CROSS-FAULT COMPLICATION OF AN IMBRICATE THRUST STACK IN THE CARTERSVILLE DISTRICT, GEORGIA

The Cartersville area was remapped at 1:12,000-scale in the early 1980's. Wide areas previously mapped as being underlain by Weisner Quartzite bedrock are actually colluvium-covered slopes that lie downhill from ridge-crest Weisner outcrops. Colluvium obscures exposures of rocks both older and younger than the Weisner. The work classified interlayered phyllitic shale, siltstone, and fine-grained sandstone of the Wilson Ridge Formation as the basal Cambrian unit. It is overlain by overlying ridge-forming, vitreous, quartz sandstone of the Weisner Quartzite. The superjacent, commonly barite-mineralized Shady Dolomite and Rome Formation highly colored, interlayered, fine-grained sandstone, phyllitic shale, and siltstone respectively are the uppermost units. The mapping also supports observations of geologists that investigated Cartersville barite deposits in the early 1900's by confirming the oldest Cambrian rocks occupy imbricate thrust-faulted slices.

Recent mapping of the area was undertaken at a scale of 1:6,000 to identify the recharge area of a prolific, high-purity spring that shows no effects of past or current land use. This work verifies both surface and subsurface observations of contemporary mining geologists that report the thrust-faulted barite deposits are truncated and offset by northwest-trending, high-angle, normal faults. The normal faults are locally marked by iron-mineralized breccia zones that obliquely cross the east dipping thrust sheets affecting a zigzag map pattern of Lower Cambrian strata. Several old iron mines south of Cartersville, are preserved as open cuts along northwest trending, brittle fault zones.

Significant aspects of this work are that barite deposits may be more extensive than previously believed and that the area aquifer – the solution-prone Shady Dolomite – is not hydraulically isolated. It is repeated in numerous east-dipping, imbricate thrust sheets. Through-going, younger normal faults likely act as conduits for groundwater flow between thrust sheets. Not only are most previously published geologic maps incorrect, but also derivative maps showing pollution susceptibility and groundwater recharge areas do not accurately portray the Cartersville area.