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At least 127 records · Page 7Linked to original sources

USGS2011

Ant-nest ichnofossils in honeycomb calcretes, Neogene Ogallala Formation, High Plains region of western Kansas, U.S.A.

Two new ant-nest trace fossils are described from calcic sandy paleosols of the Neogene Ogallala Formation in western Kansas. The ichnofossils are preserved within and below calcrete beds weathering in positive relief as carbonate-filled casts or as cavities in negative relief. Daimoniobarax ichnogenus nov. is established for burrow systems composed of vertically tiered, horizontally oriented pancake-shaped chambers connected by predominantly vertical and cylindrical shafts ~ 0.8 cm in diameter. Ichnospecies of Daimoniobarax are differentiated based on differences in the plan view outline of chambers, shaft orientation, and junctions between chambers and shafts. Daimoniobarax nephroides ichnospecies nov. is composed of an ~ 24–76 cm long vertical sequence of distinctly lobed chambers (~ 2–20 cm wide and ~ 1 cm high) arranged along sinuous to helical shafts. Chamber shape in plan view ranges from small teardrops to larger kidney- and U-shaped forms. Shafts intersect at chamber edges such that chambers appear to bud from the central shafts. Daimoniobarax nephroides is most similar to the nests of extant seed-harvester ants of the New World genus Pogonomyrmex . Such ants are specialized granivores and prefer sandy soils in arid to semi-arid grassland and desert regions. Daimoniobarax tschinkeli ichnospecies nov. is ~ 30–80 cm in vertical extent. Chambers (~ 2–30 cm wide and ~ 1 cm high) are circular to elongate or pseudopodial in plan view. Vertical shafts are straight to slightly sinuous and intersect most often toward the center of the chambers. The generalized architecture of D. tschinkeli is similar to that of the nests or nest portions of several extant ant genera, though it does not closely resemble any known modern nest. Ant ichnofossils provide valuable information on hidden biodiversity, paleohydrologic regimes, paleopedogenic processes, and paleoclimate during the time of nest occupation. Depth-related changes in chamber size and vertical spacing may also help interpret paleosurfaces and paleodepths, and serve as geopetal features.

Kansas↗

USGS2011

Late Early Permian continental ichnofauna from Lake Kemp, north-central Texas, USA

Continental trace fossils of Early Permian age are well known in the western United States from Wolfcampian (~ Asselian to Artinskian) strata, but few examples are known from Leonardian (~ Kungurian) deposits. A substantial ichnofauna from strata of the lower part of the Clear Fork Formation at Lake Kemp, Baylor County, Texas, augments the meager North American record of Leonardian continental trace fossil assemblages. Ichnofossils at Lake Kemp occur in the informally-named Craddock dolomite member of the Clear Fork Formation, which is 12–15 m above the local base of the Clear Fork. The trace-bearing stratum is an up-to-0.3 m thick, laminated to flaser-bedded, dolomitic siltstone that also contains mud cracks, raindrop impressions, microbially induced mat structures, and some land-plant impressions. We interpret the Craddock dolomite member as the feather-edge of a marine transgressive carbonate deposit of an irregular coastline marked by shallow bays or estuaries on the eastern shelf of the Midland basin, and the trace-fossil-bearing stratum at Lake Kemp is an unchannelized flow deposit on a muddy coastal plain. The fossil site at Lake Kemp yields a low to moderately diverse fauna of invertebrate and vertebrate traces. A sparse invertebrate ichnofauna consists of arthropod feeding and locomotion traces assigned to Walpia cf. W. hermitensis White, 1929 and Diplichnites gouldi Gevers in Gevers et al., 1971. Tetrapod footprints are most common and assigned to Batrachichnus salamandroides (Geinitz, 1861), cf. Amphisauropus kablikae (Geinitz and Deichmüller, 1882), and Dromopus lacertoides (Geinitz, 1861), which represent small temnospondyl, seymouriamorph, and basal sauropsid trackmakers. Both the traces and sedimentary features of the fossil horizon indicate a freshwater setting at the time of track formation, and the trace assemblage represents the Scoyenia ichnofacies and the Batrachichnus ichnofacies in an overbank environment with sheet flooding and shallow ephemeral pools on an extensive coastal plain. The Lake Kemp tetrapod track assemblage is characteristic of the global Early Permian tetrapod ichnofauna found in red beds, which is dominated by a handful of ichnogenera that include Batrachichnus, Limnopus, Amphisauropus, Dromopus, Varanopus, Hyloidichnus, Ichniotherium and Dimetropus, which are the tracks of temnospondyls, seymouriamorphs, diadectomorphs, “pelycosaurs”, “captorhinomorphs”, and araeoscelids. The Lake Kemp tracks also further document the continuity of the ichnogenera Batrachichnus, Amphisauropus and Dromopus from Wolfcampian into Leonardian time and thus support the concept that Wolfcampian and Leonardian red-bed tetrapod footprints represent a single biostratigraphic assemblage.

Texas↗

USGS2012

Water utilization of the Cretaceous Mussentuchit Member local vertebrate fauna, Cedar Mountain Formation, Utah, USA: Using oxygen isotopic composition of phosphate

While the oxygen isotopic composition of pedogenic carbonate has successfully been used to address the effects of global climate change on the hydrologic cycle, detailed regional paleohydrologic studies are lacking. Since the hydrologic cycle can vary extensively on local or regional scales due to events such as such as mountain building, and since pedogenic carbonates (calcite) form in a narrow moisture regime, other proxies, such as vertebrate remains, must be used to decipher local versus regional variations in paleohydrology. In this study, the oxygen isotopic composition (δ 18 O p ) of phosphatic remains from a diverse set of vertebrate fossils (fish, turtles, crocodiles, dinosaurs, and micro-mammals) from the Mussentuchit Member (MM) of the Cedar Mountain Formation, Utah, USA (Aptian to Cenomanian) are analyzed in order to determine differences among the available water reservoirs and water utilization of each taxon. Calculated changes in water reservoir δ 18 O w over time are then used to determine the effects of the incursion of the Western Interior Seaway (WIS) and the Sevier Mountains on paleohydrology during the MM time. Calculation of δ 18 O w from the results of isotopic analysis of phosphate oxygen suggests that turtles and crocodiles serve as another proxy for meteoric water δ 18 O that can be used as a measure of average local precipitation δ 18 O w similar to pedogenic calcite. Pedogenic calcites can be slightly biased toward higher values, however, due to their formation during evaporative conditions. Turtles and crocodiles can be used in place of pedogenic calcite in environments that are not conducive to pedogenic carbonate formation. Remains of fish with rounded tooth morphology have δ 18 O p values that predict temperatures consistent with other estimates of mean annual temperature for this latitude and time. The δ 18 O p of ganoid scales and teeth with pointed morphology, however, indicates that these skeletal materials were precipitated from water that is 18 O-enriched due to migration to either evaporatively enriched water, or 18 O-enriched estuarine waters of the Western Interior Seaway (WIS). Another possibility that cannot be discounted and assuming all morphological remains are from the same taxon, is that the pointed teeth and ganoid scales precipitated at different temperatures than rounded teeth. Mammal and herbivorous dinosaur δ 18 O p suggests they primarily drank isotopically depleted river water. Co-existence of crocodiles, turtles, and mammals allows for calculation of relative humidity from site to site and these calculations suggest humidity averaged ~ 58% and ranged between ~ 42% and ~ 76%. The δ 18 O w values estimated from semi-aquatic taxa and pedogenic calcite suggest dominance of WIS-derived moisture during their growth. Herbivorous dinosaurs particularly indicate that altitude and catchment effects from the Sevier Mountains are seemingly important for river water δ 18 O w in the fall through early spring. These data suggest that temporal changes in the isotopic composition of the MM fauna are produced by the small-scale regressive–transgressive cycles of the WIS.

Utah↗

USGS2012

A 28,000 year history of vegetation and climate from Lower Red Rock Lake, Centennial Valley, Southwestern Montana, USA

A sediment core extending to 28,000 cal yr BP from Lower Red Rock Lake in the Centennial Valley of southwestern Montana provides new information on the nature of full-glacial vegetation as well as a history of late-glacial and Holocene vegetation and climate in a poorly studied region. Prior to 17,000 cal yr BP, the eastern Centennial Valley was occupied by a large lake (Pleistocene Lake Centennial), and valley glaciers were present in adjacent mountain ranges. The lake lowered upon erosion of a newly formed western outlet in late-glacial time. High pollen percentages of Juniperus, Poaceae, Asteraceae, and other herbs as well as low pollen accumulation rates suggest sparse vegetation cover. Inferred cold dry conditions are consistent with a strengthened glacial anticyclone at this time. Between 17,000 and 10,500 cal yr BP, high Picea and Abies pollen percentages suggest a shift to subalpine parkland and warmer conditions than before. This is attributed to the northward shift of the jet stream and increasing summer insolation. From 10,500 to 7100 cal yr BP, pollen evidence of open dry forests suggests warm conditions, which were likely a response to increased summer insolation and a strengthened Pacific subtropical high-pressure system. From 7100 to 2400 cal yr BP, cooler moister conditions promoted closed forest and wetlands. Increases in Picea and Abies pollen percentages after 2400 cal yr BP suggest increasing effective moisture. The postglacial pattern of Pseudotsuga expansion indicates that it arrived later on the Atlantic side of the Continental Divide than on the Pacific side. The Divide may have been a physical barrier for refugial populations or it delimited different climate regions that influenced the timing of Pseudotsuga expansion.

Montana↗

USGS2012

Holocene seasonal variability inferred from multiple proxy records from Crevice Lake, Yellowstone National Park, USA

A 9400-yr-old record from Crevice Lake, a semi-closed alkaline lake in northern Yellowstone National Park, was analyzed for pollen, charcoal, geochemistry, mineralogy, diatoms, and stable isotopes to develop a nuanced understanding of Holocene environmental history in a region of northern Rocky Mountains that receives both summer and winter precipitation. The limited surface area, conical bathymetry, and deep water (> 31 m) of Crevice Lake create oxygen-deficient conditions in the hypolimnion and preserve annually laminated sediment (varves) for much of the record. Pollen data indicate that the watershed supported a closed Pinus -dominated forest and low fire frequency prior to 8200 cal yr BP, followed by open parkland until 2600 cal yr BP, and open mixed-conifer forest thereafter. Fire activity shifted from infrequent stand-replacing fires initially to frequent surface fires in the middle Holocene and stand-replacing events in recent centuries. Low values of δ 18 O suggest high winter precipitation in the early Holocene, followed by steadily drier conditions after 8500 cal yr BP. Carbonate-rich sediments before 5000 cal yr BP imply warmer summer conditions than after 5000 cal yr BP. High values of molybdenum (Mo), uranium (U), and sulfur (S) indicate anoxic bottom-waters before 8000 cal yr BP, between 4400 and 3900 cal yr BP, and after 2400 cal yr BP. The diatom record indicates extensive water-column mixing in spring and early summer through much of the Holocene, but a period between 2200 and 800 cal yr BP had strong summer stratification, phosphate limitation, and oxygen-deficient bottom waters. Together, the proxy data suggest wet winters, protracted springs, and warm effectively wet summers in the early Holocene and less snowpack, cool springs, warm dry summers in the middle Holocene. In the late Holocene, the region and lake experienced extreme changes in winter, spring, and summer conditions, with particularly short springs and dry summers and winters during the Roman Warm Period (~ 2000 cal yr BP) and Medieval Climate Anomaly (1200–800 cal yr BP). Long springs and mild summers occurred during the Little Ice Age, and these conditions persist to the present. Although the proxy data indicate effectively wet summer conditions in the early Holocene and drier conditions in the middle and late Holocene, none point specifically to changes in summer precipitation as the cause. Instead, summer conditions were governed by multi-seasonal controls on effective moisture that operated over multiple time scales.

Montana↗

USGS2012

Late Quaternary sedimentological and climate changes at Lake Bosumtwi Ghana: new constraints from laminae analysis and radiocarbon age modeling

The Lake Bosumtwi sediment record represents one of the longest and highest-resolution terrestrial records of paleoclimate change available from sub-Saharan Africa. Here we report a new sediment age model framework for the last ~ 45 cal kyr of sedimentation using a combination of high-resolution radiocarbon dating, Bayesian age-depth modeling and lamination counting. Our results highlight the practical limits of these methods for reducing age model uncertainties and suggest that even with very high sampling densities, radiocarbon uncertainties of at least a few hundred years are unavoidable. Age model uncertainties are smallest during the Holocene (205 yr) and the glacial (360 yr) but are large at the base of the record (1660 yr), due to a combination of decreasing sample density, larger calibration uncertainties and increases in radiocarbon age scatter. For portions of the chronology older than ~ 35 cal kyr, additional considerations, such as the use of a low-blank graphitization system and more rigorous sample pretreatment were necessary to generate a reliable age depth model because of the incorporation of small amounts of younger carbon. A comparison of radiocarbon age model results and lamination counts over the time interval ~ 15–30 cal kyr agree with an overall discrepancy of ~ 10% and display similar changes in sedimentation rate, supporting the annual nature of sediment laminations in the early part of the record. Changes in sedimentation rates reconstructed from the age-depth model indicate that intervals of enhanced sediment delivery occurred at 16–19, 24 and 29–31 cal kyr, broadly synchronous with reconstructed drought episodes elsewhere in northern West Africa and potentially, with changes in Atlantic meridional heat transport during North Atlantic Heinrich events. These data suggest that millennial-scale drought events in the West African monsoon region were latitudinally extensive, reaching within several hundred kilometers of the Guinea coast. This is inconsistent with a simple southward shift in the mean position of the monsoon rainbelt, and requires changes in moisture convergence as a result of either a reduction in the moisture content of the tropical rainbelt, decreased convection, or both.

Lake Bosumtwi↗

USGS2012

A half-million-year record of paleoclimate from the Lake Manix Core, Mojave Desert, California

Pluvial lakes in the southwestern U.S. responded sensitively to past climate through effects on rainfall, runoff, and evaporation. Although most studies agree that pluvial lakes in the southwestern U.S. reached their highest levels coeval with glacial stages, the specific timing of increased effective moisture and lake-level rise is debated, particularly for the southwesternmost lakes. We obtained a 45-m core of lacustrine sediment from Lake Manix, the former terminus of the Mojave River prior to about 25 ka, and supplemented data from the core with outcrop studies. These sediments provide a robust record of Mojave River discharge over the last half-million years. Lake Manix persisted from OIS 12 through early OIS 2, including during interstadial OIS 3 and interglacials OIS 5, 7, and 9. The ostracode faunal record displays a shift from an unexpectedly warm, summer-dominated lake hydrology during OIS 12 to predominantly colder, winter-dominated conditions afterwards. The ostracode-based stable isotope record displays a large degree of intra-sample variability and does not mimic other well-known isotopic records of climate change. Evaporation likely buffered the Manix δ 18 O record from most of the expected isotopic differences between interglacial and glacial-interval discharge. Isotopically depleted and stable lakes occurred only four to six times, most notably during OIS 7 and OIS 9. Internal drainage-basin changes also affected the isotopic record. Persistence of lakes in the Manix basin during interglacials requires atmospheric or oceanic circulation controls on the mean position of the Pacific storm track other than large ice sheets. We propose that the relative strength and sign of the Northern Annular Mode (NAM) and its influence on atmospheric river-derived precipitation is a potential explanation.

California↗

USGS2013

Diatom evidence for the onset of Pliocene cooling from AND-1B, McMurdo Sound, Antarctica

The late Pliocene, ~ 3.3–3.0 Ma, is the most recent interval of sustained global warmth in the geologic past. This window is the focus of climate reconstruction efforts by the U.S. Geological Survey's Pliocene Research, Interpretation, and Synoptic Mapping (PRISM) Data/Model Cooperative, and may provide a useful climate analog for the coming century. Reconstructions of past surface ocean conditions proximal to the Antarctic continent are essential to understanding the sensitivity of the cryosphere to this key interval in Earth's climate evolution. An exceptional marine sediment core collected from the southwestern Ross Sea (78° S), Antarctica, during ANDRILL's McMurdo Ice Shelf Project preserves evidence of dramatic fluctuations between grounded ice and productive, open ocean conditions during the late Pliocene, reflecting orbitally-paced glacial/interglacial cycling. In this near-shore record, diatom-rich sediments are recovered from interglacial intervals; two of these diatomites, from ~ 3.2 Ma and 3.03 Ma, are within the PRISM chronologic window. The diatom assemblages identified in PRISM-age late Pliocene diatom-rich sediments are distinct from those in mid-Pliocene and later Pliocene/Pleistocene intervals recovered from AND-1B, and comprise both extant taxa with well-constrained ecological preferences and a diverse extinct flora, some members of which are previously undescribed from Antarctic sediments. Both units are dominated by Chaetoceros resting spores, an indicator of high productivity and stratification that is present at much lower abundance in materials both older and younger than the PRISM-age sediments. Newly described species of the genus Fragilariopsis , which first appear in the AND-1B record at 3.2 Ma, are the most abundant extinct members of the PRISM-age assemblages. Other extant species with established environmental affinities, such as Fragilariopsis sublinearis , F . curta , Stellarima microtrias , and Thalassiothrix antarctica , are present at lower abundances. Environmental inferences drawn from extant diatom assemblages are in good agreement with those from Chaetoceros resting spores and the Fragilariopsis radiation. All three lines of evidence indicate the onset of late Pliocene cooling in the Ross Sea near-shore environment at 3.2 Ma, with intensification and possible regional persistence of summer sea ice by 3.03 Ma. An important implication of this research is the indication that the Ross Ice Shelf fluctuated dramatically on orbital timescales at a time when nearshore Antarctic conditions were only modestly warmer than present.

Palaeogeography, Palaeoclimatology, Palaeoecology↗

USGS2013

Impact of Late Holocene climate variability and anthropogenic activities on Biscayne Bay (Florida, U.S.A.): Evidence from diatoms

Shallow marine ecosystems are experiencing significant environmental alterations as a result of changing climate and increasing human activities along coasts. Intensive urbanization of the southeast Florida coast and intensification of climate change over the last few centuries changed the character of coastal ecosystems in the semi-enclosed Biscayne Bay, Florida. In order to develop management policies for the Bay, it is vital to obtain reliable scientific evidence of past ecological conditions. The long-term records of subfossil diatoms obtained from No Name Bank and Featherbed Bank in the Central Biscayne Bay, and from the Card Sound Bank in the neighboring Card Sound, were used to study the magnitude of the environmental change caused by climate variability and water management over the last ~ 600 yr. Analyses of these records revealed that the major shifts in the diatom assemblage structures at No Name Bank occurred in 1956, at Featherbed Bank in 1966, and at Card Sound Bank in 1957. Smaller magnitude shifts were also recorded at Featherbed Bank in 1893, 1942, 1974 and 1983. Most of these changes coincided with severe drought periods that developed during the cold phases of El Niño Southern Oscillation (ENSO), Atlantic Multidecadal Oscillation (AMO) and Pacific Decadal Oscillation (PDO), or when AMO was in warm phase and PDO was in the cold phase. Only the 1983 change coincided with an unusually wet period that developed during the warm phases of ENSO and PDO. Quantitative reconstructions of salinity using the weighted averaging partial least squares (WA-PLS) diatom-based salinity model revealed a gradual increase in salinity at the three coring locations over the last ~ 600 yr, which was primarily caused by continuously rising sea level and in the last several decades also by the reduction of the amount of freshwater inflow from the mainland. Concentration of sediment total nitrogen (TN), total phosphorus (TP) and total organic carbon (TOC) increased in the second half of the 20th century, which coincided with the construction of canals, landfills, marinas and water treatment plants along the western margin of Biscayne Bay. Increased magnitude and rate of the diatom assemblage restructuring in the mid- and late-1900s, suggest that large environmental changes are occurring more rapidly now than in the past.

Florida↗

USGS2013

Modern foraminifera, δ13C, and bulk geochemistry of central Oregon tidal marshes and their application in paleoseismology

We assessed the utility of δ 13 C and bulk geochemistry (total organic content and C:N) to reconstruct relative sea-level changes on the Cascadia subduction zone through comparison with an established sea-level indicator (benthic foraminifera). Four modern transects collected from three tidal environments at Siletz Bay, Oregon, USA, produced three elevation-dependent groups in both the foraminiferal and δ 13 C/bulk geochemistry datasets. Foraminiferal samples from the tidal flat and low marsh are identified by Miliammina fusca abundances of > 45%, middle and high marsh by M. fusca abundances of < 45% and the highest marsh by Trochamminita irregularis abundances > 25%. The δ 13 C values from the groups defined with δ 13 C/bulk geochemistry analyses decrease with an increasing elevation; − 24.1 ± 1.7‰ in the tidal flat and low marsh; − 27.3 ± 1.4‰ in the middle and high marsh; and − 29.6 ± 0.8‰ in the highest marsh samples. We applied the modern foraminiferal and δ 13 C distributions to a core that contained a stratigraphic contact marking the great Cascadia earthquake of AD 1700. Both techniques gave similar values for coseismic subsidence across the contact (0.88 ± 0.39 m and 0.71 ± 0.56 m) suggesting that δ 13 C has potential for identifying amounts of relative sea-level change due to tectonics.

Oregon↗

USGS2015

A 3400 year paleolimnological record of prehispanic human–environment interactions in the Holmul region of the southern Maya lowlands

The timing, magnitude and drivers of late Holocene environmental change in the Holmul region of the southern Maya lowlands are examined by combining paleoenvironmental and archeological data. Environmental proxy analyses on a ~ 3350 cal yr lacustrine sediment record include pollen, charcoal, loss on ignition, magnetic suscep- tibility, and elemental geochemistry. Archeological evidence is derived from extensive settlement surveys conducted near the study site. Results indicate nearby settlement and agricultural activity taking place in an environment characterized by open forest from around 3350 to 950 cal yr BP. The fire history shows a dramatic increase in burning during the Classic period, possibly reflecting changing agricultural strategies. A distinct band of carbonate deposited from 1270 to 1040 cal yr BP suggests decreased hydrologic input associated with drier conditions. Abrupt changes in proxy data around 940 cal yr BP indicate a cessation of human disturbance and local abandonment of the area.

Peten↗

USGS2013

Quaternary ostracodes and molluscs from the Rukwa Basin (Tanzania) and their evolutionary and paleobiogeographic implications

Much of the spectacular biodiversity of the African Great Lakes is endemic to single lake basins so that the margins of these basins or their lakes coincide with biogeographic boundaries. Longstanding debate surrounds the evolution of these endemic species, the stability of bioprovinces, and the exchange of faunas between them over geologic time as the rift developed. Because these debates are currently unsettled, we are uncertain of how much existing distribution patterns are determined by modern hydrological barriers versus reflecting past history. This study reports on late Quaternary fossils from the Rukwa Basin and integrates geological and paleoecological data to explore faunal exchange between freshwater bioprovinces, in particular with Lake Tanganyika. Lake Rukwa's water level showed large fluctuations over the last 25 ky, and for most of this period the lake contained large habitat diversity, with different species assemblages and taphonomic controls along its northern and southern shores. Comparison of fossil and modern invertebrate assemblages suggests faunal persistence through the Last Glacial Maximum, but with an extirpation event that occurred in the last 5 ky. Some of the molluscs and ostracodes studied here are closely related to taxa (or part of clades) that are currently endemic to Lake Tanganyika, but others testify to wider and perhaps older faunal exchanges between the Rukwa bioprovince and those of Lake Malawi and the Upper Congo (in particular Lake Mweru). The Rukwa Basin has a long history of rifting and lacustrine conditions and, at least temporarily, its ecosystems appear to have functioned as satellites to Lake Tanganyika in which intralacustrine speciation occurred. Paleontological studies of the Rukwa faunas are particularly relevant because of the basin's important role in the late Cenozoic biogeography of tropical Africa, and because many of the molecular traces potentially revealing this history would have been erased in the late Holocene extirpation.

Palaeogeography, Palaeoclimatology, Palaeoecology↗

USGS2014

Uranium-series ages of corals, sea level history, and palaeozoogeography, Canary Islands, Spain: an exploratory study for two Quaternary interglacial periods

We present the first U-series ages of corals from emergent marine deposits on the Canary Islands. Deposits at + 20 m are 481 ± 39 ka, possibly correlative to marine isotope stage (or MIS) 11, while those at + 12 and + 8 m are 120.5 ± 0.8 ka and 130.2 ± 0.8 ka, respectively, correlative to MIS 5.5. The age, elevations, and uplift rates derived from MIS 5.5 deposits on the Canary Islands allow calculations of hypothetical palaeo-sea levels during the MIS 11 high sea stand. Estimates indicate that the MIS 11 high sea stand likely was at least + 9 m (relative to present sea level) and could have been as high as + 24 m. The most conservative estimates of palaeo-sea level during MIS 11 would require an ice mass loss equivalent to all of the modern Greenland and West Antarctic ice sheets; the more extreme estimates would require additional ice mass loss from the East Antarctic ice sheet. Extralimital southern species of mollusks, found in both MIS 11 and MIS 5.5 deposits on the Canary Islands, imply warmer-than-modern sea surface temperatures during at least a part of MIS 11 and much warmer sea surface temperatures during at least a part of MIS 5.5. Both MIS 11 and MIS 5.5 marine deposits on the Canary Islands contain extralimital northern species of mollusks as well, indicating cooler-than-present waters at times during these interglacial periods. We hypothesize that the co-occurrence of extralimital southern and northern species of marine invertebrates in the fossil record of the Canary Islands reflects its geographic location with respect to major synoptic-scale controls on climate and ocean currents. Previous interglacials may have been characterized by early, insolation-forced warming, along with northward migration of the intertropical convergence zone (ITCZ), accompanied by weakened trade winds and diminished upwelling. This allowed the arrival of extralimital southern taxa from the tropical Senegalese faunal province. During later parts of the MIS 11 and 5.5 interglacials, decreased insolation may have resulted in southward migration of the ITCZ, strengthened trade winds, and re-establishment of upwelling. Such conditions may have brought about not only local extinction of the Senegalese fauna, but allowed southward migration of the cooler-water Mediterranean fauna to the Canary Islands in the later parts of interglacials, a complex palaeoclimate record that is mirrored in the deep-sea core record.

Canary Islands↗

USGS2014

Interpretations of evidence for large Pleistocene paleolakes in the Bonneville basin, western North America: COMMENT on: Bonneville basin shoreline records of large lake intervals during marine isotope stage 3 and the last glacial maximum, by Nishizawa et al. (2013)

Nishizawa et al. (2013) argue in support of three large paleolakes in the Bonneville basin during Marine Oxygen Isotope Stage 3 (MIS 3). If true, that would be an important contribution to paleoclimate investigations. However, the key evidence in support of their argument consists of four radiocarbon ages that are out of stratigraphic order and near the practical and theoretical limit of the dating method. The interpretation of three large MIS 3 lakes conflicts with some of their own data, as well as with independently derived stratigraphic information from the basin. Nishizawa et al. (2013) also interpret a series of radiocarbon ages of mollusk samples as indicating previously undocumented lake transgressions a few thousand years older than basal radiocarbon ages of wood samples. We believe that these interpretations are in error, and arise largely from reliance on radiocarbon ages from carbonate material. Lake records constrained by ages of non-carbonate organic materials, along with compelling stratigraphic information from unconformities and buried soils, argue for not changing interpretations of Lake Bonneville history until more supporting information for older lakes at relatively high altitudes is found.

Palaeogeography, Palaeoclimatology, Palaeoecology↗

USGS2015

An early to mid-Pleistocene deep Arctic Ocean ostracode fauna with North Atlantic affinities

An early to middle Pleistocene ostracode fauna was discovered in sediment core P1-93-AR-23 (P23, 76.95°N, 155.07°W) from 951 meter water depth from the Northwind Ridge, western Arctic Ocean. Piston core P23 yielded more than 30,000 specimens and a total of about 30 species. Several early to mid-Pleistocene species in the genera Krithe , Echinocythereis , Pterygocythereis , and Arcacythere are now extinct in the Arctic and show taxonomic affinities to North Atlantic Ocean species. Our results suggest that there was a major ostracode faunal turnover during the global climate transitions known as the Mid-Pleistocene Transition (MPT, ~ 1.2 to 0.7 Ma) and the Mid-Brunhes Event (MBE, ~ 400 ka) reflecting the development of perennial sea ice during interglacial periods and large ice shelves during glacial periods over the last 400,000 years.

Palaeogeography, Palaeoclimatology, Palaeoecology↗

USGS2015

Paleoceanographic, and paleoclimatic constraints on the global Eocene diatom and silicoflagellate record

Eocene diatom and silicoflagellate biostratigraphy are summarized and correlated with the most recent geologic time scale as well as with the global oxygen isotope and eustatic sea level curves. The global distribution of Eocene diatom/silicoflagellate-bearing sediments varies considerably, reflecting changing oceanic gateways and paleoceanography with changing patterns that are punctuated by four major depositional events. Event 1 (~ 49 million years ago, Ma), at the end of the Early Eocene Climatic Optimum (EECO), saw the cessation of diatom/silicoflagellate deposition in epicontinental regions of the North Sea region and in the northern Russia and the onset of biosilica deposition in the Arctic. Event 2 (~ 46 Ma), which coincided with intensification of the Middle Eocene cooling trend, marked the widespread expansion of diatom/silicoflagellate deposition in both the North and South Atlantic. A shift of diatom/silicoflagellate deposition from the Atlantic to the Pacific began at Event 3, at the end of the Middle Eocene Climatic Optimum (MECO) (~ 40 Ma), that was likely tied to the initial opening of the Drake Passage between Antarctica and South America. Event 4 (~ 39 Ma) coincided with a major sea level fall and a widespread deep-sea hiatus in the latest Middle Eocene. Late Eocene diatom/silicoflagellate deposition became more concentrated in middle-to-high latitude regions and coastal upwelling regions, particularly in the Pacific Ocean. Tabulation of the first and last occurrences of 132 biostratigraphically-important diatoms suggests increased species turnover during the latest Paleocene to earliest Eocene that may be in part due to a monographic effect. An increasing rate of evolution of new diatom species between ~ 46 and 43 Ma and after ~ 40 Ma coincides respectively with the widespread expansion of diatom deposition in the Atlantic and with an increased pole-to-equator thermal gradient that witnessed the expansion of diatoms in high latitude oceans and coastal upwelling settings.

Palaeogeography, Palaeoclimatology, Palaeoecology↗

USGS2015

Uranium-series ages of fossil corals from Mallorca, Spain: The "Neotyrrhenian" high stand of the Mediterranean Sea revisited

The emergent marine deposits of the Mediterranean basin have been recognized as an important record of Quaternary sea level history for more than a century. Previous workers identified what have been interpreted to be two separate high stands of sea in the late Quaternary, namely the “Eutyrrhenian” (thought to be ~ 120 ka) and the “Neotyrrhenian” (thought to be either ~ 100 ka or ~ 80 ka). On Mallorca, Spain, both of these named deposits lie close to present sea level, implying paleo-sea levels slightly above present during both marine isotope stages (MIS) 5.5/5e and either 5.3/5c or 5.1/5a. If these interpretations are correct, they conflict, at least in part, with sea level records from far-field localities. We analyzed corals from the Neotyrrhenian beds on Mallorca, which gave U-series ages from ~ 126 ka to ~ 118 ka. These ages are consistent with previously published amino acid data that show that the Neotyrrhenian and Eutyrrhenian deposits are not significantly different in age. A fossil molluscan fauna from the Neotyrrhenian deposits on Mallorca has a warm-water paleozoogeographic aspect, with nine southward-ranging species and four extralimital southern species. When compared with sea surface temperatures obtained from planktonic foraminifera and alkenones from ODP core 977 in the nearby Alboran Sea, the only time period that shows comparable warmth is MIS 5.5/5e, consistent with the U-series ages of corals from the Neotyrrhenian deposits. We propose that the Neotyrrhenian deposits are a beachrock facies of the same age as the Eutyrrhenian deposits. This interpretation is consistent with the differences in physical sedimentology of the two deposits, explains the U-series and amino acid data indicating the same age, is consistent with the very slight elevation difference of the Neotyrrhenian and Eutyrrhenian beds, and explains the similar, though not identical paleozoogeographic aspects of their fossil faunas.

Mallorca↗

USGS2016

Cenozoic sea level and the rise of modern rimmed atolls

Sea-level records from atolls, potentially spanning the Cenozoic, have been largely overlooked, in part because the processes that control atoll form (reef accretion, carbonate dissolution, sediment transport, vertical motion) are complex and, for many islands, unconstrained on million-year timescales. Here we combine existing observations of atoll morphology and corelog stratigraphy from Enewetak Atoll with a numerical model to (1) constrain the relative rates of subsidence, dissolution and sedimentation that have shaped modern Pacific atolls and (2) construct a record of sea level over the past 8.5 million years. Both the stratigraphy from Enewetak Atoll (constrained by a subsidence rate of ~ 20 m/Myr) and our numerical modeling results suggest that low sea levels (50–125 m below present), and presumably bi-polar glaciations, occurred throughout much of the late Miocene, preceding the warmer climate of the Pliocene, when sea level was higher than present. Carbonate dissolution through the subsequent sea-level fall that accompanied the onset of large glacial cycles in the late Pliocene, along with rapid highstand constructional reef growth, likely drove development of the rimmed atoll morphology we see today.

Palaeogeography, Palaeoclimatology, Palaeoecology↗