Calcretes and cryogenic structures in the area of Puerto Madryn (Chubut, Patagonia, Argentina)
Calcretes and cryogenic structures in the area of Puerto Madryn (Chubut, Patagonia, Argentina)
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DOI：
10.1080/04353676.1994.11880406
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发表时间：
1994-04
影响因子：
1.5
通讯作者：
T. Vogt;H. D. Valle
中科院分区：
文献类型：
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作者：
T. Vogt;H. D. Valle
钙质结垢物与更新世冲积矿床中的化石冰楔假形体密切相关，在巴塔哥尼亚从里奥内格罗（南纬 40°）到里奥加耶戈斯（南纬 53°）的巴塔哥尼亚广泛分布。由于该地区不存在碳酸盐岩，要问的问题是：碳酸钙从何而来，如何积累，碳酸钙与低温结构之间的这种关系意味着什么？这里使用沉积学、微形态学和化学分析描述了两个更新世冲积层（马德林港，海拔 90-100 m，蒙特马约尔，海拔 270 m）。通过比较冲积体、冰楔铸造充填物和上部块状卡雷特的特征，可以看出冲积物沉积和碳酸盐堆积没有共同的起源。这是由沿海地区的异地淤泥和钙质尘埃混合而成，由风吹动和沉积。它与低温结构的密切联系以及一些14C测年表明它是在寒冷时期积累的，对应于海洋回归和高度碳酸化大陆台的出现。在南美洲，海平面降低100-120m，大陆架就会扩大400-1000km。强烈的东风下降风的边缘向北迁移，席卷了裸露的平台。这一解释与地球物理学家在南极冰芯研究中获得的结果非常吻合，该结果表明，在寒冷的盛期，以气候干旱化、风力增强和大陆台地出现为特征，气溶胶量增加了5至30倍。同位素分析表明，东南极冰芯收集的气溶胶很大一部分来自南美大陆架。如果这些结论不能系统地外推到所有钙质结石，那么至少应该在解释更新世钙质结石的起源时考虑到它们。
Calcretes closely linked with fossil ice-wedge pseudomorphs in Pleistocene alluvial deposits are widespread in Patagonia from Rio Negro (Lat. 40°S) to Rio Gallegos (Lat. 53°S). As carbonate rocks are absent in the region, the questions to be asked are: where did the calcium carbonate come from, how did it accumulate, what does this relationship between calcium carbonate and cryogenic structures mean?Two Pleistocene alluvial levels (Puerto Madryn. at 90–100 m asl, Montemayor, 270 m asl) are described here using sedimentological, micromorphological, and chemical analyses. By comparing the characteristics of the alluvial bodies, ice-wedge cast infilling, and upper massive calerete it appears that there is no common origin of the alluvial deposit and the carbonate accumulation. This one is a mix of allochtonous silt and calcareous dust of littoral origin, blown and deposited by wind. Its close association with cryogenic structures as well as some14C datings demonstrate that it accumulated during cold periods, corresponding to marine regressions and the emergence of the highly carbonated continental platform. In South America, for a sea level lowering 100–120m, the continental shelf widened 400 to 1000km. The rim of strong easterly katabatic winds migrated northwards, sweeping the exposed platforms.This interpretation fits in well with the results obtained by geophysicists working on Antarctic ice cores, which show that during cold maxima, characterized by an aridification of climate, an increase of wind strength and the emergence of the continental platform, the aerosol amount increases 5 to 30 times. Isotopic analyses demonstrate that a large part of the aerosols collected in East Antarctic ice-cores came from South American continental shelves.If these conclusions cannot be systematically extrapolated to all calcretes, they should at least be taken into consideration for the explanation of the origin of Pleistocene calcretes.