255-5 Assessing Fold-Thrust Belt Unroofing Using Detrital Zircon Double Dating in the Alberta Foreland Basin

Session: Broad Applications of Thermochronology to Understanding Geologic Rates and Processes Through the Sedimentary Record

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Abstract:

The flexural Alberta foreland basin holds a sedimentary record useful for reconstructing Jurassic to Paleocene hinterland erosion and orogenic evolution in Canada. Turonian–Paleocene formations have been described in terms of sedimentary facies and paleoenvironments, but it is unclear when these strata record syntectonic fold-thrust belt unroofing versus sediment reworking during tectonic quiescence. Here, we present new detrital zircon U-Pb geochronology and (U-Th)/He thermochronology (ZHe) single-grain double dates from six Turonian–Paleocene units. Detrital zircon U-Pb ages indicate derivation from Neoproterozoic–Ordovician units in the fold-thrust belt source in the Turonian, and double dates reveal zircons from passive margin fold-thrust belt strata are characterized by Paleozoic and older cooling dates. There is a provenance shift in the Coniacian–early Campanian to a dominant passive margin source, which we interpret as corresponding to punctuated transpression in the distal fold-thrust belt. Simultaneously, double-dates show an increase in passive margin grains with Mesozoic cooling dates, supporting progressive erosion into passive margin strata that was thermally reset since Canadian orogenesis began in the Jurassic. Campanian–Paleocene strata record coarse clastic sedimentation during fold-thrust belt shortening known as the “Rundle Pulse,” and a Neoproterozoic–Ordovician fold-thrust belt source, supporting unroofing of deeper structural levels. The youngest pre-depositional ZHe peak populations young up-section, ~126 Ma (Turonian), ~112 Ma (Coniacian), ~119 Ma (Campanian), and ~97 Ma (Maastrichtian), reflecting progressive erosion into the fold-thrust belt. Contrastingly, the youngest pre-depositional ZHe date population in Paleocene strata is older than in underlying strata, ~145 Ma, and paired with U-Pb ages typical of Neoproterozoic–Ordovician sources. We interpret the shift towards older ZHe dates as reflecting foreland basin cannibalization during the Paleocene, consistent with Rundle Pulse thrusts uplifting Jurassic–Late Cretaceous foreland basin units. New detrital zircon double date results clarify the progression of fold-thrust belt unroofing and document foreland basin recycling during Turonian–Paleocene mountain building in Canada. 

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

doi: 10.1130/abs/2025AM-9597

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