Controls on weathering and provenance in the Amazonian foreland basin:: Insights from major and trace element geochemistry of Neogene Amazonian sediments
Controls on weathering and provenance in the Amazonian foreland basin:: Insights from major and trace element geochemistry of Neogene Amazonian sediments
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DOI：
10.1016/j.chemgeo.2005.08.010
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发表时间：
2006-02-16
期刊：
影响因子：
3.9
通讯作者：
Hérail, G
中科院分区：
文献类型：
--
作者：
Roddaz, M;Viers, J;Hérail, G
对厄瓜多尔、玻利维亚和秘鲁亚马逊前陆盆地（北、南亚马逊前陆盆地，NAFB和SAFB）中新世和上新世沉积物进行了主量和微量元素地球化学分析（分别为97和104个样品）。新近系沉积物均质化程度很好，总体上具有PAAS样组成。它们主要来源于花岗闪长质地壳。在NAFB，化学风化增加从中新世上新世CIA值类似于100。物理分选似乎在这些沉积物的化学成分中起了次要作用。Cr/Th、Th/U等化学比值和Eu异常在各层内和层间均存在差异。在SAFB，沉积物有一个PAAS样的组成与回收增加的前陆盆地的远端部分。在NAFB中，新近纪地层具有不同的物源。基性/安山质沉积物源自厄瓜多尔安第斯山脉。这些沉积物在中新世期间被困在下沉的厄瓜多尔前渊中，并在上新世期间到达伊基托斯前隆，加入伊基托斯附近的古亚马逊（亚马逊地层）。其他中新世地层具有类似于PAAS的亲和力，但相对于PAAS富含Zr和Hf，这表明它们源自再循环和分异的上大陆地壳。伊基托斯前隆的隆起可能是划分源自安第斯山脉和克拉通的水系的原因。亚马逊河第四纪洪泛平原沉积物类似PAAS，微量元素亏损，Zr和Hf富集，这表明它们来自一个再循环的分异上陆壳。总体而言，从潮汐沉积在中新世到河流沉积在晚中新世-上新世与前陆盆地动力学的变化有关的过渡，导致增加硅酸盐风化，可能对气候和全球碳循环在新近纪的后果。(c)2005 Elsevier B.V保留所有权利。
Miocene and Pliocene deposits from the Ecuadorian, Bolivian and Peruvian Amazonian foreland basin (north and south Amazonian foreland basin, NAFB and SAFB) were analyzed for major and trace element geochemistry (97 and 104 samples respectively). Neogene deposits are well homogenized and have an overall PAAS-like composition. They are mainly derived from a granodioritic crust. In the NAFB, chemical weathering increases from Miocene to Pliocene to CIA values similar to 100. Physical sorting seems to have played a minor role in the chemical composition of these sediments. Chemical ratios such as Cr/Th and Th/U and Eu anomaly vary within each formation and from one formation to another. In the SAFB, sediments have a PAAS-like composition with recycling increasing toward the distal part of the foreland basin. In the NAFB, the Neogene formations have various provenances. Basic/andesitic sediments originated from the Ecuadorian Andes. These sediments were trapped in the subsiding Ecuadorian foredeep during the Miocene and reached the Iquitos forebulge to join the paleo-Amazon near Iquitos (Amazon formation) during the Pliocene. Other Miocene formations have PAAS-like affinities but are enriched in Zr and Hf relative to the PAAS suggesting that they are derived from a recycled and differentiated upper continental crust. Uplift of the Iquitos forebulge may have been responsible for dividing drainage networks originating from the Andes and the craton. The Quaternary floodplain deposits of the Amazon River resemble PAAS with depletion in trace elements and enrichment in Zr and Hf, which indicate that they are derived from a recycled differentiated upper continental crust. Overall, the transition from tidal sedimentation in the Miocene to fluvial sedimentation in the Late Miocene-Pliocene related to a change with foreland basin dynamics have caused increasing silicate weathering that could have had consequences on climate and global carbon cycle during the Neogene. (c) 2005 Elsevier B.V All rights reserved.