We propose to drill three transects of coreholes in the mid-Atlantic U.S. Coastal Plain targeting thick (>10 m) sections of the Paleocene-Eocene Thermal Maximum (PETM), building on drilling in New Jersey by IODP Leg 174AX and Maryland-Virginia by the USGS. Previous drilling has sampled across the paleoshelf from inner neritic to deep neritic (>100 m) paleodepths and has provided important constraints on this major event, but existing cores are either depleted or contain stratigraphic gaps due to the patchwork distribution of the successions, updip dissolution, diagenesis, and the discontinuous nature of coastal zone sedimentation, which can be addressed with new cores. We plan to triple core the sections of interest at ten sites sampling the PETM, targeting the underlying normal shelf deposit of the Vincentown/Aquia Formations, a transitional interval that is expanded in updip sections and contains the Carbon Isotopic Excursion (CIE) onset, and the rapidly deposited Marlboro Clay that records a very thick CIE “core/body”. Though truncated at the top of the Marlboro Clay, very much expanded PETM sections (>10 m versus 1 m in the thickest deep-sea section) are available in this region. We will also core and sample other Eocene hyperthermals and the Cretaceous/Paleogene (K/Pg) boundary at these sites. This project will be an international collaboration with the cores archived by IODP, publication by IODP within two years, and with local logistical and support-in-kind provided by USGS and U.S. state surveys. Coring of three transects will provide new material needed to evaluate CIE initiation and subsequent CIE core/body that provides the clearest geological example of a massive release of carbon analogous to anthropogenic release.