Abstract
The Gyeokpori Formation in the Buan volcanic area primarily contains siliciclastic rocks interbedded with volcanoclastics. These sediments are characterized by a variety of soft-sediment deformation structures (SSDS). The SSDS in the Gyeokpori Formation are embedded in poorly sorted conglomerates; slump folds are also present in the formation. The deformation mechanisms and triggers causing the deformation are not yet clear. In the present study, the trigger of the SSDS in the Gyeokpori Formation was investigated using facies analysis. This included evaluation of the reworking process of both cohesive and non-cohesive sediments. The analysis indicates that the SSDS are directly or indirectly associated with the alternation of conglomerates and mud layers with clasts. These layers underwent non-cohesive and cohesive deformation, respectively, which promoted SSDS formation. The slump folds were controlled by the extent of cohesive and non-cohesive deformation experienced by the sediment layers in the slope environment. The SSDS deformation style and morphology differ, particularly in the case of reworking by slump activity. This study contributes to the understanding of lacustrine slope-related soft-sediment deformation structures.
Highlights
Soft-sediment deformation structures (SSDS) develop in unconsolidated sediments during or shortly after deposition
Two types of SSDS were studied in sediments of a sloping lacustrine fan-delta using facies analysis
The occurrence of each of them is restricted to specific locations on the fan-delta slope
Summary
Soft-sediment deformation structures (SSDS) develop in unconsolidated sediments during or shortly after deposition. Such structures occur in all sedimentary environments and are caused by liquefaction of sediments, which is sometimes followed by fluidization [1,2,3,4]. The Cretaceous Gyeokpori Formation comprises sediments that accumulated on the slope of a subaqueous fan-delta system, an environment that is favorable for creating and preserving SSDS [9,13,14,15,16,17]. The deformation mechanism and trigger of these structures are not always clear. This is partly because small differences in sediment characteristics or depositional processes can produce different SSDS. To understand the formation mechanisms of different SSDS, facies analysis [3,4] is a useful but still underexplored approach
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