川北旺苍唐家河剖面仙女洞组灰泥丘沉积特征及造丘环境分析

Construction of Mud Mounds and Their Forming Models of Xiann ¨udong Formation in Tangjiahe Section of Wangcang,North Sichuan

目前川北地区早寒武世微生物藻与古杯参与的生物礁(丘)发育特征存在较大争议。通过实测剖面与镜下分析,川北旺苍县鼓城乡唐家河剖面仙女洞组发育三期灰泥丘。对该剖面灰泥丘沉积特征进行精细研究认为:第一期灰泥丘发育在滑塌角砾灰岩之上,造丘生物主要为枝状和房室状附枝藻,主要岩性为砾屑灰岩、藻格架凝块灰岩和含云生物碎屑灰岩,发育丘基、丘核、丘盖和丘翼,后期演化为钙质砂泥岩结束生长。第二期生物丘发育在鲕粒滩间生屑灰岩之上,造丘生物主要为肾状藻,次为附枝藻,主要岩性为生物碎屑灰岩、藻格架凝块灰岩、漂浮砾岩和亮晶鲕粒灰岩,纵向上发育丘基、丘核、丘坪、丘盖和丘翼,最终再度沉积鲕粒灰岩。第三期灰泥丘发育在藻叠层灰岩之上,造丘生物为古杯和微生物藻,岩性主要为古杯灰岩、生物碎屑泥晶灰岩、藻格架凝块灰岩和藻叠层灰岩,发育丘基、丘核和丘盖。进一步分析三期灰泥丘的成丘环境认为第一期灰泥丘属于台缘斜坡环境内的斜坡灰泥丘低能沉积,经历三个演化阶段;第二期属于台地边缘灰泥丘,经历四期演化阶段;第三期为台缘高能鲕粒滩向陆一侧能量相对较低的台缘古杯灰泥丘沉积,经历三个演化阶段。剖面中灰泥丘多与鲕粒滩共存,构成丘滩复合体,为后期研究储集性能和油气富集关系具有重要的油气地质意义。

Objectives： Some sedimentary and development characteristics about the reef or mud mound, which dominated by alage and archaeocyath or archaeocyath-bearing are controversial in recent results. Methods： By the outcrop observing and microscope analysis, three phases of Mud Mounds are respectively developed in Xianntidong Formation in Tangjiahe Section of Gucheng and Wangcang County, northern Siehuan basin. Results：Based on the careful and detailed characteristics researching, it is found that the first phase of mud mound in which the mound-building organisms are dominated by slump breccia limestone, the building microorganisms includes dendritic and chambered Epiphyton, and the lithology includes calcirudyte, alage thrombolite and bioelastic limestone is composed of mound base, core, cap and flank and stopped flourish because of the evolution of calcareous sandstone. The second phase of mud mound in which the mound-building organisms are dominated by bioclastic limestone between the oolitic shoals, the building microorganisms includes primary Renalsis and secondary Epiphyton, and the lithology includes bioclastic limestone, alage thrombolite, float rudstone and oolitic sparite is composed of mound base, core, flat, cap and flank and become the oolitic shoals ultimately. The third phase of mud mound in which the mound-building organisms are dominated by alage stromatolite, the building microorganisms includes archaeoeyath and Renalsis, and the lithology includes archaeocyath limestone, bioclastic limestone, alage thrombolite and alage stromatolite limestone is composed of mound base, core and cap. Conclusion：Based on that above, we conclude that the first phase of mud mound was formed in the platform marginal slope mound environment with low energy and three evolutionary stages. The second phase of mud mound was formed in the platform margin environment with four evolutionary stages. The third phase of mound was formed landwards, which at the back of the platform marginal oolitic shoals with high energy, belong to the back platform margin arehaeocyath mound environment with low energy and three evolutionary stages. Mud mounds and oolitic shoals often developed together to form the mound-shoal complex in this section. So it will contained the geological significance of oil and gas by the research of reservoir property and oil--gas accumulation relationship.