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Scott W. Starratt

Publications and source records attributed to Scott W. Starratt.

At least 37 records · Page 2Linked to original sources
USGS2015

Holocene environmental changes inferred from biological and sedimentological proxies in a high elevation Great Basin lake in the northern Ruby Mountains, Nevada, USA

Multi-proxy analyses were conducted on a sediment core from Favre Lake, a high elevation cirque lake in the northern Ruby Mountains, Nevada, and provide a ca. 7600 year record of local and regional environmental change. Data indicate that lake levels were lower from 7600-5750 cal yr BP, when local climate was warmer and/or drier than today. Effective moisture increased after 5750 cal yr BP and remained relatively wet, and possibly cooler, until ca. 3750 cal yr BP. Results indicate generally dry conditions but also enhanced climatic variability from 3750-1750 cal yr BP, after which effective moisture increased. The timing of major changes in the Favre Lake proxy data are roughly coeval and in phase with those recorded in several paleoclimate studies across the Great Basin, suggesting regional climatic controls on local conditions and similar responses at high and low altitudes.

Nevada↗
USGS2015

Holocene diatom-derived climate history of Medicine Lake, northern California, USA

The Medicine Lake record is unusual because it responds not only to local and regional climate signals, but changes in conditions on Medicine Lake volcano during the Holocene. Ice retreated within the Medicine Lake volcano occurred around 11,400 years ago, followed by filling of two sub-basins. The absence of Cyclotella indicates that the early lake was probably less than 5 m deep. The low Abies/Artemisia ratio suggests that the climate was relatively dry. Over the next 4000 years, the level of the lake rose as relatively organic-rich fine-grained sediments filled the basin. The increase in abundance of Cyclotella also suggests that the lake gradually deepened. The abundance of Abies in the basin also increased, suggesting the presence of a deeper snowpack that existed into the late spring and summer. The increased snowpack was likely the primary water source that filled the lake during this period. About 5500 years ago, the lake flooded the shallow shelf area surrounding the two sub-basins. Variations in the abundance of Cyclotella and benthic taxa, dominated by Navicula, indicate that the area of the flooded shelf fluctuated during this interval. The abundance of Isoetes and Abies responded similarly to changes in the basin, both suggesting an increase in effective moisture. Their increase corresponds to an increase in Sequoia pollen observed at ODP Site 1019, which records the establishment of modern climatic conditions along the northern California coast (relatively warm wet winters and cool, foggy summers). A connection between coastal and inland 6 climates appears to have strengthened at about this time. These fluctuations are in part due to these changes in moisture availability, but may also be due to changes in the shape of the lake basin brought about by the movement of magma within the Medicine Lake volcano.

California↗
USGS2014

Bouse Formation in the Bristol basin near Amboy, California, USA

Limestone beds underlain and overlain by alluvial fan conglomerate near Amboy, California, are very similar in many respects to parts of the Bouse Formation, suggesting that an arm of the Pliocene Bouse water body extended across a wide part of the southern Mojave Desert. The deposits are north of the town of Amboy at and below an elevation of 290 m, along the northern piedmont of the Bristol “dry” Lake basin. The Amboy outcrops contain the Lawlor Tuff (4.83 Ma), which is also found in an outcrop of the Bouse Formation in the Blythe basin near Buzzards Peak in the Chocolate Mountains, 180 km southeast of Amboy. Bouse exposures near Amboy are ∼3.4 m thick, white, distinctly bedded, with limestone and calcareous sandstone as well as stromatolite mounds; we interpret these as nearshore deposits. The Bouse at Amboy contains ostracodes, diatoms, and mollusks that indicate saline lake or estuarine environments with an admixture of fresh-water forms. Along with wading bird tracks and a spine from a marine fish, these fossils suggest that the deposits formed in saline waters near a fresh-water source such as a perennial stream. Beds of the outcrop dip southward and are 113 m above the surface of Bristol Playa, where similar age sediments are buried 270+ m deep, indicating significant faulting and vertical tectonics in this part of the Eastern California Shear Zone during the past 5 m.y. Confirmation of the Bouse Formation at Amboy strengthens previous assignments to the Bouse Formation for mudstones in driller logs at Danby “dry” Lake, California, and suggests that areally extensive arms of the Bouse water body were west of the Blythe basin. The Bristol basin arm of the lower Bouse basin probably was restricted from the main water body by narrow passages, but Bouse sediment there is similar to that in the Blythe basin, suggesting generally similar water chemistry and environmental conditions. Examining the degree to which Bouse deposits in the western arms differed from Bouse deposits in the Blythe basin offers an approach to test whether the southernmost Bouse water body was deposited in an estuarine or lacustrine setting.

California↗
USGS2014

Preliminary analysis of the role of lake basin morphology on the modern diatom flora in the Ruby Mountains and East Humboldt Range, Nevada, USA

As paleolimnologists, we often look at the world through a 5-cm-diameter hole in the bottom of a lake, and although a number of studies have shown that a single core in the deepest part of a lake does not necessarily reflect the entire diatom flora, time and money often limit our ability to collect more than one core from a given site. This preliminary study is part of a multidisciplinary research project to understand Holocene climate variability in alpine regions of the Great Basin, and ultimately, to compare these high elevation records to the better studied pluvial records from adjacent valleys, in this case, the Ruby Valley.

Nevada↗
USGS2013

Preliminary report on the Late Pleistocene and Holocene diatoms of Swamp Lake, Yosemite National Park, California, USA

Swamp Lake, Yosemite National Park, is the only known lake in California containing long sequences of varved sediments and thus has the potential to provide a high-resolution record of climate variability. This preliminary analysis of the diatom assemblages from a 947-cm-long composite sediment core (freeze core FZ02–05; 0–67 cm, Livingstone core 02–05; 53–947 cm) shows that the lake has been freshwater, oligotrophic, and circumneutral to alkaline throughout its ~16,000-year-long history. The first sediments deposited in the lake show that the vegetation in the watershed was sparse, allowing organic matter-poor silt and clay to be deposited in the basin. The basin filled quickly to a depth of at least 5 m and remained at least that deep for most of the sediment record. Several short intervals provided evidence of large fluctuations in lake level during the Holocene. The upper 50 cm of the core contains evidence of the Medieval Climate Anomaly and Little Ice Age.

California↗
USGS2013

The late Holocene dry period: multiproxy evidence for an extended drought between 2800 and 1850 cal yr BP across the central Great Basin, USA

Evidence of a multi-centennial scale dry period between ∼2800 and 1850 cal yr BP is documented by pollen, mollusks, diatoms, and sediment in spring sediments from Stonehouse Meadow in Spring Valley, eastern central Nevada, U.S. We refer to this period as the Late Holocene Dry Period. Based on sediment recovered, Stonehouse Meadow was either absent or severely restricted in size at ∼8000 cal yr BP. Beginning ∼7500 cal yr BP, the meadow became established and persisted to ∼3000 cal yr BP when it began to dry. Comparison of the timing of this late Holocene drought record to multiple records extending from the eastern Sierra Nevada across the central Great Basin to the Great Salt Lake support the interpretation that this dry period was regional. The beginning and ending dates vary among sites, but all sites record multiple centuries of dry climate between 2500 and 1900 cal yr BP. This duration makes it the longest persistent dry period within the late Holocene. In contrast, sites in the northern Great Basin record either no clear evidence of drought, or have wetter than average climate during this period, suggesting that the northern boundary between wet and dry climates may have been between about 40° and 42° N latitude. This dry in the southwest and wet in the northwest precipitation pattern across the Great Basin is supported by large-scale spatial climate pattern hypotheses involving ENSO, PDO, AMO, and the position of the Aleutian Low and North Pacific High, particularly during winter.

California;Idaho;Nevada;Oregon;Utah↗
USGS2012

Holocene diatom flora and climate history of Medicine Lake, Northern California, USA

A 226-cm-long sediment core spanning the past ~ 11,400 years was recovered from Medicine Lake, on the Modoc Plateau in northeastern California. Diatom assemblages provide a record of lake level that is driven by local and regional climate changes and changes in basin morphology due to the activity of Medicine Lake volcano. The diatom record indicates that throughout its history, Medicine Lake was an oligotrophic lake, dominated by Cyclotella stelligera and C. pseudostelligera . Variations in lake level are suggested by changes in the structure of the diatom assemblages. The lowest part of the core (11,400 to 10,300 cal yr B.P.) contains the transition from glacial to interglacial conditions. From about 11,000 to 5500 cal yr B.P., the lake filled two small, steep-sided basins or one basin with two steep-sided sub-basins connected by a shallow shelf. During this time, the diatom evidence (Cyclotella/Navicula ratio) indicates that effective moisture increased, leading to a deeper lake. Over the past 5500 years the diatom record indicates fluctuations in lake level. The change in lake level pattern from one of increasing depth prior to about 5500 cal yr B.P. to one of variable depths may be related to changes in the morphology of the Medicine Lake basin in addition to shifts in local and regional climate. During this latter period the Cyclotella/Navicula ratio varies, suggesting that the level of the lake fluctuated, resulting in changes in colonizable shelf area.

California↗
USGS2010

Organic petrology of subbituminous carbonaceous shale samples from Chalāw, Kabul Province, Afghanistan: Considerations for paleoenvironment and energy resource potential

Neogene (?) subbituminous carbonaceous shale deposits from Chalāw, Afghanistan, were investigated through organic petrology techniques and standard coal analyses to determine paleoenvironment and potential for resource utilization. The Chalāw deposit, approximately 30 km southeast of Kabul, currently is exploited for brick making and domestic heating and cooking. Three multiple-bench channel samples of the mined bed at Chalāw were collected and evaluated. The presence of significant huminite (ranging from 0.2 to 59.0 vol.%, mineral-inclusive basis) is suggestive of a terrestrial lignin-rich precursor plant material. Measured reflectance values of 0.38–0.55% indicate subbituminous rank. This rank suggests burial depths of approximately 1500 m and maximum temperatures of approximately 50 °C. Structured liptinite macerals generally are absent except for some fluorescing morphologies interpreted to be poorly-preserved root cork suberinite. Sponge spicule bioliths including gemmoscleres and megascleres are common. These petrographic observations, in addition to high mineral matter content (33 to > 95 vol.%), medium to high sulfur content (2.1–11.5 wt.%, dry basis; db), and the presence of common gastropod? shell fragments and an aragonite-needle chalk bed are consistent with, but not directly indicative of, a marginal marine or estuarine mangrove depositional environment. However, additional data are necessary to confirm this hypothesis and deposition in a freshwater environment cannot be ruled out at this time. Commercial-scale development and utilization of the Chalāw deposit as a thermal fuel resource may be possible using a fluidized bed combustion system which could accept the low-quality mine product currently produced. Samples examined herein contain high-ash yield (45–90 wt.%, db), high total moisture content (17–39 wt.%), low calorific value (980–6860 Btu/lb, m,mmf), and have poor agglomerating properties (FSI = 0), consistent with fuels utilized in fluidized bed combustors. However, delineation of the extent of the deposit through field investigation will be necessary to make a quantified resource estimate for mine planning.

Kabul Province↗
USGS2010

The 23rd Pacific Climate Workshop (PACLIM)

The 23rd Pacific Climate Workshop (PACLIM) was held May 13–16, 2007 at the Asilomar Conference Grounds in Pacific Grove, California, in what turned out to be a relatively dry spring on the central California coast. What a change from 2006, which was the sixth wettest year of the 101 years for which records have been kept. The special session at the 2007 gathering was entitled “Abrupt Climate Change: Causes and Ecosystem Responses”, reflecting the increasing evidence for rapid climate shifts in marine and terrestrial environments.

California↗
USGS2009

Fire and vegetation history on Santa Rosa Island, Channel Islands, and long-term environmental change in southern California

The long-term history of vegetation and fire was investigated at two locations – Soledad Pond (275 m; from ca. 12 000 cal. a BP) and Abalone Rocks Marsh (0 m; from ca. 7000 cal. a BP) – on Santa Rosa Island, situated off the coast of southern California. A coastal conifer forest covered highlands of Santa Rosa during the last glacial, but by ca. 11 800 cal. a BP Pinus stands, coastal sage scrub and grassland replaced the forest as the climate warmed. The early Holocene became increasingly drier, particularly after ca. 9150 cal. a BP, as the pond dried frequently, and coastal sage scrub covered the nearby hillslopes. By ca. 6900 cal. a BP grasslands recovered at both sites. Pollen of wetland plants became prominent at Soledad Pond after ca. 4500 cal. a BP, and at Abalone Rocks Marsh after ca. 3465 cal. a BP. Diatoms suggest freshening of the Abalone Rocks Marsh somewhat later, probably by additional runoff from the highlands. Introduction of non-native species by ranchers occurred subsequent to AD 1850. Charcoal influx is high early in the record, but declines during the early Holocene when minimal biomass suggests extended drought. A general increase occurs after ca. 7000 cal. a BP, and especially after ca. 4500 cal. a BP. The Holocene pattern closely resembles population levels constructed from the archaeological record, and suggests a potential influence by humans on the fire regime of the islands, particularly during the late Holocene.

California↗
USGS2009

Holocene climate on the Modoc Plateau, northern California, USA: The view from Medicine Lake

Medicine Lake is a small (165 ha), relatively shallow (average 7.3 m), intermediate elevation (2,036 m) lake located within the summit caldera of Medicine Lake volcano, Siskiyou County, California, USA. Sediment cores and high-resolution bathymetric and seismic reflection data were collected from the lake during the fall of 1999 and 2000. Sediments were analyzed for diatoms, pollen, density, grain size (sand/mud ratio), total organic carbon (TOC), and micro-scale fabric analysis. Using both 14 C (AMS) dating and tephrochronology, the basal sediments were estimated to have been deposited about 11,400 cal year BP, thus yielding an estimated average sedimentation rate of about 20.66 cm/1,000 year. The lowermost part of the core (11,400–10,300 cal year BP) contains the transition from glacial to interglacial conditions. From about 11,000–5,500 cal year BP, Medicine Lake consisted of two small, steep-sided lakes or one lake with two steep-sided basins connected by a shallow shelf. During this time, both the pollen ( Abies / Artemisia ratio) and the diatom ( Cyclotella / Navicula ratio) evidences indicate that the effective moisture increased, leading to a deeper lake. Over the past 5,500 years, the pollen record shows that effective moisture continued to increase, and the diatom record indicates fluctuations in the lake level. The change in the lake level pattern from one of the increasing depths prior to about 6,000 cal year BP to one of the variable depths may be related to changes in the morphology of the Medicine Lake caldera associated with the movement of magma and the eruption of the Medicine Lake Glass Flow about 5,120 cal year BP. These changes in basin morphology caused Medicine Lake to flood the shallow shelf which surrounds the deeper part of the lake. During this period, the Cyclotella / Navicula ratio and the percent abundance of Isoetes vary, suggesting that the level of the lake fluctuated, resulting in changes in the shelf area available for colonization by benthic diatoms and Isoetes . These fluctuations are not typical of the small number of low-elevation Holocene lake records in the region, and probably reflect the hydrologic conditions unique to Medicine Lake.

Hydrobiologia↗
USGS1995

Latest Quaternary foraminifers and sediment transport in Pervenets Canyon, Bering Sea

A combination of microfossil and sediment analysis has been used in an attempt to understand oceanographic processes and the late Quaternary history of the Pervenets Canyon region. The primary sedimentation process in Pervenets Canyon is downslope transport. Near the shelfbreak, there is evidence of turbidite and debris-flow activity, but at the distal end of the upper canyon and on the continental slope there is no macroscopic evidence for these processes. Analysis of the foraminiferal assemblages shows that the fauna is 97.6% from the Suborder Rotaliina and about 2.0% from the Suborder Textulariina. The Suborder Miliolina accounts for approximately 0.4% of the fauna. The Pervenets Canyon fauna is most similar to other faunas from the Bering Sea, indicating a North Pacific Ocean influence on the fauna. Foraminiferal abundance and species diversity vary widely in the samples studied. The major factors controlling these values are downslope transport of sediment, disintegration of arenaceous taxa, dissolution of calcareous taxa, and diversity limited by low-oxygen bottom waters. Downslope transport of shelf species is indicated by the presence of Elphidium clavatum and E. excavatum . Shallow-shelf and low-oxygen foraminiferal faunas are often intermixed in the samples. The distribution of these low-oxygen faunas in Core 81-65 suggests that the oxygen-minimum zone fluctuated with sea level.

Marine Micropaleontology↗