Testing the limits of high-resolution whole-rock δ13Ccarb stratigraphy

Uncertainty about the effects of "diagenetic noise" on primary δ¹³C_carb signals has been a principal obstacle in interpreting whole-rock δ¹³C_carb stratigraphy. We have evaluated the fidelity of the whole-rock δ¹³C_carb signal through a high-resolution sampling of correlative marine Paleozoic sections in North America and Europe across facies transitions spanning pure limestone to calcareous black shale and sandstone. Sections altered by metosomatic (diagenetic and hydrothermal) processes were specifically targeted for comparison with pristine unaltered sections. Precise stratigraphic correlations were confirmed using bentonite fingerprinting/dating, Sr-isotope stratigraphy, and whole-rock XRF chemistry.

Our results demonstrate that whole-rock δ¹³C_carb is an extraordinarily robust signal of global marine δ¹³C compositions. Correlative sections show strikingly similar δ¹³C_carb values and patterns regardless of location, facies and rock type. Closely spaced successions of pristine limestone show highly reproducible δ¹³C_carb profiles. Remarkably, δ¹³C_carb trends cut across zones of alteration with no offset, and sections completely replaced by diagenetic/hydrothermal dolomite produce the same δ¹³C_carb profiles as their unaltered counterparts.

Our study confirms that whole-rock δ¹³C_carb is an unprecedented chronostratigraphic tool. Our high-resolution approach identified abrupt offsets in δ¹³C_carb profiles that correspond with unconformity horizons (supported by sedimentologic features) that can be correlated throughout different basins around the globe. A systematic covariation between shallowing-deepening trends and δ¹³C_carb demonstrates its primary origin. The fidelity of the high-resolution record provides previously unattainable fine-scale temporal correlation - a resolution that, ultimately, will be required to fully understand the processes that fractionate the global carbon reservoir and have led to its overarching control on Earths evolution.