Geoscience Reference
In-Depth Information
• YATERAS (YAT)—N
1-2
—Organogenic, coral-
reef limestones with a thickness not exceeding
50 m. Exotic blocks of this formation can be found
in the sediments of Maquey Formation. It is sup-
posed that some surface rivers at the top of Guaso
Plateau have lost their waters when reaching the
rocks of YAT Formation.
• Quaternary (Q)—Soils with thickness from some
centimeters to several meters. At the top of the
plateau, there are negative forms with 25 m thick
clay layer with rock debris.
The tectonic background (Fig.
2.46
) is assumed to
be a result of the geodynamic evolution of the Cuban
micro-plate at the contact with the oceanic plate—the
trench of Bartlett (Lilienberg
1983
; Cobeilla
1984
;
Rojas-Agramonte et al.
2003
). This trench predeter-
mines the existence of Oriente fault system (N
80-90) with expressed sinistral strike-slip move-
ment. It has affected the southern Sierra Maestra
mountain range, SE Cuba, and portrays the dynamics
and tectonic evolution of the southern Cuban coast in
the boundary zone between the Caribbean and North
American plates (Rojas-Agramonte et al.
2003
). The
region has been affected by historical and recent
earthquakes. The fault-plane solutions from earth-
quakes along the trench are in agreement with the
dominant ENE-WSW compression established
onshore (Rojas-Agramonte et al.
2003
). As a result,
the faults of the Oriente system have been cut and
displaced by a younger system of faults striking N
40-60.
The hydrometrical studies during the expedition
have shown that 1.2 m
3
/s of water is drained by the
karst system of Guaso Plateau (Chanov and Benderev
1993
). The feeding of the karst waters is from infil-
tration of surface waters, especially in the areas where
Charco Redondo and Yateras formations outcrop.
Guaso River disappears in a sink-hole near the cave of
Sumitero with a discharge of 300 dm
3
/s (middle of
January, 1988), and reappears as a river from the cave
El Campanario with a discharge of 500 dm
3
/s
(Andreychuk and Benderev
1991
). The modulus of
the underground stream is approximately 8 dm
3
/s
km
2
. Taking into account the season of the recording,
the quantity is the minimal one. After rains the
quantity of the water rises considerably because the
high permeability of the karst system. As an example,
the discharge rate of the river from the cave El
Campanario raised to 15-20 m
3
/s during 36 h after
strong rainfall in January, 1988. Practically, at that
time, these considerable quantities of water were not
exploited, except these from the Spring Bataldo, used
for water supply of local plant for production of sugar,
and the river from the cave El Campanario, used by a
hydro-electrical power plant.
The performed geological and geophysical inves-
tigations have proved that the karst system can be
subdivided into two hydrological units. The western
part is characterized by a clearly expressed zone of
water saturation entirely inside the karst cavities of
Charco Redondo Formation. The reason of its for-
mation is the existence of a fault barrier at the foot of
Guaso Plateau, where the karstified rocks of CHR
contact the clays of SLU Formation. Along this E-W
trending border spillways exist, being at the same
altitude and with the same chemical composition of
the water. According to geophysical data, a karstified
layer can be expected southwards of this line, repre-
senting a confined aquifer.
The geological conditions in the eastern part of
Guaso Plateau are more complicated. MAC Forma-
tion is of wide occurrence and is resistant to karstif-
ication. The existing large karst negative forms on the
surface are filled up with terra rossa. These traits and
the tectonic faults contribute to the formation of local
barriers for the water. Two rivers on the surface
gather the waters from the plateau—Guaso and
Hondoness Rivers. Hondoness River appears in the
northeastern part of the plateau, but at the contact
with the limestones of CHR Formation it is flowing
down inside the subsurface karst system. Downwards
it appears as several springs at the contact between the
limestones and the Quaternary sediments.
Guaso River is formed by a number of karst
springs on the top of the plateau and after some
kilometers disappears in Somitero of Guaso, forming
a spectacular underground river, successfully traced
by the speleological studies in the caves El Campa-
nario and Somitero. The karst system there has con-
siderable water permeability—more than 100 m
3
/s.
The performed geophysical works in 1988, using
electrical methods (vertical and azimuthal electrical
soundings), permitted detection of karst forms with
considerable dimensions, discovered and mapped
later by the speleologists. The dimensions of the
galleries are 20 m and more in diameter and their tops
are only 10-20 m below the surface. These significant
dimensions of karst galleries, formed inside relatively
