MODERN HETEROZOAN CARBONATES FROM A EUTROPHIC TROPICAL SHELF (MAURITANIA)
MODERN HETEROZOAN CARBONATES FROM A EUTROPHIC TROPICAL SHELF (MAURITANIA)
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DOI：
10.2110/jsr.2011.53
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发表时间：
2011-09-01
影响因子：
2
通讯作者：
Westphal, Hildegard
中科院分区：
文献类型：
--
作者：
Michel, Julien;Mateu Vicens, Guillem;Westphal, Hildegard
在热带以外的碳酸盐沉积体系中，典型的是异源动物或森林动物的产出。然而，在中营养到富营养条件下，热带环境中也会形成异养动物碳酸盐，但对这种异养动物热带沉积系统了解甚少。然而，在古代层序中区分热带和热带外的异源动物碳酸盐岩对于精确的古环境和古气候重建至关重要。在这里，表层全新世和更新世沉积物的北方的西海岸陆架的热带富营养化的碳酸盐沉积体系（11微克L-1叶绿素a [叶绿素a]）的一个例子进行了研究。向上涌的营养丰富的沃茨推到宽阔的南极大陆架上，在那里它们可以升温到超过25摄氏度。这种条件有利于生产的异源动物碳酸盐为主的双壳类和有孔虫，即使在这个热带环境。此外，来自沙漠腹地的风成输入提供了沉积物。由此产生的沉积物是碳酸盐相和混合碳酸盐-硅质相，其中碳酸盐的特征是热带和世界性类群的混合。底栖光合生物群不存在，而悬浮进食生物占主导地位。这种大陆架尺度上的fortagrain协会让人想起冷水碳酸盐，因此，温水的异源动物碳酸盐的识别依赖于与热带沃茨内的生物群组合与高产环境相关的关键类群。
Heterozoan or foramol production is typical in extratropical carbonate sedimentary systems. However, under mesotrophic to eutrophic conditions, heterozoan carbonates also form in tropical settings, but such heterozoan tropical sedimentary systems are poorly understood. Nevertheless, distinction between tropical and extratropical heterozoan carbonates in ancient successions is crucial for accurate paleoenvironmental and paleoclimate reconstructions. Here, surficial Holocene and Pleistocene sediments of the northern Mauritanian shelf are studied as an example of a tropical eutrophic carbonate depositional system (11 mu g.L-1 Chl-a [chlorophyll-a]). Upwelling nutrient-rich waters push onto the wide Mauritanian shelf, where they can warm up to in excess of 25 degrees C. This condition favors production of heterozoan carbonates dominated by bivalves and foraminifers, even in this tropical setting. In addition, sediments are provided by eolian input from the desertic hinterland. The resulting sediments are carbonate and mixed carbonate-siliciclastic fades, in which the carbonates are characterized by a mixture of tropical and cosmopolitan taxa. Benthic photosynthetic biota are absent while suspension-feeding organisms are dominant. This foramol grain association on a shelf scale is reminiscent of cool-water carbonates, therefore recognition of warm-water heterozoan carbonates relies on key taxa related to tropical waters within the biota assemblages associated with a highly productive environment.