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首页> 外文期刊>Journal of South American earth sciences >Facies and sequence stratigraphy of a mixed carbonate-volcaniclastic ramp in intra-arc settings: An example from the Toqui Formation (Lower Cretaceous), southern Chile (45°S)
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Facies and sequence stratigraphy of a mixed carbonate-volcaniclastic ramp in intra-arc settings: An example from the Toqui Formation (Lower Cretaceous), southern Chile (45°S)

机译：混合碳酸盐 - 火山体积斜坡的相和序列地层中的弧形设置中的位置：来自Toqui形成（下白垩纪），智利南部（45°S）的一个例子

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摘要

The Toqui Formation in the Northern Austral Basin, or Ayse ' n - Rio Mayo Basin in Central Patagonia (43 degrees-49 degrees S), is the basal member of the transgressive-regressive Coyhaique Group of Tithonian-Aptian age. A revision of the basin fill, focusing on the early transgressive units exposed in Chile and Argentina at 45 degrees-46 degrees S, is presented. In order to explain the lithological variability of the mixed calcareous-volcaniclastic Toqui Formation and the evolution of its depositional environments, a detailed sedimentological-petrographic analysis of two outcrops and four drill cores was executed at the type locality, El Toqui Mine (45 degrees S). Twenty-three lithofacies were recognized, arranged in five facies associations. The Toqui Formation comprises three facies associations (Calcareous-; Muddy-, and Sandy Volcaniclastic), and is here redefined as conformed by two members: Mantoand Mina San Antonio Members. Its Manto Member conformably overlies volcanic rocks of the Ib ' an similar to ez Fm., settled as subtidal Gilbert-type delta foresets, conforming a proximal-medial volcanic apron (KimmeridgianValanginian). The Manto Member includes mixed calcareous-volcaniclastic sandstone, bioclastic wackefloatstone, and oyster boundstone, depicted as patch-reefs developed in a carbonate mid- and outer-ramp. The Manto Member is covered by tuffaceous mudstone and volcanic sandstone of the Mina San Antonio Member, representing a prograding, eruption-fed shelf delta, conforming a medial-distal volcanic apron. Upsection, the volcaniclastic succession retrogrades into outer-shelf hemipelagic mudstone of the Katterfeld Formation. Overall, the Ayse ' n Basin depicts a not fully developed marginal basin, i.e. formed by extension but without onset of seafloor spreading. The early marine transgression is linked to a relative sea-level rise caused by tectonic subsidence (back-arc extension), and the subsequent flooding of continental, intra-arc volcanic terrains comprising a transgressive system tract. Carbonate platforms aggraded as highstand system tracts over the subtidal volcanic topography, suggesting periods of tectono-volcanic quiescence. Ramps were covered by prograding deltaic deposits, reflecting a normal regression caused by high volcaniclastic input and local, shallow intrusion-related volcanic uplift (inflation). Upwards, the volcaniclastic succession grades to prodelta and hemipelagic deposits of a major transgressive system tract. The onset of pelagic conditions depicts an important relative sea-level rise, regarded as caused by "post-rift" thermal subsidence, possibly enhanced by the Valanginian high global eustasy. Lithological differences between the Toqui Formation in Chile and the partly coeval transgressive units exposed in Argentina (44 degrees 50 '-47 degrees S), i.e. Cotidiano, Tres Lagunas, and Springhill Formations, is considered as caused by diachronic development of ramps, lateral facies changes, and differential volcaniclastic input. Deposition of the Toqui Formation thus reflects a complex interaction between tectonic subsidence, coastal volcanism, and patchreef growth.
机译：南部南部盆地的Toqui形成，或者Ayse'n - 里约米罗盆地在中央巴塔哥尼亚（43度-49度），是Tithonian-Aptian年龄的违规回归Coyhaique集团的基础成员。提出了一种修订盆地填充，专注于在智利和阿根廷暴露于45度-46秒的早期的过灾单位。为了解释混合钙质 - 火山的岩性变异性和其沉积环境的演变，在Quicaliralial，El Toqui矿区的情况下执行了两种露头和四个钻孔的详细沉积学 - 岩体分析（45度）。在五个相协会中安排了二十三个岩石遗传率。 Toqui形成包括三个相关联（钙质 - ;泥泞的和沙质火山），并且在这里重新定义为两个成员：Mantoand Mina San Antonio成员。它的Manto构件适合地覆盖了IB'类似于EZ FM的火山岩，作为对吉尔伯特型Delta小树脂，符合近侧内侧火山围裙（KimmeridgianValanginian）。 Manto构件包括混合钙质 - 火山岩砂岩，生物旋气性蜡石和牡蛎界石，被描绘为碳酸盐中和外层坡道的贴片珊瑚礁。 Manto Member由Mina San Antonio成员的凝灰岩泥岩和火山砂岩覆盖，代表促进喷发喂养的架子三角洲，符合内侧远端火山围裙。 Upsection，火山的连续逆转逆转到Katterfeld形成的外架血管泥岩。总的来说，Ayse'n盆地描绘了一个没有完全开发的边缘盆地，即通过延伸而形成，但没有海底蔓延的开始。早期的海洋违规与由构造沉降（后弧延长）引起的相对海平面上升，以及随后的大陆洪水，包括近灾系统的弧形地球。碳酸盐平台作为对阴性火山地形的高价系统束，表明构图 - 火山静态。通过促进促进型沉积物覆盖斜坡，反映了由高火山速度输入和局部浅埋的海盗隆起（通货膨胀）引起的正常回归。向上，火山的连续等级到主要近灾系统的Prodelta和Healiphic沉积物。骨质条件的发病描述了一个重要的相对海平面上升，被认为是“裂变后”热沉降，可能由瓦朗尼亚高全球南部果实类增强。智利Toqui形成与阿根廷暴露的部分剖腹侵袭单元（44度50' -47摄氏度），即Cotidiano，Tres Lagunas和Springhill形成，被认为是由斜坡，侧面的倾斜发育引起的变化，差分火山速度输入。因此，Toqui形成的沉积反映了构造沉降，沿海火山的复杂相互作用和PatchreeF的增长。

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