基于全岩心CT的遗迹化石识别及沉积环境分析:以加拿大麦凯Ⅲ油砂区块为例*

遗迹化石研究对于沉积环境分析具有重要意义。以加拿大麦凯Ⅲ油砂区块下白垩统McMurray组为研究对象,利用高分辨率岩心照片和全岩心CT扫描资料,在确认研究目的层遗迹化石发育属种、单体规模、组合类型及指相特征的基础上,分析了主力油砂层的沉积环境。结果表明: 目的层发育遗迹化石10属12种,包括Asterosoma isp.,Chondrites isp.,Diplocraterion isp.,Ophiomorpha nodosa,Palaeophycus tubularis,Planolites beverleyensis,Planolites isp.,Rosselia isp.,Skolithos verticalis,Skolithos isp.,Teichichnus isp.,Thalassinoides isp.;根据遗迹化石产状与围岩沉积特征,建立了Ophiomorpha-Skolithos、Asterosoma-Chondrites-Rosselia和Teichichnus-Rosselia￣Thalassinoides共3种遗迹组合,分别代表潮间带、潮下带以及浅海陆棚沉积环境中的遗迹化石组成特征。研究区油砂层优质储油砂体为潮间带沉积产物,潮汐砂坝、潮成砂脊为沥青的主要储集体。本研究既体现了全岩心CT资料在遗迹化石研究中的应用,也为潮坪沉积环境分析提供了有益参考。

Ichnology identification and sedimentary enviorment analysis based on CT scanning: A case study from Mackay Ⅲ oil sands,Canada

Ichnology provides a basis for identification and analysis of depositional environment. Taking the Lower Cretaceous McMurray Formation,Mackay Ⅲ oil sands,Canada as an example,the sedimentary environments of the reservoir were studied with respect to trace fossils' species,size,associations,and facies indicators by high-resolution core photos and CT data. Results indicate that there are 12 species of ten genera in the Middle and Upper McMurray Formation,including Asterosoma isp.,Chondrites isp.,Diplocraterion isp.,Ophiomorpha nodosa,Palaeophycus tubularis,Planolites beverleyensis,Planolites isp.,Rosselia isp.,Skolithos verticalis,Skolithos isp.,Teichichnus isp.,and Thalassinoides isp.. According to the features of these fossils and surrounding lithology,three combinations, including Ophiomorpha-Skolithos,Asterosoma-Chondrites-Rosselia and Teichichnus-Rosselia-Thalassinoides, are established,representing intertidal,subtidal and shallow-marine environments respectively. Sand bodies in reservoir were deposited in the intertidal setting,being the main accumulation of hydrocarbon. This study not only reflects the superiority of CT data,but also provides a reference for recognizing the tidal flat environments.