Geology Reference
In-Depth Information
Fig. 13.17
Subaqueous, delta-like body formed of bioclastic
carbonates at the 'mouth' of a subaqueous channel that cut
through the low part of an anticlinal ridge in the Pliocene forearc
basin of the Northern Island of New Zealand. The delta deposits
consist in giant tabular crossbeds, with sets 10-40 m thick and
foreset dips of 7-36°. The delta pinches out basinward into fine-
grained deposits (From Nelson et al.
2003
)
Fig. 13.18
Schematic diagrams showing the spatial distribution of
bedform types along tidal-transport pathways (net sediment trans-
port is toward the front of the diagram): (
a
) intermediate case; (
b
)
regions with limited sand; and (
c
) areas with abundant sand. The
up-current area in all examples experiences net erosion, whereas
the downstream portion experiences net deposition because of the
down-current decrease in current speed (numbers in circles). In (
c
),
tidal sand ridges (tidal sand banks) occur in the upcurrent (higher
current speed) portion of the depositional area. Such ridges pass
down-current into a tidal sand sheet that is mantled by dunes. All
of the features shown are part of the 'transgressive lag' that mantles
a flooding surface (From Belderson et al.
1982
)
