INVESTIGADORES
MELCHOR Ricardo Nestor
artículos
Título:
Changing lake dynamics and sequence stratigraphy of synrift lacustrine strata in a half-graben: an example from the Triassic IschigualastoVilla Unio´n Basin, Argentina
Autor/es:
RICARDO NESTOR MELCHOR
Revista:
SEDIMENTOLOGY
Editorial:
Blackwell Publishing Ltd.
Referencias:
Lugar: Oxford; Año: 2007 vol. 54 p. 1417 - 1446
ISSN:
0037-0746
Resumen:
Well-exposed Triassic rift strata from the IschigualastoVilla Unio´n Basin
(NW Argentina) include a 80 to ca 515 m thick lacustrine-dominated
package that can be correlated across a half-graben using key stratigraphic
surfaces (sequence boundaries, lacustrine flooding surfaces and forced
regressive surfaces). The characteristics of the synrift lacustrine fill in
different parts of the half-graben have been examined and the mechanisms
controlling sedimentation inferred. A variety of sedimentary environments
are recognized including; volcaniclastic floodplain, mildly saline lake and
playa lake, offshore lacustrine, delta front to fluvial-dominated and wavedominated
deltas, distributary and fluvial channel, and interdistributary
bay. The succession can be divided into four stratigraphic sequences (SS1 to
SS4), the oldest of which (SS1) contains volcaniclastic, fluvial and saline
lake deposits; it is thickest close to the western border fault zone, reflecting
more rapid subsidence here. Accommodation exceeded sediment and water
input during SS1. The second and third sequences (SS2 and SS3) mark the
onset of widespread lacustrine sedimentation, reflecting a balance between
accommodation creation and water and sediment fluxes. Sequences SS2 and
SS3 are represented by offshore meromictic lacustrine and deltaic deposits,
the latter mostly sourced from the flexural and southern axial margins of the
half-graben. The presence of stacked parasequences bound by lacustrine
flooding surfaces is related to climatically induced lake-level fluctuations
superimposed on variable rates of subsidence on the controlling rift border
fault zone. The youngest sequence (SS4) is represented by the deposits of
littoral lacustrine and shallow shelf deltas distinguished by a change in
lithofacies, palaeocurrents and sandstone composition, suggesting a switch
in sediment supply to the footwall margin to the NW. The change in the
sediment source is related to reduced footwall uplift, the possible presence
of a relay ramp and/or supply from a captured antecedent drainage network.
During SS4, the rate of creation of accommodation was exceeded by the
sediment and water discharge. The stratigraphic evolution of lacustrine
strata in the half-graben was mainly controlled by tectonic processes,
including subsidence rate and the growth and evolution of the border
fault zone, but changing climate (inducing changes in water balance and
lake level) and autocyclic processes (delta lobe switching) were also
important.ca 515 m thick lacustrine-dominated
package that can be correlated across a half-graben using key stratigraphic
surfaces (sequence boundaries, lacustrine flooding surfaces and forced
regressive surfaces). The characteristics of the synrift lacustrine fill in
different parts of the half-graben have been examined and the mechanisms
controlling sedimentation inferred. A variety of sedimentary environments
are recognized including; volcaniclastic floodplain, mildly saline lake and
playa lake, offshore lacustrine, delta front to fluvial-dominated and wavedominated
deltas, distributary and fluvial channel, and interdistributary
bay. The succession can be divided into four stratigraphic sequences (SS1 to
SS4), the oldest of which (SS1) contains volcaniclastic, fluvial and saline
lake deposits; it is thickest close to the western border fault zone, reflecting
more rapid subsidence here. Accommodation exceeded sediment and water
input during SS1. The second and third sequences (SS2 and SS3) mark the
onset of widespread lacustrine sedimentation, reflecting a balance between
accommodation creation and water and sediment fluxes. Sequences SS2 and
SS3 are represented by offshore meromictic lacustrine and deltaic deposits,
the latter mostly sourced from the flexural and southern axial margins of the
half-graben. The presence of stacked parasequences bound by lacustrine
flooding surfaces is related to climatically induced lake-level fluctuations
superimposed on variable rates of subsidence on the controlling rift border
fault zone. The youngest sequence (SS4) is represented by the deposits of
littoral lacustrine and shallow shelf deltas distinguished by a change in
lithofacies, palaeocurrents and sandstone composition, suggesting a switch
in sediment supply to the footwall margin to the NW. The change in the
sediment source is related to reduced footwall uplift, the possible presence
of a relay ramp and/or supply from a captured antecedent drainage network.
During SS4, the rate of creation of accommodation was exceeded by the
sediment and water discharge. The stratigraphic evolution of lacustrine
strata in the half-graben was mainly controlled by tectonic processes,
including subsidence rate and the growth and evolution of the border
fault zone, but changing climate (inducing changes in water balance and
lake level) and autocyclic processes (delta lobe switching) were also
important.