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Late Quaternary landscape evolution, environmental change, and paleoindian geoarchaeology in Middle Park, Colorado.

机译：科罗拉多州中部公园的第四纪晚期景观演化，环境变化和古印度地质考古学。

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摘要

Stratigraphic records in western Middle Park (∼2350-2800 m) in north-central Colorado provide evidence for the late Quaternary geomorphic and environmental history of a non-glaciated Southern Rocky Mountain basin. Episodes of geomorphic instability apparent in the stratigraphic record appear to coincide with changes in paleoenvironmental records from above 2750 m in north-central Colorado, suggesting that the western Middle Park landscape was sensitive to environmental changes affecting the region over the last ∼14,000 cal years. Tributaries were incised prior to 14.0 ka, but deposits older than 12.0 ka are rare. Upland erosion and incision followed by rapid aggradation in alluvial settings between 12.0 and 11.0 ka coincide with evidence for regional temperatures at or above present, and is interpreted to signal the onset of Holocene summer-wet precipitation. A widespread soil-stratigraphic marker (the Kremmling soil) represents a long period of landscape stability between 11.0 and 6.0 ka in upland and alluvial settings. Pedologic evidence from upland settings indicates the expansion of grass and forest cover to lower elevations that today are characterized by sagebrush steppe, probably during a period of increased summer precipitation relative to present. During the late Holocene, episodes of aggradation in alluvial valleys at 6.0-1.0 ka and 0.6-0.2 ka and soil formation in uplands at 5.0-3.5 ka and 2.5-1.0 ka overlap with evidence for cooling at higher elevations. Incision of valley floors documented at 1.0-0.6 ka and during the last few centuries and episodes of erosion in uplands at 3.5-2.5 ka, after 1.0 ka, and within the last few centuries, are roughly synchronous with evidence for warming. Upland and alluvial stratigraphic records are interpreted to indicate that during cool intervals summer precipitation was diminished, resulting in relative hillslope stability and gradual valley bottom aggradation, while pulses in summer precipitation accompanying warmer episodes caused basin-wide geomorphic instability. The recent increasing frequency of geomorphic instability appears to correspond with an increase in sagebrush steppe at the expense of forest and grass cover, interpreted to represent progressive drying during the late Holocene. It stands to reason that future warming, if accompanied by similar patterns in precipitation, will result in continued erosion on a landscape already at a threshold of geomorphic instability.;The reliability of radiocarbon ages based on soil organic matter (SOM) from Holocene buried soils in Middle Park, Colorado, is assessed by comparison with ages based on charcoal. On average, 14C ages of SOM from buried surface horizons are 880+/-230 14C yr younger than charcoal ages from the same horizon. Humic acid (HA) and low temperature (400°C) combustion residue (LT) fractions are 390+/-230 and 1290+/-230 14C yr younger than charcoal ages, respectively, and HA ages are on average 860+/-140 14C yr older than LT fractions. We interpret the offsets between 14C ages of charcoal and SOM fractions and the consistent offsets between the HA and LT fractions to reflect the duration of pedogenesis and different residence times of the SOM fractions examined here. The stratigraphic coherence of charcoal 14C ages suggests short residence time on the landscape, with little subsequent reworking. Radiocarbon ages of HA and LT fractions are complimentary to charcoal, and HA ages are interpreted to represent minimum ages for the onset of pedogenesis and LT ages are considered maximum ages for burial.;Geoarchaeological investigations in western Middle Park produced information important for understanding the soil-stratigraphic context of Paleoindian components (∼12.9-8.9 ka), which are associated with sheetwash mantles on upland hillslopes and alluvial valley fills. In situ components occur in a moderately developed buried soil (the Kremmling soil) formed over thin (≤1m) hillslope mantles uplands. The Kremmling soil reflects early and middle Holocene geomorphic stability in upland and alluvial settings, and represents a buried landscape with the potential to produce additional Paleoindian assemblages, though elsewhere in western Middle Park early Archaic sites occur in morphologically similar soils. While portions of all excavated sites have been lost to post-Kremmling soil erosion, several untested Paleoindian localities are likely to contain buried and in situ components. Paleoindian-age alluvium is relatively well preserved along drainage axes, but to date only a single Paleoindian-age component is recorded in alluvial settings. Whether or not this results from inadequate survey, an absence of sites, or both, is unknown, but alluvial settings deserve further investigation.
机译：科罗拉多州中北部西部中央公园（〜2350-2800 m）的地层记录为无冰川的南部洛矶山脉盆地的第四纪晚期地貌和环境历史提供了证据。在地层记录中明显出现的地貌不稳定性事件似乎与科罗拉多州中北部2750 m以上的古环境记录相吻合，这表明在过去约14,000 cal年中，西部中部公园景观对影响该地区的环境变化敏感。支流是在14.0 ka之前切开的，但早于12.0 ka的矿床很少。在12.0 ka和11.0 ka之间的冲积环境中，山地侵蚀和切割随后迅速积聚，与目前或高于目前的区域温度的证据相吻合，并被解释为全新世夏季湿润降水的开始。广泛的土壤地层标记（克雷姆林土壤）代表了高地和冲积环境中<11.0至6.0 ka的长期景观稳定性。来自高地的生态学证据表明，如今草木和森林覆盖面积已扩大到了较低的海拔高度，如今以鼠尾草草原为特征，这可能是相对于目前夏季降水增加的时期。在全新世晚期，冲积谷在6.0-1.0 ka和0.6-0.2 ka上出现了凝集，而在5.0-3.5 ka和2.5-1.0 ka上的高地土壤形成与高海拔降温的证据重叠。记录的谷底切口在1.0-0.6 ka以及最近几个世纪内，高地在3.5-2.5 ka的侵蚀事件（在1.0 ka之后以及最近几个世纪之内）与变暖的迹象大致同步。解释高地和冲积地层记录表明，在凉爽的时间间隔内，夏季降水减少，从而导致相对的山坡稳定性和山谷底部逐渐凝结，而伴随着暖潮的夏季降水的脉动引起了整个盆地的地貌失稳。最近出现的地貌不稳定性增加的频率似乎与鼠尾草草原的增加相对应，但以森林和草皮为代价，这被解释为代表全新世晚期的逐渐干燥。有理由认为，未来的变暖，如果伴随着类似的降水模式，将导致已经处于地貌不稳定阈值的景观继续受到侵蚀。;基于全新世埋藏土壤中土壤有机质（SOM）的放射性碳年龄的可靠性通过与木炭年龄的比较，评估了科罗拉多州米德尔帕克（Middle Park）的生活。平均而言，来自埋地表层的SOM的14C年龄比同一层层的木炭年龄小880 +/- 230 14C岁。腐殖酸（HA）和低温（400°C）燃烧残留物（LT）馏分分别比木炭年龄小390 +/- 230和1290 +/- 230 14C岁，并且HA年龄平均为860 +/-比LT分数早140 14C年。我们解释了木炭和SOM馏分的14C年龄之间的偏移以及HA和LT馏分之间的一致偏移，以反映此处研究的SOM馏分的成岩持续时间和不同的停留时间。木炭14C年龄的地层连贯性表明，在景观上的停留时间短，随后几乎没有返工。 HA和LT馏分的放射性碳年龄与木炭是互补的，并且HA年龄被解释为代表了成岩作用的最小年龄，而LT年龄被认为是最高的埋葬年龄。西部中部公园的地球考古学研究产生了对于理解土壤重要的信息。地层成分（〜12.9-8.9 ka）的地层背景，与高地山坡和冲积山谷填土上的薄片状地幔有关。原位成分发生在中等（仅≤1m）薄薄的山坡地幔山丘上形成的中等发育的埋藏土壤（克雷姆林土壤）中。克雷姆林地区的土壤反映了高地和冲积环境中全新世早期和中期的地貌稳定性，并代表了一种潜在的地貌景观，有可能产生更多的古印第安人组合，尽管在中西部公园的其他地方，早期的古遗址发生在形态相似的土壤中。尽管所有开挖地点的一部分已因克雷姆林发生后的水土流失而丢失，但一些未经测试的古印第安人地区可能包含埋藏的和就地的成分。古印第安时代的冲积层沿排水轴线保存得比较好，但是迄今为止，在冲积环境中只记录了单个古印第安时代的成分。这是否是由于调查不足，是否缺少场地或两者兼而有之，尚不清楚，但冲积条件值得进一步调查。

著录项

  • 作者

    Mayer, James H.;

  • 作者单位

    The University of Arizona.;

  • 授予单位 The University of Arizona.;
  • 学科 Anthropology Archaeology.;Geology.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 214 p.
  • 总页数 214
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 古人类学;地质学;
  • 关键词

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