57-4 Dating Sequence-Stratigraphic Surfaces and Systems Tracts with CA-ID-TIMS U–Pb Geochronology and Bayesian Age–Depth Modeling: Topset–Foreset–Bottomset Relations in Cenomanian–Turonian Strata of Northern Alaska

Session: Advances and Applications in Geochronology for Interpreting Stratigraphic and Basin Records, Part II

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Abstract:

Integrating high-precision geochronology with sequence stratigraphy in an age–depth framework is a powerful and possibly underutilized tactic in basin analysis. New chemical abrasion-isotope dilution-thermal ionization mass spectrometry results from tephra and detrital zircon refine the correlation between two mainly shallow-marine outcrops of Nanushuk and Seabee Formations on the central North Slope, Colville foreland basin. The Nanushuk-to-overlying-Seabee transition at each location is a transgressive surface of erosion (TSE) that is typically considered to reflect rapid flooding and sometimes used as a transgressive surface (TS) proxy. Age–depth models for ~700 m of section at Rooftop Ridge and ~300 m of section at Ninuluk Bluff provide TSE posterior ages of ~96.4 Ma and ~95.0 Ma, respectively. Stratigraphic stacking relations reveal higher-frequency (~4^th order) base-level cyclicity superimposed on lower-frequency (~3^rd order) trends and underpin ~3^rd order, intra-Nanushuk TS position interpretations, with posterior ages of ~96.9 Ma (Rooftop Ridge: ~100 m sub-TSE) and ~≥96.7 Ma (Ninuluk Bluff: ~≥200 m sub-TSE). Stratigraphic accumulation rates in lower, muddy offshore Seabee (~140 m/Ma [Rooftop Ridge] and ~160 m/Ma [Ninuluk Bluff]) are within the range of rates for upper, sandy shoreface Nanushuk (~180 m/Ma [Rooftop Ridge] and ~110 m/Ma [Ninuluk Bluff]). The updated Rooftop Ridge–Ninuluk Bluff correlation confirms diachroneity for TSE establishment, with high sedimentation rates impeding shoreline transgression rates. The TS ages overlap at 95% uncertainty, which is consistent with basin-wide transgression terminating ~20 Ma of Nanushuk (topset)–Torok (foreset–bottomset) Formations clinothem growth. Seabee is thus locally as old as ~96.9 Ma, which is the age of a tephra from lower, deep-marine Seabee that overlies Torok near the Lupine River. Deep-water successions of the oil-bearing Bermuda interval—previously described as lowstand, slope-apron deposits—are perhaps transgressive systems tract (TST) Seabee, and some upper Torok strata are more parsimoniously regarded as TST Seabee where they lie above the TS and correlate with retrogradationally stacked Nanushuk and Seabee topset deposits. Finally, younger deep-water Seabee strata that are stratigraphically perched above the flooded and TST-draped relict shelf of the Nanushuk–Torok clinothem crop out within the Chandler River valley and yield a ~93.4 Ma tephra result, providing a minimum age for the maximum flooding surface that caps the Nanushuk–Seabee TST and heralding onset of Tuluvak (topset)–Seabee (foreset–bottomset) Formations clinothem development.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9684

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