CIG   05423
CENTRO DE INVESTIGACIONES GEOLOGICAS
Unidad Ejecutora - UE
artículos
Título:
Sharp-based marine sandstone bodies in the Mulichinco Formation (Lower Cretaceous), Neuquén Basin, Argentina: remnants of transgressive offshore sand ridges
Autor/es:
SCHWARZ, E.
Revista:
SEDIMENTOLOGY
Editorial:
WILEY-BLACKWELL PUBLISHING, INC
Referencias:
Lugar: Oxford; Año: 2012 vol. 59 p. 1478 - 1508
ISSN:
0037-0746
Resumen:
The interpretation of sharp-based shallow-marine sandstone bodies encased in offshore mudstones, particularly transgressive units, has been a subject of recent debate. This contribution provides a multiple-dataset approach and new identification criteria which could help in the recognition of transgressive offshore sandstone bodies world-wide. This study integrates sedimentology, ichnology, taphonomy and palaeoecology of Mulichinco Formation strata in central Neuquén Basin (Argentina) in order to describe and interpret sharp-based sandstone bodies developed in ramp-type marine settings. These bodies are sandwiched between finer grained siliciclastics beneath and thin carbonates above. The underlying sediments comprise progradational successions from offshore mudstones to offshore-transition muddy sandstones, occasionally grading into lower-shoreface sandstones. The surfaces capping the regressive siliciclastics are flat and regionally extensive, and are demarcated by skeletal concentrations and a Glossifungites suite. They are also marked by sandstone rip-up clasts, with incrustations and borings in all sides. These surfaces are interpreted as composite discontinuities, cut during a relative sea-level fall and remodelled during the initial transgression. The overlying transgressive sandstone bodies are 3 to 7 m thick, > 4 km long and about three times longer than wide. They are composed of fine-grained sandstones with little lateral change in grain-size. Cross-stratification and/or cross-lamination are common, typically with smaller-scale structures and finer grain size towards the top. Large-scale, low-angle (5 to 8°) inclined stratification is also common, deeping at ~ 30° with respect to body elongation and dominant currents. These sandstone bodies are interpreted as offshore sand ridges, probably developed under the influence of tidal currents. Intense burrowing is typical at the top of each unit, suggesting an abandonment stage. Final deactivation favoured colonization by epibenthic-dominated communities and the formation of skeletal-rich limestones during the latest transgressive conditions. As partial reworking of pre-existing ridges occurred during this stage, the Mulichinco sandstone bodies are considered the remnants of transgressive offshore sand units. OI: 10.1111/j.1365-3091.2011.01314.x.