Abstract A Middle Miocene, ~8 m thick pyroclastic succession, reported from the Bukk Foreland Volcanic Area (BFVA) in Northern Hungary (Central Europe) specified here as the Jato Member, was produced by silicic phreatomagmatism (Phreatoplinian sensu lato). Two well-preserved outcrops ~8 km apart and inferred to be within ~10–50 km from source represent the discontinuously exposed, layered, paleosol-bounded, phreatomagmatic Jato Member. They show an identical phenocrystal assemblage of feldspar, biotite and amphibole without weathered zones or signs of erosion, that suggest deposition in one eruption phase lasting hours to months. The succession contains three subunits: 1) subunit A, 1.8 m thick, a series of well-sorted fine to coarse ash or lapilli tuff layers with constant thickness; 2) subunit B, 2.1 m thick, a series of normal-graded layers with an upper fine-grained zone containing abundant ash aggregates with a coarser-grained core and distinctively finer-grained outer rim; 3) subunit C, 4.5 m thick, a massive, poorly to well-sorted coarse ash with gas escape structures and ash aggregates at its base. The upward change of these lithofacies implies an initially sustained dry fallout-dominated deposition of ash and pumice lapilli resulting in subunit A. Subsequently, multiple wet and dilute Pyroclastic Density Currents (PDCs) dispersed subunits B and C. The general abundance of PDC-related ash aggregates in the middle-upper part of the succession (particularly in subunit B), and the transformation of a fall-dominated to a collapsing depositional regime producing wet dilute PDCs, imply the increasing influence of water during the eruption (Phreatoplinian sensu lato). The presence of water is related to an epicontinental sea during Middle to Late Miocene in the Carpatho-Pannonian region. The transition from an initial dry magmatic phase generated fallout activity followed by the emplacement of wet PDCs' rich in ash aggregates, when external water infiltrated from a surrounding lake or sea water entered the vent.

中文翻译：

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匈牙利东北部潘诺尼亚盆地的中新世 Phreatoplinian 喷发：Jató 成员

摘要 来自匈牙利北部（中欧）布克前陆火山区 (BFVA) 的中中新世约 8 m 厚的火山碎屑岩序列由硅质潜水岩浆作用 (Phreatoplinian sensu lato) 产生，这里指定为 Jato 成员。两个保存完好的露头相距约 8 公里，推测距离源头约 10-50 公里，代表不连续出露、层状、古土壤界、潜水岩浆 Jato 段。它们显示出相同的长石、黑云母和角闪石的表晶组合，没有风化带或侵蚀迹象，这表明在一个喷发阶段沉积持续数小时至数月。该系列包含三个亚单元：1) 亚单元 A，1.8 m 厚，一系列分选良好的细至粗灰或薄薄的凝灰岩层，厚度恒定；2) 亚基 B，2.1 m 厚，一系列正常级配层，上层细粒区含有丰富的灰粒聚集体，具有较粗粒的核心和明显较细的外缘；3) 亚基 C，4.5 m 厚，一种块状的、分选不良到良好的粗灰，其底部有气体逸出结构和灰聚集体。这些岩相的向上变化意味着最初持续以干沉降为主的灰分和浮石沉积导致亚基 A。随后，多个湿和稀释的火山碎屑密度流 (PDC) 分散了亚基 B 和 C。与 PDC 相关的一般丰度层序中上部的灰聚集体（特别是在亚基 B 中），以及由秋季主导的向塌陷沉积体系的转变，产生湿稀释的 PDC，暗示喷发期间水的影响越来越大（Phreatoplinian sensu lato）。水的存在与 Carpatho-Pannonian 地区中中至晚中新世期间的陆表海有关。当从周围湖泊或海水渗入的外部水进入通风口时，从初始干燥岩浆阶段的转变产生了沉降活动，然后是富含灰烬聚集体的湿 PDC 就位。