Sequence stratigraphic framework
This protocol is extracted from research article:
Strong local, not global, controls on marine pyrite sulfur isotopes
Sci Adv, Feb 26, 2021; DOI: 10.1126/sciadv.abb7403

We use the stratigraphic concepts and terms in which a seismic depositional sequence is defined by related sediment packages bounded above and below by unconformities or sequences boundaries, presumably related to variations in sea level (74). These genetically related packages are further classified by the relative sea level during their deposition into lowstand, transgressive, and highstand systems tracts (fig. S9).

Following the work of (37), stratigraphic trends in δ18Oflem, Ca/Sr, and Ca/Ti elemental ratios permit correlation of the lithofacies succession to global sea-level variability. Briefly, δ18Oflem was used to estimate past variation in sea level. We used the Ca/Ti ratio to estimate down-core variation in the CaCO3 content. Carbonate-poor intervals are commonly related to low Ca/Ti ratio, whereas high ratios are interpreted to represent carbonate-rich sections (75). The Ca/Sr ratio was used to distinguish between biogenic and detrital carbonate. As Sr is fixed by calcifying organisms at the same time as Ca, decoupling between Ca/Ti and Ca/Sr is indicative of a high detrital carbonate input (75).

In the boreholes, sequence boundaries occurred systematically at high δ18Oflem, when the Ca/Ti and Ca/Sr ratios return to background values. The maximum flooding surfaces were defined by a coeval increase in δ18Oflem, Ca/Ti, and Ca/Sr, whereas transgressive surfaces are marked by minimum δ18Oflem, and low Ca/Ti and Ca/Sr ratios (fig. S9).

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