Sea-level change influences carbon isotopic trends in both modern and ancient carbonate depositional environments. Generally, this relationship is manifested as a positive carbon isotopic excursion where the rising limb of the excursion is associated with transgression. These excursions exist because sea level can influence 1) local/regional/global carbon cycling, 2) basin restriction and meteoric influence, and 3) carbonate sedimentation. The first two processes are influenced, in part, by the large carbon reservoir represented by the terrestrial biosphere. Our goal is to explore the relationship between carbon isotopes and sea level prior to the evolution of vascular plants at a time when the terrestrial carbon reservoir was far smaller.

This study focuses on the Upper Ordovician Union Furnace section in Pennsylvania, where a previously documented ~1‰ increase in δ¹³C values in the upper Sandbian (458.4–453.0 Ma; referred to as the “baseline shift”) has been interpreted to reflect a perturbation to the global carbon cycle due to the proliferation of non-vascular plants. By focusing on the interval deposited before the “baseline shift”, we were able to examine the relationship between sea level, carbon isotopes, and some of the earliest terrestrial ecosystems. We present a high-resolution δ¹³C record directly tied to the sedimentological and sequence stratigraphic framework. By sampling genetically related packages of rock we were able to document a relationship between carbon isotopes and sea level at the sequence and parasequence level. Our results show that carbon isotopic values decreased during transgressions and increased during regressions. This seemingly inverse relationship between δ¹³C values and sea level is interpreted to reflect increased terrestrial fluxes during regression in a world devoid of vascular plants. Our results suggest that the early colonization of land by non-vascular plants impacted regional carbon cycling in the Appalachian Basin and eventually the global carbon cycle in the Late Ordovician.

海平面变化会影响现代和古代碳酸盐沉积环境中的碳同位素趋势。通常，这种关系表现为正碳同位素偏移，其中偏移的上升肢与越境有关。存在这些偏移是因为海平面会影响1）局部/区域/全球碳循环，2）流域限制和大气影响以及3）碳酸盐沉积。前两个过程部分受到以陆地生物圈为代表的大型碳库的影响。我们的目标是在陆地碳储层远小于碳储集层的时候探索维管植物进化之前碳同位素与海平面之间的关系。

本研究着重于在宾夕法尼亚州，其中以前记录〜1‰增加δ上奥陶统联盟炉部¹³ C值在上Sandbian（458.4-453.0马;被称为“基线偏移”）已被解释为反映由于非维管植物的繁殖，对全球碳循环的扰动。通过关注“基线偏移”之前沉积的时间间隔，我们能够检查海平面，碳同位素和一些最早的陆地生态系统之间的关系。我们提出了一个高分辨率δ ¹³C记录直接与沉积学和层序地层学框架联系在一起。通过对与遗传相关的岩石包进行采样，我们能够记录碳同位素与海平面在层序和副层序层之间的关系。我们的结果表明，碳同位素值在海侵过程中减少，而在回归过程中增加。δ之间的这种看似反比关系¹³ C值和海平面被解释为反映在维管植物的世界没有回归期间增加地面通量。我们的结果表明，非维管植物在土地上的早期定殖影响了阿巴拉契亚盆地的区域碳循环，并最终影响了奥陶纪晚期的全球碳循环。