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What is the official letter for the bedrock soil horizon? I know that the letters to represent the A, B, and C horizons are widespread, but the fourth layer (bedrock) is referred to with different names. Some call it the D-Horizon, some the R-Horizon, and some just say bedrock. Is there any standard or official term, and if so, what is it?

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    $\begingroup$ Is there anything in this question that the wikipedia soil horizon page doesn't answer? Or, to be more useful, could you reference that page, and use it to ask a more specific question? $\endgroup$ – naught101 Apr 19 '14 at 1:34
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    $\begingroup$ For geologists there is the Shell Standard Legend, but the problem is that most geologists never map bedrock as a unit (but need to differentiate it into lithologies) ogp.org.uk/news/2014/… $\endgroup$ – tobias47n9e Apr 19 '14 at 8:42
  • $\begingroup$ @naught101 Quoted from that Wikipedia page - "D horizons are not universally distinguished" $\endgroup$ – Timtech Apr 19 '14 at 12:41
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According to Wikipedia and Nature.com, "R Horizon" is the official letter for bedrock.

Example soil with designations that communicate the soil formation processes occurring in each horizon.

CAPTION: Example soil with designations that communicate the soil formation processes occurring in each horizon.

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It depends on which classification system you're using, which varies by country.

According to the USDA Soil Taxonomy, R is used to designate bedrock.

Other countries and classification systems may (or may not) use different letters. Check out the Compendium of On-Line Soil Survey Information for other classification systems.

To answer your second question, there are standards, depending on which classification system or country or even discipline you're in. Soil scientists in the US use the USDA soil taxonomy, or R to designate bedrock.

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