Astronomical and tectonic influences on climate and deposition revealed through radioisotopic geochronology and Bayesian age-depth modeling of the early Eocene Green River Formation, Wyoming, USA
Astronomical and tectonic influences on climate and deposition revealed through radioisotopic geochronology and Bayesian age-depth modeling of the early Eocene Green River Formation, Wyoming, USA
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DOI：
10.1130/b36584.1
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发表时间：
2023-03-16
影响因子：
4.9
通讯作者：
Jicha, Brian R.
中科院分区：
文献类型：
--
作者：
Bruck, Benjamin T.;Singer, Brad S.;Jicha, Brian R.
美国怀俄明州绿色河组威尔金斯峰段（WPM）由湖相和冲积相交替地层组成，保存了始新世早期气候最佳时期的陆地气候记录。利用7个凝灰岩的40 Ar/39 Ar透长石和206 Pb/238 U同位素年龄数据，采用贝叶斯方法建立了3个测点的年龄-深度模型。新的模型提供了两到十倍的时间分辨率相比，以前的放射性同位素年龄模型，确认偏心尺度起搏的WPM相，并允许他们直接比较天文解决方案。从CA开始。51 Ma，六个连续冲积标志层顶的全盆地洪水面的中位年龄与天文解中的短偏心率最大值相吻合。这些偏心率最大值已与超高温事件记录在海洋地层在始新世早期。早于ca的WPM地层。51 Ma的沉积速率与偏心距解没有明显的相关性，但比偏心距解的累积速率快31%~ 35%，说明天文强迫对沉积的影响受到盆地构造的调制。需要额外的高精度放射性同位素年龄来减少贝叶斯模型的不确定性，但这种方法显示了对冲积标志层和理论偏心率解之间的相位关系进行明确评估的希望。
The Wilkins Peak Member (WPM) of the Green River Formation in Wyoming, USA, comprises alternating lacustrine and alluvial strata that preserve a record of terrestrial climate during the early Eocene climatic op-timum. We use a Bayesian framework to de-velop age-depth models for three sites, based on new 40Ar/39Ar sanidine and 206Pb/238U zir-con ages from seven tuffs. The new models provide two-to ten-fold increases in tempo-ral resolution compared to previous radio-isotopic age models, confirming eccentricity-scale pacing of WPM facies, and permitting their direct comparison to astronomical solutions. Starting at ca. 51 Ma, the median ages for basin-wide flooding surfaces atop six successive alluvial marker beds coincide with short eccentricity maxima in the astronomi -cal solutions. These eccentricity maxima have been associated with hyperthermal events recorded in marine strata during the early Eocene. WPM strata older than ca. 51 Ma do not exhibit a clear relationship to the eccen-tricity solutions, but accumulated 31%-35% more rapidly, suggesting that the influence of astronomical forcing on sedimentation was modulated by basin tectonics. Additional high-precision radioisotopic ages are needed to reduce the uncertainty of the Bayesian model, but this approach shows promise for unambiguous evaluation of the phase rela-tionship between alluvial marker beds and theoretical eccentricity solutions.