Detrital zircons and sediment dispersal in the Appalachian foreland

Abstract

Seven new detrital-zircon U-Pb age analyses along with a compilation of previously published data from Mississippian-Permian sandstones in the Appalachian foreland (total n = 3564) define the provenance of Alleghanian synorogenic clastic wedges, as well as characterize the detritus available to any more extensive intracontinental dispersal systems. The samples are from the cratonward-prograding Mauch Chunk-Pottsville clastic wedge centered on the Pennsylvania salient, the cratonward-prograding Pennington-Lee clastic wedge centered on the Tennessee salient, and a southwestward-directed longitudinal fluvial system along the distal part of the foreland. Grenville-age detrital zircons generally are abundant in all samples; however, ages of the Taconic and Acadian orogenies are dominant in some samples but are minor to lacking in others. Taconic-Acadian ages are dominant in the Mauch Chunk-Pottsville clastic wedge, in parts of the longitudinal system, and in the upper part (above Middle Pennsylvanian) of the Pennington-Lee clastic wedge; but they are minor to lacking in the lower part (Upper Mississippian-Lower Pennsylvanian) of the Pennington-Lee clastic wedge. New Hf isotopic analy ses show a similar distinction between the two clastic wedges, supporting an interpretation of differences in provenance contributions during the early stages of basin filling. U-Pb ages and Hf isotopic ratios also indicate that the Mauch Chunk-Pottsville transverse dispersal fed the northern part of the longi tudinal system. A few samples in the distal southwestern part of the Mauch Chunk-Pottsville clastic wedge and adjacent parts of the longitudinal system have unusually large populations of grains with Superior and Central Plains ages. The relative distance and isolation of these samples from the Cana dian Shield, which is the primary source of Superior and Central Plains zircons, indicates likely recycling from synrift sediment, passive-margin strata, or Taconic-Acadian clastic wedges. Among the lesser components are a few grains with ages that correspond to Iapetan synrift igneous rocks and also to Pan-African-Brasiliano components of Gondwanan accreted terranes. Synorogenic zircons of the Alleghanian orogeny are very rare (seven grains in the total of 3564).

Detrital Zircon Geochronologic Constraints on Patterns and Drivers of Continental‐Scale Sediment Dispersal in the Late Mississippian

“…The strong Grenville and Acadian‐Taconic age peaks observed in the zircon age spectra for the Chesterian IVF sandstones point to more distant or potentially recycled sources for sediments. Both the Grenville and Taconic‐Acadian orogenies occurred in the Appalachian region, and comparison of our data with data from the Alleghanian Appalachian Foreland Basin, a proxy for sediment sources and likely zircon age distributions derived from the orogen, shows a high degree of similarity (Thomas et al, and references therein). The almost mirror image in age spectra between sandstones from the Hugoton Embayment and Appalachian signature derived from synorogenic clastic wedge sediments (Thomas et al, ), shown in Figure c, strongly suggests that the Appalachian region was the primary source of sediments.…”

“…Both the Grenville and Taconic‐Acadian orogenies occurred in the Appalachian region, and comparison of our data with data from the Alleghanian Appalachian Foreland Basin, a proxy for sediment sources and likely zircon age distributions derived from the orogen, shows a high degree of similarity (Thomas et al, and references therein). The almost mirror image in age spectra between sandstones from the Hugoton Embayment and Appalachian signature derived from synorogenic clastic wedge sediments (Thomas et al, ), shown in Figure c, strongly suggests that the Appalachian region was the primary source of sediments. However, it is worth noting that the percentages of Yavapai‐Mazatzal grains (1,800–1,600 Ma; up to 10%) in some samples are higher than in Appalachian sources and may point to some limited contributions from local basement uplifts such as Nemaha Uplift (Xie, O'Connor, et al, ).…”

“…Diagrams were constructed using Isoplot (Ludwig, ). (c) Kernel density estimation plots comparing detrital zircon U‐Pb ages from Chesterian incised valley fill in the Hugoton Embayment (upper curve) with compiled detrital zircon ages from Late Paleozoic successions in the Appalachian Foreland (based on Thomas et al, and references therein).…”

“…It should be noted that there is some geographic variability in the age spectra for the St. Peter sandstone, particularly for zircons <2,000 Ma and most notably for the Grenville age group (Figures c–g). Comparison of these age spectra with the compiled age distribution for the Taconic synorgenic wedge (Gray & Zeitler, ; Cawood & Nemchin, ; McLennan et al, ; Eriksson et al, ; Park et al, ; Thomas et al, ) suggests that the Appalachian area was an important source of sediments and Grenville‐age zircons during the Early to Middle Ordovician; however, its influence and contributions were not uniform.…”

“…An increasing number of studies have focused their efforts on testing various aspects of the Gehrels et al () model (e.g., Finzel, ; Benyon et al, ; Lawton et al, ; Xie, O'Connor, et al, ; Xie, Cains, et al, ; Xie, Buratowski, et al, , Xie, Anthony, & Busbey, ; Xu et al, ; Thomas et al, ; Alsalem et al, ; Kissock et al, ). However, most of these published investigations have focused on Pennsylvanian and younger strata.…”