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1.
Mineral-deposit models are an integral part of quantitative mineral-resource assessment. As the focus of mineral-deposit modeling has moved from metals to industrial minerals, procedure has been modified and may be sufficient to model surficial sand and gravel deposits. Sand and gravel models are needed to assess resource-supply analyses for planning future development and renewal of infrastructure. Successful modeling of sand and gravel deposits must address (1) deposit volumes and geometries, (2) sizes of fragments within the deposits, (3) physical characteristics of the material, and (4) chemical composition and chemical reactivity of the material. Several models of sand and gravel volumes and geometries have been prepared and suggest the following: Sand and gravel deposits in alluvial fans have a median volume of 35 million m3. Deposits in all other geologic settings have a median volume of 5.4 million m3, a median area of 120 ha, and a median thickness of 4 m. The area of a sand and gravel deposit can be predicted from volume using a regression model (log [area (ha)] =1.47+0.79 log [volume (million m3)]). In similar fashion, the volume of a sand and gravel deposit can be predicted from area using the regression (log [volume (million m3)]=–1.45+1.07 log [area (ha)]). Classifying deposits by fragment size can be done using models of the percentage of sand, gravel, and silt within deposits. A classification scheme based on fragment size is sufficiently general to be applied anywhere.  相似文献   

2.
The Arman field in western Kazakhstan is estimated to hold recoverable reserves of 3.65 million metric tons of oil and 74 million cubic meters of gas. The field began production in 1994 as a joint venture between Oryx Energy, MangistauMunaiGas, and the State Holding Company Zharkyn, and currently is operated by Royal Dutch Shell in a 50:50 joint venture with Lukoil. The geology, crude composition, and production history of Arman is outlined, followed by a review of the field development, contract structure, and operating and capital expenditures. An assessment of field profitability concludes the discussion.
Mark J. KaiserEmail:
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3.
This study extends the application of local spatial nonparametric prediction models to the estimation of recoverable gas volumes in continuous-type gas plays to regimes where there is a single geologic trend. A transformation is presented, originally proposed by Tomczak, that offsets the distortions caused by the trend. This article reports on numerical experiments that compare predictive and classification performance of the local nonparametric prediction models based on the transformation with models based on Euclidean distance. The transformation offers improvement in average root mean square error when the trend is not severely misspecified. Because of the local nature of the models, even those based on Euclidean distance in the presence of trends are reasonably robust. The tests based on other model performance metrics such as prediction error associated with the high-grade tracts and the ability of the models to identify sites with the largest gas volumes also demonstrate the robustness of both local modeling approaches.
Emil D. AttanasiEmail:
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4.
This study uses 239+240Pu-dated varved sediments from Big Round Lake, a proglacial lake on northeast Baffin Island, Arctic Canada to generate a 1000-year-long, annual-resolution record of past climate. Varve thickness is positively correlated with July–August–September temperature measured at Clyde River, 70 km to the north of the lake (r = 0.46, p < 0.001). We therefore interpret the variability and trends in varve thickness to partially represent summer temperature. The coolest Little Ice Age temperatures occurred in this record from 1575 to 1760 AD and were approximately 1.5°C cooler than today (average from 1995 to 2005 AD) and 0.2°C cooler than the last millennium (average from 1000 to 2000 AD). Pre-twentieth-century warmth occurred during two intervals, 970–1150 AD and 1375–1575 AD; temperatures were approximately 1.2°C cooler than today, but 0.1°C warmer than the last millennium. The Big Round Lake varve-thickness record contains features similar to that reconstructed elsewhere in the eastern Canadian Arctic. This high-resolution quantitative record expands our understanding of arctic climate during the past millennium.
Elizabeth K. ThomasEmail:
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5.
A Statistical Analysis of the Theoretical Yield of Ethanol from Corn Starch   总被引：1，自引：1，他引：0  
  This paper analyzes the Illinois State Variety Test results for total and extractable starch content in 708 samples of 401 commercial varieties of corn. It is shown that the normally distributed extractable starch content has the mean of 66.2% and the standard deviation of 1.13%. The corresponding maximum theoretical yield of ethanol is 0.364 kg EtOH/kg dry corn, and the standard deviation is 0.007. In the ethanol industry units, this yield translates to 2.64 gal EtOH/nominal wet bushel, and the standard deviation is 0.05 gal/bu. The U.S. ethanol industry consistently has inflated its ethanol yields by counting 5 volume percent of # 14 gasoline denaturant (8% of energy content) as ethanol. Also, imports from Brazil and higher alcohols seem to have been counted as U.S. ethanol. The usually accepted USDA estimate of mean ethanol yield in the U.S., 2.682 gal EtOH/bu, is one standard deviation above the rigorous statistical estimate in this paper.
Tad W. PatzekEmail:
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6.
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7.
Evidence from lake sediments and glacier forefields from two hydrologically isolated lake basins is used to reconstruct Holocene glacier and climate history at Hallet and Greyling Lakes in the central Chugach Mountains of south-central Alaska. Glacial landform mapping, lichenometry, and equilibrium-line altitude reconstructions, along with changes in sedimentary biogenic-silica content, bulk density, and grain-size distribution indicate a dynamic history of Holocene climate variability. The evidence suggests a warm early Holocene from 10 to 6 ka, followed by the onset of Neoglaciation in the two drainage basins, beginning between 4.5 and 4.0 ka. During the past 2 ka, the glacial landforms and lacustrine sediments from the two valleys record a remarkably similar history of glaciation, with two primary advances, one during the first millennium AD, from ~500 to 800 AD, and the second during the Little Ice Age (LIA) from ~1400 to 1900 AD. During the LIA, the reconstructed equilibrium-line altitude in the region was no more than 83 ± 44 m (n = 21) lower than the modern, which is based on the extent of glaciers during 1978. Differences between the summer temperature inferred from the biogenic-silica content and the evidence for glacial advances and retreats suggest a period of increased winter precipitation from 1300 to 1500 AD, and reduced winter precipitation from 1800 to 1900 AD, likely associated with variability in the strength of the Aleutian Low.
Darrell S. KaufmanEmail:
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8.
Two lake-sediment cores from the western and central Canadian Arctic were used to investigate late Holocene climate variability in the region. Both cores were analyzed for pollen, organic matter, biogenic silica, and magnetic susceptibility, and were dated using a combination of 210Pb and 14C techniques. Core MB01, from southwestern Victoria Island, provides a 2600-year-long record. Fossil pollen percentages, along with other parameters, suggest the occurrence of a cold period around 2400 cal year BP (450 BC), followed by slightly warmer conditions by 1800 cal year BP (150 AD), and a return to cooler conditions throughout much of the last millennium. Core SL06, from southern Boothia Peninsula, shows more subtle changes in pollen percentages over its 2500-year duration, but an increase in Cyperaceae and decrease in Oxyria pollen around 1400 cal year BP (550 AD) are indicative of warmer conditions at that time. Quantitative climate reconstructions from these pollen sequences were compared to two other pollen-based climate records from the region and indicate the presence of a widespread wet period ~1500 cal year BP (450 AD), and a cool and dry Little Ice Age. In the reconstructions based on pollen percentage data, the twentieth century summer temperature and annual precipitation in the central and western Canadian Arctic were comparable to that which occurred over the last 2500 years. However, pollen-influx values increase in the most recent sediments, suggesting high plant productivity during the late twentieth century.
Matthew C. PerosEmail:
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9.
By applying the multi-Hubbert curve analysis to coal production in the United States, we demonstrate that anthracite production can be modeled with a single Hubbert curve that extends to the practical end of commercial production of this highest-rank coal. The production of bituminous coal from existing mines is about 80% complete and can be carried out at the current rate for the next 20 years. The production of subbituminous coal from existing mines can be carried out at the current rate for 40–45 years. Significant new investment to extend the existing mines and build new ones would have to commence in 2009 to sustain the current rate of coal production, 1 billion tons per year, in 2029. In view of the existing data, we conclude that there is no spare coal production capacity of the size required for massive coal conversion to liquid transportation fuels. Our analysis is independent of other factors that will prevent large-scale coal liquefaction projects: the inefficiency of the process and either emissions of greenhouse gases or energy cost of sequestration.
Tad W. PatzekEmail:
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10.
The sediment fill of Haukadalsvatn, a lake in northwest Iceland, preserves a record of environmental change since deglaciation, 13 ka ago. The rapid sedimentation rate over the past 2 ka (ca. 4 m ka−1) provides a high-resolution archive of late Holocene environmental change. Physical and chemical environmental proxies extracted from cores from the Haukadalsvatn sediment fill provide a reconstruction of sub-decadal-scale climate variability in Iceland over the past 2 ka. Over this interval biogenic silica (BSi) reflects warm April–May temperatures, whereas total organic carbon (TOC) peaks represent an increased flux of carbon to the lake from eolian-derived soil erosion following periods of cold summers accompanied by dry, windy winters. The proxy-based temperature reconstructions show a broad interval of warmth through Medieval times, but this warmth is punctuated by multi-decadal cold intervals. The transition into the Little Ice Age occurred in two steps, with initial summer cooling 1250–1300 AD, and a more severe drop in summer temperatures between 1450 and 1500 AD; both are periods of severe explosive volcanism. Multi-decadal patterns of cold and warm conditions have some characteristics of a North Atlantic Oscillation (NAO)-like signal, but instrumental records and proxy-based reconstructions of the NAO index contain little power in the frequencies most strongly expressed in our data set. Although severe soil erosion in Iceland is frequently equated with settlement, our reconstructions indicate that soil erosion began several centuries before settlement, whereas for several centuries after settlement, when summer temperatures were relatively high, there was little or no soil erosion. Only during the transition into and during the Little Ice Age did soil erosion become a major feature of the record. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Kristín B. ólafsdóttirEmail:
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11.
The oxygen isotope ratios of diatoms (δ18Odiatom), and the oxygen and hydrogen isotope ratios of lake water (δW) of lakes in south Alaska provide insight into past changes in atmospheric circulation. Lake water was collected from 31 lakes along an elevation transect and diatoms were isolated from lake sediment from one lake (Mica Lake) in south Alaska. In general, δW values from coastal lakes overlap the global meteoric water line (GMWL). δW values from interior lakes do not lie on the GMWL; they fall on a local evaporation line trajectory suggesting source isotopes are depleted with respect to maritime lakes. Sediment cores were recovered from 58 m depth in Mica Lake (60.96° N, 148.15° W; 100 m asl), an evaporation-insensitive lake in the western Prince William Sound. Thirteen calibrated 14C ages on terrestrial macrofossil samples were used to construct an age-depth model for core MC-2, which spans 9910 cal years. Diatoms from 46, 0.5-cm-thick samples were isolated and analyzed for their oxygen isotope ratios. The analyses employed a newly designed, stepwise fluorination technique, which uses a CO2 laser-ablation system, coupled to a mass spectrometer, and has an external reproducibility of ±0.2‰. δ18Odiatom values from Mica Lake sediment range between 25.2 and 29.8‰. δ18Odiatom values are relatively uniform between 9.6 and 2.6 ka, but exhibit a four-fold increase in variability since 2.6 ka. High-resolution sampling and analyses of the top 100 cm of our lake cores suggest large climate variability during the last 2000 years. The 20th century shows a +4.0‰ increase of δ18Odiatom values. Shifts of δ18Odiatom values are likely not related to changes in diatom taxa or dissolution effects. Late Holocene excursions to lower δ18Odiatom values suggest a reduction of south-to-north storm trajectories delivered by meridional flow, which likely corresponds to prolonged intervals when the Aleutian Low pressure system weakened. Comparisons with isotope records of precipitation (δP) from the region support the storm-track hypothesis, and add to evidence for variability in North Pacific atmospheric circulation during the Holocene.
Zachary SharpEmail:
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12.
The United States has the world’s largest coal reserves and Montana the highest potential for mega-mine development. Consequently, a large-scale effort to convert coal to liquids (CTL) has been proposed to create a major source of domestic transportation fuels from coal, and some prominent Montanans want to be at the center of that effort. We calculate that the energy efficiency of the best existing Fischer–Tropsch (FT) process applied to average coal in Montana is less than 1/2 of the corresponding efficiency of an average crude oil refining process. The resulting CO2 emissions are 20 times (2000%) higher for CTL than for conventional petroleum products. One barrel of the FT fuel requires roughly 800 kg of coal and 800 kg of water. The minimum energy cost of subsurface CO2 sequestration would be at least 40% of the FT fuel energy, essentially halving energy efficiency of the process. We argue therefore that CTL conversion is not the most valuable use for the coal, nor will it ever be, as long as it is economical to use natural gas for electric power generation. This finding results from the low efficiency inherent in FT synthesis, and is independent of the monumental FT plant construction costs, mine construction costs, acute lack of water, and the associated environmental impacts for Montana.
Tad W. PatzekEmail:
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13.
Sediments in Lower Murray Lake, northern Ellesmere Island, Nunavut Canada (81°21′ N, 69°32′ W) contain annual laminations (varves) that provide a record of sediment accumulation through the past 5000+ years. Annual mass accumulation was estimated based on measurements of varve thickness and sediment bulk density. Comparison of Lower Murray Lake mass accumulation with instrumental climate data, long-term records of climatic forcing mechanisms and other regional paleoclimate records suggests that lake sedimentation is positively correlated with regional melt season temperatures driven by radiative forcing. The temperature reconstruction suggests that recent temperatures are ~2.6°C higher than minimum temperatures observed during the Little Ice Age, maximum temperatures during the past 5200 years exceeded modern values by ~0.6°C, and that minimum temperatures observed approximately 2900 varve years BC were ~3.5°C colder than recent conditions. Recent temperatures were the warmest since the fourteenth century, but similar conditions existed intermittently during the period spanning ~4000–1000 varve years ago. A highly stable pattern of sedimentation throughout the period of record supports the use of annual mass accumulation in Lower Murray Lake as a reliable proxy indicator of local climatic conditions in the past.
Pierre FrancusEmail:
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14.
We analyzed sediments of the past 2000 years from Ongoke Lake, southwest Alaska, for organic carbon, organic nitrogen, biogenic silica (BSi), and diatom assemblages at decadal to centennial resolution to infer limnological changes that may be related to climatic variation in southwestern Alaska. The chronology is based on a 210Pb profile from bulk sediments and nine AMS 14C ages from terrestrial plant macrofossils. Four of the 14C ages span a core depth interval of 60.5 cm but are statistically indistinguishable from one another with a mean of ~1300 AD, which compromises the determination of temporal trends at Ongoke Lake and comparison with other paleoclimate records. The diatom record suggests changes in the duration of ice cover and strength of thermal stratification that are probably related to temperature variation. This variation includes a cold interval around the first millennium cooling (FMC) and a warm interval spanning the medieval climate anomaly (MCA). However, the lake-sediment record shows no clear signals of temperature variation for the period of the Little Ice Age (LIA) or the twentieth century. Climatic changes during these periods may have been manifested through effective-moisture (precipitation minus evapotranspiration) variation in the Ongoke Lake area. We estimate water depths and infer effective-moisture fluctuations by applying a regional transfer function to our diatom record. Together with inferences from diatom autecologies, this water-depth reconstruction suggests that effective moisture increased steadily from 50 BC to 350 AD, which was followed by relatively dry conditions between 550 and 750 AD and relatively wet conditions between 750 and 1450 AD. Effective moisture was low from ~1450 to 1850 AD, coinciding with the LIA; an alternative age model places this interval between ~1315 and 1850 AD. During the past 150 years, effective moisture increased, with estimated water depths reaching peak values in the second half of the twentieth century. This study offers the first paleolimnological record for inferring centennial-scale climatic variation over the past two millennia from southwestern Alaska.
Feng Sheng HuEmail:
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15.
The environmental controls on modern peatland testate amoebae (Protozoa: Rhizopoda) in the North of Ireland were investigated to assess the potential for Holocene palaeoclimate research within this region. Canonical Correspondence Analysis (CCA) revealed that hydrological factors (water table depth and moisture content) are the most important abiotic controls on organism distribution. A series of partial CCAs showed that water table depth explains 15.8% and moisture content explains 5.5% of the total variance. Monte-Carlo permutation tests showed that the results are highly significant (p < 0.002; p < 0.040 respectively). Transfer functions were generated for water table depth using weighted averaging tolerance downweighted (WA-Tol) regression and for moisture content using weighted averaging partial least squares regression (WA-PLS). The performance of the models was assessed using leave-one-out cross-validation (jacknifing). After removal of outlier samples, the improved transfer functions were found to perform well with an r jack2 and root mean square error of predictionjack of 0.83, 4.99 cm for water table depth and 0.76, 4.60% for moisture content respectively. The water table transfer function was applied to a fossil peat sequence from this region and reconstruction errors were generated by 1,000 bootstrap cycles. The water table reconstruction was also carried out using an established pan-European transfer function and was found to be similar to that based on the North of Ireland dataset. This demonstrates the persistent and comparable control of hydrological variables on the distribution of testate amoebae taxa across Europe and implies that regional training sets can suffice as long as no-analogue situations are not encountered.
G. T. SwindlesEmail:
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16.
This paper analyzes energy efficiency of the industrial corn-ethanol cycle. In particular, it critically evaluates earlier publications by DOE, USDA, and UC Berkeley Energy Resources Group. It is demonstrated that most of the current First Law net-energy models of the industrial corn-ethanol cycle are based on nonphysical assumptions and should be viewed with caution. In particular, these models do not (i) define the system boundaries, (ii) conserve mass, and (iii) conserve energy. The energy cost of producing and refining carbon fuels in real time, for example, corn and ethanol, is high relative to that of fossil fuels deposited and concentrated over geological time. Proper mass and energy balances of corn fields and ethanol refineries that account for the photosynthetic energy, part of the environment restoration work, and the coproduct energy have been formulated. These balances show that energetically production of ethanol from corn is 2–4 times less favorable than production of gasoline from petroleum. From thermodynamics it also follows that ecological damage wrought by industrial biofuel production must be severe. With the DDGS coproduct energy credit, 3.9 gallons of ethanol displace on average the energy in 1 gallon of gasoline. Without the DDGS energy credit, this average number is 6.2 gallons of ethanol. Equivalent CO2 emissions from corn ethanol are some 50% higher than those from gasoline, and become 100% higher if methane emissions from cows fed with DDGS are accounted for. From the mass balance of soil it follows that ethanol coproducts should be returned to the fields.
Tad W. PatzekEmail:
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17.
For the heavily glaciated mountains of southern Alaska, few high-resolution, millennial-scale proxy temperature reconstructions are available for comparison with modern temperatures or with the history of glacier fluctuations. Recent catastrophic drainage of glacier-dammed Iceberg Lake, on the northern margin of the Bagley Icefield, exposed subaerial outcrops of varved lacustrine sediments that span the period 442–1998 AD. Here, an updated chronology of varve thickness measurements is used to quantitatively reconstruct melt-season temperature anomalies. From 1958 to 1998, varve thickness has a positive and marginally significant correlation with May–June temperatures at the nearest coastal measurement stations. Varve sensitivity to temperature has changed over time, however, in response to lake level changes in 1957 and earlier. I compensate for this by log-transforming the varve thickness chronology, and also by using a 400-year-long tree-ring-based temperature proxy to reconstruct melt-season temperatures at Iceberg Lake. Regression against this longer proxy record is statistically weak, but spans the full range of occupied lake levels and varve sensitivities. Reconstructed temperature anomalies have broad confidence intervals, but nominally span 1.1°C over the last 1500+ years. Maximum temperatures occurred in the late twentieth century, with a minimum in the late sixth century. The Little Ice Age is present as three cool periods between 1350 and 1850 AD with maximum cooling around 1650 AD. A Medieval Warm Period is evident from 1000 to 1100 AD, but the temperature reconstruction suggests it was less warm than recent decades—an observation supported by independent geological evidence of recent glacier retreat that is unprecedented over the period of record. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Michael G. LosoEmail:
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18.
Varved minerogenic sediments from glacial-fed Blue Lake, northern Alaska, are used to investigate late Holocene climate variability. Varve-thickness measurements track summer temperature recorded at Atigun Pass, located 41 km east at a similar elevation (r 2 = 0.31, P = 0.08). Results indicate that climate in the Brooks Range from 10 to 730 AD (varve year) was warm with precipitation inferred to be higher than during the twentieth century. The varve-temperature relationship for this period was likely compromised and not used in our temperature reconstruction because the glacier was greatly reduced, or absent, exposing sub-glacial sediments to erosion from enhanced precipitation. Varve-inferred summer temperatures and precipitation decreased after 730 AD, averaging 0.4°C above the last millennial average (LMA = 4.2°C) from 730 to 850 AD, and 0.1°C above the LMA from 850 to 980 AD. Cooling culminated between 980 and 1030 AD with temperatures 0.7°C below the LMA. Varve-inferred summer temperatures increased between 1030 and 1620 AD to the LMA, though the period between 1260 and 1350 AD was 0.2°C below the LMA. Although there is no equivalent to the European Medieval Warm Period in the Blue Lake record, two warm intervals occurred from 1350 to 1450 AD and 1500 to 1620 AD (0.4 and 0.3°C above the LMA, respectively). During the Little Ice Age (LIA; 1620 to 1880 AD), inferred summer temperature averaged 0.2°C below the LMA. After 1880 AD, inferred summer temperature increased to 0.8°C above the LMA, glaciers retreated, but aridity persisted based on a number of regional paleoclimate records. Despite warming and glacial retreat, varve thicknesses have not achieved pre-730 AD levels. This reflects limited sediment availability and transport due to a less extensive retreat compared to the first millennium, and continued relative aridity. Overall, the Blue Lake record is similar to varve records from the eastern Canadian Arctic that document a cool LIA and twentieth century warming. However, the occurrence and timing of events, such as the LIA and Medieval Warm Period, varies considerably among records, suggesting heterogeneous climatic patterns across the North American Arctic.
Broxton W. BirdEmail:
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19.
A lake sediment core recovered from Lake V57 on Victoria Island, Nunavut, Canada, spanning the last 2000 years, was analyzed for sub-fossil midge remains and organic-matter content (estimated by loss-on-ignition (LOI)). Significant changes in midge community composition occurred during the last 2000 years, with a distinct midge community appearing after 1600 AD. The chironomid community between 0 and 1600 AD was dominated by Heterotrissocladius, Tanytarsus, Abiskomyia, and Paracladius. At approximately 1600 AD, Heterotrissocladius decreased in relative abundance and taxa such as Corynocera ambigua, C. oliveri, Psectrocladius sordidellus type, and Pentanneurini increased in relative abundance. Previously published midge-based inference models for average July air temperature (AJAT) and summer surface–water temperature (SSWT) were applied to the subfossil midge stratigraphy. The AJAT reconstruction indicates relatively cool conditions existed between 1100 and 1600 AD, with exceptional warming occuring after 1600 AD, as lake productivity inferred from organic-matter content increased concomitantly with midge-inferred AJAT and SSWT. The cooler conditions between 1200 and 1600 AD, and the pattern of warming over recent centuries inferred from Lake V57 is broadly consistent with temperature-sensitive biogenic silica records from other sites in the central Canadian Arctic and the treeline zone to the south suggesting a regionally synchronous response to climate forcing.
David F. PorinchuEmail:
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20.
Quantitative reconstructions of mean July temperatures (T jul) based on new and previously published pollen-stratigraphical data covering the last 2000 years from 11 lakes in northern Fennoscandia and the Kola Peninsula are presented. T jul values are based on a previously published pollen-climate transfer function for the region with a root-mean-square error of prediction (RMSEP) of 0.99°C. The most obvious trend in the inferred temperatures from all sites is the general decrease in T jul during the last 2000 years. Pollen-inferred T jul values on average 0.18 ± 0.56°C (n = 91) higher than present (where “present” refers to the last three decades based on pollen-inferred T jul in core-top samples) are indicated between 0 and 1100 AD (2000–850 cal year BP), and temperatures −0.2 ± 0.47°C (n = 78) below present are inferred between 1100 and 1900 AD (850–50 cal year BP). No consistent temperature peak is observed during the ‘Medieval Warm Period’, ca. 900–1200 AD (1100–750 cal year BP), but the cooler period between 1100 and 1900 AD (850–50 cal year BP) corresponds in general with the ‘Little Ice Age’ (LIA). Consistently with independent stable isotopic data, the composite pollen-based record suggests that the coldest periods of the LIA date to 1500–1600 AD (450–350 cal year BP) and 1800–1850 AD (150–100 cal year BP). An abrupt warming occurred at about 1900 AD and the twentieth century is the warmest century since about 1000 AD (950 cal year BP).
A. E. BjuneEmail:
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