新墨西哥州格兰德河谷更新世湖泊沉积物环境磁学研究

L. Donohoo-Hurley, J. Geissman, P. Fawcett, T. Wawrzyniec, F. Goff
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引用次数: 0

摘要

环境磁数据来自于2004年从新墨西哥州的Valles Caldera获取的超过80米的更新世时代湖泊沉积物(岩心GLAD-VC3-04)。本研究的目的是通过量化磁矿物学的变化,作为气候驱动的地表过程导致的沉积物流入变化的代理,来评估在沉积时期山谷破火山口内过去的气候变化。VC3-04的典型自然剩余磁化强度(NRM)范围为3- 6 mA/m。反映磁铁矿总数的非滞后剩余磁化强度(ARM)范围为15 - 30 mA/m。交变退磁及其他岩石磁性测试结果表明,细粒磁铁矿(单畴和伪单畴磁铁矿)在大部分剖面中携带主磁化信号。VC3-04岩心没有定向,因此对NRM的古地磁评价仅限于倾斜值。VC304岩心最古老的部分约为552 + 3 ka,基于76.4m深的tephra层中sanidine的40Ar/39Ar同位素年龄测定,因此整个岩心处于当前的Brunhes时。虽然这个年表完全是正极性的,但有几个地磁“事件”反映了地磁场中短暂的高振幅定向偏差(例如,515 +/- 3 ka的卡拉布里亚岭II)已被记录为布伦什年表。在17.22 m ~ 17.30 m深度区间获得的样品显示出中等的负倾角,我们认为这代表了卡拉布里亚岭II事件。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
An envirnmental magnetism investigation of the Pleistocene lacustrine sediments from the Valle Grande, New Mexico
Environmental magnetic data are being obtained from over 80m of Pleistocene age lacustrine sediments (core GLAD-VC3-04) retrieved in 2004 from the Valles Caldera, New Mexico. The purpose of this study is to asses past climate variation within the Valles Caldera over the time period of sedimentation by quantifying variations in magnetic mineralogy as a proxy for changes in sediment influx resulting from climatically driven surficial processes. Typical intensities of natural remanent magnetization (NRM) of VC3-04 range from 3 - 6 mA/m. Intensities of anhysteretic remanent magnetization (ARM) that reflect total magnetite population, range from 15 - 30 mA/m. Results of alternating field demagnetization and other rock magnetic tests indicate that fine grained magnetite (single-domain and pseudo-single domain magnetite) carries the principal magnetization signal in much of the section. The VC3-04 core is not oriented and thus paleomagnetic evaluation of the NRM is limited to inclination values. The oldest part of the VC304 core is about 552 + 3 ka, based on 40Ar/39Ar isotopic age determination on sanidine in a tephra layer at 76.4m depth and thus the entire core is within the current Brunhes chron. Although this chron is exclusively of normal polarity, several geomagnetic “events” reflecting short-lived high amplitude directional deviations in the geomagnetic field (e.g., the Calabrian Ridge II at 515 +/- 3 ka) have been documented for the Brunhes chron. Samples obtained from the depth interval 17.22 m - 17.30 m yield moderate negative inclinations, which we interpret represent the Calabrian Ridge II event.
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