Sehsah Haytham, Kirkland Christopher L, Johnson Tim E, Abdel-Fattah Zaki A
Geology Department, Faculty of Science, Damietta University, New Damietta, 34517, Damietta, Egypt.
School of Earth and Planetary Sciences, The Institute for Geoscience Research, Timescales of Mineral Systems Group, Curtin University, Perth, WA, Australia.
Sci Rep. 2025 May 20;15(1):17534. doi: 10.1038/s41598-024-81530-8.
The transition to continental collision c. 650 Ma induced the bimodal hypsometry of the Arabian-Nubian Shield (ANS), and triggered the formation of voluminous post-amalgamation basins. The intermontane Kareim Basin is a voluminous post-amalgamation depocenter within the ANS. It comprises a thick siliciclastic fill (~ 7 km thick) that accumulated over tens of millions of years during late Neoproterozoic East African orogeny related to the amalgamation of West and East Gondwana. The basin fill consists of four main facies associations (FA1 to FA4) associated with 11 siliciclastic lithofacies and one volcaniclastic lithofacies, which are interpreted as alluvial fan to lacustrine deposits that accumulated under humid to semi-arid conditions. A conglomerate-dominated lithofacies characterizes proximal alluvial fan deposits (FA1), whereas mid to distal alluvial fan strata are represented by braided stream sandstone-dominated lithofacies and conglomerate (FA2-3). Distal fan deposits are composed mainly of sandstone and fine-grained lacustrine sediments (FA4). Tectonically-induced unconformities separate three depositional stages in the Kareim Basin. The lower stage comprises three sandstone-dominant cycles, locally separated by unconformities. The middle stage of the basin represents a stage of syn-depositional tectonic inversion, consistent with the presence of recycled basal boulders derived from the lower stage, and a divergence in the dominant paleo-current directions. Furthermore, thrust faults, tilted and overturned older strata, and the first occurrence of material derived locally from Pan-African volcanic rocks (the Dokhan Volcanic Suite) and basement gneiss domes are additional clues for the syn-depositional tectonic inversion. The upper stage comprises conglomerate-dominant cycles, and represents the transition to post-collisional extension and rapid subsidence. Detrital zircon U-Pb ages constrain the syn-depositional inversion of the basin to later than c. 635 Ma, likely coinciding with the onset of collision between West with East Gondwana.
约6.5亿年前向大陆碰撞的转变导致了阿拉伯-努比亚地盾（ANS）的双峰式地势，并引发了大量合并后盆地的形成。山间的卡里姆盆地是ANS内一个大量合并后的沉积中心。它包含一层厚厚的硅质碎屑填充物（约7千米厚），在新元古代晚期与西冈瓦纳和东冈瓦纳合并相关的东非造山运动期间，历经数千万年堆积而成。盆地填充物由四个主要相组合（FA1至FA4）组成，与11个硅质碎屑岩相和一个火山碎屑岩相相关，这些相被解释为在湿润至半干旱条件下堆积的冲积扇至湖泊沉积物。以砾岩为主的岩相表征近端冲积扇沉积物（FA1），而中至远端冲积扇地层则由辫状河砂岩为主的岩相和砾岩代表（FA2 - 3）。远端扇沉积物主要由砂岩和细粒湖泊沉积物组成（FA4）。构造诱导的不整合面将卡里姆盆地的三个沉积阶段分隔开来。下部阶段包括三个以砂岩为主的旋回，局部被不整合面分隔。盆地的中部阶段代表同沉积构造反转阶段，这与来自下部阶段的再循环基底巨石的存在以及主要古水流方向的分歧一致。此外，逆冲断层、倾斜和翻转的较老地层，以及首次出现的源自泛非火山岩（多汉火山岩套）和基底片麻岩穹窿的局部物质，是同沉积构造反转的额外线索。上部阶段包括以砾岩为主的旋回，并代表向碰撞后伸展和快速沉降的转变。碎屑锆石U - Pb年龄将盆地的同沉积反转限制在约6.35亿年之后，可能与西冈瓦纳和东冈瓦纳碰撞的开始时间一致。
