INVESTIGADORES
LESCANO Marina Aurora
congresos y reuniones científicas
Título:
HIGH-RESOLUTION CYCLOSTRATIGRAPHY ANALYSIS FROM A TlTHONlAN ALTERNATING MARL-LIMESTONES SUCCESSION VACA MUERTA FOMATION, NEUQUEN BASIN, MENDOZA, ARGENTINA
Autor/es:
PALMA, R.; CHIVELET, M.; LOPEZ GOMEZ, J.; CONCHEYRO, A.; LESCANO, M.
Lugar:
Hammamet (Tunisia)
Reunión:
Congreso; FIFTH INTERNATIONAL SYMPOSIUM OF IGCP 506; 2008
Institución organizadora:
Faculty of Sdenoes of Bizerte (FSB) Faculty of Saenoes of Tunis (FST)
Resumen:
The Neuquen back-arc Basin is located on the west margin of South
American platform between latitude of 36O and 40° S. The basin is worldwide
famous for its continuous sedimentary from the Late Triassic to Cenozoic record
comprising continental and marine clastic, carbonate and evaporitic deposits
which are up to 2,600 m in thickness. The Tithonian-Valanginian deposits are
represented by the Vaca Muerta Formation, which is widely distributed over all
the Neuquen Basin, and consists of dark bituminous shales, marls and
limestones cycles, which have been recently become the focus of a regarding
interpretation of the cycles as responses to Milankovitchian influences.
Preliminary results of cyclostratigraphy based on sedirnentological and
biostratigraphical studies on a well exposed Tithonian Vaca Muerta outcrops of
three selected sections (Loncoche Creek, Salado River, and Quebrada
Amarilla) suggest that the whole section developed during a time-interval
spanning from the Lower Tithonian (Virgatosphinctes mendozanus) to the
Upper Tithonian (Substeueroceras koeneni Zone). Nevertheless, the
recognition of detailed studies of ammonite biostratigraphy from the Salado
River section (184 m) shows lower Upper Tithonain (Corongoceras alternas
Zone) up to Upper Tithonian (Substeueroceras koeneni). The three sections are
characterized by a cmldm scale alternation of limestones and marls. From the
beginning of Tithonian, beds in the Quebrada Amarilla shows no signs of fauna1
mixing and seems to be stratigraphically complete, but it represents a
stratigraphical condensed section in relationships with another studies
successions (Loncoche Creek, and Salado River). The nannofossil assemblage
is typical for the Upper Jurassic that include Cyclagelosphaera deflandrei, C.
margerelii, Diazomatolithus lehmanii, D. galicianus, Watzanueria barnesiae, W.
britannica, W. fossacincta, W. ovata, Zeughrabdotus embergerii, and Z. erectus.
Polycostella beckmanii, a Jurassic reliable marker has been also found.
Spectral analysis of the Tithonian succession reveals the same signal for the
studies outcrops. In the Salado River section (184 m), the couplet thickness
varies between 6 and 78 cm, at a rate of 24 rnlMa. The detected periodicities
are 147 ka, 118 ka, 102 ka, 54 ka, 48 ka, 36 ka, 20 ka, and 22 ka. The
Loncoche section (154 m) the couplet thickness varies between 8 and 81 cm, at
a rate of 96 m1Ma. The detected periodicities are 398 ka, 127 ka, 91 ka, 78 ka,
34 ka, 18 ka and 22 ka. The Quebrada Amarilla section (89m) the couplet
thickness varies between 5 and 45 cm, at a rate of 17m IMa. The detected
periodicities are 77 ka, 58 ka, 44 ka, 14 ka, and 23 ka. The results of the
spectral analysis are strong indications that the Vaca Muerta succession in the
Neuquen Basin was deposited under the influence of climatic changes induced
by the orbital parameters. The peaks of 398 ka, 147 ka and 102 ka are related
to eccentricity to the earth orbit. The peaks of 77 ka, 58 ka, 44 ka and 46 ka
could be ascribed to the obliquity of the earth axis. The peaks of 22 ka, 18 ka,
ka 23 ka, and 14 ka cycles are very close to them obtained from the precession
values.