Geochemistry and petrology of a Middle Tithonian limestone-marl rhythmite in the Neuquén Basin, Argentina: depositional and burial history

Abstract

The Middle Tithonian Los Catutos Member (Vaca Muerta Formation, Neuqu6n Basin), is lithologically and geochemically similar to limestone-marl alternations from the Late Jurassic of the northern hemisphere. Both marls and limestones are pelbiomicrites and biopelmicrites principally composed of pellets, radiolaria, forams, ostracods, equinoids, spicules of sponges and gastropods, cemented by several generations of calcite cement. Smectite and interlayers are the major epiclastic components of the fraction below 2 Ixm, reflecting pedogenic processes developed on volcanogenic source rocks. More abundant kaolinite in some marls reflects stronger humid conditions in the source area and enhanced terrigenous supply. A1203 content is demonstrated to be a reliable indicator of clastic input. The same is not true for silica, often related to high biogenic productivity of siliceous organisms. Rocks show total organic carbon (TOC) contents up to 1.95% and constitute regular to good sources for hydrocarbons, although thermally immature. Rhythmites formed gently sloping mounds accumulated in a distal submarine ramp under low-energy and poorly oxygenated open-sea conditions. Sedimentation rates were high due to high productivity on the sea surface, and supply of terrigenous and carbonate sediments transported by suspension plumes originated in shallow, photic areas. 613C values correspond well with the published curves for the Tithonian sea water and with other records from Tethyan limestones. A preliminary analysis of negative excursions of 613C point to a productivity crisis or a mixture of water layers in a stratified sea with a periodicity of 400 ka, which could be a result of changes in the orbital eccentricity of the Earth. Light isotopic composition of O in bulk rocks is the result of diagenetic neomorphism and cement precipitation. Calculated palaeotemperatures from 61Sc are consistent with those derived from measured vitrinite reflectance (Ro%) and burial history reconstruction. Data indicate initial burial during the Tithonian extending up to the Lower Cretaceous, a short period of uplift (Intravalaginian tectonic phase), and renewed uplift during the Cenomanian followed by significant Late Cretaceous sedimentation and Pliocene thrusting.

Sclerobionts, Shell Morphology and Biostratinomy on Ammonites: Two Early Cretaceous Cases From the Neuquén Basin, Argentina

“…En los alrededores de Zapala, dentro de esta unidad se reconoce el Miembro Los Catutos, compuesto por calizas bioclásticas, micríticas y peloidales que han sido interpretadas por Scasso et al (2005) como ritmitas (calizas y margas) que se habrían depositado en profundidades de agua entre los 30 y 50 metros. Este miembro muestra condiciones de somerización respecto a los depósitos de la base o un fuerte cambio climático que habría inhibido el aporte clástico .…”

Sedimentology and stratigraphy of the Vaca Muerta Formation in the Cerro Domuyo area, Northern Neuquén, Argentina.

“…La Formación Vaca Muerta se caracteriza por la alternancia rítmica de margas, lutitas y calizas, que constituyen un sistema de rampa homoclinal dominado por facies de rampa externa (Spalletti et al, 2000;Scasso et al, 2002Scasso et al, , 2005Kietzmann et al, 2008;Kietzmann y Palma, 2009a), organizado en varias secuencias depositacionales cuyas facies proximales progradan hacia el oeste (e.g., Mitchum y Uliana, 1985;Legarreta y Gulisano, 1989). Sin embargo, en el margen occidental de la cuenca, se intercalan depósitos arenosos relacionados con flujos gravitatorios y remoción en masa con paleocorrientes opuestas (Miembro Huncal) que dejan en evidencia la clara asimetría de la cuenca sedimentaria (Leanza et al, 2003;Spalletti et al, 2008).…”

“…Sin embargo, los conocimientos sedimentológicos son aún de carácter general, con excepción de los estudios realizados en el sur de la cuenca (Spalletti et al, 2000(Spalletti et al, , 2008Scasso et al, 2002Scasso et al, , 2005 y el sector surmendocino (Doyle et al, 2005;Kietzmann et al, 2008Kietzmann et al, , 2011Kietzmann y Palma, 2009a).…”

Coastal Holocene carbonates of Abu Dhabi, UAE: depositional setting, sediment distribution, and role of cyanobacteria in micritization

“…Any ancient carbonate grain can be expected to have sat on the sea floor exposed to potential of infestation by blue-green algae and to develop a consequent alteration of their surface to micrite (F€ ursich et al, 1992;Scasso et al, 2005;Caron et al, 2005;Boyd, 2007). Surprisingly, many shallow-water carbonate grains preserved in the geological record do not have such envelopes.…”