TESTING DETRITAL ZIRCON VERSUS DETRITAL APATITE RECORDS OF PROVENANCE AND MAXIMUM DEPOSITIONAL AGE IN THE ACADIAN BASIN

In the Acadian basin, Upper Devonian strata may contain detrital zircon derived from the syndepositional Acadian arc (~415-360 Ma). However, these strata are also likely to contain abundant recycled Grenville-aged (1,200-900 Ma) grains. Given the greater susceptibility of apatite to chemical alteration compared to zircon, detrital apatite are less likely to record recycled influx, providing a useful tool for determining maximum depositional age (MDA) and for assessing signatures of first cycle sediment input. To test this, we performed U-Pb analysis of detrital zircon and detrital apatite from 4 samples collected from a section of Upper Devonian clastic deposits including the Hampshire Fm. and overlying basal Price Fm. near Valley Head, WV. The age distribution of detrital zircon grains from all four samples (n = 491) show ~48% of the grains are Grenville-aged, suggesting considerable recycled sediment input. Of the Appalchian-aged zircon grains, ~69% represent the Taconic orogen (480-450 Ma) and just 4% represent the Acadian orogen (410-360 Ma), also reflecting abundant recycled sediment input. Detrital zircon MDAs determined for two Hampshire Fm. samples were 444.5 ± 8.46 Ma and 397.4 ± 13.5 Ma, which are 30-70 million years older than the predicted biostratigraphic age. One sample from the overlying Oswayo Member of the Price Fm. yielded a detrital zircon MDA of 379 ± 11.4 Ma, and a sample of the Cloyd Conglomerate Member of the the Price Fm. yielded an MDA of 352.8 ± 10.1; both MDAs overlap with the ~370-360 Ma biostratigraphic ages. Of the 4 samples, only one Hampshire Fm. sample yielded robust apatite U-Pb age results (n = 59). These detrital apatite analyses consist of ~17% Grenville-aged grains, showing the predicted paucity of recycled ages, and ~68% Appalachian-aged grains. However, 28% of the Appalachian-aged grains are 330-230 Ma, which is younger than the biostratigraphic age of the Hampshire Fm. by >20 Ma and so yields an unreliable MDA. We suspect larger samples would permit recovery of sufficient apatite grains, which if subjected to more intensive textural and chemical screening to identify and eliminate diagenetically altered apatite from consideration, could enable detrital apatite to provide improved estimates of MDA and recycled sedimentary influx for the poorly-dated Hampshire Fm.