For the coarse-grained part, we measured the crystallographic orientations of individual calcite grains with EBSD (Figure 4b).
For the fine-grained part, we utilized the automatic measurements of crystallographic orientations of calcite grains within a certain area with EBSD.
We do not know the origin of the preferred c-axis orientation in the fine-grained part, which may have been inherited from that in calcite aggregates constituting the matrix of wall rocks.
However, while they cannot reproduce the finer-grained, distal ballistic field of an eruption in windy conditions, our simulations likely produce valid results for the coarser-grained part of the ballistic field.
It is also difficult to exclude explicitly the tsunami origin of unit 3; however, the laminations in its fine-grained part (units 3A and 3C) indicate recurring, more regular events (Palinkas et al., 2006) in the past.
As shown in Figure 4a, a weak preferred orientation of the c-axis, which is rotated counterclockwise by c. 30° about the vertical axis relative to the vein normal orientation, and a girdle distribution of the a-axis perpendicular to the c-axis maximum orientation were developed in the fine-grained part.
Confined fluvial channel sands (CF) and unconfined fluvial sands (UCF) range from very fine to medium-grained sand (Fig. 7b), with the medium grain-sized samples of the 22/29-2 setple set represent coarser grained basal parts of the confined channel and unconfined sheet sandbodies.
Note that the abrupt change in grain size between the fine-grained and coarse-grained parts.
From (a) fine-grained and (b) coarse-grained parts in calcite vein sample CV-1.
Since the change of grain size is abrupt, we separately measured the crystallographic orientations for the fine-grained (Figure 4a) and coarse-grained parts (Figure 4b).
In particular, the relief of internal levees, in the order of 10-20 m, prevents the lower, coarser-grained parts of flows from spreading over the entire channel belt.
