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At least 55 records · Page 3Linked to original sources
USGS1982

Sedimentology and stratigraphy of the Kanayut Conglomerate, central Brooks Range, Alaska: Report of 1980 field season

The Upper Devonian Kanayut Conglomerate crops out along the crest of the Brooks Range of northern Alaska for a distance of almost 1000 km. It ranges in thickness from 2600 m in the Atigun River area to 700 m south of Anaktuvuk Pass and has been subdivided into four regionally persistent members: (a) the basal sandstone member, consisting of marine sandstone and shale with some conglomerate; (b) the lower shale member, consisting of nonmarine quartzite, conglomerate and shale; (c) the middle conglomerate member, consisting of nonmarine pebble and cobble conglomerate and quartzite; and (d) the Stuver Member, consisting of nonmarine sandstone and shale. The Kanayut conformably overlies the Upper Devonian marine Hunt Fork Shale and is conformably overlain by the Mississippian marine Kayak Shale. The Kanayut is wholly allochthonous and has probably been transported northward on a series of thrust plates. The basal sandstone member of the Kanayut Conglomerate, which overlies prodelta turbidites of the Hunt Fork Shale, contains marginal-marine coarsening-upward channel-mouth bar sequences. It is conformably overlain by the lower shale member. Measured sections of the nonmarine members of the Kanayut show that the lower shale member ranges in thickness from 120 m to 1115 m and consists of fining-upward cycles interpreted to have been deposited by meandering streams on a broad floodplain. These cycles contain, in ascending order, channelized basal conglomerate, trough cross-stratified sandstone, and ripple-marked siltstone. The cycles are interpreted to be channel and point-bar deposits. Individual cycles average about 10 m in thickness and are separated by intervals of black, brown or maroon floodplain shale deposits. These typically contain thin coarsening-upward units that probably represent prograding levee sequences and irregular and ungraded sandstone bodies interpreted to be crevasse-splay deposits. In the Okokmilaga River area, the lower shale member contains a distinctive coarse-grained unit which is burrowed and interpreted to represent a widespread marine incursion. The middle conglomerate member, which ranges in thickness from 155 m to 525 m, consists of braidplain deposits. It contains fining-upward couplets of conglomerate and parallel-stratified or cross-stratified sandstone that average 2-7 m in thickness. The couplets record deposition in channels and on bars of braided streams. The middle conglomerate member contains the largest clasts, little or no shale, and represents the maximum progradation of nonmarine sedimentation in the Kanayut depositional system. The Stuver Member consists of fining-upward cycles that resemble those of the lower shale member. It ranges in thickness from 160 m to 1400 m and grades upward into tidal and marginal-marine deposits of the Kayak Shale. Conglomerate in the Kanayut is compositionally very mature, averaging 82 percent white, gray, black or red chert clasts, 14 percent vein quartz clasts, 3 percent quartzite clasts, and less than I percent other lithologies, mainly argillite. Although red chert is locally abundant in the Shainin Lake-Galbraith Lake area, there is little variation in conglomerate composition in the Kanayut, suggesting derivation from a single major source terrane.

Alaska↗
USGS2026

Constraining sources of mid-Pleistocene to present explosive volcanism in the Gulf of Alaska using machine learning and compositional data analysis

The long-term eruptive record of a region helps better elucidate magmatic processes at depth as well as volcanic hazards at the surface. Typically, reconstructing such records is done using proximal tephrostratigraphy and linking individual tephras to source volcanoes. These records, however, can only be accurately constructed if they are both well preserved and correctly linked to source volcanoes—not a trivial task, especially in areas such as Alaska that have experienced numerous glaciation events since the Pleistocene. This ultimately necessitates another way of assessing the long-term volcanic record such that these histories may be better discerned. Here we present data from 70 marine core tephras from the Gulf of Alaska, which have a virtually uninterrupted depositional record going back through the mid-Pleistocene. We utilize compositional data analysis techniques to quantify 37 eruptions over the span of eight cores, machine learning classification and conformal prediction algorithms to assign the most probable volcanic source(s) to each eruption, and multivariate distance-based metrics when machine learning classification algorithms are inappropriate. We find that the Mount Katmai magmatic system is the most probable volcanic source for analyzed tephras and that large volcanic centers such as Mount Katmai, Fisher Caldera, and Emmons Lake volcanic center have produced nearly invariant incompatible trace element ratio magmas, allowing for them to be confidently identified in long-term tephra records. This highlights the utility of trace elements for tephra studies, especially when paired with compositional data analysis, multivariate statistical tests, and petrologically informed discriminants.

Alaska↗
USGS2008

Late Devonian glacial deposits from the eastern United States signal an end of the mid-Paleozoic warm period

A Late Devonian polymictic diamictite extends for more than 400 km from northeastern Pennsylvania across western Maryland and into east-central West Virginia. The matrix-supported, unbedded, locally sheared diamictite contains subangular to rounded clasts up to 2 m in diameter. The mostly rounded clasts are both locally derived and exotic; some exhibit striations, faceting, and polish. The diamictite commonly is overlain by laminated siltstone/mudstone facies associations (laminites). The laminites contain isolated clasts ranging in size from sand and pebbles to boulders, some of which are striated. The diamictite/laminite sequence is capped by massive, coarse-grained, pebbly sandstone that is trough cross-bedded. A stratigraphic change from red, calcic paleo-Vertisols in strata below the diamictite to non-calcic paleo-Spodosols and coal beds at and above the diamictite interval suggests that the climate became much wetter during deposition of the diamictite. The diamictite deposit is contemporaneous with regressive facies that reflect fluvial incision during the Late Devonian of the Appalachian basin. These deposits record a Late Devonian episode of climatic cooling so extreme that it produced glaciation in the Appalachian basin. Evidence for this episode of climatic cooling is preserved as the interpreted glacial deposits of diamictite, overlain by glaciolacustrine varves containing dropstones, and capped by sandstone interpreted as braided stream outwash. The Appalachian glacigenic deposits are contemporaneous with glacial deposits in South America, and suggest that Late Devonian climatic cooling was global. This period of dramatic global cooling may represent the end of the mid-Paleozoic warm interval that began in the Middle Silurian.

Pennsylvania, Maryland, West Virginia↗
USGS2018

Geologic field-trip guide of volcaniclastic sediments from snow- and ice-capped volcanoes—Mount St. Helens, Washington, and Mount Hood, Oregon

This field guide for the International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI) Scientific Assembly 2017 focuses on volcaniclastic sediments from Mount St. Helens in Washington and Mount Hood in Oregon. The trip spends four days in the field and includes nine stops at each volcano. For completeness, this guidebook also includes sixteen optional stops in the Mount St. Helens area and three in the Mount Hood area. These two volcanoes provide excellent depositional records of the broad spectrum of volcanic hazards that involve the flow or fall of volcaniclastic particles. At the field-trip stops we will contrast and compare the different types of deposits—sediments that can be frustratingly difficult to distinguish from one another. Correct identification of deposit origin leads to a better understanding of hazards that can impact vulnerable communities at particular volcanoes. During this four-day field trip, we will spend two days in the Mount St. Helens area and two days near Mount Hood. On the first day, we will visit debris-avalanche and lahar deposits in the Toutle River valley in Washington. The second day will focus on pyroclastic density current, pyroclastic-fall, lahar, and volcano-fluvial deposits in the Lewis River drainage system near Mount St. Helens. On the third day, we will visit hyaloclastites, glacial tills, and other diamicts in the Hood River and Sandy River basins near Mount Hood. The fourth and final day will focus on distal lahar and volcano-fluvial deposits downstream of Mount Hood. What follows is an in-depth introduction to the deposits studied on this field trip. We provide criteria that are observable in the field to aid in differentiating between pyroclastic density current, pyroclastic-fall, debris-avalanche, lahar, water-flood, and glacial deposits. We also introduce the Holocene eruptive histories of Mount St. Helens and Mount Hood and discuss the processes responsible for deposit emplacement. Field-trip stops and features of interest along the route are described in detail in a road log that provides daily cumulative mileage.

Oregon, Washington↗
USGS1979

Quaternary crustal deformation along a major branch of the San Andreas fault in central California

Deformed marine terraces and alluvial deposits record Quaternary crustal deformation along segments of a major, seismically active branch of the San Andreas fault which extends 190 km SSE roughly parallel to the California coastline from Bolinas Lagoon to the Point Sur area. Most of this complex fault zone lies offshore (mapped by others using acoustical techniques), but a 4-km segment (Seal Cove fault) near Half Moon Bay and a 26-km segment (San Gregorio fault) between San Gregorio and Point Ano Nuevo lie onshore. At Half Moon Bay, right-lateral slip and N—S horizontal compression are expressed by a broad, synclinal warp in the first (lowest: 125 ka?) and second marine terraces on the NE side of the Seal Cove fault. This structure plunges to the west at an oblique angle into the fault plane. Linear, joint0controlled stream courses draining the coastal uplands are deflected toward the topographic depression along the synclinal axis where they emerge from the hills to cross the lowest terrace. Streams crossing the downwarped part of this terrace adjacent to Half Moon Bay are depositing alluvial fans, whereas streams crossing the uplifted southern limb of the syncline southwest of the bay are deeply incised. Minimum crustal shortening across this syncline parallel to the fault is 0.7% over the past 125 ka, based on deformation of the shoreline angle of the first terrace. Between San Gregorio and Point Ano Nuevo the entire fault zone is 2.5–3.0 km wide and has three primary traces or zones of faulting consisting of numerous en-echelon and anastomozing secondary fault traces. Lateral discontinuities and variable deformation of well-preserved marine terrace sequences help define major structural blocks and document differential motions in this area and south to Santa Cruz. Vertical displacement occurs on all of the fault traces, but is small compared to horizontal displacement. Some blocks within the fault zone are intensely faulted and steeply tilted. One major block 0.8 km wide east of Point Ano Nuevo is downdropped as much as 20 m between two primary traces to form a graben presently filling with Holocene deposits. Where exposed in the sea cliff, these deposits are folded into a vertical attitude adjacent to the fault plane forming the south-west margin of the graben. Near Point Ano Nuevo sedimentary deposits and fault rubble beneath a secondary high-angle reverse fault record three and possibly six distinct offset events in the past 125 ka. The three primary fault traces offset in a right-lateral sense the shoreline angles of the two lowest terraces east of Point Ano Nuevo. The rates of displacement on the three traces are similar. The average rate of horizontal offset across the entire zone is between 0.63 and 1.30 cm/yr, based on an amino-acid age estimate of 125 ka for the first terrace, and a reasonable guess of 200–400 ka for the second terrace. Rates of this magnitude make up a significant part of the deficit between long-term relative plate motions (estimated by others to be about 6 cm/yr) and present displacement rates along other parts of the San Andreas fault system (about 3.2 cm/yr). Northwestward tilt and convergence of six marine terraces northeast of Ano Nuevo (southwest side of the fault zone) indicate continuous gentle warping associated with right-lateral displacement since early or middle Pleistocene time. Minimum local crustal shortening of this block parallel to the fault is 0.2% based on tilt of the highest terrace. Five major, evenly spaced terraces southeast of Ano Nuevo on the southwest flank of Mt. Ben Lomond (northeast side of the fault zone) rise to an elevation of 240 m, indicating relatively constant uplift (about 0.19 m/ka and southwestward tilt since Early or Middle Pleistocene time (Bradley and Griggs, 1976).

California↗
USGS2009

Processes that initiate turbidity currents and their influence on turbidites: A marine geology perspective

How the processes that initiate turbidity currents influence turbidite deposition is poorly understood, and many discussions in the literature rely on concepts that are overly simplistic. Marine geological studies provide information on the initiation and flow path of turbidity currents, including their response to gradient. In case studies of late Quaternary turbidites on the eastern Canadian and western U.S. margins, initiation processes are inferred either from real-time data for historical flows or indirectly from the age and contemporary paleogeography, erosional features, and depositional record. Three major types of initiation process are recognized: transformation of failed sediment, hyperpycnal flow from rivers or ice margins, and resuspension of sediment near the shelf edge by oceanographic processes. Many high-concentration flows result from hyperpycnal supply of hyperconcentrated bedload, or liquefaction failure of coarse-grained sediment, and most tend to deposit in slope conduits and on gradients < 0.5° at the base of slope and on the mid fan. Highly turbulent flows, from transformation of retrogressive failures and from ignitive flows that are triggered by oceanographic processes, tend to cannibalize these more proximal sediments and redeposit them on lower gradients on the basin plain. Such conduit flushing provides most of the sediment in large turbidites. Initiation mechanism exerts a strong control on the duration of turbidity flows. In most basins, there is a complex feedback between different types of turbidity-current initiation, the transformation of the flows, and the associated slope morphology. As a result, there is no simple relationship between initiating process and type of deposit.

Journal of Sedimentary Research↗
USGS2011

Utah's geologic and geomorphic analogs to Mars—An overview for planetary exploration

Utah offers spectacular geologic features and valuable analog environments and processes for Mars studies. Horizontal strata of the Colorado Plateau are analogous to Mars because the overprint of plate tectonics is minimal, yet the effects of strong ground motion from earthquakes or impacts are preserved in the sedimentary record. The close proximity of analog environments and lack of vegetative cover are advantages for field and remote-sensing studies. Dry, desert climate and modern wind processes of Utah are comparable to Mars and its current surface. Analogs in Utah include eolian, sabkha and saline bodies, glacial, lacustrine, spring, alluvial, fluvial, delta, and outflow channel depositional environments, as well as volcanic landforms and impact craters. Analogous secondary processes producing modification features include: diagenetic concretions, weathering and soils, sinkholes, sapping, knobs and pinnacles, crusts and varnish, and patterned grounds. Utah's physical and chemical environments are analogous to conditions on Mars where water existed and could support microorganisms. The development of Mars includes: ancient and modern depositional records, burial and diagenesis, uplift and tectonic alteration, and modern sculpting or weathering of the surface exposures. Recent satellite images are providing unprecedented details that rival the outcrop scale. Analogs in Utah are prime field localities that can be utilized in planning future robotic and human missions to Mars, and for teaching the next generation of planetary explorers.

Utah↗
USGS2017

Stratigraphic Context of Old Crow Tephra, Holitna Lowland, Interior Southwest Alaska

A thick deposit of Old Crow tephra was discovered in a bluff exposure along the middle Holitna River near the Kulukbuk Hills (61??20???N latitude, 157??10???W longitude) in interior southwest Alaska. This locality is the southwesternmost-known deposit of Old Crow tephra in Alaska. Thickness and grain-size data from this site support a source volcano in the eastern Aleutian arc. Pleistocene stratigraphic sequences in the lowland are dominated by upward-fining eolian sand-sheet deposits and loess separated by organic silt. These deposits record at least two episodes of regional glaciation and an intervening nonglacial period (marine oxygen isotope stage 3, stage 5, or both). Old Crow tephra crops out near the top of the lower upward-fining eolian unit, indicating that the ash erupted near the end of an interval of periglacial eolian sedimentation. The sequence of eolian deposits that contain Old Crow tephra probably accumulated during the latter part of marine oxygen isotope stage 6, whereas the overlying eolian sequence formed during the last glaciation (stage 2). This stratigraphic position is consistent with other stratigraphic contexts for the tephra and with fission-track and thermoluminescence ages of ca. 140,000 ?? 10,000 yr B.P.

Quaternary Research↗
USGS2016

The Elizabeth Lake paleoseismic site: Rupture pattern constraints for the past ~800 years for the Mojave section of the south-central San Andreas Fault

The southern San Andreas Fault in California has hosted two historic surface-rupturing earthquakes, the ~M7 1812 Wrightwood earthquake and the ~M7.9 1857 Fort Tejon earthquake (e.g., Sieh, 1978; Jacoby et al., 1988). Numerous paleoseismic studies have established chronologies of historic and prehistoric earthquakes at sites along the full length of the 1857 rupture (e.g., Sieh, 1978; Scharer et al., 2014). These studies provide an unparalleled opportunity to examine patterns of recent ruptures; however, at least two significant spatial gaps in high-quality paleoseismic sites remain. At ~100 km long each, these gaps contribute up to 100 km of uncertainty to paleo-rupture lengths and could also permit a surface rupture from an earthquake up to ~M7.2 to go undetected [using scaling relationships of Wells and Coppersmith (1994)]. Given the known occurrence of an ~M7 earthquake on this portion of the SAF (1812), it is critical to fill these gaps in order to better constrain paleo-rupture lengths and to increase the probability of capturing the full spatial record of surface rupturing earthquakes. In this study, we target a new site within the 100 km long stretch of the San Andreas Fault between the Frazier Mountain and Pallett Creek paleoseismic sites (Figure 1), near Elizabeth Lake, California. Prior excavations at the site during 1998-1999 encountered promising stratigraphy but these studies were hindered by shallow groundwater throughout the site. We began our current phase of investigations in 2012, targeting the northwestern end of a 40 x 350 m fault-parallel depression that defines the site (Figure 2). Subsequent investigations in 2013 and 2014 focused on the southeastern end of the depression where the fault trace is constrained between topographic highs and is proximal to an active drainage. In total, our paleoseismic investigations consist of 10 fault-perpendicular trenches that cross the depression (Figure 2) and expose a >2000 year depositional record. These trenches reveal that the thickest section of young stratigraphy occurs at the southeastern end of the site where the fault zone projects through an area of relatively continuous sediment accumulation from a northeast-flowing drainage. This portion of the site contains a 3-m-wide pop-up structure within the fault zone that separates alternating alluvial and paludal deposits south of the fault zone from a thick organic-rich loam on the north side of the fault zone. Faults, fissures, and tilted blocks provide evidence for 4 to 5 paleoearthquakes since ca. 1250 A.D. Radiocarbon dating established that the site has a significant component of detrital charcoal producing an age spread of up to 500 years. To supplement our age chronology we incorporated ages from collections of micro-scale organic fractions and post-IR infrared stimulated luminescence dating in order to better estimate true layer ages.

Conference Paper↗
USGS2025

Hydrogeomorphic history, hydrodynamic conditions, and simulations of water levels and velocities from varying lake levels and streamflow for the Sheboygan Rivermouth and area of concern, Wisconsin

In 2011–13, the U.S. Geological Survey (USGS) conducted a study of the hydrogeomorphic setting and hydrodynamic conditions of the lower Sheboygan River and island complex within the backwater zone of Lake Michigan. Analyses of historical aerial photographs from 1938–2010 indicated that the Wildwood Islands complex had experienced mainly erosion and what was mainly one island in 1938 had eroded into about ten smaller islands and bars by 2010. Water levels, velocity and sedimentation patterns in the Sheboygan River mouth are affected by Lake Michigan water levels and seiche-related flow reversals for a potential river length of over 7 km. During the summer of 2012, when water levels in Lake Michigan were below the low water datum, seiche-related water-level fluctuations had a general range of 0.2 m and extended to just upstream of the Wildwood Islands complex, with greater variability in amplitude and frequency in the spring and fall months than in the summer. The low water level associated with the trough of a 60-90-minute seiche-related oscillation was sometimes 0.6 m lower than the low water datum. Runoff events produced river water levels during spring melt or storms that were 0.6 m above coincident Lake Michigan water levels. Frequent ice jams in the winter and early spring of 2012-13 raised river water levels to near the Lake Michigan ordinary high-water mark even though Lake Michigan water levels were at near record lows. Results from trends analyses from 1916 through 2008 indicated average annual streamflow and low flows were increasing in the Sheboygan River, but floods with an annual exceedance probability of 1 percent did not change. Simulations of a range of combinations of Lake Michigan water levels with river flows indicated that a variety of velocity patterns and water levels are possible near the Wildwood Islands complex. Simulated velocities ranged from 0 m/s during high lake levels and small river flows to 2 m/s during high lake levels and floods with an annual exceedance probability of 0.01. Silt deposition recorded in sediment cores matched locations of flow divergence in the model simulations. Time lapse photography confirmed flow reversals in the vicinity of the Wildwood Islands complex from frequent seiche oscillations. The study illustrates the large range in variability in water levels and velocities over short periods of time, and that the lake-effect zone can be greatly extended upstream during high lake levels for low-gradient rivermouth environments.

Wisconsin↗
USGS2017

Influence of the Eastern California Shear Zone on deposition of the Mio-Pliocene Bouse Formation: Insights from the Cibola area, Arizona

The Eastern California Shear Zone (ECSZ) is a wide zone of late Cenozoic strike-slip faults and related diffuse deformation that currently accommodates ~20–25% of relative Pacific–North America plate motion in the lower Colorado River region (Fig. 1A; Dokka and Travis, 1990; Miller et al., 2001; Guest et al., 2007; Mahan et al., 2009). The ECSZ is kinematically linked southward to dextral faults in the northern Gulf of California (Bennett et al., 2016a), and it may have initiated ca. 8 Ma when major strike-slip faults developed in the northern Gulf and Salton Trough region (Bennett et al., 2016b; Darin et al., 2016; Woodburne, 2017). Thus deformation related to the ECSZ occurred in the lower Colorado River region during deposition of the Bouse Formation, which is commonly bracketed between 6.0 and 4.8 Ma (House et al., 2008; Sarna-Wojcicki et al., 2011; Spencer et al., 2013) and may be as old as 6–7 Ma in the south (McDougall and Miranda Martínez, 2014, 2016). Post-4.5 Ma broad sagging is recognized along the lower Colorado River (Howard et al., 2015), but the possibility that faults of the ECSZ influenced local to regional subsidence patterns during deposition of the Bouse Formation has received little attention to date (e.g., Homan, 2014; O’Connell et al., 2016). The Bouse Formation is a widespread sequence of late Miocene to early Pliocene deposits exposed discontinuously along the lower Colorado River corridor (Fig. 1A). In the southern Blythe basin it consists of three regionally correlative members: (1) Basal Carbonate, consisting of supratidal and intertidal mud-flat marls, intertidal and shallow subtidal bioclastic grainstone and conglomerate, and subtidal marl; (2) Siliciclastic member, consisting of Colorado River-derived green claystone, red mudstone and siltstone, and cross-bedded river channel sandstone; and (3) Upper Bioclastic member fossiliferous sandy calcarenite, coarse pebbly grainstone, and calcareous-matrix conglomerate (Homan, 2014; Dorsey et al., 2016; O’Connell et al., 2016, 2017). The southern Bouse Formation has been interpreted as recording deposition in either a lake (Spencer and Patchett, 1997; Spencer et al., 2008, 2013; Bright et al., 2016) or shallow marine setting (Buising, 1990; McDougall, 2008; McDougall and Miranda Martínez, 2014; O’Connell et al., 2017). In this paper we summarize key results from five field seasons of detailed stratigraphic analysis south of Cibola, Ariz. ( . 1). The data reveal systematic stratal thinning and thickening, pinch-outs, and wedging patterns in the Bouse Formation that we conclude were produced by syn-depositional tilting in response to growth of normal faults near the eastern margin of the basin. Similar stratal patterns in other nearby areas suggest widespread structural controls on deposition of the Bouse Formation. A palinspastic reconstruction of the lower Colorado River region at 5 Ma, modified from Bennett et al. (2016), provides insight to regional fault geometries in the ECSZ that may have controlled syn-depositional tilting and subsidence in Bouse depocenters shortly prior to and during initiation of the Colorado River.

Conference Paper↗
USGS1984

Age and correlation of emerged pliocene and pleistocene deposits, U.S. Atlantic Coastal Plain

Paleontologic and paleomagnetic investigations were conducted on several hundred Pliocene and Pleistocene marine samples from five regions of the emerged Atlantic Coastal Plain: (1) the Delmarva Peninsula, (2) eastern Virginia, (3) central and northern North Carolina, (4) southern North Carolina and northeastern South Carolina, and (5) the Charleston area, South Carolina. Molluscan and ostracode interval and assemblage zonations, which are the primary means of regional correlation, have been calibrated using planktic biochronologic, paleomagnetic, radiometric and amino-acid recemization data. These multiple dating criteria were used to determine the age and, where possible, the duration of marine transgressive/regressive sequences. A correlation chart illustrates the age relationships of 27 formations from five regions. One important conclusion is some of the Yorktown Formation of Virginia and North Carolina (including the “Duplin” Formation), and some of the Raysor of South Carolina are late Pliocene in age. The late Pliocene Chowan River Formation of North Carolina is older than the early Pleistocene Waccamaw Formation of South Carolina, which in turn may be older than the James City Formation of North Carolina. During the last 1.0 million years, multiple marine transgressions occurred in each region, but the age of these middle and late Pleistocene formations often may differ from one area to the next. A significant result of the study is the evidence for the lack of time equivalence of formations in the five different regions; that is, the sequence of marine transgressions in one region does not necessarily correspond to that in another. This appears to be the result of differing subsidence and uplift histories, the patchiness of the depositional record, and the limitations of the dating techniques in light of the rapidity and frequency of sea-level fluctuations.

Delaware, Maryland, North Carolina, South Carolina↗
USGS2017

Sedimentology, sequence-stratigraphy, and geochemical variations in the Mesoproterozoic Nonesuch Formation, northern Wisconsin, USA

We use core descriptions and portable X-ray fluorescence analyses to identify lithofacies and stratigraphic surfaces for the Mesoproterozoic Nonesuch Formation within the Ashland syncline, Wisconsin. We group lithofacies into facies associations and construct a sequence stratigraphic framework based on lithofacies stacking and stratigraphic surfaces. The fluvial-alluvial facies association (upper Copper Harbor Conglomerate) is overlain across a transgressive surface by the fluctuating-profundal facies association (lower Nonesuch Formation). The fluctuating-profundal facies association comprises a retrogradational sequence set overlain across a maximum flooding surface by an aggradational-progradational sequence set comprising fluctuating-profundal, fluvial-lacustrine, and fluvial-alluvial facies associations (middle Nonesuch through lower Freda Formations). Lithogeochemistry supports sedimentologic and stratigraphic interpretations. Fe/S molar ratios reflect the oxidation state of the lithofacies; values are most depleted above the maximum flooding surface where lithofacies are chemically reduced and are greatest in the chemically oxidized lithofacies. Si/Al and Zr/Al molar ratios reflect the relative abundance of detrital heavy minerals vs. clay minerals; greater values correlate with larger grain size. Vertical facies association stacking records depositional environments that evolved from fluvial and alluvial, to balanced-fill lake, to overfilled lake, and returning to fluvial and alluvial. Elsewhere in the basin, where accommodation was greatest, some volume of fluvial-lacustrine facies is likely present below the transgressive stratigraphic surface. This succession of continental and lake-basin types indicates a predominant tectonic driver of basin evolution. Lithofacies distribution and geochemistry indicate deposition within an asymmetric half-graben bounded on the east by a west-dipping growth fault. While facies assemblages are lacustrine and continental, periodic marine incursions are probable, especially across maximum transgressive surfaces. We demonstrate a sequence-stratigraphic approach may be applied to fine-grained Precambrian sediments using traditional rock description and supporting lithogeochemistry. Identification of a characteristic lithofacies succession in Mesoproterozoic sediments demonstrates fundamental controls commonly interpreted for Phanerozoic lake systems may be extended into the Precambrian. These controls result in a predictable association of lithofacies, with distinct physical, biological, and geochemical properties. This has regional significance for carbon sequestration and the distribution of mineral and hydrocarbon resources and broader significance for addressing Mesoproterozoic paleogeographic reconstructions and questions related to the evolution of terrestrial life.

Wisconsin↗
USGS2008

Susceptibility of synthetic long-chain alkylbenzenes to degradation in reducing marine sediments

Long-chain alkylbenzenes (LCABs) synthesized for production of alkylbenzene sulfonate surfactants have been used as molecular markers of anthropogenic waste for 25 years. Synthetic LCABs comprise two classes, the tetrapropylene-based alkylbenzenes (TABs) and the linear alkylbenzenes (LABs). LABs supplanted TABs in the mid-1960s because of improved biodegradability of their sulfonated analogs. Use of LCABs for molecular stratigraphy depends on their preservation in sediments over decadal time scales. Most laboratory and field studies suggest that LABs degrade rapidly under aerobic conditions but are resistant to degradation when oxygen is absent. However, recent work indicates that LABs may not be as persistent under reducing conditions as previously thought. To assess the potential for degradation of LCABs in reducing sediments, box cores collected in 1992 and 2003 near a submarine wastewater outfall system were analyzed using gas chromatography/mass spectrometry. The TABs were effectively preserved; differences between whole-core inventories were within analytical error. By contrast, whole-core inventories of the LABs decreased by about 50−60% during the same time interval. Based on direct comparison of chemical inventories in coeval core sections, LAB transformation rates are estimated at 0.07 ± 0.01 yr −1 . These results indicate that caution should be exercised when using synthetic LCABs for reconstruction of depositional records.

Environmental Science & Technology↗
USGS2010

Geology of the Lake Mead region: An overview

The Lake Mead region contains major Miocene disruptions of structures formed during Mesozoic tectonic shortening. Erosion by the Colorado River and its tributaries has produced exceptional exposures of diverse structures and basin deposits recording the disruptions. Here we provide an overview of the results of studies of these features that started in earnest in 1934 when Chester Longwell began assessing the geology of the reservoir floor prior to impoundment of Lake Mead. The analysis was reinvigorated in the 1970s and early 1980s with geological mapping and structural and stratigraphic studies by Ernie Anderson and Bob Bohannon, as well as geochemical and volcanological studies by Gene Smith and his students, and has culminated in numerous subsequent studies.

Arizona, Nevada, Utah↗
USGS1996

Pre-1980 tephra-fall deposits erupted from Mount St. Helens, Washington

More than 100 tephra-fall deposits erupted from Mount St. Helens within about the last 40,000 years are grouped into tephra sets and layers distinguished from each other chiefly by differences in mineral composition and age. The tephra deposits record a complex history of the volcano, form important time-stratigraphic markers, and provide information about probable kinds, frequencies, and magnitudes of future eruptions.

Professional Paper↗
USGS1994

Sedimentary patterns across the Paleocene-Eocene boundary in the Atlantic and Gulf Coastal Plains of the United States

Fossiliferous clay and sand belonging to calcareous nannofossil Zones NP 9 (latest Paleocene) and NP 10 (earliest Eocene) are widespread in the US Gulf and Atlantic Coastal Plains. Although the thickness of Zone NP 9-NP 10 strata is several times greater in the eastern Gulf Coastal Plain than in the Atlantic Coastal Plain, the hiatus that usually is present between these two zones in inner neritic strata is of longer duration in the Gulf Coast. Although 6 sequences are found in Zones NP 10-NP 11 in both the Atlantic and Gulf Coastal Plains, the number of sequences in each NP zone differs in the 2 areas. There is continuous deposition across the Zone NP 9-NP 10 boundary only in the northern Atlantic Coastal Plain, where middle to outer neritic deposits record the presence of several latest Paleocene (upper Zone NP 9) events that occurred at approximately 55.2 Ma.

Atlantic Coastal Plain, Gulf Coastal Plain↗
USGS2017

A late quaternary record of eolian silt deposition in a maar lake, St. Michael Island, western Alaska

Recent stratigraphic studies in central Alaska have yielded the unexpected finding that there is little evidence for full-glacial (late Wisconsin) loess deposition. Because the loess record of western Alaska is poorly exposed and not well known, we analyzed a core from Zagoskin Lake, a maar lake on St. Michael Island, to determine if a full-glacial eolian record could be found in that region. Particle size and geochemical data indicate that the mineral fraction of the lake sediments is not derived from the local basalt and is probably eolian. Silt deposition took place from at least the latter part of the mid-Wisconsin interstadial period through the Holocene, based on radiocarbon dating. Based on the locations of likely loess sources, eolian silt in western Alaska was probably deflated by northeasterly winds from glaciofluvial sediments. If last-glacial winds that deposited loess were indeed from the northeast, this reconstruction is in conflict with a model-derived reconstruction of paleowinds in Alaska. Mass accumulation rates in Zagoskin Lake were higher during the Pleistocene than during the Holocene. In addition, more eolian sediment is recorded in the lake sediments than as loess on the adjacent landscape. The thinner loess record on land may be due to the sparse, herb tundra vegetation that dominated the landscape in full-glacial time. Herb tundra would have been an inefficient loess trap compared to forest or even shrub tundra due to its low roughness height. The lack of abundant, full-glacial, eolian silt deposition in the loess stratigraphic record of central Alaska may be due, therefore, to a mimimal ability of the landscape to trap loess, rather than a lack of available eolian sediment. ?? 2003 University of Washington. Published by Elsevier Inc. All rights reserved.

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