Proportion of Glacially To Fluvially Induced Quartz Grain Microtextures Along the Chitina River, SE Alaska, U.S.A.
Proportion of Glacially To Fluvially Induced Quartz Grain Microtextures Along the Chitina River, SE Alaska, U.S.A.
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DOI：
10.2110/jsr.2016.49
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发表时间：
2016-07
影响因子：
2
通讯作者：
D. Sweet;David Brannan
中科院分区：
文献类型：
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作者：
D. Sweet;David Brannan
颗粒表面的某些微米级断口或微结构是特定输运过程的结果。因此，这些由运输引起的微结构被用来推断古代沉积物中的沉积环境。多重输运历史使微结构记录复杂化，因为颗粒表面的改变可以减少或消除早期输运事件的信号。这项研究利用扫描电子显微镜分析表面微结构，以评估河流叠印在阿拉斯加东南部冰川奇蒂纳河∼188公里冰川衍生颗粒上的作用。结果表明，冰川诱导的微结构(即直槽、弯槽、深槽和新月形沟)的出现频率与下游距离呈负相关，但这些微结构在每个样品中都存在。反之，河流诱导的微结构(即V型裂纹和边缘圆形)的出现频率与下游距离呈正相关。至少在赤提那河流域，河流和冰川诱导的微结构比率(F/G比)通常记录了地形变化，包括主要支流汇流后河流信号增加，以及山谷冰川交汇处下游减少。这些结果表明，当缺乏其他冰川沉积学诊断指标时，可以利用古河流沉积中的石英颗粒微结构分析来推断冰川的影响。其他潜在用途也可能存在，但需要在研究其他现代冰川系统后进行评估，包括：1)利用冰川或河流诱导的微结构的下游趋势估计到古冰缘的距离；2)通过F/G比分析古冰川-河流系统的古地理。
Abstract Certain micrometer-scale fractures, or microtextures, on grain surfaces are the result of specific transport processes. Accordingly, these transport-induced microtextures are used to infer depositional setting in ancient deposits. Multiple transport histories complicate the microtextural record because modification of grain surfaces can reduce or eliminate the signal of earlier transport episodes. This study utilizes scanning electron microscopy to analyze surface microtextures to assess the role of fluvial overprint on glacially derived grains along ∼ 188 km of the proglacial Chitina River, SE Alaska. Results indicate that occurrence frequency of glacially induced microtextures (i.e., straight and curved grooves, deep troughs, and crescentic gouges) negatively correlates to distance downstream, yet these microtextures persist in every sample. Conversely, occurrence frequency of fluvially induced microtextures (i.e., v-shaped cracks and edge rounding) positively correlate to distance downstream. At least in the Chitina River watershed, the ratio of fluvially to glacially induced microtextures (F/G ratio) generally records physiographic variation, including increase in fluvial signal after a major tributary confluence, and decrease downstream from the intersection of valley glaciers. These results suggest that analysis of quartz grain microtextures in ancient fluvial deposits can be used to infer glacial influence when other diagnostic sedimentologic indicators of glaciation are lacking. Other potential uses for the proxy may exist, but need to be assessed after other modern proglacial systems are studied, including: 1) estimates of distance to paleo–ice margins using the respective downstream trends of glacially or fluvially induced microtextures, and 2) paleogeography of ancient glacio-fluvial systems through F/G ratio analysis.