Orbital calibration of the early Tithonian ? early Valanginian in the Neuquén Basin

KIETZMANN, D.A.; PALMA, R.M

MALARGÜE

Simposio; VI SIMPOSIO ARGENTINO DEL JURÁSICO; 2016

A floatingorbital scale from 10 stratigraphic sections of the early Tithonian ? early ValanginianVaca Muerta Formation has been constructed from the southern Mendoza area of the NeuquénBasin. The Vaca Muerta Formation is characterized by decimetre-scale rhythmic alternations of marls, shales and limestones, showing a well-ordered hierarchy of cycles withinthe Milankovitch frequencyband (elementary cycles,bundles and superbundles). According to biostratigraphic data, elementary cycles have a periodicity of ~21 ky, which correlates with the precession cycle of Earth?s axis. A time series was built from the thickness of elementary cycles, and corrected by removingeustatic-generated trends,in order to isolate the orbital signal. Spectralanalysis based on Blackman-Tukey method allows us to identifyfrequencies of ~90-120 ky and ~400 ky, which we interpret as the modulation of the precessional cycle by the Earth?s orbital eccentricity. The floatingorbital scale was constructed by high and low frequencyeccentricity cycles, and tied to the international time scale at the base of the Windhauseniceras internispinosum andNeocomites wichmanni Zones, where there is largest agreementon the biostratigraphy. We obtainedthe following correlation of ammonitezones: 1) The Virgatosphinctes mendozanus Zone is probably locatedat the base of the middle Tithonian(upper part of the Semiformeto FallauxiStandard Zone), but the inconsistency with paleomagneticdata would suggest anolder age. 2) The Pseudolissoceras zittelli andAulacosphinctes proximus Zones correlateswith the middle Tithonian Fallauxi to Ponti Standard Zones. 3) The Windhauseniceras internispinosum Zone would be located at the base of the upper TithonianMicrocanthum Standard Zone.4) The Corongoceras alternansZone coincideswith the upper Tithonian(Microcanthum Standard Zone and lower part of the Durangites Standard Zone).5) The Substeueroceras koeneni Zone wouldcorrelate with the Durangites Standard Zone and thelower part of the Occitanica Standard Zone. 6) The Argentiniceras noduliferum Zonecorrelates with the upper part of the Occitanica Standard Zone, and the Spiticeras damesi Zone correlates withthe Boissieri StandardZone.