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

用纳米比亚盖碳酸盐检验雪球地球假说

• 批准号: 13573003
• 负责人: KAWAKAMI Shin-ichi
• 金额: $ 6.66万
• 依托单位: Gifu University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 2001
• 资助国家: 日本
• 起止时间: 2001 至 2003
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-13573003/
• 关键词: Snowball Earth hypothesis; Neoproterozoic; Namibia; carbonate; diamictite; climate change; banded iron-formation; Precambrian; スノーボール・アース仮説

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.

这项研究的目的是检验雪球地球假说，该假说认为在新元古代，整个地球表面曾多次被冰盖覆盖。为此，我们在2001年至2003年的冬季访问了纳米比亚，并调查了与之有关的硅质岩、碳酸盐盖层和铁的形成。对福兰斯泉附近盖阿布二辉橄榄岩的岩样进行了流变学分析，结果表明，二辉橄榄岩在沉积后受到覆岩压力的压缩。将盖状碳酸盐用于地球化学分析。在盖层碳酸盐岩中发现的方解石-白云石旋回与几个露头相对应。旋回中出现的滑塌构造表明，方解石-白云石旋回在地层固结之前就已存在。这意味着盖层碳酸盐岩中的白云岩是主要成因。碳酸盐岩也被用于地质年代学研究。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化石。这些研究的结果根据新元古代冰川作用的几个工作假说进行了讨论。雪球地球假说的检验及其与埃迪卡拉型动物生命出现的关系仍然是地球科学中的重要课题。

项目成果

川上紳一, 東條文治: "約7億年前の凍てついた地球-スノーボール・アース仮説とその検証"ネイチャーサイエンス. 5. 90-97 (2002)

川上真一、东条文二：“大约7亿年前的冰冻地球——雪球地球假说及其验证”《自然科学》5. 90-97 (2002)。

Kani, T., S.Nohda: "Pb-Pb dating of the Cambrian Nama group limestones, and Sr isotopic variation of the cap carbonate ; the lower Meieberg Formation in Namibia"The Earth Monthly. 26. 164-168 (2004)

Kani, T., S.Nohda：“寒武纪 Nama 群石灰岩的 Pb-Pb 测年，以及盖碳酸盐的 Sr 同位素变化；纳米比亚下 Meieberg 组”《地球月刊》。

Tojo, B., Y.Okuda, S.Kawakami, N.Katsuta: "Calcite dolomite cycle of Rasthof cap carbonate in Namibia."The Earth Monthly. 26. 152-158 (2004)

Tojo, B.、Y.Okuda、S.Kawakami、N.Katsuta：“纳米比亚 Rasthof 帽碳酸盐的方解石白云石循环。”地球月刊。

Kawakami, S.: "the snowball Earth"Shueisha.

川上S.：《雪球地球》集英社。

Kawakami, S., S.Nohda, T.Ohno: "Problems on Neoproterozoic glaciation : working hypotheses and Their testing"The Earth Monthly. 26. 127-130 (2004)

Kawakami, S.、S.Nohda、T.Ohno：“新元古代冰川作用问题：工作假设及其检验”地球月刊。