Ground Penetrating Radar investigation of depositional architecture: the São Sebastião and Marizal formations in the Cretaceous Tucano Basin (Northeastern Brazil)

ABSTRACT: One key factor for the advance in the study of fluvial deposits is the application of geophysical methods, being the Ground Penetrating Radar one of special value. Although applied to active rivers, the method is not extensively tested on the rock record, bearing interest for hydrocarbon reservoir analogue models. The São Sebastião and Marizal formations were the subject of previous studies, which made possible the comparison of Ground Penetrating Radar survey to previous stratigraphic studies in order to identify the best combination of resolution, penetration and antenna frequency for the studied subject. Eight radar facies were identified, being six of them related to fluvial sedimentary environments, one related to eolian sedimentary environment and one radar facies interpreted as coastal sedimentary environment. The Ground Penetrating Radar data showed compatibility to sedimentary structures in the outcrops, like planar and trough cross-stratified beds. It is noted that the obtained resolution was efficient in the identification of structures up to 0.3 m using a 100 MHz antenna. In this way, the Ground Penetrating Radar survey in outcrops bears great potential for further works on fluvial depositional architecture.

摘要：河流沉积研究取得进展的关键因素之一是地球物理方法的应用，其中探地雷达（Ground Penetrating Radar）的应用价值尤为突出。尽管该方法已应用于现代活动河流的研究，但尚未在岩石记录中得到广泛验证，这一方向对油气储层类比模型研究具有重要意义。圣塞巴斯蒂昂组（São Sebastião）与马里萨尔组（Marizal）曾是既往研究的对象，相关研究使得探地雷达探测数据与既往地层学研究得以对比，从而可为本次研究确定分辨率、探测深度与天线频率的最优组合。本次研究共识别出8种雷达相，其中6种与河流沉积环境相关，1种对应风成沉积环境，剩余1种被解释为海岸沉积环境。探地雷达数据与露头中的沉积构造（如板状、槽状交错层理）具有良好的匹配性。值得注意的是，采用100 MHz天线时，本次研究所获得的分辨率可有效识别0.3米以内的沉积构造。综上，露头探地雷达探测在河流沉积构型的后续研究中具有巨大应用潜力。