印度中部普尔纳冲积盆地最年轻多巴凝灰岩火山灰的性质、产状和岩性设置

IF 1.5 4区 地球科学 Q2 GEOLOGY
Journal of Geology Pub Date : 2019-10-10 DOI:10.1086/705326
A. Srivastava, Ajab Singh
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引用次数: 10

摘要

印度中部Purna冲积盆地中最年轻的Toba Tuff灰在不同地方都有发现,其特征是浅灰色、黄褐色、灰橙粉色、松散堆积的细粒物质。它们以0.5–3.0m厚的口袋、小透镜体和不连续床的形式保存在河流环境的砂质沉积物中。根据颜色、厚度和沉积学特征,这种远端物质可分为原始灰和再加工灰。显微镜下,灰烬主要由具有气泡壁形态的玻璃碎片、次要矿物、无法识别的细粒混合物组成,很少有通道沉积物。玻璃碎片无色、透明、有棱角、未破裂,性质不变。共鉴定出六种形态类型:(1)单辐射状或两个泡壁碎片,(2)Y形或三辐射状碎片,(3)片状碎片,(4)块状碎片,(5)具有细长囊泡的碎片,以及(6)浮石碎片。不同序列的相结构显示出广泛的低能流体沉积环境。对玻璃碎片的主要元素分析显示,二氧化硅的比例很高,其次是氧化铝、钾和钠。一般来说,玻璃碎片中主要离子的高百分比反映了流纹岩岩浆的成分。灰中的矿物虽然数量较少,但以石英、长石、黑云母、角闪石、辉石、橄榄石、尿囊石和铁钛氧化物为代表。各种古气候替代物的保存也记录在胞前序列中,以根石、根石球、根际、蚂蚁痕迹和脊椎动物遗骸为代表。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Nature, Occurrence, and Lithological Setup of Youngest Toba Tuff Volcanic Ash, Purna Alluvial Basin, Central India
Youngest Toba Tuff ashes in the Purna alluvial basin of central India have been encountered at various places and are represented by light-gray, yellowish-brown, grayish-orange-pink, loosely packed, fine-grained material. These are preserved as pockets, lenticles, and discontinuous beds of 0.5–3.0-m thickness in the arenoargillaceous sediments of fluvial environments. Based on color, thickness, and sedimentological features, this distal material is divisible into primary ash and reworked ash. Microscopically, the ashes consist predominantly of glass shards with bubble-wall morphologies, minor minerals, unidentifiable fine-grain admixture, and, rarely, channel sediments. The glass shards are colorless, transparent, angular, unfractured, and unaltered in nature. A total of six morphotypes have been identified: (1) uniradiate, or two-bubble-wall, shards, (2) Y-shaped, or triradiate, shards, (3) platy shards, (4) blocky shards, (5) shards with elongated vesicles, and (6) pumice shards. Facies architecture of various successions shows broadly low-energy fluviolacustrine depositional environments. Major-element analysis of the glass shards shows a high percentage of silica, followed by alumina, potassium, and sodium. In general, high percentages of major ions in the glass shards reflect rhyolitic magma composition. The minerals in the ash, though minor in quantity, are represented by quartz, feldspar, biotite, amphibole, pyroxene, olivine, allanites, and Fe-Ti oxides. Preservations of various paleoclimatic proxies are also recorded from pretephra successions and are represented by rhizoliths, rhizolith balls, rhizosphere, ant traces, and vertebrate remains.
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来源期刊
Journal of Geology
Journal of Geology 地学-地质学
CiteScore
3.50
自引率
5.60%
发文量
0
审稿时长
3 months
期刊介绍: One of the oldest journals in geology, The Journal of Geology has since 1893 promoted the systematic philosophical and fundamental study of geology. The Journal publishes original research across a broad range of subfields in geology, including geophysics, geochemistry, sedimentology, geomorphology, petrology, plate tectonics, volcanology, structural geology, mineralogy, and planetary sciences. Many of its articles have wide appeal for geologists, present research of topical relevance, and offer new geological insights through the application of innovative approaches and methods.
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