LAYERING AND HIGH-RESOLUTION STABLE ISOTOPE RECORDS IN THE MARLBORO CLAY: TEMPORAL CONSTRAINTS FOR THE ONSET OF THE PETM

We provide a chronology for the initiation of the Carbon Isotope Excursion (CIE) and Paleocene/Eocene Thermal Maximum (PETM) that suggests carbon was released faster than the current anthropogenic rise. A causal mechanism for the CIE remains elusive in the absence of a precise release schedule for the isotopically light carbon. Previous studies have used integrated bio-magneto-stratigraphies, cycle counting, and extraterrestrial ³He accumulation rates to produce a range of estimates for the duration of the initial onset of the CIE between 750 years to 30 kyr. Durations for the total release (onset to recovery) range from 45 to 95 kyr. This uncertainty limits use of the CIE as a geologic analog for anthropogenic CO₂ emissions.

Recent work on the Paleocene/Eocene Marlboro Clay has unveiled the presence of regular thin beds (~2 cm) expressed in multiple cores and exposures throughout the Atlantic Coastal Plain. Specifically, Millville (ODP Leg 174AX) and newly recovered Wilson Lake B cores contain ~750 and 660 layers through the CIE, respectively. We analyzed bulk stable isotope composition across several of these layers within the Marlboro Clay. In each case, the beds have regular stable oxygen isotope cycles, arguing for a climatic origin. Orbital and millennial periodicities are far too long to explain the ~750 layers identified in the Millville core. Annual modulation of the insolation and freshwater fluxes plausibly explains the observed δ¹⁸O amplitudes (~1‰ with some cycles up to 2 ‰) and layer counts. This interpretation requires sedimentation rates of 2 cm/yr during the deposition of the Marlboro Clay. While high, modern locations such as the Amazon continental shelf, East China Sea and Indus fan accumulate sediments at rates that exceed 10 cm/yr.

We applied the layer chronology to the Millville core, where a high-resolution, bulk stable isotope record shows a 3.5‰ δ¹³C decrease over 12 layers across the CIE onset. The layering chronology indicates that carbon was released in a large, nearly instantaneous initial burst, followed by a protracted lower-level release lasting approximately 500 years. Such a scenario is most consistent with the release of thermogenic carbon due to LIP emplacement or a comet impact.