Summary of 40Ar/39Ar results from sediment core CRP-2A (Table 1)

40Ar/39Ar analyses of tephra and clasts of volcanic rock provide age constraints for upper parts of the CRP-2A core. Single-crystal laser-fusion analyses of anorthoclase phenocrysts from three tephra-bearing layers yielded the most precise age constraints for CRP-2A. The dated tephra layers are: 1) a 2.7-m-thick interval of pumice and ash layers between 111.5 and 114.2 meters below sea floor (mbsf) (weighted mean age = 21.44 ± 0.05 Ma, +2.2); 2) a concentration of pumice near 193.4 mbsf (23.98 ± 0.13 Ma): and 3) a concentration of pumice near 280 mbsf (24,22 ± 0.03 Ma) (all ages are calibrated relative to Fish Canyon Tuff sanidine at 27.84 Ma). The 111 to 114 mbsf tephra is almost entirely non-reworked, and the 193 mbsf and 280 mbsf tephra concentrations are interpreted as being reworked and redeposited soon after eruption. All three of the tephra ages are therefore considered to be equivalent to depositional ages. The variation in precision of these three age determinations is largely a function of phenocryst size and abundance. The accuracy of these ages is equal to the accuracy of the current calibration of the 40Ar/39Ar methode (about ± 1 %). 40Ar/39Ar results from volcanic clasts provide three additional maximum age constraints for the CRP-2A core. Single-crystal laser-fusion of sanidine phenocrysts from a rhyolitic clast from 294 mbsf yielded a precise maximum depositional age of 24.98 ± 0.08 Ma, and plateau ages of groundmass concentrates from basaltic clasts near 36.02 mbsf and 125.92 mbsf yielded maximum depositional ages of 19.18 ± 0.12 Ma, and 22.56 ± 0.14 Ma, respectively. The 40Ar/39Ar data, in association with biostratigraphic, paleomagnetic, and isotopic age constraints for CRP-2A, confirm interpretation for rapid sedimentation rates in the 36 to 280 mbsf interval, particularly in the 193 to 280 mbsf interval where they support interpretations for sedimentation cycles spanning 100 k.y. intervals. In addition to the 19 to 25 Ma ages measured from thephra layers and clasts, provenance-related ages ranging from 150 to 450 Ma were determined from clasts and individual detrital or xenocrystic crystals from CRP-2A.

针对火山碎屑（tephra）与火山岩岩屑（clasts）开展的⁴⁰Ar/³⁹Ar测年（40Ar/39Ar）分析，为CRP-2A岩心的上部地层提供了年代约束。针对3个含火山碎屑层中的歪长石斑晶（anorthoclase phenocrysts）开展单晶激光熔融分析，为CRP-2A岩心提供了精度最高的年代约束。本次定年的火山碎屑层包括：1）海底以下111.5至114.2米（meters below sea floor，缩写为mbsf）处一套厚度2.7米的浮石与火山灰层序，其加权平均年龄为21.44 ± 0.05 Ma，误差上限为+2.2；2）海底以下193.4 mbsf处的浮石富集层，年龄为23.98 ± 0.13 Ma；3）海底以下280 mbsf处的浮石富集层，年龄为24.22 ± 0.03 Ma（所有年龄均以27.84 Ma的鱼谷凝灰岩透长石（Fish Canyon Tuff sanidine）作为定年标样进行校准）。其中111.5至114.2 mbsf处的火山碎屑层几乎未发生再沉积，而193.4 mbsf与280 mbsf处的浮石富集层被认为是火山喷发后经再搬运、重新沉积的产物。因此，上述3组火山碎屑年龄均被视为等同于其沉积年龄。3组定年结果的精度差异主要取决于斑晶的粒径与丰度。本次测年结果的准确度与当前⁴⁰Ar/³⁹Ar方法的校准精度相当（约±1%）。针对火山岩岩屑的⁴⁰Ar/³⁹Ar分析，为CRP-2A岩心额外提供了3组最大年代约束。对采自海底以下294 mbsf处流纹岩岩屑中的透长石斑晶开展单晶激光熔融分析，得到精度较高的最大沉积年龄为24.98 ± 0.08 Ma；对采自海底以下36.02 mbsf与125.92 mbsf处玄武岩岩屑的基质浓缩物开展坪年龄测试，分别得到最大沉积年龄19.18 ± 0.12 Ma与22.56 ± 0.14 Ma。结合生物地层学、古地磁学与同位素年代约束数据，本次⁴⁰Ar/³⁹Ar测年结果证实了CRP-2A岩心在36至280 mbsf层段存在快速沉积的解释，尤其在193至280 mbsf层段，该结果支持了沉积旋回以10万年（k.y.）为周期的相关解释。除上述19至25 Ma的火山碎屑与岩屑测年结果外，本次研究还从CRP-2A岩心的岩屑与单个碎屑或捕虏晶中获得了150至450 Ma的物源相关年龄。