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USGS2017

Geochemical evidence of Saharan dust parent material for soils developed on Quaternary limestones of Caribbean and western Atlantic islands

Most previous workers have regarded the insoluble residues of high-purity Quaternary limestones (coral reefs and oolites) as the most important parent material for well-developed, clay-rich soils on Caribbean and western Atlantic islands, but this genetic mechanism requires unreasonable amounts of limestone solution in Quaternary time. Other possible parent materials from external sources are volcanic ash from the Lesser Antilles island arc and Saharan dust carried across the Atlantic Ocean on the northeast trade winds. Soils on Quaternary coral terraces and carbonate eolianites on Barbados, Jamaica, the Florida Keys (United States), and New Providence Island (Bahamas) were studied to determine which, if either, external source was important. Caribbean volcanic ashes and Saharan dust can be clearly distinguished using ratios of relatively immobile elements ( Al2O3 TiO2, Ti Y, Ti Zr, and Ti Th). Comparison of these ratios in 25 soils, where estimated ages range from 125,000 to about 870,000 yr, shows that Saharan dust is the most important parent material for soils on all islands. These results indicate that the northeast trade winds have been an important component of the regional climatology for much of the Quaterary. Saharan dust may also be an important parent material for Caribbean island bauxites of much greater age. ?? 1990.

Quaternary Research↗

USGS2017

Sr-Isotope record of Quaternary marine terraces on the California coast and off Hawaii

Strontium-isotopic ratios of dated corals have been obtained from submerged reefs formed during Quaternary glacial periods off the Hawaiian islands. These data, combined with data from deep-sea sediments, tightly constrain the secular variation of marine 87Sr 86Sr for the past 800,000 yr. Although long-term trends are apparent, no significant (>0.02???), rapid (<100,000 yr) excursions in 87Sr 86Sr were resolved nor did we observe any samples with 87Sr 86Sr greater than that of modern seawater. Strontium in mollusks from elevated marine terraces formed during interglacial periods on the southern California coast show resolvable and consistent variations in 87Sr 86Sr which, when compared to the trend of Quaternary marine 87Sr 86Sr, can be used to infer uplift rates and define approximate ages for the higher terraces. The Sr-isotope age estimates indicate that uplift rates vary among crustal blocks and were not necessarily constant with time. No contrast in Sr-isotopic ratios between similar-age Hawaiian and California fossils was observed, confirming that any change in marine 87Sr 86Sr from glacial to interglacial periods must be small. A realistic appraisal of the potential of Sr-isotope stratigraphy for chronometric applications in the Quaternary suggests that the technique will be limited to relatively coarse distinctions in age. ?? 1992.

Quaternary Research↗

USGS1976

Foraminiferal biostratigraphy of the shelf edge: a key to late Quaternary paleoenvironments

Foraminiferal assemblages in eight piston cores from West Flower Garden Bank at the edge of the Texas continental shelf contain a nearly complete record of late Quaternary paleoclimatic and geologic events. The faunas are divisible into three distinct successive biofacies on the basis of both planktonic and benthic foraminifers: the basal Inflata Facies accumulated in cool shallow waters during late Pleistocene glaciation; the middle Crassaformis Facies represents a deepening sea that had warming surface waters; the upper Cultrata Facies is characteristic of the Holocene outer-shelf environment. Sea level was at -73 m and -53 m at the end of deposition of the Inflata and Crassaformis Facies, respectively. The biostratigraphic events at West Flower Garden Bank can be accurately correlated with those recorded in the middle and inner shelf and in deep-sea cores. The sequence of late Quaternary sea level and paleotemperature changes in the northern Gulf of Mexico can thereby be reconstructed. Eventually, this knowledge can be integrated with similar data from the shelf edge in other parts of the world to help bridge the gap between the known Quaternary record of the deep sea and that of the continents. ?? 1976.

Palaeogeography, Palaeoclimatology, Palaeoecology↗

USGS1985

Quaternary sedimentation of the Alaskan Beaufort shelf: Influence of regional tectonics, fluctuating sea levels, and glacial sediment sources

The offshore stratigraphy of the Quaternary Gubik Formation of Arctic Alaska has been studied on high-resolution seismic profiles with a maximum sub-seafloor penetration of about 100 m. In general, marine transgressive subunits of the Gubik Formation are wedge-shaped on the shelf, thickening slightly seaward to the shelf break, beyond which they are offset by landslides and slumps. Beneath the eastern third of the Alaskan Beaufort shelf, active folding has created two persistent structural depressions, the Eastern and Western Wedge Terranes, in which the wedge morphology is especially well developed. The youngest transgressive marine wedge, which was deposited in such a way as to fill these depressions, leaving a generally flat present-day shelf surface, is inferred to be late Wisconsin or younger in age because it overlies a prominent disconformity interpreted to have been formed during the late Wisconsin glacial sea-level minimum. The thickness of this youngest wedge, Unit A, locally exceeds 40 m on the outer shelf, yet apparently relict gravel deposits collected from its seabed surface indicate that the depositional rate is presently quite low on the middle and outer shelf. Lithologies of the gravels are exotic to Alaska, but similar to suites exposed in the Canadian Arctic Islands. These observations suggest a depositional scenario in which the retreating Laurentide Ice Sheet shed sediment-laden icebergs from the Canadian Arctic Islands into the Arctic Ocean following the late Wisconsin glacial maximum. These bergs were then rafted westward by the Beaufort Gyre and grounded on the Alaskan shelf by northeasterly prevailing winds. Especially large numbers of bergs accumulated in the wedge terrane embayments-created as sea level rose-and melted there, filling the embayments with their sedimentary cargo. As glacial retreat slowed, depositional rates on the shelf dwindled. This mode of deposition in the Alaskan Beaufort wedge terranes may be typical of early post-glacial transgressive phases throughout Quaternary time. It has resulted in the preservation of disconformities that apparently formed during glacioeustatic lowstands, and whose seaward termination depths, appropriately corrected, may yield estimates of lowstand magnitudes. Knowledge of global sea-level fluctuations back through the Sangamon Interglacial (oxygen isotope stage 5e) and possible correlations with dated onshore deposits have facilitated a tentative correlation of major disconformities in the Beaufort Sea record with major 18O enrichment maxima in the oxygen isotope curve back through stage 8. In this tentative scheme, close similarities between the two data sets occur both in magnitudes and in numbers of fluctuations intervening between major correlation points. Further testing of the Quaternary depositional model suggested here and of the resulting sea level curve awaits the collection and dating of core samples from the Beaufort wedge terranes.

Alaska↗

USGS1987

Multiple sources of alkanes in Quaternary oceanic sediment of Antarctica

Normal alkanes ( n -C 13 n -C 36 ), isoprenoid hydrocarbons ( i -C 15 , i -C 16 , i -C 18 , i -C 19 , and i -C 20 ) triterpanes (C 27 C 32 ), and (C 27 C 29 ) are present in low concentrations offshore Antarctica in near-surface, Quaternary sediment of the Wilkes Land continental margin and of the western Ross Sea. The distributions of these hydrocarbons are interpreted relative to possible sources and processes. The hydrocarbons appear to be mixtures of primary and recycled material from marine and terrigenous sources. The n -alkanes are most abundant and are characterized by two distinct populations, one of probable marine origin and the other likely from terrigenous, vascular plant sources. Because the continent of Antarctica today is devoid of higher plants, the plant-derived hydrocarbons in these offshore sediments probably came from wind-blown material and recycled Antarctic sediment that contains land-plant remains from an earlier period of time. Isoprenoid hydrocarbons are partially recycled and mainly of marine origin; the dominance of pristane over phytane suggests oxic paleoenvironmental conditions. Both modern and ancient triterpanes and steranes are present, and the distribution of these indicates a mixture of primary and recycled bacterial, algal, and possible higher-plant materials. Although the sampled sediments were deposited during the Quaternary, they apparently contain a significant component of hydrocarbons of pre-Quaternary age.

Organic Geochemistry↗

USGS1996

Thermoluminescence and new 14C age estimates for late quaternary loesses in southwestern Nebraska

Loess of late Quaternary age mantles most of Nebraska south of the Platte River Valley. At least five late Quaternary loesses are recognized: from oldest to youngest, one or more undifferentiated pre-Illinoian loesses, the Loveland Loess, the Gilman Canyon Loess, which exhibits a well developed soil and rests unconformably on the Sangamon soil, the Peoria Loess capped by the Brady soil, and the Bignell Loess, which is distributed discontinuously. Previous research shows that the Loveland Loess is Illinoian, the Gilman Canyon Loess and Peoria Loess are Wisconsin, and the Bignell Loess is Holocene. We present here the first thermoluminescence (TL) age estimates and new 14 C ages for these late Quaternary loesses at two key sections in southwestern Nebraska, the Eustis ash pit and the Bignell Hill road cut. TL age estimates from all samples collected from Eustis ash pit and Bignell Hill were internally consistent. TL and 14 C age estimates from these two sections generally agree and support previous age determinations. The TL age estimate on Loveland Loess indicates deposition at 163 ka. TL and radiocarbon age estimates indicate that Gilman Canyon Loess, believed to be deposited during the Farmdale interstade, first began to accumulate at about 40 ka: the lower part of the Gilman Canyon Loess is 36 ka at Eustis and the middle of the unit is 30 ka at Bignell Hill. The lower and upper parts of the Peoria Loess give age estimates of 24 ka and 17 ka, respectively. TL age estimates for deposition of the Bignell Loess are 9 ka near the base, in agreement with radiocarbon age estimates, and 6 ka immediately below the modern soil, substantiating its Holocene age. Comparisons of TL age estimates with δ 18 O and insolation curves which show loess deposition during interglacial and interstadial as well as glacial periods, indicate that loess deposition on the Great Plains can occur under a variety of climatic conditions.

Geomorphology↗

USGS2008

Micropaleontologic record of late Pliocene and Quaternary paleoenvironments in the northern Albemarle Embayment, North Carolina, U.S.A.

Micropaleontological data provide a strong actualistic basis for detailed interpretations of Quaternary paleoenvironmental change. The 90 m-thick Quaternary record of the Albemarle Embayment in the mid-Atlantic coastal plain of the USA provides an excellent opportunity to use such an approach in a region where the details of Quaternary environmental change are poorly known. The foraminiferal record in nine cores from the northern Outer Banks, east of Albemarle Sound, North Carolina, indicates the deposition of subhorizontal, mostly open-marine early to late Pleistocene units unconformably upon a basement of late Pliocene reduced-oxygen, fine-grained, shelf-basin deposits. Pollen data record several warm–cool fluctuations within the early to mid-Pleistocene deposits. Diatom data indicate that some fresh and brackish-water units occur within the generally open-marine Pleistocene succession. A channel cut by the paleo-Roanoke River during the last glacial sea-level lowstand occurs in the northern part of the study area. Pollen indicates that the basal fluvial valley fill accumulated in cooler than modern climate conditions in the latest Pleistocene. Overlying silts and muds accumulated under cool climatic, estuarine conditions according to diatom and pollen data. Radiocarbon ages from the estuarine deposits indicate that the bulk of these sediments accumulated during the latest Pleistocene. The estuarine channel-fill deposits are overlain by Holocene open-marine sands deposited as the rising sea transgressed into the estuary approximately 8.5 to 9.0 kyr BP. Within the barrier island drill cores of this study, fully marine sedimentation occurred throughout the Holocene. However, immediately west of the present barrier island, mid- to late Holocene estuarine deposits underlie the modern Albemarle Sound. The islands that currently form a continuous barrier across the mouth of Albemarle Sound have a complex history of Holocene construction and destruction and large portions of them may be less than 3 kyr old. The barrier island sands overlie open-marine sands of Colington Shoal in the north and to the south overlie fluvial and marine sand filling paleo-Roanoke tributary valleys. The Pleistocene sediments underlying the northern Outer Banks study area are mainly of open inner to mid-shelf origin. If, as is likely, sea level continues to rise, a return to such environmental conditions is likely in the near future.

North Carolina↗

USGS2009

Estimation of the tectonic slip-rate from Quaternary lacustrine facies within the intraplate Albacete province (SE of Spain)

The Quaternary lacustrine basin of Cordovilla (CB) represents one of the most active tectonic areas of the Prebetic Zone (Albacete, SE of Spain). The Quaternary sedimentary deposits of this basin are mainly endoreic lacustrine carbonate and alluvial deposits, developed in a semi-arid climate (Pleistocene-present). The basin is a NW-SE-elongated graben bounded by a major right-lateral oblique-fault, the Pozohondo Fault. This fault trends NW-SE, with an approximate trace of 55 km, and is composed of various segments which are identified by fault scarps. In order to establish the slip-rate of the most active segment of the Pozohondo Fault, called the Cordovilla segment, we carried out a detailed study of the affected Quaternary lacustrine deposits. We found that the lacustrine facies could be related to episodic moderate paleoearthquakes. The slip-rate is calculated to be 0.05 and 0.09 mm/yr, using radiometric dating for the vertical offsets of the lacustrine facies. A trenching study at the northern part of the Cordovilla segment revealed two events caused by paleoearthquakes, with the most recent expressed as an oblique-fault off-setting a poorly-developed soil. The magnitude of the last event was greater than 6, using various empirical relationships for the fault displacement and the surface-length rupture. We estimate episodic activity across the Cordovilla segment, to be characterized by moderate-sized paleoearthquakes (M6), which is in agreement with the tectonic context of an intraplate zone of the Iberian plate. ?? 2009 Elsevier B.V.

Sedimentary Geology↗

USGS1997

Tertiary and Quaternary tectonic faulting in southernmost Illinois

Tertiary and/or Quaternary tectonic faulting is documented in three areas of southernmost Illinois: the Fluorspar Area Fault Complex (FAFC) in Pope and Massac Counties, the Ste. Genevieve Fault Zone (SGFZ) in Alexander and Union Counties, and the Commerce Fault Zone (CFZ) in Alexander County. In the FAFC, faults that strike NE and NNE displace Mounds Gravel (late Miocene to early Pleistocene) and, locally, the Metropolis terrace gravel (Pleistocene; pre-Woodfordian). No Woodfordian or younger deposits are deformed. Faults typically outline narrow, linear grabens that formed under tension with a component of strike slip. North-south to NW-trending vertical faults near the southeast end of the SGFZ displace Eocene sediments. Again, faults outline narrow grabens and show indications of strike slip. Deformed Quaternary sediments have not been observed. The CFZ, which trends northeast, displaces Mounds Gravel in Illinois and units as young as Peoria Silt (Woodfordian) in Missouri. Quaternary movement has been interpreted as right-lateral strike-slip. The CFZ coincides with a subtle gravity and magnetic lineament and seems to reflect a major feature in the basement. Surface expression in Illinois is subtle, but mafic and ultramafic intrusions, hydrothermal alteration and small faults align with the Commerce geophysical lineament. Earthquake foci in Missouri and Illinois lie on or close to the CFZ; some focal mechanisms fit the fault trend. Among these structures, only the CFZ exhibits slip that conforms to the current stress field (principal compressive stress axis E-W to ENE-WSW). Possibly, the stress field changed during Neogene time. Alternatively, high fluid pressures or local stress concentrations may have induced slip on less favorably oriented fractures. Tighter constraints are needed on timing, magnitude, and direction of Neogene displacement.

Illinois↗

USGS2000

206Pb-230Th-234U-238U and 207Pb-235U geochronology of Quaternary opal, Yucca Mountain, Nevada

U–Th–Pb isotopic systems have been studied in submillimeter-thick outermost layers of Quaternary opal occurring in calcite–silica fracture and cavity coatings within Tertiary tuffs at Yucca Mountain, Nevada, USA. These coatings preserve a record of paleohydrologic conditions at this site, which is being evaluated as a potential high-level nuclear waste repository. The opal precipitated from groundwater is variably enriched in 234 U (measured 234 U/ 238 U activity ratio 1.124–6.179) and has high U (30–313 ppm), low Th (0.008–3.7 ppm), and low common Pb concentrations (measured 206 Pb/ 204 Pb up to 11,370). It has been demonstrated that the laboratory acid treatment used in this study to clean sample surfaces and to remove adherent calcite, did not disturb U–Th–Pb isotopic systems in opal. The opal ages calculated from 206 Pb∗/ 238 U and 207 Pb∗/ 235 U ratios display strong reverse discordance because of excess radiogenic 206 Pb∗ derived from the elevated initial 234 U. The data are best interpreted using projections of a new four-dimensional concordia diagram defined by 206 Pb∗/ 238 U, 207 Pb∗/ 235 U, 234 U/ 238 U activity , and 230 Th/ 238 U activity . Ages and initial 234 U/ 238 U activity ratios have been calculated using different projections of this diagram and tested for concordance. The data are discordant, that is observed 207 Pb∗/ 235 U ages of 170 ± 32 (2σ) to 1772 ± 40 ka are systematically older than 230 Th/U ages of 34.1 ± 0.6 to 452 ± 32 ka. The age discordance is not a result of migration of uranium and its decay products under the open system conditions, but a consequence of noninstantaneous growth of opal. Combined U–Pb and 230 Th/U ages support the model of slow mineral deposition at the rates of millimeters per million years resulting in layering on a scale too fine for mechanical sampling. In this case, U–Pb ages provide more accurate estimates of the average age for mixed multiage samples than 230 Th/U ages, because ages based on shorter-lived isotopes are nonlinearly biased by younger mineral additions. Use of the combined U–Th–Pb technique to date Yucca Mountain Quaternary opals significantly extends the age range beyond that of the 230 Th/U dating method and shows that selected fracture pathways in the unsaturated zone felsic tuffs of Yucca Mountain have been active throughout the Quaternary.

Geochimica et Cosmochimica Acta↗

USGS1997

Transgressive systems tract development and incised-valley fills within a quaternary estuary-shelf system: Virginia inner shelf, USA

High-frequency Quaternary glacioeustasy resulted in the incision of six moderate- to high-relief fluvial erosion surfaces beneath the Virginia inner shelf and coastal zone along the updip edges of the Atlantic continental margin. Fluvial valleys up to 5 km wide, with up to 37 m of relief and thalweg depths of up to 72 m below modern mean sea level, cut through underlying Pleistocene and Mio-Pliocene strata in response to drops in baselevel on the order of 100 m. Fluvially incised valleys were significantly modified during subsequent marine transgressions as fluvial drainage basins evolved into estuarine embayments (ancestral generations of the Chesapeake Bay). Complex incised-valley fill successions are bounded by, or contain, up to four stacked erosional surfaces (basal fluvial erosion surface, bay ravinement, tidal ravinement, and ebb-flood channel-base diastem) in vertical succession. These surfaces, combined with the transgressive oceanic ravinement that generally caps incised-valley fills, control the lateral and vertical development of intervening seismic facies (depositional systems). Transgressive stratigraphy characterizes the Quaternary section beneath the Virginia inner shelf where six depositional sequences (Sequences I-VI) are identified. Depositional sequences consist primarily of estuarine depositional systems (subjacent to the transgressive oceanic ravinement) and shoreface-shelf depositional systems; highstand systems tract coastal systems are thinly developed. The Quaternary section can be broadly subdivided into two parts. The upper part contains sequences consisting predominantly of inner shelf facies, whereas sequences in the lower part of the section consist predominantly of estuarine facies. Three styles of sequence preservation are identified. Style 1, represented by Sequences VI and V, is characterized by large estuarine systems (ancestral generations of the Chesapeake Bay) that are up to 40 m thick, have hemicylindrical wedge geometries, and occur within large, coast-oblique trending depressions (paleo-estuaries). Style 1 is dominated by fluvial through estuary-mouth depositional systems (Seismic Facies 1-4). Style 2 sequence preservation, represented by Sequences III and II, is dominantly an inner shelf and shoreface succession with a seaward-thickening tabular wedge geometry that does not exceed 15 m in thickness. These shoreface and inner shelf depositional systems of the upper transgressive systems tract (Seismic Facies 9) and highstand systems tract (Seismic Facies 7 and 11) are not associated with paleo-estuaries. Style 3 sequence preservation is represented by Sequence 1, the Holocene Sequence. It consists of lower transgressive systems tract fluvial-estuarine, lagoonal, and tidal-inlet fill deposits (Seismic Facies 1-6, and 8) overlain by upper transgressive systems tract shelf and shoreface sands (Seismic Facies 9). Style 3 has a crenulated wedge geometry, and is thickest beneath and seaward of the modern Chesapeake Bay mouth. It thins northward and landward onto Late Pleistocene interfluvial highs on the basinward side of the southern Delmarva Peninsula.

Marine Geology↗

USGS2009

Moderate rates of late Quaternary slip along the northwestern margin of the Basin and Range Province, Surprise Valley fault, northeastern California

The 86-km-long Surprise Valley normal fault forms part of the active northwestern margin of the Basin and Range province in northeastern California. We use trench mapping and radiocarbon, luminescence, and tephra dating to estimate displacements and timing of the past five surface-rupturing earthquakes on the central part of the fault near Cedarville. A Bayesian OxCal analysis of timing constraints indicates earthquake times of 18.2 ± 2.6, 10.9 ± 3.2, 8.5 ± 0.5, 5.8 ± 1.5, and 1.2 ± 0.1 ka. These data yield recurrence intervals of 7.3 ± 4.1, 2.5 ± 3.2, 2.7 ± 1.6, and 4.5 ± 1.5 ka and an elapsed time of 1.2 ± 0.1 ka since the latest surface-rupturing earthquake. Our best estimate of latest Quaternary vertical slip rate is 0.6 ?? 0.1 mm/a. This late Quaternary rate is remarkably similar to long-term (8-14 Ma) minimum vertical slip rates (>0.4-0.5 ± 0.3 mm/a) calculated from recently acquired seismic reflection and chronologic and structural data in Surprise Valley and the adjacent Warner Mountains. However, our slip rate yields estimates of extension that are lower than recent campaign GPS determinations by factors of 1.5-4 unless the fault has an unusually shallow (30°-35°) dip as suggested by recently acquired seismic reflection data. Coseismic displacements of 2-4.5 ± 1 m documented in the trench and probable rupture lengths of 53-65 km indicate a history of latest Quaternary earthquakes of M 6.8-7.3 on the central part of the. Surprise Valley fault.

California↗

USGS1996

Origin of Bermuda's clay-rich Quaternary paleosols and their paleoclimatic significance

Red clayey paleosols that are chiefly the product of aerosolic dust deposition are interbedded in the Quaternary carbonate formations of the Bermuda oceanic island system. These paleosols provide a basis for reconstructing Quaternary atmospheric circulation patterns in the northwestern Atlantic. Geochemical analyses were performed on representative paleosol samples to identify their parent dust source. Fine-grained fractions were analyzed by energy-dispersive X ray fluorescence to determine trace element (Zr, Y, La, Ti, and Nb) concentrations and to derive geochemical signatures based on immobile element ratios. These ratios were compared with geochemical signatures determined for three possible sources of airborne dust: (1) Great Plains loess, (2) Mississippi River Valley loess, and (3) Saharan dust. The Zr/Y and Zr/La ratios provided the clearest distinction between the hypothesized dust sources. The low ratios in the paleosol B horizons most closely resemble Saharan dust in the <2-μm size class fraction. Contributions from the two North American loessial source areas could not be clearly detected. Thus Bermuda paleosols have a predominantly Saharan aerosolic dust signature. Saharan dust deposition on Bermuda during successive Quaternary glacial periods is consistent with patterns of general circulation models, which indicate that during glacial maxima the northeast summer trade winds were stronger than at present and reached latitudes higher than 30°N despite lower-than-present sea surface temperatures in the North Atlantic.

Journal of Geophysical Research D: Atmospheres↗

USGS1952

Magmatic differentiation in tertiary and quaternary volcanic rocks from Adak and Kanaga Islands, Aleutian Islands, Alaska

Samples of 17 volcanic rocks of Tertiary and Quaternary age from Adak and Kanaga islands have been chemically analyzed and studied microscopically. Spectrograms have been made of 10 of them. The rocks from Adak represent one center of possibly older Tertiary age and two centers of younger Tertiary or Quaternary age. The rocks from Kanaga Island represent both a shield volcano of possibly Tertiary age, partly destroyed by the formation of a caldera, and a young cone of Quaternary age that has grown within the caldera. All the rocks are basalt or andesite. Modally, all are characterized by relatively large crystals of plagioclase more calcic than andesine, and by one or more of the following ferromagnesian minerals: olivine, hypersthene, augite, and hornblende. Apatite and iron ores are common, and late silica minerals and orthoclase occur interstitially in the groundmasses of some rocks . As analyses of no more than four samples are available for each center, the small differences between sets of analyses representing different centers are of doubtful significance. Consequently, the analyses representing all the centers have been plotted on each of the several diagrams used. The several types of variation diagrams show that the province is a calc-alkaline one. The alkali-lime index is in the neighborhood of 63. This very high value is comparable with that for Katmai and is only slightly less than the maximum for the Japanese volcanic rock series. The quantities of minor constituents present are not exceptional for the rock types analyzed; the rocks from Adak are apparently more strontium-rich than those from Kanaga . The chemical analyses of the more basic rock types, as compared with the average analysis of plateau basalt, suggest that the Aleutian parental magma could have been derived from a plateau basalt magma by the addition of plagioclase and the subtraction of pyroxene, iron ore, and some quartz. The distribution of the minor elements can be explained more easily by postulating that, at least on Kanaga Island , some sediments have been assimilated. The derivation of the analyzed rocks from the Aleutian parental magma is most easily explained by the hypothesis that the plagioclase remained in suspension while the ferromagnesian minerals were settling out.

Alaska↗

USGS2019

Late Quaternary sea-level history of Saipan, Commonwealth of the Northern Mariana Islands, USA: A test of tectonic uplift and glacial isostatic adjustment models

In 1979, S. Uyeda and H. Kanamori proposed a tectonic model with two end members of a subduction-boundary continuum: the “Chilean” type (shallow dip of the subducting plate, great thrust events, compression, and uplift of the overriding plate) and a “Mariana” type (steep dip of the subducting plate, no great thrust events, tension, and no uplift). This concept has been used to explain variable rates of Quaternary uplift around the Pacific Rim, yet no uplift rates have been determined for the Mariana Islands themselves, one of the end members in this model. We studied the late Quaternary Tanapag Limestone, which rims much of the eastern and southern coasts of Saipan, Northern Mariana Islands, with elevations of ∼13 m to ∼30 m. Samples from 12 well-preserved corals ( Acropora , Porites , and Goniastrea ) yielded U-series ages ranging from ca. 134 ka to ca. 126 ka. These ages correlate the emergent reef of the Tanapag Limestone with the last interglacial period, when sea level was several meters above present. Ages and measured reef elevations from the Tanapag Limestone, along with paleo–sea-level data, yield relatively low late Quaternary uplift rates of 0.002–0.19 m/k.y., consistent with the Uyeda-Kanamori model. A review of data from other localities near subduction zones around the Pacific Basin, however, indicates that many coastlines do not fit the model. Uplift rates along the Chilean coast are predicted to be relatively high, but field studies indicate they are low. On some coastlines, relatively high uplift rates are better explained by subduction of seamounts or submarine ridges rather than subduction zone geometry. Despite the low long-term uplift rate on Saipan, the island also hosts an emergent, low-elevation (+3.9–4.0 m) reef with corals in growth position below a notch (+4.2 m). The corals are dated to 3.9–3.1 ka. The occurrence of this young, emergent reef is likely not due to tectonic uplift; instead, it is interpreted to be the result of glacial isostatic adjustment processes after the end of the last glacial period. Our findings are consistent with similar observations on tectonically stable or slowly uplifting islands elsewhere in the equatorial Pacific Ocean and agree with numerical models of a higher-than-present Holocene sea level in this region due to glacial isostatic adjustment processes.

Northern Mariana Islands, Saipan↗

USGS2023

Ages of the granitic basement of Long Valley Caldera, California, USA, and siting of the Quaternary granite-rhyolite pluton

The leucogranitic crystal-mush pluton beneath the iconic Long Valley Caldera, California, USA, released >820 km 3 of crystal-poor Pleistocene rhyolite, which was hosted by numerous Mesozoic granitic plutons, only a few of which had been dated until now. Reported here are U-Pb zircon ages, determined by sensitive high-resolution ion microprobe−reverse geometry (SHRIMP-RG), for 11 circumcaldera granitoids, all of them either Triassic or Cretaceous. Growth of the 35-km-wide Quaternary rhyolite-leucogranite plutonic reservoir was fostered by collocation of (1) a dense swath of late Pliocene basaltic vents, (2) a left-stepping extensional reentrant in the rangefront fault zone of the Sierra Nevada batholith, and (3) a sharp offset of the Proterozoic continental margin as represented by the Sr-isotope 0.706 line. We further consider whether the basement architecture of as many as 26 separate Triassic and Cretaceous plutons and intervening septa and pendants of Paleozoic metasedimentary rocks influenced siting of the Quaternary pluton and whether the ragged margin of Proterozoic lithosphere helped to focus asthenospheric edge upwelling that intensified crustal melting and intrusion in both the Triassic and the Quaternary.

California↗

USGS2004

Deformation of quaternary strata and its relationship to crustal folds and faults, south-central Puget Lowland, Washington State

Folded Quaternary deposits across the south-central Puget Lowland, an area just south of the Seattle fault that extends across the Seattle uplift and its boundary with the adjacent Tacoma basin, provide increased resolution of the character and rate of crustal deformation. They also constrain alternative, and partly incompatible, views of crustal structure previously suggested by geophysical investigations. Tectonic deformation has been progressive for at least the past few hundred thousand years: older sediments display greater deformation than the youngest exposed deposits in the study area. Strain rates across the Seattle uplift have probably been between 0.25 and 1.0 mm/yr during this period, accounting for ???10% of the total strain shortening of the western Washington crust. The Seattle uplift displays Quaternary deformation across its full north-south extent and has structural discontinuities at both its northern and southern boundaries. Previous workers have already established the faulted nature of its northern boundary; exposed Quaternary strata across its southern boundary display intense folding, the location of which generally corresponds to the projection of a "Tacoma fault" suggested by prior geophysical studies. ?? 2004 Geological Society of America.

Geology↗

USGS2012

The Quaternary thrust system of the northern Alaska Range

The framework of Quaternary faults in Alaska remains poorly constrained. Recent studies in the Alaska Range north of the Denali fault add significantly to the recognition of Quaternary deformation in this active orogen. Faults and folds active during the Quaternary occur over a length of ∼500 km along the northern flank of the Alaska Range, extending from Mount McKinley (Denali) eastward to the Tok River valley. These faults exist as a continuous system of active structures, but we divide the system into four regions based on east-west changes in structural style. At the western end, the Kantishna Hills have only two known faults but the highest rate of shallow crustal seismicity. The western northern foothills fold-thrust belt consists of a 50-km-wide zone of subparallel thrust and reverse faults. This broad zone of deformation narrows to the east in a transition zone where the range-bounding fault of the western northern foothills fold-thrust belt terminates and displacement occurs on thrust and/or reverse faults closer to the Denali fault. The eastern northern foothills fold-thrust belt is characterized by ∼40-km-long thrust fault segments separated across left-steps by NNE-trending left-lateral faults. Altogether, these faults accommodate much of the topographic growth of the northern flank of the Alaska Range. Recognition of this thrust fault system represents a significant concern in addition to the Denali fault for infrastructure adjacent to and transecting the Alaska Range. Although additional work is required to characterize these faults sufficiently for seismic hazard analysis, the regional extent and structural character should require the consideration of the northern Alaska Range thrust system in regional tectonic models.

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