1.3 MB - Instituto de Ciencias de la Tierra Jaume Almera

36 Carbonates Evaporites (2011) 26:29–40
at the valley bottom. The depressions originated from
glacial, karstical and snow activity (Smart 1986; Alonso
1998). The entrances of caves are mainly situated in
sinkholes or glaciokarst depression and represent cave
passages truncated by erosion. Torca Teyera is located
under a free karren with a lot of closed depressions, gravity
deposits and some glacier cirques.
The nivation forms include one moraine and some cirques
originated by snow activity. The nivation cirques are
observed in some walls of dolines and in scarps oriented to
the NE or SW. The snow moraine is located under one
nival cirque. Glacial forms cover till deposits, horns, arête,
cirques and moraines. A glacial valley is observed in the
NW of Torca Teyera shaft. Till deposits, mainly formed by
limestone pebbles and boulders, sand and mud, are found
in this valley. In some cases, boulders of limestone in
certain facies are found on the bedrock of limestone with
other facies. The till is often presented in moraines of 1- to
6-m wide and 50- to 60-m long. The horns are degraded
and are situated in the peaks where some arêtes converge.
The cirques are greatly degraded by karstification and their
size is between 100 and 300 m. The only periglacial evidence
is a rock glacier shown on the eastern part of the
map. The deposit is formed by limestone gravels and
boulders, and presents some transverse and longitudinal
ridges and furrows.
Gravitational forms include debris fall, talus deposits
and rock avalanches and are situated under scarps and in
sinkholes. The debris fall generally consists of angular
pebbles and gravels of limestone. The talus deposits are
mostly formed of limestone pebbles and gravel, sand and
mud; these are usually vegetated. The rock avalanches are
formed from disorganization of angular boulders and
pebbles of limestone in the NE of the map.
Some geomorphological features (till, closed depressions,
cirques, arêtes, gravity deposits and the rock glacier)
are mainly orientated following the NW–SE and NE–SW
directions. This trend represents the orientation of the
bedding, thrusts and the main faults.
Geologic mapping and structural research
The cavity surrounding of the geological map was formed
by both the cave development and the tectonics (Fig. 5b).
The surroundings of Torca Teyera were formed by 1,000 m
of limestone of the Valdeteja and Picos de Europa Formations
stacked vertically. The limestone is divided into
three strata domain as defined by Bahamonde et al. (2007):
(1) toe of slope and basin facies, (2) slopes facies and (3)
platform top facies. The toe of slope and basin facies
include well-stratified coarse-grained beds formed by
breccias, bioclastic pack to grainstone limestone, chert and
shales. The slopes facies consist of massive limestone,
123
breccias and boundstone with botryoidal cement fans. The
platform top facies include stratification rocks, mainly
formed by skeletal pack, to grainstone limestone and pink
fossil-rich limestone. Moreover, an andesitic dyke is recognized
in the western middle part of the geological map.
The cavity studied is developed on limestone affected by
an NW–SE trending, subvertical and SW-directed thrusts
and other faults, the direction of which is SE–NW, SW–NE
or N–S (Figs. 5b, 6a). Two sequences of thrusts have been
recognized based on their geometric relationships. The first
sequence dips 50–70 NE and is interrupted by an out-ofsequence
anomaly, which dips by 80–90° NE.
Figure 5a shows 2,367 fractures in the study area; these
are represented in a rose diagram (Fig. 6b). The plot shows
three groups of fractures with directions: (1) NE–SW, (2)
N–S and (3) NW–SE. The first group represents 45% of the
total fractures and the second group represents another 17%.
The direction of the cave passages are analyzed by another
rose diagram (Fig. 6c). On comparing both (fracture and
cave direction) rose diagrams, the first structural control of
the orientation can be semiqualitatively established. The
dispersion of values of the shaft orientation is greater than
the fracture data, although the NW–SE direction of the cave
is noted. The group considered as Fracture 1 is the most
abundant collection, but its influence on the cavity development
is less than the group considered as Fracture 2. This
method does not consider the influence of the bedding and
the intersection between discontinuities; consequently, it is
only a first approximation to the structural factor.
Seven families of joints have been established on the
stereographic projection. The average plane of each family
is represented in Fig. 7a. The families J2, J3 and J5 correspond
to the fractures already recognized in a previous
work (Borreguero 1986). The density plot of the orientation
and dip of the passages has been shown in gray scale on the
stereographic projection (Fig. 7a) to compare the main
orientations and dips of the joints, the bedding and the cave
passages. Figure 7a highlights that subvertical cave passages
(Group 1 of galleries) are conditioned by the joint
families J1, J3, J4 and J6, as well as their intersections. The
galleries belonging to Group 2 (N10°W/20°N) are mainly
controlled by the intersection between the families J5 and
J6. The passages dipping down 20° to the NE (Group 3)
are ruled by the intersection between family J1, J2, J5 and
J7. The latter group of passages consists of horizontal
galleries in the direction N125°E and follows the bedding
(Fig. 7b).
Conclusions
The use of a multidisciplinary methodology including the
speleological cave survey, geomorphological mapping and