PosterPDF Available

TYPES OF HYPERPYCNAL FLOWS AND RELATED DEPOSITS IN LACUSTRINE AND MARINE BASINS

Abstract

poster presented in the ISC2018
Carlos Zavala GCS Argentina SRL, Interna 1320, 8000 Bahía Blanca, Argentina.
Departamento de Geología, Universidad Nacional del Sur, San Juan 670, 8000 Bahía Blanca, Argentina.
czavala@gcsargentina.com
INTRODUCTION
A hyperpycnal flow forms when a land derived dense flow (sediment gravity flow) enters a marine
or lacustrine water reservoir. As a consequence of its excess in density, the flow plunges in coastal
areas generating a highly dynamic and often long lived dense underflow. Depending on the charac-
teristics of the parent flow (flow duration and flow type) and basin salinity the resulting deposits
(hyperpycnites) can be very variable.
According to flow duration, hyperpycnal flows can be classified into short lived (SLHF) or long
lived (LLHF) hyperpycnal flows. SLHF lasts for minutes or hours, and are mostly related to small
mountainous river discharges, alluvial fans, collapse of natural dams, landslides, volcanic erup-
tions, jökulhlaups, etc. LLHF last for days, weeks or even months, and are mostly associated to
medium to large size river discharges.
Concerning the characteristics of the incoming flow, hyperpycnal flows can be initiated by
non-Newtonian (cohesive debris flows), Newtonian supercritical (lahars, hyperconcentrated flows,
and concentrated flows) or Newtonian subcritical flows (bedload, sandy or muddy dominated fully
turbulent flows).
Once plunged, non-Newtonian and Newtonian supercritical flows require steep slopes to accelera-
te, allow the incorporation of ambient water and develop flow transformations to evolve into a
turbidity current and travel farter basinward. When advancing on static seawater, the turbidite
flow should necessarily displace backward the ambient water. This results in a flow divergence at
the head, and the generation of a return current that should maintain in suspension all materials
transported by the advancing turbulent flow. This permanent resuspension at head area derives in
an overall excellent grain sorting and a continuous "washing" of the sandy turbulent suspension.
CONCLUSIONS
Hyperpycnal flows can be originated from different
subaerially derived sediment gravity flows.
Cohesive debris flows, hyperconcentrated flows and
concentrated (granular) flows are typical of high gradient
settings (mountainous areas), and related to highly
discontinuous (episodic) events.
• Once in the basin, these high density hyperpycnal flows
require acceleration and entrainment of ambient water to
transform into more diluted flows.
These conditions are only possible in high gradient basin
slopes. The final deposit lack of extrabasinal light
materials like plant remains, wood and charcoal.
Turbulent flows at river mouths can be episodic or long
lived (sustained).
Episodic turbulent flows usually don’t form important
hyperpycnal flow deposits, since these accumulations are
located very close to the littoral delta front.
Sustained turbulent flows can plunge and travel a long
distance along the basin floor, also across near flat basin
areas. Since the entrainment of ambient water is very low,
these flows can transport extrabasinal light materials and
fresh water far from the coast line.
Hyperpycnal flows related to sustained turbulent flows
can be pebbly, sandy or muddy dominated.
REFERENCES
Katz, T., Hinat, H., Eyal, G., Steiner, Z., Braun, Y., Shalev, S., Good-
man-Tchernov, B.N., 2015. Desert flash floods form hyperpycnal flows
in the coral-rich Gulf of Aqaba, Red Sea. Earth Plentary Sci. Lett. 417
417, 87–98.
Mutti, E., 1992. Turbidite sandstones. AGIP - Istituto di Geologia
Università di Parma, 275 pp.
Simpson, J. E., 1987. Gravity currents: In the environment and the
laboratory. John Wiley & Sons, New York, Chichester, Brisbane, and
Toronto. 244 p.
Zavala, C., Arcuri, M., Blanco Valiente, L., 2012a. The importance of
plant remains as a diagnostic criteria for the recognition of ancient
hyperpycnites. Revue de Paléobiologie 11, 457-469.
Zavala, C., and Arcuri, M., 2016. Intrabasinal and Extrabasinal
turbidites: origin and distinctive characteristics. Sedimentary Geology.
DOI: 10.1016/j. sedgeo.2016.03.008.
SUSTAINED TURBULENT FLOWS
Sustained turbulent flows are originated from rivers in flood, with sediment concentrations
higher than 35 kg/m3 (sea water). Depending on their sediment load, sustained hyperpycnal
flows can be classified into pebbly, sandy or muddy dominated.These flows have a slow moving
leading head with low entrainment of ambient water. Consequently, they can transfer a huge
volume of freshwater and continental organics farther basinward. Typical characteristics of
entrabasinal turbidites include (1) complex beds with gradual and recurrent changes in sediment
grain size and sedimentary structures, (2) mixture of extrabasinal & intrabasinal components, (3)
internal and discontinuous erosional surfaces and (4) lofting rhythmites in marine settings.
Sandy dominated hyperpycnal flows are turbulent flows with a suspended load
composed of fine grained sand.
Bedload is possible at proximal positions. In contrast with pebbly dominated
hyperpycnal flows, clasts are made of clay, and are of intrabasinal origin (eroded
from the basin bottom when carving hyperpycnal channels).
Proximal facies include sandstones with cross bedding and aligned
clay clasts, followed downstream by massive, laminated and
rippled sandstones.
Muddy dominated hyperpycnal flows are turbulent flows with a suspended load domi-
nated by the clay-silt fraction. These flows are relatively heavy loaded and commonly eroded
the underlying soupy substrate, incorporating intrabasinal mud and organics.
Proximal deposits display sharp/erosional basal contacts, with rare bedload (flocs) and mud
ripple facies. Since suspended load doesn’t depend on flow velocity, lofting is not possible even
in marine settings.
Muddy hyperpycnites
compose graded beds of silt/clay often showing
abundant plant remains and intrabasinal
components. Upper Jurassic - Lower Cretaceous
Vaca Muerta Formation, Neuquen Basin.
LDTC
LDTC
Newtonian
(fluid flows)
Non
Newtonian
(plastic)
Types of hyperpycnal flows
SLHF
Flow origin Flow evolution & deposit
SUPERCRITICALSUBCRITICAL
TURBULENT LAMINAR
Cohesive debris flows
Short lived hyperpycnal flows
High Density Short Lived Flows
entering the basin (inertia dominated)
Common in Alluvial Fans
Small mountanious rivers
Flash floods
Low Density Long Lived (sustained) Flows
entering the basin (subcritical flows)
Commonly associated to medium to
large size rivers
LOW
HIGH
HIGH
LOW
LOW
LOW
NO
NO
NO
YES
YES
NO
Matrix strength
Buoyancy
Matrix strength
Dispersive pressure
Escaping pore fluid
Dispersive pressure
Escaping pore fluid
Large scale turbulence
Turbulence
(bedload and suspended load)
Turbulence
(bedload and suspended load)
Turbulence
(suspended load)
Sediment
Support
Mechanisms
Entrainment
of ambient
water Lofting
Hyperconcentrated
flows
Concentrated
(granular) flows
Pebbly dominated
Sandy dominated
Muddy dominated
Require steep slopes to accelerate,
incorporate ambient water and transform
into dilute turbidity currents
No steep slopes are necessary. Flow can
travel for long distances since the flow is
sustained by the river discharge
Hyperpycnites
of difficult
differentiation
from
intrabasinal
flow deposits
ENTRAINMENT OF AMBIENT WATER
ENTRAINMENT OF AMBIENT WATER
ENTRAINMENT OF AMBIENT WATER
“Typical”
hyperpycnites
sustained LDTC & bedload
sustained LDTC & bedload (clay clasts)
sustained LDTC (fluid mud flows) Muddy
hyperpycnites
LLHF
Long lived hyperpycnal flows
Local source
time
time
d
d
FP= Flow Plunge FT= Flow Transformation HJ= Hydraulic Jump LDTC= Low Density Turbidity Current
FP ft hj
hj
hj
CDF HCF-GF
HCF-GF
GF
LDTC
LDTC
LDTC
FP
FP
FP
FP
FP
Regional source
Origin and significance of hyperpycnal flows in lacustrine and marine basins
Different flow types of subaerial origin
Characteristics, diagnostic criteria and reservoir significance
2 cm
PLUNGE POINT
PLUNGE POINT
marine / lacustrine basin
marine / lacustrine basin
fall-out of silt / clay
collapse of silt / clay
bedload
deposits
poorly known
muddy bedload
facies
suspended
load deposits
fallout of
clat/silt
(lacustrine)
fallout of
clat/silt
lofting due to
density reversal
(marine basins)
collapse of suspended materials
(sand size)
erosion & dragging
of clay clasts
erosion & bulking of intrabasinal components
continental
continental
SANDY DOMINATED
SUSTAINED HYPERPYCNAL
FLOW
MUDDY DOMINATED
SUSTAINED HYPERPYCNAL
FLOW
PARENT FLOW
PARENT FLOW
FLOW
FLOW
DEPOSITS
DEPOSITS
”TYPICAL” HYPERPYCNITES
MUDDY HYPERPYCNITES
SHF (S)
SHF (M)
S1-S2-S3
B1s-B2s-B3s S4
S4
???
L
Pebbly dominated hyperpycnal flows are turbulent flows with associated bedload,
inherited from the original fluvial discharge. Bedload is possible because of dragging exerted by
the overpassing long-lived turbulent flow. Proximal facies include matrix rich conglomerates,
followed downstream by massive, laminated and rippled sandstones. In marine settings freshwater
can induce buoyancy reversal (lofting).
PLUNGE POINT
marine / lacustrine basin
dragging collapse of silt / clay
bedload
deposits suspended
load deposits
fallout of
clat/silt
(lacustrine)
lofting due to
density reversal
(marine basins)
collapse of suspended materials
(sand size)
continental
PEBBLY DOMINATED
SUSTAINED HYPERPYCNAL
FLOW
PARENT FLOW
FLOW
DEPOSITS
”TYPICAL” HYPERPYCNITES
SHF (B)
S1-S2-S3
B1-B2-B3 S4
L
COHESIVE DEBRIS FLOWS (CDF)
Sediment concentration: > 2050 kg/m3
Due to its muddy matrix, these flows are quite impermeable to entrain new water from the
basin. If the CDF decreases its velocity, it can be “frozen” due to the internal cohesion provided
by the muddy matrix.
PLUNGE POINT
marine / lacustrine basin
acceleration & entrainment of ambient water
LOSS OF
PLANT
MATERIAL
continental
COHESIVE DEBRIS
FLOW
PRIMARY
DEPOSIT
PARENT FLOW
FLOW
DEPOSITS
DEPOSITS THAT RESEMBLE INTRABASINAL TURBIDITES
CDF GFHCF LDTC
hjftft
F7-F9
F4-F6
F2-F3
F1
Primary CDF deposits with coal clasts Guarico Flysch (Eocene, Venezuela)
F1 F1
These flows can result in primary CDF deposit,
or can transform into more diluted flows by
acceleration and entrainment of ambient water
Primary deposits results from cohesive freezing,
and can be recognized by their matrix supported
fabric with extrabasinal components like
charcoal clasts, wood and plant remains.
Primary deposits are usually located in high
gradient settings located close to source areas.
On the contrary, deposits resulting from flow
transformations lack of plant material, and can
resemble those typical of intrabasinal flows.
HYPERCONCENTRATED FLOWS (HCF)
Sediment concentration: between 1600 – 2050 kg/m3
Hyperconcentrated flows are faster and largely more dangerous than cohesive debris flows.
Essentially inertia dominated laminar flow also affected by large scale turbulence.
F2-F3 F4-F6
PLUNGE POINT
marine / lacustrine basin
acceleration & entrainment of ambient water
LOSS OF
PLANT
MATERIAL
HYPERCONCENTRATED
FLOW
continental
PARENT FLOW
FLOW
DEPOSITS
DEPOSITS THAT RESEMBLE INTRABASINAL TURBIDITES
HCF GF LDTC
hj
ft
F7-F9
Hyperconcentrated flows can result in primary coarse grained
poorly sorted deposit, or can transform into more diluted
flows by acceleration and entrainment of ambient water.
Primary deposits can be recognized by extrabasinal
components like charcoal clasts, wood and plant remains.
Their occurrence is typical of high gradient settings, close to
source areas.
CONCENTRATED (GRANULAR) FLOWS
Sediment concentration: between 530 – 1600 kg/m3
PLUNGE POINT
marine / lacustrine basin
acceleration & entrainment of ambient water
residual
deposit
LOSS OF
PLANT
MATERIAL
primary
deposit
continental
GRANULAR FLOW
PARENT FLOW
FLOW
DEPOSITS
DEPOSITS THAT RESEMBLE
INTRABASINAL TURBIDITES
GF GF LDTC
hj
F7-F9
F4-F5 F6
Concentrated (granular) flows usually accumulate massive to laminated coarse grained deposits
(facies F4 – F5) (Mutti, 1992). These flows can transform into more diluted flows by acceleration
and entrainment of ambient water. Primary deposits can be recognized by their coarse grained
and the presence of extrabasinal components like charcoal clasts, wood and plant remains. Their
occurrence is also typical of high gradient settings, located close to source areas.The
transformation between a concentrated (inertia dominated) flow into a low density turbidity
current (gravity dominates) involves an hydraulic jump. The low density flow reworks the residual
coarse grained deposit, resulting in cross bedded coarse grained sandstones (F6).
H2
H1V1
V2
sl/ cl
sl/ cl
ss ss
ss
ss Zone of mixing
with ambient water
(entrainment)
Zone of reincorporation
of coarse mat erials (ss)
into the main flow
ß
Detail of the head of an Intrabasinal turbidite. Note that fine-grained and lighter materials (like plant remains and charcoal clasts) are not reincorporated in the
main flow and will remain in suspension, being derived to the flow tail by the return current (U2). Modified from Simpson, 1987; Zavala et al., 2012.
The coarsest sandy fraction is rein-
corporated into the advancing flow,
while lighter materials will be se-
gregated to the tail. Consequently,
these turbidites cannot transport
land-derived light materials as
charcoal or plant debris for long
distances. Turbidity current depo-
sits derived from flow transforma-
tions are difficult to differentiate
from those related to intrabasinal
turbidites.
Katz et al., 2015
AMBIENT
WATER
... Based on prior work (Middleton and Hampton, 1973;Lowe, 1979;Yuan et al., 2016;Zavala and Arcuri, 2016;Zavala, 2018), the sediment gravity flows in the study area were classified into intrabasinal sediment gravity flows (ISGFs) induced by slope failures and extrabasinal sediment gravity flows (ESGFs) generated by floods. The ISGFs and ESGFs were further classified according to sediment-support mechanisms and rheological properties. ...
... According to Bates (1953), hyperpycnal flow forms at a coast when a denser river plunges below less dense basin waters. Although almost all documented hyperpycnal flows are related to turbidity currents, there is no relationship between hyperpycnal flow and flow rheology (Zavala, 2018). Therefore, the term "cohesive hyperpycnal flow" was proposed to characterize the hyperpycnal flows originating from subaerial debris flows. ...
... Turbulent hyperpycnal flows originate from rivers in floods. The sediments within the flows are supported by turbulence and bedload can exist at the flow bases due to the dragging provided by overpassing turbulent flows (Zavala, 2018). In this study, CSCs, PS2, SINGBSs, and associations of CLSs and PLSs above scours were interpreted to be related to turbulent hyperpycnal flows ( Fig. 6; Table 2). ...
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