(Table 3) Radiocarbon ages from different Holes of IODP Exp339

Younger Sand layers (YSLs) have been identified in drill cores of a Late Glacial to Early Holocene muddy contourite succession from the Gulf of Cádiz. In this study, we evaluate the grain size characteristics of the YSL, which display bi-gradational grading, with inverse grading (from silt to fine- or medium-grained sand) followed by normal grading (from fine- or medium-grained sand to silt). Radiocarbon dating shows that the YSL formed at three distinct times: 1) the Bølling-Allerød (sites U1387 and U1386); 2) the Younger Dryas (site U1390), and; 3) the beginning of the Boreal (site U1389). Ichnological analyses and radiocarbon dating of cores from drill site U1389C indicate that the YSLs consist of reworked materials deposited at a high sedimentation rate. The results of sedimentological analyses, ichnological treatment, spatial distributions, and radiocarbon dating of the YSLs suggest that the possibility of an origin of the YSLs is tsunami-related but later reworked by bottom current. However, the source areas of the sandy sediments remain unclear, although our results show them to be variable and area dependent. Some sandy deposits are transported by the Mediterranean Outflow Water (MOW) from the proximal sector of the Gulf of Cádiz Contourite Depositional System (CDS), which is close to the Strait of Gibraltar. However, in other cases it is more probable that local gravity flows, which are the result of instability on adjacent margins, provide the sandy material.

年轻砂层（Younger Sand Layers，YSLs）已在加的斯湾晚冰期至早全新世泥质等深岩序列的钻探岩心中被识别出来。本研究对该年轻砂层的粒度特征展开系统评估，其发育双递变层理：先为逆粒序（从粉砂过渡至细砂或中砂），随后转为正粒序（从细砂或中砂过渡至粉砂）。放射性碳定年结果显示，年轻砂层形成于三个不同的时期：1）博林-阿勒罗德暖期（U1387与U1386站位）；2）新仙女木期（U1390站位）；3）北方期初期（U1389站位）。对U1389C钻探站位岩心的遗迹学分析与放射性碳定年结果表明，年轻砂层由高沉积速率下沉积的再改造物质构成。针对年轻砂层的沉积学分析、遗迹学研究、空间分布特征及放射性碳定年结果显示，其成因大概率与海啸相关，但后续被底流改造。尽管研究结果显示砂质沉积物的物源具有多变性且受站位影响，但其具体物源区仍不明确。部分砂质沉积物由地中海流出水（Mediterranean Outflow Water，MOW）从紧邻直布罗陀海峡的加的斯湾等深岩沉积体系（Gulf of Cádiz Contourite Depositional System，CDS）近岸区段搬运而来；而在其他情形下，更有可能是相邻陆缘失稳引发的局部重力流提供了砂质物质。