Page 119 - Volcanic Textures A Guide To The Interpretation of Textures In Volcanic Rocks

Fig. 46 Particle-support mechanisms and different end-member types of sediment gravity flows (granular mass
flows) in which the interstitial fluid is water. Modified from Collinson and Thompson (1989).

Fig. 47 Laminar versus turbulent mass-flow types (sediment gravity flows). Modified from Lowe (1979).

Deposition begins as the flows decelerate. Coarse and Single sedimentation units have thicknesses ranging
dense particles initially settle rapidly from suspension, from several centimeters to several tens of centimeters.
forming a relatively massive to weakly graded layer, and Successive turbidity currents may be rapidly generated
subsequent deposition of finer particles involves both and deposit a stack of sedimentation units which lack the
traction and suspension that generate cross-bedded and fine, suspension-settled mud layer (amalgamated
laminated layers (Fig. 49A; 29.1-2). Complete turbidites). This is a common situation in near-source
sedimentation units thus typically show a vertical settings. In distal settings, sedimentation units lack the
sequence that reflects gradually changing depositional lower, massive, coarse-grained layer of the ideal
processes during progressive aggradation in sequence, and are dominated by the finer upper
response to flow deceleration (Bouma sequences — divisions.
Bouma, 1962).

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