Testing of the Snowball Earth hypothesis in terms of the cap carbonates, Namibia

本研究的目的是验证“雪球地球”假说，该假说认为在新元古代，整个地球表面多次被冰原覆盖。为此，我们在2001年至2003年的冬季访问了纳米比亚，调查了双晶岩、盖层碳酸盐和与双晶岩相关的铁地层。利用在Fransfountain附近的Ghaab二晶岩中采集的岩石样本进行流变学分析，发现二晶岩在沉积后受到覆盖层压力的压缩。利用盖层碳酸盐岩进行地球化学分析。在拉斯索夫盖层碳酸盐岩中发现的方解石白云岩旋回在几个露头中具有相关性。旋回中出现了滑塌构造，说明方解石白云岩旋回在地层固结前就存在。说明盖层碳酸盐岩白云岩为原生成因。碳酸盐岩也被用于年代学研究。还研究了在纳米比亚南部和俄罗斯白海地区发现的埃迪卡拉纪化石。从新元古代冰川作用的几个假设出发，对这些研究结果进行了讨论。雪球地球假说的检验及其与埃迪卡拉类动物出现的关系仍然是地球科学的重要课题。

The purpose of this study is to test the Snowball Earth hypothesis, which suggests that the entire Earth surface was covered with icesheet in several times during Neoproterozoic era. For this purpose, we visited Namibia in winter seasons from 2001 to 2003 and investigated ouccrops of diamictites, cap carbonates, and iron formations associated with diamictites. The rock specimens sampled from Ghaab diamictites near Fransfountain was used for rheological analysis which revealed that the diamicites was compressed by the overburden pressures after deposition. The cap carbonates were used for geochemical analysis. The calcite dolomite cycles found in Rasthof cap carbonates were correlated in several outcrops. A slump strucutes occurring in the cycles suggested that the calcite dolomite cycles existed before the strata was consolidated. This means that the dolomites of cap carbonates were primary origin. The carbonate rocks were also used for geochronological studies. The Ediacaran fossils found in southern Namibia and the White Sea area, Russia were also studied. The results of these studies were discussed in terms of several working hypotheses of the Neoproterozoic glaciation. The testing of the Snowball Earth hypothesis and its relation to the emergence of animal life of the Ediacaran type are still important topics in Earth Science.