Conserving Maine’s Fossil Heritage: The Trout Valley Formation along Wadleigh Mountain Road, Scientific Forest Management Area Report to the Baxter Park Authority 25 December 2014 Paul Dougherty ‘16, Mary Furth ‘15, Zach Hartnett ‘15, Kate Kerin ‘17, Patt Lamom ‘17, Dan Leaman ‘15, Kathy Lipshultz ‘16, Dylan Markey ‘16, Stefan Sandreuter ‘16, Amanda Veth ‘15, and Robert A. Gastaldo1 CORRESPONDING AUTHOR DEPARTMENT OF GEOLOGY COLBY COLLEGE WATERVILLE, ME 04901 INTRODUCTION in Baxter State Park by a USGS geologist, Doug Rankin (Dorf and Rankin, 1962), during field The advent of plant colonization of the mapping in northern Maine. continents during the Devonian Period (419–359 Million years ago) set the stage for The Trout Valley Formation is located revolutionary adaptations that impacted the way unconformably above a volcanic unit, the in which Earth operates, and continue to impact Traveler Mountain Rhyolite, created during the the biosphere, today. The planet’s transition to northwestward migration of the mountain the Middle Devonian, known as the Emsian to building episode known as the Acadian orogeny Eifelian (408-387 Ma), witnessed plants (Bradley et al., 2000). The mountain building undergoing radical evolutionary innovation and event marks the collision of a tectonic plate, the clade biodiversification, resulting in their Avalon terrane, with the North American plate, domination of the continental landscape in during which time a volcanic island chain, or which the animal kingdom followed their lead. magmatic arc, was located to the east of the land Traits evolved in early land plants allowed for mass. This volcanic island was welded onto the increased stabilization of substrates, increased continent during the collision of the tectonic nutrient availability in soils, and became the food plates and ceased to exist, leaving a thick source for terrestrial arthropods and, succession of volcanic and plutonic rocks in subsequently, vertebrate expansion into new Maine. The Traveler Mountain Rhyolite is ecological space (Allen and Gastaldo, 2006). To interpreted to represent volcanic flows associated understand these revolutionary adaptations and with the caldera of one of these earliest Devonian the profound effects they passed onto modern volcanoes (406-407 Ma; Bradley and Tucker, ecosystems, it is essential to study fossil 2002). Erosion of these rocks, along with assemblages from this time interval. One weathering, transport, and deposition of their internationally recognized locality that plays a sediments, resulted in the deposition of the Trout fundamental and critical role in our Valley Formation to the northwest of the Acadian understanding of Middle Devonian ecosystems highlands in a structural syncline. Based on is the Trout Valley Formation (Andrews et al., microfossil (palynological) data, these non-marine 1977, 1985), first recognized along Trout Brook deposits, which now include conglomerate, -1- sandstone, and siltstone, accumulated between material, nor do they have any record of what the late Emsian (Lower Defonian) to early fossils exist here. Eifelian (Middle Devonian; McGregor, 1992), postdating the main phase of mountain building, During construction of Wadleigh Mountain and leaving them southeast of the deformation Road, bedrock was fractured and materials front (Bradley et al., 2000). The environments in pushed to the roadside, exposing surfaces that which these sediments accumulated are eventually will become weathered, if left to the interpreted as ancient soils (paleosols) next to elements, with the accompanying deterioration river systems transporting coarse-and-fine clastic and loss of all fossils. A salvage-rescue collection sediments to a coastline under brackish water of the assemblages unearthed along a portion of influence (estuarine: Selover et al., 2005; Allen Wadleigh Mountain Road was undertaken in and Gastaldo, 2006). It is within these September, 2014, to preserve part of the park’s depositional settings that the fossil assemblages natural history and supplement previously are preserved. published research results. The current report is designed to provide the project results to the The Trout Valley Formation is renowned for its Baxter State Park Authority, which include an Devonian-aged fossils, with Dorf and Rankin assessment of paleobiodiversity (systematic (1962) first recognizing both plants and identification), plant-and-invertebrate taphonomy invertebrates in rocks exposed along Trout (processes responsible for fossil preservation), and Brook (Fig. 1). Earliest representatives of the a paleoenvironmental reconstruction of the area plant group colloquially known as “psilophytes,” in which the fossils were preserved. as well as eurypterids, ostracodes, bivalves, and Representative samples will be sent to the Maine estherids were identified by them. Subsequently, State Museum where they will curated for future the plant fossils became the focus of studies in paleobiology and natural history of the paleobotanical studies from which major plant state, with the remainder of collections housed in groups were identified and the early history of the Department of Geology, Colby College. colonization evaluated (e.g., Andrews et al., 1977, 1985; Kasper et al., 1985; Gensel and MATERIALS AND METHODS Edwards, 1984, 2001). More recent studies centered on developing an understanding of the A general survey of bedrock exposures and plant taphonomic nature of these assemblages roadway metal adjacent to Wadleigh Mountain within the context of their depositional Road (N 46E 08.030', W068E 56.943') was taken environments (Selover et al., 2005; Allen and and fossiliferous sites reconnoitered over a Gastaldo, 2006). Materials that comprise all distance of 1.1 km (0.68 mi), beginning near published studies, to date, originate from rock where Lynx Road joins the roadway in the SFMA exposed either along Trout Brook or its and heading westward (Fig. 1). The survey began tributaries, South Branch, Ponds Brook, and Dry close to the road juncture (BP01/02) and ended Book. In 2004, the Baxter State Park Authority where a thick, unfossiliferous sandstone was developed road extensions in the Scientific encountered (RG 1). In total, thirteen (13) fossil- Forest Management Area (SFMA), one of which bearing localities were identified and named, runs parallel to Trout Brook. At that time, new along with their GPS coordinates, from which fossiliferous rock was exposed during bulldozing 161 fossiliferous hand samples were recovered. of Wadleigh Mountain Road but, to date, the Where possible, new bedding surfaces were Park had not commissioned a survey of the exposed using standard field techniques to search for unweathered specimens. Basic lithologic -2- The primary publications to which specimens were compared include: Andrews et al. (1977), Kasper et al., (1985), and Allen and Gastaldo (2006) for paleobotany; Tasch (1980), RASNY (1998), and Selover et al. (2005) for the macroinvertebrates; and Miller (1991), Seilacher (2007), and Olivero and Gaillard (2007) for trace fossils. Exploratory R- and Q-mode cluster analyses were undertaken to determine relationships amongst Figure 1– General locality maps of study site. (A) State of the fossil assemblages. Randomized data input for Maine with star designating the approximate position of Trout Brook Crossing. (B) Thirteen sampling sites along Wadleigh clustering applied the Sorensen’s binary–presence Mountain Road in the Scientific Forest Management Area. or absence–coefficients using UPGMA (Unweighted Pair Group Method with features were identified in the field, including Arithmetic Mean). Dendrograms illustrating grain size and color, and the presence or absence results for both assemblages (Q-mode) and of primary structures (e.g., ripples, cross beds, variables (R-mode), along with the original data fining up intervals) noted for each site. Hand set, were constructed. Cluster results were plotted samples were numbered (locality plus sample on a base map to determine if any trends existed number designation), wrapped and boxed, and in the collections. transported to Colby College for further analysis and systematic identification. All fossil-bearing RESULTS and non-fossil-bearing samples are property of Baxter State Park, and their removal was under The Trout Valley Formation consists of the supervision of Mrs. Jean Hoekwater, Park conglomerate, sandstone, and siltstone that were Naturalist, and with the permission of Jensen subjected to low grade metamorphism (Allen and Bissell, Park Director. Gastaldo, 2006). Silty sandstone, sandy siltstone, and siltstone–the finest grain sizes amongst the Lithologic and taphonomic features of site- rock types– are more likely to host fossil material specific fossil assemblages, and systematics of than the coarser-grained sandstone and plants, invertebrates, and ichnofossils (trace conglomerate. Therefore, these lithologies were fossils) in hand samples were recorded in an examined along the roadway and found to be Excel database. Teams of two coauthors were fossiliferous. responsible for acquiring the following data sets: plant taphonomy (Lipshultz and Furth), Lithologies paleobotany (Dougherty and Veth), invertebrate taphonomy (Hartnett and Leaman), invertebrate Lithic Wacke Facies: A single sandstone facies is paleontology (Lamom and Kerin), and ichnology exposed at RG1 (Fig. 1) near the base of the (Markey and Sandreuter). Morphological section. It is a comprised of medium–coarse, characters useful in the classification to