Subterranean transport and deposition of quartz by ants in sandy sites relevant to age overestimation in optical luminescence dating
Subterranean transport and deposition of quartz by ants in sandy sites relevant to age overestimation in optical luminescence dating
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DOI：
10.1016/j.jas.2012.11.006
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发表时间：
2013-04
影响因子：
2.8
通讯作者：
W. Jack Rink;James S. Dunbar;W. Tschinkel;Christina L. Kwapich;A. Repp;W. Stanton;David K. Thulman
中科院分区：
文献类型：
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作者：
W. Jack Rink;James S. Dunbar;W. Tschinkel;Christina L. Kwapich;A. Repp;W. Stanton;David K. Thulman
在佛罗里达州塔拉哈西附近的阿巴拉契科拉国家森林，使用天然砂和彩色砂（3份天然无色石英，1份彩色石英）的组合创建了一个人工分层砂场地。在佛罗里达收获蚁（Pogonomymrex badius）群落的表面放置12层沙，每层沙的水平宽度为1 × 1 m，厚度为10 cm，深度为2 m（下两层为50 cm厚）。蚁群挖了一个巢穴，7个月后，将沙层挖掘到底部，以验证沙粒在蚁巢内向上移动而未到达表面的假设。蚂蚁穿透了12层彩色层中的11层，达到了130厘米的深度。收集了39层蚁室地板的醋酸粘屑，在显微镜下计数彩色沙粒。超过16000粒谷物被发现在原来没有它们的地层中。其中，超过80%的人被明确上调。这意味着可能有多达54,000颗向上移动的颗粒存在（未着色与着色的比例为3:1）。就光学发光（OSL）定年而言，这意味着大量的谷物不会因为运输到地表（这里定义为地下运输）而被光学归零，如果这个遗址是古老的，那么就会发现许多比它们目前所在的地层更古老的谷物，即使只有一群收获蚁扰乱了这些地层。除此之外，腔室和隧道的回填可能对OSL样品的地下运输成分的存在做出更大的贡献。我们认为，蚂蚁对沙质考古遗址的年龄分布有显著影响。文献中已经记录了这种干扰的多个例子。与我们的结果最相关的是最近对北美沙质环境中前克洛维斯时代和古印第安时代考古遗址的OSL年代学研究，这些遗址可能受到石英砂颗粒的蚂蚁生物扰动的损害。在这里，我们详细研究了一次蚂蚁筑巢事件对受影响沉积物年龄高估的潜在影响。由此我们发现，在相同体积的沙子中，只要12次涉及回填腔室的生物扰动，就会导致每50粒样品中存在1粒污染物。
An artificial layered sandy site was created using a combination of native sand and colored sand (3 parts native uncolored quartz, 1 part colored quartz) in Apalachicola National Forest near Tallahassee, Florida. Twelve layers of sand, each 1 by 1 m in horizontal extent by 10 cm in thickness were emplaced to a depth of 2 m followed by implantation at the surface of a Florida harvester ant (Pogonomymrex badius) colony (the lower two layers were 50 cm thick). The colony excavated a nest, and after 7 months, the sand layers were excavated to the base to test the hypothesis that sand grains were moved upward within the ant nest without reaching the surface. The ants penetrated 11 of the 12 colored layers reaching a depth of 130 cm. Thirty nine sticky-acetate peels of ant chamber floors were collected and colored sand grains were counted under a microscope. More than 16,000 grains were identified in layers that did not originally host them. Of these, more than 80% were unambiguously moved upward. This means that possibly as many as 54,000 upwardly mobile grains were present (ratio of 3:1 uncolored to colored). In relation to optical luminescence (OSL) dating, this means that grains that would not have been optically zeroed by transport to the surface (defined here as subterranean-transported) were present in abundance, and that if the site was ancient, there would have been found many grains that were older than the layers they presently reside in, even if only one colony of harvester ants had disturbed the layers. This is in addition to the fact that backfilling of chambers and tunnels may contribute even more significantly to the presence of a subterranean-transported component of an OSL sample. We conclude that ants can significantly affect the age distributions in sandy archaeological sites. Multiple examples of such disturbances have been documented in the literature. Most relevant to our results are recent studies of the OSL chronology of Pre-Clovis-age and Palaeoindian age archaeological sites in sandy environments in North America that may have been compromised by ant bioturbation of quartz sand grains. Here we have examined in detail the potential effects of one episode of ant nest-building on the age overestimation of affected sediments. From this we found that as few as 12 episodes of bioturbation involving backfilling of chambers in the same volume of sand could lead to the presence of 1 contaminant grain per 50 grains of sample.