臺中區頭嵙山層之堆積及其古流之研究

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题名:	臺中區頭嵙山層之堆積及其古流之研究
作者:	蔡裕偉
贡献者:	地質系
关键词:	古流堆積臺中頭嵙山層
日期:	1991-06
上传时间:	2020-12-30 09:43:29 (UTC+8)
摘要:	此次主要研究台灣西部台中區大茅埔-雙冬斷層以西之頭嵙山層之岩相變化、沉積構造及砂岩之顆粒分析，以探討其堆積及古流之情形。頭嵙山層之標準露頭位於台中縣豐原市東的頭嵙山。此地層依其岩性可分為二段，其下段為香山砂岩段，而其上段為火炎山礫岩段。台中區之頭嵙出層香山砂岩段主要為海相砂頁岩之互層，並含海棲及非海棲化石，且普遍可見大型交錯層、波痕、分級層、球狀與枕頭狀構造及生物痕跡化石。此大型交錯層之力位顯示當時之古流自古中央山脈向西、西北及西南流動。此段之厚度在本區西部海岸約有一千公尺，自此向東增厚至草屯一帶達二十公尺以上，然後向中央山脈逐次減薄並尖滅。台中區頭嵙出層香山砂岩段之等厚線明題地沿車籠埔斯層不連續。台中區頭嵙山層香山砂岩段之砂岩顆粒之中值為1.80~3.95φ，其平均值為 2.18~5.22φ，其標準差為0.99~3.60φ，即淘選普通到甚不良，而其歪度皆為正值 (0.27~0.78 )。其砂岩主要屬於拖曳或濁流沉積物。其砂岩組織之成熟度為非成熟到亞成熟。由此香山砂岩岩段可能堆積於河流-濱海-淺海環境，且當時來源地之構造活動劇烈，而其沉積速率很高。台中區頭嵙山層火炎山礫岩段主要為陸相礫岩之厚層，間夾砂岩薄層，並台海棲及非海棲化石。此段經常可見高角度之礫組構及逆分級層。此礫組構之方位顯示當時之古流自古中央山脈向西、西北及西南流動。此段之厚度在本區西部海岸一帶僅約有五百公尺，自此向東草屯一帶增厚至約一千公尺以上，然後向東逐次減薄並尖滅。其等厚線沿車籠埔斷層不連續。其砂岩層之出現頻率由下往上(年青部份)逐次減少。其堆積環境可能為河流-三角洲-濱海。台灣西部台中區之頭嵙山盆地之中心位於草屯附近。由此次依據交錯層與礫組構之有向性測定之古流研究顯示其沉積物主要來自古中央山脈之古第三紀及中新世變質岩及新第三紀沉積岩。此古流自古中央山脈向西、西北及西南流動並攜帶大量沉積物，而堆積於台灣西部台中區之頭嵙出盆地。台灣西部台中區堆積頭嵙山層時，其來源地之造山運動及侵蝕作用之強度隨時間而逐漸加強，而其盆地之沉積率逐次超過其下降率，因此其沉積環境由深逐漸變淺，而成為海退相沉積現象。 The purpose of this study is to describe the lithofacies changes,sedimentary structures, and grain size analysis of the sandatones inthe Pleistocene Toukoshan Formation in the Taichung area, westernTaiwan, and to elucidate the sedimentation and paleocurrent of theToukoshan time. The type locality of the Toukoshan Formation islocated at the Toukoshan in the east of the Fengyuan city, Taichungarea. The Toukoshan Formation is subdivided into the HsiangshanSandstone Member in the lower part and the Huoyenshan ConglomerateMember in the upper part. The Hsiangshan Sandstone Member is characterized by the alternating beds of marine sandstone and shale, containing marine and nonmarine fossils. Large-scale cross- stratifications, ripple marks, ball-andpillow structure, and ichnofossils are very common. Based on the dataof the orientations of cross-strata, the transporting agencies were fromthe ancient Central Range of Taiwan towards the northwest, west,ana southwest during the Hsianshan time. The thickness of the Shiangshan Sandstone Member ranges from about 1000m in the western coastof Taichung area to more than 2000m on the Tsaotun belt and graduallythicken from the western coast eastward to this belt and thins outeastward the Central Ranges of Taiwan. The isopachs of this memberare markedly discountinuous along the Chelungpu fault. The Phi medians of the sandstones in the Hsiangshan SandstoneMember vary from 1.80 to 3.95, the phi means from 2.18 to 5.22, thephi deviations from 0.99 to 3.60 (moderately to very poorly sorted),and the phi skewness from 0.27 to 0.78 (fine to strongly fine skewed).Most the sandstones in the Hsiangshan Sandstone Member are tractioncurrent deposits or turbidites, and the textural maturity is imatureto submature. The Hsiangshan Sandstone sequence in the Taichungarea may have been deposited in a fluvial-littoral-neritic environments.The tectonism in the source area were very intensive and the ratesof sedimentation were high during the deposition of this sequence. The Huoyenshan Conglomerate Member of the Toukoshan Formationin Taichung area is characterized by thick beds of non-marine conglomerate, interbedded with the thin layers of sandstone, containingmarine and non-marine fossils. Higher-anglle imbrication of gravelsand graded bedding are very common. Based on the data of the orientations of gravel fabric and the horizontal variation of maximum grainsize, the transporting agencies were from the ancient Central Rangeof Taiwan towards the northwest, west, and southwest during the Huoyenshan time. The thichness of the Huoyenshan Conglomerate Memberranges from about 500m in the western coast of Taichung area to morethan 1000m on the Tsaotun belt. It gradually thickens from the western coast eastward to this belt and thins out toward the east. Theisopachs of this member are slightly discontinuous along the Chelungpufault. The appearance frequency of the sandstone layer in the Huoyenshan Sandstone Member decreases from the lower part toward theupper part. The Huoyenshan Conglomerate sequence were probablydeposited in a fluvial-deltaic-littoral environments. The tectonic intensity of the diastrophism in the source areaincreased with time and the rates of sedimentation slightly exceededthat of subsidence of depositional site during the deposition of theToukoshan Formation in the Taichung area of western Taiwan, beingregressive sedimentation.
關聯:	華岡理科學報 8 民80.06 頁151-169
显示于类别:	[理學院] 學報-華岡理科學報

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