Multi-scale influence of topography on depositional architecture of long-term transgressive successions (Jurassic, Neuquén Basin, Argentina)

POYATOS-MORÉ, M.; SCHWARZ, E.; BOYA, S.; GOMIS-CARTESIO, L.; MIDTKANDAL, I.

Congreso; 35th International Meeting of Sedimentology; 2019

IAS

Shallow-marine successions deposited during long-term transgressions are considered to develop relatively thin and well-sorted deposits. Thick transgressive successions are rarely preserved in the stratigraphic record, although a few examples are described in subsurface and outcrop studies of rift basins. In these settings, reworking by active shelf processes and biogenic activity often result in partial or complete destruction of primary sedimentary structures; bed boundaries and geometries might become homogenized, and stacking patterns and stratigraphic sequences more difficult to define. In this study, an outcrop example from the Lower-Middle Jurassic of northern Neuquén Basin (Argentina) is presented, with the aim to a) refine the depositional model of a longterm transgressive succession in an early post-rift setting; and b) to constrain controls on stratigraphic architecture and lateral facies variability, and their response to postdepositional processes. To do this, a 10 km continuous exposure, with detailed mapping, sedimentary logging and physical correlation of stratigraphic units, integrated with subsurface, biostratigraphic and ichnological data. The succession shows an overall retrogradational fining-upward development, with severalminor order regressive units. The lower part of the succession comprises laterallydiscontinuous (10´s m-long), coarse-grained transitional deposits, dominated by 10´s m-thick coarsening-up packages and discrete m-scale erosive conglomeratic lenses, interpreted asmouth-bars and distributary channel-fills. Above these, the middle and upper parts of thesuccession cover the entire length of the outcrop (>4.5 km) and thicken gradually southwards, although subsurface data reveals a fault-controlled, limited regional extension.They comprise laterally-continuous (>100´s m-long) fine-grained shallow-marine deposits, dominated by