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At least 379 records · Page 21Linked to original sources
USGS1993

Late Quaternary paleoceanography of the Pervenets Canyon area of the Bering Sea: Evidence from the diatom flora

Sediments from three gravity cores from an east-west shelf-to-slope transect along the axis of Pervenets Canyon in the northern Navarin basin, Bering Sea were analyzed for diatoms. The diatom floras present in the cores were divided into four assemblages following Sancetta (1981). The Bering Basin (deep water open ocean) and Sea Ice (ice cover at least six months per year) Assemblages were dominant in each core. The taxa that comprise the Bering Shelf Assemblage (continental shelf) indicate that downslope transport plays only a minor part in the development of the thanatocenoses. The presence (up to 10% of the total valve count) of the Productivity Assemblage, which consists mainly of poorly silicified, easily dissolved taxa, indicates that nutrient flux is relatively high in the region. Several taxa can be used as proxy indicators for specific water masses. Neodenticula seminae (Simonsen & Kanaya) Akiba & Yanagisawa is indicative of Holocene open marine (deep water) conditions. Nitzschia cylindra (Grunow) Hasle and N. grunowii Hasle are both associated with sea ice and are thought to indicate late Pleistocene conditions. The relative downcore abundance of these taxa was used to approximate the Pleistocene- Holocene boundary (recognized in Core 80–65 at a depth of about 75 cm).

Diatom Research↗
USGS1997

Episodic nature of earthquake activity in stable continental regions revealed by palaeoseismicity studies of Australian and North American Quaternary faults

Palaeoseismic investigations of recent faulting in stable continental regions of Australia, North America and India show that these faults typically have a long-term behaviour characterised by episodes of activity separated by quiescent intervals of at least 10 000 and commonly 100 000 years or more. Long recurrence intervals such as these are well documented by detailed studies of the faults that ruptured during the 1986 Marryat Creek, South Australia and 1988 Tennant Creek, Northern Territory earthquakes. Thus, neotectonic features associated with stable continental region faults such as scarps and grabens commonly have subtle geomorphic expression and may be poorly preserved. Many potentially hazardous faults in stable continental regions are aseismic, which is one reason why the inventory of these faults is incomplete. Although they may be currently aseismic, faults in stable continental regions that are favourably oriented for movement in the current stress field could produce damaging earthquakes, often in unexpected places. Comprehensive palaeoseismic investigations of modern and prehistoric faulting events in stable continental regions are needed to understand the long-term behaviour of these faults, and thereby, improve seismic-hazard assessments.

Australian Journal of Earth Sciences↗
USGS2025

Geochemical evidence for the origin of late Quaternary loess, Seward Peninsula, Alaska

Loess is the most widespread surficial deposit in the state of Alaska. Although loess of last glacial age is common in mid-continental North America, records of last glacial loess in Alaska have been elusive. Here we report a record of last glacial loess on the Seward Peninsula, along with studies of a transect of loess localities also thought to date to the last glacial period. Highly diverse hypotheses on the origin of loess on the Seward Peninsula include local volcanic rocks and mountain ranges to the north and south, as well as offshore deposits. We present particle size and mineralogical and geochemical data that indicate that the most likely sources for loess in this part of eastern Beringia are glaciogenic silt particles of the Kobuk River and Noatak River, both of which drain the Brooks Range to the northeast. Northeasterly paleowinds were therefore responsible for loess on the Seward Peninsula. Such winds probably occurred during late summer or early autumn, when river discharge was at a minimum but temperatures were still above freezing. Northeasterly winds during the last glacial period are in good agreement with a recent paleoclimate model.

Alaska↗
USGS2025

Late Quaternary pollen record from southwest Seward Peninsula, western Alaska, and the vegetation history of central Beringia

Pollen analysis of samples from a coastal exposure near Teller, southwestern Seward Peninsula, Alaska, provides a record of vegetation and climate spanning the Last Glacial Maximum (LGM) through the Holocene. The site is near the center of the former Bering Land Bridge (BLB). The oldest pollen-bearing sediment unit is a loess deposit of LGM age, with pollen assemblages that closely resemble LGM assemblages from other key sites in central Beringia spanning 16° of latitude. These fossil assemblages represent vegetation composed primarily of grasses, sedges, Artemisia , willows, and forbs and are interpreted to represent steppe–tundra, associated with dry climates and summer temperatures cooler than at present. LGM mosses did not accumulate insulating layers of peat; the summer active soil layer was deeper than at present. Permafrost with ice wedges and loess deposition were widespread. A regional transition from steppe–tundra vegetation to a dwarf shrub–sedge–moss mesic-to-wetland vegetation began in central Beringia with the onset of Bølling–Allerød (B-A) warming at 14,700 cal yr BP. Warming events of the B-A and early Holocene resulted in widespread development of thermokarst terrain on the BLB and on ice-rich terrain in Western Alaska. Mesic climates and vegetation developed on the BLB during the marine transgression and because of B-A and early Holocene warming. Early Holocene warming allowed some boreal forest species such as alders to begin colonizing Western Alaska from the interior.

Alaska↗
USGS2006

Dolomitization of Quaternary reef limestones, Aitutaki, Cook Islands

Six holes were drilled to depths of 30–69 m in the shallow lagoon of Aitutaki in the southern Cook Islands. One hole encountered pervasively dolomitized reef limestones at 36 m subbottom depth, which extended to the base of the drilled section at 69·3 m. This hole was drilled near the inner edge of the present barrier reef flat on the flank of a seismically defined subsurface ridge. Both the morphology and biofacies indicate that this ridge may represent an outer reef crest. Mineralogy, porosity and cementation change in concert downhole through three zones. Zone 1, 0–9 m, is composed of primary skeletal aragonite and calcite with minor void-filling aragonite and magnesian calcite cement of marine phreatic origin. Zone 2, 9–36 m, is composed of replacement calcite and calcite cement infilling intergranular, intragranular, mouldic and vuggy porosity. Stable isotopes (mean δ 18 O=—5·4‰ PDB for carbonate; δD =—50‰ SMOW for fluid inclusions) support the petrographic evidence indicating that sparry calcite cements formed in predominantly freshwater. Carbon isotope values of —4·0 to —11·0‰ for calcite indicate that organic matter and seawater were the sources of carbon. Zone 3, 36–69·3 m, is composed of replacement dolostone, consisting of protodolomite with, on average, 7 mol% excess CaCO 3 and broad and weak ordering X-ray reflections at 2·41 and 2·54 A. The fine-scale replacement of skeletal grains and freshwater void-filling cements by dolomite did not significantly reduce porosity. Stable isotopes (mean δ 18 O=+2·6‰ 0 PDB for dolomite; maximum δD =—27‰ SMOW for fluid inclusions) and chemical composition indicate that the dolomite probably formed from seawater, although formation in the lower part of a mixed freshwater-seawater zone, with up to 40% freshwater contribution, cannot be completely ruled out. The carbon (δ 13 C=2·7‰) and magnesium were derived from seawater. Low-temperature hydrothermal iron hydroxides and associated transition metals occur in void space in several narrow stratigraphic intervals in the limestone section that was replaced by dolomite. The entire section of dolomite is also enriched in these transition metals. The metals dispersed throughout the dolostone section were introduced at the time of dolomitization by a different and later episode of hydrothermal circulation than the one(s) that produced the localized deposits near the base of the section. The primary reef framework is considered to have been deposited during several highstands of sea level. Following partial to local recrystallization of the limestone, a single episode of dolomitization occurred. Both tidal and thermal pumping drove large quantities of seawater through the porous rocks and perhaps maintained a wide mixing zone. However, the isotopic, geochemical and petrographic data do not clearly indicate the extent of seawater mixing.

Sedimentology↗
USGS2005

Species-energy relationship in the deep sea: A test using the Quaternary fossil record

Little is known about the processes regulating species richness in deep-sea communities. Here we take advantage of natural experiments involving climate change to test whether predictions of the species-energy hypothesis hold in the deep sea. In addition, we test for the relationship between temperature and species richness predicted by a recent model based on biochemical kinetics of metabolism. Using the deep-sea fossil record of benthic foraminifera and statistical meta-analyses of temperature-richness and productivity-richness relationships in 10 deep-sea cores, we show that temperature but not productivity is a significant predictor of species richness over the past c. 130 000 years. Our results not only show that the temperature-richness relationship in the deep-sea is remarkably similar to that found in terrestrial and shallow marine habitats, but also that species richness tracks temperature change over geological time, at least on scales of c. 100 000 years. Thus, predicting biotic response to global climate change in the deep sea would require better understanding of how temperature regulates the occurrences and geographical ranges of species. ??2005 Blackwell Publishing Ltd/CNRS.

Ecology Letters↗
USGS2011

Late Pliocene and Quaternary Eurasian locust infestations in the Canary Archipelago

The Canary Archipelago has long been a sensitive location to record climate changes of the past. Interbedded with its basalt lavas are marine deposits from the principal Pleistocene interglacials, as well as aeolian sands with intercalated palaeosols. The palaeosols contain African dust and innumerable relict egg pods of a temperate‐region locust (cf. Dociostaurus maroccanus Thunberg 1815 ). New ecological and stratigraphical information reveals the geological history of locust plagues (or infestations) and their palaeoclimatic significance. Here, we show that the first arrival of the plagues to the Canary Islands from Africa took place near the end of the Pliocene, ca. 3 Ma, and reappeared with immense strength during the middle Late Pleistocene preceding MIS (marine isotope stage) 11 (ca. 420 ka), MIS 5.5 (ca. 125 ka) and probably during other warm interglacials of the late Middle Pleistocene and the Late Pleistocene. During the Early Holocene, locust plagues may have coincided with a brief cool period in the current interglacial. Climatically, locust plagues on the Canaries are a link in the chain of full‐glacial arid–cold climate (calcareous dunes), early interglacial arid–sub‐humid climate (African dust inputs and locust plagues), peak interglacial warm–humid climate (marine deposits with Senegalese fauna), transitional arid–temperate climate (pedogenic calcretes), and again full‐glacial arid–cold climate (calcareous dunes) oscillations. During the principal interglacials of the Pleistocene, the Canary Islands recorded the migrations of warm Senegalese marine faunas to the north, crossing latitudes in the Euro‐African Atlantic. However, this northward marine faunal migration was preceded in the terrestrial realm by interglacial infestations of locusts.

Lethaia↗
USGS1981

Late Quaternary environmental history of Lake Valencia, Venezuela

Chemical, paleontological, and mineralogical analyses of a 7.5-meter core from the middle of Lake Valencia, Venezuela, have provided information on the paleoclimatic history of this low-elevation, low-latitude site for the last 13,000 years. The data show that dry climates existed in this region from 13,000 years before present (B.P.) until about 10,000 years B.P. The Lake Valencia Basin was occupied by intermittent saline marshes at that time. About 10,000 years B.P., a permanent lake of fluctuating salinity formed and arboreal plant communities replaced the earlier dominant xeric herbaceous vegetation and marsh plants. By 8500 years B.P., Lake Valencia reached moderate to low salinities and discharged water; the modern vegetation became established at that time. After 8500 years B.P., the lake twice ceased discharging as a result of reduced watershed moisture. The second of these drying episodes is still in progress and has been aggravated by human activities in the watershed.

Lake Valencia↗
USGS1961

Late quaternary history of the snake river in the American Falls region, Idaho

While mapping the American Falls region, we found evidence that contributes to the middle Pleistocene to Recent history of the Snake River, and indirectly to the history of overflow of Lake Bonneville. Middle Pleistocene to recent rocks in the valley are mainly lacustrine and fluvial silts and clays, with some sand, gravel, basalt, and a few thin tuff beds. The formation of terraces can be correlated with events both up- and downstream. The Snake River was at least once, and possibly twice, dammed and diverted by eruptions of basalt, resulting in the formation of lakes and deposition of lacustrine beds. A rather flat-lying, thin, but persistent gravel at the base of one lake bed formation may represent a glacial period, possibly Illinoian, during which the Snake River had a large volume. Overflow of water from Lake Bonneville into the Snake River system, by way of the Marsh Creek-Portneuf valley, laid down a deltaic-fluvial deposit here named the Michaud Gravel. At this time the Snake River, greatly augmented by Lake Bonneville overflow, began to cut channels through and around a lava dam. Terraces between Aberdeen, American Falls, and Pocatello were formed during the existence of the lake in which the Michaud Gravel was deposited and by fluvial processes after drainage of the lake. At one stage in the downcutting, bars of huge basalt boulders were built across the mouths of abandoned spillways. Radiocarbon dating and geologic evidence from the area between Preston and Soda Springs, Idaho, suggest that basalt flows diverted the Bear River into Lake Bonneville, perhaps causing it to overflow. This diversion probably occurred about 33,000 years ago. This dating accords with events in the American Falls region.

Idaho↗
USGS1964

Late quaternary sea-level change and crustal rise at Boston, Massachusetts, with notes on the autocompaction of peat

The compression of peat beneath its own weight (autocompaction) is discussed, and it is shown that because of this process radiocarbondated samples of salt-marsh peat or peaty sediment, other than very thin samples cut from the base of the deposit, cannot be correlated with sea level without construction of a sea-level change curve from other types of data. With rising sea level there is a maximum thickness of salt-marsh peat for any given productivity of marsh grass. Because of this limitation, most marshes older than about 5500 years B.P. have been drowned. An important effect of peat autocompaction is the intrusion of wood into older peat horizons and the juxtaposition of wood of different ages. Wood, therefore, should be avoided in the dating of peat profiles. The roots of salt-marsh plants generally descend a foot or more beneath the rhizomes, contaminating older horizons insofar as radiocarbon dating is concerned. This contamination tends to make dates from marsh samples err on the young side. Sixteen radiocarbon dates from the Boston area are used to construct a sea-level curve going back to 14,000 years B.P. Relative sea level was at +60 feet or higher 14,000 years B.P., dropping sharply to approximately -70 feet about 10,000 years B.P. From a low of -70 feet, sea level rose steadily to about -2 feet approximately 3000 years B.P. Since then sea level appears to have kept close to its present level, probably fluctuating about a foot during the course of the stillstand. A crustal movement curve, based on the relative sea-level curve for Boston and the eustatic curve, indicates that about 290 feet of crustal rise occurred between 14,000-6000 years B.P., with a maximum rate of uplift of about 0.2 foot per year at 12,750 years B.P., and that from 6000 to 3000 years B.P., crustal subsidence occurred at Boston. © 1964, The Geological Society of America, Inc.

Massachusetts↗
USGS1965

Late quaternary geologic history of the lower Chippewa Valley, Wisconsin

The lower Chippewa Valley in west-central Wisconsin extends 65 miles from the Cary terminal moraine in Chippewa County to the Mississippi River Valley. The Chippewa Valley and its tributaries were filled with a valley train of sand and gravel during the maximum stand of the Cary ice, and entrenchment of this deposit has formed the Wissota terrace, a prominent geomorphic feature that can be traced the length of the valley. Several lower terraces in the valley indicate progressive downcutting of the Wissota terrace sediments. Erosion and deposition in the Mississippi Valley are closely linked to the post-Cary history of the lower Chippewa Valley, for these factors controlled the outlet level of the Chippewa River. This outlet was substantially lower than at present throughout much of post-Cary Pleistocene and early Recent time. The modern Chippewa River has built a delta into the Mississippi Valley. The Chippewa River is aggrading the lower part of its valley, a meandering river is slowly eroding the central part; stream erosion in the upper part is restricted by sills of hard bedrock.

Wisconsin↗
USGS1973

Evidence for Quaternary movement on the McKinley strand of the Denali fault in the Delta River area, Alaska

Offset Holocene alluvial fans and drainages along the McKinley strand of the Denali fault near the Delta River in the east-central Alaska Range indicate as much as 50 to 60 m of right-lateral displacement during the last 10,000 yrs. Vertical movement of 6 to 10 m during the same time interval is reflected by south-facing scarps along the trace of the fault. All but possibly 1 m of the lateral movement is thought to predate the 1830 neoglacial ice advance. Older drainages have been offset in a right-lateral sense since early Wisconsin or Illinoian time by as much as 6.5 km or, alternatively, by as little as 1 km.

Alaska↗