Geology Reference
In-Depth Information
complete records can be interpreted in the context of
the dynamic tidal model and several examples are
noted below.
1.4.1
Hindostan Whetstone Beds
(Pennsylvanian, Indiana)
Figures
1.2
and
1.3
show both a segment of core and a
bar chart of the laminae thicknesses from the Hindostan
Whetstone beds found in Orange County, Indiana
(Kvale et al.
1989
). Neap-spring cycles in this chart
occur more frequently than crossovers indicating that
these tides were synodically driven and hence related
to the dominance of the M
2
and S
2
over the O
1
and K
1
constituents. Some caution is needed, however, in
interpreting crossover patterns because the absence of
a single half-day event could cause an apparent cross-
over. Ways to infer completeness of a tidal pattern are
discussed by Kvale et al. (
1999
). Suffice it to state that
with suitably long tidal rhythmite records, such as
presented here, it is possible to interpret crossover
patterns with some confidence.
This example clearly shows a diurnal inequality,
and, as such, O
1
must be significant. There appears to
be a lack of a pronounced semimonthly inequality
(anomalistic cycle) suggesting that N
2
was relatively
weak. Therefore, tides that deposited the Hindostan
Whetstone beds were dominated by the constituents
M
2
, S
2
, and O
1
followed by K
1
and N
2
.
Fig. 1.8
Resulting tide predicted from the stacking of 9 different
tidal constituents. Horizontal units are in hours (Modified from
MacMillan, 1966 in Kvale, (
2006
) and used by permission from
Marine Geology)
1.4.2
Brazil Formation (Pennsylvanian,
Indiana)
tide at Booby Island exhibits a tropically driven
neap-spring cyclicity comparable to the tide depicted
in Fig.
1.4
except that it also exhibits a strong semidi-
urnal component that is driven by M
2
. Progressing fur-
ther south into the Gulf of Carpentaria, the strengths of
K
1
and O
1
increase relative to M
2
creating a tide that is
dominantly diurnal.
Figure
1.4
show a segment of core and a bar chart of
laminae thicknesses from the Brazil Formation of
Daviess County, Indiana (Kvale and Archer
1990
;
Kvale and Mastalerz
1998
). The neap-spring cycles in
this example occur at the same frequency as the cross-
overs indicating that these tides were driven by the
tropical period and hence reflect a dominance of O
1
and K
1
over S
2
and M
2
. A weak semidiurnal signal
occurs during the neap tides and indicates that M
2
had
some amplitude and importance in the resulting tide.
The Brazil Formation rhythmites, like the whetstone
beds discussed above, lack a prominent semimonthly
inequality suggesting a weak N
2
tidal constituent. It
can be inferred from this data base that the Brazil
1.4
Ancient Tides
Some tidal rhythmites in the rock record preserve long
(several months worth), relatively complete succes-
sions of daily or semidaily tidal deposition. Particularly
