阿布鲁佐早上新世前陆盆地体系格架中的Roccacaramanico砾岩(Maiella构造单元):地层和构造意义

IF 1 4区 地球科学 Q4 GEOSCIENCES, MULTIDISCIPLINARY
F. Brozzetti, Francesca Cerritelli, D. Cirillo, S. Agostini, G. Lavecchia
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引用次数: 3

摘要

在意大利阿布鲁佐地区Maiella构造单元的上第三系演替中,在较短的时间跨度内沉积了粗糙的砾屑层,以下简称Roccacaramanico砾岩(RCC),沉积时间接近中新世-上新世界线。RCC的生物地层特征受到有孔虫和纳米化石组合研究的限制。事实上,RCC的泥质互层属于Sphaeroidinellopsis spp.生物带和属于上新世早期的MNN12纳米化石带。先前的研究将这种砾岩与亚平宁盆地沉积重力流联系起来,然而,由于缺乏详细的成分数据和区域尺度的沉积学研究,只有关于源区和引发RCC沉积的事件性质的一般假设被制定出来。在这里,我们介绍了对Maiella构造单元内的碾压砾岩的原始调查结果,该构造单元位于向西由Morrone-Porrara逆冲构造单元划分,向东南由Molise异质单元划分的区域。在这个地区,一个相当连续的RCC层位,暴露在Maiella背斜的两侧,被详细地绘制和记录。我们的岩石地层分析允许对RCC的沉积机制做出假设,并揭示了它由几个(6到10个)主要沉积事件组成,产生了局部合并的多粒碎屑层。我们的相分析强调,以往的研究普遍低估了层的整体厚度,并且在最南端(Palena, Taranta Peligna和Lama dei Peligni)检查的露头中,RCC的特征是厚度更高,粒度更粗,分选更差,与最北部地区(Roccacaramanico, San Nicolao和San Valentino)相比,通道更明显。对Maiella南部地区近缘性较大的相类型的识别,以及RCC层位沉积构型的整体几何重建表明,与之前的假设相反,主要的沉积物重力流来自盆地的东南边缘。古海流资料也证实了这一结果,证明北流方向为SSE-NNW。RCC的成分分析表明,碎屑几乎完全为钙质组成,而硅塑性组分则较为分散,主要以细粒基质形式存在。不同时代的内台地相、生物构造边缘相、斜坡相、过渡相和盆地相碎屑在各层间混杂。尽管如此,这些数据使我们能够推断沉积物供应的来源,以及在盆地周围地区,在迈西尼亚-上新世边界附近,正在经历侵蚀的地层序列。考虑到我们在现场测量的厚度值或其他从深测井中获得的厚度值,最终实现了RCC体积的定量评估,并将这些厚度应用于一组穿越Maiella背斜的恢复地质剖面。我们的计算提供了约700平方公里的最小面积和约7平方公里的保守体积估计,这允许有效地适用于碾压混凝土,即“巨型床”的定义。这突出了其作为Abruzzi演替最东端区域标志层的重要性,其明确的地层位置(跨越中新世/上新世年代地层界线)更加强调了这一重要性。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
The Roccacaramanico Conglomerate (Maiella Tectonic Unit) in the frame of the Abruzzo early Pliocene Foreland Basin System: stratigraphic and structural implications
In the upper Tertiary succession of the Maiella Tectonic Unit (Abruzzo, Italy), coarse calciclastic layers, hereinafter referred to as Roccacaramanico Conglomerate (RCC), were deposited during a short time span which approximates the Miocene-Pliocene boundary. The biostratigraphic characterization of RCC is well constrained by previous studies of foraminifer and nannofossil assemblages. In fact the pelitic interbeds of the RCC are attributed to the Sphaeroidinellopsis spp. Biozone and to the MNN12 Nannofossil Zone belonging to the earliest Pliocene.Previous works referred this conglomerate to Apennine- fed sediment gravity-flows however, in the absence of detailed compositional data and of a regional-scale sedimentological study of the layers, only generic hypotheses on the source-area and on the nature of the event which triggered the RCC deposition, were formulated.Here we present the results of an original investigation on the RCC cropping out within the Maiella Tectonic Unit, in the area delimited westward by the Morrone-Porrara thrust and, towards south-east, by the Molise allochthonous Units.In this area, a fairly continuous RCC horizon, exposed on both limbs of the Maiella anticline, was mapped and logged in detail. Our lithostratigraphic analysis allowed to make hypotheses on depositional mechanisms of RCC and revealed that it consists of several (six to ten) major depositional events producing locally amalgamated pluri- metric clastic layers.Our facies analysis highlighted that previous studies had generally underestimated the overall thickness of the layers and that in the southernmost examined outcrops (Palena, Taranta Peligna and Lama dei Peligni), the RCC is characterized by higher thickness, coarser grain-size, poorer sorting and more pronounced channeling compared to that cropping out in northernmost areas (Roccacaramanico, San Nicolao and San Valentino). The recognition of facies-types characterized by greater proximality in the southern Maiella area, and the overall geometric reconstruction of the depositional architecture of the RCC horizon, suggests that, contrary to what was previously assumed, the major sediment gravity-flows were fed from the south-eastern edge of the basin. This result is also confirmed by the paleocurrent data, testifying northward flowing currents directed SSE-NNW.The compositional analysis of RCC, highlighted an almost totally calcareous composition of the clasts and a poor and scattered siliciclastic fraction, mainly occurring as fine grained matrix. Clasts showing inner platform, bio-constructed margin, ramp, transitional and basinal facies, of different ages, are mixed throughout the layers. Nevertheless, these data allowed us to make inferences on the provenance of the sediment supply and on the stratigraphic successions that were undergoing erosion in the area surrounding the basin, around the Messinian-Pliocene boundary.A quantitative assessment of the RCC volume was finally achieved, taking into account either the thickness values we measured in the field or other obtained from deep well-logs, and applying these thicknesses to a set of restored geological sections crossing the Maiella anticline. Our calculation provides a minimum area extent of ~ 700 km2 and a conservative volume estimates of ~ 7 km3 which allows to effectively apply to the RCC, the definition of “mega-bed”. This highlights its importance as a regional marker horizon of the easternmost Abruzzi succession, an importance that is even more emphasized by its clear stratigraphic position, straddling the Miocene/ Pliocene chrono-stratigraphic boundary.
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来源期刊
Italian Journal of Geosciences
Italian Journal of Geosciences GEOSCIENCES, MULTIDISCIPLINARY-
CiteScore
2.90
自引率
11.10%
发文量
25
审稿时长
>12 weeks
期刊介绍: The Italian Journal of Geosciences (born from the merging of the Bollettino della Società Geologica Italiana and the Bollettino del Servizio Geologico d''Italia) provides an international outlet for the publication of high-quality original research contributions in the broad field of the geosciences. It publishes research papers, special short papers, review papers, discussion-and-replies for their rapid distribution to the international geosciences community. The journal is firstly intended to call attention to the Italian territory and the adjacent areas for the exceptional role they play in the understanding of geological processes, in the development of modern geology and the Earth sciences in general. The main focus of the journal is on the geology of Italy and the surrounding sedimentary basins and landmasses, and on their relationships with the Mediterranean geology and geodynamics. Nevertheless, manuscripts on process-oriented and regional studies concerning any other area of the World are also considered for publication. Papers on structural geology, stratigraphy, sedimentology, basin analysis, paleontology, ecosystems, paleoceanography, paleoclimatology, planetary sciences, geomorphology, volcanology, mineralogy, geochemistry, petrology, geophysics, geodynamics, hydrogeology, geohazards, marine and engineering geology, modelling of geological process, history of geology, the conservation of the geological heritage, and all related applied sciences are welcome.
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