Study on the gravitational flow directions of the Maracangalha Formation (Early Cretaceous), Bom Despacho, NNE area of Itaparica Island, Bahia, Brazil

ABSTRACT: The objective of the present study was to interpret the direction of gravitational sedimentary flows in the turbidite deposits of the Maracangalha Formation (Recôncavo Basin), indicating their source areas. Thus, the indicative deformational structures existing in the formation were analyzed. The structures observed ranged from brittle to highly ductile and viscous states, with a diversity of deformational styles. A total of 284 planar and linear measurements was collected in three distinct subareas, separated according to their degree of deformation. The structures found were separated into four groups according to their formation process: (i) pre-deformation structures; (ii) plastic deformation structures; (iii) intrusion structures (fluidization), related to either early or syn-sedimentation events; and finally (iv) brittle deformation structures, with late sedimentation. Some structures were observed to be good indicators of apparent mass movement direction, which yielded predominantly SSW directions, suggesting a partially confined flow, parallel to the main axes of Recôncavo Basin, towards its depocenter.

摘要：本研究旨在解读马拉坎加尔哈组（Maracangalha Formation）雷孔卡沃盆地（Recôncavo Basin）浊积岩沉积中的重力沉积流流向，以明确其物源区。为此，我们对该地层中的指示性变形构造展开分析。所观测到的构造覆盖脆性至高度韧性、黏性的变形状态，变形样式丰富多样。研究团队在依据变形程度划分的三个独立子区域内，共采集了284组平面与线性测量数据。根据形成过程，所发现的构造可分为四类：（i）变形前构造；（ii）塑性变形构造；（iii）与早期或同沉积事件相关的侵入构造（流液化作用）；以及（iv）形成于沉积晚期的脆性变形构造。部分构造可有效指示表观块体运动方向，其结果以SSW（南南西）向为主，表明该流动整体处于半约束状态，且平行于雷孔卡沃盆地主轴线，向其沉积中心运移。