INVESTIGADORES
SPALLETTI Luis Antonio
artículos
Título:
Variability of continental depositional systems during lowstand sedimentation: an example from the Kimmeridgian of the Neuquén Basin, Argentina.
Autor/es:
SPALLETTI, L.A.; VEIGA, G.D.
Revista:
Latin American Journal of Sedimentology and Basin Analysis
Editorial:
Asociación Argentina de Sedimentología
Referencias:
Año: 2007 vol. 14 p. 85 - 104
ISSN:
1669-7316
Resumen:
Abstract: Several second order lowstand wedges are recognized in the Jurassic-Early Cretaceous
sedimentary record of the backarc Neuquén Basin (central-west Argentina). They are distinguished
by sharp based continental and marginal marine siliciclastic deposits encased in offshore shales.
The Kimmeridgian lowstand wedge was developed slightly after the emergence of the Andean
magmatic arc and the tectonic inversion of previous intrabasinal extensional structures. As a result,
the Neuquén Basin was compartmentalized into three main depocentres characterised by widespread
continental sedimentation under arid to semiarid climatic conditions. A fluvial-dominated system
characterised by systematic downstream changes in architectural style is recognized in the
Northwestern Depocentre. A gravely and sandy bedload fluvial system was developed in the southern
upstream sector, while ticker beds of finer-grained sediments formed in a distal ephemeral fluvial
system prevail in the downstream part of the system. The overall fining upward stacking pattern of
the sedimentary record in the Northwestern Depocentre accompanied by frequent development of
soil horizons and darker deposits suggests a change towards higher accommodation and high
water table emplacement. In the Southwestern and Eastern Depocentres, the sedimentary successions
show a conspicuous internal transition from fluvial ephemeral fluvial systems to aeolian systems.
However, the lowstand deposits of the Eastern Depocentre are characterised by a larger areal
distribution and a thicker record of both the fluvial and the aeolian deposits. Marked changes in
thickness and in the depositional style of the fluvial and aeolian facies associations within the
Southwestern and Eastern depocentres indicate that the sedimentary infill was controlled by
systematic variations in accommodation. Low accommodation conditions favoured a high degree of
lateral migration of fluvial channels with substantial erosion of fine-grained deposits and the
development of sinuous-crested aeolian dunes typically associated with wet interdune deposits.
Under higher accommodation conditions the fluvial deposits show a retrogradational stacking with
preservation of thick packages of fine-grained sediments, while a large sand sea characterised by
amalgamation of dune deposits was developed in the aeolian-dominated uppermost successions.
The detailed analysis of the Kimmeridgian lowstand wedge of the Neuquén Basin illustrates how
facies and stratigraphic organisation responded to regional and temporal changes in basin
configuration, accommodation, sediment supply and water table position. The Kimmeridgian
lowstand deposits are geographically distributed as the subsequent transgressive deposits and
reveal no major basinward shift during the early stages of sequence stacking. However, they show
a much more complicated facies distribution. Consequently, the lowstand wedge deposits better
reflect the complex interplay of episodic local tectonism, siliciclastic source area variation and
climatic change.Several second order lowstand wedges are recognized in the Jurassic-Early Cretaceous
sedimentary record of the backarc Neuquén Basin (central-west Argentina). They are distinguished
by sharp based continental and marginal marine siliciclastic deposits encased in offshore shales.
The Kimmeridgian lowstand wedge was developed slightly after the emergence of the Andean
magmatic arc and the tectonic inversion of previous intrabasinal extensional structures. As a result,
the Neuquén Basin was compartmentalized into three main depocentres characterised by widespread
continental sedimentation under arid to semiarid climatic conditions. A fluvial-dominated system
characterised by systematic downstream changes in architectural style is recognized in the
Northwestern Depocentre. A gravely and sandy bedload fluvial system was developed in the southern
upstream sector, while ticker beds of finer-grained sediments formed in a distal ephemeral fluvial
system prevail in the downstream part of the system. The overall fining upward stacking pattern of
the sedimentary record in the Northwestern Depocentre accompanied by frequent development of
soil horizons and darker deposits suggests a change towards higher accommodation and high
water table emplacement. In the Southwestern and Eastern Depocentres, the sedimentary successions
show a conspicuous internal transition from fluvial ephemeral fluvial systems to aeolian systems.
However, the lowstand deposits of the Eastern Depocentre are characterised by a larger areal
distribution and a thicker record of both the fluvial and the aeolian deposits. Marked changes in
thickness and in the depositional style of the fluvial and aeolian facies associations within the
Southwestern and Eastern depocentres indicate that the sedimentary infill was controlled by
systematic variations in accommodation. Low accommodation conditions favoured a high degree of
lateral migration of fluvial channels with substantial erosion of fine-grained deposits and the
development of sinuous-crested aeolian dunes typically associated with wet interdune deposits.
Under higher accommodation conditions the fluvial deposits show a retrogradational stacking with
preservation of thick packages of fine-grained sediments, while a large sand sea characterised by
amalgamation of dune deposits was developed in the aeolian-dominated uppermost successions.
The detailed analysis of the Kimmeridgian lowstand wedge of the Neuquén Basin illustrates how
facies and stratigraphic organisation responded to regional and temporal changes in basin
configuration, accommodation, sediment supply and water table position. The Kimmeridgian
lowstand deposits are geographically distributed as the subsequent transgressive deposits and
reveal no major basinward shift during the early stages of sequence stacking. However, they show
a much more complicated facies distribution. Consequently, the lowstand wedge deposits better
reflect the complex interplay of episodic local tectonism, siliciclastic source area variation and
climatic change.