High-resolution correlation patterns in the turbidite systems of the Hecho Group (South-Central Pyrenees, Spain)

Abstract

Detailed bed-by-bed correlations in sheetlike lobes and basin-plain elements of the Hecho Group were carried out through a hierarchical decomposition based on three orders of correlation. This procedure provides the most detailed correlation framework with chronostratigraphic significance. First-order decomposition is based on physical correlation by mapping of major megaturbidites. Second-order decomposition consists in matching a series of marker beds within first-order units, leading to the definition of units several metres thick. Finally, third-order decomposition relies on the matching of serial features within second-order packages (number, vertical arrangement and facies features of beds), and further testing the coherence of the downstream evolution of facies in single beds. Sheetlike lobes and basin plain are closely related and display a distinctive sheet-like geometry. Basin-plain beds are deposited by the same flows that build the sheetlike lobes, with the existence of a transitional facies change from the lobe to the basin-plain. Thickening of some beds towards the basin plain due to ponding of the fine-grained (silt and mud) divisions, a diagnostic feature of the basin plain, controls the sheet-like stacking pattern by balancing the wedging-out of thinner lobe beds upcurrent from, or within, the basin plain. As a consequence, the whole area can be geomorphically classified as a basin plain, which comprises both lobe and basin plain facies associations.