Abstract
Abstract Based on field geological surveys of two deep-water sedimentary outcrops in the Yanchang formation of the Ordos Basin, X-ray diffraction analysis, elemental geochemical analysis, and polarizing microscope observations were conducted to investigate the causes of various sedimentary structures inside the massive sand bodies from deep-water debris flow. A genesis model of deep-water debris-flow sandstone is established: during the handling of the mass transport complexes in the basin slope, the soft sandy sedimentary layer with relatively strong shear resistance tears the soft muddy sedimentary layer with weak shear resistance and pulls various clumps inside the muddy layer. Finally, debris-flow massive sandstones with rich sedimentary structures are formed. Through argon ion polishing and field emission scanning electron microscopy, the debris-flow sandstones mainly develop micron-scale pores, and the pore radius is mainly distributed in the range of 1–8 µm. The sedimentary rocks from the semi-deep lake to deep lake facies only have a small number of nano-scale pores, and the pore radius is distributed between 20 and 120 nm.
Highlights
Genetic mechanisms of deep-water sandstones have attracted considerable attention in both the petroleum industry and sedimentology research [1,2,3]
According to the sandy debris flow identification basis proposed by Shanmugam [13], floating mudstone clasts are important sedimentary structures that develop within massive sandstones
Many of the samples were collected from mudstone clasts, muddy coatings of the intraclasts within the massive sandstones, associated debris-flow mudstones, and laminated mudstones for trace element geochemical analysis
Summary
Genetic mechanisms of deep-water sandstones have attracted considerable attention in both the petroleum industry and sedimentology research [1,2,3]. Deep-water gravity flow deposits include rockslides, slumps, liquefied sediment flows, sandy debris flows, muddy debris flows, and turbidites [8,9] Of these deposits, debris-flow sandstones have good reservoir properties such as great thickness and wide distribution that have gradually attracted more attention [2,6,10,11,12]. One is that during the process of sandy slump and muddy debris flow formation, debris-flow mudstone in the shallow water area was drawn into the overlying sandy sediments [14]. Another type is believed to be eroded by the early
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