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At least 469 records · Page 26Linked to original sources

USGS2011

Response of lake chemistry to atmospheric deposition and climate in selected Class I wilderness areas in the western United States, 1993-2009

The U.S. Geological Survey, in cooperation with the U.S. Department of Agriculture Forest Service, Air Resource Management, conducted a study to evaluate long-term trends in lake-water chemistry for 64 high-elevation lakes in selected Class I wilderness areas in Colorado, Idaho, Utah, and Wyoming during 1993 to 2009. Understanding how and why lake chemistry is changing in mountain areas is essential for effectively managing and protecting high-elevation aquatic ecosystems. Trends in emissions, atmospheric deposition, and climate variables (air temperature and precipitation amount) were evaluated over a similar period of record. A main objective of the study was to determine if changes in atmospheric deposition of contaminants in the Rocky Mountain region have resulted in measurable changes in the chemistry of high-elevation lakes. A second objective was to investigate linkages between lake chemistry and air temperature and precipitation to improve understanding of the sensitivity of mountain lakes to climate variability.

Colorado;Idaho;Utah;Wyoming↗

USGS2019

2017 Monitoring and tracking wet nitrogen deposition at Rocky Mountain National Park

The Colorado Department of Public Health and Environment (CDPHE), the National Park Service (NPS), and the U.S. Environmental Protection Agency (EPA) issued the Nitrogen Deposition Reduction Plan (NDRP) in 2007 to address the effects and trends of nitrogen deposition at Rocky Mountain National Park (RMNP). The agencies chose a glidepath approach to reduce wet nitrogen deposition to a level of 1.5 kilograms of nitrogen per hectare per year (kg N/ha/yr) by the year 2032 to protect sensitive ecosystems within RMNP from adverse effects. Another goal of the NDRP is to “reverse the trend of increasing nitrogen deposition at the park.” Trends in wet deposition data were analyzed at three sites in RMNP and three regional sites outside of the park. Wet nitrogen deposition (5-year rolling average) at Loch Vale in RMNP was 3.3 kg N/ha/yr, which is above the glidepath (2.4 kg N/ha/yr) in 2017. Wet nitrogen deposition has not decreased at RMNP or other sites in the region over the long-term. Ammonium concentrations showed a statistically significant increasing trend at all sites and nitrate concentrations showed a significant decreasing trend at four of the five sites over the period of record. In more recent years (2011-2017), wet nitrogen deposition showed no significant trend at monitoring sites in RMNP. Ammonium concentrations also showed no significant trend over the short-term, however nitrate concentrations did significantly decrease at two of the six sites.

Colorado↗

USGS2003

A 38,000-year record of floods and debris flows in the Ilo region of southern Peru and its relation to El Niño events and great earthquakes

Previous work throughout the Ilo region of south coastal Peru has documented the existence of flood and debris-flow deposits produced by two El Niño events evidently much more severe than any in recent history. These two events have been dated to ca. AD 1300–1400 and AD 1607–08. The Late Pleistocene to Holocene record of older sedimentary deposits in this region is dominated by flood and debris-flow deposits of similar scale. These older deposits have been described and dated from three coastal, alluvial-fan sites. These deposits, which are as old as 38 200 years, are dominated by massive debris-flow deposits, several tens of cm thick, typically composed of cobble- and boulder-sized clasts in a matrix of silty sand, with characteristics indicating generation by heavy rainfall in an arid environment. Twenty-two radiocarbon dates and a single infrared-stimulated luminescence date show that particularly severe El Niño events occurred throughout the Late Pleistocene and two of three divisions of the Holocene with significantly different frequencies. The period of greatest activity was during the Early Holocene when at least six such events took place during a period of ca. 3600 years, beginning near the end of the Younger Dryas ca. 12 000 years ago. One of these events produced a debris flow that may have caused abandonment of the Paleo-Indian site at Quebrada Tacahuay, one of the oldest on the Andean coast. No severe events took place during the Middle Holocene between ca. 8400 and 5300 years ago, when a wide variety of other paleoclimate proxy records indicate that the El Niño–Southern Oscillation regime was particularly weak. Since ca. 5300 years ago, four of these severe events have taken place. The Late Pleistocene sequence is constrained by only two dates, which indicate that at least ten severe events took place between ca. 38 200 and 12 900 years ago. Mechanisms probably responsible for generating these large-scale deposits include: (1) ‘Mega-Niños’ that produced anomalously heavy rainfall along most or all of the central Andean coast; (2) El Niños that occurred shortly after great earthquakes that produced large amounts of sediment; or (3) El Niños that produced anomalously heavy local rainfall. The existence of these large-scale deposits in the Ilo region implies a level of hazard much higher than indicated by the historical record alone

Palaeogeography, Palaeoclimatology, Palaeoecology↗

USGS2019

Short-term geomorphological and riparian vegetation responses to a 40-year flood on a braided, dryland river

In December 2010, a 40-yr flood occurred in the lower Virgin River (SE Nevada, southwestern U.S.), a braided river segment with riparian vegetation largely dominated by invasive shrubs in the genus Tamarix. We assessed geomorphological and vegetation responses to this large magnitude disturbance event by comparing pre- and post-flood remote sensing and field survey data in four river reaches. Analyses of orthophotos and LiDAR-derived topography showed that both the active channel area and channel width increased between ~80 and 258%, representing an increase from 13% to 30% of the total river corridor area. Erosion predominated in the outer bends of the enlarged channel and deposition in the pre-flood channel, causing local avulsions of the low-flow channel. Field-based topographic data recorded before and after the flood in 385 plots also showed that deposition occurred in parts of the floodplain that were not eroded. Two thirds of woody vegetation cover (mainly dominated by Tamarix, with some native shrub Pluchea sericea) was lost in areas that eroded (~20% of the river corridor). In the remaining ~80% of stable river corridor (aggrading or no change in elevation) Tamarix remained dominant. Following erosion, but also where sediment deposition predominated under the Tamarix canopy, the most common colonizing vegetation in the understory was comprised of annual plants, especially Salsola tragus. Overall, our study supported previous studies describing large floods in braided rivers: we documented the first phase of a cycle of channel widening and increase in vegetation heterogeneity that is commonly followed by narrowing and vegetation homogenization. We underscore the importance of rivers with mostly unregulated flood regimes as laboratories for understanding eco-hydrologic feedbacks.

Nevada↗

USGS2024

Climatic variability as a principal driver of primary production in the southernmost subalpine Rocky Mountain lake

Mountain lakes are sensitive indicators of anthropogenically driven global change, with lake sediment records documenting increased primary production during the twentieth century. Atmospheric nutrient deposition and warming have been attributed to changes in other Western mountain lakes, however, the intensity of these drivers varies. We analyzed a sediment core representing a 270-year record from Santa Fe Lake, New Mexico, to constrain the southern margin of Rocky Mountain lakes and quantify patterns of change in lake biogeochemistry, production, and diatoms since 1750. Lake sediments were dated using 210 Pb and analyzed for carbon (C), nitrogen (N), stable isotopes (δ 13 C, δ 15 N), diatoms, and phototrophic pigments. The abundance of cyanobacteria, purple sulfur-reducing bacteria, and diatom pigments were elevated during the stable conditions of the Little Ice Age; these phototrophic groups declined in the late 1800s and reached a minimum by 1950. From 1950 to 2020, sediments recorded an increased abundance of cryptophyte, diatom, and chlorophyte groups. The C and N (percentage dry mass) increased after 1950, whereas δ 15 N and δ 13 C values declined. Changes since the mid-twentieth century are contemporaneous with warming trends in the Southwest and modest deposition of atmospheric N. Our findings highlight the geographic variability of mountain lake responses to changing environmental conditions.

New Mexico↗

USGS2008

Coarse-clast ridge complexes of the Caribbean: A preliminary basis for distinguishing tsunami and storm-wave origins

Coastal gravel-ridge complexes deposited on islands in the Caribbean Sea are recorders of past extreme-wave events that could be associated with either tsunamis or hurricanes. The ridge complexes of Bonaire, Jamaica, Puerto Rico (Isla de Mona), and Guadeloupe consist of polymodal clasts ranging in size from sand to coarse boulders that are derived from the adjacent coral reefs or subjacent rock platforms. Ridge-complex morphologies and crest elevations are largely controlled by availability of sediments, clast sizes, and heights of wave runup. The ridge complexes are internally organized, display textural sorting and a broad range of ages including historical events. Some display seaward-dipping beds and ridge-and-swale topography, and some terminate in fans or steep avalanche slopes. Together, the morphologic, sedimentologic, lithostratigraphic, and chronostratigraphic evidence indicates that shore-parallet ridge complexes composed of gravel and sand that are tens of meters wide and several meters thick are primarily storm-constructed features that have accumulated for a few centuries or millennia as a result of multiple high-frequency intense-wave events. They are not entirely the result of one or a few tsunamis as recently reported. Tsunami deposition may account for some of the lateral ridge-complex accretion or boulder fields and isolated blocks that are associated with the ridge complexes. Copyright ?? 2008, SEPM (Society for Sedimentary Geology).

Journal of Sedimentary Research↗

USGS2006

Water resources of Monroe County, New York, water years 2000-02: Atmospheric deposition, ground water, streamflow, trends in water quality, and chemical loads in streams

This report, the fifth in a series that presents analyses of the hydrologic data collected in Monroe County since 1984, interprets data from four surface-water-monitoring sites in the Irondequoit Creek basin (Irondequoit Creek at Railroad Mills, East Branch Allen Creek at Pittsford, Allen Creek near Rochester, and Irondequoit Creek above Blossom Road); and from three sites on tributaries to the Genesee River (Oatka Creek at Garbutt, Honeoye Creek at Honeoye Falls, and Black Creek at Churchville) and from the Genesee River at Charlotte Docks. It also interprets data from a site on Northrup Creek, which provides information on nutrient loads delivered to Long Pond, a small eutrophic embayment of Lake Ontario. The report also includes water-level and water-quality data from nine observation wells in Ellison Park, and atmospheric-deposition data from a collection site at Mendon Ponds. Atmospheric Deposition : Average annual precipitation for 2000–02 was 33.11 in., 0.94 in. below normal. Average annual loads of some chemical constituents in atmospheric deposition for 2000–02 differed considerably from those for the previous period of record. Loads of all nutrients except ammonia decreased by amounts ranging from 28 percent (ammonia + organic nitrogen and phosphorus) to 2 percent (nitrite + nitrate), whereas ammonia loads an increased by 8 percent. Loads of dissolved sodium and total zinc in atmospheric deposition increased by 56 percent, and 54, percent respectively, over the previous period of record. Average annual loads of other constituents showed decreases ranging from 41 percent (dissolved magnesium) to 17 percent (dissolved chloride). Loads of all nutrients deposited in the Irondequoit Creek basin from atmospheric sources during 2000–02 greatly exceeded those transported by Irondequoit Creek. The ammonia load deposited in the basin was 165 times the load transported at Blossom Road (the most downstream site); the ammonia + organic nitrogen load was 2.8 times greater, orthophosphate 9.7 times greater, total phosphorus 1.2 times greater, and the nitrite + nitrate load was 1.6 times greater. Average yields of dissolved chloride and dissolved sulfate from atmosphoric sources were much less than those transported by streamflow at Blossom Road—chloride was about 1.5 percent and sulfate about 9.1 percent of the amount transported by Irondequoit Creek. Ground water : Ground-water-levels and water quality data were collected from 9 observation wells in Ellison Park in Monroe County. All wells except Mo 2 and Mo 659 are in the flood plain of Irondequoit Creek. Water levels indicate frequent reversals in direction of lateral flow toward or away from Irondequoit Creek, and all wells except Mo2 and Mo 659 respond to water level fluctuations in the Creek. Trend tests on water levels for the period of record indicate a slight upward trend in water levels at all nine wells, two of which (Mo 3 and Mo 667) were statistically significant. Concentrations of ammonia and ammonia + organic nitrogen showed a general decrease for the current period of record. Total phosphorus concentrations showed an increase at four wells and a decrease at four wells. Water quality data showed that the highest median concentrations of nutrients continues to occur in Mo 667 and the highest median concentrations of common ions was at Mo 664. Streamflow : Statistical analysis of long-term (greater than 15 years) streamflow records for unregulated streams in Monroe County indicated that annual mean flows for water years (A water year is the 12-month period from October 1 through September 30 of the following year.) 2000–02 generally were in the normal range (75th to 25th percentile), although Allen Creek continued to show a significant downward trend in mean monthly streamflow during the 1984–2002 water years. Chemical Concentration in Streams : Concentrations of several constituents in streams of the Irondequoit Creek basin showed statistically significant (α = 0.05) trends from the beginning of their period of record through 2002. Three of the four Irondequoit Creek sites (Allen Creek, Blossom Road, and Railroad Mills) showed downward trends in ammonia (4.6 to 12.0 percent per year) and ammonia + organic nitrogen (2.8 to 5.3 percent per year). Allen Creek showed downward trends in nitrite + nitrate and total phosphorus (both 1.2 percent per year), and Irondequoit Creek above Blossom Road showed an upward trend in orthophosphate (1.8 percent per year). Three Irondequoit Creek sites showed upward trends in dissolved chloride: Railroad Mills (4.8 percent per year), Allen Creek, and Blossom Road (both 1.9 percent per year). Allen Creek showed a downward trend in sulfate of 0.98 percent per year, whereas Blossom Road showed a downward trend in suspended solids of 4.0 percent per year. Volatile suspended solids showed an upward trend of 3.2 percent per year at Allen Creek and a downward trend of 2.2 percent per year at Blossom Road. Northrup Creek in western Monroe County, showed significant downward trends in concentrations of volatile suspended solids (2.5 percent per year), total phosphorus (5.3 percent per year), and orthophosphate (9.9 percent per year). The Genesee River at Charlotte Docks showed downward trends in volatile suspended solids (2.1 percent per year) and ammonia + organic nitrogen (4.5 percent per year). Oatka Creek at Garbutt showed an upward trend of 21.4 percent per year in turbidity. Chemical Loads in Streams : Mean annual yields (pounds or tons per square mile) of many constituents at the Irondequoit Creek sites were lower than those in previous reporting periods. Suspended solids and nitrite + nitrate yields were lower at three of the sites, and yields of volatile suspended solids, ammonia, and total phosphorus were lower at two of the sites. East Branch Allen Creek showed lower yields for five of the nine constituents for 2000–02, than for previous reporting periods. The decreased yields at East Branch Allen Creek are likely due to the Jefferson Road stormflow-detention basin and the much lower than normal runoff for the 2000–02 period.

New York↗

USGS2009

Photomosaics and logs of trenches on the San Andreas Fault near Coachella, California

The Coachella paleoseismic site is located on the San Andreas Fault along the northeast edge of the Coachella Valley in southern California east of Dillon Road and south of Avenue 44. Three benched trenches, a total of more than 950 m, were excavated across the fault zone as part of an Alquist-Priolo fault investigation study. These trenches exposed a thick section of latest Holocene lacustrine, fluvial, and shoreline deposits. Only the central and eastern trenches exposed faulting so we confined our investigations to those two trenches. In the central trench, we photographed and logged in detail both walls of about 70 m of the trench where it spanned several zones of complex faulting which form a 15-m-wide depression. After carefully cleaning the trench walls, we put up a 1- by 0.5-m string- and nail-grid. We photographed each 1- by 0.5-m panel individually and then photologged features directly on these unrectified photos. The photos were digitally rectified later to remove distortion caused by irregularities in the trench walls and to correct the slight distortion introduced by the camera lens. The rectified photos were spliced together to make photomosaics of the trench walls. Most of the field linework and descriptions were then transferred to the rectified photomosaics. For the eastern trench, we took a set of overview photographs of the full length (about 200 m) of each wall. These photographs were taken from the top of the trench towards the opposite wall. Because the photographs were taken at a downward angle, there is significant distortion. We logged directly on these photos in the field, recording significant contacts, primarily between lacustrine and subaerial deposits, along with descriptions. For this report, we spliced together these unrectified overview photos and transfered field linework and some descriptions. For both trenches, contacts and lithologhic descriptions of stratigraphic units, faults and carbon sample locations are indicated on the photomosaics. Lacustrine deposits are tinted to better show deformation across the fault zones. Evidence for six paleoearthquakes rated as “probable” is indicated with red stars that contain the sequential event number (1 is most recent event). Evidence for two additional “possible” paleoearthquakes is indicated with blue stars. The sedimentary deposits contain abundant dateable material which includes detrital charcoal, lenses of organic material formed in-situ, and shells. Two organic fractions, humic acids and acid-alkali-acid-pretreated (AAA), were dated for 13 of 15 samples taken from organic layers and both dates are shown for these samples on the photomosaics and tables 1 and 2. All radiocarbon dates are in 14 C years B.P. (considered to be A.D. 1950). Horizontal distance is measured along the trenches from the southwest ends of the logged exposures (marked as 0 m), and depth is measured from the highest points on the ground surface within the logged exposures. Bench locations are indicated by white lines and gaps in the photomosaics. Note that faults and contacts that are somewhat oblique to the trench walls occasionally appear disconnected owing to the approximately 1 m width of the benches.

California↗

USGS2001

Geologic evidence of earthquakes at the Snohomish Delta, Washington, in the past 1200 yr

Exposed channel banks along distributaries of the lower Snohomish delta in the Puget Lowland of Washington reveal evidence of at least three episodes of liquefaction, at least one event of abrupt subsidence, and at least one tsunami since ca. A.D. 800. The 45 measured stratigraphic sections consist mostly of 2–4 m of olive- gray, intertidal mud containing abundant marsh plant rhizomes. The most distinctive stratigraphic unit is a couplet comprising a 0.5−3-cm-thick, laminated, fining-upward, tsunami-laid sand bed overlain by 2−10 cm of gray clay. We correlated the couplet, which is generally ∼2 m below the modern marsh surface, across an ∼20 km 2 area. Sand dikes and sand-filled cracks to 1 m wide, which terminate upward at the couplet, and sand volcanoes preserved at the level of the sand bed record liquefaction at the same time as couplet deposition. Differences in the type and abundance of marsh plant rhizomes across the couplet horizon, as well as the gray clay layer, suggest that compaction during this liquefaction led to abrupt, local lowering of the marsh surface by as much as 50–75 cm. Radiocarbon ages show that the tsunami and liquefaction date from ca. A.D. 800 to 980, similar to the age of a large earthquake on the Seattle fault, 50 km to the south. We have found evidence for at least two, and possibly as many as five, other earthquakes in the measured sections. At two or more stratigraphic levels above the couplet, sand dikes locally feed sand volcanoes. Radiocarbon ages and stratigraphic position suggest that one set of these dikes formed ca. A.D. 910–990; radiocarbon ages on a younger set indicate a limiting maximum age of A.D. 1400–1640. We also interpret a sharp lithologic change, from olive-gray, rhizome-rich mud to grayer, rhizome-poor mud, ∼1 m above the couplet, to indicate a second abrupt lowering of the marsh surface during an earthquake ca. A.D. 1040– 1400, but no conclusive liquefaction structures have been identified at this horizon. Two distinctive coarse-sand laminae, 30–80 cm below the couplet, may record tsunamis older than A.D. 800. Thus, study shows that in the past ∼1200 yr, this part of Washington's Puget Lowland has been subjected to stronger ground shaking than in historic times, since ca. 1870.

Washington↗

USGS2017

A loess–paleosol record of climate and glacial history over the past two glacial–interglacial cycles (~ 150 ka), southern Jackson Hole, Wyoming

Loess accumulated on a Bull Lake outwash terrace of Marine Oxygen Isotope Stage 6 (MIS 6) age in southern Jackson Hole, Wyoming. The 9 m section displays eight intervals of loess deposition (Loess 1 to Loess 8, oldest), each followed by soil development. Our age-depth model is constrained by thermoluminescence, meteoric 10 Be accumulation in soils, and cosmogenic 10 Be surface exposure ages. We use particle size, geochemical, mineral-magnetic, and clay mineralogical data to interpret loess sources and pedogenesis. Deposition of MIS 6 loess was followed by a tripartite soil/thin loess complex (Soils 8, 7, and 6) apparently reflecting the large climatic oscillations of MIS 5. Soil 8 (MIS 5e) shows the strongest development. Loess 5 accumulated during a glacial interval (~ 76–69 ka; MIS 4) followed by soil development under conditions wetter and probably colder than present. Deposition of thick Loess 3 (~ 43–51 ka, MIS 3) was followed by soil development comparable with that observed in Soil 1. Loess 1 (MIS 2) accumulated during the Pinedale glaciation and was followed by development of Soil 1 under a semiarid climate. This record of alternating loess deposition and soil development is compatible with the history of Yellowstone vegetation and the glacial flour record from the Sierra Nevada.

Wyoming↗

USGS1982

Depositional history of Louisiana-Mississippi outer continental shelf

A geological study was undertaken in 1981 in the Louisiana-Mississippi outer continental shelf for the Bureau of Land Management. The study included a high-resolution seismic reflection survey, surficial sediment sampling and surface current drifter sampling. Approximately 7100 sq km of the Louisiana-Mississippi shelf and upper slope were surveyed. The sea floor of the entire area is relatively smooth except for occasional areas of uplift produced by diapiric intrusion along the upper slope. Characteristics of the topography and subsurface shelf sediments are the result of depositional sequences due to delta outbuilding over transgressive sediments with intervening periods of erosion during low sea level stands. Little evidence of structural deformation such as faults, diapirs, and shallow gas is present on the shelf and only a few minor faults and scarps are found on the slope. Minisparker seismic records in combination with air gun (40 and 5 cu in) and 3.5-kHz subbottom profile records reveal that seven major stages of shelf development have occurred since the middle Pleistocene. The shelf development has been controlled by the rise and fall of sea level. These stages are defined by four major unconformities, several depositions of transgressive sediments, sequences of river channeling and progradational delta deposits. Surficial sediment sample and seismic records indicate tat the last major depositional event was the progradation of the St. Bernard Delta lobe. This delta lobe covered the northwestern and central regions. Surficial sediments in most of the study area are the product of the reworking of the San Bernard Delta lobe and previous progradations.

Open-File Report↗

USGS2024

Chronology and Paleoenvironment of the Tunga Formation, a new lowermost Miocene sequence in the East Pisco Basin of southern Peru

The East Pisco Basin, occupying the coastal plain of Peru between 13°S and 16°S, is widely known for its extensive Eocene to Quaternary biosiliceous deposits and excellent preservation of fossil marine vertebrates. Biochronologic studies published over the past 35 years record a hiatus of about 13 million years (*32–19 Ma) separating the youngest Paleogene deposits (Otuma Formation) from the oldest Neogene deposits (Chilcatay Formation). We describe a newly identified Lower Miocene depositional sequence that lies below documented Chilcatay strata, rich in diatoms and benthic foraminifers, which we name the Tunga Formation. A low-latitude diatom assemblage from the Tunga Formation indicates an age of 21.6 to 20.5 Ma age, whereas an ash within basal Tunga strata yields an 206Pb/238U weighted mean age of 20.58 ± 0.13 Ma. Benthic foraminifer paleodepth analysis and the diatom assemblage of the Tunga Formation indicate deposition took place along the continental margin at upper bathyal depths under hypoxic conditions beneath highly productive waters, a scenario also supported by the presence of abundant clupeoid fish scales and dolomitized horizons. The Tunga Formation is characterized by a profound scarcity of cetacean fossils, unlike the cetacean-rich neritic sediments of the overlying Chilcatay Formation.

East Pisco Basin↗

USGS1998

The ichnologic record of the continental invertebrate invasion; evolutionary trends in environmental expansion, ecospace utilization, and behavioral complexity

The combined study of continental trace fossils and associated sedimentary facies provides valuable evidence of colonization trends and events throughout the Phanerozoic. Colonization of continental environments was linked to the exploitation of empty or under-utilized ecospace. Although the nonmarine trace fossil record probably begins during the Late Ordovician, significant invasion of nonmarine biotopes began close to the Silurian-Devonian transition with the establishment of a mobile arthropod epifauna (Diplichnites ichnoguild) in coastal marine to alluvial plain settings. Additionally, the presence of vertical burrows in Devonian high-energy fluvial deposits reflects the establishment of a stationary, deep suspension-feeding infauna of the Skolithos ichnoguild. The earliest evidence of plant-arthropod interaction occurred close to the Silurian-Devonian boundary, but widespread and varied feeding patterns are known from the Carboniferous. During the Carboniferous, permanent subaqueous lacustrine settings were colonized by a diverse, mobile detritus-feeding epifauna of the Mermia ichnoguild, which reflects a significant palaeoenvironmental expansion of trace fossils. Paleozoic ichnologic evidence supports direct routes to the land from marginal marine environments, and migration to lakes from land settings. All nonmarine sedimentary environments were colonized by the Carboniferous, and subsequent patterns indicate an increase in ecospace utilization within already colonized depositional settings. During the Permian, back-filled traces of the Scoyenia ichnoguild record the establishment of a mobile, intermediate-depth, deposit-feeding in-fauna in alluvial and transitional alluvial-lacustrine sediment. Diversification of land plants and the establishment of ecologically diverse plant communities through time provided new niches to be exploited by arthropods. Nevertheless, most ot the evolutionary feeding innovations took place relatively early, during the Late Palaeozoic or early Mesozoic. A stationary deep unfauna, the Camborygma ichnoguild, was developed in Triassic transitional alluvial-lacustrinbe deposits. Terrestrial environments hosted the rise of complex social behavioral patterns, as suggested by the probable presence of hymenopteran and isopteran nests in Triassic paleosols. An increase in diversity of trace fossils is detected in Triassic-Jurassic eolian deposits, where the ichnofauna displays more varied behavioral patterns than their Paleozoic counterparts. Also, a mobile, intermediate-depth, deposit-feeding infauna, the Vagorichnus ichnoguild, was established in deep lake environments during the Jurassic. In contrast to Paleozoic permanent subaqueous assemblages typified by surface trails, Jurassic ichnocoenoses are dominated by infaunal burrows. High density of infaunal deposit-feeding traces of the Planolites ichnoguild caused major disruption of lacustrine sedimentary fabrics during the Cretaceous. Most insect mouthpart classes, functional feeding groups, and dietary guilds were established by the end of the Cretaceous. Diversification of modern insects is recorded by the abundance and complexity of structures produced by wasps, bees, dung-beetles, and termites in Cretaceous-Tertiary paleosols. The increase in bioturbation migrated from fluvial and lake-margin settings to permanent subaqueous lacustrine environments through time.

Palaios↗

USGS2008

Holocene climate and climate variability of the northern Gulf of Mexico and adjacent northern Gulf Coast: A review

Marine records from the northern Gulf of Mexico indicate that significant multidecadal- and century-scale variability was common during the Holocene. Mean annual sea-surface temperature (SST) during the last 1,400 years may have varied by 3°C, and excursions to cold SST coincide with reductions in solar output. Broad trends in Holocene terrestrial climate and environmental change along the eastern portion of the northern Gulf Coast are evident from existing pollen records, but the high-frequency details of climate variability are not well known. Continuous and well-dated records of climate change and climate variability in the western portion of the northern Gulf Coast are essentially lacking. Information on Holocene floods, droughts, and storm frequency along the northern Gulf Coast is limited. Records of floods may be preserved in continental shelf sediments, but establishing continuity and chronologies for sedimentary sequences on the shelf presents challenges due to sediment remobilization and redeposition during storms. Studies of past storm deposits in coastal lakes and marshes show promise for constructing records of past storm frequency. A recent summary of sea-level history of the northern Gulf Coast indicates sea level was higher than modern sea level several times during the last few thousand years.

Alabama, Florida, Louisiana, Mississippi, Texas↗

USGS2012

Tectonic influences on the preservation of marine terraces: Old and new evidence from Santa Catalina Island, California

The California Channel Islands contain some of the best geologic records of past climate and sea-level changes, recorded in uplifted, fossil-bearing marine terrace deposits. Among the eight California Channel Islands and the nearby Palos Verdes Hills, only Santa Catalina Island does not exhibit prominent emergent marine terraces, though the same terrace-forming processes that acted on the other Channel Islands must also have occurred on Santa Catalina. We re-evaluated previous researchers' field evidence and examined new topographic, bathymetric, and stream-profile data in order to find possible explanations for the lack of obvious marine terrace landforms or deposits on the island today. The most likely explanation is associated with the island's unresolved tectonic history, with evidence for both recent uplift and subsidence being offered by different researchers. Bathymetric and seismic reflection data indicate the presence of submerged terrace-like landforms from a few meters below present sea level to depths far exceeding that of the lowest glacial lowstand, suggesting that the Catalina Island block may have subsided, submerging marine terraces that would have formed in the late Quaternary. Similar submerged marine terrace landforms exist offshore of all of the other California Channel Islands, including some at anomalously great depths, but late Quaternary uplift is well documented on those islands. Therefore, such submarine features must be more thoroughly investigated and adequately explained before they can be accepted as definitive evidence of subsidence. Nevertheless, the striking similarity of the terrace-like features around Santa Catalina Island to those surrounding the other, uplifting, Channel Islands prompted us to investigate other lines of evidence of tectonic activity, such as stream profile data. Recent uplift is suggested by disequilibrium stream profiles on the western side of the island, including nickpoints and profile convexities. Rapid uplift is also indicated by the island's highly dissected, steep topography and abundant landslides. A likely cause of uplift is a restraining bend in the offshore Catalina strike-slip fault. Our analysis suggests that Santa Catalina Island has recently experienced, and may still be experiencing, relatively rapid uplift, causing intense landscape rejuvenation that removed nearly all traces of marine terraces by erosion. A similar research approach, incorporating submarine as well as subaerial geomorphic data, could be applied to many tectonically active coastlines in which a marine terrace record appears to be missing.

California↗

USGS2017

Oxygen stable isotopic disparities among sympatric small land snail species from northwest Minnesota, USA

The oxygen isotopic composition (δ 18 O) of land snail shells can be a valuable paleoenvironmental archive if the climatic parameters that influence the isotopic system are fully understood. Previous calibration studies have examined a limited number of species or individuals, and most have focused on larger (> 10 mm) taxa, which do not represent the dominant shell material in the Quaternary fossil record. In this study, we evaluate the δ 18 O values of small land snails (< 10 mm), which are common in modern settings and are often preserved in a wide array of Quaternary geologic and archeologic deposits. Our primary goal was to determine if coexisting species record equivalent isotopic information in their shells, regardless of differences in their ecology, dietary habits, behavior, and/or body size. We collected and analyzed 265 individuals of 11 species from 12 sites in northwest Minnesota (USA), which exhibits extremely abundant and diverse terrestrial malacofauna in North America. We did not observe significant correlations between shell δ 18 O values and the type of ecosystem (forest/grassland) or hydrologic setting (upland/lowland). However, the majority of species differed significantly in shell δ 18 O values. Larger taxa ( Catinella , Succinea , Discus ) consistently yielded higher δ 18 O values than smaller taxa ( Euconulus , Gastrocopta , Hawaiia , Vallonia ), by up to ~ 3‰. These isotopic offsets among sympatric taxa could be attributed to a number of physical, behavioral, and/or evolutionary traits, including the ability of larger species to tolerate drier conditions better than their smaller counterparts, differences in their preferred microhabitats or phylogentic non-independence. Regardless of the reason, our results imply that researchers should not combine isotopic data from different types of land snails without first investigating modern specimens to determine if it is appropriate. Moreover, our data suggest that combining instrumental climate data, a snail flux-balance model, and shell δ 18 O values can help us to better understand the ecology of land snails.

Minnesota↗

USGS2011

Provenance of Des Moines lobe till records ice-stream catchment evolution during Laurentide deglaciation

Mapping and analysis of deposits of the Des Moines lobe of the Laurentide Ice Sheet, active after the Last Glacial Maximum (LGM), reveal several texturally and lithologically distinct tills within what had been considered to be a homogeneous deposit. Although the differences between tills are subtle, minor distinctions are predictable and mappable, and till sheets within the area covered by the lobe can be correlated for hundreds of kilometres parallel to ice flow. Lateral till‐sheet contacts are abrupt or overlap in a narrow zone, coincident with a geomorphic discontinuity interpreted to be a shear margin. Till sheets 10 to 20 m thick show mixing in their lower 2 to 3 m. We suggest that: (i) lithologically distinct till sheets correspond to unique ice‐stream source areas; (ii) the sequence of tills deposited by the Des Moines lobe was the result of the evolution and varying dominance of nearby and competing ice streams and their tributaries; and (iii) in at least one instance, more than one ice stream simultaneously contributed to the lobe. Therefore the complex sequence of tills of subtly different provenances, and the unconformities between them record the evolution of an ice‐catchment area during Laurentide Ice Sheet drawdown. Till provenance data suggest that, after till is created in the ice‐stream source area, the subglacial conditions required for transporting till decline and incorporation of new material is limited.

Boreas↗

USGS2010

Petrology and geochemistry of the 2006 eruption of Augustine Volcano: Chapter 15 in The 2006 eruption of Augustine Volcano, Alaska

Deposits from the 2006 eruption of Augustine Volcano, Alaska, record a complex history of magma mixing before and during the eruption. The eruption produced five major lithologies: low-silica andesite scoria (LSAS; 56.5 to 58.7 weight percent SiO 2 ), mostly during the initial explosive phase; high-silica andesite pumice (HSA; 62.2 to 63.3 weight percent SiO 2 ), prevalent during the continuous phase; dense low-silica andesite (DLSA; 56.4 to 59.3 weight percent SiO 2 ), predominantly during the late effusive phase; and dense intermediate andesite (DIA) and banded clasts, present throughout the eruption but most abundant in the continuous phase. The DIA and banded clasts have compositions that fall between and partially overlap the ranges noted above. All rock types are phenocryst-rich (36 to 44 volume percent), containing plagioclase, orthopyroxene, augite, Fe-Ti oxides, olivine, and rare amphibole, apatite, and anhydrite. Glasses from tephra and flow-deposit clasts range from 66 to nearly 80 weight percent SiO 2 and represent highly evolved melt relative to the bulk rock compositions. Fe-Ti oxides recorded f O2 ~2 log units above the Ni-NiO buffer and temperatures of 904±47°C and 838±14°C from LSAS and HSA samples, respectively, with the intermediate lithologies falling in the middle of these ranges. The dense low-silica andesite and scoria (collectively LSA) are compositionally nearly identical, and trace-element patterns show that the HSA is not the result of shallow crustal fractionation of the LSA. The petrological and geochemical data indicate that two-component magma mixing between the LSA and HSA caused the compositional spread in eruptive products. The phenocryst population in the LSA suggests that it represents a hybrid formed from the HSA and an unerupted, basaltic “replenishing” magma. On the basis of petrological and geophysical observations reported here and elsewhere in this volume, the HSA was stored as a crystal-rich mush with its top at ~5-km depth. An influx of basalt remobilized and partially mixed with a portion of the mush, forming the hybrid LSA. The lower viscosity LSA ascended towards the surface as a dike, erupting during the explosive phase in mid-January 2006. In late January, a large explosion produced the first significant volumes of HSA, followed by several days of rapid HSA effusion during the eruption’s continuous phase. After a three-week hiatus marked by elevated gas output, signifying an open system, degassed LSA erupted during the final, effusive phase. Consistency in eruptive styles and compositions suggests that the HSA magma body may have been similarly rejuvenated during the past several eruptions.

Alaska↗