Palaeoclimatic interprétation of clay minerals in marine deposits : an outlook from the continental origin.
Palaeoclimatic interprétation of clay minerals in marine deposits : an outlook from the continental origin.
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DOI：
10.1016/s0012-8252(99)00054-9
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发表时间：
2000-03
影响因子：
12.1
通讯作者：
M. Thiry
中科院分区：
文献类型：
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作者：
M. Thiry
由于粘土矿物在现代海洋中的分布似乎受现代气候的控制，因此，古代沉积物中的海洋粘土已被广泛用于重建古气候。本文主要从粘土矿物的大陆成因来探讨这一问题，并指出气候对一般海洋沉积物影响的回顾性分析的困难。我们研究如何土壤的发展和行为，先后被改造和古风化物保存，集中在热带潮湿气候的指示高岭石土壤的审查。从粘土矿物发育到最终在盆地中沉积，经历了以下几个阶段：（1）景观中大量高岭石古风化物的持续存在，可能严重改变沉积记录中高岭石的古气候信号;虽然世界各大洋近代沉积物中的高岭石与潮湿气候带相一致，但这主要是因为主要的高岭石和铝土矿古表面与目前高岭石仍发育的热带地区相一致。(2)在高纬度和寒冷的条件下，在富含CO2的古大气中，甚至不寻常的酸性风化与干燥气候的深层高岭石剖面可能的发展是误导古气候重建的古环境。(3)侵蚀和迁移过程总是在一定程度上使信号模糊不清，因为基岩和不同土层的侵蚀产物常常混合在一起，主要排水系统可能包括不同气候带的土壤。(4)土壤粘土组合到达盆地不可避免地滞后于它们在大陆上的形成，可能发生在大陆土壤形成之后几百万年，当时气候可能发生了相当大的变化。指出沉积学家和古气候学家应考虑土壤与沉积粘土矿物之间关系的复杂性。土壤形成速度缓慢，因此，在海洋粘土的古气候记录的分辨率可能不会接近1或2马。目前，海相粘土组合的古气候解释充其量只能提供相当广泛的古气候信息。这种方法无法达到与其他技术（如同位素或微体化石研究）相同的分辨率。粘土矿物组合可以提供整体气候影响的综合记录，而其他技术更有可能揭示局部或暂时的气候。
As distribution of clay minerals in modern oceans seems to be controlled by contemporary climates, marine clays in ancient deposits have been widely used to reconstruct palaeoclimates. In this review, we examine this question mainly from the continental origin of the clay minerals and show the difficulties of retrospective analysis of the influence of climate on common marine deposits. We examine successively how soils develop and behave, are reworked and palaeoweatherings are preserved, focusing the review on kaolinitic soils indicative of tropical wet climates. Several stages intervene between the time of clay mineral development in soils and their final deposition in the basin: (1) The persistence over geological times of huge amounts of kaolinitic palaeoweathering materials in the landscapes may seriously alter the palaeoclimatic signal of kaolinite in the sedimentary record. Although the kaolinite deposited in recent sediments of the world oceans is consistent with wet climatic zones, this is mainly because the major kaolinitic and bauxitic palaeosurfaces coincide with the tropical areas where kaolinite is still developing at present. (2) Possible development of deep kaolinitic profiles at high latitudes and cold conditions, under CO2-enriched palaeoatmospheres, or even by unusual acidic weathering linked with dry climates is misleading palaeoenvironments for palaeoclimatic reconstruction. (3) Erosion and transport processes always cloud the signal to some extent, because frequently, erosion products from the bedrock and different soil horizons will be mixed and major drainage systems may include soils of different climatic zones. (4) The arrival of the soil clay assemblages in the basin inevitably lags against their formation on the continent and may occur several million years after formation of the soils on the continent and climate may have considerably changed at that time. It is pointed out that sedimentologists and palaeoclimatologists should consider the complexity of the relations between soil and sedimentary clay minerals. Soil formation rates are slow and therefore the resolution of the palaeoclimatic record in marine clay may not be closer than 1 or 2 Ma. At present, the palaeoclimatic interpretations of marine clay assemblages are yielding, at best, nothing more than rather broad palaeoclimatic information. This approach cannot achieve the same degree of resolution as other techniques such as isotope or microfossil studies. Clay mineral assemblages may provide integrated records of overall climatic impacts, whereas other techniques are more likely to reveal local or temporary climates.