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

At least 667 records · Page 37Linked to original sources

USGS2026

Long-term intermittent connection between the western Snake River Plain and Columbia basin: A two-phased incision history of Hells Canyon

For more than a century, researchers have debated the route of the Snake River across the northern Cordillera and U.S. Pacific Northwest, including the associated incision history of Hells Canyon. Here, we use detrital zircon U-Pb provenance analysis of Miocene strata upstream and downstream of Hells Canyon to constrain the evolution in fluvial pathways over time. Downstream of Hells Canyon, we show that the ca. 10−6 Ma Clarkston Heights gravel was dominantly sourced from the nearby Salmon and Clearwater rivers but also with substantial input from drainages that now flow into the western Snake River Plain. These same western Snake River Plain drainages were contributing to time-equivalent Lake Idaho strata, upstream of Hells Canyon, indicating a Hells Canyon fluvial connection between the western Snake River Plain and Columbia basin before 6 Ma. Results from Lake Idaho strata suggest a two-phased lacustrine history in the western Snake River Plain: Before ca. 6.0 Ma, lake strata were derived from local tributaries, suggesting that the western Snake River Plain was isolated from the modern upper Snake River system. Between ca. 4.3 Ma and 2.2 Ma, the source area expanded to include eastern tributaries in conjunction with migration of high-standing topography of the Yellowstone hotspot. Our results challenge the long-held hypothesis of “capture” of the Snake River through Hells Canyon. Instead, we infer that Hells Canyon was a long-established route for outflow of lakes occupying the western Snake River Plain, possibly intermittently, during a ca. 10−2 Ma phase of slow regional incision, followed by rapid incision in Hells Canyon starting ca. 2 Ma in conjunction with erosion of the topographic barrier impounding Lake Idaho.

Idaho, Oregon↗

USGS2026

Petrography and mineralogy of selected pre-Middle Jurassic basement rocks beneath the Atlantic and Gulf Coastal Plains in Florida

Florida is covered by flat-lying sedimentary strata of the Atlantic and Gulf Coastal Plains. These strata have accumulated since Middle Jurassic time. The pre-Middle Jurassic, or basement, rocks that underlie the Coastal Plain in Florida are known only from drill cores and cuttings recovered from a relatively small number of boreholes. This data report presents petrographic observations and the results of X-ray diffraction analyses of basement rocks from 18 boreholes across Florida in support of the identification, discrimination, and correlation of units for a subcrop geologic map of pre-Middle Jurassic rocks composing Florida’s sub-Coastal Plain geology.

Florida↗

USGS2026

The 3D Elevation Program—Supporting North Dakota's economy

Introduction As the northernmost Great Plains State encompassing two geomorphological areas divided by the Missouri River, North Dakota has varied needs for high-resolution elevation data. The top industry in North Dakota is agriculture and related products, and the fastest growing sector is natural resources led by oil and gas extraction and mining, all of which contribute to the State’s economy (U.S. Department of Agriculture, National Agricultural Statistics Service, 2024b). Critical applications that meet the State’s management needs depend on light detection and ranging (lidar) data that provide a highly detailed three-dimensional (3D) model of the Earth’s surface and aboveground features. The 3D Elevation Program (3DEP; refer to sidebar) is managed by the U.S. Geological Survey (USGS) in partnership with Federal, State, Tribal, U.S. territorial, and local agencies to acquire consistent lidar coverage at quality level 2 or better (table 1) to meet the many needs of the Nation and North Dakota. The status of available and in-progress 3DEP baseline lidar data in North Dakota is shown in figure 1. 3DEP baseline lidar data include quality level 2 or better, 1-meter or better digital elevation models, and lidar point clouds, and must meet the Lidar Base Specification 2025 Rev. A (https://www.usgs.gov/3dep/lidarspec) or newer requirements. The National Enhanced Elevation Assessment (Dewberry, 2012) identified user requirements and conservatively estimated that availability of lidar data would result in at least $12.39 million in new benefits annually to the State. The top nine North Dakota business uses for 3D elevation data, which are based on the estimated annual conservative benefits of 3DEP, are shown in table 2.

North Dakota↗

USGS2026

Geologic map of pre-Middle Jurassic basement rocks beneath the Atlantic and Gulf Coastal Plains in Florida

Much of the southeastern United States, including all of Florida, is covered by flat-lying sedimentary strata of the Atlantic and Gulf Coastal Plains which have accumulated since Middle Jurassic time. The pre-Middle Jurassic rocks that underlie these coastal plains in Florida, here collectively referred to as “basement,” are known only from a relatively small number of boreholes. This scientific investigations map presents an interpretation of the basement geology in a 1:1,000,000-scale subsurface geologic map with supporting text, data, and figures. The subsurface mapping methodology integrates petrographic, geochronological, thermochronological, geochemical, and mineralogical analyses of drill cores and cuttings in the context of regional geophysical data. The pre-Middle Jurassic rocks of Florida consist of the Gondwanan (West African) Suwannee terrane which was accreted to Laurentia during the Alleghanian orogeny and subsequently intruded by Permian granites, superposed by early Mesozoic rift basins, and partially overlain by bimodal Jurassic volcanic rocks. The younger basement components, specifically the Southwest Florida volcanic province, North Florida tholeiites, early Mesozoic rift basins, and Alleghanian granitoids, have correlative and contemporaneous units throughout the Appalachian orogen. In contrast, Florida’s older basement rocks, including Paleozoic siliciclastic strata of the Suwannee basin, North Florida volcanic series, Osceola and Gaskin intrusive complexes, and the St. Lucie Metamorphic Complex, have neither surface exposures nor unequivocal correlates. Major structures include early Mesozoic normal faults and northwest-striking transfer zones such as the Jay fault. Many of these faults define the boundaries of subbasins within the South Georgia rift system. Top-of-basement structure contours show gentle arches and embayments that are also recognized in overlying coastal plain strata.

Florida↗

USGS2026

Glacier fed deltas and new age constraints for glacial Lake Grand Gorge in the northern Catskill Mountains of New York State, USA

Ice-dammed lakes were common along the southern margin of the Laurentide Ice Sheet during deglaciation. In the Schoharie Valley of the northern Catskill Mountains, New York, a 171 km 2 lake known as glacial Lake Grand Gorge formed in an interlobate area. Previous researchers suggested that deltas developed into this glacial lake from meltwater supplied by the adjacent Hudson Lobe during deglaciation. This study investigates stratigraphy and sedimentology of Pleistocene deltas and lake deposits to determine the source of meltwater and sediment. Detailed examination of stratigraphy from quarries, stream exposures, and new exploration borings was combined with radiocarbon and OSL geochronology to establish event stratigraphy. Sedimentologic and geomorphic data from deltas in the Manor Kill and Platter Kill Valleys demonstrates that braided outwash was supplied directly from the Westerlo Sublobe that crossed the northeastern escarpment of the Catskill Mountains. New geochronologic data indicates that the lake was established by 28 ka and likely persisted to at least 22 ka. Insects and twigs recovered from lake sediments complement the OSL data and indicate: (1) that the lake was present significantly earlier than previous deglacial models predict, and (2) that it existed in an ice-free area of the northern Catskill Mountains during the last glacial maximum of the MIS 2 glaciation.

New York↗

USGS2026

Temperate lake heatwaves accelerate non-linearly as timing synchronizes across a diverse landscape

Temperate lakes are experiencing intensifying heatwaves, or prolonged periods of anomalously warm water, with potentially severe ecological consequences. Previous studies have predominantly used linear trend analyses to understand heatwave dynamics, potentially masking temporal acceleration patterns and shifts in variance. Here, we analyzed long-term, nonlinear trends in heatwave frequency, intensity, and timing across 4391 New York lakes using simulated daily surface water temperatures from an Entity-Aware Long Short-Term Memory deep learning model (validated root mean square error = 1.82°C; 1980–2020). We applied generalized additive mixed models to quantify complex temporal patterns while accounting for lake-specific effects and environmental characteristics (lake surface area, elevation, and latitude). All heatwave metrics demonstrated nonlinear and dynamic temporal trends. Heatwave frequency showed early increases in the number of events (0.05–1.32 events during the 1980s) followed by accelerated growth after 2000; other metrics exhibited more complex decadal patterns. Temporal variance increased significantly for both heatwave frequency ( τ = 0.73, p < 0.001) and intensity ( τ = 0.33, p = 0.003). Lake characteristics drove some heatwave dynamics; smaller lakes experienced higher intensities and complex elevation-latitude interactions varying by heatwave metric. Spatial patterns revealed increasing heterogeneity for heatwave intensity and frequency while heatwave timing homogenized to earlier dates across the landscape. Our findings reveal nonlinear heatwave dynamics with increasing variability, which may reduce predictability and intensify ecological vulnerabilities beyond current projections.

New York↗

USGS2026

Novel avian papillomaviruses identified in a south polar skua sampled on Ross Island, Antarctica

Papillomaviruses are small circular DNA viruses that infect epithelial cells of their hosts. Avian papillomaviruses are poorly sampled/documented compared to those infecting humans. We used a viral metagenomic approach to identify viruses from the oral swab taken from a deceased south polar skua ( Stercorarius maccormicki ) found at Cape Royds, Ross Island, Antarctica in late 2024. We identified three papillomaviruses and determined their complete genomes, Stercorarius maccormicki papillomavirus (SmacPV) 1-3. SmacPV1 is the most divergent of the three SmacPVs, sharing 62% genome-wide pairwise identity to SmacPV2 and SmacPV3 and <63.5% to other avian papillomaviruses. The genomes of SmacPV2 and SmacPV3 represent two new papillomavirus types sharing 82.4% genome-wide pairwise identity with each other and <72% to other papillomaviruses. SmacPV2 and SmacPV3 phylogenetically cluster with sequences of the Rissa tridactyla papillomavirus 1 from black-legged kittiwake ( Rissa tridactyla ), Larus smithsonianus papillomavirus 1 from American herring gull ( Larus smithsonianus ) and Fratercula arctica papillomavirus 1 from Atlantic puffin ( Fratercula arctica ), and they collectively represent a new papillomavirus species. These are the first papillomaviruses to be identified in Stercorarius spp . and add to the handful of known papillomaviruses in identified avian species. We also expand the known host range of papillomaviruses in Antarctic animals, which previously included Adélie penguins ( Pygoscelis adeliae ), Weddell seals ( Leptonychotes weddellii ), Antarctic fur seals ( Arctocephalus gazella ), leopard seals ( Hydrurga leptonyx ) and emerald notothen ( Trematomus bernacchii ).

Archives of Virology↗

USGS2026

The Great Salt Lake (Utah, USA) acoustic and sedimentary archive of Wasatch Front earthquakes

As the largest low-relief basin in the western United States, the Great Salt Lake offers an opportunity to explore acoustic and sedimentary archives of earthquake ruptures in a shallow terminal basin. Here, we use subbottom compressed high intensity radiated pulse (Chirp) profiles and sedimentary cores to address questions related to how Great Salt Lake sediments respond to surface rupture and earthquake shaking and whether the lake is sensitive to both Great Salt Lake fault (GSLF) and Wasatch fault zone (WFZ) earthquakes. Chirp profiles reveal laterally continuous seismic stratigraphy with vertically displaced strata, onlap surfaces, and growth stratigraphy produced by GSLF surface ruptures. We identify and date two ruptures on the Fremont Island section and three on the Antelope Island section; temporal overlap of these ruptures supports synchronous rupture of both sections. Combined with previous data, our results yield a record of four Holocene surface-rupturing (M W 6.9−7.3) earthquakes on the GSLF with a mean recurrence of ∼3.2 k.y. Sediment cores include ≤41-cm-thick, massive, homogeneous to normally graded disturbance beds that interrupt laminated bioclastic sediment. Disturbance bed correlations yield four lacustrine earthquake deposits since ca. 1.7 ka; the youngest possibly records the most recent GSLF surface rupture whereas older deposits were likely produced by WFZ earthquakes. Modeled historical earthquakes yield a Great Salt Lake sediment disturbance shaking threshold of MMI ∼VI, controlled in part by the lake-bottom expression of the GSLF scarp. Our integration of primary (fault-related) and secondary (shaking-related) earthquake evidence improves our understanding of sediment disturbance processes and the archival potential of low-relief lake basins.

Utah↗

USGS2026

Fault sources of the 2020 southern Puerto Rico seismic sequence and the regional tectonic structure

The 2020 southwestern Puerto Rico seismic sequence occurred in an area not known for seismic activity and included multiple normal and strike‐slip focal mechanisms. The largest earthquake, M w 6.4, caused significant damage and permanent shoreline subsidence. The locations of the ruptured faults have been explored extensively using seismological and geodetic evidence, but no consensus has been reached. Here, we report the results of a high‐resolution seismic reflection survey that identified a north‐verging 20 km long curved normal fault spanning the upper reach of the Guayanilla canyon, which we call the Guayanilla Canyon fault. Part of the fault likely ruptured during the M w 6.4. The concave‐to‐the‐north fault bounds a south‐dipping ∼1 km deep asymmetric basin. This long‐lived structure, identified also on sediment isopach and magnetic anomaly maps, appears to control the formation of the Guayanilla canyon system, the only submarine drainage system in southern Puerto Rico, suggesting a relationship among seismic activity, geomorphology, and reef development. Our seismic reflection data do not support the existence of previously published major seismogenic faults in the area, such as the north‐northeast–south‐southwest Guayanilla fault zone, the Northern Boqueron Bay‐Punta Montalva fault, or a northwest–southeast strike‐slip fault, suggested to have ruptured as part of the M w 6.4 earthquake. We identified smaller faults in the survey area, some of which can be correlated with seafloor expressions, and/or with changes in sediment thickness and magnetic anomalies, and/or with moderate‐sized earthquakes. Multiple seismic images of Investigator fault, a prominent mid‐slope feature parallel to the south coast of Puerto Rico, show buried low‐angle thrusts and an abrupt change in the attitude of the overlying sediments, leading us to interpret this feature as the expression of a boundary between the now‐inactive upper accretionary prism of Muertos trough and a buried back‐arc basin that overlies the arc basement of Puerto Rico.

Puerto Rico↗

USGS2026

Assessing the state of hydrologic science in the Upper Klamath Basin—A comprehensive review of data, tools, and models

Water demand in the Upper Klamath Basin (UKB) from various stakeholders and ecological needs often outstrips available supply, leading to persistent management challenges. This study reviews the state of hydrologic science within the UKB as of 2025—specifically, the tools, data, and models available for assessing five key components of the water system: (1) surface water; (2) precipitation; (3) evapotranspiration; (4) groundwater; and (5) water use. The UKB water supply is critical for Native American communities, regional agriculture, and federally listed fishes and faces challenges from competing needs, climate variability, and operational/regulatory requirements. We assess existing datasets, regional and national models, and historical studies to understand the available resources and identify gaps that may hinder integrated water assessments and management. Our findings indicate areas where improvements in data collection and model precision could improve the accuracy of water-availability forecasts and support water-management practices. This review can inform near-term forecasting, assist in optimizing water-resource data collection and management strategies, and support regional water-availability assessments of the basin.

Oregon↗

USGS2026

Quantifying Chinook Salmon habitat across flow regimes: High resolution modeling in Oregon’s Willamette River basin

The Santiam and McKenzie River basins of western Oregon provide critical habitat for federally listed Upper Willamette River Spring Chinook salmon ( Oncorhynchus tshawytscha ). Streamflows in each basin are regulated in part by high-head multi-purpose dams; however, quantitative linkages between regulated streamflows and downstream habitat for juvenile and adult Chinook salmon remain limited. This study integrates high-resolution topo-bathymetric lidar, two-dimensional hydraulic models, and novel detailed sediment distribution models to evaluate habitat across a range of flows for over 400 river km. Results suggest that habitat quantity for two juvenile life stages (fry and parr) differs in response to streamflow; fry habitat appears to be relatively insensitive to streamflow, except in the downstream-most reaches of each river, while parr habitat generally increases from low to moderate flows, yet decreases at higher flows. Spawning habitat is largely inversely related to streamflow and is primarily limited by suitable substrate availability, likely reflecting sediment retention effects of upstream dams. Additionally, streamflow thresholds were identified where redd desiccation risk increases significantly with declining streamflow. These findings provide managers with spatially explicit tools to evaluate flow management tradeoffs during critical rearing and spawning periods and provide insights into habitat dynamics in large, regulated rivers. This work demonstrates how high-resolution modeling can support quantification of habitat at the landscape level.

Oregon↗

USGS2026

Quantifying Landsat’s contributions to U.S. agricultural and forestry applications

The Landsat program has provided over 54 years of multispectral imagery, contributing vital information for agricultural and forestry scientific research and operational activities. Freely available Landsat data have enabled scientists to analyze land use patterns, assess ecological impacts, and develop strategies for sustainable management. We explored Landsat’s pivotal role through the lens of the United States Group on Earth Observations 2023 Earth Observation Assessment (EOA). The EOA included comprehensive surveys of more than 2000 federally supported Earth observation data products. We subsequently analyzed how Landsat satellite data and derived products support agricultural and forestry-related priorities compared to other Earth observation inputs. We evaluated both direct and indirect applications of the data, identifying key users across federal agencies and assessing how Landsat data contribute to critical products, services, and objectives. The results indicate that Landsat provides key information to support diverse activities across agriculture and forestry sectors, such as enhancing food supply, improving resilience to disaster and disturbance events, maximizing ecosystem productivity and conservation, and supporting regulatory requirements and decision-making. The Landsat OLI and TIRS sensors ranked 4th and 10th, respectively, out of 1171 Earth observation inputs identified in the study, underscoring their value to agriculture and forestry.

Remote Sensing↗

USGS2026

Continental-scale prediction of hydrologic signatures and processes

Understanding how dominant hydrologic processes and their drivers vary across diverse continental-scale landscapes is critical for hydrologic modeling and water management applications. Our research addresses this question by synthesizing large-sample watershed datasets, Caravan and GAGES-II, and developing random forest models to identify patterns in hydrologic function. We assessed dominant processes by examining hydrologic signatures – summary indicators of watershed function derived from hydroclimatic time series and random forest models across 14 146 gauged United States watersheds. The results reveal clear continental-scale gradients in hydrologic processes, including baseflow, overland flow, storage, and water balance losses. Our map of dominant processes highlights, for example, the transition from baseflow to fast responses and back to baseflow along the elevation gradient from the Appalachian spine, through the Piedmont, to the Eastern Coastal Plain; a distinct outer ring around the Great Lakes region; and sharp contrasts between coastal and inland processes in the West. Variable importance analysis from random forest models show that processes in the western U.S. are primarily controlled by climate, whereas in the eastern U.S., soil, geology, and topography play larger roles, with distinct human influences apparent in urban areas. Our approach of estimating dominant processes and their drivers facilitates extending process knowledge from research watersheds to the continental scale, assessing current hydrological understanding, and evaluating hydrological model structures.

conterminous United States↗

USGS2026

Bright spot in eDNA monitoring: Early detection of invasive New Zealand mudsnails (Potamopyrgus antipodarum) prompted effective rapid response for fish hatchery

The New Zealand mudsnail (NZMS; Potamopyrgus antipodarum ) is a widespread aquatic invasive species that is parthenogenic, requiring only a single individual to initiate an infestation. Fish hatcheries–which are critical infrastructure that raise fish to support conservation, recreation, and subsistence fisheries–frequently use local water sources to provide cool water and are especially vulnerable to NZMS invasion from the contamination of water supplies. If an invasion proceeds undetected, hatcheries pose a risk for compounding the spread of NZMS because their operations transfer live organisms and associated water between hatchery facilities and, when stocking, to rivers and lakes. The U.S. Fish and Wildlife Service's Alchesay National Fish Hatchery, located on the Fort Apache Indian Reservation in Whiteriver, Arizona, produces trout to stock in Tribal reservoirs, lakes, and rivers across the southwestern U.S. New Zealand mudsnails were first documented in Arizona in 1995, are now widespread in this region, and occur at the confluence of the hatchery's outflow with the North Fork White River. Contamination of water supplies is the principal pathway for NZMS invasion into the hatchery. Here, we describe early detection environmental DNA (eDNA) surveillance efforts for NZMS at Alchesay National Fish Hatchery. Positive eDNA detections initiated a chain of events that ultimately led to four NZMS individuals being discovered and a rapid response eradication effort. Follow-up eDNA sampling and visual observation efforts after the eradication effort have yielded no detections of NZMS eDNA. We credit the success of this case with four key elements: rapid turnaround times, a robust quality assurance scheme, a proactive eDNA sampling design, and established partnerships. To our knowledge, this is the first published case of eDNA monitoring being used for early detection and successful rapid response for complete removal of an invasive species in a fish hatchery.

Arizona↗

USGS2026

Rain interacts with directional wind to cause nest failures within breeding colonies of Western and Clark's Grebes

Western Grebe ( Aechmophorus occidentalis ) and Clark's Grebe ( Aechmophorus clarkii ) populations have declined across their range, and they are species of high conservation concern. Cascade Reservoir in central Idaho supports one of the largest breeding colonies of Aechmophorus grebes in North America (and the largest in Idaho), but few offspring are produced from the colony in most years. Low fecundity and little natal recruitment may be the proximate cause of Aechmophorus grebe population declines, but the ultimate cause of low recruitment is not known. One hypothesis for the low fecundity at Cascade Reservoir (and at other grebe colonies in the region) is that waves on freshwater breeding lakes inundate nests and cause pairs to abandon their nests. We tested that hypothesis by examining whether nest survival was negatively associated with changes in daily water level, daily peak wind speed and daily peak wind direction (i.e. winds that push water into the breeding colony). We also included daily mean temperature and daily total precipitation to evaluate a more general hypothesis that weather events caused nest failures. We used aerial imagery obtained from repeated drone flights to create encounter histories for 3888 Aechmophorus grebe nests to then estimate daily nest survival and evaluate whether daily water level, daily peak wind speed and daily peak wind direction (as predicted by the wind-driven wave hypothesis) were important causes of nest failure relative to other factors that commonly affect daily nest survival in birds. Nesting success was alarmingly low and we found some support for the wave inundation hypothesis; the results suggest that nesting attempts are more likely to fail on days with precipitation combined with winds blowing into the colony. Our results are the first to show that wind and precipitation affect the nest fate of Aechmophorus grebes.

Idaho↗

USGS2026

Assessment of Chinook Salmon smolt survival at offsite release locations in the Sacramento River across wet and dry years

We used acoustic telemetry to estimate survival of tagged release groups, and quantify differences between alternative hatchery release strategies. To assess whether offsite release could increase survival of hatchery fish relative to those released at the hatchery, we compare survival during emigration of hatchery fall Chinook Salmon (FCS, Oncorhynchus tshawytscha ) smolts released onsite, at Coleman National Fish Hatchery (NFH), to those released at alternative offsite locations downstream in the upper Sacramento River, California. Approximately 300 fish in each release group were implanted with acoustic tags in the 3-year study during 2019, 2021, and 2022. Environmental conditions in the emigration corridor varied between study years, with extended high flows in 2019, whereas drought conditions and a flat hydrograph occurred in 2021 and 2022. Survival across years appeared to reflect environmental conditions, with higher overall survival seen in 2019. Survival differences between release sites generally showed higher cumulative survival to Knights Landing or Chipps Island for the downstream release groups, compared to the onsite releases during 2021 and 2022. This information suggests hatchery releases of FCS from Coleman NFH at downstream release sites may benefit emigration survival during years of drought and sub-optimal in-river conditions, compared to standard onsite releases. Hatchery managers can use information from this study to diversify the portfolio of release strategies, which may be useful to buffer against extreme variations of adult abundance by spreading risks across space and time. Ultimately, offsite releases may be a useful tool for adaptive management of these culturally, ecologically, and economically important salmon populations.

California↗

USGS2026

Differences among runs of Chinook Salmon in routing probability at the Georgiana Slough-Sacramento River junction

The survival of juvenile Chinook Salmon ( Oncorhynchus tshawytscha ) depends on the specific migration route they take through the Sacramento–San Joaquin Delta. Factors such as flow magnitude, flow direction, and distribution of fish across the channel significantly affect the likelihood of their entering routes with lower survival probabilities. Management strategies to mitigate the entry of endangered winter-run and threatened spring-run Chinook Salmon into the interior Delta—particularly through Georgiana Slough—involve flow regulation and the installation of a bioacoustic fish fence. Monitoring the effectiveness of these measures has primarily relied on acoustically-tagged, juvenile, hatchery-reared, late-fall-run Chinook Salmon, which are easier to obtain and can accommodate larger tags compared to other runs. Previous studies explored how flow dynamics affect routing probabilities of late-fall-run Chinook Salmon, but there is a lack of understanding about how routing probabilities vary among runs. We leveraged data from 15 previous studies comprising 3,004 acoustically-tagged fish across all four runs, over a 12-year period, to assess the effects of run on routing probability into Georgiana Slough, while accounting for variation in flow dynamics. We employed logistic regression to model the influence of tidal flow metrics, time of day (day and night), and run type on the probability of juvenile Chinook Salmon being routed into Georgiana Slough. Our analysis revealed that reverse flow during incoming tides influenced the routing probabilities of all runs. An increased proportion of flow into Georgiana Slough, meant an increased probability for all runs to be routed into Georgiana Slough. Late-fall-run Chinook Salmon also showed a greater probability of routing into Georgiana Slough during the night than during the day, whereas the opposite was true for other runs. These differences in routing probability affect our understanding of how management actions intended to reduce routing into Georgiana Slough may differentially affect the four runs of Chinook Salmon in the Sacramento River.

Callifornia↗

USGS2026

Paleocene-Eocene dinoflagellate biostratigraphy in the central Delaware coastal plain

Dinoflagellate cyst palynology and lithostratigraphy from three continuously cored boreholes (Blackbird, Smyrna, and Woodland Beach), supplemented by calcareous nannofossil biostratigraphic data, were used to refine the age and correlation of three Paleocene-Eocene formations in northern Delaware: the Vincentown, Manasquan, and Shark River. Lithologic logs reveal significant facies changes in the upper Paleocene Vincentown Formation over a short distance (*9 km) southeastward, transitioning from very permeable glauconite-quartz-shell-rich sands that form the regionally important Rancocas/Aquia aquifer to much less permeable muddy sands and sandy muds. These lithologic changes represent a shift from nearshore, clear, warm-water, carbonate-rich sand shoals to mud-dominated deeper-water, offshore shelfal environments. Dinocyst assemblages including Areoligera gippingensis, Cribroperidinium giuseppei, and Stenodinium meckelfeldensis confirm the Paleogene ages and track these paleoceanographic changes from shallow coastal settings updip to neritic or outer marine settings downdip. The Vincentown Formation is unconformably overlain by the lower Eocene Manasquan Formation, which consists predominantly of silt and clay with relatively consistent lithology across the study area, representing general neritic or open marine conditions. Lithology, dinoflagellate cyst assemblages, and calcareous nannofossil data indicate that the Marlboro Clay and its record of the onset of the Paleocene-Eocene Thermal Maximum (PETM) global warming event is absent from the Paleocene-Eocene transition at these sites, with an unconformity marking the boundary between the Vincentown and Manasquan formations. The youngest unit examined, the Eocene Shark River Formation, unconformably overlies the Manasquan Formation and consists of interbedded clayey silts and sands, with dinoflagellate assemblages suggesting a return to coastal or inner neritic settings. Calcareous nannofossil zones recognized from the Woodland Beach core corroborate the depositional ages determined using dinoflagellates throughout the sequence, confirming the chronostratigraphic framework for these important coastal plain units.

Delaware↗