Abstract Fossil trackways in the Jura-Triassic rift basin of the Connecticut River Valley are important to geoheritage for their quality, preservation, and role in the history of geology, especially of ichnology. Discovered in the early 1800s, these trackways of small to large, bipedal, three-toed animals came to the attention of Edward Hitchcock, a prolific geologist and natural theologian. His first publication on the subject was in January 1836 and, in the same year, William Buckland included parts of the report, with illustrations, in his Bridgewater Treatise. Hitchcock and Buckland are credited with establishing the field of ichnology, the study of track and trails. Within the first decade, other traces documented include four-footed tracks, fish fossils, invertebrate burrows, plant impressions, ripple marks and raindrop impressions; few bones have ever been discovered in the valley. Early fossil-track collectors included Hitchcock, James Deane, Dexter Marsh and Roswell Field. Specimens quickly made their way to Europe, and publications brought the tracks to international attention, in both science and literature. In nineteenth-century discussions, the three-toed trackway makers – birds or dinosaurs? – were particular subjects of interest and debate. These fossil trackways remain well known and studied today, with several preserved field sites and museum collections.

Abstract Geoparks and the valorization of sites with a strong geoheritage component is a new frontier for sustainable tourism. A UNESCO special recognition was established in 2015, and much work has been undertaken in establishing sites in Europe and Asia, yet only five localities have been recognized by UNESCO in North America. This paper discusses three sites relevant to geoheritage – Pulpit Rock in Massachusetts, Montmorency Falls in Quebec and Niagara Falls in New York and Ontario – which were visited in 1863 by the newly appointed professor of geology at Bologna University, Giovanni Capellini. During his four-month journey across northeastern North America, he made sketches, took notes and collected more than 2000 specimens that together provide a depth of perspective on the importance of the geoheritage of the sites he visited. We chose these sites, among the many visited by Capellini, because Niagara Falls is now seeking UNESCO recognition, and the other two, though no longer fully accessible, remain important tourist sites and areas of geological interest.

ABSTRACT The Avalon terrane of southeastern New England is a composite terrane in which various crustal blocks may have different origins and/or tectonic histories. The northern part (west and north of Boston, Massachusetts) correlates well with Avalonian terranes in Newfoundland, Nova Scotia, and New Brunswick, Canada, based on rock types and ages, U-Pb detrital zircon signatures of metasedimentary rocks, and Sm-Nd isotope geochemistry data. In the south, fewer data exist, in part because of poorer rock exposure, and the origins and histories of the rocks are less well constrained. We conducted U-Pb laser ablation–inductively coupled plasma–mass spectrometry analysis on zircon from seven metasedimentary rock samples from multiple previously interpreted subterranes in order to constrain their origins. Two samples of Neoproterozoic Plainfield Formation quartzite from the previously interpreted Hope Valley subterrane in the southwestern part of the southeastern New England Avalon terrane and two from the Neoproterozoic Blackstone Group quartzite from the adjacent Esmond-Dedham subterrane to the east have Tonian youngest detrital zircon age populations. One sample of Cambrian North Attleboro Formation quartzite of the Esmond-Dedham subterrane yielded an Ediacaran youngest detrital zircon age population. Detrital zircon populations of all five samples include abundant Mesoproterozoic zircon and smaller Paleoproterozoic and Archean populations, and are similar to those of the northern part of the southeastern New England Avalon terrane and the Avalonian terranes in Canada. These are interpreted as having a Baltican/Amazonian affinity based primarily on published U-Pb and Lu-Hf detrital zircon data. Based on U-Pb detrital zircon data, there is no significant difference between the Hope Valley and Esmond-Dedham subterranes. Detrital zircon of two samples of the Price Neck and Newport Neck formations of the Neoproterozoic Newport Group in southern Rhode Island is characterized by large ca. 647–643 and ca. 745–733 Ma age populations and minor zircon up to ca. 3.1 Ga. This signature is most consistent with a northwest African affinity. The Newport Group may thus represent a subterrane, terrane, or other crustal block with a different origin and history than the southeastern New England Avalon terrane to the northwest. The boundary of this Newport Block may be restricted to the boundaries of the Newport Group, or it may extend as far north as Weymouth, Massachusetts, as far northwest as (but not including) the North Attleboro Formation quartzite and associated rocks in North Attleboro, Massachusetts, and as far west as Warwick, Rhode Island, where eastern exposures of the Blackstone Group quartzite exist. The Newport Block may have amalgamated with the Amazonian/Baltican part of the Avalon terrane prior to mid-Paleozoic amalgamation with Laurentia, or it may have arrived as a separate terrane after accretion of the Avalon terrane. Alternatively, it may have arrived during the formation of Pangea and been stranded after the breakup of Pangea, as has been proposed previously for rocks of the Georges Bank in offshore Massachusetts. If the latter is correct, then the boundary between the Newport Block and the southeastern New England Avalon terrane is the Pangean suture zone.

ABSTRACT Southeastern New England is largely composed of Ediacaran granitoid and related volcanic rocks formed during the main phase of arc-related magmatism recorded in West Avalonian lithotectonic assemblages extending through Atlantic Canada to eastern Newfoundland. In situ Lu-Hf analyses presented here for zircons from the Dedham, Milford, and Esmond Granites and from the Lynn-Mattapan volcanic complex show a restricted range of εHf values (+2 to +5) and associated Hf- T DM model ages of 1.3–0.9 Ga, assuming felsic crustal sources. The most evolved granites within this suite lie in a belt north and west of the Boston Basin, whereas upfaulted granites on the south, as well as the slightly younger volcanic units, show more juvenile Hf isotopic compositions. Similar inferences have been drawn from previously published Sm-Nd isotopic signatures for several of the same plutons. Collectively, the isotopic compositions and high-precision U-Pb geochronological constraints now available for southeastern New England differ in important respects from patterns in the Mira terrane of Cape Breton Island or the Newfoundland Avalon zone, but they closely resemble those documented in the Cobequid and Antigonish Highlands of mainland Nova Scotia and New Brunswick’s Caledonia terrane. Particularly significant features are similarities between the younger than 912 Ma Westboro Formation in New England and the younger than 945 Ma Gamble Brook Formation in the Cobequid Highlands, both of which yield detrital zircon age spectra consistent with sources on the Timanide margin of Baltica. This relationship provides the starting point for a recent model in which episodic West Avalonian arc magmatism began along the Tonian margin of Baltica and terminated during diachronous late Ediacaran arc-arc collision with the Ganderian margin of Gondwana.

ABSTRACT We present a tectonic model for the generation of quartzofeldspathic veins and pegmatite dikes found in southern New England that proposes the following: (1) Hydraulic fracturing produces the initial fracture that opens to become a vein, and (2) oscillating differential stress produces a gradient in interstitial fluid pressure that draws the melt to the dilating walls of the fracture. Oscillating fluid pressures at the dike walls lead to oscillating rates of crystallization, and thus to alternating aplitic and pegmatitic textures in dikes as thin as a few centimeters. Excess alkalis and SiO 2 (aq) lower the solidus temperature of the granitic liquid and thus stabilize a peralkaline silicate liquid without crystallization. This silicate liquid is capable of crystallizing only quartz, only feldspars, or both. Crystallization of this liquid lowers its pH and accounts for the mineralogical zoning consisting of quartz cores, feldspathic mantles, and muscovite-bearing margins common in many quartzofeldspathic veins.

ABSTRACT Dinosaur tracks have been illustrated since they were first found. The earliest illustrations depicted dinosaur tracks as the work of mythical beings. With the advent of scientific inquiry into dinosaur tracks in the nineteenth century, natural explanations were sought for the fossil tracks. Illustrations of the period were relatively realistic but were influenced by then-current beliefs and were constrained by the artists’ skills and by what scientists considered salient. In the mid-nineteenth century, the first photographs were used for the scientific study of fossil tracks. Photography eliminated some limitations of artistic talent and showed complete specimens, not just aspects that were deemed salient. The ability to compare and name similar tracks from disparate authors and places became easier. Advances in photography, laser scanning, optical scanning and lidar, and the ability to manipulate images with computers, have enabled the modern synthesis of illustrating dinosaur tracks, which combines many types of images. With each advance and the adoption of newer technologies, the older methods have not been retired. Rather, we have continued to see new uses for old methods and an integration of illustrative styles. For Patrick. Your friendship and your vision will be so deeply missed.

The 2021 GSA Northeastern, Southeastern, joint North-Central/South-Central, and Cordilleran Section Meet-ings were held virtually in spring 2021 during continued restrictions on travel and large gatherings due to COVID-19. Eleven groups put together field guides, taking participants on treks to states from Connecticut to Nevada in the United States, to Mexico, and to Italy, and covering topics as varied as bedrock geologic map-ping, geochemistry, paleodrainage, barrier islands, karst, spring systems, a southern Appalachian transect, Ordo-vician and Mississippian stratigraphy, high-energy events, Cretaceous arc granites and dextral shear zones, and Mesoproterozoic igneous rocks. This volume serves as a valuable resource for those wishing to discover, learn more about, and travel through these geologically fascinating areas.