Geologic Unconsolidated Mineral Substrate surface is ≥ 80% Gravel, with a Gravel size of 2 millimeters to < 4,096 millimeters.

CMECS Substrate Component: Substrate Subclass

1.3.1

Anthropogenic Impact, aRPD and RPD Depth, Benthic Depth Zones, Co-Occurring Elements, Coral Reef Zone, Energy Intensity, Induration, Percent Cover (Fine), Mineral Precipitate, Percent Cover (Coarse), Seafloor Rugosity, Small-Scale Slope, Substrate Descriptor, Substrate Layering, Surface Pattern, Temporal Persistence

S

Gravel Substrate

Derived Unit

The CMECS Coarse, Mixed, and Fine Unconsolidated Mineral Substrate Classes and subordinate units use Folk (1954) terminology to describe particle sizes of loose mineral substrates as shown in the ternary diagram in Figure 7.2 . Units with bracketed letters, e.g., [G], [(g)sM], correspond to the labeled polygons in Figure 7.2, using conventions from Folk (1954).

Due to the importance of different particle sizes of Gravel as habitat for many organisms, Gravel subgroup particle sizes (Boulder, Cobble, Pebble, Granule) must be identified whenever particle sizes are known or can be estimated within any mix and at any level of classification. Examples: Gravel Mixes -> Pebble Mixes, Muddy Sandy Gravel -> Muddy Sandy Cobble, Gravelly Sand -> Bouldery Sand

When classifying Mixes, or when there is a need to identify specific particle sizes beyond the Subgroup definitions, the Subgroup terms for the Gravel Group (Boulder, Cobble, Pebble, Granule), Sand Group (Very Coarse Sand, Coarse Sand, Medium Sand, Fine, Sand, Very Fine Sand), and Mud Group (Silt, Silt-Clay, Clay) may optionally be substituted for the Group term. Examples: Muddy Sandy Gravel -> Silty Sandy Gravel, Slightly Gravelly Sandy Mud -> Slightly Gravelly Sandy Clay, Gravelly Muddy Sand -> Gravelly Muddy Coarse Sand, Slightly Gravelly Sand -> Slightly Gravelly Medium Sand

The Co-occurring Elements Modifier (see Section 10.6.2, p. 213, FGDC-STD-018-2012) may be used to describe mixes of origins as well as the presence of secondary substrate units within the observational unit (i.e., image frame, sampling grid cell, etc.)

When classifying mixes of two different Gravel Subgroup particle sizes, use combinations of the Subgroup unit names with the overall dominant size first. Examples: Boulder-Cobble, Cobble-Boulder, Cobble-Granule, Pebble-Granule, Granule-Boulder.

See also: implementation guidance for all Substrate Component units.

Attribute Change (Unit Type)

Editorial Change (defintion re-worded)

Change in level up (Group to Subclass)

Name Change

Attribute Change (revised unit code)