Sedimentation and sediment redistribution on the Cocos Ridge from two seismic acquisition cruises,NEMO-3 and MV1014

We use digital seismic reflection profiles within a 1° * 1° survey area on the Cocos Ridge (COCOS6N) to study the extent and timing of sedimentation and sediment redistribution on the Cocos Ridge. The survey was performed to understand how sediment focusing might affect paleoceanographic flux measurements in a region known for significant downslope transport. COCOS6N contains ODP Site 1241 to ground truth the seismic stratigraphy, and there is a seamount ridge along the base of the ridge that forms a basin (North Flank Basin) to trap sediments transported downslope. Using the Site 1241 seismic stratigraphy and densities extrapolated from wireline logging, we document mass accumulation rates (MARs) since 11.2 Ma. The average sediment thickness at COCOS6N is 196 m, ranging from outcropping basalt at the ridge crest to ~ 400 m at North Flank Basin depocenters. Despite significant sediment transport, the average sedimentation over the entire area is well correlated to sediment fluxes at Site 1241. A low mass accumulation rate (MAR) interval is associated with the 'Miocene carbonate crash' interval even though COCOS6N was at the equator at that time and relatively shallow. Highest MAR occurs within the late Miocene-early Pliocene biogenic bloom interval. Lowest average MAR is in the Pleistocene, as plate tectonic motions caused COCOS6N to leave the equatorial productivity zone. The Pliocene and Pleistocene also exhibit higher loss of sediment from the ridge crest and transport to North Flank Basin. Higher tidal energy on the ridge caused by tectonic movement toward the margin increased sediment focusing in the younger section.

本研究利用科科斯海岭（Cocos Ridge）1°×1°调查区域（COCOS6N）内的数字地震反射剖面（digital seismic reflection profiles），探究科科斯海岭上的沉积作用与沉积物再分布的范围及时间尺度。此项调查旨在明确沉积物聚焦作用会如何影响这一以下坡搬运作用显著为特征的区域内的古海洋通量测量结果。COCOS6N区域包含大洋钻探计划（Ocean Drilling Program, ODP）1241站位，用于实地验证地震地层学特征；同时海岭基底处发育有海山脊，其围限形成了用于捕获下坡搬运沉积物的北翼盆地（North Flank Basin）。
借助1241站位的地震地层学数据以及由电缆测井外推得到的沉积物密度，本研究重建了11.2 Ma以来的沉积物堆积速率（mass accumulation rates, MARs）。COCOS6N区域的平均沉积物厚度为196 m，取值范围从海岭脊顶的出露玄武岩延伸至北翼盆地沉积中心处的约400 m。
尽管存在显著的沉积物搬运作用，但整个区域的平均沉积作用与1241站位的沉积物通量具有良好的相关性。尽管当时COCOS6N位于赤道且水体相对较浅，其低堆积速率区间仍与“中新世碳酸盐崩溃”事件区间相吻合。
最高的堆积速率出现于晚中新世-早上新世的生物勃发期。更新世的平均堆积速率最低，这是由于板块构造运动使得COCOS6N脱离了赤道生产力带。
上新世和更新世期间，海岭脊顶的沉积物流失并被搬运至北翼盆地的现象也更为显著。由于向大陆边缘运动的构造活动引发了海岭上更强的潮汐能，较年轻地层中的沉积物聚焦作用也随之增强。