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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Stratigraphy and age of the Cappadocia ignimbrites, Turkey: reconciling field constraints with paleontologic, radiochronologic, geochemical and paleomagnetic data
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Stratigraphy and age of the Cappadocia ignimbrites, Turkey: reconciling field constraints with paleontologic, radiochronologic, geochemical and paleomagnetic data

机译：土耳其卡帕多细亚火山岩的地层和年龄：利用古生物学，放射年代学，地球化学和古磁数据协调田间约束

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The stratigraphy and age of the Neogene Cappadocia ignimbrites (Central Turkey) have been inferred in previous studies from fieldwork and K-Ar age determinations. The resulting stratigraphic schemes, however, differed from each other, suggesting that further studies were required to produce a reliable succession. In this paper, we examine the chronostratigraphy of mammalian remains recovered in the continental sediments interbedded with the Cappadocia ignimbrites. Using recent advances in mammalian chronostratigraphy, we evaluate selected taxa and faunal associations to place new and independent constraints on the ignimbrite ages. The biostratigraphically bracketed ages concur with some published radiometric dates, but they disagree with others, principally at localities where major stratigraphic discrepancies have arisen in the literature. In order to reconcile these apparent inconsistencies, we combine, at selected sites, our field observations with the biostratigraphic and radiometric age limits, and we compare these with the available geochemical and magnetic data. This allows us to present revised age estimates, and a revised stratigraphy which includes the correlation of the local Sofular deposits with the large-volume Goerdeles ignimbrite. The issues faced in this study apply to other ignimbrite provinces in the world. For instance, ignimbrite eruption frequency in Cappadocia is higher than the resolution of many published K-Ar ages. Furthermore, different K-Ar ages have led to the description of individual and distinct ignimbrites that fieldwork and geochemical data allow to merge into a single ignimbrite. Argon loss from pumice samples leading to radiometric "rejuvenation" provides a likely explanation for most stratigraphic discrepancies. Cappadocia is the only documented ignimbrite field in which the chronostratigraphy of vertebrate remains provides better constraints on some ignimbrite ages than scattered K-Ar dates. We further argue that K-Ar dates from the Cappadocia area are too imprecise to establish a reliable magnetostratigraphic scheme for the ignimbrite succession, with the exception of the ～2.8 Ma Valibaba Tepe ignimbrite.
机译：在以前的研究中，通过实地调查和K-Ar年龄测定推断出了新近纪Cappadocia ignimbrite（土耳其中部）的地层和年龄。但是，由此产生的地层方案互不相同，这表明需要进行进一步的研究才能产生可​​靠的演替。在本文中，我们研究了与卡帕多细亚火山岩夹层的大陆沉积物中恢复的哺乳动物遗迹的年代地层学。利用哺乳动物年代地层学的最新进展，我们评估了选定的分类单元和动物区系协会，以对火成岩年龄施加新的独立约束。在生物地层学上加括号的年龄与一些已公布的放射线测量日期一致，但它们与其他日期不同，主要是在文献中出现主要地层差异的地方。为了调和这些明显的不一致之处，我们在选定的地点将我们的现场观察结果与生物地层和辐射年龄限制相结合，然后将其与可用的地球化学和磁数据进行比较。这使我们能够提供修订后的年龄估算值，以及修订后的地层学，其中包括本地索非拉沉积物与大体积Goerdeles火成岩的相关性。这项研究面临的问题也适用于世界上其他易燃的省份。例如，卡帕多细亚的火山岩喷发频率高于许多已发表的K-Ar年龄的分辨率。此外，不同的K-Ar年龄导致了对单个和不同火成岩的描述，野外工作和地球化学数据允许将其合并成一个火成岩。浮石样品中的氩气损失导致放射性“回春”，这为大多数地层差异提供了可能的解释。卡帕多细亚是唯一有记录的火成岩领域，其中脊椎动物遗迹的年代地层学对某些火成岩年龄的约束比散布的K-Ar日期更好。我们进一步认为，除了〜2.8 Ma Valibaba Tepe火成岩以外，来自卡帕多西亚地区的K-Ar年代太不精确，无法为火成岩演替建立可靠的磁地层学方案。

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