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At least 217 records · Page 12Linked to original sources

USGS1984

Stratiform tourmalinites in metamorphic terranes and their geologic significance

Stratiform tourmalinites are significant minor rock types in many regional metamorphic terranes of the world. Tourmalinites are more widespread than previously recognized and are especially common in Proterozoic and early Paleozoic sequences dominated by clastic metasedimentary rocks. They consist of conformable layers made up primarily of quartz and abundant tourmaline, the latter typically exceeding 15% to 20% of rock volumes. A few tourmalinites display striking sedimentary structures such as graded bedding, cross-laminations, slump and flame structures, and rip-up clasts. These and other geologic features provide important constraints for assessing the origin of these rocks, and they suggest that tourmalinites form by the early diagenetic modification of a primary boron-rich chemical precipitate. Tourmalinites are significant in preserving a valuable record of unusual chemical and paleogeographic conditions in clastic sedimentary basins, and in their close association with a variety of stratabound mineral deposits.

Geology↗

USGS2011

Widespread inclination shallowing in Permian and Triassic paleomagnetic data from Laurentia: Support from new paleomagnetic data from Middle Permian shallow intrusions in southern Illinois (USA) and virtual geomagnetic pole distributions

Recent paleomagnetic work has highlighted a common and shallow inclination bias in continental redbeds. The Permian and Triassic paleomagnetic records from Laurentia are almost entirely derived from such sedimentary rocks, so a pervasive inclination error will expectedly bias the apparent polar wander path of Laurentia in a significant way. The long-standing discrepancy between the apparent polar wander paths of Laurentia and Gondwana in Permian and Triassic time may be a consequence of such a widespread data-pathology. Here we present new Middle Permian paleomagnetic data from igneous rocks and a contact metamorphosed limestone from cratonic Laurentia. The exclusively reversed Middle Permian magnetization is hosted by low-Ti titanomagnetite and pyrrhotite and yields a paleomagnetic pole at 56.3??S, 302.9??E (A95=3.8, N=6). This pole, which is unaffected by inclination shallowing, suggests that a shallow inclination bias may indeed be present in the Laurentian records. To further consider this hypothesis, we conduct a virtual geomagnetic pole distribution analysis, comparing theoretical expectations of a statistical field model (TK03.GAD) against published data-sets. This exercise provides independent evidence that the Laurentian paleomagnetic data is widely biased, likely because of sedimentary inclination shallowing. We estimate the magnitude of this error from our model results and present and discuss several alternative corrections. ?? 2011 Elsevier B.V.

Tectonophysics↗

USGS2008

On the in situ aqueous alteration of soils on Mars

Early (>3 Gy) wetter climate conditions on Mars have been proposed, and it is thus likely that pedogenic processes have occurred there at some point in the past. Soil and rock chemistry of the Martian landing sites were evaluated to test the hypothesis that in situ aqueous alteration and downward movement of solutes have been among the processes that have transformed these portions of the Mars regolith. A geochemical mass balance shows that Martian soils at three landing sites have lost significant quantities of major rock-forming elements and have gained elements that are likely present as soluble ions. The loss of elements is interpreted to have occurred during an earlier stage(s) of weathering that may have been accompanied by the downward transport of weathering products, and the salts are interpreted to be emplaced later in a drier Mars history. Chemical differences exist among the sites, indicating regional differences in soil composition. Shallow soil profile excavations at Gusev crater are consistent with late stage downward migration of salts, implying the presence of small amounts of liquid water even in relatively recent Martian history. While the mechanisms for chemical weathering and salt additions on Mars remain unclear, the soil chemistry appears to record a decline in leaching efficiency. A deep sedimentary exposure at Endurance crater contains complex depth profiles of SO4, Cl, and Br, trends generally consistent with downward aqueous transport accompanied by drying. While no model for the origin of Martian soils can be fully constrained with the currently available data, a pedogenic origin is consistent with observed Martian geology and geochemistry, and provides a testable hypothesis that can be evaluated with present and future data from the Mars surface. ?? 2008 Elsevier Ltd.

Geochimica et Cosmochimica Acta↗

USGS2025

Seismic intensities, ground motions and basin amplification from the 2022 Mw 6.4 Ferndale, California intraslab earthquake

On December 20, 2022, a Mw 6.4 earthquake occurred at a depth of 18 km within the subducting Gorda plate in the Mendocino Triple Junction (MTJ), one of the most seismically active regions of the contiguous United States, causing widespread damage to local communities. Here we document the seismic intensities, ground motions, and basin amplification effects recorded by this earthquake across Humboldt County as part of an ongoing scientific effort to understand subduction zone earthquake hazards. Modified Mercalli Intensity (MMI) values from our post-earthquake field survey report shaking intensities as high as VIII (Severe). Strong ground motion data from 54 seismic stations were processed to calculate amplitude and frequency content parameters across Northern California. The maximum calculated geometric mean PGA and PGV are 1053 cm/s 2 and 52 cm/s (respectively), both recorded within the 3 km deep Eel River sedimentary basin. Comparisons with four published Ground Motion Prediction Equations indicate that PGA and PGV measurements align with expected attenuation-distance patterns for intraslab earthquakes of this nature. Within the Eel River Basin, ground motions for frequencies above 1 Hz are amplified, with respect to reference stations, by factors greater than 2. Our findings suggest that peak ground motions were mainly caused by sedimentary basin site-effects within the Eel River basin, although rupture directivity may have also increased ground motion amplitudes locally. While the Ferndale area is primarily impacted by shallow intraslab earthquakes, our results also raise questions about site-response and basin amplification hazards from a potential megathrust earthquake. The high seismicity rates of the southernmost Cascades call for stronger regional preparedness and improved strategies to mitigate the effects of such a large-scale disaster.

California↗

USGS2015

Seismic velocities within the sedimentary succession of the Canada Basin and southern Alpha-Mendeleev Ridge, Arctic Ocean: evidence for accelerated porosity reduction?

The Canada Basin and the southern Alpha-Mendeleev ridge complex underlie a significant proportion of the Arctic Ocean, but the geology of this undrilled and mostly ice-covered frontier is poorly known. New information is encoded in seismic wide-angle reflections and refractions recorded with expendable sonobuoys between 2007 and 2011. Velocity–depth samples within the sedimentary succession are extracted from published analyses for 142 of these records obtained at irregularly spaced stations across an area of 1.9E + 06 km 2 . The samples are modelled at regional, subregional and station-specific scales using an exponential function of inverse velocity versus depth with regionally representative parameters determined through numerical regression. With this approach, smooth, non-oscillatory velocity–depth profiles can be generated for any desired location in the study area, even where the measurement density is low. Practical application is demonstrated with a map of sedimentary thickness, derived from seismic reflection horizons interpreted in the time domain and depth converted using the velocity–depth profiles for each seismic trace. A thickness of 12–13 km is present beneath both the upper Mackenzie fan and the middle slope off of Alaska, but the sedimentary prism thins more gradually outboard of the latter region. Mapping of the observed-to-predicted velocities reveals coherent geospatial trends associated with five subregions: the Mackenzie fan; the continental slopes beyond the Mackenzie fan; the abyssal plain; the southwestern Canada Basin; and, the Alpha-Mendeleev magnetic domain. Comparison of the subregional velocity–depth models with published borehole data, and interpretation of the station-specific best-fitting model parameters, suggests that sandstone is not a predominant lithology in any of the five subregions. However, the bulk sand-to-shale ratio likely increases towards the Mackenzie fan, and the model for this subregion compares favourably with borehole data for Miocene turbidites in the eastern Gulf of Mexico. The station-specific results also indicate that Quaternary sediments coarsen towards the Beaufort-Mackenzie and Banks Island margins in a manner that is consistent with the variable history of Laurentide Ice Sheet advance documented for these margins. Lithological factors do not fully account for the elevated velocity–depth trends that are associated with the southwestern Canada Basin and the Alpha-Mendeleev magnetic domain. Accelerated porosity reduction due to elevated palaeo-heat flow is inferred for these regions, which may be related to the underlying crustal types or possibly volcanic intrusion of the sedimentary succession. Beyond exploring the variation of an important physical property in the Arctic Ocean basin, this study provides comparative reference for global studies of seismic velocity, burial history, sedimentary compaction, seismic inversion and overpressure prediction, particularly in mudrock-dominated successions.

Geophysical Journal International↗

USGS2015

Physical subdivision and description of the water-bearing sediments of the Santa Clara Valley, California

A thick Quaternary alluvial section fills a sedimentary basin beneath the Santa Clara Valley, California, located within the San Andreas Fault system at the south end of San Francisco Bay. This section consists of an upper sequence about 1,000 feet thick containing eight sedimentary cycles and a lower fine-grained unit as thick as several hundred feet. Together these constitute the Quaternary Santa Clara Basin. The section overlies an irregular unconformity with more than 1,200 feet of relief cut into the underlying bedrock. This stratigraphy is determined through study of new wells and seismic reflection profiles, together with a sample of the many thousands of water wells in the valley. It represents a major change and improvement in understanding of the basin, particularly with regard to the upper cyclic sequence, which forms a large groundwater system that is an important resource in the San Francisco Bay region. Each of the eight sedimentary cycles consists of a coarse-grained bottom interval overlain by a fine-grained top, with the coarse bottom forming a permeable sheet that is more or less continuous around the basin and the fine top forming a similarly extensive, relatively impermeable confining layer. This stratigraphic organization contrasts with most previous views, which have considered the coarse sediment in the basin to occur as scattered, discrete lenses and (or) sinuous channel sands, all embedded in a predominantly fine-grained section. Temperature logs in several wells demonstrate that the fine cycle tops do limit vertical movement of groundwater, although this may not be the case where those tops are thin to perhaps locally absent around parts of the basin margin. Age control has been obtained from previous work, in which the sedimentary cycles were correlated with the marine oxygen isotope record and the ages of two deeper Quaternary unconformities were estimated, and from detailed paleomagnetic study of cores from the new wells by E.A. Mankinen. Despite careful search of the cores, very few fossils were found, and none that are helpful in subdividing the section. No tephra (volcanic ash) was recovered, and the few carbon samples found and dated radiometrically are limited to the upper 120 feet of the section. The upper cyclic section ranges in age from 0 to somewhat older than 718 thousand years (ka), and the lower fine-grained section lies between unconformities with estimated ages of 950 and 1500 ka. Reflections in the seismic profiles indicate that layering in the basin is subparallel to the ground surface, and this fact, together with the continuous stratigraphic detail provided by geophysical logs of the new wells, allows the confident interwell correlation required to delineate the sedimentary cycles. The sequence of layers within any one cycle tends to persist laterally between the wells in the dataset, which are spaced 1 to 3 km apart, with most changes occurring gradually. The eight cycles, in contrast, tend to differ from each other in the details of their internal organization. Maps and cross sections show the elevations of cycle boundaries and the underlying bedrock surface, the varying thicknesses of the cycles and of their fine tops and coarse bottoms, and the aggregate thickness of coarse layers in those bottom intervals. Coarse sediment is more abundant toward some parts of the basin margin and in the southern part of the basin. Cycle boundary surfaces are relatively smooth, and their shapes are consistent with having been intercycle topographic surfaces. The underlying bedrock surface has a relief of more than 1,200 feet and deepens toward the center of the basin and the west edge of the fault-bounded Evergreen Basin, which is concealed beneath the east side of the Quaternary basin. The absence of consistent abrupt changes in thicknesses or boundary elevations across the basin or in cross section indicates that the interior of the basin is largely unfaulted, with the Silver Creek strand of the San Andreas system at the west edge of the Evergreen Basin being the sole exception. The east and west margins of the Santa Clara Basin, in contrast, are marked by reverse and thrust fault systems.

California↗

USGS1999

Wide-angle seismic recordings from the 1998 Seismic Hazards Investigation of Puget Sound (SHIPS), western Washington and British Columbia

This report describes the acquisition and processing of deep-crustal wide-angle seismic reflection and refraction data obtained in the vicinity of Puget Lowland, the Strait of Juan de Fuca, and Georgia Strait, western Washington and southwestern British Columbia, in March 1998 during the Seismic Hazards Investigation of Puget Sound (SHIPS). As part of a larger initiative to better understand lateral variations in crustal structure along the Cascadia margin, SHIPS participants acquired 1000 km of deep-crustal multichannel seismic-reflection profiles and 1300 km of wideangle airgun shot lines in this region using the R/V Thompson and R/V Tully. The Tully was used to record airgun shots fired by the Thompson in two different geometries: (1) expanding spread profiles (ESPs) and (2) constant offset profiles (COPs). Prior to this reflection survey, we deployed 257 Reftek and 15 ocean-bottom seismic recorders to record the airgun signals at far offsets. All data were recorded digitally on large-capacity hard disks. Although most of these stations only recorded the vertical component of motion, 95 of these seismographs recorded signals from an oriented 3-component seismometer. By recording signals generated by the Thompson's marine air gun array, operated in two differing geometries having a total volume of 110 and 79 liters (6730 and 4838 cu. in.), respectively, the arrays of wide-angle recorders were designed to (1) image the crustal structure, particularly in the vicinity of crustal faults and Cenozoic sedimentary basins, (2) determine the geometry of the Moho, and (3) image the subducting Gorda and Juan de Fuca plates. Nearly 33,300 air gun shots were recorded along several seismic lines. In this report, we illustrate the expanding spread profiles acquired using the Thompson and Tully, describe the land and ocean-bottom recording of the air gun signals, discuss the processing of the land recorder data into common receiver gathers, and illustrate the processed wide-angle seismic data collected using the Refteks and ocean-bottom seismometers. We also describe the format and content of the archival tapes containing the SEGY-formated, common-receiver gathers for the Reftek data. Data quality is variable but SHIPS appears to have successfully obtained useful data from almost all the stations deployed to record the airgun shots. Several interesting arrivals were observed: including refractions from the sedimentary basin fill in several basins, refractions from basement rocks forming the upper crust, Pg, refractions from the upper mantle, Pn, as well as reflections from within the crust and from the top of the upper mantle, PmP. We separately archived more than 30 local earthquakes recorded by the Reftek array during our deployment.

Washington↗

USGS2019

Tourmaline boron and strontium isotope systematics reveal magmatic fluid pulses and external fluid influx in a giant iron oxide-apatite (IOA) deposit

Tourmaline is a common boron-bearing mineral in hydrothermal system and has been widely used as a mineral probe to reconstruct geological processes because of its broad range in composition and resistance to metasomatic alteration. The origin of Kiruna-type iron oxide-apatite (IOA) deposits, commonly linked to andesitic subvolcanic or volcanic rocks, is highly controversial. Constraints on the evolution of these mineralizing systems are needed to advance understanding of the ore-forming process. In this study, we apply in situ elemental and combined B-Sr isotopic analyses of tourmaline to elucidate the nature and evolution of the subsurface hydrothermal system associated with IOA mineralization in the giant Taocun deposit, eastern China. Taocun is hosted at the top of a diorite intrusion and exhibits three stages of hydrothermal alteration that contain tourmaline: pre-ore Na alteration (Tur I), syn-ore magnetite formation and associated Ca-Fe alteration (Tur II), and post-ore Ca-Mg alteration with sulfide veins (Tur III). Compositional data for each stage of tourmaline plot along the “oxy-dravite”–povondraite join, which is indicative of precipitation from relatively oxidizing fluids. Ranges of Sr-isotopic compositions in Tur I (0.7065–0.7078) and Tur II (0.7068–0.7076) are identical to those of the igneous host rocks, indicating precipitation from magmatic-hydrothermal fluids. The range of B-isotopic compositions in Tur I (δ 11 B values of −6.3‰ to −1.2‰) is also consistent with a magmatic source. Higher δ 11 B values (−2.4‰ to 5.4‰) obtained from Tur II are mainly ascribed to Rayleigh fractionation in the magmatic-hydrothermal system as tourmaline precipitated. Post-ore Tur III has a wide range of mostly lower B-isotopic compositions (−8.5‰ to 0.8‰) that record another pulse of magmatic fluid input. This interpretation is supported by the enrichment of Na, Li, Be, W, Sn, V, and Ti in Tur III, relative to Tur I and II. However, the higher Sr-isotope composition (0.7076–0.7086) of Tur III and available O-isotope composition (−7‰ to 3.5‰) of fluids of this stage record the infiltration of meteoric ground water from adjacent sedimentary country rocks. The results suggest that the Taocun IOA deposit formed in a magmatic-hydrothermal system characterized by two (or more) pulses of magmatic fluid discharge from subvolcanic diorite intrusions, followed by the influx of external ground water as the system waned. This study highlights the utility of tourmaline as a robust geochemical and isotopic monitor of ore-forming processes in such systems.

Ningwu IOA district↗

USGS2012

Holocene aridification of India

Spanning a latitudinal range typical for deserts, the Indian peninsula is fertile instead and sustains over a billion people through monsoonal rains. Despite the strong link between climate and society, our knowledge of the long‐term monsoon variability is incomplete over the Indian subcontinent. Here we reconstruct the Holocene paleoclimate in the core monsoon zone (CMZ) of the Indian peninsula using a sediment core recovered offshore from the mouth of Godavari River. Carbon isotopes of sedimentary leaf waxes provide an integrated and regionally extensive record of the flora in the CMZ and document a gradual increase in aridity‐adapted vegetation from ∼4,000 until 1,700 years ago followed by the persistence of aridity‐adapted plants after that. The oxygen isotopic composition of planktonic foraminifer Globigerinoides ruber detects unprecedented high salinity events in the Bay of Bengal over the last 3,000 years, and especially after 1,700 years ago, which suggest that the CMZ aridification intensified in the late Holocene through a series of sub‐millennial dry episodes. Cultural changes occurred across the Indian subcontinent as the climate became more arid after ∼4,000 years. Sedentary agriculture took hold in the drying central and south India, while the urban Harappan civilization collapsed in the already arid Indus basin. The establishment of a more variable hydroclimate over the last ca. 1,700 years may have led to the rapid proliferation of water‐conservation technology in south India.

Geophysical Research Letters↗

USGS2003

Quaternary sedimentation and subsidence history of Lake Baikal, Siberia, based on seismic stratigraphy and coring

The long, continuous, high-latitude, stratigraphic record of Lake Baikal was deposited in three broad sedimentary environments, defined by high-resolution seismic-reflection and coring methods: (1) turbidite depositional systems, by far the most widespread, characterizing most of the margins and floors of the main basins of the lake, (2) large deltas of major drainages, and (3) tectonically or topographically isolated ridges and banks. Holocene sedimentation rates based on radiocarbon ages vary by more than an order of magnitude among these environments, from less than about 0.03 mm/yr on ridges and banks to more than about 0.3 mm/yr on basin floors. Extrapolating these rates, with a correction for compaction, yields tentative estimates of about 25 and 11 Ma for the inception of rifting in the Central and North basins, respectively, and less than 6 Ma for the 200-m sediment depth on Academician Ridge. The Selenga Delta has the distinctive form of a classic prograding Gilbert-type delta, but its history appears to represent a complex combination of tectonism and sedimentation. The central part of the delta is underlain by prograding, shallow-water sequences, now several hundred meters below the lake surface. These deposits and much of the delta slope are mantled by fine-grained, deep-water, hemipelagic deposits whose base is estimated to be about 650,000 years old. Modern coarse-grained sediment bypasses the delta slope through fault-controlled canyons that feed large, subaqueous fans at the ends of the South and Central basins. These relations, along with abundant other evidence of recent faulting and the great depths of the Central and South basins, suggest that these two rift basins have experienced a period of unusually rapid subsidence over the last 650,000 years, during at least part of which sedimentation has failed to keep pace.

Lake Baikal↗

USGS1999

The Cenomanian/Turonian carbon burial event, Bass River, NJ, USA: Geochemical, paleoecological, and sea-level changes

The Bass River borehole (ODP Leg 174AX) recovered approximately 200 ft (61 m) of upper Cenomanian to lower Turonian strata from the New Jersey Coastal Plain, USA, including the expression of a global carbon burial event. The Cenomanian/Turonian (C/T) boundary is recognized at Bass River at ???1935.5 ft (589.9 m) based on the contact of nannofossil Microstaurus chiastius and Eiffellithus eximius Subzones of the Parhabdolithus asper Zone. Carbon isotopic records of both Gavelinella and Epistomina show a large (>2???) increase immediately below the C/T boundary, with maximum values of 6??? in Epistomina and 4.3??? in Gavelinella. The ??13C offset between these taxa is constant and we conclude that Epistomina, like Gavelinella, faithfully records seawater ??13C changes. Above the sharp ??13C increase, elevated ??13C and sedimentary organic carbon (>0.9%) values continue into the lower Turonian, culminating in a sharp ??13C decrease. High ??13C values in the uppermost Cenomanian-lower Turonian at Bass River correlate with a global carbon burial event recorded in Europe and the U.S. Western Interior; we estimate the duration of this event at Bass River as 400-500 k.y. Although the carbon burial event occurred during a long-term eustatic rise (10 m.y. scale), it occurs within a 1-2 m.y. long sequence at Bass River that indicates no relationship with sea-level lowering on the m.y. scale. The carbon burial event does not appear to be associated with maximum flooding either, indicating little correlation with sea-level rise on a m.y. scale. Within the sequence spanning the carbon event, there are at least 4 shallowing-upward parasequences (durations ???350-460 k.y.) indicated by changes in abundance and type of Epistomina species, ??18O variations, and minor lithologic variations. The highest occurrences of 6 Epistomina species and the origination of Epistomina sliteri Olsson n. sp. are associated with the parasequences and possibly with higher ??18O values. There is no clear association of parasequence boundaries inferred at Bass River with the carbon burial event; thus, there does not appear to be a relationship of the event with sea-level change on the 100 k.y. scale. We conclude that while the organic carbon burial event was associated with a general long-term (10 m.y. scale) eustatic rise, the initiation and termination of the peak organic burial event itself were unrelated to sea-level change.

Journal of Foraminiferal Research↗

USGS2014

Cenozoic mountain building on the northeastern Tibetan Plateau

Northeastern Tibetan Plateau growth illuminates the kinematics, geodynamics, and climatic consequences of large-scale orogenesis, yet only recently have data become available to outline the spatiotemporal pattern and rates of this growth. I review the tectonic history of range growth across the plateau margin north of the Kunlun fault (35°–40°N) and east of the Qaidam basin (98°–107°E), synthesizing records from fault-bounded mountain ranges and adjacent sedimentary basins. Deformation began in Eocene time shortly after India-Asia collision, but the northeastern orogen boundary has largely remained stationary since this time. Widespread middle Miocene–Holocene range growth is portrayed by accelerated deformation, uplift, erosion, and deposition across northeastern Tibet. The extent of deformation, however, only expanded ~150 km outward to the north and east and ~150 km laterally to the west. A middle Miocene reorganization of deformation characterized by shortening at various orientations heralds the onset of the modern kinematic regime where shortening is coupled to strike slip. This regime is responsible for the majority of Cenozoic crustal shortening and thickening and the development of the northeastern Tibetan Plateau.

Book chapter↗

USGS2007

Stratigraphy of Colorado River deposits in lower Mohave Valley, Arizona and California

Deposits in lower Mohave Valley and upper Topock Gorge near Topock, Arizona and Park Moabi, California record a succession of depositional and erosional events since late Miocene time that relate to the development of the Colorado River. Upper Miocene alluvial fans were deposited toward a depocenter east of the present valley bottom, indicating there was no valley outlet then through the area of Topock Gorge. The lower Pliocene Bouse Formation subsequently accumulated to thicknesses of at least 330 m in ancestral Mohave Valley before most of it was incised by a Colorado River that carried clasts as large as 0.9 m and drained southward through ancestral Topock Gorge. Pliocene fluvial sandstone and conglomerate exposed in this area record 160 m of subsequent aggradation. One or more sedimentary sequences of varied fluvial, paludal, and alluvial fan environments accumulated on the margin of the floodplain in Pleistocene time, including during deposition of the upper Pleistocene Chemehuevi Formation of Longwell (1936). River boulders as large as 1.2 m derived from Pliocene gravel were deposited in terraces along the river during later incision. Vertebrate fossil finds and historical descriptions of the 19th century enrich the history of the area

Arizona, California↗

USGS2015

Comment on "Donders, T.H. 2014. Middle Holocene humidity increase in Florida: climate or sea-level? Quaternary Science Reviews 103:170-174."

Donders (2014) has recently proposed that the climate of Florida became progressively wetter over the past 5000 years in response to a marked strengthening of the El Niño regime. This reconstruction is largely based on a re-analysis of pollen records from regions north of Lake Okeechobee ( Fig. 1 ) using a new set of pollen transfer functions. Donders concluded that a latitudinal gradient in precipitation prevailed across Florida since the mid Holocene, but the overall trend was toward progressively wetter conditions from 5000 cal BP to the present. Donders (2014) also proposed that this climatic trend extended across South Florida despite contrary paleo-records from the Everglades. In particular he singled out the Northeast Shark River Slough (NESRS) record of Glaser et al. (2013) as an atypical local signal of paleo-environmental change that was biased by a misinterpretation of the ecology of pine and Amaranthaceae (Amaranth family). In response to this direct critique of our paleo-environmental interpretation, we wish to point out that: Our interpretation of the NESRS sedimentary sequence (site 4, Fig. 1 A) was based on multiple lines of evidence that all indicate a shift from wetter to drier (i.e. less wet) conditions that occurred after 2800 cal BP. A similar climatic shift from wetter to less wet conditions was reported for this time interval from other sites in the Everglades ( Willard et al., 2006 and Willard and Bernhardt, 2011 ) and also from the Caribbean region to the east ( Hodell et al., 1991 , Hodell et al., 1995 and Higuera-Gundy et al., 1999 ). The NESRS site is located in an area where runoff collected from a 10,000 km 2 wetland prior to 1900 AD when most of the drainage from the Everglades was channeled to the sea through the narrow Shark River Slough. The sedimentary sequence at the NESRS site should therefore contain an integrated record of hydrological change across the pre-historical Everglades ( Glaser et al., 2012 ). In addition this essentially non-forested wetland is well suited to accumulate a representative sample of the regional pollen rain in its sediments (e.g. Jaccobson and Bradshaw, 1981 and Prentice, 1985 ).

Florida↗

USGS1998

Streamflow characteristics for the Black Hills of South Dakota, through water year 1993

This report summarizes streamflow records and describes streamflow characteristics for streams draining the Black Hills of western South Dakota. Monthly and annual streamflow records are tabulated for all available years of record, through water year 1993, for 129 continuous-record gaging stations, including 111 stations for which records of daily flow are available and 18 stations for which only monthly records are available. Various summary statistics and graphics are presented for stations with sufficient periods of record. In addition to streamflow summaries, records of monthend contents are presented for five reservoirs operated by the Bureau of Reclamation in the Black Hills area. Streamflow characteristics are described for four categories of hydrogeologic settings, including interior sedimentary basins, interior crystalline basins, interior basins downstream of loss zones (loss-zone basins), and exterior basins. All of the interior basins are located predominantly within the outermost extent of the outcrop of the Inyan Kara Group and the exterior basins are located predominantly beyond this outcrop. Distinct differences in variability of annual and monthly streamflow are described for the four categories of hydrogeologic settings. The interior sedimentary basins, which are dominated by springflow from headwater areas, have the smallest variability in both annual and monthly flow, as a group. The exterior basins, as a group, have the largest variability in both annual and monthly flow. Streamflow variability for the interior crystalline basins, which are composed primarily of Precambrian and Tertiary igneous and metamorphic rocks, generally falls midway between the interior sedimentary and exterior basins. Loss-zone stations, which are located downstream of loss zones that occur where streams cross outcrops of the Madison Limestone and other overlying sedimentary units, exhibit the widest range in streamflow variability of any of the categories. Most of the loss-zone basins have springs located upstream of the gaging stations, but downstream of the loss zones. Flow at several of the loss-zone stations is dominated by large and consistent springflow; however, flow at other loss-zone stations is dominated by streamflow losses or by tributary inflows between the loss zones and the gaging stations, which results in extremely variable streamflow characteristics. It is demonstrated that springflow in Battle, Spring, Elk, and Bear Butte Creeks is much more variable than in Cascade Springs, Fall River, Beaver Creek, and Redwater River. Interior crystalline basins and exterior basins are shown to be much more responsive to climatic conditions than the springflow-dominated basins. Zero-flow months have been recorded for all of the exterior basins and most of the interior crystalline basins; however, zero-flow months have not been recorded for any of the interior sedimentary basins. Zero-flow months have not been recorded for the loss-zone stations with large, consistent springflow; however, zero-flow months are common for loss-zone stations with smaller, less consistent springs. Direct surface runoff is demonstrated to be uncommon for outcrops of the Madison Limestone and Minnelusa Formation. Examination of streamflow records for two basins with large outcrops of these formations indicates that direct surface runoff seldom occurs. Annual streamflow is shown to increase from south to north, which is consistent with climatic patterns for the area. Annual yield generally is larger for all of the interior categories than for the exterior basins; however, this is consistent with larger precipitation and smaller evapotranspiration rates at higher elevations. Annual yields generally are largest for the interior sedimentary basins; however, all of these basins are located in the northern Black Hills. Interior crystalline basins located in the northern Black Hills have annual yields that are comparable with interior sedimentary basins.

South Dakota↗

USGS2018

Climate stability in Central Anatolia during the Messinian Salinity Crisis

Deposition of large amounts of evaporites and erosion of deep canyons within the Mediterranean Basin as a result of reduced basin connectivity with the Atlantic Ocean and the epicontinental Paratethys Sea characterized the Messinian Salinity Crisis (MSC, 5.97–5.33 Ma). The influence of the MSC on Mediterranean environmental conditions within the basin itself has been intensely studied from marine records, but reconstructing the impact of the MSC on circum-Mediterranean continental climate has been hampered by the absence of continuous sedimentary archives that span the duration of the event. Here, we report results of a continental record of carbon (δ 13 C) and oxygen (δ 18 O) isotopes from lake carbonates framed by new magnetostratigraphic and 40 Ar/ 39 Ar dating, as well as by existing mammal stratigraphy (Kangal Basin, central Anatolia). The sampled section records continuous fluvio-lacustrine sedimentation from ~6.6 Ma to 4.9 Ma, which spans the MSC and the Miocene-Pliocene boundary. This dataset so far represents the only continuous continental paleoenvironmental record of the MSC in the circum-Mediterranean realm. The Kangal Basin isotope record indicates a low degree of evaporation. Furthermore, covariance between δ 13 C and δ 18 O suggests a coupling between lake water balance and biologic productivity. Variations in δ 13 C and δ 18 O therefore likely reflect changes in the amount of incoming precipitation, rather than changes in δ 18 O values of incoming precipitation. The most prominent spike in δ 13 C and δ 18 O occurs during the acme of the MSC and is therefore interpreted to have resulted from a decrease in the amount of incoming moisture correlative to a period of vigorous erosion and sea level lowering in the Mediterranean Basin. Major sea level lowering of Mediterranean basin waters during the acme of the MSC could have therefore led to slightly dryer conditions over Anatolia, which is also suggested by modeling studies. Overall, changes in δ 13 C and δ 18 O values are small. Therefore, we surmise that the MSC had limited effects on the paleoenvironmental and paleoclimatic conditions in the Anatolian interior.

Palaeogeography, Palaeoclimatology, Palaeoecology↗

USGS2018

Late Neogene–Quaternary tephrochronology, stratigraphy, and paleoclimate of Death Valley, California, USA

Sedimentary deposits in midlatitude continental basins often preserve a paleoclimate record complementary to marine-based records. However, deriving that paleoclimate record depends on having well-exposed deposits and establishing a sufficiently robust geochronology. After decades of research, we have been able to correlate 77 tephra beds exposed in multiple stratigraphic sections in the Death Valley area, California, United States. These correlations identify 25 different tephra beds that erupted from at least five different volcanic centers from older than 3.58 Ma to ca. 32 ka. We have informally named and determined the ages for seven previously unrecognized beds: ca. 3.54 Ma tuff of Curry canyon, ca. 3.45 Ma tuff of Furnace Creek, ca. 3.1 Ma tuff of Kit Fox Hills, ca. 3.1 Ma tuff of Mesquite Flat, ca. 3.15 Ma tuff of Texas Spring, 3.117 ± 0.011 Ma tuff of Echo Canyon, and the ca. 1.3 Ma Amargosa ash bed. Several of these tephra beds are found as far northeast as central Utah and could be important marker beds in western North America. Our tephrochronologic data, combined with magnetic polarity data and 40 Ar/ 39 Ar age determinations, redefine Neogene sedimentary deposits exposed across 175 km 2 of the Death Valley area. The alluvial/lacustrine Furnace Creek Formation is a time-transgressive sedimentary sequence ranging from ca. 6.0 to 2.5 Ma in age. The ca. 2.5–1.7 Ma Funeral Formation is typically exposed as a proximal alluvial-fan facies overlying the Furnace Creek Formation. We have correlated deposits in the Kit Fox Hills, Salt Creek, Nova Basin, and southern Death Valley with the informally named ca. 1.3–0.5 Ma Mormon Point formation. In addition, our correlation of the late Pleistocene Wilson Creek ash bed 15 in the Lake Rogers deposits represents the first unambiguous sequences deposited during the Last Glacial Maximum (marine isotope stage [MIS] 2) in Death Valley. Based on this new stratigraphic framework, we show that the Pliocene and Pleistocene climate in Death Valley is consistent with the well-established marine tropical/subtropical record. Pluvial lakes in Death Valley and Searles Valley began to form ca. 3.5–3.4 Ma in the late Pliocene during MIS MG5. Initiation of lakes in these two hydrologically separated valleys at the same time at the beginning of a cooling trend in the marine climate record suggests a link to a cooler, wetter (glacial) regional climate in North America. The Death Valley lake persisted until ca. 3.30 Ma, at the peak of the M2 glaciation, after which there is no evidence of Pliocene lacustrine deposition, even at the peak of the Northern Hemisphere Glaciation (ca. 2.75 Ma). If pluvial lakes in the Pliocene are an indirect record of glacial climate conditions, as they are for the Pleistocene, then a glacial climate was present in western North America for ∼200,000 yr during the Pliocene, encompassing MIS MG5–M2. Pleistocene pluvial lakes in Death Valley that formed ca. 1.98–1.78 Ma, 1.3–1.0 Ma, and ca. 0.6 Ma (MIS 16) are consistent with other regional climate records that indicate a regional glacial climate; however, Death Valley was relatively dry at ca. 0.77 Ma (MIS 19), when large lakes existed in other basins. The limited extent of the MIS 2 marsh/shallow lake in the Lake Rogers basin of northern Death Valley reflects the well-known regional glacial climate at that time; however, Death Valley received relatively lower inflow and rainfall in comparison.

Geological Society of America Bulletin↗

USGS2023

Mineralogical, magnetic and geochemical data constrain the pathways and extent of weathering of mineralized sedimentary rocks

The oxidative weathering of sulfidic rock can profoundly impact watersheds through the resulting export of acidity and metals. Weathering leaves a record of mineral transformation, particularly involving minor redox-sensitive phases, that can inform the development of conceptual and quantitative models. In sulfidic sedimentary rocks, however, variations in depositional history, diagenesis and mineralization can change or overprint the distributions of these trace minerals, complicating the interpretation of weathering signatures. Here we show that a combination of bulk mineralogical and geochemical techniques, micrometer-resolution X-ray fluorescence microprobe analysis and rock magnetic measurements, applied to drill core samples and single weathered fractures, can provide data that enable the development of a geochemically consistent weathering model. This work focused on one watershed in the Upper Colorado River Basin sitting within the Mesaverde Formation, a sedimentary sandstone bedrock with disseminated sulfide minerals, including pyrite and sphalerite, that were introduced during diagenesis and subsequent magmatic-hydrothermal mineralization. Combined analytical methods revealed the pathways of iron (Fe), carbonate and silicate mineral weathering and showed how pH controls element retention or release from the actively weathering fractured sandstone. Drill core logging, whole rock X-ray diffraction, and geochemical measurements document the progression from unweathered rock at depth to weathered rock at the surface. X-ray microprobe analyses of a 1-cm size weathering profile along a fracture surface are consistent with the mobilization of Fe(II) and Fe(III) into acidic pore water from the dissolution of primary pyrite, Fe-sphalerite, chlorite, and minor siderite and pyrrhotite. These reactions are followed by the precipitation of secondary minerals such as of goethite and jarosite, a Fe-(oxyhydr)oxide and hydrous Fe(III) sulfate, respectively. Microscale analyses also helped explain the weathering reactions responsible for the mineralogical transformations observed in the top and most weathered section of the drill core. For example, dissolution of feldspar and chlorite neutralizes the acidity generated by Fe and sulfide mineral oxidation, oversaturating the solution in both Fe-oxides. The combination of X-ray spectromicroscopy and magnetic measurements show that the Fe(III) product is goethite, mainly present either as a coatings on fracture surfaces in the actively weathering region of the core or more homogeneously contained within the unconsolidated regolith at the top of the core. Low-temperature magnetic data reveal the presence of ferromagnetic Fe-sulfide pyrrhotite that, although it occurs at trace concentrations, could provide a qualitative proxy for unweathered sulfide minerals because the loss of pyrrhotite is associated with the onset of oxidative weathering. Pyrrhotite loss and goethite formation are detectable through room-temperature magnetic coercivity changes, suggesting that rock magnetic measurements can determine weathering intensity in rock samples at many scales. This work contributes evidence that the weathering of sulfidic sedimentary rocks follows a geochemical pattern in which the abundance of sulfide minerals controls the generation of acidity and dissolved elements, and the pH-dependent mobility of these elements controls their export to the ground- and surface-water.

Colorado↗