Earth orbital rhythms links timing of Deccan trap volcanism phases and global climate change

TL;DR

New astronomically calibrated marine records link two major late Maastrichtian shifts in seawater 187Os/188Os at 66.49 and 66.28 Ma to Deccan trap eruption phases and synchronous global carbon-cycle and climate changes. The authors argue for earlier, larger, and compositionally distinct Deccan volatile emissions, including a sulfur-rich phase before the main warming.

Key findings

• Two major decreases in marine 187Os/188Os occur at 66.49 Ma and 66.29 to 66.28 Ma, contemporaneous with Deccan trap eruption phases and disruptions of the global carbon cycle.
• The first Os shift at 66.49 Ma coincides with a major Hg peak at 66.50 Ma and a negative 0.2‰ benthic δ18O shift from 66.50 to 66.45 Ma, indicating a maximum 1°C deep-sea warming.
• From 66.30 to 66.28 Ma, a rapid 0.3‰ to 0.4‰ shift toward lighter benthic δ13C is synchronous with the second Os decrease; deep-sea warming of 3° to 4°C starts at 66.30 Ma and culminates at 66.19 Ma, marking the late Maastrichtian warming event.
• A positive benthic δ13C shift from 66.35 to 66.30 Ma is attributed to an especially sulfur-rich Deccan phase; Os box modeling requires weathering of 1.2 × 10^5 to 1.8 × 10^5 km3 basalt for the first shift and 4.4 × 10^5 to 6.6 × 10^5 km3 for the second.

Methods

• The study integrates new and published data from Pacific DSDP/ODP Sites 577, 1209, and 1210 and South Atlantic DSDP/ODP Sites 525, 527, 528, 1262, and 1267, plus the Tunisian Elles section, using XRF core scanning, benthic δ13C and δ18O, Os isotopes, magnetostratigraphy, and cyclostratigraphy.
• New measurements include 404 benthic foraminifer stable isotope samples, 18 Os isotope samples at Site 1209 and 23 at Site 1262, and 32 oriented paleomagnetic cube specimens; records were correlated at the precession-cycle level, counting 85 precession cycles back from the K/Pg boundary and using 111 tie points between Shatsky Rise and Walvis Ridge.
• The authors use an astronomically calibrated age model and cyclostratigraphic age model, plus LOSCAR carbon-cycle experiments with 10,000 GtC, 10,000 GtS, and combined C+S emissions over 100 kyr, and a simple 1-box marine Os cycle model.

Limitations

• The paper states that the lack of narrow constraints on both Os concentration and isotopic composition in Deccan trap basalt propagates into notable uncertainties in modeled eruptive volumes, and that it is difficult to assess whether the required Os was supplied by basalt weathering because the basalts are in the lowermost Deccan sequence.
• The paper states that some data were digitized from graphs, introducing uncertainty, though it says this did not affect any conclusion; it also notes that sedimentation rates diverge in the older interval likely because of a missing precession cycle around 276.5-m composite depth at Site 1209, with no correction implemented for the oldest part.
• Evident from the text: the Os box model depends on assumed Os concentrations and isotopic compositions, and the orbital solutions for short eccentricity are described as never precise beyond 60 Ma, so the chronology relies on long-eccentricity tuning and precession-cycle counting.