-1A进行研究，两块结壳都具有典型的三层构造。对MHD56结壳采取了钙质超微化石地层学研究，发现了大量化石，共鉴别出20属41种，划分出了古新世至更新世的6个化石组合带，由下至上为：Neocrepidolithus fossus-Discoaster megastypus；Zygodiscus sigmoides—Cyclicargolithus luminis；Reticulofenestra umbilica—Cyclicargolithus marismontium；Discoaster calculosus—Helicosphaera ampliaperta；Sphenolithus moriformis—S．neoabies；Sphenolithus neoabies—Umbellosphaera tenuis组合带。化石组合面貌显示，该结壳从下至上包括从古新世至晚上更新世的沉积序列。按目前所推测的年代方案，该结壳最底层的年龄为古近纪古新世(56.3～59.8Ma)，其项部为新近纪更新世(0.5Ma)以来的沉积。在Ⅰ层和Ⅱ层之间存在一个大的沉积间断，在Ⅱ层内包含一个小的沉积间断。深海沉积间断可能是由于强烈的底层水侵蚀作用或溶蚀作用造成的，也可能是由海洋表层生产力的迅速下降引起的无沉积作用导致的，但因局部环境的差异仍会出现生长间断的拉长和缩短。MHD56最底层结壳的生长速率变化于0.8～3.7mm／Ma；中层结壳的生长速率变化于0.8～3.7mm／Ma。而M17D-1A中钙质超微化石含量甚微，化石保存不好，因此采用了Co成分法进行定年。M17D-1A结壳的下、中及上分层结壳的生长年代分别于古近纪晚渐新世(24～30Ma)、晚渐新世(24Ma)至新近纪上新世(1.4Ma)及近代的第四纪期间生长(＜1.4Ma)；下层生长速率变化于0.8～3.7mm／Ma；中层结壳的生长速率变化于2.5～5.2mm／Ma。两块结壳的生长速率均落在目前公认的结壳生长速率(1～10mm／Ma)范围内。两块富钴结壳的初始生长时间与太平洋变冷、碳酸盐溶解速率增加、底层流活动增强，火山活动频繁发生的古海洋学事件发生的时间是十分吻合的，说明结壳的开始生长与古海洋环境和地质事件密切相关。渐新世／中新世(O／M)期间古气候的“骤变”及发生的磷酸盐化作用是导致西太平洋三层构造结壳中，下、中层发生构造和色泽变化的主要原因。更多还原

【Abstract】 With the potential economic value, comprehensive utilization of Co-rich crusts and earlier exploitation than mentallic nodules, Cobalt-rich crusts become the most important as the "Blue land circling". This work has studied two Co-rich crusts of MHD56 and M17D-1A from Northwest Pacific. For the study on crust MHD56, a large number of calcareous nannofossils have been found and biostratigraphy has been set up. In this work, 41 species of 20 genera have been identified and illustrated. Six calcareous nannofossil zones have been divided, as Neocrepidolithus fossus—Discoaster megastypus; Zygodiscus sigmoides — Cyclicargolithus luminis; Reticulofenestra umbilica — Cyclicargolithus marismontium; Discoaster calculosus — Helicosphaera ampliaperta; Sphenolithus moriformis—S. neoabies; Sphenolithus neoabies—Umbellosphaera tenuis assemblages. The ages of fossil assemblages indicate that the Co-rich crust accumulation is from Paleocene to Pleistocene. The MHD56 crust shows 3 structural layers: compact upper layer, porous middle layer and compact lower layer. Studies show that the age of porous middle layer was formed from late Miocene to late Pliocene (0.5～11.9Ma)and the lower layer was formed from late Paleocene to late Oligocene (56.3～23.2Ma). Furthermore, a sedimentation hiatus has been observed, which was caused by intensive bottom water’s corrosion or none deposition which genegated by superficial ocean productive power rapidly falling down. The bottom growing rate of the crust MHD56 was 0.8～3.7mm/Ma, and the middle layer 0.8～3.7mm/Ma. Since few fossils have been found from the crust M17D-1A, the Co-method dating has been used. The crust M17D-1A was also divided into 3 layers: the bottom layer of late Oligocene (24～30Ma), with growing rate of 0.8— 3.7mm/Ma; the middle layer of late Oligocene (24Ma) to Pliocene (1.4Ma), at 2.5～ 5.2mm/Ma rate; and the upper layer of Quaternary (<1.4Ma). Both crusts are of growingrates at 1 ～ 10mm/Ma that is the normal rate in general. The inceptive growing time was accordant with the time of the palaeoceanography events such as Pacific cooling, speeding up of the carbonate solution, strengthening of bottom current and frequent volcano eruptions which inicates a response of the initial growth of Co-rich crust to the paleoceanic and geologic events. The rapid environmental change around the O/M boundary is probably the major cause of the changes of structure, color, luster, and elemental composition between the middle and lower layers. The boundary between the middle and lower layers is of important indication on growing time.更多还原