湘南晚白垩世风成砂岩及其环境气候意义
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南京大学地球科学与工程学院

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编号为42172106和41372106联合资助的成果。收稿日期:2024-01-;改回日期:2024-02-;责任编辑:*通讯


Late Cretaceous eolian sandstones in southern Hunan province: Indicative of paleo- environment and climate
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1.School of Earth Sciences and Engineering,Nanjing University,Nanjing,210023;2.Jiangsu,China

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    摘要:

    风成砂岩作为气候指针广泛应用于古气候分析。华南晚白垩世风成砂岩的环境及气候研究尚存不足,古风向成因解释存在较大争议!本文对湖南南部长沙盆地、醴-攸盆地和茶-资盆地红花套组砂岩的岩相、结构特征和古风向进行了综合分析。结果显示:砂岩风化色多呈橘红、砖红色,层系组厚一般3?10 m,可达20 m以上,发育大型高角度斜层理;碎屑颗粒以细粒砂为主,分选磨圆中等-较好;石英边缘发育红棕、褐色沙漠漆;颗粒表面见碟形、新月形、V形等撞击坑;砂岩颗粒支撑,颗粒间多铁泥质填隙;砂丘由再活化面(R)、叠置界面(S)、砂丘间迁移面(I)分隔。这些特征表明湖南红花套组砂岩系风成成因。同时,这些风成砂岩相不仅垂向上发育在下伏罗镜滩组冲积扇体系之上,侧向也显示与冲积扇岩相交互与共生。冲积扇以阵发性碎屑流、泥质流沉积为特征,属于旱地扇类型。风成砂岩相与旱地扇相组合指示干旱-半干旱气候,可能形成于相对温凉气候条件。风成砂岩在盆地中的分布局限特点及与近源冲积扇相伴生规律指示华南晚白垩世风成砂形成于山间砂丘环境,并非沙海型沙漠产物。研究区风成砂丘砂岩中存在NE和SE两组盛行地表去向古风向记录,与现代行星风系风向不甚匹配,可能是行星风系、东亚季风和局部反-折射风向叠加的综合印记。

    Abstract:

    As a climatic proxy, eolian sandstones have been applying in the paleoclimatic analysis. For the Late Cretaceous eolian sandstones in South China, lithofacies and paleoclimatic indications have been deficient, while paleowind system has been dispute in the paleowind directions. In this study, we conducted integrating analyses of lithofacies, texture, and paleowind directions for the eolianites from the Honghuatao Formation of the Changsha Basin, Li-You Basin, and Cha-Zi Basin, middle-southern Hunan. Results show that sandstones are orange-red and brick-red with large and high-angle cross-beddings, in which laminal set is often 3?10 m thick, even up to ~20 m; detrital grains are dominated by fine sand with medium-good roundness and sorting; reddish brown and / or dark brown Fe-varnish are common along the quartz edge; impact scars of dish-, V-, and crescent- shape generally occur on quartz surface; sandstones are characterized by grain-supported and Fe-mud matrix textures; and main surfaces of reactivation surfaces (R), interdune migration surfaces (I), and superimposition surfaces (S) bound the dunes. They together indicate the sandstones of the Honghuatao Formation are eolian in origin. These eolianites had been built onto the underlain Luojingtan alluvial fan conglomerates and both laterally interfinger out each other. The alluvial fan lithofacies is featured by pulse debris and muddy gravity current sediments, manifesting arid alluvial type. Eolian sandstone and associated arid alluvial fan lithofacies suggest the (semi-) arid climate, possibly in a relative cooling condition. Low distribution in basin and association with proximal-source alluvial fan facies indicate the Late Cretaceous eolian sandstones have been accumulated in an intermontane dune environment rather than in a sand-sea desert. Two sets of paleowind directions SE and NE are predominantly recognized from the eolian sandstones, which are not compatible with those of modern planetary wind system. It is proposed that they two sets of prevailing wind directions might be a superposition imprints of modern planetary, East Asia monsoon, and local reflection-refraction wind systems.

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  • 收稿日期:2024-01-11
  • 最后修改日期:2024-02-16
  • 录用日期:2024-02-17
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