If feature E were a mature, well-sorted, medium-grained siliciclastic sedimentary rock, it could be a:

Question

If feature E were a mature, well-sorted, medium-grained siliciclastic sedimentary rock, it could be a:

BlackTom AI · Accepted Answer

A mature, well-sorted, medium-grained siliciclastic rock is most consistent with a quartz-rich sandstone. 1) Relevant knowledge points and concepts - Siliciclastic rocks are composed of silicate mineral fragments (clasts), typically transported and deposited as sand, silt, or gravel. - Textural maturity refers to grain size and sorting (well-sorted = grains of similar size; medium-grained = sand-sized within a specific range). - Compositional maturity refers to mineral stability during transport: quartz is very stable; feldspar is less stable and breaks down during chemical weathering and transport. - Grain-size classes: sand = 0.0625–2 mm; medium sand ≈ 0.25–0.5 mm. Conglomerates are >2 mm (pebbles, cobbles); shales are <0.0625 mm (clay/mud). 2) Step-by-step reasoning - The rock is siliciclastic (so carbonate rocks like limestone are excluded). - It is medium-grained: that places it in the sand-size range (0.25–0.5 mm), so the correct rock type must be a sandstone rather than shale (too fine) or conglomerate (too coarse). - It is well-sorted and mature: well-sorted indicates uniform sand-sized grains and significant transport or reworking; maturity (both textural and compositional) implies dominance of stable minerals—mainly quartz—because less-stable minerals (e.g., feldspar) are removed by abrasion and chemical weathering. 3) Intermediate facts and checks - Exclude shale: shale consists of clay and silt (<0.0625 mm) and is very fine-grained. - Exclude conglomerate: consists of coarse clasts >2 mm, poorly sorted. - Exclude feldspar-rich sandstone (arkose): arkose implies abundant feldspar and relatively immature composition; feldspar-rich rocks are typically less well-weathered and often poorly sorted. - Exclude limestone: limestone is a chemical/biochemical carbonate rock, not siliciclastic. 4) Why the correct answer is correct Quartz-rich sandstone matches all descriptors: siliciclastic composition (silicate grains), medium grain size (sand-sized), well-sorted texture, and compositional/textural maturity (high quartz content due to prolonged transport and weathering). 5) Why other options are incorrect (brief) - Feldspar-rich sandstone (arkose): compositionally immature (high feldspar) and typically less well-sorted. - Limestone: carbonate, not siliciclastic. - Shale: too fine-grained (mudstone/clay), not medium-grained. - Conglomerate: too coarse and poorly sorted. 6) Conclusion Therefore, the best choice is quartz-rich sandstone, which matches the provided correct answer: quartz-rich sandstone.

If feature E were a mature, well-sorted, medium-grained siliciclastic sedimentary rock, it could be a:单项选择题

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