249
El Yali area: two raisings, one sinking followed by a new raising (Noguera 1956),
and a rising associated to the 1985 earth quake (Barrientos and Kausel 1990).
Thus, the development of El Yali and the system it belongs to, obeys to the interaction of several dynamic factors that have determined the geomorphological evolution that the central Chilean coast has experienced during the last 18,000 years
(Fariña et al. 2012).
Marine transgressions occurred during the last glaciation (14,000 years ago) and
during the middle Holocene (6000 years ago) allowed the accumulation of marine
and/or fluviomarine sediment throughout the basin (Fariña et al. 2012). The tectonic
activity expressed in the co-seismic vertical movements that characterized the last
3000 years (Lower Holocene), produced the regional raising of the coast that caused
the emersion of a littoral terrace where is located the wetland. A sign of this process
is gneiss block present to the southwest of the lagoon Colejuda (Contreras-López
et al. 2014).
As result of the coastal raising, a marine regression occurs and initiates the progradation of the coastal line by means of eolic and fluvial sedimentary processes
(Paskoff et al. 2000). The existence of fluvial refills and transgressive and parabolic
dunes in the area indicates that progradation occurred through sedimentary loads
from Rapel and Maipo rivers, by means of littoral drift and eolical transport (Paskoff
and Manríquez 2004).
Paleoclimatic studies based on the analysis lacustrine sediment cores from
lagoons Matanzas (Jenny et al. 2000; Villa-Martínez 2002) and Colejuda (ValeroGarcés et al. 2010, cited by Fariña et al. 2012) suggest that the evolution of the
wetlands complex has been mostly modeled by changes in eolic sedimentations and
significant variations in precipitations associated to ENSO (El Niño – Southern
Oscillation), which increases in frequency and intensity during the Holocene.
Pollen, sediment, geochemical and chironomid fossils analyses show that 5000–
3300 years ago lagoon Matanzas was a littoral lagoon with moderate to low salinity
conditions (Villa-Martínez 2002). During this period, precipitations had important
fluctuations, showing two rainy intervals, 4900–4800 years ago and 4500–3300 years
ago, separated by an dryer interval 4800–4500 years ago (Villa-Martínez 2002).
From 3300 to 2600 years ago there would have occurred an important increment
in salinity, probably representing a change in the system from a littoral lagoon a
hyper-saline lake (Villa-Martínez 2002). Likely this change would be related with
the closure of lagoon Matanzas basin, some 2600 years ago, due to predominance
of eolic sedimentary processes that formed a dunes chord that presently dam this
system (Fariña et al. 2012; Paskoff and Manríquez 2004; Martínez 2009), and that
is locate immediately to the north of Navidad Formation (Encinas et al. 2006), a
geological formation that attracted great interest from the naturalist Charles Darwin
when he passed by this area in 1834 (Darwin 1846). This consolidated dune (El
Convento), with an extension of over 1000 ha, is one of the most important in the
region (Castro-Avaria 2015). Nowadays, it is difficult to appreciate its extension,
due to the efforts realized during the twentieth century to consolidate its advance by
planting pines and eucalyptus (Albert 1900). These plantations contribute to hide
the presence of the dune.
8 El Yali National Reserve: A System of Coastal Wetlands in the Southern…
El Yali area: two raisings, one sinking followed by a new raising (Noguera 1956),
and a rising associated to the 1985 earth quake (Barrientos and Kausel 1990).
Thus, the development of El Yali and the system it belongs to, obeys to the interaction of several dynamic factors that have determined the geomorphological evolution that the central Chilean coast has experienced during the last 18,000 years
(Fariña et al. 2012).
Marine transgressions occurred during the last glaciation (14,000 years ago) and
during the middle Holocene (6000 years ago) allowed the accumulation of marine
and/or fluviomarine sediment throughout the basin (Fariña et al. 2012). The tectonic
activity expressed in the co-seismic vertical movements that characterized the last
3000 years (Lower Holocene), produced the regional raising of the coast that caused
the emersion of a littoral terrace where is located the wetland. A sign of this process
is gneiss block present to the southwest of the lagoon Colejuda (Contreras-López
et al. 2014).
As result of the coastal raising, a marine regression occurs and initiates the progradation of the coastal line by means of eolic and fluvial sedimentary processes
(Paskoff et al. 2000). The existence of fluvial refills and transgressive and parabolic
dunes in the area indicates that progradation occurred through sedimentary loads
from Rapel and Maipo rivers, by means of littoral drift and eolical transport (Paskoff
and Manríquez 2004).
Paleoclimatic studies based on the analysis lacustrine sediment cores from
lagoons Matanzas (Jenny et al. 2000; Villa-Martínez 2002) and Colejuda (ValeroGarcés et al. 2010, cited by Fariña et al. 2012) suggest that the evolution of the
wetlands complex has been mostly modeled by changes in eolic sedimentations and
significant variations in precipitations associated to ENSO (El Niño – Southern
Oscillation), which increases in frequency and intensity during the Holocene.
Pollen, sediment, geochemical and chironomid fossils analyses show that 5000–
3300 years ago lagoon Matanzas was a littoral lagoon with moderate to low salinity
conditions (Villa-Martínez 2002). During this period, precipitations had important
fluctuations, showing two rainy intervals, 4900–4800 years ago and 4500–3300 years
ago, separated by an dryer interval 4800–4500 years ago (Villa-Martínez 2002).
From 3300 to 2600 years ago there would have occurred an important increment
in salinity, probably representing a change in the system from a littoral lagoon a
hyper-saline lake (Villa-Martínez 2002). Likely this change would be related with
the closure of lagoon Matanzas basin, some 2600 years ago, due to predominance
of eolic sedimentary processes that formed a dunes chord that presently dam this
system (Fariña et al. 2012; Paskoff and Manríquez 2004; Martínez 2009), and that
is locate immediately to the north of Navidad Formation (Encinas et al. 2006), a
geological formation that attracted great interest from the naturalist Charles Darwin
when he passed by this area in 1834 (Darwin 1846). This consolidated dune (El
Convento), with an extension of over 1000 ha, is one of the most important in the
region (Castro-Avaria 2015). Nowadays, it is difficult to appreciate its extension,
due to the efforts realized during the twentieth century to consolidate its advance by
planting pines and eucalyptus (Albert 1900). These plantations contribute to hide
the presence of the dune.
8 El Yali National Reserve: A System of Coastal Wetlands in the Southern…