Abstract The Town Creek locale in Jackson, Mississippi exposes fossiliferous strata through stream erosion and provides evidence for stratal doming atop an extinct volcano. Charles Lyell (1797–1875) investigated the locale on his second visit to North America (1845–46) and concluded that Town Creek fossils were older than Vicksburg fossils, and that strata dipped westward from Jackson. In the 1850s, Mississippi's state geologist Eugene Hilgard (1833–1916) recognized the first volcanic doming evidence and correctly concluded that a ‘local upheaval’ had elevated the Jackson area. Subsequent research revealed an extinct volcano as Jackson Dome's source, explaining the strata dip and Lyell's observation that Jackson's Eocene fossils were older than Vicksburg fossils, later identified as Oligocene. The Jackson fossiliferous strata, known today as the Moodys Branch Formation, exquisitely preserves fossils that have contributed to numerous scientific investigations. The Town Creek locale was threatened in 2003 when a proposed flood control project would have inundated it. Scientists rallied for the preservation of the geologically and historically important Town Creek, and today it remains as a geoheritage site available to scientists and the public, with a state historical marker noting its geological importance. Long-term preservation of the locale is needed but not guaranteed.

Abstract Detrital zircon from the Upper Jurassic Norphlet Formation in the vicinity of Mobile Bay, AL reflects a Laurentian provenance, with U-Pb age populations including dominant Paleozoic (265-490 Ma) and Grenville (950-1250 Ma) age. Twenty-three zircon grains from a sandstone sample recovered from the upper part of the Norphlet formation in well permit# 9863-OS-46-B show a population of 850-920 Ma zircon that is not observed in stratigraphically older samples. As there are very few sources for zircon of this age in southeastern United States, we interpret derivation from either the Goiás magmatic arc of Brazil; the conglomeratic sandstone of the eastern Yucatan peninsula; and/or Mixteca terrain of Mexico as probable sources. Previous study of 850-920 Ma zircon grains from the Goiás magmatic arc shows an origin from a depleted mantle without any crustal contamination (Hf (t) = +8 to +12); however, the same age zircons in eastern Yucatan and Mixteca terrain indicate crystallization from magmas having a strong crustal signature (Hf (t) = -3.2 to -3.8). Detrital Neoproterozoic zircon grains in the Norphlet Formation shows a wide Hf (t) range (-5.1 to +11.9) for the 850-920 Ma zircons, indicating sediments influx to the Gulf of Mexico basin during late Norphlet time was a mix of material from all of these sources during the Norphlet deposition. We propose that sediments from the Goiás magmatic arc probably were transported to the Mixteca terrain through a paleo-fluvial system; given the proximity of Mixteca terrain to southern North America during Late-Early Jurassic, we infer that erosion of Mixteca terrane sedimentary rocks supplied sediment to the Norphlet erg in the eastern Gulf of Mexico. Alternately, the Neoproterozoic grains may have been derived directly from the Goiás arc and transported to the eastern Gulf of Mexico by a proto-Orinoco river that developed during Jurassic-Early Cretaceous time.