Th e Interrelationship Between Tectonics and Climate
DeLuca and Eriksson (1989) distinguished two
contrasting fl uvial assemblages in the Chinle Formation of New Mexico. They suggested that proximal,
basin-margin rivers fo rming a tranverse drainage
system were ephemeral, whereas the main basincenter rivers were perennial. Their evidence for perennial flow is not strong, as discussed earlier in this
chapter, consisting as it does mainly of comparisons
with the mainly perennial rivers that formed the
basis for the Platte and South Saskatchewan fl uvial
models, with which their rocks are compared. The
evidence for ephemeral flow and arid conditions is
much stronger, consisting of many of the sedimentological attributes discussed in this chapter. However,
the explanation DeLuca and Eriksson (1989) offered
for the contrasting fluvial styles is not unreasonable.
They suggested that in the basin center the
·
water
table was closer to the surface, in part because of
groundwater recharge which kept the rivers flowing
during seasonal dry periods. Hobday et al. (1981)
noted a similar climatic differentiation in presentday south Texas, where "semiarid, caliche-soil,
chaparal conditions commonly prevail on uplands
while nearby contemporaneous riverbottoms sustain a humid subtropical assemblage of bald cypress
and willows, all owing to different microclimate as
dictated by water table conditions and associated
soil moisture regimes."
Luttrell (1993) suggested a downstream change
from perennial to intermittent in the rivers that deposited the Kayenta fluvial system of the Colorado
Plateau. Again, the evidence for perennial flow
seems weak, based mainly on the scale of the channels and macroforms in the proximal part of the
basin (a criterion discussed earlier in this chapter).
However, the downstream change from perennial to
ephemeral is one that characterizes many arid basins
in modern deserts1 for example1 the inland basins of
western China, where snow-fed mountain streams
enter hot1 lowland deserts, such as the Taklamakam
Desert of Tarim Basin.
Miocene fluvial and lacustrine deposits of the
Madrid Basin, Spain, reveal numerous differences
between northern and eastern margins of the basin
(Alonso Zarza et al. 1992). In part, these differences
refl ect differences in sediment sources and tectonic
activity, but it also appears that there were subtle
climatic differences between the two areas that may,
in part, have been caused by topographic effects. The
northern margin may been under the influence of a
relatively dry climate and is characterized by alluvial
fans with abundant debris flows and immature
calcrete paleosols. The eastern margin may have
443
been in a more humid setting and was the site for the
accumulation of sandy braided stream deposits with
generally more mature paleosols that show pedofacies relationships to the channels.
12.1 1 The Interrelationship
Between Tectonics am! Climate
The importance of the orographic effect on the control of local climates has long been known. For example, it is common knowledge that the temperate
rain forests of the west coast of North America depend in large measure on the adiabatic rainfall generated from westerly winds as they rise over the
Cordilleran mountains. The presence of a significant
rain shadow downwind, in such areas· as the upper
Fraser Valley (Kamloops) and the Okanogan Valley
of British Columbia, is equally well known. Another
example is the Dead Sea Rift (Manspeizer 1985). The
orographic effect of the uptilted rift shoulder west of
the rift is the generation of high rainfallj some of this
flows west in perennial streams draining into the
Mediterranean, but it also feeds ephemeral streams
draining into the Dead Sea rift. The difference in
annual rainfall between the rift crest and the rift
valley is substantial, at > 800 mm/year on the rift
shoulder, in the vicinity ofJerusalem, and < 100 mm/
year in the Dead Sea area.
Knowledge of this type of effect is readily applied
to regional paleogeographic and paleoclimatic interpretations. For example, Besly's (1988) suggestion of
the rainshadow effects of the Variscan Mountains
(Late Paleozoic) in northwest Europe was discussed
earlier in this chapter. Miall (1984b) invoked regional tectonically-related climatic variations as a
possible control on the distribution of fluvial
lithofacies assemblages in the Paleogene fluvial deposits of Arctic Canada. He suggested that the unusual abundance of coals (and of fossil vertebrates)
in central Ellesmere Island could be an indication of
a locally humid climate related to adiabiatic rainfall
generated by the effects of regional uplifts to the east
and north of the depositional basin, whereas lithofacies in Eclipse Trough, in the area of northwest
Baffin Island, indicate a predominance of ephemeral
rivers and a drier climate, possibly related to the
passage of westerly winds over the broad interior
plains of the Arctic Platform.
Evidence fr om fluvial lithofacies) coupled with
floral, isotopic, and other evidence, indicates a
gradual global cooling during the Cenozoic. Major
DeLuca and Eriksson (1989) distinguished two
contrasting fl uvial assemblages in the Chinle Formation of New Mexico. They suggested that proximal,
basin-margin rivers fo rming a tranverse drainage
system were ephemeral, whereas the main basincenter rivers were perennial. Their evidence for perennial flow is not strong, as discussed earlier in this
chapter, consisting as it does mainly of comparisons
with the mainly perennial rivers that formed the
basis for the Platte and South Saskatchewan fl uvial
models, with which their rocks are compared. The
evidence for ephemeral flow and arid conditions is
much stronger, consisting of many of the sedimentological attributes discussed in this chapter. However,
the explanation DeLuca and Eriksson (1989) offered
for the contrasting fluvial styles is not unreasonable.
They suggested that in the basin center the
·
water
table was closer to the surface, in part because of
groundwater recharge which kept the rivers flowing
during seasonal dry periods. Hobday et al. (1981)
noted a similar climatic differentiation in presentday south Texas, where "semiarid, caliche-soil,
chaparal conditions commonly prevail on uplands
while nearby contemporaneous riverbottoms sustain a humid subtropical assemblage of bald cypress
and willows, all owing to different microclimate as
dictated by water table conditions and associated
soil moisture regimes."
Luttrell (1993) suggested a downstream change
from perennial to intermittent in the rivers that deposited the Kayenta fluvial system of the Colorado
Plateau. Again, the evidence for perennial flow
seems weak, based mainly on the scale of the channels and macroforms in the proximal part of the
basin (a criterion discussed earlier in this chapter).
However, the downstream change from perennial to
ephemeral is one that characterizes many arid basins
in modern deserts1 for example1 the inland basins of
western China, where snow-fed mountain streams
enter hot1 lowland deserts, such as the Taklamakam
Desert of Tarim Basin.
Miocene fluvial and lacustrine deposits of the
Madrid Basin, Spain, reveal numerous differences
between northern and eastern margins of the basin
(Alonso Zarza et al. 1992). In part, these differences
refl ect differences in sediment sources and tectonic
activity, but it also appears that there were subtle
climatic differences between the two areas that may,
in part, have been caused by topographic effects. The
northern margin may been under the influence of a
relatively dry climate and is characterized by alluvial
fans with abundant debris flows and immature
calcrete paleosols. The eastern margin may have
443
been in a more humid setting and was the site for the
accumulation of sandy braided stream deposits with
generally more mature paleosols that show pedofacies relationships to the channels.
12.1 1 The Interrelationship
Between Tectonics am! Climate
The importance of the orographic effect on the control of local climates has long been known. For example, it is common knowledge that the temperate
rain forests of the west coast of North America depend in large measure on the adiabatic rainfall generated from westerly winds as they rise over the
Cordilleran mountains. The presence of a significant
rain shadow downwind, in such areas· as the upper
Fraser Valley (Kamloops) and the Okanogan Valley
of British Columbia, is equally well known. Another
example is the Dead Sea Rift (Manspeizer 1985). The
orographic effect of the uptilted rift shoulder west of
the rift is the generation of high rainfallj some of this
flows west in perennial streams draining into the
Mediterranean, but it also feeds ephemeral streams
draining into the Dead Sea rift. The difference in
annual rainfall between the rift crest and the rift
valley is substantial, at > 800 mm/year on the rift
shoulder, in the vicinity ofJerusalem, and < 100 mm/
year in the Dead Sea area.
Knowledge of this type of effect is readily applied
to regional paleogeographic and paleoclimatic interpretations. For example, Besly's (1988) suggestion of
the rainshadow effects of the Variscan Mountains
(Late Paleozoic) in northwest Europe was discussed
earlier in this chapter. Miall (1984b) invoked regional tectonically-related climatic variations as a
possible control on the distribution of fluvial
lithofacies assemblages in the Paleogene fluvial deposits of Arctic Canada. He suggested that the unusual abundance of coals (and of fossil vertebrates)
in central Ellesmere Island could be an indication of
a locally humid climate related to adiabiatic rainfall
generated by the effects of regional uplifts to the east
and north of the depositional basin, whereas lithofacies in Eclipse Trough, in the area of northwest
Baffin Island, indicate a predominance of ephemeral
rivers and a drier climate, possibly related to the
passage of westerly winds over the broad interior
plains of the Arctic Platform.
Evidence fr om fluvial lithofacies) coupled with
floral, isotopic, and other evidence, indicates a
gradual global cooling during the Cenozoic. Major