Murphy Marble Belt

Much of Georgia's marble is quarried from bodies lying in an sinuous band extending from near Murphy, North Carolina, into north central Georgia. Alabama's Sylacauga marbles may be an extension of this band. Named the Murphy Marble Belt for its exposures in North Carolina, this band's structure is often interpreted as a syncline (the Murphy Syncline) exposing continuous marble deposits along its flanks. Matrix surrounding Murphy Marble comprises moderately metamorphosed sediments apparently deposited in deep water, perhaps offshore of Proto-North America's continental shelf.

Recent re-interpretations of Murphy structure suggest that its marble deposits may be:

• A collection of discontinuous marble pods -- metamorphosed reef and platform fragments -- embedded in metamorphosed tectonic melange.
  or
• Metamorphosed Ridge and Valley carbonates -- Shady Dolomite and/or Conasauga formation -- transported upward along thrust faults. (See below.)

Many segments of the Murphy Belt exhibit parallel valleys with strata dipping east or southeast, as seen in this section looking north.

For many years, structure has been interpreted as a syncline overturned to the west, with valleys resulting from dissolution of carbonate rock.

Alternately, dipping strata may represent thrust sheets, with valleys resulting from erosion of fault zones.

On contour and shaded-relief maps, much of the Murphy Belt clearly shows a pair of parallel valleys (See above) separated by a central ridge (often labeled "Dividing Ridge"). Closer inspection shows that this central ridge is flanked in many areas by multiple valleys and ridges, now dissected by cross-cutting streams.

While a synclinal carbonate-erosion model might explain one set of parallel valleys, flanking valleys require multiple carbonate layers, presumably in overturned folds.

Alternately -- and perhaps more simply -- valleys may reflect multiple thrust faults or splays; however, if multiple thrust faults exist, it is likely that they would have been detected by some of the many geologists who have worked in the Murphy belt . . . not certain, but likely.

Similar sets of parallel ridges and valleys are present in the Gold Belt and the Brevard Zone. The mechanism of ridge and valley formation in these zones is not certain; unlike ridges and valleys in the Ridge and Valley province, they don't appear to be associated with thrust faults. Also is it not clear that these ridges are uniformly composed of erosion-resistant rock.

For further information on geology of the Murphy Marble Belt, consult:

• Georgia Geological Society Guidebook, v.8, no. 1, Geology of the Murphy Belt and Related Rocks, Georgia and North Carolina
• Georgia Geological Society Guidebook, v.9, no. 1, Excursions in Georgia Geology
• Georgia Geological Society Guidebook, v.16, no. 1, The Cartersville Fault Problem Revisited
• Georgia Geological Society Guidebook, v. 22, no. 1, Geologic Features of Eastern Pickens, Dawson, and Western Lumpkin Counties, Georgia
• Georgia Geologic Survey Bulletin 63, Stratigraphy, structure, and mineral resources of the Mineral Bluff Quadrangle, Georgia
• Georgia Geologic Survey Bulletin 75, The Murphy Syncline in the Tate Quadrangle, Georgia
• U.S. Geological Survey Professional Paper 1475

Located on Georgia Geologic Map.