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Difficulty: HardExplicit Detail Retrieval

In his 1891 synthesis of pelagic sedimentation based on samples collected during the Challenger expedition, oceanographer John Murray categorized deep-sea deposits into terrigenous and pelagic types. While terrigenous sediments accumulated rapidly along continental margins through riverine runoff, pelagic deposits—comprising biogenic oozes and red clay—accumulated in abyssal basins far from landmasses. Murray noted that calcareous oozes, predominantly composed of globigerina shells, dominated depths shallower than 4,500 meters, but dissolved rapidly below this threshold due to increased hydrostatic pressure and cold, carbon-dioxide-rich bottom waters. Below this calcium carbonate compensation depth, red clay—derived from atmospheric dust, volcanic ash, and extraterrestrial spherules—formed the primary deposit. Crucially, Murray observed that manganese nodules were found almost exclusively within these low-accumulation red clay zones rather than in rapidly depositing calcareous oozes, positing that nodule growth required vast spans of uninhibited metallic oxide precipitation uninterrupted by organic sedimentation.

Based on the passage, which of the following circumstances did Murray identify as characteristic of the locations where manganese nodules predominantly formed?

  1. Sedimentation consisted primarily of red clay rather than rapidly accumulating biogenic oozes.Answer
  2. B
    The surrounding water column maintained low hydrostatic pressure, allowing globigerina shells to remain intact.
  3. C
    Terrigenous runoff continuously supplied dense mineral sediments to the ocean floor.
  4. D
    Extraterrestrial spherules within the sediment acted as catalysts that accelerated metallic oxide precipitation.
  5. E
    Cold, carbon-dioxide-rich bottom waters dissolved competing organic and inorganic deposits.

Answer

Murray identified that manganese nodules formed predominantly in regions where sedimentation consisted primarily of red clay rather than rapidly accumulating biogenic oozes.
The passage explicitly states that Murray found manganese nodules almost exclusively within low-accumulation red clay zones rather than in rapidly depositing calcareous oozes, because nodule growth required uninterrupted metallic oxide precipitation.

Step-by-Step Solution

1
Locate the specific passage segment discussing manganese nodules.
The final sentence states that Murray observed manganese nodules 'almost exclusively within these low-accumulation red clay zones rather than in rapidly depositing calcareous oozes.'
Explicit detail retrieval requires matching the specific assertion in the passage to the corresponding statement in the choices.
2
Compare the retrieved detail with the available options.
The choice noting that sedimentation consisted primarily of red clay rather than rapidly accumulating biogenic oozes accurately paraphrases the explicit passage text.
Biogenic oozes (calcareous oozes composed of globigerina shells) are directly contrasted with red clay zones in the text.

Key Concept

Explicit Detail Retrieval from Academic Prose
Estimated Time:2m 0s
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Explicit Detail Retrieval

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