Middle–Upper Pleistocene tephras in the Papua New Guinea highlands

IF 1.2 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY
C. Pain
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引用次数: 1

Abstract

Abstract Eighteen Middle–Upper Pleistocene (ca 200 ka) tephra units in the highlands of Papua New Guinea (PNG) are mapped and described. The study area is about 24 000 km2, extending from Tari in the west to Kainantu and the Kassam Pass in the east. It is estimated that at least 75 000 km2 of highland PNG received ≥50 cm tephra from various highland sources, and the total volume would have been well over 300 km3. Total tephra thicknesses near sources are >20 m, with thicknesses of individual units near source ranging from 1–2 to >4 m. Several units were deposited with coarse ash and lapilli basal layers that have been weathered to fine ash and clay sizes. Hagen, Giluwe and Yelia volcanoes are the main sources, with smaller centres near Giluwe and north of Hagen also producing mappable tephra units. One unit (Birip) was erupted about 40 ka, but most of the tephra units are 200 ka and older. Volumes of tephra suggest that many of the eruptions had volcanic explosivity indices of 4–6. On stable bedrock, tephras are present on slopes up to 35°, demonstrating the high stability of the tephra materials. Gaps in the tephra cover coincide with bedrock that weathers to unstable regolith where tephras did not accumulate; the tephra cover thus provides an indicator of bedrock stability. Mapped tephra units provide the potential for correlation of other Quaternary materials and can be used as widespread marker beds. The tephras are also important as the parent material for the dominant agricultural soils in the highlands. KEY POINTS In the highlands of Papua New Guinea at least 75 000 km2 received >50 cm of tephra mainly from Hagen, Giluwe and Yelia volcanoes. This work extends knowledge of highland volcanic history, which will allow correlation of surfaces and events across the highlands. The tephras are important parent materials of soils that support highly productive agriculture in the highland valleys. The long-term stability of tephra-covered slopes maintains a soil cover for thousands, if not tens of thousands, of years.
巴布亚新几内亚高地的中上更新世蕨
摘要十八中上更新世(约200 ka)tephra单元在巴布亚新几内亚(PNG)高地的地图和描述。研究面积约为24000 平方公里,西起塔里,东至凯南图和卡萨姆山口。据估计,至少有75000人 巴布亚新几内亚接收的高地面积≥50平方公里 来自不同高地来源的cm tephra,总体积将远远超过300 km3.震源附近的总火山灰层厚度>20 m、 震源附近单个单元的厚度范围从1–2到>4 m.几个单元沉积有粗灰和火山灰基底层,这些基底层已风化为细灰和粘土尺寸。Hagen火山、Giluwe火山和Yelia火山是主要来源,Giluwe附近和Hagen北部的较小中心也产生了可绘制的火山灰岩单元。一个单元(Birip)在40左右爆发 ka,但大多数tephra单位是200 ka及以上。火山灰的体积表明,许多火山喷发的火山爆发指数为4-6。在稳定的基岩上,火山灰岩存在于高达35°的斜坡上,表明火山灰岩材料的高度稳定性。火山灰覆盖层中的缝隙与基岩重合,基岩风化为不稳定的风化层,火山灰没有堆积;因此,tephra覆盖层提供了基岩稳定性的指标。绘制的火山灰岩单元提供了与其他第四纪物质进行对比的潜力,可以用作广泛的标志层。苔草也是高地主要农业土壤的重要母质。关键点在巴布亚新几内亚高地,至少75000平方公里的面积超过50 厘米的火山灰岩,主要来自哈根火山、吉鲁韦火山和耶利亚火山。这项工作扩展了高地火山历史的知识,这将使整个高地的表面和事件相互关联。苔草是支持高原山谷高产农业的重要土壤母质。被火山灰覆盖的斜坡的长期稳定性即使不是数万年,也能维持数千年的土壤覆盖。
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来源期刊
Australian Journal of Earth Sciences
Australian Journal of Earth Sciences 地学-地球科学综合
CiteScore
2.80
自引率
8.30%
发文量
45
审稿时长
6-12 weeks
期刊介绍: Australian Journal of Earth Sciences publishes peer-reviewed research papers as well as significant review articles of general interest to geoscientists. The Journal covers the whole field of earth science including basin studies, regional geophysical studies and metallogeny. There is usually a thematic issue each year featuring a selection of papers on a particular area of earth science. Shorter papers are encouraged and are given priority in publication. Critical discussion of recently published papers is also encouraged.
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