罗平生物群产出层位氧碳稳定同位素的初步研究  

Oxygen and Carbon Isotopic Compositions of Middle Triassic Carbonates from the Dawazi Section of Luoping,Yunnan:Implications for Paleoenvironment of the Luoping Lagersttte

作　　者：孙媛媛[1] 刘俊[1,2] 吕涛[1] 许效松[1] 张启跃[1] 楼雄英[1] 江新胜[1] 

机构地区：[1]中国地质调查局成都地质调查中心,成都610081 [2]香港大学地球科学系

出　　处：《地质学报》2009年第8期1110-1117,共8页Acta Geologica Sinica

基　　金：中国地质调查局区域地质调查项目(编号1212010610211)资助成果

摘　　要：为了解云南罗平地区新近发现的罗平生物群的古环境信息,我们对其产出层位——中三叠统关岭组二段大凹子剖面的碳酸盐岩进行了全岩氧碳稳定同位素测试。测试结果显示,中三叠世安尼期Pelsonian亚期大凹子剖面δ13C值分布范围在-4.5‰～1.1‰之间,平均为-3.03‰,δ18O值分布在-5.2‰～-1.0‰之间,平均为-3.36‰。同位素数据的相关性分析显示大凹子剖面的同位素值受后期大气水参与的成岩作用影响较小。结合沉积学和古生物学的证据,我们提出了一个假说:δ13C值明显偏负的层位主要是由硫酸菌的还原作用所导致。这种活动所释放的H2S也部分解释了罗平生物群大规模死亡的原因。在排除掉成岩作用的影响之后,本剖面δ13C分布在-3.0‰～1.1‰之间,平均值为-1.44‰,δ18O分布在-3.5‰～-2.5‰之间,平均值为-2.94‰。尽管如此,与同时期其他有关剖面相比,大凹子剖面δ13C值仍然偏低,对此我们进行了探讨和解释,并利用高水位时期的δ18O数据作为基本资料对罗平地区的古海水温度进行了恢复。结果显示其温度值分布在27～32℃之间,平均为29℃左右,说明罗平地区当时气候比较温暖。To understand the paleoenvironment of Pelsonian Dawazi section of the Luoping Lagerstatte analyzed carbon and oxygen isotopes using the whole rock carbonates from this section. The result shows that 313C and 3180 of the mid-Trassic Dawazi distribute between -4.5‰- 1.1‰ and between -5.2‰- 1.0‰ respectively. The average value of 313C is -3.03‰ while 3180 is -3.36‰. The relevant analysis of 313C and δ^18O reveals little effect from meteoric water involved diagenesis. Combined with the sedimentological and paleontological evidences, it is suggested that the negative shift of 313C in the obvious negative horizons may be caused by the reduction of the sulfur bacteria. The H2S released by the activity of the sulfur bacteria can partially explain the large-scale demise of Luoping Lagerstatte. After excluding influence by the diagenesis, the 813 C and δ^18 O of this profile ranges between from -3. 0‰ to 1. 1‰ （averaging to -1.44‰） and -3.5‰ to -2.5‰ （averaging to -2.94‰）, respectively. Even so, 313C values of the Dawazi profile are still low compared to those of other sections. The paleotemperature in the Luoping area was restored using 3180 data in this study. Our result shows that the average temperature of seawater in the Pelsonian of Luoping was about 29℃, indicating a warm paleoenvironment during that period.

关 键 词：罗平生物群 稳定同位素 古温度 关岭组 

分 类 号：P597.2[天文地球—地球化学] TE37[天文地球—地质学]