Geology Reference
In-Depth Information
relative elevation
of surface (cm)
+50
% time
exposed
Laminations &
Sedimentary Structures
“Diagnostic”
Biota
Burrowing
Organisms
Sub-
Environment
+25
0
-25
100
Levee crest
&
backslope
Thin lams.
Mm- to cm-
scale lams.
Mm-scale
Worm and
insect tubes
Schizothryx
Sparse biota
Schizothryx
MHW
Mudcracks
80
H.A.M.
Black mangroves
Halophyte grass
Shrubs
Fenestrae
crabs
Scytonema
60
Mm-scale
Polychaete
worm
tubes
Disrupted
laminations
MTL
Alpheus
burrows and
bioturbation.
Mangrove
rhizoturbation
Mats grazed
by
gastropods
Red mangroves
Gastropods
Mangrove
pond
40
Cm-scale
Alpheus
Laminations
destroyed
by
bioturbation
Red mangroves
Gastropods
Foraminifera
Open
pond
MLW
Abundant
Calianassa
burrows, and
bioturbation.
Mangrove
rhizoturbation
(from above)
20
Cm-scale
Calianassa
Channel
floor
0
Levee
crest
+40
Microbial marsh
Channel
margin
Levee
slope
High
algal
marsh
Open
pond
Mangrove pond
Low algal marsh
MHW
+20
MHW
MTL
0
MTL
MLW
meters
-20
100
200
0
50
Fig. 19.2
Relations among environments, topography, and rela-
tive amount of time exposed to the atmosphere (Modifi ed from
Ginsburg et al. 1977), illustrating close relations between eco-
logic-depositional environments and the relative frequency of
exposure (“Exposure Index” of Ginsburg 1977) and relation to
relative elevation and subenvironment, (
upper
). In this area, each
elevation range has a unique assemblage of biota and sedimentary
features. Geomorphic display (
bottom
) of distribution of subenvi-
ronments on a representative channel-to-pond topographic
transect; note the dampening of the tidal range into the pond
areas include red mangroves (
Rhizophora mangle
)
(Fig.
19.4a
), but sediments have a less diverse biota
than adjacent pond deposits, and only cerithid
gastropods and
Batophora
(a non-calcifying green
alga) are common (Fig.
19.4b
). Low-mid intertidal
deposits are grey, reduced carbonate mud (Fig.
19.4c
),
with a distinct H
2
S odor. Laminations here are
destroyed by bioturbation (polychaete worm and
