STRUCTURAL AND STRATIGRAPHIC FRAMEWORK AND THE ORGANIZATION OF PREHISTORIC QUARRIES OCCURRING WITHIN THE WALLKILL RIVER VALLEY

Stratigraphy/sedimentology are first-order controls on chert raw materials in the Wallkill River Valley, New Jersey/New York. Spatial continuity of the Cambrian-Ordovician carbonate depositional ramp provided tens of kilometers of continuous raw materials. This continuity was disrupted by post-depositional tectonics, which deformed the carbonates into southwest plunging, Taconic folds offset by Alleghanian normal, reverse, and antithetic faults. The fold-fault system recrystallized and redistributed the chert-bearing carbonates, stacking them in repeated fault slices throughout the valley.

Wallkill carbonates are divided into three outcrop belts. The eastern belt preserves Cambrian Hardyston to Ordovician Ontelaunee formations as gently dipping beds in normal-fault grabens. The central belt presents Hardyston to Cambrian Upper Allentown formations in the eastern limbs of folds offset by reverse faults. The western belt bears Hardyston to Martinsburg Formation in the cores and western limbs of folds offset by reverse and antithetic faults.

In the eastern belt, shallowly dipping Leithsville cherts (Wallkill Member) possess diagenetic and recrystallization fabrics that imposed challenges for prehistoric miners. However, shallow dip and graben constriction provided a predictable and easily obtainable raw material source.

Steeply dipping Limeport Formation in the central belt bears chert as underlinings of stromatolites, replacement of algal and oolites, and pressure solution halos. The Stonehenge Formation bears cherts as selective algal replacements. Structural complexity of folds offset by reverse faults ensures that resulting quarries are small and difficult to engineer.

Reverse fault slices of the western belt preserve steeply dipping Rickenbach and Epler beds, marking the evaporitic shoreline of the Lower Ordovician. Rickenbach/Epler cherts are ooid, evaporite and stromatolite replacements, dilation breccias and paleo-karst features. Resulting quarries are small and discontinuous, but highly organized. Contrastingly, massive chert-replaced limestones of the Ontelaunee Formation, housed in folds offset by antithetic faults, replace stromatactis mounds. The large mounds permit Beaver Run and Harmonyvale quarries to be the largest and best organized in the region.