Detrital Zircon Evidence for Amazonian Provenance of Upper Jurassic Norphlet Formation in North Central Gulf, Mobile Bay: Implications for Paleoriver Systems in South and Central America

摘要

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 Goias 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 Goias 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 Goias 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 Goias arc and transported to the eastern Gulf of Mexico by a proto-Orinoco river that developed during Jurassic-Early Cretaceous time.