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Tithonian stratigraphy and ammonite fauna of the Vaca Muerta Formation in Mallín Quemado (Neuquén Basin, Argentina), with remarks on the Andean chronostratigraphy

Garrido A. C., Parent H, Brambilla L.

Volumina Jurassica

2018

Vol. 16, no 1

1--26

In the Cerro Mallín Quemado area (Sierra de la Vaca Muerta) the three members of the Vaca Muerta Formation (Portada Covunco, Los Catutos and Pichi Moncol) can be recognized, including the whole of the Tithonian rock-record. The ammonite fauna does not show significant differences with respect to that of the nearby locality Pampa Tril, but the record of faunal horizons is patchier. Eighteen species of ammonites were recorded through the studied sections, covering the whole of the Andean Tithonian. The current chronostratigraphic zonation of the Andean Tithonian is briefly discussed, updated and correlated with the most recent literature. From the current succession of ammonite bio-horizons previously defined in the basin, only three (picunleufuense alpha, picunleufuense beta and falculatum) were recognized definitely. Four other bio-horizons (perlaevis, erinoides, internispinosum alpha and vetustum) were recognized only tentatively, because the typical assemblages of morphotypes (morpho-species) were not clearly or completely recognized. The current regional time-correlation chart dated by the ammonite bio-horizons of the Neuquén Basin along a 70°W transect is updated with the results of the present study and additional information recently obtained from other localities

Additional Tithonian and Berriasian ammonites from the Vaca Muerta Formation in Pampa Tril, Neuquén Basin, Argentina

Parent H., Schweigert G., Scherzinger A., Garrido A. C.

Volumina Jurassica

2017

Vol. 15, no 1

139--154

The ammonite fauna of the Tithonian–Berriasian of the Vaca Muerta Formation in Pampa Tril has been recently described in detail. New important specimens and additional information are presented in this paper. The phyletic evolution of Choicensisphinctes, passing from C. platyconus to C. erinoides is confirmed, as well as the sexual dimorphic correspondence of this latter with C. mendozanus. A microconch of the genus Krantziceras is described for the first time. New specimens of Substeueroceras koeneni identical to the paralec¬totype, along with material already described from the koeneni Hz. (Koeneni Zone), point to the fixation of this horizon as the type horizon of the species. New specimens of Subthurmannia boissieri from the Damesi Zone match clearly the range of variation of this species in Spain, thus providing an element for time-correlation with the Tethyan standard scale. Additional material from the internispinosum alpha Hz. confirms the origin of W. internispinosum from C. proximus by the inception of an evolutionary innovation in the juvenile ontogeny.

Towards a consistent Oxfordian/Kimmeridgian global boundary: current state of knowledge

Wierzbowski A., Atrops F., Grabowski J., Hounslow M., Matyja B. A., Olóriz F., Page K., Parent H., Rogov M. A., Schweigert G., Villaseñor A. B., Wierzbowski H., Wright J. K.

Volumina Jurassica

2016

Vol. 14, no. 1

15--49

New data are presented in relation to the worldwide definition of the Oxfordian/Kimmeridgian boundary, i.e. the base of the Kimmeridgian Stage. This data, mostly acquired in the past decade, supports the 2006 proposal to make the uniform boundary of the stages in the Flodigarry section at Staffin Bay on the Isle of Skye, northern Scotland. This boundary is based on the Subboreal-Boreal ammonite successions, and it is distinguished by the Pictonia flodigarriensis horizon at the base of the Subboreal Baylei Zone, and which corresponds precisely to the base of the Boreal Bauhini Zone. The boundary lies in the 0.16 m interval (1.24–1.08 m) below bed 36 in sections F6 at Flodigarry and it is thus proposed as the GSSP for the Oxfordian/ Kimmeridgian boundary. This boundary is recognized also by other stratigraphical data – palaeontological, geochemical and palaeomagnetic (including its well documented position close to the boundary between magnetozones F3n, and F3r which is placed in the 0.20 m interval – 1.28 m to 1.48 m below bed 36 – the latter corresponding to marine magnetic anomaly M26r). The boundary is clearly recognizable also in other sections of the Subboreal and Boreal areas discussed in the study, including southern England, Pomerania and the Peri-Baltic Syneclise, Russian Platform, Northern Central Siberia, Franz-Josef Land, Barents Sea and Norwegian Sea. It can be recognized also in the Submediterranean-Mediterranean areas of Europe and Asia where it correlates with the boundary between the Hypselum and the Bimmamatum ammonite zones. The changes in ammonite faunas at the boundary of these ammonite zones – mostly of ammonites of the families Aspidoceratidae and Oppeliidae – also enables the recognition of the boundary in the Tethyan and Indo-Pacific areas – such as the central part of the Americas (Cuba, Mexico), southern America, and southern parts of Asia. The climatic and environmental changes near to the Oxfordian/Kimmeridgian boundary discussed in the study relate mostly to the European areas. They show that very unstable environments at the end of the Oxfordian were subsequently replaced by more stable conditions representing a generally warming trend during the earliest Kimmeridgian. The definition of the boundary between the Oxfordian and Kimmeridgian as given in this study results in its wide correlation potential and means that it can be recognized in the different marine successions of the World.