MAXIMUM DEPOSITIONAL AGES BASED ON DETRITAL ZIRCON GEOCHRONOLOGY: AN EXAMPLE FROM THE BASAL WILCOX GROUP IN THE EASTERN GULF COASTAL PLAIN

Determining accurate depositional ages is crucial for understanding sedimentary basin evolution and regional tectonics. We present LA-ICPMS detrital zircon U-Pb geochronology (N=1, n=345) from the basal Wilcox Group in northeastern Mississippi to determine the maximum depositional age (MDA) and define stratigraphic ages in the eastern Gulf Coastal Plain. The detrital age spectrum is defined by a dominant Mesoproterozoic (1250-900 Ma; Grenville) population alongside smaller Archean (2800-2600 Ma; Wyoming), Paleoproterozoic (1800-1600 Ma; Yavapai-Mazatzal), Mesoproterozoic (1550-1300 Ma; Granite-Rhyolite), Neoproterozoic (800-500 Ma; Peri-Gondwana or Wichita Mountains), Paleozoic (490-270 Ma; Appalachian), and Mesozoic-Cenozoic (< 250 Ma; western North America Cordillera) populations. The presence of grains with ages close to the depositional age (syndepositional detrital zircons) provides an opportunity to compare various approaches for MDA determinations. The youngest single grain (YSG) yields an Eocene age of 53.8 ± 2.4 Ma, while a weighted mean average (WMA) of the youngest population (YP2σ3+, n=4) yields a Paleocene age of 56.2 ± 1.2 Ma. These results would require a reevaluation of Wilcox Group stratigraphic ages because both ages overlap with the Paleocene-Eocene boundary. A WMA of the second youngest population (SYP2σ3+, n=10) yields a Paleocene age 59.7 ± 0.6 Ma, which agrees with the MDA determinations by the YSG and WMA methods in previous detrital zircon studies throughout the eastern Gulf Coastal Plain and northern Mississippi Embayment. A maximum likelihood age (MLA) yields an age of 59.1 ± 0.7 Ma. Our data requires that sediment was routed from volcanic and or plutonic sources in the western North America Cordillera to the eastern Gulf Coastal Plain and show that larger sample sizes increase the probability of capturing syndepositional grains, potentially providing more accurate MDA representation of the true depositional age of a stratigraphic interval.