ABSTRACT The Fernow Experimental Forest (the “Fernow”) is an 1860-ha (4600-acre) research forested watershed in Parsons, West Virginia, USA. The Fernow has been in operation since 1934 and has historically been the site of timbering and silvicultural research programs. Beginning in the 1950s, a water quality research program was established in the Fernow to assess the effects of different forestry management techniques on water quantity and quality. As a result, most peer-reviewed research from the Fernow has focused on water quality data directly related to forestry efforts with little mention of the effects of geology, hydrogeology, or climate on water resources in the Fernow. Further, the Fernow is representative of Appalachian headwater mountain watersheds and is a protected and secure research site in the greater Monongahela National Forest. This, in combination with the long-term data records from the water research program, make the Fernow an ideal location for further geologic and hydrologic investigations in forested mountain watersheds. The geology of the Fernow is dominated by moderately dipping Paleozoic-aged strata with local karst features (e.g., springs) occurring in one unit. The hydrology of the Fernow consists of intermittent and perennial streams that are reactive to seasonal weather patterns. This field guide serves as an overview of the geology and hydrology of the Fernow and surrounding region to be used as a teaching and recruitment tool to advance the geologic understanding of Allegheny Mountain headwaters.

ABSTRACT During the Pleistocene, the Laurentian Ice Sheet extended southward into northwestern Pennsylvania. This field trip identifies a number of periglacial features from the Appalachian Plateaus and Ridge and Valley provinces that formed near the Pleistocene ice sheet front. Evidence of Pleistocene periglacial climate in this area includes glacial lake deposits in the Monongahela River valley near Morgantown, West Virginia, and Sphagnum peatlands, rock cities, and patterned ground in plateau areas surrounding the Upper Youghiogheny River basin in Garrett County, Maryland, and the Laurel Highlands of Somerset County, Pennsylvania, USA. In the high-lying basins of the Allegheny Mountains, Pleistocene peatlands still harbor species characteristic of more northerly latitudes due to local frost pocket conditions. Pleistocene fauna preserved in a cave deposit in Allegany County, Maryland, record a diverse mammalian assemblage indicative of taiga forest habitat in the Ridge and Valley province.

ABSTRACT With waterfalls and the deepest gorge in Pennsylvania, Ohiopyle State Park provides opportunities to observe a variety of habitats and three-dimensional (3-D) exposures of the Pennsylvanian sandstone most responsible for shaping Laurel Highlands landscapes. Evidence for the relationship between bedrock, ancient climates, and the landscape can be observed at some of the most scenic natural features of the park: Baughman Rock Overlook, Cucumber Falls, Ohiopyle Falls, Meadow Run Waterslide and Cascades, and Youghiogheny River Entrance Rapid. Channel azimuths and lateral variations in thickness of upper Pottsville fluvial/deltaic sandstone suggest that deposition was influenced by deformation of this part of the Allegheny Plateau during the Alleghanian orogeny. Geologic features of Pottsville sandstone outcrops include a 10-m- (~33-ft-) long Lepidodendron fossil and a 3-D exposure of a meter-high Pennsylvanian subaqueous sand dune and scour pit. Cosmogenic age dating has indicated very slow erosion of hard sandstone in an upland location at Turtlehead Rock and informed estimation of Pleistocene/Holocene waterfall retreat rates of Ohiopyle and Cucumber Falls. Bedrock exposures supporting scour habitats along the Youghiogheny River occur only in a limited area of Youghiogheny Gorge where knickpoint migration and bedrock erosion were relatively recent. Geologic factors, including locations of major tributaries, development of bars that constrict river flow, and proximity of Homewood sandstone outcrops as sources of boulder obstacles in the river, contributed to the class, location, and nature of whitewater rapids in the lower Youghiogheny River.

ABSTRACT This field guide presents a one-day trip across the northern Virginia Blue Ridge geologic province and highlights published geologic mapping of Mesoproterozoic rocks that constitute the core of the Blue Ridge anticlinorium and Neoproterozoic cover-sequence rocks on the fold limbs. The guide presents zircon SHRIMP (sensitive high-resolution ion microprobe) U-Pb crystallization ages of granitoid rocks and discusses the tectonic and petrologic evolution of basement rocks during the Mesoproterozoic. U-Pb data show more of a continuum for Blue Ridge Mesoproterozoic magmatic events, from ca. 1.18–1.05 Ga, than previous U-Pb TIMS (thermal ionization mass spectrometry)-based models that had three distinct episodes of plutonic intrusion. All of the younger dated rocks are found west of the N-S–elongate batholith of the Neoproterozoic Robertson River Igneous Suite, suggesting that the batholith occupies a fundamental Mesoproterozoic crustal boundary that was likely a fault. Narrow belts of paragneiss may represent remnants of pre-intrusive country rock, but some were deposited close to 1 Ga according to detrital zircon U-Pb ages. For late Neoproterozoic geology, the guide focuses on lithologies and structures associated with early rifting of the Rodinia supercontinent, including small rift basins preserved on the eastern limb of the anticlinorium. These basins have locally thickened packages of clastic metasedimentary rocks that strike into and truncate abruptly against Mesoproterozoic basement along apparent steep normal faults. Both basement and cover were intruded by NE-SE–striking and steeply dipping, few-m-wide diabase dikes that were feeders to late Neoproterozoic Catoctin Formation metabasalt that overlies the rift sediments. The relatively weak dikes facilitated the deformation that led to the formation of the Blue Ridge anticlinorium during the middle to late Paleozoic as the vertical dikes were transposed and rotated during formation of the penetrative cleavage. This field trip generally follows the GSA guide published in GSA Field Guide 57 (available at https://pubs.geoscienceworld.org/gsa ): Burton, W.C., and Schindler, J.S., 2020, Proterozoic and Paleozoic evolution of the Blue Ridge geologic province in northern Virginia, USA, in Swezey, C.S., and Carter, M.W., eds., Geology Field Trips in and around the U.S. Capital: Geological Society of America Field Guide 57, p. 1–19, https://doi.org/10.1130/2020.0057(01) .

ABSTRACT The North American continent has a rich geologic record that preserves evidence for tectonic processes throughout much of Earth’s history. Within this long history, however, particular times—e.g., “turning points”—have had specific and lasting impact on the evolution of Laurentia (ancestral North America). This volume is focused on seven of these “turning points”: (1) The Neoarchean (2.7–2.5 Ga), characterized by cratonization and the Kenoran orogen(s); (2) the Paleoproterozoic (1.9–1.7 Ga) and the initial assembly of Laurentia; (3) the Mesoproterozoic (1.5–1.4 Ga) Andean-style margin on the southern edge of Laurentia with the Pinware-Baraboo-Picuris orogeny; (4) the 1.2–1.0 Ga Midcontinent rift, and the Grenville orogeny and assembly of Rodinia; (5) the 700–500 Ma Neoproterozoic breakup of Rodinia; (6) the mid-Paleozoic (420–340 Ma) closure of the Iapetus and Rheic oceans and the development of the Appalachian-Caledonian orogen; and (7) the Jurassic–Paleogene (200–50 Ma) assembly of the North American Cordilleran margin by terrane accretion and subduction. The assembled chapters provide syntheses of current understanding of the geologic evolution of Laurentia and North America, as well as new hypotheses for testing. The inclusion of work from different geological time periods within a single volume provides continent-wide perspectives on the evolution of tectonic events and processes that acted on and within Laurentia.

The North American continent has a rich record of the tectonic environments and processes that occur throughout much of Earth history. This Memoir focuses on seven “turning points” that had specific and lasting impacts on the evolution of Laurentia: (1) The Neoarchean, characterized by cratonization; (2) the Paleoproterozoic and the initial assembly of Laurentia; (3) the Mesoproterozoic southern margin of Laurentia; (4) the Midcontinent rift and the Grenville orogeny; (5) the Neoproterozoic breakup of Rodinia; (6) the mid-Paleozoic phases of the Appalachian-Caledonian orogen; and (7) the Jurassic–Paleogene assembly of the North American Cordillera. The chapters in this Memoir provide syntheses of current understanding of the geologic evolution of Laurentia and North America, as well as new hypotheses for testing.