Microfossils detected in a block of ancient dense clay coated with a ferromanganese crust, Clarion-Clipperton Province, East Equatorial Pacific@en

The area in study is characterized by a regional stratigraphic hiatus from Early Miocene to Quaternary. Deposits from Late Eocene to Early Miocene occur on the bottom surface or under a thin sedimentary cover. Ferromanganese nodules, mostly of Oligocene age, formed on surface layers of Tertiary or Quaternary sediments. A detailed micropaleontological study of a block of dense ancient clay coated with a ferromanganese crust was carried out. Composition of found radiolarian and diatomaceous complexes proved that the crust formed in Quaternary on an eroded surface of Late Oligocene clay. In Quaternary Neogene sediments were eroded and washed away by bottom currents. It is likely that the erosion began 0.9-0.7 Ma at the beginning of the \"Glacial Pleistocene\". The erosion could be initiated by loosening and resuspension of surface sediments resulting from seismic activity generated by strong earthquakes in the Central America subduction zone. The same vibration maintained residual nodules at the seafloor surface. Thus, for the area in study a common reason and a common Quaternary interval for formation of the following features is supposed: a regional stratigraphic hiatus, formation of residual nodule fields, and position of ancient nodules on the surface of Quaternary sediments.本研究区域存在早中新世至第四纪的区域性地层间断（stratigraphic hiatus）。始新世晚期至早中新世的沉积物赋存于底界面或薄沉积盖层之下。多数形成于渐新世的铁锰结核（ferromanganese nodules），发育于第三纪或第四纪沉积物的表层。研究人员对一块覆有铁锰结壳的致密古黏土块开展了详细的微古生物学研究。所发现的放射虫（radiolarian）与硅藻组合的组分特征证实，该结壳形成于第四纪的晚渐新世黏土侵蚀面之上。第四纪时期，新近纪沉积物被底流侵蚀并冲刷殆尽。此次侵蚀大概率始于更新世冰期伊始的0.9~0.7 Ma。侵蚀的触发因素可能是中美洲俯冲带（Central America subduction zone）强地震引发的地震活动，导致表层沉积物松动并再悬浮；同一震动过程还使得残留结核得以留存于海底表面。据此，本研究区域可推断存在统一成因与统一第四纪形成时段，用以形成以下三类特征：区域性地层间断、残留结核床的形成，以及古结核赋存于第四纪沉积物表层的现象。