Where the buffalo roam: Boundaries and the politics of scale in the yellowstone region

For more than twenty years, the state of Montana has pursued a controversial policy of lethal control to manage winter migrations of bison from Yellowstone National Park. In the late 1990s, as the state and a number of federal agencies attempted to cooperatively outline a more palatable scenario for bison management, local environmental groups became active participants in the debate. This paper examines the strategies pursued by these organizations in the course of their attempt to construct a new, ecosystem-level territorial space and jurisdictional scale for bison, and places their struggle within the context of existing work in geography on the politics of scale. Ultimately, the failure of their efforts illustrates some of the important constraints faced by social groups that attempt to create new territorial regimes and new scales of resistance in the interstices of existing political structures.     

Trace-element geochemistry of individual glass shards of the Old Crow tephra and the age of the Delta glaciation, central Alaska

Two widespread tephra deposits constrain the age of the Delta Glaciation in central Alaska. The Old Crow tephra (ca. 140,000 ± 10,000 yr), identified by electron microprobe and ion microprobe analyses of individual glass shards, overlies an outwash terrace coeval with the Delta glaciation. The Sheep Creek tephra (ca. 190,000 yr) is reworked in alluvium of Delta age. The upper and lower limiting tephra dates indicate that the Delta glaciation occurred during marine oxygen isotope stage 6. We hypothesize that glaciers in the Delta River Valley reached their maximum Pleistocene extent during this cold interval because of significant mid-Pleistocene tectonic uplift of the east-central Alaska Range.     

Seismicity of the Bering Glacier region and its relation to tectonic and glacial processes

We relocated over 1000 earthquakes of magnitude > 0.1 occurring between 1973 and 2001 in the Bering Glacier region of southern Alaska. We used first-motion data from these events to determine focal mechanisms and directly invert for stress orientations. Our results indicate that much of the seismicity in the region is occurring within the North American plate in a zone where an inferred structure, which lies beneath Bering Glacier, intersects the Chugach-St. Elias fault system. Stress-field analysis indicates that the events in the Bering Glacier surge reservoir region are likely occurring on northeast-trending thrust faults, consistent with previous modeling that suggested thrust faulting would be enhanced in regions of ice draw down. We also observe a stress field compatible with either high-angle normal or reverse faulting in regions located northwest of the Bering Glacier. This may indicate localized complexities in interactions between the Bering Glacier structure and the Chugach-St. Elias fault system.     

Tectonic evolution of the Brooks Range ophiolite, northern Alaska

Analysis of internal structures of the Brooks Range ophiolite at the three largest and well-exposed klippen reveals a NE–SW structural grain that may parallel the original axis of magmatism of a slow spreading marginal ocean basin. Sub-parallel directions of lattice fabrics in olivine of mantle peridotite and shape fabrics in pyroxene and plagioclase of layered gabbro indicate that asthenospheric and magmatic flow was closely coupled. These structures, including the petrologic moho, mostly dip steeply to the NW and SE, with slightly oblique flow lineations. Sedimentary and volcanic cover deposits also dip SE. The few exposures found of sheeted dike complexes generally strike parallel, but dip orthogonal to both the petrologic moho and cover deposits. These structural features are locally disturbed by syn- and post-magmatic normal faults emblematic of slow-spreading ridge processes. However, the consistent geometry of structures over a distance of 200 km demonstrates not only that the magmatic system was organized in a similar manner to an oceanic ridge, but that there was little to no rotation of individual klippe during tectonic emplacement.Ductile fabrics related to tectonic emplacement yield top-to-the NNW sense of shear indicators. The basal thrust and accompanying serpentinized shear zone is mostly flat-lying and truncates the steeply dipping ductile fabric of the ophiolite. This relationship and paleomagnetic data from the igneous sequence suggest that flow fabrics were most likely moderately inclined at the time the ophiolite formed. Similar relationships are found at diapiric centers along oceanic ridges and in other ophiolite bodies.     

芦山—天全地区大溪砾岩岩石学特征及物源区分析

大溪砾岩为一套厚层碳酸盐质砾岩,具有砾石含量高,砾石分选、磨圆较好的特点。据砾石统计、薄片分析、古生物鉴定、古流分析及重矿物组合表明,大溪砾岩中砾石主要来自龙门山区的泥盆系—三叠系,填隙物中的石英碎屑可能主要来自杂岩体。大溪砾岩的砾石成分有向上趋于复杂的特点。     

黑龙江省老黑山盆地下白垩统穆棱组砂岩地球化学特征及其地质意义

为研究黑龙江老黑山盆地下白垩统穆棱组砂岩的源岩属性和源区大地构造背景,在穆棱组进行系统取样,开展地球化学特征和显微镜下分析。研究结果表明：穆棱组砂岩主量元素显示Fe2O3的含量小于FeO,CaO的含量大于MgO的含量,稀土元素具有轻稀土富集、重稀土平坦、多数样品的δEu值具有负异常等特征,样品间微量元素的富集和亏损差异明显。相关系列判别图解表明穆棱组源岩未经沉积再循环作用,属于短距离搬运堆积,且源岩主要为来自上地壳的长英质岩石,但存在多个物源。结合砂岩地球化学特征和Dickinson图解及区域构造背景认为,物源区主要形成于印支运动晚期活动大陆边缘构造背景下的再旋回造山源区和基底隆起区,源岩主要来自于晚三叠世—早中侏罗世的长英质火山岩和侵入岩,而少量可能来自于晚二叠世的变质岩。     

贺兰山北段晚三叠世沉积物源分析

贺兰山北段晚三叠世地层分布较广泛,其物源问题是进行鄂尔多斯盆地西北部原盆边界恢复和其两侧盆地该时期面貌恢复的关键,而对此存在一定的争议。该研究以贺兰山北段的沉积—构造背景为约束,通过晚三叠世地层的砾石成分、古流向、稀土元素、锆石测年及沉积趋势等物源分析方法综合运用,指出贺兰山北段晚三叠世不存在东部物源,银川古隆起不存在;物源来自西北部的阿拉善地块和兴蒙造山带太古代—古元古代的变质岩（片麻岩和变粒岩等）和岩浆岩,部分为阿拉善地块古生代和早中三叠世的沉积岩及岩浆岩。贺兰山西北部具有近物源和快速堆积的特点。同时,贺兰山北段晚三叠世物源具有多源性,其经历了多期的构造改造,恢复物源区演化模式对周邻造山带和块体的演化具有深远意义。     

Mapping the top of the permafrost using surface direct current resistivity survey

 Data from a direct current resistivity survey and geologic logs from boreholes were used to map the top of permafrost at a remote air force installation in Alaska. This study resulted from a remedial investigation that was conducted at Eielson Air Force Base near Fairbanks, Alaska, under the federal Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) regulations. The depth and continuity of the permafrost was important in determining the fate of petroleum contamination that was inadvertently discharged to the ground during earlier air force operations. The results indicate that the top of permafrost forms a highly irregular surface. In general, however, the top of permafrost forms a diagonal ridge at the center of the contour grid that is bordered on each side by troughs. Received: 21 November 1995 · Accepted: 5 March 1996     

Neogene diatoms from the Sandy Ridge section, Alaska Peninsula: Significance for stratigraphic and paleogeographic reconstructions

Fossil diatoms from the Milky River Formation of the Sandy Ridge section, Alaska Peninsula are analyzed. Data on stratigraphic distribution of diatoms and silicoflagellates are presented. Based on presence of stratigraphically important forms (Neodenticula kamtschatica, Thalassiosira oestrupii, Cosmiodiscus insignis), the assemblages studied are correlated with the North Pacific Cenozoic diatom zones. An assemblage similar to that of subzone “b” of the Neodenticula kamtschatica Zone (Barron and Gladenkov, 1995) indicates the latest Miocene-initial early Pliocene (5.5-4.8 Ma) age of its host deposits. Additional species of biostratigraphic importance (Thalassiosira temperei, Th. latimarginata, and others) refine ages of different parts of the section. In particular, age of stratigraphically lowest beds bearing Astarte (mollusks valuable for establishing the Bering Strait opening) were dated at 5.5-5.4 Ma. Some paleogeographic inferences are made from analysis of composition of the diatom assemblages.     

美国阿拉斯加金矿资源特征及远景区预测

阿拉斯加位于北美洲西北部,是美国最大的州,经历了约2亿年的地质构造演化,具有丰富的矿产资源,尤其是以岩金为主的黄金资源。中国对阿拉斯加地区研究较少,中文资料匮乏。通过研究,为保护中国黄金资源和推动中国企业在阿拉斯加“走出去”走出去提供了基础资料。收集资料发现,阿拉斯加金矿资源主要分布在东南部、西南部、中南部、中部和西部地区。金矿类型分为造山型、深成岩体型、侵入相关型、石英脉型、砂金型。通过分析阿拉斯加地质资料确定了4个远景区,由2个 Ⅰ 级远景区、1个 Ⅱ 级远景区和1个 Ⅲ 级远景区组成。建议中国企业关注 Ⅰ 级远景区。阿拉斯加金矿资源可利用性评价良好,值得中国企业关注。     

10Be ages of late Pleistocene deglaciation and Neoglaciation in the north‐central Brooks Range,Arctic Alaska

We present a chronology of late Pleistocene deglaciation and Neoglaciation for two valleys in the north‐central Brooks Range, Alaska, using cosmogenic ¹⁰Be exposure dating. The two valleys show evidence of ice retreat from the northern range front before ～16–15 ka, and into individual cirques by ～14 ka. There is no evidence for a standstill or re‐advance during the Lateglacial period, indicating that a glacier advance during the Younger Dryas, if any, was less extensive than during the Neoglaciation. The maximum glacier expansion during the Neoglacial is delimited by moraines in two cirques separated by about 200 km and dated to 4.6 ± 0.5 and 2.7 ± 0.2 cal ka BP. Both moraine ages agree with previously published lichen‐inferred ages, and confirm that glaciers in the Brooks Range experienced multiple advances of similar magnitude throughout the late Holocene. The similar extent of glaciers during the middle Holocene and the Little Ice Age may imply that the effect of decreasing summer insolation was surpassed by increasing aridity to limit glacier growth as Neoglaciation progressed. Copyright © 2012 John Wiley & Sons, Ltd.     

Field report: Exploring the Doonerak fenster of the central Brooks Range,Alaska, USA

Arctic Alaska is a ‘suspect’ terrane that encompasses approximately 20% of Alaska, stretching from the southern Brooks Range all the way to the continental shelves of the Chukchi and Beaufort Seas. Although the origin and subsequent travels of this large crustal fragment are debated among geologists, most researchers agree upon its composite nature and exotic origin. To constrain the early geological history of this terrane, we describe a recent expedition to the Doonerak fenster of the central Brooks Range. This area has long been regarded as a key locality for understanding the structural evolution of the Mesozoic–Cenozoic Brooks Range orogen; however, our target was different: a unique sequence of volcanic and siliciclastic rocks (Apoon assemblage) exposed beneath a profound pre-Mississippian unconformity, which we argue is of key importance to understanding the early Paleozoic tectonic history of northern Alaska and the greater Arctic.     

重庆巫山玉米洞遗址晚更新世鼠科动物化石

重庆市巫山县玉米洞遗址出土有大量的哺乳动物化石,是华南中-晚更新世大熊猫-剑齿象动物群的重要组成部分,其中晚更新世中-晚期的鼠科动物较为丰富,在层位上对应于MIS4和MIS2时期。形态学观察显示玉米洞的鼠科化石分别属于5属10种：笔尾树鼠(未定种)Chiropodomys sp.、中华姬鼠Apodemus draco、大耳姬鼠A.latronum、小林姬鼠A.sylvaticus、郑氏攀鼠Vernaya zhengi、巨攀鼠V.giganta、爱氏巨鼠Leopoldamys edwardsi、社鼠Niviventer confucianus、安氏白腹鼠N.andersoni和高原白腹鼠N.excelsior。这一组合既显示了浓厚的华南色彩,也有明显的自身特色,即Chiropodomys sp. 的出现和N.excelsior占据优势地位。鼠科化石的生境分析表指示了晚更新世中-晚期玉米洞遗址与现代类似但更为湿冷的森林或森林灌丛环境。玉米洞遗址鼠科化石的研究丰富了中国中-晚更新世大熊猫-剑齿象动物群中小哺乳动物化石的记录。

     

Late Pleistocene and Holocene glaciation of the Fish Lake valley,northeastern Alaska Range,Alaska

We reconstructed a chronology of glaciation spanning from the Late Pleistocene through the late Holocene for Fish Lake valley in the north‐eastern Alaska Range using ¹⁰Be surface exposure dating and lichenometry. After it attained its maximum late Wisconsin extent, the Fish Lake valley glacier began to retreat ca. 16.5 ka, and then experienced a readvance or standstill at 11.6 ± 0.3 ka. Evidence of the earliest Holocene glacial activity in the valley is a moraine immediately in front of Little Ice Age (LIA) moraines and is dated to 3.3–3.0 ka. A subsequent advance culminated at ca. AD 610–900 and several LIA moraine crests date to AD 1290, 1640, 1860 and 1910. Our results indicate that ¹⁰Be dating from high‐elevation sites can be used to help constrain late Holocene glacial histories in Alaska, even when other dating techniques are unavailable. Close agreement between ¹⁰Be and lichenometric ages reveal that ¹⁰Be ages on late Holocene moraines may be as accurate as other dating methods. Copyright © 2009 John Wiley & Sons, Ltd.     

Moraine chronosequence of the Donnelly Dome region, Alaska

We present ¹⁰Be exposure ages from moraines in the Delta River Valley, a reference locality for Pleistocene glaciation in the northern Alaska Range. The ages are from material deposited during the Delta and Donnelly glaciations, which have been correlated with MIS 6 and 2, respectively. ¹⁰Be chronology indicates that at least part of the Delta moraine stabilized during MIS 4/3, and that the Donnelly moraine stabilized ∼ 17 ka. These ages correlate with other dates from the Alaska Range and other regions in Alaska, suggesting synchronicity across Beringia during pulses of late Pleistocene glaciation. Several sample types were collected: boulders, single clasts, and gravel samples (amalgamated small clasts) from around boulders as well as from surfaces devoid of boulders. Comparing ¹⁰Be ages of these sample types reveals the influence of pre/post-depositional processes, including boulder erosion, boulder exhumation, and moraine surface lowering. These processes occur continuously but seem to accelerate during and immediately after successive glacial episodes. The result is a multi-peak age distribution indicating that once a moraine persists through subsequent glaciations the chronological significance of cosmogenic ages derived from samples collected on that moraine diminishes significantly. The absence of Holocene ages implies relatively minor exhumation and/or weathering since 12 ka.     

Carbonates within a Pleistocene glaciomarine succession, Yakataga Formation, Middleton Island, Alaska

Uplifted during the 1964 Alaskan earthquake, extensive intertidal flats around Middleton Island expose 1300 m of late Cenozoic (Early Pleistocene) Yakataga Formation glaciomarine sediments. These outcrops provide a unique window into outer shelf and upper slope strata that are otherwise buried within the south‐east Alaska continental shelf prism. The rocks consist of five principal facies in descending order of thickness: (i) extensive pebbly mudstone diamictite containing sparse marine fossils; (ii) proglacial submarine channel conglomerates; (iii) burrowed mudstones with discrete dropstone layers; (iv) boulder pavements whose upper surfaces are truncated, faceted and striated by ice; and (v) carbonates rich in molluscs, bryozoans and brachiopods. The carbonates are decimetre scale in thickness, typically channellized conglomeratic event beds interpreted as resedimented deposits on the palaeoshelf edge and upper slope. Biogenic components originated in a moderately shallow (ca 80 m), relatively sediment‐free, mesotrophic, sub‐photic setting. These components are a mixture of parautochthonous large pectenids or smaller brachiopods with locally important serpulid worm tubes and robust gastropods augmented by sand‐size bryozoan and echinoderm fragments. Ice‐rafted debris is present throughout these cold‐water carbonates that are thought to have formed during glacial periods of lowered sea‐level that allowed coastal ice margins to advance near to the shelf edge. Such carbonates were then stranded during subsequent sea‐level rise. Productivity was enabled by attenuation of terrigenous mud deposition during these cold periods via reduced sedimentation together with active wave and tidal‐current winnowing near the ice front. Redeposition was the result of intense storms and possibly tsunamis. These sub‐arctic mixed siliciclastic‐carbonate sediments are an end‐member of the Phanerozoic global carbonate depositional realm whose skeletal attributes first appeared during late Palaeozoic southern hemisphere deglaciation.