CIG   05423
CENTRO DE INVESTIGACIONES GEOLOGICAS
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
High-frequency carbonate-siliciclastic interactions in siliciclastic-dominated systems: distinguishing between coeval and reciprocal sedimentation in a Lower Cretaceous epeiric sea.
Autor/es:
SCHWARZ, E.; VEIGA, G. Y SPALLETTI, L.
Lugar:
Houston
Reunión:
Congreso; 2014 AAPG Annual Convention and Exhibition; 2014
Institución organizadora:
American Association of Petroleum Geologists
Resumen:
The presence of carbonate strata within siliciclastic‐dominated marine successions poses
serious challenges for palaeoenvironmental reconstructions and reservoir characterization,
and unambiguous interpretations can emerge only when the spatial vs. temporal relationship
between carbonate production and siliciclastic input is well understood. This study documents
high‐frequency sequences (probably of 4th‐5th order) formed during Greenhouse conditions
(Hauterivian) and Transitional/Icehouse conditions (Valanginian) in the epeiric sea of the
Neuquén Basin, which were investigated across outcrop and subsurface transects parallel to
depositional dip.
Hauterivian high‐frequency sequences (< 25 m thick) comprise coarsening‐upward successions
from offshore siliciclastic mudstones and siltstones with storm‐related beds, passing into
lower‐shoreface bioturbated sandstones. Cross‐bedded mixed deposits are capping the
successions, and both biogenic (bivalve‐dominated) and non‐biogenic (ooids) carbonate grains
are common. These high‐frequency sequences, bounded by flooding surfaces, represent
mostly normal regressive conditions during low‐amplitude, likely eustatically‐controlled,
relative sea‐level changes. Coeval sedimentation occurred in the upper‐shoreface setting, but
carbonate shedding was negligible basinward.
Valanginian high‐frequency sequences, though similar in scale and duration, have a different
internal architecture. Carbonate‐dominated strata are bounded by erosional surfaces, they
have a wider range of facies (ooid grainstones to skeletal wackestones), and commonly show a
retrogradational staking. Carbonate packages are overlain by shallowing‐upward, pure
siliciclastics successions, comprising from offshore mudstones to shoreface cross‐bedded
sandstones. Carbonate and siliciclastic packages represent contrasting depositional systems
and reciprocal sedimentation. A carbonate‐dominated ramp developed during transgressive
conditions, whereas deltas and associated shoreface system formed during progradational
(highstand) conditions. Eustatic‐based, sea‐level changes alone cannot explain these highfrequency
cycles. In addition, severe intracyclic climate changes from arid (carbonates) to
humid (siliciclastics) phases could have trailed sea‐level rises and highstand conditions,
respectively. Glacial‐interglacial climatic shifts are common in icehouse conditions, and could
have taken place in the relatively cold Valanginian period.