T4 Critical Minerals and Framework Geology: The USGS Earth Mapping Resources Initiative (Earth MRI) and Related Activities I

Sunday, 9 October 2022
8:00 AM - 12:00 PM
601

STRATIGRAPHIC FRAMEWORK OF THE HIGH-PRIORITY FALL ZONE AND MIDDLE SHORELINES PLACER FOCUS AREAS, DRAKE AND RED OAK QUADRANGLES, ATLANTIC COASTAL PLAIN, NORTH CAROLINA, USA

Paper number: T4-13
Program: Technical Sessions
Time: 11:05 AM – 11:20 AM

Authors

Abstract

The NC Geological Survey acquired EARTH MRI funds to map detailed stratigraphy (24K scale) in Red Oak and Drake 7.5-minute quadrangles to identify placers with REE minerals in updip Atlantic Coastal Plain strata along-strike from existing placer mines. Red Oak, situated in the Fall Zone Placer focus area, is west of Drake, which staddles the boundary (the Kenly paleoshoreline) between the Fall Zone and Middle Shorelines focus areas. A 2021 airborne geophysical survey footprint that followed the VA-NC Fall Zone included both quads. A 24K map of bedrock exists for Red Oak, but not Drake. Elevations range from 92 m in Red Oak to 27 m in Drake.

Relict Pliocene and Quaternary landforms are preserved here; hence 3D subsurface mapping strategies were applied. Geomorphology derived from 10 ft LiDAR DEMs helped plan the subsurface analysis. Cores to basement were collected along profiles chosen to transect specific geomorphic features. To date, 3,130 ft of core at 100 drill sites were collected to define the stratigraphy, mineral resource prospectivity, and depth to basement (bedrock and saprolitized metamorphic rocks and granitoids).

Using 3D mapping methods, sedimentary facies formerly assigned to the Yorktown, Chowan River and Bacons Castle Formations are redefined and tracked relative to major paleoshorelines: the Kenly Scarp equivalent with a toe at ~50 m, and a second, more-landward scarp with several downstepping notches between 62 – 58 m. Both features are lower in elevation than the Coats/Orangeburg (84 m) and Wilson Mills (75 m) scarps as defined in NC.

Stratigraphy here is complex: marine/estuarine terrace deposits occur as aprons around topographic highs of exposed saprolite or bedrock, but the highs may be capped by older Coastal Plain units. Between the two shorelines, Carolina Bays have prominent rims, and thin surficial gravels are common. Two marine units overlie the basement: 1) bluish-gray mollusk-rich facies, the ‘Yorktown Formation’, but may be the younger Chowan River, and 2) a yellow unit consisting of a set of upward coarsening parasequences with no macrofossils. Upward-fining surficial feldspathic units and other facies may overlie the marine units both west and east of the Kenly shoreline. Heavy mineral sands are distributed within these surficial deposits, including potential Cretaceous units at 92 m.

Geological Society of America Abstracts with Programs. Vol. 54, No. 6

doi: 10.1130/abs/2022AM-379132

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