ASKING OLD ROCKS NEW QUESTIONS: CHRONOSTRATIGRAPHIC SIGNIFICANCE OF CARBON ISOTOPES TO PALEOZOIC STRATIGRAPHY

The growth of high-resolution (<1 million years) δ¹³C_carb stratigraphy over the past decade has begun to shed new light on some of the long-stranding problems of Paleozoic stratigraphy. Detailed carbon isotope stratigraphy has proven particularly useful when correlating biostratigraphic zones not typically found in the same strata (e.g. conodonts and graptolites). Furthermore, the necessity of a biostratigraphic zonation matching the resolution of the δ¹³C_carb stratigraphy has promoted new biostratigraphic research greatly increasing the resolution of biostratigraphic zones. The Wenlock (Silurian) is the best example of this, where a decade ago, the most commonly used global conodont zonation contained four zones. Today, the global standard conodont zonation for the Wenlock contains over twenty zones, each precisely correlated with δ¹³C_carb stratigraphy.

Carbon isotope stratigraphy can also be used as a paleoclimate/paleoceanographic proxy for global climate change during the Paleozoic. The climatic questions being asked by this research often require a resolution of data better than the 1-2 million year average for typical Paleozoic biostratigraphic zones. The integration of high-resolution δ¹³C_carb stratigraphy and high-resolution biostratigraphy during the past few years has vastly increased our ability to correlate geographically disparate sections providing insight into some of the long-standing problems of Paleozoic stratigraphy, such as the placement of the Ordovician-Silurian boundary in the Midcontinent of North America and the precise correlation of the golden spike for the Llandovery-Wenlock boundary at Leasows, UK.

The need to redefine the age and correlation of chronostratigraphic boundary strata containing the record of global climate change has meant that some of the previous environmental interpretations of these intervals need to be re-examined. Without the ability to precisely correlate sections globally, the interpretation of the Paleozoic record of global climate change remains speculative. To this end, carbon isotope δ¹³C_carb stratigraphy has helped demonstrate the need for renewed basic stratigraphic research.