Provenance and paleogeography of post-Middle Ordovician, pre-Devonian sedimentary basins on the Gander composite terrane, eastern and east-central Maine: implications for Silurian tectonics in the northern Appalachians

Abstract

Recent mapping in eastern and east-central Maine addresses long-standing regional correlation issues and permits reconstruction of post-Middle Ordovician, pre-Devonian paleogeography of sedimentary basins on the Ganderian composite terrane. Two major Late Ordovician-Silurian depocenters are recognized in eastern Maine and western New Brunswick separated by an emergent Miramichi terrane: the Fredericton trough to the southeast and a single basin comprising the Central Maine and Aroostook-Matapedia sequences to the northwest. This Central Maine/Aroostook-Matapedia (CMAM) basin received sediment from both the Miramichi highland to the east and highlands and islands to the west, including the pre-Late Ordovician Boundary Mountains, Munsungun-Pennington, and Weeksboro-Lunksoos terranes. Lithofacies in the Fredericton trough are truncated and telescoped by faulting along its flanks but suggest a similar basin that received sediment from highlands to the west (Miramichi) and east (St. Croix).Deposition ended in the Fredericton trough following burial and deformation in the Late Silurian, but continued in the CMAM basin until Early Devonian Acadian folding. A westward-migrating Acadian orogenic wedge provided a single eastern source of sediment for the composite CMAM basin after the Salinic/Early Acadian event, replacing the earlier, more local sources. The CMAM, Fredericton, and Connecticut Valley-Gaspé depocenters were active immediately following the Taconian orogeny and probably formed during extension related to post-Taconian plate adjustments. These basins thus predate Acadian foreland sedimentation.Structural analysis and seismic reflection profiles indicate a greater degree of post-depositional crustal shortening than previously interpreted. Late Acadian and post-Acadian strike-slip faulting on the Norumbega and Central Maine Boundary fault systems distorted basin geometries but did not disturb paleogeographic components drastically.

SHRIMP U–Pb zircon evidence for age, provenance, and tectonic history of early Paleozoic Ganderian rocks, east-central Maine, USA

“…Emergent highlands composed of Ganderian basement rocks supplied sediment to the adjacent Fredericton and CMAM depocenters from the Late Ordovician through Late Silurian (Ludman et al 2017). These sedimentary rocks were subsequently folded during the Salinic orogeny, and again during Early Devonian (Acadian) accretion of Avalonia (Fyffe et al 2011).…”

“…Age and relationship among cover sandstone units have been problematic for many years because of sparse bedrock exposures and similar lithologies and bedding styles, lack of distinctive marker horizons, and extremely rare fossil age control. Lithofacies and paleocurrent analyses indicate deposition in two distinct sedimentary regimes: a Late Ordovician to Late Silurian phase in which several emergent pre-Silurian belts shed sediment locally into the adjacent basins (Ludman et al 2017), and a Late Silurian to Middle Devonian regime in which sandstones deposited in a NW-migrating Acadian foreland basin swamped the original source areas with sediment from a single eastern source (Bradley et al 2000;Bradley and O'Sullivan 2016).…”

“…Interpretation of the immediate source of detrital zircons must take into account not only their age spectra but, wherever possible, sedimentologic and lithofacies evidence for the sediment source. There is strong evidence for the immediate source of the cover rock sediment in CMAM (Ludman et al 2017) and the Fredericton trough (Fyffe 1995), but lacking that evidence for the basement rocks, it is only possible to speculate about their ultimate provenance by comparing their detrital zircon barcodes with those of potential source terranes.…”

“…Several lines of evidence indicate that most CMAM and Fredericton sediment was recycled from Ganderian sources with little input from external terranes. First, the Miramichi and several other Ganderian basement terranes in Maine were emergent highlands by the late Ordovician (Hirnantian) immediately after accretion of the main body of Ganderia to Laurentia, and were clearly sources of sediment for both CMAM (Bradley and Hanson 2002;Bradley and O'Sullivan 2016;Hopeck 1998;Pankiwskyj et al 1976) and the Fredericton trough (Fyffe 1995;Ludman et al 2017).…”

“…To reach CMAM, Laurentian sediment would have had to traverse the deep-water Connecticut Valley-Gaspé trough Pinet 2005, 2016) and bypass the exhumed Boundary Mountains, Munsungun, and Weeksboro-Lunksoos Lake basement terranes. To reach the Fredericton trough, the sediment would have had to traverse the entire deep-water CMAM and then bypass the Miramichi terrane (Ludman et al 2017). Tightly folded rocks of CMAM today span a width of 160 km, but the undeformed depocenter was at least three to five times wider (Bradley et al 2000) and would have been a formidable barrier to transport of Laurentian sediment.…”