Barium intensities and tie points between holes of Leg 208

The Paleocene - Eocene thermal maximum (PETM) is one of the best known examples of a transient climate perturbation, associated with a brief, but intense, interval of global warming and a massive perturbation of the global carbon cycle from injection of isotopically light carbon into the ocean-atmosphere system. One key to quantifying the mass of carbon released, identifying the source(s), and understanding the ultimate fate of this carbon is to develop high-resolution age models. Two independent strategies have been employed, cycle stratigraphy and analysis of extraterrestrial Helium (HeET), both of which were first tested on Ocean Drilling Program (ODP) Site 690. Both methods are in agreement for the onset of the PETM and initial recovery, or the clay layer (“main body”), but seem to differ in the final recovery phase of the event above the clay layer, where the carbonate contents rise and carbon isotope values return toward background values. Here we present a state-of-the-art age model for the PETM derived from a new orbital chronology developed with cycle stratigraphic records from sites drilled during ODP Leg 208 (Walvis Ridge, Southeastern Atlantic) integrated with published records from Site 690 (Weddell Sea, Southern Ocean, ODP Leg 113). During Leg 208, five Paleocene – Eocene (P-E) boundary sections (Sites 1262 to 1267) were recovered in multiple holes over a depth transect of more than 2200 m at the Walvis Ridge yielding the first stratigraphically complete P-E deep-sea sequence with moderate to relatively high sedimentation rates (1 to 3 cm/kyr). A detailed chronology was developed with non-destructive X-ray fluorescence (XRF) core scanning records on the scale of precession cycles, with a total duration of the PETM now estimated to be ~ 170 kyr. The revised cycle stratigraphic record confirms original estimates for the duration of the onset and initial recovery, but suggests a new duration for the final recovery that is intermediate to the previous estimates by cycle stratigraphy and HeET.古新世-始新世极热事件（Paleocene-Eocene thermal maximum, PETM）是最为人熟知的瞬时气候扰动案例之一，其伴随短暂却剧烈的全球变暖区间，以及大量轻同位素碳注入海-气系统引发的全球碳循环剧变。量化碳释放总量、甄别碳源、厘清该碳最终归宿的关键之一，在于构建高分辨率年代模型。目前已采用两种独立研究方法：旋回地层学与地外氦（extraterrestrial Helium, HeET）分析，二者最初均在大洋钻探计划（Ocean Drilling Program, ODP）690站位开展测试验证。两种方法在PETM的起始阶段与初始恢复阶段（即黏土层“主体”）的结果一致，但在黏土层之上的事件最终恢复阶段出现分歧——该阶段碳酸盐含量上升、碳同位素值向背景值回落。本文基于大洋钻探计划208航次（南大西洋沃尔维斯海脊）钻探站位的旋回地层学记录，并整合大洋钻探计划113航次（南大洋威德尔海）690站位的已发表数据，构建了全新的轨道年代学框架，由此得到PETM当前最先进的年代模型。在208航次中，研究人员在沃尔维斯海脊2200余米的深度剖面上，借助多个钻孔采集到5个古新世-始新世（P-E）界线剖面（1262至1267站位），由此获得首个地层学序列完整的古新世-始新世深海沉积序列，其沉积速率处于中等至较高水平（1~3 cm/kyr）。研究人员依托非破坏性X射线荧光（X-ray fluorescence, XRF）岩芯扫描数据，以岁差周期为尺度构建了精细年代框架，如今估算PETM的总持续时长约为17万年。修正后的旋回地层学记录证实了此前对PETM起始与初始恢复阶段时长的估算，但提出最终恢复阶段的新时长介于旋回地层学与地外氦分析得到的先前估算值之间。