Provenance of Syn-rift Clastics in the Eastern Gulf of Mexico: Insight from U-Pb Detrital Zircon Geochronology and Thin Sections

Abstract

zircon geochronology, supplemented by thin section petrography, point counting, and well logs, were used to constrain the provenance of basal Triassic/Jurassic (?) clastic sedimentary rocks in the Eastern Gulf of Mexico (EGOM). Basal clastics were deposited as synrift strata into half grabens present along the EGOM and eastern margin of Laurentia that formed during the initial break up of Pangea. Samples used in this study were collected from the South Florida Basin (SFB) and the South Georgia Rift (SGR). Previous studies of post-rift Jurassic sediment in the Gulf of Mexico has identified a change in source from Laurentian dominated sources in southern Mississippi/Alabama, to Gondwanan dominated sources in the Florida Apalachicola Embayment/offshore. Comparing the provenance of initial syn-rift strata to postrift strata is used to identify initial sediment sources into the EGOM rift basins, and how provenance changed over time. Detrital zircons were collected from five SFB well cutting samples from the Jurassic (?) Wood River Formation and proximal basal sandstones, and six SGR well cutting samples from the Triassic (?) Newark Supergroup, as well as one sample from offshore southern Florida basement. Predominant age populations for the SFB are consistent with a Pan-African origin (525-680 Ma, 1900-2200 Ma). Samples from the SGR are dominated by Laurentian sources (265-330 Ma, 350-420 Ma, 430-490 Ma, 900-1300 Ma), as well as secondary Pan-African sources (525-680 Ma, 1900-2200 Ma). Provenance data is supported by thin section point counting and well logs. Samples in the northern SGR are predominantly derived from Laurentian sources, while the southern samples 3137 and 1854 are a mix of Laurentian and Gondwana signatures. K-S test comparisons of basal sandstones from this study and post-rift Jurassic Norphlet Formation samples from Lovell (2010) and Lisi (2013) show little correlation between samples, implying they do not share similar sources. The exception is the offshore Apalachicola Embayment samples, which indicates that the SGR may have been a potential source for Jurassic sediment in the northern EGOM. The integration of geochronology and petrographic techniques in this study suggests a mix of primarily sedimentary sources from the Suwannee Terranes and metamorphic sources from Laurentia supplied the initial sediment into the EGOM. Results from this study can be used to better constrain tectonic terranes and paleogeography of the early EGOM.

Reconstructing the Mesozoic evolution of the Gulf of Mexico Basin: A new model incorporating optimised and focused lithospheric deformation

“…The U-Pb analyses of well data from the northern GoM reveal that the youngest depositional age of the red beds extended only until 205 Ma, followed by a significant hiatus until the deposition of post-rift salt at 169 Ma (Dickinson et al, 2010;Umbarger, 2018;Wiley, 2017). The cause of this missing stratal gap remains unknown.…”

“…The ~40 Myr hiatus between the syn-rift red bed deposits and the Louann salt deposits in the Eagle Mills Formation poses an important conundrum. Zircon analysis from the Wood River Formation of the South Florida Basin and outcrops of the Dockum Group north of the Ouachita-Marathon orogenic belt indicates deposition ages of approximately 235-195 Ma (Wiley, 2017) and 234-200 Ma (Umbarger, 2018), respectively, leaving a gap between the Louann Salt and the Triassic deposits (Dickinson et al, 2010). Limited exposure of early Mesozoic outcrops south of the Ouachita Mountains and only few drilled wells below the autochthonous Louann Salt in the onshore USA, makes the geological record in the western GoM after the Permian period unclear (Snedden & Galloway, 2019).…”