DOLOMITE CEMENTATION IN A TIDALLY INFLUENCED SYSTEM: THE UPPERMOST AGRIO FORMATION, NEUQUÉN BASIN, ARGENTINA

COMERIO MARCOS; PAZOS PABLO JOSÉ; FERNÁDEZ DIANA ELIZABETH; TINEO DAVID; SIAL ALCIDES NÓBREGA

Puerto Madryn

Conferencia; 9TH INTERNATIONAL CONFERENCE ON TIDAL SEDIMENTOLOGY; 2015

CENPAT - AAS

The Lower Cretaceous Agrio Formation was defined by Weaver (1931) and it represents the last extensive transgression from the palaeo-Pacific ocean which spread throughout almost the entire Neuquén Basin (Fig. 1a). The Upper Hauterivian?Lower Barremian, mixed siliciclastic-carbonate ramp system, known as the Agua de la Mula Member (Leanza & Hugo, 2001) provides excellent exposures of tidal deposits associated with dolomitic beds (Fig. 1b). These beds exhibit in many cases diagnostic features which permit their identification in the field; they form major erosion-resistant ledges and are characterized by red to brown weathering color (sensu Munsell color system). In such cases they contrast incolor with the interbedded light gray to pale yellow fine-grained sandstones, pale olive to dark gray illitic-rich mudstones and pale yellow to grayish brown bioclastic to oolitic wackestones, packstones and grainstones.Even though dolomite-rich beds (up to 75 %by weight of dolomite) related to intertidal and subtidal facies were previously well described in the uppermost part of the studied succession at Mina La Continental area (Tunik et al., 2009), no geochemical information was provided. In this work we present some data about the isotopic signatures (δ18O and δ13C) from dolomitic beds of this interval, present not only in outcrops proximal to Mina La Continental (e.g. Cerro Rayoso), but also at Bajada del Agrio, Agua de la Mula, Mina San Eduardo as well as at Loma La Torre localities (Fig. 1a). Previous works in the uppermost part of the Agua de la Mula Member at Bajada del Agrio (Fernández & Pazos, 2012) and Cerro Rayoso areas (Pazos et al., 2012) have documented the interplay between normal marine to marginal marine siliciclastic-carbonate deposits. At Bajada del Agrio, the uppermost 65 m show five main facies, from wave-influenced deposits: (1) oolitic-skeletal bar; (2) transgressive pelites and coquinas (bioclastic conglomerates); (3) progradational coarsening-upward sandstones, interpreted as subaqueous fluvial discharges in the way of hyperpycnal flows; to tide-dominated ones:(4) heterolithic deposits with IHS and channelized bodies; and (5) heterolithic and carbonatic deposits (Fernández & Pazos, 2012).