广西凌云下甲二叠纪沉积灰岩墙和角砾灰岩体的成因及地质意义
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摘要
20世纪70年代,广西地质八队在凌云下甲水晶矿区识别出中二叠世茅口期的沉积灰岩脉呈近直立状穿插在中泥盆统东岗岭阶或上泥盆统融县组灰岩中,同时在同层位识别出中二叠世茅口期生物碎屑灰岩胶结石炭纪—早二叠世生物碎屑角砾形成的角砾灰岩体。但对其成因解释与地质事实矛盾。笔者识别出沉积灰岩脉内有地震软沉积物流充填物和正常海底沉积物,同时识别出灰岩脉是台地边缘同沉积断层的伴生张裂隙,角砾灰岩体是同沉积断层产生的陡崖崩塌物及断层角砾岩。从而认为中二叠世时,由于频繁的同沉积正断层活动,使中、上泥盆统成为凌云地区碳酸盐岩台地的陡崖。一次新的断裂活动,在陡崖上形成张性裂隙,或者使已有裂隙张开,并诱发地震。最初,地震引发的碎屑流灌入裂隙,首先落入裂隙中的是中二叠世以前形成的固体岩石,可来自石炭系等,接着是台地上形成的内碎屑流,最后在安定期,台地形成的内碎屑也可缓慢落入裂隙中。与此同时,台地的断层陡崖崩塌,形成角砾灰岩体,其成分大部分是地震诱发的角砾岩。
In 1978, Guangxi 8th Geological Team identified the limestone neptunian dykes of Maokouan stage, Middle Permian, roughly upright in the Middle Devonian Donggangling Formation and Upper Devonian Rongxian Formation. In the same place, limestone breccias of the Maokouan stage, Middle Permian, cemented Carboniferous—Early Permian bioclastics and formed breccia talus. The limestone neptunian dykes were interpretated as reopened axial cleavages in paleo-unconformity surface and immediately filled with transgressive sediments; or giant tensile fractures in carbonate platform in response to the seafloor spreading of the Youjiang basin and filled with syn-spreading sediments. The limestone breccia talus were explained as karst breccias caused by paleo-anticline uplift. But those explanations couldn't accord with following observations. First, limestone neptunian dykes didn't occur only in axis plane of anticline. Second, there is no any observation back up that giant fissures wouldn't cut through whole Carboniferous to Devonian beds. Third, the Late Paleozoic strata in the Lingyun area were successive, in other words, there were no karst breccias. This study identified earthquake-caused liquefied sediments flows in limestone neptunian dykes. The study also identified that the limestone dykes were tensile fracture caused by syn-sediment faulting. The limestone breccia talus were shelf margin escarpment breccias and fault breccias caused by syn-sediment faulting. It is the long distance faulting along the Lingyun carbonate platform margin during Middle Permian that made the Middle Devonian be revealed in the Middle Permian seafloor and occurred tensile fractures which be filled with Middle Permian earthquake-caused liquefied soft flows and formal sediments. This consideration is accorded with that information from lava in Youjiang basin and the neighbor areas.
In 1978, Guangxi 8th Geological Team identified the limestone neptunian dykes of Maokouan stage, Middle Permian, roughly upright in the Middle Devonian Donggangling Formation and Upper Devonian Rongxian Formation. In the same place, limestone breccias of the Maokouan stage, Middle Permian, cemented Carboniferous—Early Permian bioclastics and formed breccia talus. The limestone neptunian dykes were interpretated as reopened axial cleavages in paleo-unconformity surface and immediately filled with transgressive sediments; or giant tensile fractures in carbonate platform in response to the seafloor spreading of the Youjiang basin and filled with syn-spreading sediments. The limestone breccia talus were explained as karst breccias caused by paleo-anticline uplift. But those explanations couldn't accord with following observations. First, limestone neptunian dykes didn't occur only in axis plane of anticline. Second, there is no any observation back up that giant fissures wouldn't cut through whole Carboniferous to Devonian beds. Third, the Late Paleozoic strata in the Lingyun area were successive, in other words, there were no karst breccias. This study identified earthquake-caused liquefied sediments flows in limestone neptunian dykes. The study also identified that the limestone dykes were tensile fracture caused by syn-sediment faulting. The limestone breccia talus were shelf margin escarpment breccias and fault breccias caused by syn-sediment faulting. It is the long distance faulting along the Lingyun carbonate platform margin during Middle Permian that made the Middle Devonian be revealed in the Middle Permian seafloor and occurred tensile fractures which be filled with Middle Permian earthquake-caused liquefied soft flows and formal sediments. This consideration is accorded with that information from lava in Youjiang basin and the neighbor areas.
引文
广西壮族自治区地质局第八地质队,淮南煤炭学院.1978.广西凌云早二叠世沉积灰岩脉和沉积灰岩体的发现及其对研究古构造的意义.见:国际交流地质学术论文集(一).北京:地质出版社:272~278.
邝国敦.2001.桂西晚古生代深水沉积研究的新进展.广西地质,14(3):1~6.
黄宏伟,杜远生,黄志强,陈海.2007.广西丹池盆地晚古生代震积岩及其构造意义.地质论评,53(5):577~585
邝国敦,吴浩若.2002.桂西晚古生代深水地层.地质科学,37(2):152~164.
陆刚,胡贵昂,张能,张耿,潘艺文,彭阳.2006.右江盆地二叠纪生物礁时空分布和沉积构造演化新知.地质论评,52(2):190~197.
彭阳,胡贵昂,陆刚,章雨旭,乔秀夫.2004.桂西北晚古生代地层中的沉积灰岩墙研究进展.地质论评,50(6):613~619.
彭阳,李岩,胡贵昂,陆刚,乔秀夫.2007.广西桂林庙头上泥盆统融县组中的灰岩脉和角砾灰岩体及其成因.地质论评,53(6)736~742.
乔秀夫,彭阳,高林志.2002.桂北二叠纪灰岩墙(脉)的地震成因解释,地质通报,21(2):102~104.
张继淹,1995,广西水下沉积岩脉群特征及形成机理,中国区域地质,(4):309~311.
邝国敦.2001.桂西晚古生代深水沉积研究的新进展.广西地质,14(3):1~6.
黄宏伟,杜远生,黄志强,陈海.2007.广西丹池盆地晚古生代震积岩及其构造意义.地质论评,53(5):577~585
邝国敦,吴浩若.2002.桂西晚古生代深水地层.地质科学,37(2):152~164.
陆刚,胡贵昂,张能,张耿,潘艺文,彭阳.2006.右江盆地二叠纪生物礁时空分布和沉积构造演化新知.地质论评,52(2):190~197.
彭阳,胡贵昂,陆刚,章雨旭,乔秀夫.2004.桂西北晚古生代地层中的沉积灰岩墙研究进展.地质论评,50(6):613~619.
彭阳,李岩,胡贵昂,陆刚,乔秀夫.2007.广西桂林庙头上泥盆统融县组中的灰岩脉和角砾灰岩体及其成因.地质论评,53(6)736~742.
乔秀夫,彭阳,高林志.2002.桂北二叠纪灰岩墙(脉)的地震成因解释,地质通报,21(2):102~104.
张继淹,1995,广西水下沉积岩脉群特征及形成机理,中国区域地质,(4):309~311.
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