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Growing evidence suggests that land generated sediment gravity flows are the most important source of clastic sediments into marine and lacustrine sedimentary basins. These sediments are mostly transferred from source areas during exceptional river discharges (river floods). During floods rivers discharge a sediment-water mixture having a bulk density that often exceeds that of the water in the receiving water body. Consequently, when these flows enter a marine or lacustrine basin they plunge and move basinward as a land-derived underflow or hyperpycnal flow. Depending on the grain-size of suspended materials, hyperpycnal flows can be muddy or sandy. Sandy hyperpycnal flows also can carry bedload resulting in sandy to gravel composite beds with sharp to gradual internal facies changes laterally associated with lofting rhythmites. Lofting occurs because flow density reversal due to the buoyant effect of freshwater when a waning turbulent flow loses part of the sandy load. On the contrary, muddy hyperpycnal flows are loaded by a turbulent suspension of silt and clay. Since the concentration of silt and clay don’t decrease with flow velocity, muddy hyperpycnal flows will be not affected by lofting and the flow will remain attached to the sea bottom until its final deposition. The last characteristics commonly result in cm-thick graded shales disposed over an erosive base with dispersed plant debris and displaced marine microfossils. Deposits related to hyperpycnal flows are hyperpycnites. Although hyperpycnites display typical and diagnostic characteristics that allow a clear recognition, these deposits are often misinterpreted in the literature as Sandy debrites, shoreface, estuarine of fluvial deposits. The correct identification and interpretation of hyperpycnites provides a new frontier for the understanding and prediction of conventional and unconventional reservoirs.
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2018 ZAVALA C,et al.Hyperpycnal flows and hyperpycnites: Origin and distinctive characteristics 1
ZAVALA C,et al.Hyperpycnal flows and hyperpycnites: Origin and distinctive characteristics
AuthorCZAVALA Carlos(1964-)PhD,Professor of National University of the SouthArgentina. Chairman of the Geological Society of Argen-
tina and consultant of several national oil companies in South America. Address: (B800JUF3) Calle Interna 1320,Bahía Blanca,Bue-
nos Aires,Argentina.
Articl ID1673-8926201801-0001-27 DOI10.3969/j.issn.1673-8926.2018.01.001
Cite ZAVALA CPAN S X. Hyperpycnal flows and hyperpycnitesOrigin and distinctive characteristics. Litho-
logic Reservoirs20183011-27.
Hyperpycnal flows and hyperpycnitesOrigin and distinctive characteristics
ZAVALA Carlos1,2PAN Shuxin3
1.GCS Argentina SRL. Interna 1320Bahía Blanca B800 JUF3Argentina
2.Departamento de GeologíaUniversidad Nacional del SurSan Juan 670Bahía Blanca B800 JUF3Argentina;
3.Research Institute of Petroleum Exploration & Development-Northwest, PetroChina, Lanzhou 730020, China
AbstractGrowing evidence suggests that land generated sediment gravity flows are the most important source
of clastic sediments into marine and lacustrine sedimentary basins. These sediments are mostly transferred from
source areas during exceptional river discharges (river floods). During floods rivers discharge a sediment-water
mixture having a bulk density that often exceeds that of the water in the receiving water body. Consequently,
when these flows enter a marine or lacustrine basin they plunge and move basinward as a land-derived underflow
or hyperpycnal flow. Depending on the grain-size of suspended materials, hyperpycnal flows can be muddy or
sandy. Sandy hyperpycnal flows also can carry bedload resulting in sandy to gravel composite beds with sharp to
gradual internal facies changes laterally associated with lofting rhythmites. Lofting occurs because flow density
reversal due to the buoyant effect of freshwater when a waning turbulent flow loses part of the sandy load. On the
contrary, muddy hyperpycnal flows are loaded by a turbulent suspension of silt and clay. Since the concentration
of silt and clay dont decrease with flow velocity, muddy hyperpycnal flows will be not affected by lofting and
the flow will remain attached to the sea bottom until its final deposition. The last characteristics commonly result
in cm-thick graded shales disposed over an erosive base with dispersed plant debris and displaced marine micro-
fossils. Deposits related to hyperpycnal flows are hyperpycnites. Although hyperpycnites display typical and diag-
nostic characteristics that allow a clear recognition, these deposits are often misinterpreted in the literature as san-
dy debrites, shoreface, estuarine of fluvial deposits. The correct identification and interpretation of hyperpycnites
provides a new frontier for the understanding and prediction of conventional and unconventional reservoirs.
Key wordshyperpycnal flowshyperpycnitesdeep water sedimentaryturbulent flow
Rivers are far the main responsible of transfer-
ring sediments from producing areas to the basin. Ac-
cording to Syvitski et al.2003present rivers trans-
fer to the ocean about 25 GT/year of sedimentsthis
is more than 90% of the total sediment influx from ter-
restrial sources. The river mouth was historically con-
sidered the zone where most terrigenous sediments ac-
cumulatedue to the drastic deceleration and loss of
confinement of these stream flows when reaching the
coast. Neverthelessgrowing evidences demonstrate
that a lot of sediments can bypass this coastal area
during river floodsallowing the transfer of a huge
volume of sediments hundreds of kilometers basin-
ward. This situation is possible because most rivers at
least once a year Mulder & Syvitski1995dis-
charge a mixture of water and sediments having a
bulk density that exceeds that of the receiving water
body hyperpycnal flows since Bates 1953. As a
consequencefluvial discharges plunge in coastal ar-
eas and travel basinward as fluvial derived sediment
gravity flows. The volume of sediments transferred in
each flow can be enormous. Mulder et al. 2003
shown that during a single hyperpycnal discharge of
the Var River that lasts 18 hoursthe volume of sedi-
ments transferred to the marine was equivalent to that
transported in 20 years under normal conditions. Con-
sequentlyonly a limited fraction of the sediments is
retained in the littoral areas since most of the sedi-
ment are transported to the shelf and deeper areas dur-
ing periodical floods.
This change in paradigm has important conse-
quences for the sedimentology and reservoir signifi-
cance of shelfal and deep marine/lacustrine systems
since predicts the existenceand allows the explana-
tion of the occurrence of sandstone depositschan-
nels and lobeslocated far from the coast line not re-
lated to a sea/lake level fall.
The study of 230 actual fluvial systems revealed
that most rivers84%produce periodical hyperpyc-
nal dischargesMulder & Chapron2011in their as-
sociated marine basins. These data strongly suggest
that hyperpycnal flow deposits hyperpycnites
should be very common in recent and ancient succes-
sions. Neverthelessthe occurrence of recent and an-
cient hyperpycnites are poorly quoted in the geologi-
cal literature. Probablya large number of hyperpyc-
nal deposits do exist in the geological recordand
have been wrongly interpreted as estuarinefluvial
deltaiclittoral delta front and delta plain),storm
tempestiteshoreface and sandy debrite deposits.
1 Hyperpycnal flows
Bates1953introduced a rational classification
of deltasconsidering the relationship between the
density of the incoming flowriver discharge Drre-
spect to that of the receiving water bodylake or sea
Dw. BasicallyBates recognized three categories
termed Hypopycnal flowHomopycnal flow and Hy-
perpycnal flowFig. 1.
A Hypopycnal flowFig. 1 Aforms when the
river discharge is less dense respect to the density of
the reservoir water Dr<Dw. In this situation the
stream flow experienced a rapid deceleration and loss
of confinement at the river mouthwith the conse-
quent accumulation of the coarser grained fractions in
coastal areasforming mouth bars. Freshwatersus-
pended fine grained materialssilt/clayand plant re-
mains form a buoyant plume that can extend some dis-
tance from the coastline. The collapse of these materi-
als compose a fine grained prodelta. The typical result
of hypopycnal flows are marine and eventually lacus-
trine littoral deltas. The shape of these littoral deltas
will be controlled by the existence of not of diffusion
processes at the coastwave or tidesresulting in
fluvialwave or tidal dominated deltassee the popu-
lar classification of Galloway1975.
Homopycnal flowFig. 1 Bcorresponds to the
situation when the incoming flow has a similar densi-
ty respect to that of the receiving water bodyDr=
Dw. In this particular case all the sediment fractions
carried-up by the fluvial stream rapidly collapse at the
river mouth. In rivers having coarse grained bedload
this results in steep-gradient deltasGilbert-type del-
tasdominated by debris fallsavalanches. The ho-
mopycnal condition is almost exclusive of sediment-
free bedload dominated stream flows entering fresh-
water lakes.
Figure 1Classification of deltas according to Bates
1953considering the relationship between the
density of the incoming flowriver discharge or Dr
respect to that of the receiving water bodylake or sea
or Dw. AHypopycnal flowDr<Dw. B
Homopycnal flowDr=Dw. CHyperpycnal flowDr>
2018 ZAVALA C,et al.Hyperpycnal flows and hyperpycnites: Origin and distinctive characteristics 3
A hyperpycnal flowFig. 1 Coccurs when the
density of the incoming flow is higher than that of the
water in the reservoir Dr>Dw. In delta systems
this situation originated when a subaerial systemi.e.
a riverdischarges a mixture of water and sediment
having a bulk density which is greater than that of the
receiving water body. In the case of the marine envi-
ronmenta concentration of 35-45 kg/m3of suspend-
ed sediment is required in the fluvial discharge to
overcome the density contrast with sea waterMulder
and Syvitski1995. On freshwater lakeshyperpyc-
nal flows are very commonsince only 1 kg/m3of
suspended sediment is required in the incoming flow
to went hyperpycnalTab. 1. When this situation oc-
cursthe fluvial discharge sinks below the sea water
forming a hyperpycnal flow Bates1953which
can travel considerable distances carrying large vol-
umes of sediment directly supplied from a river in
flood. A hyperpycnal flow can be a sediment gravity
flowbut not all sediment gravity flows are hyperpyc-
nal flows. A subaqueous sediment gravity flow can
only be considered as hyperpycnalfrom the Greek
ὑπέρ hypermeaning "over"pycnal = density
from Greekπυκνόςpuknosmeaning "dense"if it
was originated in the continent. This is because the
hyperpycnal condition is achieved at the coastac-
cording to the density contrast between incoming and
receiving fluids. Consequentlysediment gravity
flows generated within the basinas the case of mass-
transport complexesintrabasinal turbiditestempes-
titescascaditesand turbulent flows derived from
convective instabilityParsons et al.2001should
not be considered true hyperpycnal flows.
Table 1Critical sediment concentration in fluvial inflows required to produce a hyperpycnal flow in marine and lacustrine
basins. After Mulder and Syvitski1995. Density differences of sea water are related to latitudinal variations.
Hyperpycnal flows originated from a river dis-
charge are characterized by a turbulent suspension
with interstitial freshwater. When this relatively dens-
er fluvial discharge plunges in coastal areasthe re-
sulting downward flowhyperpycnal flowinduces a
downwelling in surface reservoir watersprogressive-
ly avoiding the formation of buoyanthypopycnal
plumesFig. 1 C. Consequentlyduring a hyperpyc-
nal dischargefreshwater and other relatively light
materials originally transported within the fluvial dis-
chargelike plant debrisleavestrunks and char-
coalare forced to sink and to travel basinward with-
in the hyperpycnal discharge.
Depending on the duration of the relatively
dense subaerial dischargea hyperpycnal flow can be
episodic or sustainedlong lived. An episodic hyper-
pycnal flow usually last few hours and commonly de-
velops in fan- delta settings with steep gradients and
small catchment areas. Since these hyperpycnal dis-
charges are relatively highly concentrated and short
livedthese deposits commonly have a limited distri-
bution in the associated basin. In high gradient delta
slopes they can also trigger intrabasinal sediment
gravity flows. Their deposits could be very variable
depending on the original density of the incoming
flowcohesive debris flowhyperconcentrated flow
turbulent flowand their possible evolution into intra-
basinal turbidites. According to their higher rele-
vancethis paper will be focused only in sustained
long livedhyperpycnal flows and their deposits.
2 Sustained hyperpycnal flows
Hyperpycnal discharges associated to medium to
large-sized rivers can last for weeks or even months
depending on climate and the size and shape of the as-
sociated fluvial drainage area. These last characteris-
tics results in turbidity currents that will be very dif-
ferent compared to those associated to intrabasinal
Critical concentration
required to produce a
hyperpycnal flow
Sea water
Fresh water
sediment gravity flows. Fig.2 summarizes the main
characteristics of long livedsustainedhyperpycnal
flows. These characteristics include
An origin related to a direct fluvial discharge
which is often characterized by long lived flows with
fluctuating changes in velocity and concentration.
Common occurrence of associated bedload pro-
cessescarrying terrestrial and basinal eroded compo-
nentswith shear provided by the passing- by long
lived hyperpycnal flow.
A turbulent flow having a light interstitial fluid
freshwatertogether with other light components in
suspensionlike plant remnantsleavestrunksetc.
Figure 2Main characteristics of long-lived hyperpycnal flows and their typical depositsFrom Zavala et al.2008 a
Zavala et al.2011. The complexity of these flows results in the accumulation of composite bedsZavala et al.2007.
Sustained hyperpycnal flows consist of three dis-
tinctive partsthe plunge regionthe main bodyand
the leading headKassem & Imran2001. In con-
trary to intrabasinal turbidity currentssustained hy-
perpycnal flows have a slow moving and non-erosion-
al leading- headZavala et al.2011Zavala & Ar-
curi 2016and main erosion and deposition occurs in
the flow body instead of the flow headDe Rooij &
Dalziel2001Peakall et al.2001Zavala et al.
2006 aZavala et al.2011. Field observations of re-
cent and ancient hyperpycnal deposits indicate that
some fine hyperpycnites are composed of an inverse-
ly gradedwaxing flowbasal unitfollowed in tran-
sition by a normally gradedwaning flowunitMul-
der & Alexander2001Mulder et al.2003Zavala
et al.2006 a. The inversely graded interval is accu-
mulated at the flow headand commonly starts with
climbing ripplesZavala et al.2006 asuggesting a
flow speed smaller than 0.2 m/s for the advancing
leading head. Nakajima2006described hyperpyc-
nites in the central Japan Sea 700 km away from the
Toyama Bay. This author estimates a flow speed of
0.3 m/s and a hyperpycnal discharge lasting for about
3 or 4 weeks to achieve the indicated distance.
As a consequence of the low interaction of the
flow head with ambient watershyperpycnal flows
can transport freshwater and plant debrisif anyfor
long distances basinwardFig. 2as long as the river
discharge is maintainedPrior et al.1987Zavala et
al.2011. This fact is supported by an increasing
number of direct measurements and observations that
revealed that the original freshwater supplied by a sus-
tained river discharge and its associated content of ter-
restrial light materials can travel long distances with-
out substantial mixing with ambient waters. As an ex-
ampleJohnson et al.2001see also Farnsworth
2000reported over 12 yrthe direct association be-
tween extreme turbidity activity in the Monterrey Sub-
marine Canyon and largest flood events in the nearby
Salinas RiverCalifornia. These hyperpycnal flows
were studied at different research stationslocated be-
tween 5.2 and 22 km far from the river mouthand
water depths ranging between 230 and 1170 meters.
The studied hyperpycnal flows are characterized by
fresher and warmer water that extended to depths be-
low 1000 mcarrying substantial amount of terrestri-
al organic carbonBaudin et al.2010. A large tur-
bidity current in the Zaire submarine valley at
4000 meters and 330 km seaward of the Congo River
mouth was registered by Khripounoff et al.2003
composed of warm and turbulent flows with veloci-
ties exceeding the 121.4 cm/s. This discharge lasted
2018 ZAVALA C,et al.Hyperpycnal flows and hyperpycnites: Origin and distinctive characteristics 5
for about 10 daysand transported basinward large
amounts of fine 0.15 to 0.2 mmquartz sand and
large plants debriswoodleavesand roots. These
hyperpycnal flows were probably related to flooding
episodes in the Congo RiverSavoye et al.2009
since they correlate with submarine cable breaks
across the canyonHeezen et al.1964. More re-
cently Kao et al. 2010observed at 180 km off
southwestern Taiwan an anomalously warm and low
salinity turbid water current at 30003700 m depths
immediately after Typhoon Morakot in 2009thus
proven the ability of freshwater to travel long distanc-
es during hyperpycnal events. The direct input of
freshwaters meteoric- watersin deep- water turbi-
dites via hyperpycnal flows has also being proposed
by Mansurbeg et al.2006for the formation of ka-
olinite owing to the dissolution of detrital silicates in
the ShetlandFaroes Basin on the British continental
shelf. Recently Gwiazda et al. 2015documented
the presence of the pesticide DDT in recent sediments
from the Monterey Submarine Canyon located in wa-
ter depths deeper than 3000 meters. These chemicals
were transported up to 250 km basinward from the
present canyon head during hyperpycnal discharges
of the Salinas and Pajaro Rivers. Since DDT was only
applied on land in California between 1944 and
1972the presence of this pesticide suggests not only
the activity of the Monterrey Fan during the present
Highstandbut also the ability of hyperpycnal flows
to transport extrabasinal elements like DDT and
freshwaterfor long distances with limited mixing
with ambient waters.
Main key points to understand why freshwater
and plant debris can achieve such a long distances
probably reside in athe slow moving headcom-
pared with the velocity along the main bodywhich
prevent the development of strong turbulence vortices
and substantial mixing with basin watersblofting
processes at flow head and flow lateralsespecially
in marine settingswhich avoid the reincorporation
of the lifted-up water and sedimentsand cthe con-
tinuous fluvial dischargewhich supply the energy to
maintain turbulence and flow velocity for long dis-
3 Hyperpycnal flow depositshyper-
A hyperpycniteMulder et al.2003is the de-
posit of a hyperpycnal flow. Hyperpycnites are basi-
cally extrabasinal turbidites having distinctive and at
present poorly known facies characteristics Zavala
and Arcuri 2016. Its origin is closely related to a di-
rect fluvial dischargeMutti et al.1996and results
in facies types and depositional features that often re-
semble those considered as typical of fluvial environ-
mentsbedloadmeandering etc.but commonly as-
sociated with clear marine and lacustrine indicators.
The transfer and accumulation of a huge volume of
continental sediments during a single long-lived flood
frequently results in confusing facies types from a
conventional point of view. The resulting clastic sedi-
mentary bodies can be biostratigraphically sterile or
can display a wide range of water depth indicators.
Very thick hyperpycnites often lack or show rare and
very specific trace fossils favoring the confusion of
these strata with estuarine deposits. As for every sedi-
ment gravity flowthe location and thickness of
coarse grained hyperpycnal sedimentary bodies are
very sensitive to the contemporaneous subaqueous to-
pographyoften resulting in the accumulation of very
thick laminated or structureless sandstone bodies of
difficult interpretation using non- hyperpycnal facies
This complex scenario of multiple interaction be-
tween intra and extrabasinal elements results in depo-
sitional bodies of difficult interpretation according to
conventional facies models. Commonly sedimentolo-
gists feel lost when dealing with these depositsand
are forced to assign conventional depositional envi-
ronments supported on weak an inconsistent evidence
i.e the interpretation of thick fine grained massive
sandstones as estuarine or shoreface deposits.
Key points to unravel the characteristics and
complexity of hyperpycnal flow deposits reside in the
understanding the main processes that govern the
movement of sustained hyperpycnal flows. Sustained
hyperpycnal flows are fully turbulent flowswith a
relatively bulk density provided by denser suspended
particlesbasically fine- grained sandsilt and clay.
The relative proportions of these elements in the tur-
bulent suspension could be highly variableand will
result in the accumulation very different facies associ-
ations. Coarse grained materials could not be support-
ed by turbulence at the velocities commonly achieved
by sustained hyperpycnal flowsbut can be dragged
at the base as bedload by shear forces provided by the
passing- by flow. Finallyin the case of marine ba-
sinsthe buoyant effect of the freshwater transported
within the hyperpycnal discharge can induce the den-
sity reversalloftingof the flow when part of the
suspended load is loss by deposition. These three ele-
ments will result in typical facies categories that will
give important information about1position of the
studied section respect to the whole systemproximal
and lateral indexes2system dimensions and ex-
pected facies changesreservoir predictionand 3
salinity of the basin.
The characteristics above discussed result in the
accumulation of three main facies families related to
the three main elements that govern the movement of
almost all sustained hyperpycnal discharges in marine
settingsbedloadsuspended load and loftingFig.
3. These facies categories are here termed as Bbed-
load related sedimentary faciesSsuspended-load
related sedimentary faciesand Llofting related sed-
imentary facies.
Figure 3Main sedimentary processes and related facies
families originated during hyperpycnal discharges with
associated bedload in marine basins.From Zavala et al.
2006 bZavala2008Zavala et al.2011.
Each facies family is in turn composed of indi-
vidual facies types differentiated according to some
distinctive internal characteristics. The proposed fa-
cies tract is shown in Fig. 4and their constituting fa-
cies will be discussed in detail along the following
pages. All the hyperpycnal flow- related sedimentary
facies recognized in this paper resulted from changes
in flow competence and flow capacity as the hyperpy-
cnal flow wanes during its travel basinwardlong dis-
tanceand towards the flow lateralsshort distance.
Competence refers to the large size clast that a flow
can carrywhereas capacity concerns to the total vol-
ume of carried sediment. These facies types display
distinguishing and characteristic depositional features
that often easily allow to diagnose the hyperpycnal or-
igin of the deposits. In the following sectionmain
typical characteristics of facies related to bedload
suspended load and lofting processes will be dis-
Figure 4Genetic facies tract for the analysis of sustained
hyperpycnites with associated bed load. AFacies
association along the depositional system. BLateral facies
changes towards flow margins. Modified after Zavala &
3. 1 Facies related to bedload processes facies
Type Bbedload relatedfacies family includes
a broad spectrum of coarse grained deposits accumu-
lated by the join occurrence of1shear/drag forces
exerted by the overpassing long- lived turbulenthy-
2018 ZAVALA C,et al.Hyperpycnal flows and hyperpycnites: Origin and distinctive characteristics 7
perpycnalflow over coarse grained materials carried
as bedloadand2partial fallout of fine-grained sus-
pended load trapped at the rising flow bottom. As a
consequencethe texture of hyperpycnal bedload de-
posits are essentially bimodalreflecting the join ac-
cumulation of sediments related to these two domi-
nant processesbedload and suspended load. The ac-
cumulation of facies B type deposits is associated to a
change in flow competencesince the flow progres-
sively losses its ability of transporting large clasts as
saltationsliding and rolling. Since rolling is influ-
enced by clast shapewell rounded clasts often can
travel longer distances independently of the individu-
al clast size. A direct consequence of rolling is imbri-
cationsince during rolling non spherical clasts tend
to rest in a stable positionFig. 5. Imbrication sug-
gests that large clasts were free to move and rotate at
the base of an overpassing non- cohesive turbulent
flow. Consequentlythe recognition of clast imbrica-
tion in these deposits is very important because pro-
vides a diagnostic criterion for the recognition of flu-
idnon- cohesiveflows. Large clasts are probably
transported by sliding and rolling whereas the finest
materials composing the matrix would correspond to
suspended load materials trapped at the low velocity
and relatively high concentrated basal zoneManville
and White2003. The occurrence of large clasts
floatingin a sandy matrix is therefore a conse-
quence of a combination of basal grain-to-grain inter-
action and hindered settling grain supporting mecha-
nismsand should not be wrongly interpreted as an
evidence of flow cohesioni.e. sandy debris flow or
sandy debrites of Shanmugam & Moiola1995
Shanmugam 2008. Sandy debris flow deposits were
interpreted as accumulated from sediment gravity
flows characterized by a plastic rheology and a lami-
nar statewhere deposition occurs in masse
through cohesive freezingShanmugam 2016. This
last proposed mechanism cannot adequately explain
clast imbrication and the well sorted fine grained san-
dy matrix of somesandy debritessee pag. 30
5052 and also Fig. 19 of Shanmugam 2016. Ac-
cording to these evidencesis here interpreted that
thesandy debritesrecognized in the Triassic of the
Ordos Basin in ChinaLi et al.2011Zou et al.
2012probably correspond to bedload facies devel-
oped at the base of sustained turbulenthyperpycnal
Figure 5The occurrence of bedload at the base of
sustained turbulent flows often results in bimodal deposits
composed of aligned and imbricated large clasts floating in
a matrix of fine to medium grained massive sandstones.
Coarse grained particles transported as bedload
can be extrabasinal mostly composed of rounded
and well-rounded pebbles and gravelsintra or extra-
basinal clay chips and clay clasts),intrabasinal
fragments of mollusks and other lacustrine or marine
body fossilsor a mixture thereof. The existence of
extrabasinal components in B facies suggests that bed-
load was probably inherited from the original subaeri-
al fluvial discharge.
Three main categories of bedload facies are rec-
ognizedZavala et al.2011termed B1B2 and
B3Fig. 4. In the case of sandy successions with the
exclusive occurrence of clay claststhese categories
are named B1 sB2 s and B3 sFig. 4.
3.1.1 Facies B1
Facies B1 is composed of massive and crudely
stratified conglomerates with abundant medium to
fine- grained sandstone matrix. Largest clasts appear
floatingin the sandy matrix or imbricated follow-
ing diffuse subhorizontal alignments facies B1
Figs. 6 A and 6 B. The overall texture is matrix sup-
portedalthough some varieties of clast supported
conglomerates are recognized facies B1 cFig. 6
C. Depending on the energy and duration of the asso-
ciated fluvial dischargethe deposits can show nor-
malinverse or internal complex vertical changes in
grain size. Field relationships suggest that a vertical
evolution between facies B1 c and B1 Fig. 6 C
could be related to a progressive decrease of drag
forces exerted by the overpassing turbulent flow. In
systems that lack coarse grained clasticsB1 facies
could be entirely composed of matrix or clast support-
ed clay clastsfacies B1 sFig. 6 D.
Figure 6Field examples of B1 facies. A & BExample of facies B1 in Eocene deep water deposits from the Pampatar
FormationMargarita IslandVenezuela. Note the fine grained matrix and clast imbricationi. CClast supported
conglomeratesfacies B1 cin shelfal turbidites from the Jurassic Los Molles FormationNeuquén BasinArgentina. D
Conglomerates composed of clay clastsfacies B1 sfloating in a fine grained sandy matrix. Jurassic Los Molles Formation
Neuquén BasinArgentina.
3.1.2 Facies B2
Facies B2 is composed of sandstonespebbly
sandstonesand fine-grained conglomerates with low
angle asymptotic cross stratification. This type of
cross bedding forms at the base of a sustained turbu-
lent flow with sand-size suspended loadand shows
several distinguishing characteristics respect to that
formed at the base of sediment-free streamflowsor
open channelsthe last very common in subaerial
fluvialenvironments. Streamflow dunesor grain-
flow dunesFig. 7 Aare characterized by high an-
gle foresets with flow separation. Flow separation pro-
vokes a zone of hydraulicshadowimmediately af-
ter the brink pointFig. 7 Awith no surficial cur-
rents. This hydraulic shadow forces coarse grained
materials transported as bedload along the stoss side
to accumulateresulting in the generation of repeated
gravitational avalanches at the lee side. Gravitational
avalanches are inertia flows that accumulates longitu-
dinally graded laminasFig. 8 A. In consequence
cross bedded sets originated from sediment-free flows
are characterized by an overall fining upward trend
Fig. 7 Ewith sharp and high angle basal boundar-
iesoften erosional. Grainfall dunesFig. 7 Bon
the contraryare formed by flow expansion. Flow ex-
pansion at the foreset provokes a gradual decrease in
flow velocity with the consequent collapse of sus-
pended materialsfine grained sandstonesalong the
2018 ZAVALA C,et al.Hyperpycnal flows and hyperpycnites: Origin and distinctive characteristics 9
lee side. This sediment fallout along the dune front re-
sults in asymptotic cross beddingFigs. 8 A-Doften
accompanied with abundant plant remainsand small
clay chipsat the lower foreset Figs. 8 B & 8 D.
Asymptotic cross beddings typically compose thicken-
ing and coarsening upward successionsFigs. 7 B
8 B & 8 Cresulting from the dominance of suspend-
ed load at the lower foreset and bedload in the upper
foresetFig. 7 B.
Figure 7Main differences between cross bedding generat-
ed at the base of a streamflow Agrainflow dunesre-
spect to that originated at the base of a sustained turbulent
flow with abundant sand- sized suspended materials B
grainfall dunes.
Large clasts in facies B2 often appear floating in
a medium to coarse grained sandstone matrixFig.
8 Calong foreset laminas that in general does not ex-
ceed 20 degrees in inclination. Depending on the rate
of sediment fallout from the overpassing turbulent
flowbedset bounding surfaces can be erosionallike
an anisotropic hummocky cross stratificationor tran-
sitionalforming climbing dunes in the sense of
Mutti et al.1996.
Field observations suggest a close association of
this facies with channel fill deposits. In gravel- free
systemsfacies B2 is almost entirely composed of
medium to coarse grained sandstonesFigs. 8 B &
8 Doften displaying abundant clay clasts and plant
remains in the lower foreset. This sandstone variety
of facies B2 is termed facies B2 sFig. 5. If clay
clasts are numerous and of small sizethis structure
can easily be confused with a tidal bundle. The key
for a correct interpretation resides in differentiating
the small clay clasts from a true mud couplet. Like fa-
cies B2facies B2 s relate to the migration of straight
or sinuous bedforms at the base of a long lived turbu-
lent flow carrying high suspended load.
Figure 8Field and core examples of facies B2. A & D
Low angle asymptotic cross bedding in deep water deposits
the Pampatar Formation Margarita IslandVenezuela.
Note in D the abundant clay chips draping the foresets. B
Core exampledaylight and UVof asymptotic cross bed-
ding in shallow marine channels from the Lower Creta-
ceous of the West Siberian BasinRussia. Note the coars-
ening upward grain size and the abundant plant remains in
the lower foreset. CAsymptotic cross bedding in Pleisto-
cene coarse grained lacustrine deposits of the Hua-
renchenque FormationNeuquén BasinArgentina. Note
the coarsening upward trend. EContrasting example
showing a cross bedding related to a subaerial streamflow
fluvial deposits. Note the abrupt basal boundary and the
fining upward trend. Huarenchenque Formation
Neuquén BasinArgentina.
3.1.3 Facies B3
Facies B3 is characterized by medium-grained to
pebbly sandstones with diffuse horizontal to subhori-
zontal stratification and levels of small aligned peb-
blesFigs. 9 A & 9 B. Pebbles appear dispersed or
aligned often showing imbrication. From a textural
viewpointthis facies is characterized by a strongly
bimodal grain- size distributionwith large clasts
floatingon a sandy matrix. These characteristics re-
flect simultaneous deposition of small and large parti-
cles by two distinct mechanismsiaccretion of the
sandy matrix from a turbulent suspension as the flow
loses capacityandiiprogressive emplacement of
pebbles as the flow loses the competence to roll them.
The sandy variety of this faciesfacies B3 sis char-
acterized by aligned clay clasts Fig. 9 C9 D &
9 Ecommonly associated with plant fragments. Fa-
cies B3 composes tabular to lenticular bodies often
filling erosive depressions. It is interpreted that these
facies accumulated by the combined effect of bedload
and the gravitational segregation of sandstone materi-
als transported by turbulence in the overpassing hy-
perpycnal turbulent flow. In shallow water settings
B3 facies may display low angle diverging and trun-
cated laminae which closely resemble gravelly hum-
mocky cross stratification facies B3 h in Fig. 4.
Mutti et al.1994suggested that subaerially-derived
gravity flows may develop an internal oscillatory
component during their downslope travelling through
the setting in motion of standing bodies of water in
the shallower parts of receiving water bodies.
3. 2 Facies related to the collapse of suspended
load facies S
The S facies family is mostly fine grainedfine
grained sandstone & siltstone. It is composed of sedi-
ments transported as suspended load within a sus-
tained turbulent flow and accumulated by a gradual
gravitational collapse as the flow wanes and loses
flow capacity. These deposits often form thick and in-
ternally complex beds that can be massive or charac-
terized by traction plus fallout sedimentary structures.
3.2.1 Facies S1
Facies S1 is one of the most common facies with-
in the facies tract of hyperpycnal systems. This facies
composed tabular fine to medium grained massive
sandstone bedsFig. 10. These sandstones usually
integrate monotonous and very thick successions in-
ternally showing subtle and gradual grain-size varia-
tionsFig. 10 D. Small floating clay chips are com-
mon and could appear dispersed within the sandstone
body or grouped towards the top of the bed Fig.
10 Bclose to the boundary with facies related to
more diluted flows facies S2. Carbonaceous re-
mainscharcoal Fig. 10 Fand woody fragments
are also common within massive sandsoften display-
ing entire leafs with exceptional preservation Fig.
10E. Leaves in massive sands can be very abundant
and have been proposed as the main source of hydro-
carbons in the Kutei BasinIndonesiaSaller et al.
2006. S1 facies mostly lack any kind of bioturba-
tion. Neverthelesssome massivevery thick inter-
vals show isolated Ophiomorpha Fig. 10 Cand
Thalassinoideswhich can be related to crustaceans
Figure 9Field and core examples of facies B3. According
to the presence offloatingclaststhis facies has been
wrongly interpreted as related to sandy debris flowssandy
debrites. APebbly sandstones with aligned pebbles
showing imbrication. The last suggests the join occurrence
of bedload and suspended load in aggrading beds.
Pleistocene lacustrine deposits of the Huarenchenque
FormationNeuquen BasinArgentina. BPebbly
sandstones with imbricated pebbles. Eocene deep water
deposits of the Pampatar FormationMargarita Island
Venezuela. CCore example of massive sandstones with
aligned clay clastsfacies B3 s. Lower Cretaceous of the
West Siberian BasinRussia. DB3 s facies with
imbricated clay clasts. Lower Cretaceous lacustrine
deposits of the Rayoso FormationNeuquén Basin
Argentina. ESandstones with aligned clay clasts. Lower
Jurassic outer shelf deposits of the Los Molles Formation
Neuquén BasinArgentina. iImbrication.
2018 ZAVALA C,et al.Hyperpycnal flows and hyperpycnites: Origin and distinctive characteristics 11
doomed pioneersbulked and transported by the
turbulent flow from shallower areasGrimm and Foll-
The origin of this facies would be related to the
progressive aggradation from the bottom by long
lived flows Fig. 11having high suspended load
Sanders1965Kneller and Branney1995Cama-
cho et al.2002. This progressive aggradation has
been proposed as a mechanism that inhibits the forma-
tion of primary sedimentary structures at the basal lay-
er. Massive deposits could therefore be related to the
absence of a sharp boundary between the moving
flow and the depositbut rather a zone of aggrading
transition characterized by a high sediment concentra-
tion associated with water escape. Experimental stud-
iesBanerjee1977Arnott and Hand1989Sum-
ner et al.2008indicate that this facies originates
from a turbulent flow with fallout rates greater than
0.44 mm/s. For smaller fallout rates at similar flow ve-
locitiesthe result will be laminated sands similar to
facies S2.
Figure 11Diagram showing the accumulation of massive
sandstone deposits with plant debris at the base of a long
lived and waning turbulent flow. C= flow concentration
u= flow velocity. From Zavala et al.2012. Modified after
Kneller & Branney1995.
The high rates of fallout of sand- size materials
results in the trapping of plant debris and other light
componentsleavestransported within the turbulent
flow in the interstices of sandstone grainsFig. 11.
Also this rapid fallout results in a loose packing re-
sponsible of an original very high primary porosity of
massive sandstones. In general S1 facies is character-
ized by a well sorted fabricFig. 12since the maxi-
mum available grain size in a turbulent suspension is
limited by flow velocity. Neverthelesssmaller grain
size particlessilt and clayare commonly found par-
tially filling the interstices. These silts and clay are
part of suspended materials trapped together during
the collapse of fine grained sand at the lower bound-
ary. Fig.12 shows an example of massive fine grained
sandstones microphoto and laser grain sizefrom
the Pliocene of Trinidad. Note the relative well sort-
ing of these fine to very fine grained sandstonesusu-
ally showing abundant associated plant debris.
Figure 10Field and core examples of facies S1. A
Massive fine grained sandstones. YK fieldCretaceous
of Siberian BasinRussia. BMassive sandstones with
clay chipscchon top. Lacustrine sandstone lobes in
the Triassic Ordos BasinChina. CMassive fine
grained sandstones with Ophiomorpha nodosa traces
as doomed pioneers. Miocene sandstone lobes in the
Columbus BasinTrinidad & Tobago. DTabular
deep water sandstone lobes in the Eocene Pampatar
FormationMargarita IslandVenezuela. EEntire
leaves in deep water massive sandstones. Eocene of
Tierra del FuegoArgentina. FMassive sandstones
with entire leaves and charcoalchclasts. Deep water
deposits in the Eocene of Tierra del FuegoArgentina.
Figure 12. Microphotographyaand laser grain size analysisbof massive sandstones of Pliocene turbidites in Trinidad.
Inablack components are plant debris. This deposit is mainly composed of poorly consolidated fine to very fine grained
In structurally controlled depocentersthe indi-
vidual thickness of single massive sandstone bodies
can be dramatically increasedAmy et al.2007
with individual beds that in some cases exceeds the
45 meters in thickness Arcuri and Zavala2007
2008. This phenomenon is a consequence of the trap-
ping of a fluid and subcritical sediment gravity flow
in topographically confined depocentersFig. 13.
Figure 13. Accumulation of very thick massive sandstone bodies in structurally confined depocenters. The hyperpycnal flow
is guided by the slow moving leading head trying to reach the lower topographic positions. If the flow istrappedin
confined depocentersit is forced to decelerate and accumulate forming lens-shaped thick sandstone accumulations. After
Zavala et al.2011.
3.2.2 Facies S2
Facies S2 is composed of tabularfine- grained
sandstone bodies showing subhorizontal parallel lami-
nationfacies S2Fig. 14or internally low angle
diverging and truncating hummocky- likelamina-
tionfacies S2 hFigs. 5 and 14 Ddisposed over a
sharp or transitional boundary. Individual laminae are
millimeter thick and in some cases are bounded by
thin levels showing abundant micacarbonaceous ma-
terialFigs. 14 C14 F & 14 Gand even charcoal
Fig. 14 E. Facies S2 appears in close association
with massiveS2and climbing ripple S3struc-
2018 ZAVALA C,et al.Hyperpycnal flows and hyperpycnites: Origin and distinctive characteristics 13
turesand often shows parting and other current linea- tion structures like those marked by heavy minerals.
Laminated sandstones are common in turbidite
bedsBouma 1962. Neverthelessthe interpretation
of the origin of laminated fine grained sandstones has
been controversial since similar features were generat-
ed in flume experiments with unidirectional stream
flows at upper flow regimeSimons et al.1965.
HoweverSanders1965noted that parallel lamina-
tion related to turbulent flows often grades laterally in-
to climbing ripplessuggesting a common origin by
traction plus fallout processes. This last conclusion is
also consistent with the experiments conducted by Ar-
nott and Hand1989and Sumner et al.2008and
it is also supported by the common association of fa-
cies S2 with massive intervalsfacies S1Figs. 14 C
& 14 Eoften constituting very thick rhythmical suc-
cessions. In hyperpycnal flowslaminated fine-
grained sandstones represents a transitional facies be-
tween massive sandstonesfacies S1and sandstones
with climbing ripples facies S3. The transition
from massiveS1to laminatedS2facies occurs at
similar flow velocities because a decrease in the rate
of sediment fallout below 0.44 mm/sSumner et
al.2008. On the other handthe passage between
laminated S2and climbing rippled sandstones
S3responds to a decrease in flow velocitySand-
ers1965with a consequent increase in the fallout
rateFig. 15.
Figure 14Core and field selected
examples of facies S2. A
Laminated fine-grained sandstones
in shelfal sandstone lobes. Upper
Miocene of Columbus Basin
Trinidad & Tobago. BLaminated
sandstonesS2on top of massive
bedsS1. Eocene Pampatar
FormationMargarita Island
Venezuela. DLaminatedS2and
HCS like structuresS2 hin
Lower Cretaceous lacustrine lobe
deposits of the Rayoso Formation
Neuquén BasinArgentina. C
Laminated sandstonesS2
alternating with massive
sandstonessuggesting cyclic
changes in the rate of fallout. Black
lines are plant remainsarrows.
Shelfal sandstone lobes of the
Lower Cretaceous Centenario
FormationNeuquén Basin
Argentina. Cyclic alternance of
massive and laminated fine grained
sandstones. Note the charcoal clast
arrow. Shelfal sandstone lobe
deposits. Mayaro Formation
Pliocene of Trinidad & Tobago. F
MassiveS1and laminated fine
grained sandstones in lobe deposits
of the Triassic Ordos basinChina.
Note the plant remainsarrows.
GPlat view of laminated
sandstones showing abundant plant
remains. Triassic Ordos Basin
Figure 15The origin of massiveS1laminatedS2and climbing rippledS3sandstones as related to changes in the
rate of sediment fallout and decrease in flow velocity of sustained turbulent suspensions. The repeated and cyclic variation of
these conditions with timeflow fluctuationsFFresult in the alternance of massive-laminated or laminated-rippled beds.
In consequencein long lived and fluctuating hy-
perpycnal flowsFFFig. 15the cyclic alternance
between S1- S2Figs. 14 C & 14 Eis produced by
cyclic changes in the rate of fall outwhile the alter-
nance between S2 and S3 is related to cyclic changes
in flow velocityFig. 15. The alternance between
massive and rippled sandstones is not hydraulically
In flows having a lateral anisotropy on velocity
and rate of sediment falloutthe unbalanced grown of
single laminas can result in low angle and laterally di-
verging beds bounded by internal and discontinuous
erosional surfacesfacies S2 hFigs. 4 A and 14 D.
These forms are similar to isotropic hummocky cross
stratification related to combined flowHarms et al.
19751982Southard1991Mutti et al.1994
Morsilli & Pomar2012but can also occur in la-
custrine systemsFig. 14 D.
3.2.3 Facies S3
Facies S3 is composed of tabular to irregular
fine- grained sandstone bodies with climbing ripples
Fig. 16. Individual sets are up to 5 cm thick with as-
ymptotic lower foresetscommonly showing mica
and small plant remainsFigs. 16 B & 16 D. If the
angle of climb is maintained for long periodsthe
bedset can showpseudo cross beddingFig. 16 A.
Flume experiments demonstrate that current rip-
ples are stable bedforms developed at the base of
streamflows moving at low velocities0.1 0.4 m/
sover sandy substratesGuy et al.1966. The exis-
tence of ripples not always implies depositionsince
ripples can occur in erosionaltransfer or deposition-
al context. A critical point to understand the deposi-
tion from ripples is the angle of climbsee the discus-
sion in Harms19751982. The angle of climb is
directly proportional to the rate of fallout. In the case
of climbing ripplesthe high angle of climbcritical
or supercritical climbing ripplesHunter 1977im-
plies that sediments accumulated in the ripple foreset
not derived from erosion at the stoss sidebut are sup-
plied from an overpassing and waning turbulent flow.
Consequentlyclimbing ripples are considered a diag-
nostic sedimentary structure indicative of turbulent
flows with high suspended sandy loadJopling and
Walker1968Ashley et at.1982Mulder and Alex-
ander2001Sumner et al.2008Jobe et al.
2012. Facies S3 often grades horizontally and verti-
cally with facies S2Sanders1965Zavala et al.
2006 bthus evidencing a common origin for both
faciescontrolled by fluctuationsFF Fig. 16 Bin
the velocity of the overpassing turbulent flow. In shal-
low water environments affected by combined flows
ripples can show aggrading wave structuresFacies
S3 wFig. 16 Esuggesting sediment fallout associ-
ated with unidirectional to oscillatory flows.
2018 ZAVALA C,et al.Hyperpycnal flows and hyperpycnites: Origin and distinctive characteristics 15
Figure 16Selected field and core examples of facies S3. AFine-grained sandstones with climbing ripplesfacies S3
interbedded with laminated sandstones. Note the high angle of climbing that provokes apseudo cross bedding. Lower
Cretaceous Rayoso FormationNeuquén Basin Argentina. BCyclic alternance between rippledS3and laminatedS2
sandstonessuggesting velocity fluctuationsFFin the parent flow. Eocene Pampatar FormationMargarita Island
Venezuela. CClimbing ripples grading upward into fallout structures. Lower Cretaceous Vikulovskaya Formation
Siberian BasinRussia. DClimbing ripples. Black lines are plant debris. Triassic lacustrine deposits in the Ordos Basin
China. Wave modified climbing ripplesS3 wwith abundant plant remains. Upper Pliocene Morne LEnfer Formation
Trinidad & Tobago.
3.2.4 Facies S4
Facies S4 is characterized by massive to laminat-
ed graded siltstones and mudstonesdisposed over
sharp or erosional basal boundaries. It is composed of
the finest materials transported by the hyperpycnal
flowwhich accumulated by normal settling when
the flow completely stopped. Consequentlyfacies
S4 is useful to identify boundaries between different
hyperpycnal events. The differentiation of facies
S4 from prodelta / shelfal mudstones may be diffi-
cultand sometimes requires micropaleontological
studiessince facies S4 often contain a mixture of
continental/shallow water species. In coarse grained
sandy-gravellysystems this facies is typical of non-
marine hyperpycnal flow depositsbecause in marine
settings fine grained materials are commonly lofted-
up by the buoyancy provided by the lighter interstitial
fluidfreshwaterand accumulate as facies LFig.
17 A & 17 B. S4 facies is also important in muddy
hyperpycnal flows in marine settings. Since these fine
grained hyperpycnal flows are mostly loaded by a
mixture of silt and mudthe loading provided by the
sediment concentration does not directly depend on
the flow velocityand flow reversionloftingdoes
not occurFig. 17 C.
The final deposit of muddy hyperpycnal flows
will be centimeter to meter thick graded mudstone
bedsoften disposed over sharp or erosional basal
boundariesFig. 18. Internallythese deposits can
show a mixture of intrabasinal and extrabasinal fossil
remnantsFig. 18 D. In contrary to lofting deposits
where plant debris are disposed along plane beds
plant remains are commonly dispersed within the
mudstone bedsFig. 19. The existence of erosional
basal boundariesflamesand cyclic changes in
grain size suggests that muddy hyperpycnal flows are
highly dynamic currentsFig. 19. These evidences
are against the traditional model ofnormal fallout
previously assumed as the main depositional mecha-
nism for the accumulation of mud in offshore areas.
Muddy hyperpycnal flows are fluid flows capable of
eroding the muddy soupy substrate. The internal cy-
clic changes in the grain size suggests also the exis-
tence of long livingpulsatingflows. These flows
are an efficient mechanism for erodingtransferring
and accumulate intrabasinal an extrabasinal organic
matter in the inner basin. The rapid burial contributes
in preserving the organic matter from oxidation at not
totally anoxic bottoms.
Figure 17Composition of hyperpycnal flows and
their resulting deposits in marine settings. A and B
Sandy hyperpycnal flow withAor withoutB
associated bedload. CMuddy hyperpycnal flow.
According to the abundance of silt/clay fractions in
the parent flow in Athe flow lofts at very low
velocities allowing the development of plane bed
and ripples on top of the bed. In Bthe low content
of silt/clay results in lofting at higher velocities
respect to those required for develop parallel
lamination and ripples. In consequence the resulting
bed will be composed of massive sandstonesS1
overlaid by lofting deposits. Note also that density
reversalloftingdoesnt occur in muddy
hyperpycnal flowsCsince the flow bulk density
dont decrease with flow velocity. Modified after
Zavala & Arcuri2016.
Figure 18Selected core examples of
S4 facies in cores of the Upper Jurassic
Lower Cretaceous Vaca Muerta Formation
Neuquén BasinArgentina. A-CStacked
beds related to muddy hyperpycnal flows.
Note the basal erosional contact and the
overall normal grading of the deposit.
Internallythese deposits commonly show
subtle grain-size changes that suggests
pulsating flows. DDetail of plant remains
on plant viewarrowssuggesting an
extrabasinal origin of these beds.
2018 ZAVALA C,et al.Hyperpycnal flows and hyperpycnites: Origin and distinctive characteristics 17
Figure 19Example of deposits related to muddy hyperpycnal flowsFacies S4. ALine tracing of the three graded beds
shown in B. Note the erosional surface at the base of bed 2and the flames at the top of bed 1suggesting an erosional fluid
muddy flow moving from left to right. Flames in 1 also indicate that the flow was moving over asoupysubstrate. Plant
remains are abundant. BGeneral view showing the location of photomicrographs ab and cwith examples of small and
dispersed plant debris. Lower Jurassic Los Molles FormationNeuquén BasinArgentina. After Zavala & Arcuri2016.
3. 3 Facies related to flow lofting facies L
Facies L is characterized by widely extended
thinmillimeter thickcouplets of siltstones and very
fine grained sandstonesoften showing abundant
plant debris and micas on bounding surfaces Fig.
20. These couplets display abundantsmall scale
load cast structurescommonly associated with syn-
eresis cracks and siderite nodules. Trace fossils are
scarce and mostly limited to some forms of Palaeo-
phycus. These laminated levels can form bedsets up
to 0.5 meters thicktermed lofting rhythmitesZava-
la et al.2006 c2008 balternating with shelfal or
hemipelagic shalesbut more commonly associated
with massive sandstones facies S1Figs. 20 C
20 D.
Individual levels display a variable thickness
from few millimeters up to one centimeterand are
separated by thin layers with abundant plant debris
Figs. 20 B and 20 E. Plant debris provides a defini-
tive evidence of a direct connection between the fluvi-
al system and the marine/lacustrine related basinPet-
ter and Steel2005Lamb2008Zavala et al.
2012. The absence of tractive structures in these
sandstones suggests an accumulation by normal set-
tling from a suspension cloud elevated over the depo-
sitional surface.
Lofting rhythmites accumulate from a pulsating
lofting plumewhich is a typical feature of hyperpyc-
nal inflows in marine environments. A hyperpycnal
flow is basically a heterogeneous mixture of compo-
nents having different individual densities. According
to their lower density respect to marine watersaver-
aged surface density 1.025 g/cm3
freshwater1.0 g/
charcoal0.208 g/cm3
and plant debris0.09-
0.55 g/cm3
are considered buoyant componentsFig
22. On the other handsand2.2 - 2.8 g/cm3
2.4 2.8 g/cm3
and clay2.7 2.8 g/cm3
load components. Under certain conditions of veloci-
tythese components are mixed in different propor-
tions within a turbulent flow providing an average
bulk density. If this bulk density is above the thresh-
old of sea water densitythe flow will be attached to
the sea bottom. On the contraryif the flow loses part
of the load componentsi.e. sand - siltby deposi-
tionthe flow will lift from the substrate through
buoyancy reversalSparks et al.1993Kneller &
Buckee2000Mutti et al.2003Hesse et al.
2004Hesse and Khodabakhsh2006forming loft-
ing plumes charged with fine- grained sediments
plant debris and micas
Figure 21 Buoyant and load components as the basic
constituents of a turbulent hyperpycnal flow. After Zavala
et al.2011.
Lofting rhythmites mostly accumulate at flow
marginsZavala et al.2011Fig. 4 Band show a
more extended distribution compared with that of the
main hyperpycnal flow. Facies L constitutes a diag-
nostic and characteristic element of hyperpycnal sedi-
mentation in marine settings since it suggests the exis-
tence of a less dense interstitial fluid freshwater
with respect to that of the environmentmarine wa-
Figure 20Field and core examples of
facies Llofting rhythmites. ADeposits
of lofting rhythmitesLinterbedded with
shelfal mudstonesM. Inner shelf
deposits of the Lower Jurassic Los Molles
FormationNeuquén BasinArgentina. B
Plant view of lofting deposits shown in A.
Note the abundant plant remains. C & D
Lofting depositsFacies Linterbedded
with massive sandstonesFacies S1. Black
lines are plant remains. Cretaceous of the
Siberian BasinRussia. EPlant view of
Dwith abundant mica and plant remains.
2018 ZAVALA C,et al.Hyperpycnal flows and hyperpycnites: Origin and distinctive characteristics 19
terderived from direct fluvial dischargeZavala et
al.2006 c2012. Vertical and lateral relationships
between L and S S1S2 and S3facies are not
sharpand result in transitional categoriesFig. 4 B
termed S1/Lmassive sandstones with discontinuous
siltstone levels Fig. 22),S2/L laminated sand-
stones with abundant plant debris and micasand S3/
Lsiltstone levels interbedded with sandstones with
small and low angle climbing ripples.
Analysis of thin sections Fig. 23of lofting
rhythmites provides clear evidences about the origin
of this feature apart of giving some diagnostic criteria
for its recognitionZavala et al.2008 b2012. Ac-
cording to its accumulation from normal settlingthe
deposition of fine- grained materials from lofting
plumes is very selective. The free fallout of fine
grained clastic materials from suspension clouds is
governed by the Stokeslaw. The genetic analysis of
the thin section of Fig. 23 allows to tract the origin of
lofting rhythmites.
Figure 23Thin sectionaand grain-size analysisbof lofting deposits in the Pliocene of the Columbus BasinTrinidad
& Tobago. Fallout of sand-silt materials from suspension clouds are normally gradedand are bounded by thin levels of
plant debristrapped by the next wave of sand fallout. After Zavala et al.2012.
Fig. 24 shows a step- by- step accumulation of
lofting rhythmitesaccording to the interpretation of
the microphotograph shown in Fig. 23. InAa het-
erogeneous lofting cloud is introduced by a hyperpyc-
nal wavein a lateral position respect to the main
flow. InBthe free fallout of different grain- sized
clastic materials results in a normally graded interval
with silt and oriented micas on top. According to their
low densityleaves and plant materials remain in sus-
pension. InC),a new suspension cloud is intro-
duced by a new wave during the same hyperpycnal
discharge. The free fallout of largest sand grains forc-
es the deposition of leaves and plant fragments. As a
consequencea thin level of carbonaceous materials
develops in between massive sand-silt levels.
Figure 22Outcrop showing the lateral
relationship between massive sand-
stones facies S1and lofting facies
L. Transitional levels include massive
sandstones with levels of plant debris
facies S1/L. Lower Jurassic Los
Molles FormationNeuquen BasinAr-
Figure 24Lofting rhythmites are the result of the repeated aggradation of fine grained materials from suspension clouds
related to the buoyant inversion of hyperpycnal flows at flow margin areas. Explanations in the figure. Modified from Zavala
et al.2008 b2012.
2018 ZAVALA C,et al.Hyperpycnal flows and hyperpycnites: Origin and distinctive characteristics 21
4 Depositional elementschannel fill
lobes and levee deposits
In contrary to intrabasinal surge liketurbi-
ditessustained hyperpycnal discharges result in very
dynamic jet flows in the sense of Hoyal et al.
2003capable of travel for long distances on gentle
or flat basin slopes. The energy that allows such long
travel is provided by the continuous pumping from
the river flood. Consequentlythe distance achieved
by the hyperpycnal discharges will directly depend on
the duration of the associated river discharge and the
topography of the related basin. According to the com-
mon accumulation of climbing ripples at the leading
head of sandy hyperpycnal flowsit is assumed an av-
erage velocity of advance of the hyperpycnal flow of
20 cm/sclimbing ripples develop at flow velocities
ranging from 15 to 25 cm/sAshley et al.1982. At
this velocitya sustained river discharge of about two
months will be required to achieve a distance of 1
000 km along sea bottom. In contrary to that of the
leading headthe velocity along the flow body can be
highaccording to the evidences provided by sedi-
mentary structures and internal erosional surfaces.
The understanding of the basinward evolution of a hy-
perpycnal flow is crucial to understand the final depo-
sitional geometry of channels fills and lobes. The ini-
tial flow path will be traced by the advance of the
leading headwhich will move basinward trying to
reach the lower topographic positions of the basin
landscape. In this contextthe existence of structural-
ly controlled closed topographic lows will result in a
flowtrappingand the forced accumulation of very
thick and discontinuous massive sandstone bodies
due to the associated high rates of fallout. In the
case of more regulargentle or flatlandscapethe
acceleration of these jet flows along the flow body re-
sult in erosion and channel incision. The conceptual
step by step evolution of hyperpycnal channel fill
sandstone bodies comprise three stages1initial
deposition2erosion & bypassand3channel
fillFig. 25.
The initial deposition stages are characterized by
traction plus fallout depositsS3-S2 faciesand asso-
ciated leveeL faciesaccumulated during the flow
acceleration immediately after the arriving of the flow
leading head1 in Fig. 25. The progressive increase
in the flow velocity at the flow axis results in strong
turbulence at the jet region. Once the erosional thresh-
old is exceeded2 in Fig. 25the erosion of the sub-
Figure 25. Depositional schema
showing the step by step origin
of hyperpycnal channel fill
deposits. In 1 the arrival of the
flow leading head accumulated
traction plus fallout deposits. In
2high velocities at flow axis
produces a flute-like basal
erosional surface. In 3during
flow slackeningthe
hyperpycnal flow infills the
previous erosional relief.
Modified from Zavala et al.
2008 b.
strate provokes a linear flute- like erosional scour
Hoyal et al.2003with associated levee deposits
L faciesat both sides. This second stage is charac-
terized also by an important sediment bypassallow-
ing the basinward transfer of a huge volume of sedi-
ments. The interplay of erosiontemporary deposi-
tion and bypass in this stage results in bedloadB1
B2 and B3 faciesand suspended loadS1 faciesde-
posits at the channel bottomoften associated with
lateral accretion in case of meandering channels.
The Lateral accretion associated to hyperpycnal chan-
nel fills is characterized by an aggrading component
Fig. 26.
Figure 26. Field example of lacustrine hyperpycnal channel fill with lateral accretion. Note that in contrary to lateral
accretion of subaerial fluvial channelsthis kind of lateral accretion has an aggrading component. Flow direction is
perpendicular to the outcrop. Lower Cretaceous Rayoso FormationNeuquen BasinArgentina.
The final channel infill occurs during stage 3
which is characterized by an overall fluctuating wan-
ing flow. The associated deposit comprises sand size
materials collapsed from the sustained turbulent flow
S1S2 and S3 facieswith associated levee depos-
its al flow marginsL facies. In contrary to fluvial
channel fillsthe evolution and infill of hyperpycnal
channels result in positive topographic elements on
the sea bottom. This sedimentary induced relief will
control the location of the future hyperpycnal chan-
nelsresulting in compensation cycles in the sense of
Mutti & Sonnino1981. Compensation cycles pro-
vides a very complex scenario for detailed correlation
of sandstone bodies.
The transition from channels to lobes occurs
when the sustained hyperpycnal flow loses the capaci-
ty of eroding the substrate. In topographicallyfault
controlled depocentersthe flow could be forced to
wane and accumulate according to fill and spill pro-
cesses. Thefill and spillprocess is relatively well
known from the study of deposition related to dilute
sediment-gravity flowsturbiditeson topographical-
ly irregular basinsor minibasinslocated on the con-
tinental slope of the Gulf of Mexico and the Tertiary
Alpine basinsWinker1996Sinclair & Tomasso
2002Toniolo et al.2006. This process involved at
least four stages1Flow pondingwhere incom-
ing flows are totally trappeddepositing thicksheet-
like sandmud couplets.2Flow strippingwhere
the finermore dilute portion of the flow is able to es-
cape over the confining topography to be deposited
elsewhere.3Flow bypasswhen flows traversing
over the filled basin and transfer the sediments into a
deeper position.4Backfilling of the basin during
the final stageusually with meandering channelle-
vee complexes with low sand/mud ratiosSinclair &
Tomasso2002. Fig. 27 depicts the process of fill
and spill in the offshore of the Columbus Basinin
Trinidad & Tobago. During the initial infill of the
fault controlled depressionsFig. 27 Athe hyperpyc-
nal discharge flows along the axis of the depocenter
1 in Fig. 27 Aand the associated deposits com-
pose thick intervals of massive and laminated sand-
stonesFig. 28. The infill of the former depocenter
2018 ZAVALA C,et al.Hyperpycnal flows and hyperpycnites: Origin and distinctive characteristics 23
forces the flow to bypass this area and accumulate in
a deeper areaFig. 27 B. In consequencethe final
accumulation in the first depocenter will be dominat-
ed by fine grained lofting deposits2 in Fig. 27 B
Figure 28. Thick massive sandstone bodies in the Mayaro
FormationPlioceneColumbus BasinTrinidad &
Tobago. Thick massive sandstones result from the
accumulation in structurally controlled basin floor
In more topographically regular basinschan-
nels usually extend for 10s to 100s of kilometers
until the transported sediments spread out as terminal
lobes. Fig. 29 provides an exceptional example for
discussing the origin and distribution of hyperpycnal
channelsand their relationship with littoral deltas.
This marvelous seismic time slice correspond to Late
Cretaceous shallow to deep water lacustrine deposits
of the Nengjiang Formation in Songliao BasinChi-
na. Littoral deltas clearly develop in the northern ar-
eafrom where hyperpycnal flows are triggered dur-
ing exceptional river dischargesriver flood. Initial-
ly these channels are straightbut become meander-
ing at the lower slope. Integration of coreswell
logsand seismic allows to estimate an averaged
channel width of 500 metersmaximum 900 meters.
Channels extend up to 80 km from littoral delta ar-
easand show a sinuosity ranges from 1.35 up to
1.71average 1.54. The channel end is characterized
by more laterally extended lobe depositstypically
covering an area from 4 to 10 km2. It is interesting to
Figure 27. 3 D model showing the
progressive infill of fault controlled
depocenters and its control in the
stacking pattern of the associated
reservoirs.Adepicts the initial
and main infillresulting from the
accumulation of thick sandstone
packages1 in the well logby
axial hyperpycnal flows. Once the
first depocenter is almost filled
Bthe flow bypass towards a
deeper depocenterresulting in the
accumulation of lofting deposits
2 in the well logat the top of the
previously filled depocenter.
note that in hyperpycnal systems main sandstone ac-
cumulation not necessarily occur at lobe area. Chan-
nel fill deposits constitutes also important clastic res-
5 Discussion and conclusions
Growing evidences suggests that hyperpycnal
flows areand have beena very common and impor-
tant mechanism for transferring huge volume of sedi-
ments from producing areas to marine and lacustrine
depositional basins. Neverthelesstheir related depos-
its are still poorly recognized in the literature. Our ig-
norance of present clastic depositional environments
especially subaqueous onesresulted in an overem-
phasis ofgeomorphological environmentshaving
little or no preservation potential in the geological re-
cord. As an examplea number of littoral geomorpho-
logic featureslike strand painsestuariestidal flat
barrier islandetchave been created during the Ho-
locene by the rapid marine flooding more than
120 m of sea level riseover a mature continental
landscape. These temporary geomorphologic features
have been thenupgradedto the category ofdeposi-
tional systemand their sedimentary models have
been applied to explain the origin of very thick suc-
cessions of clastic deposits. Consequentlyit is high-
ly probable that a number of lacustrine and marine hy-
perpycnites were wrongly described and interpreted
in the literature as fluvialshorefaceestuarineor
strand plain deposits. The correct interpretation of the
significance of these deposits will require further stud-
This paper provides a synthesis of the main char-
acteristics of hyperpycnal flows and their deposits.
Neverthelessour understanding of these deposits is
still very limitedand new studies and effort will be
required in the next years to achieve a complete
knowledge of the characteristics and significance of
hyperpycnal systems.
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... Ante esta situación, la descarga fluvial se hunde debajo del agua marina formando un flujo hiperpícnico que puede viajar considerables distancias, acarreando grandes volúmenes de sedimentos directamente desde un río en crecida. Además, durante la descarga hiperpícnica el agua dulce y otros materiales relativamente livianos originalmente transportados dentro de la descarga fluvial, como restos vegetales, hojas, troncos y carbón, son forzados a hundirse y viajar hacia el interior de la cuenca (Zavala y Pan, 2018). ...
... Un flujo hiperpícnico episódico usualmente dura unas pocas horas y desarrolla un fan-delta con gradientes pronunciados y pequeñas áreas de captación. Mientras que los flujos hiperpícnicos sostenidos se producen por descargas de grandes ríos que pueden durar semanas o incluso meses dependiendo del clima, el tamaño y la forma del área de drenaje fluvial asociada (Zavala y Pan, 2018;Zavala 2020). ...
... Interpretación: esta facies sería el producto de procesos de tracción-decantación, debido a la agradación progresiva del fondo a partir de flujos de larga duración con alta carga suspendida (Sanders 1965, Kneller y Branney 1995, Camacho et al. 2002. Esta agradación progresiva ha sido propuesta como un mecanismo que inhibe la formación de estructuras sedimentarias, ya que no existiría un contraste definido entre el flujo y el depósito sino más bien una zona de transición agradante, caracterizada por una alta concentración de sedimentos asociado a escape de agua (Zavala y Pan, 2018). La presencia de clay chips y restos de amonoideos en esta facies sería el producto de la erosión e incorporación de materiales intracuencales en los flujos en su trayecto de movilización por el fondo marino. ...
Se realizó un estudio multidisciplinario de detalle sobre el tramo basal de la Sección “Don Silverio” perteneciente a la Formación Los Molles, en la Subcuenca de Picún Leufú, Neuquén. El objetivo del presente trabajo es contribuir al conocimiento integral de la Formación Los Molles (Jurásico Temprano-Medio) al sur de la Dorsal de Huincul y evaluar el potencial oleogenético de la sección estudiada. A partir del estudio sedimentológico/estratigráfico, se reconocieron hiperpicnitas fangosas y arenosas depositadas en un Delta Hiperpícnico Subacuático. Este delta se habría desarrollado en porciones distales de la plataforma, por debajo de la acción de oleaje, durante períodos de mayor eficiencia del sistema deltaico. En cuanto al análisis de la materia orgánica palinológica, se reconoció una predominancia absoluta de materia orgánica de origen continental. Un total de 4 palinofacies tipo fueron definidas, las cuales reflejan las diferentes condiciones de depositación y energía presentes en los diferentes flujos hiperpícnicos. En base a la variedad de taxones continentales reconocidos (Cheirolepidiaceae, Araucariaceae, Botryococcaceae, entre otros) y las diferencias de requerimientos paleoecológicos que tienen cada uno de ellos, se evidencia el largo camino y los distintos ambientes que atravesaron los flujos hiperpícnicos hasta alcanzar la cuenca receptora. A partir del análisis geoquímico de las muestras, se reconoce que los valores de carbono orgánico total son mayores al 1% en casi todos los casos, lo que permitiría asociar a estas rocas con buena a muy buena capacidad de generación de hidrocarburos. Sin embargo, los bajos valores obtenidos de S2 no confirman dicha asignación, por lo que finalmente se las clasifica como rocas con pobre potencial. El querógeno presente es de tipo III/IV y IV, constituido por materia orgánica esencialmente rica en carbohidratos de plantas vasculares. La interpretación del potencial oleogenético que se obtiene a partir del análisis palinológico presenta una correlación con los resultados obtenidos a partir del estudio geoquímico, por lo que la sección de estudio no cumple con las condiciones para ser considerada un buen reservorio no convencional de tipo shale gas.
... They form at river mouths when a river in flood directly discharges a mixture of fresh water and sediment into a less dense standing body of water (Zavala et al., 2012). A hyperpycnite is the sedimentary deposit of a hyperpycnal flow (Bates, 1953;Zavala et al., 2011Zavala et al., , 2012Slater et al., 2017;Zavala and Pan, 2018). Laminated siltstone beds with climbing ripples, and graded siltstone beds with erosional basal boundaries, are common within the suspended-load facies of a hyperpycnite (Mulder et al., 2003;Zavala and Pan, 2018). ...
... A hyperpycnite is the sedimentary deposit of a hyperpycnal flow (Bates, 1953;Zavala et al., 2011Zavala et al., , 2012Slater et al., 2017;Zavala and Pan, 2018). Laminated siltstone beds with climbing ripples, and graded siltstone beds with erosional basal boundaries, are common within the suspended-load facies of a hyperpycnite (Mulder et al., 2003;Zavala and Pan, 2018). Sandstone and siltstone beds with climbing ripples are one of the most common units within hyperpycnites, and represent ripple migration (Mulder et al., 2003;Zavala and Pan, 2018). ...
... Laminated siltstone beds with climbing ripples, and graded siltstone beds with erosional basal boundaries, are common within the suspended-load facies of a hyperpycnite (Mulder et al., 2003;Zavala and Pan, 2018). Sandstone and siltstone beds with climbing ripples are one of the most common units within hyperpycnites, and represent ripple migration (Mulder et al., 2003;Zavala and Pan, 2018). Normally graded siltstone beds accumulate by normal settling when the flow completely stops, and correspond to fluid flows capable of eroding the muddy soupy substrate; these muddy graded beds are typically found as sharp-based, centimetre-thick, stacked intervals and commonly lack internal fabric (Slater et al., 2017;Zavala and Pan, 2018). ...
Hydrocarbon production from the Lower Triassic Montney Formation in northeastern British Columbia, occurs primarily from unconventional reservoirs consisting predominantly of fine-to coarse-grained siltstone beds. In this area, the lithostratigraphy of the formation is difficult to characterize due to the complexities associated with subtle grain-size variation, diminutive biogenic structures, lateral facies variability, and distribution of local discontinuities. Detailed sedimentologic and stratigraphic analyses are essential for understanding and refining the depositional models and stratigraphic framework of the Montney Formation. Based on detailed core examination focused on sedimentological, paleontological and ichnological characteristics, eleven lithofacies and three recurring facies associations are identified within the Lower Triassic Montney Formation in northeastern British Columbia. The lithofacies identified are interpreted to have been deposited in offshore, offshore transition and lower shoreface settings, along a storm-dominated mixed siliciclastic-carbonate ramp. Facies associations include FA(A): siliciclastic distal offshore transition to distal offshore; FA(B): mixed siliciclastic carbonate, storm-influenced offshore to offshore transition; and FA(C): storm-dominated siliciclastic offshore transition to lower shoreface. Trace fossil assemblages correspond to a stressed Cruziana Ichnofacies, and are overall characterized by low diversity (1–6 ichnogenera), small size trace fossils (1–12 mm in diameter), and variable bioturbation intensity (0–6). The vertical variation in SDI values reflect changes in physico-chemical conditions during deposition of the Montney Formation, particularly across the Smithian-Spathian boundary. Understanding the lateral-facies variability and overall stratigraphic architecture of the Montney Formation in northeastern BC, constitute key elements in defining and correlating existing and new potential hydrocarbon reservoirs in the area.
... Turbidity currents were commonly voluminous and of a sustained type, depositing thick beds in quasi-steady flow conditions. They were generated by river floods as hyperpycnal flows (Parsons et al., 2001;Zavala et al., 2018). Moreover, along the basin's active tectonic margin, voluminous sediment gravity flows could have been generated by earthquakes or retrogressive slumping -i.e. ...
... Frictional freezing and/or rapid suspension fallout (Lowe, 1982) of sediment-laden currents (Collinson and Mountney, 2019). Hyperpycnal flows deposits (Zavala et al., 2018) due to storm activity and/or to river floods Sl ...
The submarine Iváň Canyon oriented parallel along the front of the Western Carpathian fold and thrust belt and the foreland of the Bohemian Massif has been studied on numerous 2D seismic sections and available borehole cores. The canyon can be followed over the distance of more than 75 km indented within the sedimentary infill of the Alpine-Carpathian Foredeep from Lower Austria into the Czech Republic. Seismic data reveal up to 600m depth of the canyon and its width of 2.5–6 km. The canyon is characterized by a low sinuosity planform architecture with an axial main channel and several tributary channels of varying dimensions. Six recognised seismic facies were identified, separated by three erosional surfaces, which led to recognition of seven evolutional stages of the canyon. Facies analysis, clast composition and heavy mineral spectra indicate derivation from a siliciclastic source area, cannibalization of an older basin infill and an important role of sustained low-density turbidity currents in transport and deposition. The strontium isotope stratigraphy data supported by microbiostratigraphy and by foraminiferal δ¹⁸O and δ¹³C isotope analysis confirmed, that the depositional history of the canyon infill lasted from the upper Burdigalian/Langhian boundary up to the lower Serravalian, with the dominance of Langhian deposits in its infill. The formation and depositional history of the canyon is explained by the complicated structural and depositional history of the Alpine-Carpathian Foreland basin during the lower/middle Miocene transition and middle Miocene (Langhian) with a dominant role of tectonic subsidence and basin re-configuration accompanied by eustatic sea-level fluctuations. The Iváň Canyon as axial channel developed in the elongate foreland basin reveals several differences if compared to typical ancient submarine canyons in the passive margin settings.
... Only the uppermost 50 cm of the core show a departure from this trend, showing low and overall homogenous D50 values apart from two small intervals (Fig. 2). The occurrence of coupled CU and FU trends in a prodeltaic environment, is usually interpreted as an indication of deposition during the waxing and waning period of river discharge, respectively, evidencing alternate phases of increasing and decreasing velocity of hyperpycnal flows (Mulder et al., 2003;Khripounoff et al., 2012;Zavala and Pan, 2018). The finer-grained levels can be interpreted as the final stage of flow deposition or as due to the successive hemipelagic sedimentation (Budillon et al., 2005). ...
... Therefore, we interpret the reiteration of such sedimentary sequences as the depositional units associated with flash-floods generated hyperpycnal flows. Such events are likely to occur in front of river mouths (Mulder et al., 2003;Zavala and Pan, 2018) and are frequently influenced by seasonal (winter) rainstorms in the Mediterranean region (Budillon et al., 2005;Lobo et al., 2015). ...
Plastic pollution affects all oceans and sequestration of plastics in sediments is considered its ultimate sink. We report evidence of macroplastic burial retrieved within a sediment core collected at 38 m depth at the mouth of the Mazzarrà River, a torrential river able to carry a large amount of sediment during seasonal flash-floods. Two macroplastic items were found at 68 and 255 cm below the core top (corresponding to the seafloor). Their association with terrestrial vegetal debris and their inclusion in decimetre-thick sandy/silty intervals showing coarsening- and fining-upward trends, suggest that they were deposited by hyperpycnal flows possibly triggered by flood events. These findings testify the potential of sedimentary flows in burying macroplastic at depth below the seafloor, especially in nearshore prodelta environments. Furthermore they raise the quest on the magnitude of macroplastic storage in the subsurface and on the lack of specific devices and strategies for their reckoning.
... Wave-ripple bedforms on top would suggest the post-depositional reworking by bidirectional currents. In general, this facies is characterized by a well-sorted fabric, due to the maximum available grain size in a turbulent suspension is limited by flow velocity and competence (Zavala and Pan, 2018). Bioclastic levels in this facies could suggest gradual changes in flow conditions, characterized by internal erosion, transport and deposition of bioclasts as bedload (traction-saltation). ...
... Therefore, facies FL may have an alternative origin related to migrating floccule ripples (Schieber et al., 2007;Schieber and Southard, 2009;Schieber and Yawar, 2009). Regarding facies FM, the distinction between massive mudstones accumulated in prodelta or shelfal settings can be very difficult (Zavala and Pan, 2018). ...
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Recent advances in the understanding of deltaic deposits provide new tools for the study and analysis of deltaic deposits in shallow epicontinental seas. After the introduction of sequence stratigraphic concepts, meter-scale coarsening and thickening upward successions have been considered as "para-sequences" originated by high-frequency sea-level changes. Nevertheless, recent studies enhanced the importance of wave-aided low-dense hyperpycnal flows in transporting fine-grained sediments in shallow shelfal areas. These poorly-known (and at the same time very common) types of delta, known as hyperpycnal littoral deltas (HLD), develop very low gradient progradational units, controlled by changes in the sediment supply instead of sea level changes. These small-scale progradational units are very common in shallow epicontinental seas like the Lower Cretaceous Agrio Formation in the Neuqu en Basin. This study provides a first detailed analysis of hyperpycnal littoral deltas from the Agua de la Mula Member (upper Hauterivianelower Barremian) of the Agrio Formation. This unit has been studied in three locations near Bajada del Agrio locality in the central part of the Neuqu en Basin, Argentina. Six sandy facies, three heterolithic facies, three muddy facies and four calcareous facies were recognized. From facies analysis, three facies associations could be determined, corresponding to offshore/prodelta, distal ramp delta and proximal ramp delta. The three stratigraphic sections discussed in this study are internally composed of several small-scale sequences showing a coarsening and thickening upward pattern, transitionally going from muddy to sandy wave-dominated facies, and ending with calcareous bioclastics levels on top. These small-scale sequences are interpreted as delta
... In general, the Fe/Mn and U/Th values gradually decreased from early highstand normal regression to forced regression (Fig. 4B), suggesting a change in palaeoclimate from a humid and reducing to an arid and oxidative condition. (Zavala et al., 2006, Xian et al., 2018bZavala et al., 2018). Massive sandstones consist of composite rhythms with inverse-normally grain size in facies Sc ( Fig. 7D) indicating that the flow underwent a waxing-waning process, which are the products of hyperpycnal flows related to flood discharges fluctuations (Mulder et al., 2003;Zavala et al., 2016;Xian et al., 2018b;Chen et al., 2021;Liu et al., 2022). ...
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Sedimentary processes of marine turbidite systems under sea-level changes have been the focus of deep-water sedimentology. Compared with well-studied marine basins, the products of deep-water sediment gravity flows responding to lake-level changes in closed lacustrine basins are still poorly understood. In this study, we integrate cores of 10 exploratory wells, logs of 280 development wells, 3D seismic data and geochemical elements from the Eocene Dongying Depression, Bohai Bay Basin, East China to investigate sedimentary mechanisms and depositional architecture of lacustrine turbidite systems under lake-level changes. The studied strata are divided into three parasequence sets (PSS4~PSS2), corresponding to early highstand normal regression with ascending trajectories, late highstand normal regression with flat trajectories, and forced regression with descending trajectories, respectively. From early highstand normal regression to forced regression, the ratios of Fe/Mn and U/Th reveal that the humid climate shifted to the arid climate. More lithofacies clues indicate that turbidites in highstand normal regression were triggered by river floods, whereas counterparts in forced regression were related to sediment failures. There are different architectural features of turbidite systems in three regression stages. PSS4 developed a series of channel belts within which individual channel elements are aggraded vertically. PSS3 is composed of a channelized lobe formed by individual distributary channels migrating laterally. PSS2 is characterized by a suite of compensational stacking debrite tongues. Climate forcing is a crucial factor controlling depositional architecture of the turbidite systems. A relatively humid climate during highstand normal regression led to rising lake-level and frequent floods, which are conducive to the formation of hyperpycnal-fed channel-lobe systems. Nevertheless, during forced regression under an arid climate, the strong progradational clinothems were prone to failure and sediment remobilization, resulting in debrite tongue complexes. This study highlights depositional differences of lacustrine turbidites during regression stages under the control of climate. Meanwhile, it also provides a new predictive model for deep-water hydrocarbon exploration and production in lacustrine basins worldwide.
The lacustrine conglomerate reservoirs of the Lijin sag, Bohai Bay Basin, East China, were studied to understand the roles of depositional and diagenetic events on reservoir quality, using integrated seismic data, well logs, core observations, optical petrography, SEM-EDS, cathodoluminescence, and fluid inclusion microthermometry. The results show a fan delta with well-connected conglomerate bodies deposited during a highstand system tract (HST) and a nearshore subaqueous fan with weakly connected conglomerate bodies deposited in a transgressive system tract (TST). The conglomerates are mainly classified as feldspathic litharenite. The porosity and permeability of the fan delta vary from 0.1% to 17.4% and 0.01 to 457.6 mD, respectively. The porosity and permeability vary from 2.02 to 16.2% and 0.02 to 237.2 mD in the nearshore subaqueous fan. Mechanical compaction, dissolution, and cementation together are noteworthy diagenetic processes. Compaction is the dominant factor in reducing porosity; cementation has a destructive effect, while dissolution improves reservoir quality. Feldspar dissolution leads to kaolinite, illite, dickite precipitation, and deteriorating reservoir quality. The probable sources of meteoric water flux in the deep-burial environments are related to the falling lake level during the HST. Fluid inclusion analysis revealed that quartz overgrowths were formed during the mesodiagenetic stage. The depositional environment and grain sizes are essential factors controlling reservoir quality. The effect of grain size and sorting coefficients on reservoir quality varies as a function of retrogradation and progradation sequences. The higher the porosity and permeability, the coarser the particle sizes in the retrogradation sequences. In the progradation sequences, poorly sorted sediments have higher porosity and permeability than well-sorted sediments. The braided channel embodies the best reservoir quality in the TST, while the distributary channel represents the best reservoir in the HST. The formation mechanism of the high-quality reservoirs is ascribed to the sedimentary facies, compaction resistance, and mineral dissolution. Overall, the conglomerate reservoirs developed in the HST are relatively better than those in the TST because they have greater labile fragments, resulting in more dissolution. This study demonstrated that for successful assessment of conglomerate reservoirs in the Lijin area and similar reservoirs elsewhere, reservoirs characterization must link sequence stratigraphy, facies, and diagenesis to understand the high-quality reservoir distribution to support the predrill evaluation of reservoirs.
Field observational previously indicated a mouth bar of a fan delta could exhibit a fining or coarsening upward trend, which bring a new challenge to the identification of mouth bar in subsurface studies due to the lack of morphological descriptions. Previous studies have indicated that effluent behavior in river-mouth system can affect the vertical grain-size trend of mouth bar, but the drivers and magnitude of this phenomenon is not understood. We conducted flume experiments to investigate the mechanism and controlling factors of vertical grain-size trend of mouth bar. Experiment with a steeper slope of the substrate layer, greater discharge, higher sediment/water ratio, and coarser sediment induced a fining-upward trend of mouth bar, because the effluent was dominated by strong inertia. Mouth bar in the experiment with a gentler slope of the substrate layer, smaller discharge, lower sediment/water ratio, and finer sediment exhibited a coarsening-upward trend dominated by the friction-dominated effluent. The relationship between the vertical grain-size trend of mouth bar and the gradients of foreset bedding in small-scale flume models and the cut-off of 15–18° are applicable in natural systems. Identifying depositional setting to infer depositional process in river-mouth system and analyzing the plane geometry of sandbodies are two steps in the interpretation of ancient fan deltaic rock record.
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Emplacement of submarine landslides, or mass‐transport deposits, can radically reshape the physiography of continental margins, and strongly influence subsequent sedimentary processes and dispersal patterns. Typically, progressive healing of the complicated relief generated by the submarine landslide occurs prior to progradation of sedimentary systems. However, subsurface and seabed examples show that submarine channels can incise directly into submarine landslides. Here, the evolution of a unique exhumed example of two adjacent, and partially contemporaneous, submarine channel‐fills is documented. The channels show deep incision (>75 m), and steep lateral margins (up to 70°), cut into a >200 m thick submarine landslide. The stepped basal erosion surface, and multiple terrace surfaces, are mantled by clasts (gravels to cobbles) reflecting periods of bedload‐derived sedimentation, punctuated by phases of downcutting and sediment bypass. The formation of multiple terrace surfaces in a low aspect ratio confinement is consistent with the episodic migration of knickpoints during entrenchment on the dip slope of the underlying submarine landslide. Overlying sandstone‐rich channel‐fills mark a change to aggradation. Laterally stacked channel bodies coincide with steps in the original large‐scale erosion surface, recording widening of the conduit; this is followed by tabular, highly aggradational fill. The upper fill, above a younger erosional surface, shows an abrupt change to partially‐confined tabular sandstones with normally graded caps, interpreted as lobe‐fringe deposits, which formed due to down‐dip confinement, followed by prograding lobe deposits. Overlying this, an up‐dip avulsion induced lobe‐switching and back‐stepping, and subsequent failure of a sandstone body up‐dip led to emplacement of a sandstone‐rich submarine landslide within the conduit. Collectively, this outcrop represents episodic knickpoint‐generated incision, and later infill, of a slope adjusting to equilibrium. The depositional signature of knickpoints is very different from existing models, but is likely reflective of other highly erosional settings undergoing large‐scale slope adjustment.
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Turbidity currents triggered at river mouths form an important highway for sediment, organic carbon, and nutrients to the deep sea. Consequently, it has been proposed that the deposits of these flood-triggered turbidity currents provide important long-term records of past river floods, continental erosion, and climate. Various depositional models have been suggested to identify river-flood-triggered turbidite deposits, which are largely based on the assumption that a characteristic velocity structure of the flood-triggered turbidity current is preserved as a recognizable vertical grain size trend in their deposits. Four criteria have been proposed for the velocity structure of flood-triggered turbidity currents: prolonged flow duration; a gradual increase in velocity; cyclicity of velocity magnitude; and a low peak velocity. However, very few direct observations of flood-triggered turbidity currents exist to test these proposed velocity structures. Here we present direct measurements from the Var Canyon, offshore Nice in the Mediterranean Sea. An acoustic Doppler current profiler was located 6 km offshore from the river mouth, and provided detailed velocity measurements that can be directly linked to the state of the river. Another mooring, positioned 16 km offshore, showed how this velocity structure evolved down-canyon. Three turbidity currents were measured at these moorings, two of which are associated with river floods. The third event was not linked to a river flood and was most likely triggered by a seabed slope failure. The multi-pulsed and prolonged velocity structure of all three (flood- and landslide-triggered) events is similar at the first mooring, suggesting that it may not be diagnostic of flood triggering. Indeed, the event that was most likely triggered by a slope failure matched the four flood-triggered criteria best, as it had prolonged duration, cyclicity, low velocity, and a gradual onset. Hence, previously assumed velocity-structure criteria used to identify flood-triggered turbidity currents may be produced by other triggers. Next, this study shows how the proximal multi-pulsed velocity structure reorganizes down-canyon to produce a single velocity pulse. Such rapid-onset, single-pulse velocity structure has previously been linked to landslide-triggered events. Flows recorded in this study show amalgamation of multiple velocity pulses leading to shredding of the flood signal, so that the original initiation mechanism is no longer discernible at just 16 km from the river mouth. Recognizing flood-triggered turbidity currents and their deposits may thus be challenging, as similar velocity structures can be formed by different triggers, and this proximal velocity structure can rapidly be lost due to self-organization of the turbidity current.
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Based on the integrated analysis of seismic, drilling and core data, a large channel-fan system of hyperpycnal flow origin was found in the Qijia-Gulong area of the Nen 1 Member of the Cretaceous Nenjiang Formation in the Songliao Basin. The hyperpycnal flow in this area, which originated from the edge of the basin and then passed the northern delta, formed a complete channel-fan system in the deepwater area. The channel-fan system comprises straight channels and meandering channels extending from north to south over a straight distance of more than 80 km with a width of 100900 m, and distal fan lobes at the channel tip cover a maximum area of 20 km 2. This system, which is dominated by fine-grained deposits, contains massive sandstone, sedimentary structures of flow-water origin, and internal erosion surfaces; it also contains abundant continental organic clasts and exhibits evidence of bed-load and suspended-load transportation mechanisms. The hyperpycnite sequence contains pairs of coarsening-upward lower sequences and fining-upward upper sequences, reflecting the dynamic features of cycles in which floods first strengthen and then weaken. A new sedimentary model has been built for hyperpycnites in the Songliao Basin.
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According to its original conception, turbidites have been related to slope instability of previously accumulated shallow water deposits. These are intrabasinal (I) turbidites, since the parent flow derived from a subaqueous sediment failure originated within the basin, and are characterized by an interstitial fluid having a similar density compared to that of the ambient water. In recent years, growing evidences support that turbidites can also be originated by direct discharges of rivers in flood. These fluvial discharges (via hyperpycnal flows) accumulate extrabasinal (E) turbidites, since the parent flow is originated on land, and is composed of interstitial freshwater. This paper provides for the first time a sedimentological criterion to differentiate between intrabasinal and extrabasinal turbidites (here called I and E turbidites respectively). Intrabasinal turbidites, related to slope instability, are affected by several hydraulic jumps and flow transformations during their travel basinward. They are characterized by a fast moving head and high flow entrainment. On the contrary, pure extrabasinal turbidites are fully turbulent flows, characterized by a slow moving head and limited flow entrainment. The last result in the common occurrence of extrabasinal light components (as plant debris and charcoal) in the deposit, which are derived from the fluvial parent flow. The occurrence of plant remains is here considered a diagnostic criterion for the recognition of extrabasinal (hyperpycnal) turbidites. Main plant bearing hyperpycnal facies are medium to fine grained sandstone beds showing low angle asymptotic cross stratification, massive and laminated bedding, climbing ripples and lofting rhythmites.
Deep-lacustrine transformation of sandy debrites into turbidites in the downslope direction is evident in the Upper Triassic Yanchang Formation of the Ordos Basin, central China. This facies trend is used as a template for predicting the distribution of reservoir facies of the Huaqing oilfield, which contains 100-million-tonnes of oil reserves. Based on examination of conventional cores from 30 wells, four major types of lithofacies have been recognized: (1) fine-grained massive sandstone with floating mudstone clasts and planar clast fabric (sandy debrite); (2) fine-grained sandstone and siltstone showing contorted bedding, sand injection, and ptygmatic folding (sandy slump), (3) fine-grained sandstone with thin layers of normal grading and flute casts (turbidite), and (4) mudstone with faint laminae (suspension fallout). Thick sandy debrite units occur beneath the delta-front facies, implying progradation. The lake margin is dominated by sandy debrites, whereas the lake center is dominated by turbidites. In our study area, sandy debrites constitute the producing petroleum reservoirs, but turbidites are non reservoirs. The proposed model is characterized by (1) delta-fed multiple source (line source), (2) absence of channels, and (3) downslope transformation of proximal sandy debrites into distal turbidites. This downslope transformation of sandy debrites into turbidites may be applicable to other deep-lacustrine basins worldwide for predicting reservoir distribution.
The origin of lofting rhythmites. Lessons from thin sections
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[69] ZAVALA C,BLANCO VALIENTE L, VALLEZ Y. The origin of lofting rhythmites. Lessons from thin sections. AAPG Hedberg Conference"Sediment Transfer from Shelf to Deepwater -Revisiting the Delivery Mechanisms" ,March 3-7, 2008 -Ushuaia-Patagonia, Argentina, 2008 b.
Towards a genetic facies tract for the analysis of Hyperpycnal deposits:Keynote address. AAPG Hedberg Conference"Sediment transfer from shelf to deepwater -revisiting the delivery mechanisms" ,March 3-7, 2008 -Ushuaia-Patagonia, Argentina,
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[73] ZAVALA C. Towards a genetic facies tract for the analysis of Hyperpycnal deposits:Keynote address. AAPG Hedberg Conference"Sediment transfer from shelf to deepwater -revisiting the delivery mechanisms" ,March 3-7, 2008 -Ushuaia-Patagonia, Argentina, 2008.