Geology Reports⌕ Search

SEARCH · Geology Reports

Results for “The Depositional Record”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 721 records · Page 40Linked to original sources
USGS1999

Town Lake bottom sediments : a chronicle of water quality changes in Austin, Texas, 1960-98

Town Lake, the last in the chain of Highland Lakes on the Colorado River, runs through the center of Austin, Texas. On any given day, grebes and coots dot the water, rowers skim alongside, and the sparkle of the sun on the water can be admired from the adjacent hike and bike path and from the windows of nearby office buildings. During the summer months, crowds gather along the shores of Town Lake to watch as many as 1 million Mexican Free-Tail bats emerge from under the Congress Avenue bridge. But below the lazily moving azure water lies a bed of sediment about 1 meter (m) thick?sediment that has been deposited gradually since the reservoir was formed in 1959 and that has been recording changes in water quality since that time. What can this sediment tell us about the history of water quality in the Colorado River? And what does it say about the effects of the rapid urbanization of Austin and the future health of our environment?

Texas↗
USGS2006

Preliminary surficial geologic map database of the Amboy 30 x 60 minute quadrangle, California

The surficial geologic map database of the Amboy 30x60 minute quadrangle presents characteristics of surficial materials for an area approximately 5,000 km2 in the eastern Mojave Desert of California. This map consists of new surficial mapping conducted between 2000 and 2005, as well as compilations of previous surficial mapping. Surficial geology units are mapped and described based on depositional process and age categories that reflect the mode of deposition, pedogenic effects occurring post-deposition, and, where appropriate, the lithologic nature of the material. The physical properties recorded in the database focus on those that drive hydrologic, biologic, and physical processes such as particle size distribution (PSD) and bulk density. This version of the database is distributed with point data representing locations of samples for both laboratory determined physical properties and semi-quantitative field-based information. Future publications will include the field and laboratory data as well as maps of distributed physical properties across the landscape tied to physical process models where appropriate. The database is distributed in three parts: documentation, spatial map-based data, and printable map graphics of the database. Documentation includes this file, which provides a discussion of the surficial geology and describes the format and content of the map data, a database 'readme' file, which describes the database contents, and FGDC metadata for the spatial map information. Spatial data are distributed as Arc/Info coverage in ESRI interchange (e00) format, or as tabular data in the form of DBF3-file (.DBF) file formats. Map graphics files are distributed as Postscript and Adobe Portable Document Format (PDF) files, and are appropriate for representing a view of the spatial database at the mapped scale.

Open-File Report↗
USGS2005

Late Quaternary history of the Atacama Desert

Of the major subtropical deserts found in the Southern Hemisphere, the Atacama Desert is the driest. Throughout the Quaternary, the most pervasive climatic influence on the desert has been millennial-scale changes in the frequency and seasonality of the scant rainfall, and associated shifts in plant and animal distributions with elevation along the eastern margin of the desert. Over the past six years, we have mapped modern vegetation gradients and developed a number of palaeoenvironmental records, including vegetation histories from fossil rodent middens, groundwater levels from wetland (spring) deposits, and lake levels from shoreline evidence, along a 1200-kilometre transect (16–26°S) in the Atacama Desert. A strength of this palaeoclimate transect has been the ability to apply the same methodologies across broad elevational, latitudinal, climatic, vegetation and hydrological gradients. We are using this transect to reconstruct the histories of key components of the South American tropical (summer) and extratropical (winter) rainfall belts, precisely at those elevations where average annual rainfall wanes to zero. The focus has been on the transition from sparse, shrubby vegetation (known as the prepuna) into absolute desert, an expansive hyperarid terrain that extends from just above the coastal fog zone (approximately 800 metres) to more than 3500 metres in the most arid sectors in the southern Atacama.

Atacama Desert↗
USGS1974

Dendritic dry valleys in the cone karst of Puerto Rico

The depressions in the cone karst (Kegelkarst) of the area west of Ciales in the Lares Limestone are alined in dry valleys that have dendritic patterns. These valleys apparently record the former existence of a cover of noncalcareous clastic material that was deposited on the limestone in late Tertiary time. One system of dendritic dry valleys ends at an abandoned meander of the Rio Grande de Manati, which is about 60 m above the present floor of the river. Another system leads to large masses of "blanket sand" near the town of Florida. These valleys were apparently eroded during the late Pliocene or very early Pleistocene when sea level was at least 80 m higher than it is today.

Puerto Rico↗
USGS2008

Mineral chemistry and shrimp U-Pb Geochronology of mesoproterozoic polycrase-titanite veins in the sullivan Pb-Zn-Ag Deposit, British Columbia

Small polycrase-titanite veins 0.1-2 mm thick cut the tourmalinite feeder zone in the deep footwall of the Sullivan Pb-Zn-Ag deposit, southeastern British Columbia. Unaltered, euhedral crystals of polycrase and titanite 50-100 ??m in diameter are variably replaced by a finer-grained alteration-induced assemblage composed of anhedral polycrase and titanite with local calcite, albite, epidote, allanite, and thorite or uranothorite (or both). Average compositions of the unaltered and altered polycrase, as determined by electron-microprobe analysis, are (Y0.38 REE0.49 Th0.10 Ca0.04 Pb0.03 Fe0.01U0.01) (Ti1.48 Nb0.54 W0.04 Ta0.02)O6 and (Y0.42 REE0.32 Th0.15 U0.06 Ca0.04 Pb0.01 Fe0.01) (Ti1.57 Nb0.44 W0.04 Ta0.02)O6, respectively. The unaltered titanite has, in some areas, appreciable F (to 0.15 apfu), Y (to 0.40 apfu), and Nb (to 0.13 apfu). SHRIMP U-Pb geochronology of eight grains of unaltered polycrase yields a weighted 207Pb/206Pb age of 1413 ?? 4 Ma (2??) that is interpreted to be the age of vein formation. This age is 50-60 m.y. younger than the ca. 1470 Ma age of synsedimentary Pb-Zn-Ag mineralization in the Sullivan deposit, which is based on combined geological and geochronological data. SHRIMP ages for altered polycrase and titanite suggest later growth of minerals during the ???1370-1320 Ma East Kootenay and ???1150-1050 Ma Grenvillian orogenies. The 1413 ?? 4 Ma age for the unaltered polycrase in the veins records a previously unrecognized post-ore (<1470 Ma) and premetamorphic (>1370 Ma) mineralizing event in the Sullivan deposit and vicinity. The SHRIMP U-Pb age of the polycrase and high concentrations of REE, Y, Ti, Nb, and Th in the veins, together with elevated F in titanite and the absence of associated sulfides, suggest transport of these high-field-strength elements (HFSE) by F-rich and S-poor hydrothermal fluids unrelated to the fluids that formed the older Fe-Pb-Zn-Ag sulfide ores of the Sullivan deposit. Fluids containing abundant REE, HFSE, and F may have been derived from a geochemically specialized magma such as those that form alkaline granites, pegmatites, or carbonatites. In an alternative model. preferred here, these fluids were associated with a rift-related, crustal metasomatic event in the region. Determination of a Mesoproterozoic age for the polycrase-titanite veins establishes the first known occurrence of pre-Grenvillian REE-rich mineralization in the Belt-Purcell basin.

Canadian Mineralogist↗
USGS2016

Impacts of shore expansion and catchment characteristics on lacustrine thermokarst records in permafrost lowlands, Alaska Arctic Coastal Plain

Arctic lowland landscapes have been modified by thermokarst lake processes throughout the Holocene. Thermokarst lakes form as a result of ice-rich permafrost degradation, and they may expand over time through thermal and mechanical shoreline erosion. We studied proximal and distal sedimentary records from a thermokarst lake located on the Arctic Coastal Plain of northern Alaska to reconstruct the impact of catchment dynamics and morphology on the lacustrine depositional environment and to quantify carbon accumulation in thermokarst lake sediments. Short cores were collected for analysis of pollen, sedimentological, and geochemical proxies. Radiocarbon and 210 Pb/ 137 Cs dating, as well as extrapolation of measured historic lake expansion rates, were applied to estimate a minimum lake age of ~1400 calendar years BP. The pollen record is in agreement with the young lake age as it does not include evidence of the “alder high” that occurred in the region ~4000 cal yr BP. The lake most likely initiated from a remnant pond in a drained thermokarst lake basin (DTLB) and deepened rapidly as evidenced by accumulation of laminated sediments. Increasing oxygenation of the water column as shown by higher Fe/Ti and Fe/S ratios in the sediment indicate shifts in ice regime with increasing water depth. More recently, the sediment source changed as the thermokarst lake expanded through lateral permafrost degradation, alternating from redeposited DTLB sediments, to increased amounts of sediment from eroding, older upland deposits, followed by a more balanced combination of both DTLB and upland sources. The characterizing shifts in sediment sources and depositional regimes in expanding thermokarst lakes were, therefore, archived in the thermokarst lake sedimentary record. This study also highlights the potential for Arctic lakes to recycle old carbon from thawing permafrost and thermokarst processes.

Alaska↗
USGS1985

Uranium-series dating of sediments from Searles Lake: Differences between continental and marine climate records

One of the major unresolved questions in Pleistocene paleoclimatology has been whether continental climatic transitions are consistent with the glacial δ 18 O marine record. Searles Lake in California, now a dry salt pan, is underlain by sediment layers deposited in a succession of lakes whose levels and salinities have fluctuated in response to changes in climate over the last 3 × 10 6 years. Uranium-series dates on the salt beds range from 35 × 10 3 to 231 × 10 3 years. This range of dates allows identification of lake-sediment horizons that are time correlatives of the boundaries of marine isotope stages from the recent 3/4 boundary back to the 8/9 boundary. The 5/6 boundary coincided with a deepening of the lake, but the analogous 1/2 boundary coincided with desiccation. The 3/4, 4/5, 6/7, 7/8, and 8/9 boundaries correspond in age to horizons that record little or no change in sedimentation or climate. These hydrologic results demonstrate that the continental paleoclimate record at this mid-latitude site does not mimic the marine record.

California↗
USGS2022

Luminescence sediment tracing reveals the complex dynamics of colluvial wedge formation

Paleoearthquake studies that inform seismic hazard rely on assumptions of sediment transport that remain largely untested. Here, we test a widespread conceptual model and a new numerical model on the formation of colluvial wedges, a key deposit used to constrain the timing of paleoearthquakes. We perform this test by applying luminescence, a sunlight-sensitive sediment tracer, at a field site displaying classic colluvial wedge morphostratigraphy. The model and data comparison reveals complex sediment transport processes beyond the predictions of either conceptual or numerical models, including periods of simultaneous debris and wash facies forming processes, erosion, and reworking. These processes could lead to preservation bias, such as incomplete or overinterpretable paleoearthquake records, given the right environmental conditions. Attention to the site-specific mechanics of fault zone depositional systems, such as via sediment tracing, may buffer against the possible effects of preservation bias on paleoseismic study.

Science↗
USGS2007

Sinter-vein correlations at Buckskin Mountain, National district, Humboldt County, Nevada

At Buckskin Mountain (elev 2,650 m, 8,743 ft), Humboldt County, Nevada, a hydrothermal system, imposed on a middle Miocene volcanic sequence with contrasting permeabilities and tensile strengths, produced alteration assemblages controlled by elevation, from Hg-mineralized sinter to subjacent precious metal veins over a vertical distance exceeding 790 m. Sinter and epiclastic deposits, interpreted to be remnant paleosurface basinal strata enclosed by 16.6 to 16.1 Ma rhyolites, overlie older volcaniclastic basinal deposits and were part of a regional fluvial-lacustrine system developed among ca. 16 to 12 Ma basalt-rhyolite eruptive centers throughout the northern Great Basin. Because of contrasting erosional resistance among altered and unaltered rocks, Buckskin Mountain represents inverse topography with sinter and silicified epiclastic deposits at the summit. Sinter and veins, correlated by common elements, similar mineralogy, age constraints, textures, S isotope compositions, and fluid inclusion microthermometry, were deposited by sinter-vein fluid, the first of two sequential hydrothermal fluid regimes that evolved in response to magmatism, tectonism, hydrology, and topography. Thermal quenching of distally derived sinter-vein fluid in planar conduits caused deposition of banded quartz-silicate-selenide-sulfide veins ???270 to > 440 m below sinter at 16.1 Ma; vei??ns were initially enveloped by zoned selvages of proximal K-feldspar + K-mica + quartz + pyrite and distal illite + chlorite + calcite + pyrite. Mixing of sinter-vein fluid with local meteoric water in saturated basinal deposits caused deposition of silica, Hg-Se-S-Cl minerals, and precious metals in sinter and epiclastic deposits. Elevated ???Se/???S in sinter-vein fluid, and the relatively large stability fields of reduced aqueous selenide species in the temperature range of 250?? to <100??C, enabled (but was not the cause of) codeposition of selenide-sulfide minerals and common element associations in veins and sinter. Acid-sulfate fluid of the second fluid regime was derived from oxidation of H2S and other volatiles exsolved from sinter-vein fluid. Acid-sulfate fluid produced (1) a subhorizontal zone of partially leached basinal deposits and rhyolite from the paleosurface to a depth of ???60 m, and (2) laterally pervasive zones, ???100 to 200 m thick, of quartz + alunite ?? hematite and quartz + kaolinite + pyrite in volcaniclastic deposits immediately beneath partially leached rocks, but this fluid did not decompose selenide-sulfide-precious metal phases in sinter. Paragenetically late vein and wall-rock assemblages, including marcasite + pyrite, calcite, and kaolinite-replaced K minerals, record deeper transition of sinter-vein fluid into acid-sulfate fluid in vein conduits. This transition occurred as regional subsidence, manifested by the Goosey Lake depression immediately east of Buckskin Mountain, lowered the pieziometric surface at Buckskin Mountain, terminated sinter deposition, and caused boiling and/or degassing of sinter-vein fluid. The timing of subsidence is recorded by a decrease in alunite ages, from ca. 15.8 to 15.6 Ma, with depth below sinter. Lateral replacement of sinter and partially leached epiclastic deposits and rhyolite by opal-A marks the termination of the two hydrothermal regimes that lasted ???0.5 m.y. and followed rhyolitic volcanism of similar duration. Veins and sinter display textures that attest to plastic deformation, spalling, and gravitational settling, and indicate fluid-flow direction, velocity, and density stratification which, with conduit topology, may have influenced precious metal tenor in the veins. Components of sinter and veins were transported as colloids, formed in supersaturated sinter-vein fluid, that aggregated or coagulated as incompetent gelatinous layers in shallow pools and in underlying, near-vertical conduits in rhyolite and initially crystallized as opal and chalcedony. The low thermal conductivity of ho

Economic Geology↗
USGS2019

Evidence for plunging river plume deposits in the Pahrump Hills member of the Murray formation, Gale crater, Mars

Recent robotic missions to Mars have offered new insights into the extent, diversity and habitability of the Martian sedimentary rock record. Since the Curiosity rover landed in Gale crater in August 2012, the Mars Science Laboratory Science Team has explored the origins and habitability of ancient fluvial, deltaic, lacustrine and aeolian deposits preserved within the crater. This study describes the sedimentology of a ca 13 m thick succession named the Pahrump Hills member of the Murray formation, the first thick fine‐grained deposit discovered in situ on Mars. This work evaluates the depositional processes responsible for its formation and reconstructs its palaeoenvironmental setting. The Pahrump Hills succession can be sub‐divided into four distinct sedimentary facies: (i) thinly laminated mudstone; (ii) low‐angle cross‐stratified mudstone; (iii) cross‐stratified sandstone; and (iv) thickly laminated mudstone–sandstone. The very fine grain size of the mudstone facies and abundant millimetre‐scale and sub‐millimetre‐scale laminations exhibiting quasi‐uniform thickness throughout the Pahrump Hills succession are most consistent with lacustrine deposition. Low‐angle geometric discordances in the mudstone facies are interpreted as ‘scour and drape’ structures and suggest the action of currents, such as those associated with hyperpycnal river‐generated plumes plunging into a lake. Observation of an overall upward coarsening in grain size and thickening of laminae throughout the Pahrump Hills succession is consistent with deposition from basinward progradation of a fluvial‐deltaic system derived from the northern crater rim into the Gale crater lake. Palaeohydraulic modelling constrains the salinity of the ancient lake in Gale crater: assuming river sediment concentrations typical of floods on Earth, plunging river plumes and sedimentary structures like those observed at Pahrump Hills would have required lake densities near freshwater to form. The depositional model for the Pahrump Hills member presented here implies the presence of an ancient sustained, habitable freshwater lake in Gale crater for at least ca 10 3 to 10 7 Earth years.

Sedimentology↗
USGS2020

A new stratigraphic framework and constraints for the position of the Paleocene-Eocene boundary in the rapidly subsiding Hanna Basin, Wyoming

The Paleocene–Eocene strata of the rapidly subsiding Hanna Basin give insights in sedimentation patterns and regional paleogeography during the Laramide orogeny and across the climatic event at the Paleocene–Eocene Thermal Maximum (PETM). Abundant coalbeds and carbonaceous shales of the fluvial, paludal, and lacustrine strata of the Hanna Formation offer a different depositional setting than PETM sections described in the nearby Piceance and Bighorn Basins, and the uniquely high sediment accumulation rates give an expanded and near-complete record across this interval. Stratigraphic sections were measured for an ~1250 m interval spanning the Paleocene–Eocene boundary across the northeastern syncline of the basin, documenting depositional changes between axial fluvial sandstones, basin margin, paludal, floodplain, and lacustrine deposits. Leaf macrofossils, palynology, mollusks, δ13C isotopes of bulk organic matter, and zircon sample locations were integrated within the stratigraphic framework and refined the position of the PETM. As observed in other basins of the same age, an interval of coarse, amalgamated sandstones occurs as a response to the PETM. Although this pulse of relatively coarser sediment appears related to climate change at the PETM, it must be noted that several very similar sandstone bodies occur with the Hanna Formation. These sandstones occur in regular intervals and have an apparent cyclic pattern; however, age control is not sufficient yet to address the origin of the cyclicity. Signs of increased ponding and lake expansion upward in the section appear to be a response to basin isolation by emerging Laramide uplifts.

Wyoming↗
USGS2001

Constraining controls on carbonate sequences with high-resolution chronostratigraphy: Upper Miocene, Cabo de Gata region, SE Spain

A high-resolution chronostratigraphy has been developed for Miocene shallow-water carbonate strata in the Cabo de Gata region of SE Spain for evaluation of local, regional and global factors that controlled platform architecture prior to and during the Messinian salinity crisis. Paleomagnetic data were collected from strata at three localities. Mean natural remanent magnetization (NRM) ranges between 1.53 ?? 10-8 and 5.2 ?? 10-3 Am2/kg. Incremental thermal and alternating field demagnetization isolated the characteristic remanent magnetization (ChRM). Rock magnetic studies show that the dominant magnetic mineral is magnetite, but mixtures of magnetite and hematite occur. A composite chronostratigraphy was derived from five stratigraphic sections. Regional stratigraphic data, biostratigraphic data, and an 40Ar/39Ar date of 8.5 ?? 0.1 Ma, for an interbedded volcanic flow, place the strata in geomagnetic polarity Chrons C4r to C3r. Sequence-stratigraphic and diagenetic evidence indicate a major unconformity at the base of depositional sequence (DS)3 that contains a prograding reef complex, suggesting that approximately 250 000 yr of record (Subchrons C3Br.2r to 3Br.1r) are missing near the Messinian-Tortonian boundary. Correlation to the GPTS shows that the studied strata represent five third- to fourth-order DSs. Basal units are temperate to subtropical ramps (DS1A, DS1B, DS2); these are overlain by subtropical to tropical reefal platforms (DS3), which are capped by subtropical to tropical cyclic carbonates (Terminal Carbonate Complex, TCC). Correlation of the Cabo de Gata record to the Melilla area of Morocco, and the Sorbas basin of Spain indicate that early - Late Tortonian ramp strata from these areas are partially time-equivalent. Similar strata are extensively developed in the Western Mediterranean and likely were influenced by a cool climate or influx of nutrients during an overall rise in global sea-level. After ramp deposition, a sequence boundary (SB3) in Cabo de Gata correlates with a sequence boundary in Morocco and a published third-order eustatic fall suggesting at least a partial eustatic control for the sequence boundary. Coral reefs began to develop earlier in Cabo de Gata than at Melilla or Sorbas, arguing for local factors affecting this major environmental transition. Later Messinian reefs (DS3) from all areas are time-equivalent, suggesting a regional or global control on their formation. Some Halimeda-rich horizons in the Western Mediterranean are not time-equivalent event strata as hypothesized by others. Correlation of the relative sea-level curve for the fringing reef complex (DS3) with a published eustatic curve suggests at least a partial third-order global eustatic control for the highstand part of the sequence. Downstepping DS3 reefs and initial subaerial exposure of earlier DS3 reef strata approximately correlate with initiation of a series of subaerial unconformities in the South Pacific. The longer-term relative fall in sea-level during DS3 downstepping reef progradation does not correlate with a published third-order eustatic fall. Eustatic sea-level fluctuations may have been associated with initiation of the Mediterranean Messinian salinity crisis, but the longer-term fall may have been linked to tectonic uplift in the Mediterranean region. Widespread distribution of 'TCC-style' cycles of approximately the same age suggests a regional (Western Mediterranean) or global control on sea-level change responsible for TCC cycles. In addition, four subaerial exposure-capped TCC cycles may correlate with similar subaerial unconformities in the South Pacific, suggesting at least a partial eustatic control on TCC cyclicity. The high rates of relative sea-level change needed to generate a minimum of 25-30 m sea-level changes associated with each cycle are consistent with glacio-eustacy along with rapid evaporitic drawdown in the Mediterranean. ?? 2001 Elsevier Science B.V. All rights reserved.

Palaeogeography, Palaeoclimatology, Palaeoecology↗
USGS2025

A 400-k.y. perspective on arc volcanism: An exceptional explosive eruption record from Central Mexico

Volcanic eruption records provide key information for hazard planning but suffer from a time-dependent loss of resolution, hindering long-term evaluations of volcano behavior. Here, we investigate an exceptional sedimentary sequence from Lake Chalco, on the SE edge of Mexico City, which provides a perspective on volcanic activity over hundred-thousand-year time scales, and we develop a methodological and analytical protocol applicable to core datasets globally. The lava-dominated base of the sequence (~105 m) is followed by ~155 m of lateral-collapse derived deposits and overlain by ~295 m of lacustrine sediments containing at least 450 visible tephra fall deposits (TFDs), spanning 400 k.y. These TFDs include 205 events sourced from large-magnitude (predominantly volcanic explosivity index [VEI] ≥5) silicic explosive eruptions, principally from regional polygenetic sources, and 205 deposits from the nearby Sierra Chichinautzin volcanic field (SCVF). A gradual decline in both frequency and apparent magnitude in the silicic eruption record is consistent with the gradual migration of volcanism south along the adjacent Sierra Nevada volcanic range, toward Popocatépetl. In contrast, the SCVF-derived deposits imply persistent but episodic activity, on time scales of 40–70 k.y., suggesting that the SCVF has been more continuously active than previously recognized. Decoupled trends between the SCVF and regional silicic sources implies that the total magmatic flux is not dictated at the arc scale, or by external (e.g., climatic) drivers, but instead reflects the independent development of individual volcanic systems. The records indicate a minimum long-term frequency of impactful eruptions on Mexico City to be one per 900 years (>1 cm tephra deposited) or 9000 years (≥10 cm tephra).

Central Mexico↗
USGS2016

First records of Canis dirus and Smilodon fatalis from the late Pleistocene Tule Springs local fauna, upper Las Vegas Wash, Nevada

Late Pleistocene groundwater discharge deposits (paleowetlands) in the upper Las Vegas Wash north of Las Vegas, Nevada, have yielded an abundant and diverse vertebrate fossil assemblage, the Tule Springs local fauna (TSLF). The TSLF is the largest open-site vertebrate fossil assemblage dating to the Rancholabrean North American Land Mammal Age in the southern Great Basin and Mojave Desert. Over 600 discrete body fossil localities have been recorded from the wash, including an area that now encompasses Tule Springs Fossil Beds National Monument (TUSK). Paleowetland sediments exposed in TUSK named the Las Vegas Formation span the last 250 ka, with fossiliferous sediments spanning ∼100–13 ka. The recovered fauna is dominated by remains of Camelops and Mammuthus , and also includes relatively common remains of extinct Equus and Bison as well as abundant vertebrate microfaunal fossils. Large carnivorans are rare, with only Puma concolor and Panthera atrox documented previously. Postcranial remains assigned to the species Canis dirus (dire wolf) and Smilodon fatalis (sabre-toothed cat) represent the first confirmed records of these species from the TSLF, as well as the first documentation of Canis dirus in Nevada and the only known occurrence of Smilodon in southern Nevada. The size of the recovered canid fossil precludes assignment to other Pleistocene species of Canis . The morphology of the felid elements differentiates them from other large predators such as Panthera , Homotherium , and Xenosmilus , and the size of the fossils prevents assignment to other species of Smilodon . The confirmed presence of S. fatalis in the TSLF is of particular interest, indicating that this species inhabited open habitats. In turn, this suggests that the presumed preference of S. fatalis for closed-habitat environments hunting requires further elucidation.

PeerJ↗
USGS1998

New Tertiary stratigraphy for the Florida Keys and southern peninsula of Florida

Seven lithologic formations, ranging in age from Oligocene to Pleistocene, were recently penetrated by core holes in southernmost Florida. From bottom to top, they are the early Oligocene Suwannee Limestone; late-early Oligocene-to-Miocene Arcadia Formation, basal Hawthorn Group; late Miocene Peace River Formation, upper Hawthorn Group; newly proposed late Miocene-to-Pliocene Long Key and Stock Island Formations; and Pleistocene Key Largo and Miami Limestones. The rocks of the Suwannee Limestone form a third-order sequence. Although the entire thickness was not penetrated, 96 m of Suwannee core from one well contains at least 50 vertically stacked, exposure-capped limestone cycles, presumably related to rapid eustatic fluctuations while experiencing tropical to subtropical conditions. The Arcadia Formation is a composite sequence containing four high-frequency sequences composed of multiple vertically stacked carbonate cycles. Most cycles do not show evidence of subaerial exposure and were deposited under more temperate conditions, relative to the Suwannee Limestone. The Arcadia Formation in southernmost Florida is bounded by regional unconformities representing third-order sequence boundaries. Post-Arcadia transgression produced a major backstepping of sediment accumulation above the upper sequence boundary of the Arcadia Formation. The Peace River Formation, composed of diatomaceous mudstones, has been identified only beneath the Florida peninsula and is not present beneath the Florida Keys. Deposition occurred during marine transgressive to high-stand conditions and a local phosphatization event (recorded in northeast Florida). The transgression is possibly related to a global rise in sea level, which resulted in upwelling of relatively cooler, relatively nutrient-rich water masses onto the Florida Platform. It is proposed that the absence of Peace River sediments beneath the Keys is due to sediment bypass of the upper surface of the Arcadia, a result of sediment sweeping by an ancestral Florida current. During late Miocene to Pliocene time in the Florida Keys, siliciclastics of the Long Key Formation and fine-grained carbonates of the Stock Island Formation prograded toward the southern edge of the Florida Platform and downlapped onto the regional unconformity at the top of the Arcadia. Shallow-marine Pleistocene limestones (Key Largo and Miami Limestones), deposited during tropical to subtropical conditions, drape over accretionary successions of the Long Key and Stock Island Formations.

Florida↗
USGS1990

Phreatomagmatic and phreatic fall and surge deposits from explosions at Kilauea volcano, Hawaii, 1790 a.d.: Keanakakoi Ash Member

In or around 1790 a.d. an explosive eruption took place in the summit caldera of Kilauea shield volcano. A group of Hawaiian warriors close to the caldera at the time were killed by the effects of the explosions. The stratigraphy of pyroclastic deposits surrounding Kilauea (i.e., the Keanakakoi Ash Member) suggests that the explosions referred to in the historic record were the culmination of a prolonged hydrovolcanic eruption consisting of three main phases. The first phase was phreatomagmatic and generated well-bedded, fine fallout ash rich in glassy, variably vesiculated, juvenile magmatic and dense, lithic pyroclasts. The ash was mainly dispersed to the southwest of the caldera by the northeasterly trade winds. The second phase produced a Strombolian-style scoria fall deposit followed by phreatomagmatic ash similar to that of the first phase, though richer in accretionary lapilli and lithics. The third and culminating phase was phreatic and deposited lithic-rich lapilli and block fall layers, interbedded with cross-bedded surge deposits, and accretionary lapilli-rich, fine ash beds. These final explosions may have been responsible for the deaths of the warriors. The three phases were separated by quiescent spells during which the primary deposits were eroded and transported downwind in dunes migrating southwestward and locally excavated by fluvial runoff close to the rim. The entire hydrovolcanic eruption may have lasted for weeks or perhaps months. At around the same time, lava erupted from Kilauea's East Rift Zone and probably drained magma from the summit storage. The earliest descriptions of Kilauea (30 years after the Keanakakoi eruption) emphasize the great depth of the floor (300-500 m below the rim) and the presence of stepped ledges. It is therefore likely that the Keanakakoi explosions were deepseated within Kilauea, and that the vent rim was substantially lower than the caldera rim. The change from phreatomagmatic to phreatic phases may reflect the progressive degassing and cooling of the magma during deep withdrawal: throughout the phreatomagmatic phases magma vesiculation contributed to the explosive interaction with water by initiating the fragmentation process: thereafter, the principal role of the subsiding magma column was to supply heat for steam production that drove the phreatic explosions of the final phase. ?? 1990 Springer-Verlag.

Bulletin of Volcanology↗
USGS2021

Ocean floor manganese deposits

Much of the dissolved Mn delivered to the oceans is slowly oxidized and precipitated alongside varying amounts of Fe into Mn and ferromanganese (FeMn) mineral deposits that occur extensively in the deep ocean wherever sediment accumulation is low and substrate is available. FeMn crusts grow as pavements on rock outcrops throughout the global ocean whereas nodules form as individual FeMn-encrusted particles on the sediment-covered abyssal plains. Both crusts and nodules are composed predominantly of Fe and Mn oxide minerals that precipitate from seawater and for some nodules also from porewaters of deep-sea sediment. In contrast, hydrothermal oxide deposits consist predominantly of Mn or Fe oxide. FeMn crusts and nodules exhibit very high specific surface areas that allow them to scavenge abundant metals and other elements, recording the history of the source waters. Crusts especially serve as an important record of paleoceanographic conditions over the past 70 + million years. Critical metals essential to many computer, military, and green technologies are enriched in crust and nodule deposits to concentrations high enough to compare with, or exceed, typical terrestrial deposits, and they can be considered as potential resources for mining in the near future. Twenty-three contracts pertaining to exploration for nodules and crusts have been signed with the International Seabed Authority, and resource/reserve, baseline, and environmental impact assessments are underway. Many challenges remain to be addressed before full-scale mining of marine FeMn deposits will occur. However, their unique genesis and the growing worldwide need for rare and critical metals keep these deep-ocean deposits relevant to industry, scientists, and governments.

Book chapter↗
USGS2011

Wetland vegetation in Manzala lagoon, Nile Delta coast, Egypt: Rapid responses of pollen to altered nile hydrology and land use

The pollen record in a sediment core from Manzala lagoon on the Nile delta coastal margin of Egypt, deposited from ca. AD 1860 to 1990, indicates rapid coastal wetland vegetation responses to two primary periods of human activity. These are associated with artificially altered Nile hydrologic regimes in proximal areas and distal sectors located to ∼1200 km south of Manzala. Freshwater wetland plants that were dominant, such as Typha and Phragmites , decreased rapidly, whereas in the early 1900s, brackish water wetland species ( e.g. , Amaranthaceae) increased. This change occurred after closure of the Aswan Low Dam in 1902. The second major modification in the pollen record occurred in the early 1970s, after Aswan High Dam closure from 1965 to 1970, when Typha pollen abundance increased rapidly. Massive population growth occurred along the Nile during the 130 years represented by the core section. During this time, the total volume of lagoon water decreased because of conversion of wetland areas to agricultural land, and input of organic-rich sediment, sewage (municipal, agricultural, industrial), and fertilizer in Manzala lagoon increased markedly. Although the wetland plant community has continued to respond to increasingly intensified and varied human-induced pressures in proximal sectors, the two most marked changes in Manzala pollen best correlate with distal events ( i.e. , closure of the two dams at Aswan). The study also shows that the two major vegetation changes in Manzala lagoon each occurred less than 10 years after closure upriver of the Low and High dams that markedly altered the Nile regime from Upper Egypt to the coast.

Manzala Lagoon↗