ABSTRACT Hotspots represent the ephemeral introduction of nutrients into an environment, and occur in both the modern and geologic past. The annual deposition of deciduous leaves in temperate forests, tree falls, animal excrement, and vertebrate carcass deposition all result in the pulsed introduction of nutrients to an ecosystem. Hotspots are critical for providing limiting nutrients, including nitrogen and carbon, to be incorporated into soil microbial biomass and plant biomass. For vertebrate ­carcasses, following the release of labile compounds from soft tissues, bones are often left behind, and provide a more recalcitrant reservoir of organic carbon and nitrogen, phosphorus, calcium, and, in some environments, water, for micro- and macro-fauna. Taphonomy—the physical, chemical, and biological processes following plant or animal death—studied in modern systems can be used to interpret hotspot processes operating in the past. East Tennessee is a region where studies of modern and fossil vertebrate hotspots have provided new insights into taphonomy. This guide describes two hotspot localities in east Tennessee—the Miocene-aged Gray Fossil Site in Gray, Tennessee, and the Anthropology Research Facility (“the Body Farm”) at the University of Tennessee, Knoxville, a human decomposition experimental site. The goal of this interdisciplinary field guide is to provide a view of nutrient hotspots from their formation in the modern to their preservation over geologic time.

Geologic structure often controls the location of recharge points, flow paths, velocities, and discharge locations in karst regions such as Morell Cave and its springshed, Bluff City, Tennessee. This study explores groundwater recharge points, velocities, and discharge locations within the Morrell springshed and its associated cave. Two dye tracing experiments were conducted in the spring and fall of 2012 to identify recharge sources, delineate the springshed, and to interpret structural controls for groundwater flow. The experiments confirmed that allogenic recharge from the northern slopes of Holston Mountain enters the karst system through swallets and flows to the northwest following dominant joint trends that transect local folds. When the groundwater reaches Morell Cave, the flow is redirected northeast and parallels a shallow thrust fault, along which Morell Cave has developed, before resurging at Morell Spring. Using a joint-path flow model, groundwater velocities ranged from 0.04–0.007 m/s, which is consistent with typical groundwater velocities in karst systems.

The creation of new outcrops through construction is an important source of field data for geologists, especially in parts of the Appalachians with limited rock exposure. Users of Google Earth for field research often encounter disparities between the digital topography and the current-day Earth's surface, as newly formed outcrops may not be represented in the topography. Such is the case along sections of the I-26 corridor in Unicoi County, northeastern Tennessee. Twenty-four kilometers of U.S. 23 (future I-26) was widened to four lanes from Sams Gap at the North Carolina–Tennessee line to the Nolichucky River near Erwin, Tennessee, in the early 1990s. The series of outcrops created along the corridor provide an exceptional traverse through Grenvillian-age basement and cover strata which contain numerous stacked Alleghanian thrust sheets and shear zones. Near mile marker 44 along I-26, an ~250 m-long and 65 m-high outcrop was formed as part of the early 1990s construction. Google Earth satellite and Street View images show the outcrop, but the digital terrain in Google Earth does not reflect the approximate 150,000 m 3 of rock removed to form this roadcut. To correct for this, terrain modifications were made with Sketch-Up by copying and virtually excavating the landscape. The SketchUp model was then imported into Google Earth to show the outcrop and interstate as it looks today, with the interstate passing uninterrupted through a ridge rather than draping over hilly topography. This technique can be applied to any area in Google Earth where a mismatch exists between real and virtual topography.

New geologic mapping, petrology, and U-Pb geochronology indicate that Mesoproterozoic crust near Mount Rogers consists of felsic to mafic meta-igneous rocks emplaced over 260 m.y. The oldest rocks are compositionally diverse and migmatitic, whereas younger granitoids are porphyritic to porphyroclastic. Cathodoluminescence imaging indicates that zircon from four representative units preserves textural evidence of multiple episodes of growth, including domains of igneous, metamorphic, and inherited origin. Sensitive high-resolution ion microprobe (SHRIMP) trace-element analyses indicate that metamorphic zircon is characterized by lower Th/U, higher Yb/Gd, and lower overall rare earth element (REE) concentrations than igneous zircon. SHRIMP U-Pb isotopic analyses of zircon define three episodes of magmatism: 1327 ± 7 Ma, 1180–1155 Ma, and 1061 ± 5 Ma. Crustal recycling is recorded by inherited igneous cores of 1.33–1.29 Ga age in 1161 ± 7 Ma meta-monzogranite. Overlapping ages of igneous and metamorphic crystallization indicate that plutons of ca. 1170 and 1060 Ma age were emplaced during episodes of regional heating. Local development of hornblende + plagioclase + quartz ± clinopyroxene indicates that prograde metamorphism at 1170–1145 Ma and 1060–1020 Ma reached upper-amphibolite-facies conditions, with temperatures estimated using Ti-in-zircon geothermometry at ~740 ± 40 °C during both episodes. The chemical composition of 1327 ± 7 Ma orthogranofels from migmatite preserves the first evidence of arc-generated rocks in the Blue Ridge, indicating a subduction-related environment that may have been comparable to similar-age systems in inliers of the Northern Appalachians and the Composite Arc belt of Canada. Granitic magmatism at 1180–1155 Ma and ca. 1060 Ma near Mount Rogers was contemporaneous with anorthosite-mangerite-charnockite-granite (AMCG) plutonism in the Northern Appalachian inliers and Canadian Grenville Province. Metamorphism at ca. 1160 and 1060 Ma correlates temporally with the Shawinigan orogeny and Ottawan phase of the Grenvillian orogeny, respectively, suggesting that the Blue Ridge was part of Rodinia dating back to ca. 1180 Ma.

The Burnsville fault juxtaposes Precambrian Laurentian crust and the Ashe metamorphic suite within the Fries thrust sheet of the Blue Ridge thrust complex of western North Carolina. The Burnsville fault and adjacent Ashe metamorphic suite accommodated high strain at amphibolite facies (~700 °C and ~9 kbar) during the Acadian orogeny and then were tilted southeast during Alleghanian thrusting. Deformation resulted in three kilometer-scale structural domains: the Burnsville fault dextral strike-slip domain, the “transitional” domain, and the Otter Knobs domain. Structures recording the finite flattening plane are subparallel; those southeast of the Burnsville fault shear zone are rotated counterclockwise by ~10°–15°, consistent with a component of dextral shear. Across strike into the transitional domain, shear sense indicators become scarce, fabric grades to S > L, and lineations change from subhorizontal to downdip. Across strike into the Otter Knobs domain, lineations grade to moderately southwest-plunging, and the orientation distribution of poles to foliation indicates moderately southwest-plunging folding. The macroscale Otter Knobs fold, a tight-to-isoclinal synform in which the hinge line, associated lineations, and minor fold hinges plunge moderately southwest, is interpreted to represent this structural element. No evidence of oblique or reverse shear is observed. The across-strike changes between these coeval domains are consistent with heterogeneous wrench-dominated (10°–20° from the plate boundary) transpression. Changes across strike from the Otter Knobs domain into the transitional domain record part of the deformation path for a zone with an “effective” convergence angle of 14°–18°, including the rotation of structures recording the maximum incremental stretch.