Data: 2014-06-30 03:00 PM
Orador/Formador: Dr. Nicolas Waldmann
Local: IPMA Algês Lisboa
Contacto email: info@ipma.pt
Contacto telefónico: 214770000
A multi-proxy approach combining seismic reflection profiling and detailed analyses of long
sedimentary cores retrieved from Lago Fagnano, southernmost South America, allowed addressing
questions regarding past regional environmental changes. More than 800 km of geophysical survey,
combining simultaneously high-resolution 3.5 kHz (pinger) single-channel and 1 in3 airgun
multi-channel systems, allowed visualizing both the most recent lacustrine sediments and oldest
deposits, respectively. The concepts of seismic sequence stratigraphy were applied to the
sedimentary infill to reconstruct past environmental conditions. The combination of geophysical
data from the lacustrine basin with geomorphological studies allowed assigning a sequence of
subaquatic moraines within Lago Fagnano seismic stratigraphy. During the Last Glacial Maxima, the
Fagnano glacier occupied the lake basin spreading through three different lobes and reaching a
maximum length of ~130 km. A set of submerged frontal moraines covered by lacustrine infilling
identified in the seismic survey suggests occasional eastward re-advances of the paleo-glacier
within the overall westward deglaciation pattern. Radiocarbon dating permitted estimation of
sedimentation rate providing an indirect age for one of these intervals of glacier re-advance. This
major glacier advance seems to be synchronous with the Antarctic Cold Reversal (ACR) and was
probably more severe in magnitude in this region than the Northern Hemisphere Younger Dryas
Chronozone (YDC). The combined geophysical, sedimentological and geochemical record of Lago Fagnano
revealed recurrent mass wasting events during the entire Holocene. The spatial and temporal
distribution of twenty-two megaturbidite events was catalogued within the lake.
Simultaneously-triggered basin-wide lateral slope failure and formation of megaturbidites are
interpreted as fingerprints of paleo-seismicity along the MFT fault zone. The proposed age model
revealed an 800-1000 years recurrence of slope failure and megaturbidite formation. These results
provide unique data about the frequency and plausible magnitude of Holocene earthquakes in Tierra
del Fuego. Hence, this first record of past slope failure in Lago Fagnano is a corner-stone for
further studies related to geohazards in Tierra del Fuego. - CV de Dr. Nicolas Waldmann