How are my field descriptions of sediment analysed?
Your field descriptions of surface sediment type are determined by visual and tactile inspection of (wet) samples and constituents (primary descriptors) differentiated according to the Udden – Wentworth grade scale: shell, rock and gravel (>2000µm); coarse sand (>500 µm); sand (>250 µm); fine sand (>63 µm); and mud (<63 µm). The primary descriptors are written down from left to right in decreasing order of abundance: e.g. Mud/Sand is mud with sand, where mud is determined as the dominant constituent (by volume). For more information, download Understanding Sediment (871kb pdf) To convert the qualitative visual/tactile field descriptions to quantitative values (percentage composition by volume), the field observations are first collapsed to pseudo-geological generic classifications involving the five descriptors mud, fine sand, sand, coarse sand and gravel. This is where we use your field description and assign it to a grain size. For example, "Shell Grit" is replaced with "coarse sand"
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