Conference PaperPDF Available

"Hydrodynamics of lacustrine hyperpycnal flows: lessons from the Lower Cretaceous Rayoso Formation, Neuquén Basin, Argentina (SKT)" Abstract Book

Authors:

Abstract

A number of flume experiments conducted in the past on sediment-free stream flows allowed to get a precise understanding of the relationships between sedimentary structures and flow velocity for different grain sizes at different water depths. As an example, these experiments showed that a waxing streamflow moving over a substrate composed of unconsolidated fine-grained sand will start generating current ripples followed by planar lamination and finally antidunes. Consequently, a deposit composed of laminated sandstones followed by ripples are commonly interpreted as accumulated by a waning unidirectional current. Nevertheless, the careful analysis of outcrops suggests that these results are of limited application for understanding the hydrodynamics of sediment laden turbulent flows from their deposits. Although massive sandstones (Bouma’s Ta) are very common in the sedimentary record, this sedimentary structure cannot be generated in flumes by streamflows. In recent years a new sets of flume experiments were conducted aimed in studying sediment laden turbulent flow deposits using large tanks of sediment-water mixtures and circular flumes. However, from a technical standpoint it is very difficult to sustain these dilute sediment gravity flows in flume experiments more than few minutes. Consequently, the understanding of the relationships between flow dynamics and sedimentary structures for sustained sediment laden turbulent flows is for far less understood. These limitations of flume experiments make the description and interpretation of fossil sedimentary structures and their relationships a very important tool to get a precise understanding of the hydrodynamics of dilute sediment gravity flows. The excellent exposures of lacustrine fine grained sandstones in the Lower Cretaceous Rayoso Formation constitute a natural laboratory to analyze the significance of gradual vertical and lateral changes between sedimentary structures. Rippled, laminated, massive, and cross bedded fine grained sandstones revealed an origin related to a complex interaction between sedimentation rate, flow velocity and shear stress. Careful observation shows that the ideal vertical sequence for a waning sustained sediment laden turbulent flow with associated bedload is composed of low angle cross bedded sandstones with clay chips, followed by massive to diffuse laminated sandstones with aligned clay clasts, massive sandstones, diffuse laminated sandstones, laminated sandstones and climbing ripples. The passage from cross bedded to diffusely laminated sandstones with clay chips is interpreted as originated by flow unconfinement. The transition from sandstones with clay clasts to massive sandstones is related to a decrease in flow competence associated to a decrease in flow velocity and related shear stress. The transition between massive to laminated sandstones is associated to a decrease in the rate of sediment fallout. Finally, the transition between planar lamination and climbing ripples is related to a decrease in flow velocity. The vertical recurrence of sedimentary structures is interpreted as an indication of fluctuations in the velocity and flow capacity of the long lived parent flow. The existence of flame structures at the base of massive sandstones is interpreted as an indication of an accumulation by a laminar flow generated at the base of a sustained turbulent flow (body transformation).
“Sedimentology to face societal challenges
on risk, resources and record of the past”
Abstract Book
ISBN 978-88-944576-2-9
Session 5.D - New advances in Lacustrine sedimentology
Pingsheng WEI (Research institute of petroleum exploration & development-Northwest
(NWGI), PetroChina, Lanzhou, China); Huaqing LIU (Research institute of petroleum
exploration & development-Northwest (NWGI), PetroChina, Lanzhou, China); Shuxin PAN -
pansx@ petrochina.com.cn (Research institute of petroleum exploration & development-
Northwest (NWGI), PetroChina, Lanzhou, China); Carlos Zavala (Universidad Nacional del
Sur, Buenos Aires, Argentina)
Lacustrine basins are important oil & gas-productive areas of the world. In
recent years, lacustrine sedimentology has made great achievement in term of
source-sink system analysis, shallow-water delta, beachbar, deep-water
sediments, fine-grained deposits, lacustrine carbonate, events deposits, deep
reservoir forming mechanism and seismic sedimentology. Even so, problems
and challenges of the lacustrine sedimentology are widely existed and needed
to carry out innovation. The main idea of this theme is innovation and new
exploration fields of lacustrine deposits. Specific subthemes may be referenced
but not limited to the following eight aspects.
Subthemes:
- The gravity flow of lacustrine basins (hyperpycnal flows, MTDs, debris flow,
sublacustrine landslide, turbidity flow)
-Fine grained deposition and unconventional resources
-Beach and bar of lacustrine basins
-Shallow-water delta
- Lacustrine carbonate, mixed deposits and reservoir
- Modern lacustrine analogues
-Lacustrine hydrodynamics (waves, alongshore currents, bottom currents)and
related sediments
- Other new field of exploration and development
Session 5.D - 1430
Hydrodynamics of lacustrine hyperpycnal flows: lessons from the Lower
Cretaceous Rayoso Formation, Neuquén Basin, Argentina (SKT)
Carlos Zavala (1)
(1) GCS ARGENTINA SRL. UNIVERSIDAD NACIONAL DEL SUR
A number of flume experiments conducted in the past on sediment-free stream flows allowed
to get a precise understanding of the relationships between sedimentary structures and flow
velocity for different grain sizes at different water depths. As an example, these experiments
showed that a waxing streamflow moving over a substrate composed of unconsolidated fine-
grained sand will start generating current ripples followed by planar lamination and finally
antidunes. Consequently, a deposit composed of laminated sandstones followed by ripples
are commonly interpreted as accumulated by a waning unidirectional current. Nevertheless,
the careful analysis of outcrops suggests that these results are of limited application for
understanding the hydrodynamics of sediment laden turbulent flows from their deposits.
Although massive sandstones (Bouma’s Ta) are very common in the sedimentary record,
this sedimentary structure cannot be generated in flumes by streamflows. In recent years a
new sets of flume experiments were conducted aimed in studying sediment laden turbulent
flow deposits using large tanks of sediment-water mixtures and circular flumes. However,
from a technical standpoint it is very difficult to sustain these dilute sediment gravity flows in
flume experiments more than few minutes. Consequently, the understanding of the
relationships between flow dynamics and sedimentary structures for sustained sediment
laden turbulent flows is for far less understood. These limitations of flume experiments make
the description and interpretation of fossil sedimentary structures and their relationships a
very important tool to get a precise understanding of the hydrodynamics of dilute sediment
gravity flows. The excellent exposures of lacustrine fine grained sandstones in the Lower
Cretaceous Rayoso Formation constitute a natural laboratory to analyze the significance of
gradual vertical and lateral changes between sedimentary structures. Rippled, laminated,
massive, and cross bedded fine grained sandstones revealed an origin related to a complex
interaction between sedimentation rate, flow velocity and shear stress. Careful observation
shows that the ideal vertical sequence for a waning sustained sediment laden turbulent flow
with associated bedload is composed of low angle cross bedded sandstones with clay chips,
followed by massive to diffuse laminated sandstones with aligned clay clasts, massive
sandstones, diffuse laminated sandstones, laminated sandstones and climbing ripples. The
passage from cross bedded to diffusely laminated sandstones with clay chips is interpreted
as originated by flow unconfinement. The transition from sandstones with clay clasts to
massive sandstones is related to a decrease in flow competence associated to a decrease
in flow velocity and related shear stress. The transition between massive to laminated
sandstones is associated to a decrease in the rate of sediment fallout. Finally, the transition
between planar lamination and climbing ripples is related to a decrease in flow velocity. The
vertical recurrence of sedimentary structures is interpreted as an indication of fluctuations in
the velocity and flow capacity of the long lived parent flow. The existence of flame structures
at the base of massive sandstones is interpreted as an indication of an accumulation by a
laminar flow generated at the base of a sustained turbulent flow (body transformation).
Our ambition is, as stated in the meeting title,
to dicuss, compare and promote researches able to cope
with the societal changes from the specic perspective
of the Sedimentology and Sedimentary Geology.
We hope to invole in the meeting also scientic
communities that, although not directly focused
on the sedimentology, use reconstruction
of sedimentary processes and of stratigraphic record
as main investigation tools, such as marine geology,
volcanology, extraterrestrila geology, archeology.

Supplementary resource (1)

ResearchGate has not been able to resolve any citations for this publication.
ResearchGate has not been able to resolve any references for this publication.