Abstract Abstract: The Williams Ranch Member of the upper Cutoff Formation in the Guadalupe and Delaware Mountains, west Texas, U.S.A., consists of six offlapping lithologic units. The deposits formed during carbonate turbidite deposition across a drowned Early Permian carbonate platform. They have an areal extent of more than 20,000 km 2 and reach a maximum thickness of at least 113 m. At the terminal margin of the older platform, the carbonate turbidites were partially redistributed by mass-transport events (MTEs) onto the slope and basin floor. Deposits formed during individual mass-transport events (MTE bodies) comprise the bulk of the Williams Ranch Member basinward from the drowned margin for at least 28 km along a transect oblique to depositional dip. MTE bodies are interbedded with undeformed carbonate turbidites and contain soft-sediment folds, faults, and extensional and shortening lineations, as well as termination surfaces (beds terminated from above and/or below). Turbidite deposition and subsequent mass transport caused general basinward thickening of the Williams Ranch Member from the drowned margin, where the Cutoff Formation is missing, to the basin floor. Deposition responded to, and modified, inherited bathymetric relief. Compared to isopach thins, isopach thicks formed in bathymetric lows and locally formed bathymetric highs. Isopach thicks contain more undeformed strata and show more soft-sediment folds. These relationships suggest better preservation of strata in structurally controlled inherited bathymetric lows. In general, MTE bodies are preferentially deposited in these paleobathymetric lows. A minimum of six vertically stacked MTE bodies are recognized in the main study area with thicknesses ranging from less than one to tens of meters. MTE bodies show a general S-to-SSE paleotransport direction, with significant local variation, reflecting either underlying bathymetric relief and/or different source locations. Repeated MTEs resulted in a reduction of the overall basin gradient and created local positive bathymetry. Sand fairways and ponded sheet deposits in the overlying Brushy Canyon Formation are focused in bathymetric lows, and sands thin and onlap onto bathymetric highs.

Abstract Studies of Quaternary dune fields during pluvial intervals have shown that, given appropriate shifts in climate, eolian sand seas can become verdant landscapes with widespread surface water. The Early Jurassic Navajo Sandstone of the western interior United States, although it appears superficially to have been an immense, arid, active dune sea during the entirety of its depositional history, contains subtle evidence of pluvial episodes. In situ fossil tree stumps, abundant dinosaur tracks, bioturbated strata up to 20 m thick, and large stromatolite-bearing, mass flow-capped interdune deposits bear witness to long-lived pluvial episodes. The Navajo accumulated within the tropics; dunes were swept by cross-equatorial winds in winter and watered by monsoonal rains in summer. Most of the evidence for pluvial conditions occurs around the southern and eastern margins of the Navajo dune sea, in the lower half of the formation.

Abstract The history of fault initiation and reactivation in the southern Rocky Mountains remains highly debated, as does the region’s exhumation history. Nowhere has the evidence been more contested than in the southern Sangre de Cristo Mountains, where major, 30+ km dextral separations of basement rocks and their aeromagnetic anomalies have been attributed to Proterozoic, Ancestral Rocky Mountain and Laramide orogenies. Since the sum of these dextral separations is in the range of 100 km, unambiguous determination of the age(s) of faulting would have major implications to Rocky Mountain tectonics. Likewise, the history of exhumation and stabilization of the western North American craton provides an important example of continental lithospheric evolution. This field trip will start by visiting excellent exposures of spectacularly brecciated yet indurated basement rocks and flanking Paleozoic sedimentary rocks along the Picuris-Pecos fault system, which has 37 km of dextral separation of Proterozoic contacts. Hypotheses for the age(s) of slip will be examined in light of stratigraphic and fault relationships, thin section petrography and isotopic analyses. The region’s history of fault reactivation and associated K-metasomatism will be discussed by combining thermochronology, largely based on new 40Ar/39Ar K-feldspar analyses, with recent seismic data across the Laramide front of the Sangre de Cristo Mountains. The regional tectonic implications of new geologic mapping, fault analyses, 40Ar/39Ar thermochronology and seismic studies will be discussed on the outcrop, with a full examination of all hypotheses.

Abstract Paleogene and Neogene faults and fractures on the eastern edge of the Colorado Plateau are present in Mesaverde Group coal and sandstone beds. Recent observations of coal cleat orientation in relation to faults in coal mines have significant impacts for mine planning in the area. Faults, coal cleats, and natural fractures are interpreted to show a structural evolution of the Mesaverde Group through time. This field trip will include a visit to two active underground coal mines, the Bowie Resources’ Bowie No. 2 Mine, and Mountain Coal’s West Elk Mine. Mine geologists will discuss structural styles including fault orientations and timing, cleat development, and rotation. Geologic encounters ranging from fault flooding, subsidence, mine fires, methane gas problems, and land use restrictions will also be discussed. Coal cleat development and open-mode fractures in adjacent sandstones will be observed on outcrops and compared to underground measurements in coal mines in the Somerset Coal Field, Colorado’s most productive. Coal cleat orientations along a reverse fault in one mine will show rotation in relation to possible Neogene age displacement. This two-day trip begins at the Convention Center in downtown Denver, Colorado. Participants will be transported in vans westbound on Interstate 70 to Glenwood Springs, then south on State Highway 82 to Carbondale, then southwest on State Highway 133 to Somerset, with a lunch stop in Redstone to observe 100-year-old coking coal beehive-shaped ovens. The first afternoon will include a stop at Paonia Reservoir Dam for introductory remarks on the regional fracture development of the Somerset Coal Field and a mine tour at the West Elk Mine, which has encountered warm water flooding in large-scale faults associated with the West Elk Mountain uplift. We will head to Paonia for dinner and overnight. The second day will include a stop at the reclaimed Bowie No. 1 portal to observe fracture patterns on the west side of the coal field and an underground tour of the Bowie No. 2 Mine and possibly the new Bowie No. 3 Mine, where the mine geologist will discuss observations of coal cleat orientation changes in relation to faulting. Recent coalbed methane exploration in the southern Piceance Basin will also be addressed. Then we will drive a four-hour route back to Denver with a quick stop at the Muddy Creek Landslide, a 2.5 mi2 (6.5 km2) active earth flow complex.

Abstract The Cretaceous-Tertiary (K-T) boundary section at the West Bijou Site is remarkable because many of the methods used to constrain the position of a terrestrial K-T boundary have been successfully applied to a local section. These include palynology, magnetostratigraphy, shocked quartz and iridium analysis, vertebrate paleontology, geochronology, and paleobotany. The West Bijou Site K-T boundary records the extinction of the Wodehouseia spinata Assemblage Zone palynoflora (21%), followed immediately by the presence of a fern-spore abundance anomaly (74%) and the subsequent appearance of the P1 palynoflora. This palynological extinction is coincident with the presence of shock-metamorphosed quartz grains (5+ planes of parallel lamellae) and an iridium spike of 619 ± 32 parts per trillion within the 3-cm-thick boundary claystone. The boundary lies within a reversely magnetized interval, recognized as subchron C29r, substantiated by a radiometrically dated tuff 4.5 m below the boundary with an age of 65.73 ± 0.13 Ma. Dinosaur remains attributable to the late Maastrichtian Triceratops Zone were discovered 4 m below the boundary clay, and a partial jaw of a diagnostic Pu1 mammal was discovered 12 m above. Fossil plants are most abundant in the Paleocene and document a low diversity ecosystem recognizable as the southernmost extension of the FUI disaster recovery flora that radiated in North America following the K-T boundary cataclysm.

Abstract Recent geoarchaeological research on the High Plains of northwestern Kansas has yielded new information regarding the location of buried landscapes that may harbor the material record of the earliest humans in the region. Soil-stratigraphic and geomorphic investigations in playas and in the valleys of small, intermittent streams (draws) located high in drainage networks indicate these geomorphic setting were zones of slow sedimentation and episodic soil development during the terminal Pleistocene and early Holocene. Deeply buried paleosols in the draws have yielded Clovis and possibly pre-Clovis cultural deposits, and a landscape/soil-stratigraphic model has been developed to systematically search for additional early sites in buried contexts. This field guide presents results of geoarchaeological investigations at five Paleo-Indian sites in the upper Beaver Creek drainage basin. Also, locations with buried Paleo-Indian landscapes but no recorded sites are described.

Abstract Along a transect across the Front Range from Denver to the Blue River valley near Dillon, the trip explores the geologic framework and Laramide (Late Cretaceous to early Eocene) uplift history of this basement-cored mountain range. Specific items for discussion at various stops are (1) the sedimentary and structural record along the upturned eastern margin of the range, which contains several discontinuous, east-directed reverse faults; (2) the western structural margin of the range, which contains a minimum of 9 km of thrust overhang and is significantly different in structural style from the eastern margin; (3) mid- to late-Tertiary modifications to the western margin of the range from extensional faulting along the northern Rio Grande rift trend; (4) the thermal and uplift history of the range as revealed by apatite fission track analysis; (5) the Proterozoic basement of the range, including the significance of northeast-trending shear zones; and (6) the geologic setting of the Colorado mineral belt, formed during Laramide and mid-Tertiary igneous activity.

Abstract The Central Front Range of the Colorado Rockies is dominated by an early Proterozoic (ca. 1.8–1.7 Ga) metamorphosed volcanic and sedimentary sequence. In terms of plate tectonics, these rocks are interpreted as island arc, backarc, and sedimentary basin-fill units formed during the accretion of Colorado onto the North American craton. Despite good exposures, which we will be able to observe throughout the field trip, and their proximity to a large metropolitan area, these rocks are still not well understood. New research is under way to better understand accretionary processes in this region. The boundaries of the Central Front Range arc sequence are currently undefined. On the east and west, the sequence is terminated by Laramide-age faulting. The Pike’s Peak Batholith obscures the southern boundary, and the northern boundary is problematic. The main units present in the Central Front Range arc sequence are amphibolites, felsic gneisses, calc-silicate gneisses, mica schists and gneisses, iron formations, metagraywackes, quartzites, and metaconglomerates. These units as a whole are often called the “Idaho Springs Formation,” which is no longer considered a valid formation name. The degree of metamorphism is generally upper amphibolite grade, high temperature–low pressure. Anatectic conditions were reached in the felsic gneisses and mica schists over much of the area. This field trip examines these units in an area of slightly lower grade, where the character of the rocks is not masked by complications of anatectic melting.

ABSTRACT Sedimentary rocks, ranging in age from Pennsylvanian to Cretaceous, crop out in the vicinity of the Dakota hogback. The rocks overlie Precambrian igneous and metamorphic rocks. The strata were deformed in late Cretaceous and early Tertiary time and dip to the east. Downcutting occurred in the Tertiary and Quaternary, formed the major canyons, and was interrupted by intervals of alluvial deposition east of the range front. Landslides mantle the east front of the hogback.

Abstract The South Cañon Number 1 Coal Mine fire, in South Canyon west of Glenwood Springs, Colorado, is a subsurface fire of unknown origin, burning since 1910. Subsidence features, gas vents, ash, condensates, and red oxidized shales are surface manifestations of the fire. The likely success of conventional fire-containment methodologies in South Canyon is questionable, although drilling data may eventually suggest a useful control procedure. Drill casings in voids in the D coal seam on the western slope trail are useful for collecting gas samples, monitoring the temperature of subsurface burning, and measuring the concentration of gases such as carbon monoxide and carbon dioxide in the field. Coal fire gas and mineral condensates may contribute to the destruction of floral and faunal habitats and be responsible for a variety of human diseases; hence, the study of coal gas and its condensation products may prove useful in understanding environmental pollution created by coal mine fires. The 2002 Coal Seam Fire, which burned over 12,000 acres and destroyed numerous buildings in and around Glenwood Springs, exemplifies the potential danger an underground coal fire poses for igniting a surface fire.

Abstract This field trip in the vicinity of the Florissant fossil beds includes five stops that examine the Precambrian Cripple Creek Granite and Pikes Peak Granite, and the late Eocene Wall Mountain Tuff, Thirtynine Mile Andesite lahars, and Florissant Formation. The Cripple Creek Granite and Pikes Peak Granite formed in balholilhs ca. 1.46 and 1.08 Ga, respectively. Uplifted during the Laramide Orogeny of the Late Cretaceous and early Tertiary, the Precambrian rocks were exposed along a widespread erosion surface of moderate relief by the late Eocene. The late Eocene volcanic history of the Florissant area is dominated by two separate events: (1) a caldera eruption of a pyroclastic flow that resulted in the emplacement of the Wall Mountain Tuff, a welded tuff dated at 36.73 Ma; and (2) stratovolcanic eruptions of tephra and associated lahars from the Guffey volcanic center of the Thirtynine Mile volcanic field. This volcanic activity from the Guffey volcanic center had a major influence on the development of local landforms and on sedimentation in the Florissant Formation, which was deposited in a fluvial and lacustrine setting and is dated as 34.07 Ma. The Florissant Formation contains a diverse flora and insect fauna consisting of more than 1700 described species. Most of these fossils are preserved as impressions and compressions in a diatomaceous tuffaceous paper shale and as huge petrified trees that were entombed in a lahar deposit.

Abstract A revised lithostratigraphy for Lower Paleozoic strata in New Mexico and west Texas was developed through detailed sedimentological study of the Bliss and Hitt Canyon Formations within a refined temporal framework assembled from precise biostratigraphic (trilobite and conodont) and chemostratigraphic (carbon isotope) data. Member boundaries within the Hitt Canyon now correspond with mappable and essentially isochronous horizons that represent major depositional events that affected sedimentation in basins throughout Laurentian North America. This trip is designed to examine these and other important intervals, such as the extinction horizons at the base and top of the Skullrockian Stage, and to demonstrate the utility of associated faunas and isotopic excursions for correlation within and beyond the region.

Abstract This field trip focuses on the impacts of geologic hazards, natural resources development, and other geologic features on human activity along the mountain front west of the Denver metropolitan area. The trip serves both as a trip for those in the Denver area and as a model of how common, technically oriented field trips can be converted into trips to educate the general public about such impacts. The many consequences of living with geology present questions about how geologic characteristics and processes should be recognized and mitigated. The questions’ answers involve complex economic and political issues that must be answered on an individual or regional basis. The primary job of the geologic community is to educate the public about the impacts and their consequences so that informed public policy decisions can be made.

Abstract This field trip will visit a modern, large-scale underground block cave mining operation at the world-class Urad-Henderson porphyry molybdenum deposits on and beneath Red Mountain, in the historic Dailey-Jones Pass mining districts, Clear Creek County, Colorado. The underground tour summarizes the Henderson deposit geology and the current status of mining operations, and offers the opportunity to examine and collect rock specimens. The surface tour summarizes the regional and local geologic and structural setting of the deposits, and surface features that define and characterize the outer, peripheral parts of the intrusive-hydrothermal system. The mine is located in the northern Colorado Mineral Belt, in the Front Range of the Rocky Mountains, ∼75 km west of Denver. The deposits consist of molybdenite-bearing, quartz vein stockworks at the cupola apices of highly evolved, silica-rich, subalkaline, leucorhyolite/leucogranite porphyry stocks. The system formed over ∼3.0 m.y. between ca. 27 and 30 Ma by at least 23 intrusive events. Emplacement of the Red Mountain intrusive center and a second intrusive center at Woods Mountain may have been controlled by the NNE-trending Berthoud Pass–Vasquez Pass structural zone, a major Laramide-reactivated Precambrian shear/fault zone. A peripheral, 7.5 × 12.0 km, NNE-elongated, elliptical, pervasive chlorite alteration zone contains a well-developed system of radial quartz and base-precious metal veins.