浅析中元古界和白垩系红层中泥裂的特征和古环境意义  

Preliminary Analysis on Characterization of Mud-Cracks in Meso-proterozoic Red Beds and Cretaceous Danxia Red Beds and Their Paleo-Environmental Implications

作　　者：毛学刚[1] 刘秀铭[1,2] 

机构地区：[1]福建师范大学地理研究所,福州350007 [2]麦考瑞大学环境与地理系

出　　处：《亚热带资源与环境学报》2016年第3期20-28,共9页Journal of Subtropical Resources and Environment

基　　金：福建省公益类科研院所专项(2015R1034-5);福建省教育厅项目(JA15137);国家自然科学基金(U1405231;41210002)

摘　　要：泥裂在现代环境和地质时期都很常见,是细粒沉积物浸水后出露于水面之上蒸发干裂而形成,泥裂的出现说明沉积物曾出露于地表水面之上,地质时期常被作为干旱化或干湿交替环境的标志。然而,泥裂可在沉积物出露水面之上很短时间内形成,泥裂本身并不足以反映其古环境,需结合沉积物特征分析。本研究详细阐述太行山中元古界红层和白垩系丹霞红层中不同形式的泥裂特征,与现代泥裂形成环境对比,结合红层的环境意义和磁性矿物特征,初步探讨地质时期红层中泥裂所代表的古环境。泥裂表明沉积物曾出露于水面之上,红层形成和稳定需要长时间处于透水性较好的氧化环境;对红层中泥裂的磁学分析可知,赤铁矿是其中主要的磁性矿物,含量非常高,赤铁矿形成并稳定于干燥的氧化环境;综合分析认为:红层中泥裂形成后长期处于相对干燥的氧化环境,受水下还原环境影响时间较短。根据红层中泥裂代表的古环境可以推断,太行山中元古界红层和白垩系红层发育泥裂所在的层位可能以长期干燥氧化环境为主。Mud-cracks are universal in both modern and geological environments. Fine sediment （ mud, clay or fine sand） initially beneath water level develops cracks once exposed in air due to evaporation. The presence of mud-cracks infers that the sediment was once over water level, traditionally regarded as clues of aridity or seasonal aridity in geology periods. However, mud-cracks are able to form over water level in so short time that it is insignificant for paleo-environmental interpretation which should be combined with sediment features. Herein red mud-cracks formed in Meso-proterozoic Era in Taihang Mountain and Cretaceous Danxia red beds are described in details. And the paleo-environmental significance of red mud-cracks is interpreted by combining modern mud-cracks, paleo-environmental implication of red beds and magnetic minerals. The red beds formed and stabilized in long term well-drained oxic conditions, and magnetic measurements demonstrated that hematite which forms in dry oxic conditions dominates in red mud-cracks. It is thus suggested that arid environment prevailed during the formation of red mud-cracks, while the reducing environment beneath water level is relatively quite short or ignorable. Consequently, the red mud-cracks in Taihang Mountain red beds and Danxia red beds likely infer the prevalence of arid environment.

关 键 词：泥裂 红层 氧化环境 

分 类 号：P53[天文地球—古生物学与地层学]