Abstract Chickies Rock rises abruptly from the east bank of the Susquehanna River at Columbia, Pennsylvania, where it breaks through a ridge held up by massively bedded quartzite. Here in the 1830s, Samuel Haldeman recognized long straight tubes that he later described as Skolithos linearis , penetrating the quartzite. Uncertain about the nature of these cylindrical ‘vermiform or linear’, unbranched ‘stems’, Haldeman first treated them as a subgenus of Fucoides , to which root-like traces were then often assigned. By the time James Hall first illustrated the species in 1847, Haldeman was sure they were burrows of a worm-like animal, as the name he had chosen implied. Since 1960, Donald Wise has developed a detailed analysis of structural deformation of the Chickies Anticline, using the Skolithos burrows as ‘plumb-bobs’ against which Taconic rotation of the rock fabric can be measured. Wise showed that later Alleghanian deformation produced prominent folds with external rotation up to twice as great as that of the rock fabric itself. Now conserved as a county park, Chickies Rock attracts many visitors. Its cliff-top is a superb viewpoint from which to contemplate progressive westward migration of the Appalachian drainage divide, ongoing since the late Jurassic opening of the Atlantic Ocean.

Abstract The Great American Bank, deposited along the Cambro-Ordovician coast of Laurentia, consists of over 3000 m of carbonate deposits. Middle Cambrian Ledger Formation dolomitized ooid shoals and partially dolomitized microbial reefs, exposed in the Magnesita Refractories quarry (York, Pennsylvania), formed on the shelf margin [de Wet, Dickson, Wood, Gaswirth, Frey, 1999 , “A new type of shelf margin deposit: rigid microbial sheets and unconsolidated grainstones riddled with meter-scale cavities,” Sedimentary Geology vol. 128, pp. 13-21; de Wet, Frey, Gaswirth, Mora, Rahnis, Bruno, 2004 , “Origin of meter-scale submarine cavities and herringbone calcite cement in a Cambrian microbial reef, Ledger Formation (USA),” Journal of Sedimentary Research vol. 74, pp. 914-923; de Wet, Hopkins, Rahnis, Murphy, Dvortetsky, 2012 , “High energy shelf margin carbonate facies: microbial sheet reefs, ooid shoals, and intraclast grainstones: Ledger Fm. (Middle Cambrian), Pennsylvania.” In Derby, Fritz, Longacre, Morgan, Sternbach (Editors), The Great American Carbonate Bank: The Geology and Economic Resources of the Cambrian–Ordovician Sauk Megasequence of Laurentia , Memoir 98: American Association of Petroleum Geologists, Tulsa, Oklahoma, p. 245a–251a (extended abstract) and p. 421–450]. This depositional setting meant that Ledger strata were well positioned to be bathed in updip migrating burial fluids during shallow burial. Shallow subsurface fluids precipitated dolomite with different types of textural preservation: fabric retentive (mimetic) and fabric obscuring. Ooid shoals were pervasively dolomitized due to high primary porosity and permeability, but, because adjacent microbial reefs were syndepositionally cemented, they formed local aquitards that funneled porefluids into shoal and grainstone channel deposits. Local to regional faulting, associated with Paleozoic burial, created additional permeable conduits for dolomitizing fluids to infiltrate reef strata. Both fabric retentive and fabric obscuring dolomite types have overlapping geochemical and δ 18 O and δ 13 C signatures, interpreted as representative of a single porefluid origin. The similarity in isotopic and geochemical results between the calcite reef rocks and dolomites suggests that the porewaters were primarily buried marine water, mixed with Mg 2+ enriched porewater associated with diagenetic stabilization of high-Mg calcite to low-Mg calcite. The δ 18 O values provide evidence that diagenetic porewaters re-equilibrated with higher temperature burial fluids, but δ 13 C values and trace elements reflect at least a partial Cambrian seawater signature. Primary fabric preservation is interpreted as a function of the rate of dolomitization rather than different porefluid compositions. Baroque (saddle) dolomite cements precipitated from higher temperature fluids associated with deeper burial. Mesozoic uplift and regional faulting accompanied Pangean rifting, producing a karst Cambrian-Triassic unconformity. Ledger Formation deposits are patchily dedolomitized, forming coarse calcite lenses, typically containing red Triassic sediment. Petrographic and geochemical data (trace elements and stable isotopes) show that the diagenetic fluids responsible for dedolomitization were primarily low temperature meteoric waters associated with karstification.

Abstract The Appalachian Piedmont in south-central Pennsylvania and north-central Maryland contains metasedimentary siliciclastic rocks (phyllites to quartzites) that were deposited largely offshore of Laurentia, prior to and during the early history of the Iapetan Ocean. The Peach Bottom area is centered on the belt of Peach Bottom Slate and overlying Cardiff Quartzite, which is surrounded by the late Neoproterozoic and early Paleozoic rocks of the Peters Creek and Scott Creek (new name) Formations. Their provenance was the Brandywine and Baltimore microcontinents that lay farther offshore of the Laurentian coast. This area also includes an ophiolitic mélange that formed in front of an advancing island arc in Iapetus. All these rocks lay largely undisturbed throughout much of the Paleozoic, experiencing only chlorite-grade greenschist facies metamorphism through deep burial. Alleghanian thrusting associated with the growth of the Tucquan anticline imparted their present widespread, monocline, steep southeast dip of the bed-parallel foliation.

Abstract This field trip explores igneous layering in the Morgantown Sheet, southeastern Pennsylvania, a Jurassic diabase intrusion that is part of the Central Atlantic Magmatic Province, formed during rifting of Pangea. The Pennsylvania Granite Quarry (Stop 1) is a dimension stone quarry in the southern side of the sheet, in which the cut walls display intermittent modal layering crosscut by channels of mafic diabase. Plagioclase-rich layers overlie pyroxene-rich layers in packages with slightly concave-up “wok” shapes ~ 0.3–0.4 m in dimension and ~ 0.35–0.5 m thick. Mafic diabase — both layers and crosscutting channels—contain 15–25 modal percent orthopyroxene phenocrysts and are interpreted as basaltic magma replenishments. Orientations of layering and channels suggest this part of the sheet was originally a horizontal sill ~ 400 m thick, at about six kilometers depth, and that the sheet was tilted 20° – 25° to the north after crystallization. The Dyer aggregate quarry (Stop 2) is in the northeast side of the sheet that dips ~ 80° southeast (Birdsboro dike). Here, rhythmic plagioclase-pyroxene layering also dipping ~ 80° is found in the interior and near the margin of the ~ 255-m-wide dike. Augite and plagioclase compositions are very similar in samples from different vertical heights in the sheet, suggesting localized rather than sheet-wide fractionation. We compare the Morgantown Sheet layering to similar features in the Palisades sill, New Jersey, and Basement sill, Antarctica, and discuss models for their formation.

Storms create stresses on karst systems that can alter the pathways and travel-times of water, solutes, and sediment. Flow contribution during storms is not only a matter of activation of new conduits, but is also a complex combination of water from conduits, enlarged fractures, and fractured matrix. In order to obtain evidence of pathway changes, we sampled three karst springs of varying size and maturity using data loggers for conductivity and water level, and storm water samplers for suspended sediment. The largest spring (Arch Spring) had the lowest conductivity of the three springs, indicating mainly conduit pathways at base flow. The high conductivity of base flow at the Nolte and Bushkill Springs pointed to contributions from slower-moving water in the fractured matrix. During storms, Arch Spring showed a consistent pattern of conductivity with a slight increase, then a large decrease, indicating an initial fracture flush of high-conductivity water, then passage of low-conductivity water from the precipitation. During storms, the conductivity of the middle-sized spring (Nolte Spring) either dropped immediately, or increased sharply then declined as storm water reached the spring. The smallest spring (Bushkill Spring) had a predictable conductivity pattern, with a sharp decrease and gradual recovery, suggesting shorter paths during storms than base flow. Sediment concentrations during storms were lowest at Nolte Spring and higher at Bushkill and Arch Springs, indicative of the fast flow through conduits or enlarged fractures suggested by the latter two springs during storms. The storm-water pathways vary from spring to spring and from storm to storm. These data show the importance of continuous monitoring to understand spring behavior.

Lititz Spring in southeastern Pennsylvania and a nearby domestic well were sampled for 9 months. Although both locations are connected to conduits (as evidenced by a tracer test), most of the year they were saturated with respect to calcite, which is more typical of matrix flow. Geochemical modeling (PHREEQC) was used to explain this apparent paradox and to infer changes in matrix and conduit contribution to flow. The saturation index varied from 0.5 to 0 most of the year, with a few samples in springtime dropping below saturation. The log P co 2 value varied from −2.5 to −1.7. Lower log P co 2 values (closer to the atmospheric value of −3.5) were observed when the solutions were at or above saturation with respect to calcite. In contrast, samples collected in the springtime had high P co 2 , low saturation indices, and high water levels. Geochemical modeling showed that when outgassing occurs from a water with initially high P co 2 , the saturation index of calcite increases. In the Lititz Spring area, the recharge water travels through the soil zone, where it picks up CO 2 from soil gas, and excess CO 2 subsequently is outgassed when this recharge water reaches the conduit. At times of high water level (pipe full), recharge with excess CO 2 enters the system but the outgassing does not occur. Instead the recharge causes dilution, reducing the calcite saturation index. Understanding the temporal and spatial variation in matrix and conduit flow in karst aquifers benefited here by geochemical modeling and calculation of P co 2 values.

Abstract Within the Piedmont Uplands Section of southeastern Pennsylvania lies a metamorphic terrane containing the Peach Bottom Slate. The Peach Bottom Formation has been the center of attention for both quarrymen and geologists for more than 200 years. This probably early Paleozoic unit, underlying “Slate Ridge,” has been mined in Lancaster and York Counties, Pennsylvania, and Harford County, Maryland. The Peach Bottom Slate was judged the best building slate in the world at the 1850 World Exposition in London. Although mining terminated in the 1940s, the effect of the slate on the community and its heritage is well preserved today. The main purpose of the field trip is to examine some of main landmarks of the slate’s cultural effects, including a visit to a Welsh cemetery and a view of the district’s largest quarry. We also will seek an understanding of how the slate industry’s history has been preserved. Some problems of the regional geology also will be addressed. At our first two stops in Chester and Lancaster Counties, we will examine serpentinite within the Baltimore Mafic Complex. Our next stop in Lancaster County is a key exposure showing the relationship between the Peach Bottom Formation and its neighboring rock units. Despite much research on the structural implications of these rocks, the interpretation is still “up in the air.” Your opinions will be very much welcomed.

Abstract Welcome to the Appalachian landscape! Our field trip begins with a journey across Fall Zone (Fig. 1 ), named for the falls and rapids on streams flowing from the consolidated rocks of the Appalachians onto the unconsolidated sediments of the Coastal Plain. The eastern U.S. urban centers are aligned along the Fall Zone, the upstream limit of navigation. Typically, the rocks west of the Fall Zone are part of the Piedmont province. This province exposes the metamorphic core of the Appalachian Mountains exhumed by both tectonics and erosion. At least four major phases of deformation are preserved in Piedmont rocks, three Paleozoic convergent events that closed Iapetus, followed by Mesozoic extension that opened the Atlantic Ocean. A record of Cretaceous to Quaternary exhumation of the Appalachians is preserved as Coastal Plain sediments. Late Triassic and Jurassic erosion is preserved in the syn-extensional fault basins, such as the Newark basin, or is buried beneath Coastal Plain sediments (Fig. 1 ). The trip proceeds northwest across the Fall Zone and Piedmont and into the Newark basin. Late Triassic and Jurassic fluvial red sandstone, lacustrine gray shale, and black basalt were deposited in this basin. The Newark basin is separated from the Blue Ridge by a down to the east normal fault that locally has contemporary microseismicity. The Blue Ridge represents a great thrust sheet that was emplaced from the southeast during the Alleghenian orogeny (Permian). The summits of the Blue Ridge are commonly broad and accordant. Davis (1889) projected that accordance westward to the summits of the Ridge and Valley to define his highest and oldest peneplain—the Schooley peneplain. North and west of the Blue Ridge is the Great Valley Section of the Ridge and Valley Province (Fig. 1 ). Where we cross the Great Valley at Harrisburg, it is called the Cumberland and Lebanon valleys. This section is underlain by lower Paleozoic carbonate, shale, and slate folded and faulted during the lower Paleozoic Taconic orogeny. The prominent ridge on the west flank of the Great Valley is Blue or Kittatinny Ridge. It is the first ridge of the Ridge and Valley Province; the folded and faulted sedimentary rocks of the Appalachian foreland basin, deformed during the Alleghenian orogeny. Drainage during most of the Paleozoic was to the northwest, bringing detritus into the Appalachian foreland basin. The drainage reversed with the opening of the Atlantic Ocean and southeast-flowing streams established courses transverse to the strike of resistant rocks, like the Silurian Tuscarora Sandstone holding up Blue Mountain. West and north of the Ridge and Valley is the Allegheny Plateau, that part of the Appalachian foreland that was only gently deformed during Alleghenian shortening. Our trip will traverse that part of the plateau called the Pocono Plateau which is underlain by Devonian to Penn-sylvanian sandstone. At the conclusion of our trip, we will reverse our transverse of the Appalachians by traveling from the Pocono Plateau to the Ridge and Valley, to the Great Valley, to the Newark Basin, to the Piedmont, and then to one of the great Fall Zone cities—Philadelphia—via the Lehigh and Schuylkill rivers.