Valley-and-Ridge Province (PA-MD-WV) & Appalachian Plateau (NY)

The Valley and Ridge Province of Pennsylvania and Maryland exposes the fold-thrust belt (FTB) formed during the Alleghanian orogeny in the Appalachians. The FTB involves rocks ranging in age from Cambrian to Pennsylvanian (570-290 million years old) that were deformed mainly during the Pennsylvanian-Permian Alleghanian orogeny (~290-240 million years ago); evidence for earlier orgenies (Ordovician Taconic orogeny and Devonian Acadian orogeny) is mainly in the form of clastic wedges that were deposited during those periods.

The rocks show mesoscopic evidence for early layer parallel shortening (LPS cleavage and penetrative strain features, wedge-faulting, wrench-faulting and kink folding. This was followed by northwest-vergent thrust faulting, accompanied by large scale active (fault propagation) and passive (fault bend) folding and the growth of fault duplexes; multiple generations of fibrous slickenside surfaces developed during faulting and flexural slip folding. During the late stages there was further northwestward-vergent subhorizontal faulting and orogen-parallel extension (giving rise to vein systems). Overall the deformation progressed from the hinterland toward the foreland, and on to the plateau, where deformation is seen in the form of thrust faulting, broad folding and systematic joint sets.

The contractional deformation features are overprinted by Triassic (~240-210 million year old) extension that gave rise to (half-) grabens (e.g. Gettysburg Basin) that were filled with Triassic sediments.

Here are a selection of pictures from our 2006 and 2007 Spring field trips.

Geology

Keuka Lake, one of the finger-lakes on the Appalachian Plateau	Plumose structure on joint face in sandstones of the Ithaca Member of Genesee Group, Watkins Glen, NY
Towanda (Bridge Street) fault in the Towanda (Lock Haven) Formation at Towanda, PA. This is a North-dipping thrust fault on the Appalachian Plateau	Channels and cross-beds within the Catskill Formation along US Rte 15 just south of Liberty, PA
Bear Valley Strip Mine near Shamokin, PA showing the Whaleback Anticline and the South Syncline (exposed on the East Wall). Structures are developed in sandstones of the Pennsylvanian Llewellyn Fm	Curved slickenlines on pre-folding wrench fault that continued to be active during progressive folding so that it had normal dip slip at the end stages of deformation
Steep north limb of Whaleback Anticline showing late stage extension faults (forming “horizontal graben”) that allowed vertical extension in fold limbs	Early wedge fault in steep north limb of whaleback anticline
Deformed tree trunk at the northwest corner of the quarry	Ironstone nodules on south wall showing selective extensional fracturing resulting from competency difference with surrounding rock
Thin Cleavage Duplex in Devonian Marcellus Formation near Selinsgrove Junction, PA	Cleavage and faults within the Cleavage Duplex
Triassic conglomerates at eastern edge of Gettysburg Triassic Basin	Fairfield quarry in Triassic limestone at western edge of the Gettysburg Triassic Basin
Road-cut through Sideling Hill syncline along US Rte 40 west of Hancock, MD. The rocks in the fold-core comprise the coal-bearing Mississippian Purslane Formation.	Core of the syncline showing prefolding wedging in sandstone beds in both limbs of the syncline
Second-order structures on east limb of Wills Mountain anticline along railroad cut at Cedar Cliff, south of Cumberland, MD. Silurian McKenzie and Wills Creek Formations show fault propagation folding with the steep limb cut by imbricate faults out of the core of the anticline	Structures in steeply dipping west limb of Wills Mountain anticline along railroad cut at Pinto, south of Cumberland, MD. Folding and faulting in Silurian McKenzie formation near east end of outcrop belt
Deformed mud-cracks in Wills Creek Formation on west limb of Wills Mountain anticline at Pinto railroad cut	Conjugate sets of en echelon veins in Silurian Tonoloway limestone on west limb of Wills Mountain anticline near west end of Pinto railroad cut
Paw Paw anticline in the Devonian Braillier Formation at the tunnel north of Paw Paw, WV. This is a second order fold west of the Sideling Hill syncline	Fibrous slickensides on successive bedding surfaces on the west limb of the Paw Paw anticline indicating flexural slip folding
The battlefield at Gettysburg, PA in the middle of the Triassic Basin	Looking east across the Valley and Ridge Province from Sideling Hill, MD

People

Camping near Gettysburg, PA, 2006	Group (2006) at Camp Singewald, the Johns Hopkins University field camp near Clear Spring, MD
Overlook at Gettysburg battlefield	Lunch