Temporal Variation in U-Pb Geochronology of the Norphlet Formation in the Eastern Gulf of Mexico, Mobile Bay: Connection Between Sediment Provenance and Reservoir Quality

Abstract

Previous work has shown that eolian dune sandstone facies of the Norphlet Formation in Mobile Bay, Alabama, reflects an overall Laurentian provenance based on U-Pb detrital zircon geochronology. This study is the first attempt to detect temporal variation in provenance by collecting five samples over the upper 88 feet of the Norphlet Formation from a single borehole core taken from the well permit # 9863-OS-46-B, Mobile Bay. Detrital zircon U-Pb ages determined by LA-ICPMS reveal that the upper four samples collected from between 22,002 and 22,073 feet are characterized by abundant Grenville (950 – 1250 Ma) ages that makes up 51-55% of the sample. These samples also exhibit minor peaks at 360 Ma, 420 Ma, and 460 Ma, which were likely derived from Acadian and Taconic orogenies. The lowermost sample, collected at 22,090 feet, has a significant population of 850-920 Ma ages that constitutes 30 % of the sample. There are few sources of 850-920 Ma zircon in the southeastern US; possible sources include basement of Avalonia preserved in the Mixteca terrain (Oaxaquia microplate), as well as the eastern Amazonia Goiás magmatic arc of northern South America. If 850-920 Ma zircon originated from the Goiás arc, they may have been routed to the EGOM through multiple pathways. One proposed model suggests 850-920 Ma zircon were reworked from Paleozoic sedimentary rocks in the Mixteca terrain and/or Goiás arc and transported to the EGOM by marine or eolian processes during Jurassic time; ultra-long transport for eolian detritus has been documented for other modern and ancient erg systems using detrital zircon tracers. An alternative model proposes that the collision between Gondwana (Oaxaquia microplate on the Colombian margin) and Laurentia may have juxtaposed the Goiás magmatic arc of Amazonia and/or Oaxaquia microplate of Avalonia against the southeastern boundary of Laurentia during late Paleozoic. During this collision, 850-920 Ma zircon were eroded from these terranes and shed toward southeastern Laurentia. During subsequent opening of the EGOM, reworking of late Paleozoic deposits shed these 850-920 Ma zircon into the Mobile bay area. Results of this study represent the first data suggesting erosion of rocks in the EGOM conjugate margin contributed clastic influx to the early EGOM basin.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016