A high-resolution stratigraphic record of the Early Eocene Arctic continental shelf from the foreland of the Brooks Range, Alaska

Paleogene stratigraphic records with absolute chronology would facilitate better reconstruction of polar hothouse paleoenvironments and regional petroleum systems frameworks. To this end, we present lithologic descriptions of 100s of m of measured stratigraphic sections, chemical abrasion thermal ionization mass spectrometry U–Pb geochronology of volcanic ash layers, high-resolution organic carbon isotope (δ13Corg) stratigraphy, and palynology, from the Franklin Bluffs locality on the coastal plain of Arctic Alaska. Basal stratigraphic sections (10s of m) consist of terrestrial delta plain strata. The sections record a δ13Corg excursion of approximately -4‰ that we associate with one of the three primary Early Eocene carbon isotope excursions (hereafter, CIEs) and a sequence boundary associated with that event. Overlying stratigraphic sections (100s of m) consist of shallow marine strata and record 14 parasequences. Carbon isotope δ13Corg chemostratigraphy and a weighted mean U–Pb age of a tephra (~52.3 Ma) indicate the shallow marine sections span ~52.3–50.0 Ma, a timeframe that spans much of the Early Eocene Climatic Optimum and hyperthermal events within it. The uppermost group of measured sections (100s of m) consists of at least four parasequences, records progradation from shallow marine to non-marine environments, and dates to <47.6 Ma.

We argue that the δ13Corg stratigraphy can be correlated to global reference curves and reflects the global carbon cycle. The pacing of parasequences is similar to CIEs recorded in these sections. We argue that either sea level and/or modulations in sediment supply control the pacing of parasequences. The former mechanism is consistent with the erosional unconformity overlying the CIE in non-marine strata. The latter mechanism is consistent with stratigraphic trends in TOC suggesting organic matter dilution during the highest sediment flux to the continental shelf. This work also constrains a >5 Myr retrogradation/progradation cycle in the Early to Middle Eocene, similar to eustatic trends.