宣城地区龙潭组页岩沉积环境与有机质富集

安徽宣城地区上二叠统龙潭组海陆过渡相页岩不仅是我国下扬子区重要的烃源岩，也是目前我国页岩气勘探的重要层位之一。为研究海陆过渡相页岩沉积环境与有机质富集的关系，以港地1井和两个露头剖面为研究对象，系统开展了有机地球化学测试、有机岩石学研究、氩离子抛光—扫面电镜观察、元素地球化学分析等工作。结果表明:下扬子宣城地区龙潭组页岩沉积时期处于暖湿型气候，沉积水体处于氧化—贫氧状态，具有高的生物生产力和沉积速率。海陆过渡相富有机质页岩的形成，不是由单一因素所决定的，而是由古气候、水体氧化还原性质、古生产力、沉积速率等多个要素相互配置与耦合的结果，这些因素都会直接或者间接地影响有机质的供给或者有机质的埋藏和保存。其中，温湿型气候不仅有利于陆源高等植物的生长，而且会促进生物地球化学作用，使得母岩化学风化程度加大，向水体输入的营养物质增多，有利于菌藻类等低等水生生物勃发，高等植物碎屑和低等水生生物共同为富有机质页岩沉积提供了丰富的有机质来源。宣城地区晚二叠世沉积时期，较高的古生产力为海陆过渡相富有机质页岩的形成提供了良好的物质基础，有机质产生后进一步埋藏和保存，虽然富氧水体环境不利于有机质保存，但高的沉积速率可以缩短有机质在富氧水体中暴露的时间，使得有机质来不及被氧化或分解，也可造成有机质的富集。

Sedimentary Environment and Organic Matter Accumulation for the Longtan Formation Shale in Xuancheng Area

The marine-continental transitional organic-rich shale in the Longtan Formation in Xuancheng area,Anhui Province is not only considered as an excellent source rock in the Lower Yangtze region,but also one of the important layers of shale gas exploration in China.In order to clarify the relationship between sedimentary environment and organic matter accumulation in such a setting,a case study was carried out from one core(Gangdi-1 well)and two outcrops(Changqiao outcrop and Daoshanchong outcrop)by conducting organic geochemical test,organic petrologic study,argon ion polishing-scanning electron microscopy(SEM)observation,elemental geochemical analysis.Results show that the transitional shale in the Longtan interval in Xuancheng area was deposited in a complex paleoenvironment that was mainly characterized by a warm and humid paleoclimate,oxic-dysoxic conditions,a high paleoproductivity,and a high sedimentary rate.Besides,the transitional shale formation is not determined by a single factor,but is the result of the mutual configuration and coupling of multiple factors such as paleoclimate,paleoredox conditions,paleoproductivity,and sedimentary rate.All these factors will directly or indirectly affect the supply or preservation of organic matter.Furthermore,the warm and humid paleoclimate not only facilitates the growth of higher plants,but also promotes the biogeochemical process,and thus accelerates the chemical weathering rate of the parent rock and increases the input of nutrients to the water column,which is conducive to the blooms of lower aquatic organisms.Both higher plant debris and lower aquatic organisms together provide abundant organic matter sources.Moreover,during the transitional shale deposition in the Longtan interval,the high paleoproductivity could create abundant organic matter.After organic matter was produced,it was further buried and preserved.Although the oxidizing water environments are usually unfavorable for organic matter preservation,a higher sedimentary rate tends to shorten organic matter exposure time in the decomposition region of aerobic bacteria,and some organic matters cannot be oxidized or degraded through the rapid burial,further promoting organic matter accumulation.