Conference PaperPDF Available

THE ROLE OF FLUID MUD FLOWS IN THE ACCUMULATION OF ORGANIC RICH SHALES. THE UPPER JURASSIC-LOWER CRETACEOUS VACA MUERTA FORMATION, NEUQUÉN BASIN, ARGENTINA

Abstract and Figures

RESUMEN El rol de los flujos fluidos de fango en la acumulación de fangolitas bituminosas. Formación Vaca Muerta (Tithoniano temprano-Valanginiano temprano), Cuenca Neuquina, Argentina. Durante los últimos años, el avance de técnicas no convencionales de explotación de hidrocarburos puso especial interés en obtener una mejor comprensión de los procesos sedimentarios que controlan la acumulación de materiales finos con abundante contenido orgánico. Bajo este escenario, en Argentina el principal foco de estudio ha sido puesto en la Formación Vaca Muerta, dadas las excelentes propiedades que presenta esta unidad como reservorio no convencional de hidrocarburos. En esta contribución se presenta un estudio integrado de afloramiento y subsuelo orientado al análisis sedimentológico de la Formación Vaca Muerta. El estudio de afloramiento se focalizó en el análisis de procesos de sedimentación de materiales finos en cortes pulidos de concreciones carbonáticas. Por otro lado, el estudio de subsuelo permitió abordar un análisis sedimentológico de alta resolución en testigos corona provenientes de ocho pozos exploratorios de la Formación Vaca Muerta. Las evidencias encontradas en los intervalos analizados permitieron reconocer una gran variedad de depósitos asociados a flujos fluidos de fango. Su origen se relaciona a dos procesos principales: flujos hiperpícnicos fangosos de larga duración (origen extracuencal) y flujos de fango intracuencales asociados a procesos de resedimentación. Los flujos de fango intracuencales serían más frecuentes en sectores próximos al quiebre de la plataforma, generando depósitos con bajo contenido orgánico. Por otro lado, los flujos hiperpícnicos fangosos de origen extracuencal habrían actuado como excelentes medios de transferencia de sedimentos finos y materia orgánica desde áreas emergidas hasta zonas internas de la cuenca, atravesando relieves de muy baja pendiente. En su trayectoria cuenca adentro, habrían incorporado material intracuencal previamente depositado creando depósitos de origen mixto. La rápida transferencia de fango rico en materia orgánica (tipo II y III) hacia sectores internos de la cuenca habría permitido alcanzar un soterramiento rápido y eficiente, evitando su exposición en el fondo marino. Este proceso habría favorecido la preservación de fangos bituminosos en sectores internos de la Cuenca Neuquina. Palabras clave: flujos fluidos de fango (extracuencales, intracuencales), preservación de la materia orgánica, fangolitas bituminosas
Content may be subject to copyright.
THE ROLE OF FLUID MUD FLOWS IN THE ACCUMULATION OF ORGANIC-
RICH SHALES. THE UPPER JURASSIC-LOWER CRETACEOUS VACA MUERTA
FORMATION, NEUQUÉN BASIN, ARGENTINA
Germán Otharán1,2,3, Carlos Zavala1,2, Mariano Arcuri1,2, Denis Marchal4, Guillermina Köhler4,
Mariano Di Meglio1,2 and Agustín Zorzano1
1: GCS Argentina S.R.L, Florencio Molina Campos 150, 8000, Bahía Blanca, Argentina, gotharan@gcsargentina.com,
czavala@gcsargentina.com, marcuri@gcsargentina.com, mdimeglio@gcsargentina.com, zorzano@gcsargentina.com
2: Departamento de Geología, Universidad Nacional del Sur, Av. Alem 1253, cuerpo B´- 2º Piso, 8000 Bahía Blanca,
Argentina.
3: CONICET
4: Pampa Energía S.A., denis.marchal@pampaenergia.com, guillermina.kohler@pampaenergia.com
Palabras clave: flujos fluidos de fango (extracuencales, intracuencales), preservación de la materia orgánica,
fangolitas bituminosas
RESUMEN
El rol de los ujos uidos de fango en la acumulación de fangolitas bituminosas. Formación Vaca Muerta
(Tithoniano temprano-Valanginiano temprano), Cuenca Neuquina, Argentina.
Durante los últimos años, el avance de técnicas no convencionales de explotación de hidrocarburos
puso especial interés en obtener una mejor comprensión de los procesos sedimentarios que controlan la
acumulación de materiales nos con abundante contenido orgánico. Bajo este escenario, en Argentina el
principal foco de estudio ha sido puesto en la Formación Vaca Muerta, dadas las excelentes propiedades
que presenta esta unidad como reservorio no convencional de hidrocarburos. En esta contribución se
presenta un estudio integrado de aoramiento y subsuelo orientado al análisis sedimentológico de la
Formación Vaca Muerta. El estudio de aoramiento se focalizó en el análisis de procesos de sedimentación
de materiales nos en cortes pulidos de concreciones carbonáticas. Por otro lado, el estudio de subsuelo
permitió abordar un análisis sedimentológico de alta resolución en testigos corona provenientes de
ocho pozos exploratorios de la Formación Vaca Muerta. Las evidencias encontradas en los intervalos
analizados permitieron reconocer una gran variedad de depósitos asociados a ujos uidos de fango.
Su origen se relaciona a dos procesos principales: ujos hiperpícnicos fangosos de larga duración
(origen extracuencal) y ujos de fango intracuencales asociados a procesos de resedimentación. Los
ujos de fango intracuencales serían más frecuentes en sectores próximos al quiebre de la plataforma,
generando depósitos con bajo contenido orgánico. Por otro lado, los ujos hiperpícnicos fangosos de
origen extracuencal habrían actuado como excelentes medios de transferencia de sedimentos nos y
materia orgánica desde áreas emergidas hasta zonas internas de la cuenca, atravesando relieves de muy
baja pendiente. En su trayectoria cuenca adentro, habrían incorporado material intracuencal previamente
depositado creando depósitos de origen mixto. La rápida transferencia de fango rico en materia orgánica
(tipo II y III) hacia sectores internos de la cuenca habría permitido alcanzar un soterramiento rápido y
eciente, evitando su exposición en el fondo marino. Este proceso habría favorecido la preservación de
fangos bituminosos en sectores internos de la Cuenca Neuquina.
61
10º Congreso de Exploración y Desarrollo de Hidrocarburos
Simposio de Recursos No Convencionales: Hacia una Nueva Convención
IAPG Instituto Argentino del Petróleo y el Gas
VOLVER
IAPG Instituto Argentino del Petróleo y el Gas
62 Simposio de Recursos No Convencionales: Hacia una Nueva Convención
INTRODUCTION
During the last years, the study of fine-grained sedimentary deposits has received growing
attention due to the advance in the development of shale reservoirs, leading to detailed geological
surveys on a variety of unconventional resource shales. In addition, recent laboratory research
(Schieber et al. 2007, Schieber and Southard 2009, Schieber and Yawar 2009, Schieber et al.
2013) and oceanographic expeditions in off-shore and deep marine environments (Baudin et al.
2010, 2017a, b, Biscara et al. 2011, Stetten et al. 2015, Mignard et al. 2017) have provided novel
information about the mechanisms that control mud distribution and accumulation, contributing
to a gradual paradigm shift in mudstone sedimentology (Bhattacharya and MacEachern 2009,
Macquaker et al. 2010, Schieber et al. 2010, Abouelresh and Slatt 2011, Bohacs et al. 2014, Wilson
and Schieber 2014, 2015, Lazar et al. 2015a, Schieber 2016, Zavala and Arcuri 2016).
The study of fine-grained sedimentary rocks constitutes a great challenge. First of all, the
fine-grained nature (<62.5 μm) and the repeated lithofacies alternations demand the development
of high resolution sedimentological analyses. In addition, the common occurrence of high
mechanical compaction creates a disruption of the deposit primary fabric, flattening almost every
primary feature (Schieber et al. 2010). Mechanical compaction is such an effective process in
mud deposits because of the large primary pore spaces, exceeding 70 or even 80% at shallow
burial depths (Enos and Sawatsky 1981, Goldhammer 1997, Lash and Blood 2004). As burial
increases, the gradual expulsion of the water stored in the pore network of the sediment causes
an important thickness reduction. For a long time, compaction effect was not considered at the
moment of describing sedimentary structures in fine-grained deposits. As a consequence, almost
every laminated mudstone used to be described as parallel-laminated, relating its origin to fallout
processes in low energy depositional environments. In fact, the described “parallel lamination”
is not a diagnostic criteria of hemi-pelagic deposits, since its parallel-laminated aspect can be a
product of the flattening caused by compaction. Consequently, careful examinations are essentially
required for capturing and describing rock heterogeneities in terms of bedding bounding surfaces,
grain size variations and physical sedimentary structures. These primary features constitute key
attributes for studying mudstone depositional processes.
In Argentina, the Upper Jurassic – Lower Cretaceous Vaca Muerta Formation is composed
of organic-rich mudstones and carbonates dominated by type II kerogen, representing South
America’s main unconventional reservoir (Askenazi et al. 2013, Stinco and Barredo 2014,
Vallejo and González 2016). For a long time, these deposits were described and interpreted as a
monotonous mudstone succession accumulated by fallout deposition in quiet and anoxic slope to
basinal marine settings (Leanza 1973, Leanza et al. 1977, Legarreta et al. 1981, Gulisano et al. 1984,
Mitchum and Uliana 1985, Legarreta and Gulisano 1989, Legarreta and Uliana 1991). However,
recent sedimentological analyses and reservoir characterization have revealed that the Vaca Muerta
IAPG Instituto Argentino del Petróleo y el Gas 63
The role of fluid mud flows in the accumulation of organic-rich shales.
The upper jurassic-lower cretaceus Vaca Muerta Formation, Neuquén Basin, Argentina
Formation is a highly heterogeneous stratigraphic unit whose depositional processes are largely
more variable(Askenazi et al. 2013, Kietzmann et al. 2014a, 2016, Galeazzi et al. 2014, Zeller et
al. 2015, González et al. 2016). In fact, this formation displays distinct lithofacies alternating at
centimeter to millimeter scale having variable contents of carbonate and organic matter, features
that influence its reservoir quality and production performance.
This study is focused on providing new sedimentological evidences for a better understanding
of Vaca Muerta organic-rich shales occurrence and distribution. For this purpose, high resolution
sedimentological analyses were performed on subsurface cores and outcrop cut and polished
samples corresponding to relatively uncompacted intervals preserved in early diagenetic calcareous
concretions. The evidences found in the studied intervals suggest that the Vaca Muerta Formation
was deposited under a more complex scenario than previously assumed, where hemi-pelagic
deposition was probably subordinated to intrabasinal and extrabasinal fluid mud flow events. This
contribution discusses the importance of mudstone depositional processes for future exploration
of unconventional resources in the Vaca Muerta Formation and other shale reservoirs.
GEOLOGICAL BACKGROUND
The Neuquén basin is a triangular-shaped back-arc basin developed during the Mesozoic in
the western margin of Gondwana (Mosquera et al. 2011). It is located in the eastern side of the
Andes in west central Argentina and central Chile, between 32º and 40º S (Fig. 1). The basin
boundaries are defined by the Sierra Pintada belt to the northeast and the North Patagonian
Massif towards the southeast, whereas the occidental margin is defined by the Andean magmatic
arc. It presents a northwest-southeast elongated shape that covers more than 160,000 km2 (Vergani
et al. 1995), with a sedimentary infill of at least 7,000 m of continental and marine siliciclastic,
carbonate and evaporite deposits. Historically, the Neuquén basin has been widely studied because
of its importance as an oil-bearing basin, with vast research developed on conventional clastic
reservoirs. Nevertheless, the crescent hydrocarbon production from unconventional reservoirs
have promoted the onset of several geological studies on the main unconventional targets.
The origin of the Neuquén basin is related to the convergence of the South American plate
with the southern segment of the Nazca-Pacific plate (Hogg 1993). This tectonic scenario caused
a flexural subsidence of the continental crust behind a stationary magmatic arc, resulting in
the development of different back-arc basins during the Permo-Triassic (Mpodozis and Ramos
1989, Vergani et al. 1995). Under such tectonic settings, the basin fill evolution was controlled by
repeated sea-level oscillations that conditioned the basin connection with the paleo-Pacific Ocean
(Legarreta and Uliana 1991, Mutti et al. 1994). As a result, periods of high eustatic sea level resulted
in fast marine flooding coming from the paleo-Pacific Ocean, providing anoxic to sub-toxic marine
conditionsoptimum for source rock development (Legarreta 2002). On the other hand, lowstand
IAPG Instituto Argentino del Petróleo y el Gas
64 Simposio de Recursos No Convencionales: Hacia una Nueva Convención
periods caused forced regressions and the consequent development of evaporites and non-marine
clastics. These flooding-desiccation events are repeatedly manifested in the stratigraphic record of
the Neuquén basin. According to Zavala et al. (2006), periods of marine disconnection are usually
associated to regional unconformities defined by sharp lithologic contacts between continental
and marine deposits. Also, in places some angularity can be detectable, what suggesta tectonic
overprint. The basin accommodation space increased progressively above such unconformities,
resulting in the accumulation of transgressive successions over the former continental deposits
(Fig. 1).
The sedimentary evolution of the Neuquén basin can be divided into three main depositional
stages (Zavala and González 2001): The first stage (UpperTriassic-Lower Jurassic) represents the
syn-rift phase, characterized by the deposition of volcanic and volcaniclastic materials (Precuyo
Figure 1. Geological map and main stratigraphic column for the central area of the Neuquén basin (After Zavala et al. 2006).
IAPG Instituto Argentino del Petróleo y el Gas 65
The role of fluid mud flows in the accumulation of organic-rich shales.
The upper jurassic-lower cretaceus Vaca Muerta Formation, Neuquén Basin, Argentina
Group) along hemi-graben depocenters (Gulisano 1981). The second stage (Lower-Upper Jurassic)
is characterized by a mainly clastic prograding marine to continental succession (Cuyo and Lotena
groups) deposited over a tectonically induced irregular relief. The third stage (Upper Jurassic-
Upper Cretaceous) is a marine to continental succession up to 6,000 m thick (Mendoza, Rayoso,
and Neuquén groups). During this last stage, a global high eustatic sea level stand favored a
maximum expansion of marine deposits throughout the basin, with the consequent development
of the main source rock unit (Vaca Muerta Formation). The basin was totally disconnected from
the paleo-Pacific Ocean in the late early Cretaceous. Finally, the establishment of a compressive
tectonic regime during the late Cretaceous and the Cenozoic caused an uplift of the western part
of the basin, providing widespread, north-south oriented outcrops that constitute different fold
and thrust belts. Therefore, oil bearing deposits are mainly preserved on the eastern margin of the
Neuquén basin (Fig. 1).
THE VACA MUERTA FORMATION
The Vaca Muerta Formation (Weaver 1931, enmend. Leanza 1973) constitutes a thick, widely
distributed stratigraphic unit developed during the lateJurassic-early Cretaceous in the Neuquén
basin. In the Neuquén province domain, this unit is mainly composed of dark, bituminous
fine-grained mudstones thinly interbedded with gray siliceous/calcareous fine-to coarse-grained
mudstones. These fine-grained deposits are also alternating with limestones and minor sandstone
intervals. As mentioned by Stinco and Barredo (2014), the Vaca Muerta Formation constitutes
South America’s main unconventional reservoir (Askenazi et al. 2013, Vallejo and González 2016),
with total organic carbon (TOC) contents between 3-8 %, Ro max (%) 0.8-2, hydrogen Index 400-
800 mg HC/gtoc, SPI 5 to 20 t HC/m2 and a kerogen type I-II/IIS (Legarreta and Villar 2015).
This sedimentary succession comprises the lower part of the Mendoza Group (Stipanicic et al.
1968), also referred to as the Lower Mendoza Mesosequence (Legarreta and Gulisano 1989).
The Lower Mendoza Mesosequence is an upper Kimmeridgian-lower Valanginian
shallowing-upward sedimentary cycle comprising all the deposits between the Intramalm and
the Intravalanginian unconformities. At the base, this cycle starts with non-marine clastics of the
Tordillo Formation (Kimmeridgian), which are sharply overlaid by off-shore to basinal marine
deposits of the Vaca Muerta Formation (lower Tithonian-lower Valanginian). The origin of these
deposits is related to a global sea level rise that took place during the early Tithonian, causing a
rapid and catastrophic marine flooding from the paleo-Pacific Ocean (Mutti et al. 1994). The initial
flooding event was such an important transgression that exceeded all previous paleogeographical
boundaries, displaying a typical retrogradational stacking pattern. Subsequently, an important
clastic input from the North Patagonian Massif caused the development of a western-northwestern
prograding mixed-shelf system during a regional highstand context (Leanza et al. 2011).
IAPG Instituto Argentino del Petróleo y el Gas
66 Simposio de Recursos No Convencionales: Hacia una Nueva Convención
At the subsurface, towards the eastern margin of the basin, the Vaca Muerta Formation is
diachronically covered by shallow marine carbonates and clastics of the Quintuco and Loma
Montosa formations (upper Tithonian-lower Valanginian), and the continental deposits of the
Puesto Gonzalez Formation (lower Valanginian, Mitchum and Uliana 1985). At the same time,
in the southern domain (Picún Leufú sub-basin, Fig. 1), these nearshore clastics and carbonates
are grouped into the Carrín Cura and Picún Leufú formations, whereas the continental deposits
match into the Bajada Colorada Formation (Leanza et al. 2011). These units constitute the proximal
facies of the Tithonian-Valanginian system, being totally replaced by off-shore to basinal facies
of the Vaca Muerta Formation towards distal basin positions. In basin inner zones, the Vaca
Muerta Formation is characterized by organic-rich fine-grained deposits up to 1,200 m thick, also
including slope turbidites referred to the Huncal Member (lower Berrasian, Leanza et al. 2003).
The former outstanding seismic stratigraphic analyses (Mitchum and Uliana 1985) recognized
nine depositional sequences for the lower Tithonian-lower Valanginian system (Sequence A-I,
Mitchum and Uliana1985). According to Leanza et al. (2011), this system comprises three main
evolutionary stages: a lower ramp system developed during the early-middle Tithonian (Sequences
A, B and C) followed by a slope configuration extended from the late Tithonian up to the Berrasian
(Sequences D, E, and F), and a final stage of shelf-break configuration (Sequences G, H and I)
developed during the early Valanginian (Mitchum and Uliana 1985).
Mitchum and Uliana (1985) magnificent work was recently complemented by an integrated
regional seismic stratigraphic analysis developed during the IX CONEXPLO (Galeazi et al. 2014).
It was conducted by professionals from the industry and academic researchers who integrated the
latest 3D seismic data with well logs, geochemical and core data from newly drilled wells, including
also outcrop studies for a better characterization of the lower Tithonian-lower Valanginian system.
The results of this study were later published as a special publication by the IAPG (Vallejo and
González 2016), suggesting the presence of 6 seismic units (Fig. 2, Sattler et al. 2016). These units
are characterized by distinctive seismic stacking patterns separated by regional horizons, having
a great correspondence with the previous seismic-stratigraphic framework (Mitchum and Uliana
1985). As mentioned by Desjardins et al. (2016), different clinoform types have been recognized
within the lower Tithonian-lower Valanginian system (Dominguez et al. 2017). In a regional context,
an initial mixed-ramp configuration composed of low angle clinoform geometries with a typical
agradational pattern (Units 1-2, Fig. 2) is followed by a well-defined progradational arrangement
with oblique and sigmoidal clinoform types defining a shelf-break(Units 3-6). Clinoform origin
within the Vaca Muerta Formation is currently under increasing debate. Present-day research on
this topic are suggesting different sedimentary processes, including: contornites, downwelling-
triggered off-shore bottom currents, bottom Ekman transport, muddy hyperpycnal flows and
muddy turbidity currents (Desjardins et al. 2016).
IAPG Instituto Argentino del Petróleo y el Gas 67
The role of fluid mud flows in the accumulation of organic-rich shales.
The upper jurassic-lower cretaceus Vaca Muerta Formation, Neuquén Basin, Argentina
METHODS
This study comprises an integrated high-resolution sedimentological analysis of outcrop
samples and subsurface cores of 8 different wells (Fig. 2). Rock description was performed following
the nomenclature proposed by Lazar et al. (2015b).
OUTCROP STUDIES
High resolution sedimentological analyses were performed in early-diagenetic carbonate
concretions (Figs. 3a and b) that preserve an exceptional record of mudstone depositional history
(Otharán and Zavala 2016, 2018, Otharán et al. 2017a). These syn-sedimentary concretionary
bodies grow near sediment-water interface at shallow burial depths, providing a compaction-
resistant framework capable of preserving a “frozen” record of the deposit primary fabric
(Westphal et al. 2000, Lash and Blood 2004, Abouelresh and Slatt 2012, Marshall and Pirrie 2013,
Kietzmann et al. 2014b, McNeill et al. 2015). The employed method consists in sampling different
Figure 2. Seismic cross-section from Sattler et al. (2016) with projection of wells 1, 2 and 5 core intervals. Additional seismic
cross sections for wells from the central (wells 3 and 4) and southern areas (wells 6, 7 and 8) are also presented (B-B’, C-C’). The
surfaces defined by Sattler et al. (2016) are plotted in the satellite image according to Dominguez et al. (2017).
IAPG Instituto Argentino del Petróleo y el Gas
68 Simposio de Recursos No Convencionales: Hacia una Nueva Convención
carbonate concretions that at first sight exhibit primary sedimentary features (Fig. 3c). Afterwards,
the samples are cut using a rock cutting machine and then polished through steel discs using a
silicon carbide abrasive. Finally, the polished slabs are digitally scanned and processed for a better
characterization (Fig. 3d).
The studied samples were collected from the basal deposits of the Vaca Muerta Formation
in inner basin positions, close to Huncal and Rahueco localities (Fig. 2). This basal succession
is characterized by dark, bituminous organic-rich mudstones rhythmically intercalated with
calcareous concretions up to 1 m thick, with common beef and tuff levels occurrence (Otharán et
al. 2017a). It represents the initial transgressive deposits of the Vaca Muerta Formation over the
continental deposits of the Tordillo Formation, matching within the Unit 1 of Sattler et al. (2016),
which is equivalent to the Sequence A of Mitchum and Uliana (1985).
CORE STUDIES
In contrast with stratigraphically-isolated outcrop samples, core studies provide a continuous
stratigraphic record of fine-grained successions, supporting the performance of high-resolution
sedimentological analyses. A total core data of 412 m from 8 wells property of Pampa Energía
S.A. and Vista Oil & Gas were carefully examined (Fig. 2).Primary rock attributes (e.g. texture,
bedding, composition, physical sedimentary structures, bioturbation degree) were captured using
a specific software designed for stratigraphic column description (LithoHero®, Iparraguirre et al.
2016). Nevertheless, the purpose of this study was to describe and illustrate different event beds
within the Vaca Muerta mixed-system, trying to establish a genetic linkage between outcrop and
subsurface fluid mud flow deposits (FMFd). Also, based on the seismic-stratigraphic framework
developed by Sattler et al. (2016, Fig. 2), the authors have proposed to analyze FMFd occurrence
within the Vaca Muerta mixed system, trying to establish their lateral facies changes at different
system positions (shelf-slope-basin). For this purpose, when possible, the studied cores were
projected into the seismic cross-sectionof Sattler et al. (2016). For those wells located distant from
this transect, additionalseismic cross-sectionare presented (Fig2).
The studied cores are widely distributed across the lower Tithonian-lower Valangian mixed
system, comprising a whole spectrum of facies from mainly shelfal areas (SE, Wells 3-8) towards
inner basin positions (NW, Wells 1-2, Fig. 2). It must be clarified that the mention of proximal-
distal system positions in this work does not refer to the cores position respect to the ancient
coastline. Instead, this concept is employed to illustrate their relative position within the study
area, being proximal cores those located towards the SE area (defined by Sattler et al. 2016) and
distal the ones situated at the NW margin, whereas central ones are those comprised between the
SE and NW areas (Fig. 2).
IAPG Instituto Argentino del Petróleo y el Gas 69
The role of fluid mud flows in the accumulation of organic-rich shales.
The upper jurassic-lower cretaceus Vaca Muerta Formation, Neuquén Basin, Argentina
Core studied intervals
Most of the core intervals from the SE and central areas match within the basal transgressive
deposits of the Vaca Muerta Formation, presenting a typical aggrading to low-angle prograding
seismic stacking pattern. They are mainly comprised within the Unit 1 of Sattler et al. (2016), with the
exception of Wells 3 and 5 cores, which also go through agradding to low-angle pograding clinoforms of
the Unit 2. Particularly, Well 6 core spread to the basal contact of the Vaca Muerta Formation withthe
underlying continental deposits of the Tordillo Formation. On the other hand, core intervals from the
NW margin did not attempt to sample the basal transgressive sequence (Unit 1). Particularly, in Well 1
two different core intervals have been studied: a lower interval situated within bottomset segments of low
angle clinoforms corresponding to the Unit 2 (Sattler et al. 2016), and an upper interval matching with an
important transgression that defines the onset of the Unit 5, presenting a typical retrogradational seismic
stacking pattern (Desjardins et al. 2016). Well 2 core is located in high-angle foresets of prograding
sigmoidal clinoforms present at the B2-B3 interval of the Unit 4 (Marchal et al. 2016).
Figure 3. a) Example of an early-diagenetic calcareous concretion in the Vaca Muerta Formation. b) Line drawing of the con-
cretion exhibited in a). Note the differential compaction between the sediments within the concretion and those adjacent to it
(highly-compacted fissile mudstones). c)Early-diagenetic carbonate concretion with perfect preservation of the primary lamina-
tion. d)Scanned and digitally-processed cut and polished slab of the carbonate concretion exhibited in c.
IAPG Instituto Argentino del Petróleo y el Gas
70 Simposio de Recursos No Convencionales: Hacia una Nueva Convención
RESULTS
OUTCROP STUDIES
Description
The sedimentological analysis of the Vaca Muerta Formation carbonate concretions has
revealed the common occurrence of micro-erosional surfaces and low-angle lamina truncations
within different mudstone beds (Fig. 4). These deposits are mainly composed of carbonate-cemented
detrital mud (clay floccules and silt grains) with abundant plant remains and subordinated carbonate
skeletal grains. The resulting beds, rarely thicker than 5 cm, are commonly characterized by a
basal micro-erosional surface over which mud deposition occurs (Figs. 4a, f and g). At times, bed
boundaries are defined by an orange-coloured oxidized pyritic interval (Figs. 4a, b and c). These
pyrite concentrations can be helpful to identify bed limits when contacts among beds and internal
lamination distinction becomes challenging due to the lack of textural or compositional changes.
A wide range of primary sedimentary structures have been recognized within the studied samples,
including: 1) current mud ripples (McR, Figs. 4d, e, f, g and h), 2) planar, continuous to discontinuous
parallel lamination with occasional low-angle lamina truncations (MfL, MmL, McL, Figs. 4e, f, g and h),
3) massive beds (MfM, Figs. 4e and f; McM, Figs. 4g and h) and 4) thin massive laminae with repeated
transitional grain size variations (normal-inverse grading trends, Figs. 4g, h and 5a). Current mud ripples
are similar to those originally described in laboratory flumes (Schieber et al. 2007). They are characterized
by downlapping foresets that can be either composed of coarse silt grains (Figs. 4d, e and f) or clay floccules
that act hydrodynamically as very fine-grained sand (floccule ripples, Figs. 4g and h). The foresets are
commonly downlapping onto a sharp, scoured surface (Fig. 4g) and they may overlay parallel-laminated
mudstones (McL, Figs. 4d, e and f). Upwards, mud ripples are replaced by massive fine to medium-
grained mudstones that towards the top of the bed turn into organic-rich, bituminous mudstones.
Additionally, post-depositional sedimentary structures are common features of the studied
mud deposits. These include shallow depth soft-sediment deformation structures developed in
soup-like muddy bottoms (flame and convolute lamination, Figs. 2d and f) and flute marks (Figs.
3a and b) related to deeper, cohesive and strength-firm muddy substrates (Dzulynski and Sanders
1962, Allen 1969). No signatures of biological sedimentary structures have been recognized within
the concretions (burrows, tracks and trails are absent).
Interpretation
The afore mentioned sedimentary features have an important sedimentary sense in terms of
mud depositional processes in inner basin environments. Micro-erosional surfaces within different
IAPG Instituto Argentino del Petróleo y el Gas 71
The role of fluid mud flows in the accumulation of organic-rich shales.
The upper jurassic-lower cretaceus Vaca Muerta Formation, Neuquén Basin, Argentina
Figure 4. Primary sedimentary features in carbonate concretions. a) Mudstone beds displaying a basal micro-erosional surface
(red arrows, E). Boundary between beds are defined by an oxidized pyritic interval (yellow arrows, Py). Internally, beds are mas-
sive and parallel-laminated.b) Close up of figure a). Appreciate the abundance of plant debris (e). c) Mudstone beds separated by
erosional surfaces with associated pyritic intervals. In this case, plant debris (e, extrabasinal components) are found together with
fossiliferous skeletal grains(i, intrabasinal components). d) Mud ripples in coarse mudstones (McR). Ripples are interbedded
with laminated coarse mudstones (McL). e, f) Outcrop (e) and cut and polished slab (f) of a carbonate concretion. Note the
presence of soft-sediment deformation structures (McD) under erosional surfaces (E). Parallel-laminated facies (MmL, McL) and
mud ripples (McR) are developed above the erosional surface. g, h) Samples from a same carbonate-cemented bed. Note how the
erosional surface exhibited in g is absent in h, where a sharp contact is present. Also, in figure h, mud ripples crest is truncated
(E), what suggest the occurrence of subtle erosion. This erosional episode is not recorded in figure g, where mud ripples (McR)
grade upwards to massive coarse mudstones (McM).
IAPG Instituto Argentino del Petróleo y el Gas
72 Simposio de Recursos No Convencionales: Hacia una Nueva Convención
mudstone beds suggest the occurrence of high-energy events capable of eroding substantial
quantities of mud from the basin floor. These events are interpreted as bottom fluid mud flows
transporting fine-grained clastics, minor carbonate skeletal grains and particulate organic matter
in fully turbulent conditions.
Fluid mud flows are basically low-density muddy turbidity currents which, according to
the flow velocity and the sediment concentration, can have a variable erosion capacity (Fig. 4).
The erosion magnitude of each fluid mud flow event can be estimated by the recognition of
firm/soupy substrate conditions at bed boundaries (flute marks vs soft-sediment deformation
structures). It is generally accepted that mud erodibility is essentially controlled by its water
content, being easier to erode soft-soupy muds than firm ones (Potter et al. 1980).Particularly,
flute marks suggest a flow separation under severe velocity conditions at a place where the seafloor
presents geomorphological irregularities, creating powerful eddies capable of eroding the cohesive
muddy seafloor (Allen 1969). According to this, the presence of a firm substrate could be related
to an erosional event produced by the overpassing of a rapid flow capable of completely removing
the topmost soupy mud from the bottom, incorporating the eroded material to its sedimentary
load (Fig. 5a,Otharán et al. 2017a). Furthermore, pyrite concentrations at bed boundaries (Figs. 4a,
b and c) could be associated to the erosion of substantial quantities of mud by bottom fluid mud
flows (Schieber 1998, Schieber and Baird 2001).
On the other hand, the preservation of soft-sediment deformation structures underneath an
erosional surface (McD, Figs. 4e and f) suggests an overpassing flow with lower erosion capacity,
enabling a partial preservation of the uppermost soupy mud. As remarked by Sanders (1965),
when the seafloor is cohesive but hydroplastic instead of being firm, the passage of a turbulent
flow may cause a deformation of the bed over which the current passes, creating soft-sediment
deformation structures. Flume experiments developed by Einsele et al. (1974) have demonstrated
that plastic muds with 70 % porosity required current velocities of 150 cm/s to produce soft-
sediment deformation structures due to current drag on the sediment surface (Schieber 1998).
The primary sedimentary structures recognized in the analyzed fluid mud flow deposits
(FMFd) are related to fluctuations in the flow velocity, turbulence and sediment concentration.
Depending on the sedimentfallout rate,theresulting mud deposits can exhibit quite different
stacking patterns. High fallout rates promote a rapid accumulation of the suspended load, resulting
massive mudstone beds. On the other hand, low rates of sediment fallout are going to produce
parallel-laminated (medium fallout rate) and rippled (low fallout rate) deposits.Particularly,
rippled-mudstone deposits suggest some bedload transport of the coarsest materials that are
progressivelyfalling out of the suspension cloud.Otherwise, the common occurrence of massive
deposits above the rippled-faciescould represent a rapid accumulation of the suspended load as
the flow velocity decreases. The organic-rich finest-grained facies located at the top of each bed
could be related to the progressive waning and extinction of the flow. The organic matter perfect
IAPG Instituto Argentino del Petróleo y el Gas 73
The role of fluid mud flows in the accumulation of organic-rich shales.
The upper jurassic-lower cretaceus Vaca Muerta Formation, Neuquén Basin, Argentina
Figure 5. a) Close up of the sample shown in Figure 3d. This sample is characterized by repeated fining-coarsening upwards
trends at lamina scale, which represents flow fluctuations (acceleration-deceleration phases) in a long-lasting fluid mud flow
event. b) Flow fluctuations can be a possible explanation for the origin of the bed shown in a). The graphic shows the relation-
ship between the flow velocity and the duration time (t1-t4) of a long-lasting fluid mud flow event. The resultant sedimentary
structuresand grain-size variations recorded in mudstone strata are believed to occur in response to flow fluctuations.
IAPG Instituto Argentino del Petróleo y el Gas
74 Simposio de Recursos No Convencionales: Hacia una Nueva Convención
preservation added to the absence of bioturbation in these deposits suggest either arapid burial or
a sub-environment with anoxic to sub-toxic bottom water conditions.
Another distinctive characteristic of the analyzed FMFd is the presence of thin massive laminae
with repeated fining-coarsening upward trends (Fig. 5a). These grain size variations are related
to quasi-steady fluid mud suspensions with common flow velocity fluctuations (acceleration-
deceleration phases). Therefore, during the acceleration phase the coarsest materials would be
settling out from suspension (when the flow velocity is under muderosion threshold) whereas
the finest grained sediments would remain in transport (Fig. 5b). However, at the flow velocity
peak stage the current can exceed the threshold velocity for mud erosion, creating internal lamina
truncations and micro-erosional surfaces (Figs. 4f and h). After the peak stage, the decrease of the
flow velocity favors a progressive accumulation of fine-grained mud (Fig. 5b).
Origin of fluid mud flows
According to Macquaker et al. (2010), the source of energy for the ignition of fluid mud flows
in marine basins can be provided by waves, currents, gravity processes or by an interaction of any
of these mechanisms. Particularly, sediment gravity flows can be important delivery mechanisms
for the basinward transfer of mud. These include muddy hyperpycnal flows (extrabasinal muddy
turbidity currents, Zavala and Arcuri 2016) and intrabasinal surge-type muddy turbidity currents
similar to the “unifites” described by Blanpied and Stanley (1981) and the turbiditic mud layers
of Rupke and Stanley (1974). Likewise, combined flows such as storm events (tempestites) and
wave-enhanced sediment gravity flows (WESGFs, Macquaker et al. 2010) can be significant mud
redistribution mechanisms.
The recognized flow fluctuations (Fig5) are interpreted as the result of direct river discharges
during important flood events (Otharán et al. 2017a, Fig6). Each flood event would be capable of
generating quasi-steady muddy hyperpycnal flows that may be sustained for days, weeks, or even
months (Mulder et al. 2003, Zavala et al. 2006, 2011, 2014, Nakajima 2006, Soyinka and Slatt 2008,
Bhattacharya and MacEachern 2009, Chang and Chun 2012, Wilson and Schieber 2014, 2015,
Zavala and Arcuri 2016, Azpiroz-Zabala et al. 2017). These long-lasting events would be able to
transfer significant volumes of plant debris and fine-grained sediments for long distances towards
distal basinal settings (Nakajima 2006, Soyinka and Slatt 2008, Bhattacharya and MacEachern
2009, Abouelresh and Slatt 2011, Slatt 2011, Wilson and Schieber 2014, 2015, Li et al. 2015,
Schieber 2016, Zavala and Arcuri 2016, Poyatos-Moré et al. 2016).
As previously discussed, flow fluctuations can produce normal to inverse-graded deposits
(Fig. 5a) as well as low-angle lamina truncations, scour marks and subtle erosional surfaces within
a single hyperpycnal deposit (Figs. 4e, f, g and h). Such erosional features are the signature of the
flood peak stage, where the waxing flow have already exceeded the threshold velocity for mud
IAPG Instituto Argentino del Petróleo y el Gas 75
The role of fluid mud flows in the accumulation of organic-rich shales.
The upper jurassic-lower cretaceus Vaca Muerta Formation, Neuquén Basin, Argentina
erosion (Fig. 5b). Occasionally, the flow can completely erode the initial hyperpycnal deposit,
leading out to an incomplete record of the hyperpycnal event (Figs. 4g and h). The last could
result in a normally-graded bed accumulated over an erosional surface once the flow velocity
started to decrease (deceleration phase, Zavala et al. 2006). In these situations, the differentiation
between muddy hyperpycnites and typical normally-graded deposits such as mud turbidites and
tempestites becomes challenging (Mulder and Alexander 2001, Mulder et al. 2003, Bhattacharya
and MacEachern 2009, Wilson and Schieber 2014, Schieber 2016).
The erosion capacity of muddy hyperpycnal flows enables the incorporation of intrabasinal
components (e.g. carbonate mud, microfossils and skeletal grains, type II organic matter) to the
primary extrabasinal sedimentary load (e.g. detrital mud, plant debris). For this reason, another
diagnostic criterion for a hyperpycnal origin of fluid mud flows is the bed composition, characterized
by compositionally mixed (siliciclastic-carbonate) deposits exhibiting both autochthonous (type
II) and allochthonous (type III) organic matter content. This was recently proved in organic-rich
muddy sediment cores recovered from the distal part of the Ogooue turbidite system (Biscara et al.
2011, Mignard et al. 2017) as well as in the Congo mud-rich deep-sea turbidite system (Baudin et al.
2010, 2017a, b, Stetten et al. 2015), where muddy hyperpycnal deposits contain mixtures of marine
and terrigenous organic matter. Therefore, the passage of hyperpycnal flows through shelf/ramp
environments would have favored the erosion and incorporation of intrabasinal components to
the former extrabasinal sedimentary load.
In contrast with intrabasinal fluid mud flows, muddy hyperpycnal flows would be able to go
through very low gradient reliefs, since the flow power is provided by sustained river discharges
(Fig. 6). This could explainwhy the studiedmuddy hyperpycnitesare associated to the Vaca Muerta
Formation basal deposits accumulated in a low gradient mixed-ramp system (Fig. 2).
CORE STUDIES
The studied core intervals display different types of mudstone beds alternating with tuffaceous
intervals, bedding parallel fibrous veins (beefs) and carbonate cemented beds (Figs. 7 and 8).
Figure 6. Long-lasting muddy hyperpycnal flows associated to important river flood events. Sustained river discharges allow the-
se flows to travel along very low-gradient reliefs, incorporating intrabasinal materials into their original extrabasinal sedimentary
load.
IAPG Instituto Argentino del Petróleo y el Gas
76 Simposio de Recursos No Convencionales: Hacia una Nueva Convención
Occasionally, bindstones can be present, displaying a characteristic biogenic lamination. In the
NW area, fine-grained organic-richmudstoneswith abundant filament bivalves and ammonite
fauna predominate, including also thick beef veinsand early-diagenetic carbonate concretions(Fig.
7). On the other hand, central areas are characterized by fine-to coarse-grained fossiliferous and
calcareousmudstones withlesser beef intervals (Fig. 8). Particularly, the SE area isrepresented by
highly bioturbated fine-grained carbonates and calcareous mudstones in the Well 5, where as in
Wells 6-8 fine-to coarse grained dolomitized mudstones dominate. It must be remarked that tuff
levels and beefs are significantly reduced from the NWto the SE area, where they occurrence is
really scarce. Bioturbation degree can be significant within tuffaceous deposits, which also exhibit
an important diagenetic overprint characterized by sparite cement precipitation.
Subsurface cores commonly exhibit subtle micro-erosional surfaces within distinct mudstone
beds (Fig. 8), which is directly linked to fluid mud flow events. These fluid mud flow deposits
(FMFd) can be stratigraphically isolated within background sedimentation (e.g. hemi-pelagic
mudstones and tuffs, biogenic carbonates) or they may define a full interval dominated by fluid
mud flow deposition (Fig. 8).
FMFd description
FMFd in the analyzed cores of the Vaca Muerta Formation are primarily detectable by erosive
bed contacts in proximal-central system positions (Figs. 9a, b and c), whereas in distal settings their
recognition is more challenging, being only manifested by mm-thick sulfate-rich (pyrite/sphalerite)
intervals defining sharp mudstone contacts (Figs. 9d and e). Beds can reach at most 4 cm in thickness.
They are commonly characterized by a mixture of extrabasinal and intrabasinal components (Fig. 9f).
FMFd are essentially mixed (siliciclastic-calcareous) mudstones having variable carbonate
content according to theirposition within the system. Beds are commonly normally graded,
exhibiting medium-to coarse-grained calcareous mud above the basal scoured surface (Figs. 9a,
b, c and d).At times, the carbonate fraction is present as skeletal grains (e.g. microfossils, Figs. 9b
and c) while in others instances it may be only manifested as coarse-grained calcareous mud (Figs.
7, 8 and 9d). Flute marks and soft-sediment deformation structures can be commonly associated
to FMFd bounding surfaces (Figs. 9a, c, d and e). Alternatively, these beds can also exhibit a
basal concentration of calcitizied/argillizied tuffaceous coarse-grained mud (Fig. 9a) or a pyritic
concentration above beds boundary. Normally, organic-rich fine-grained deposits are displayed
towards the top of each FMF bed.
Internally, FMFd can be either massive, parallel-laminated or normal/inverse-graded (Fig. 9).
As an exception, Well 2 core interval is characterized by parallel-laminated fine-to coarse-grained
mudstones with common low-angle lamina truncations and sin-sedimentary deformational
sedimentary structures (micro-slumps, Fig. 10). Bioturbation is generally absent within FMFd.
IAPG Instituto Argentino del Petróleo y el Gas 77
The role of fluid mud flows in the accumulation of organic-rich shales.
The upper jurassic-lower cretaceus Vaca Muerta Formation, Neuquén Basin, Argentina
Figure 7. Partial stratigraphic column for the Well 1lower core interval (A-A’, Fig. 2; Unit 2).
IAPG Instituto Argentino del Petróleo y el Gas
78 Simposio de Recursos No Convencionales: Hacia una Nueva Convención
Figure 8. Partial stratigraphic column for the Well 3 core interval (B-B’, Fig. 2; Unit 1).
IAPG Instituto Argentino del Petróleo y el Gas 79
The role of fluid mud flows in the accumulation of organic-rich shales.
The upper jurassic-lower cretaceus Vaca Muerta Formation, Neuquén Basin, Argentina
ORIGIN OF FMFD
Grain size variations within single FMF beds (Figs. 8, 9a, 9b and 9c) are interpreted as the result
of flow fluctuations during long lasting muddy hyperpycnal events (Fig. 6). In the FMFd examples
exhibited in Figure 8, the interlamination between silt and clay size calcareous mud is interpreted
as simultaneous deposition from a unique, long lasting hyperpycnal event. This interpretation is
also supported by the mixed composition of these beds, which are integrated by both extrabasinal
and intrabasinal elements (Fig. 9e).Regarding the relative light weight of carbonate components,
they commonly constitute the coarsest-grained fraction of some muddy hyperpycnites (Figs. 9b,
c and d). Recent flume experiments developed with carbonate mud demonstrated that, in spite of
the contrasting mineralogy, mud carbonate present a similar hydrodynamic behavior as siliciclastic
mud (Schieber et al. 2013). Other FMF beds exhibit a basal coarse-grained tuffaceous mud deposit
over bed boundaries, which is upwards transitionally replaced by mediumto fine-grained detrital
Figure 9. Examples of FMFd from Wells 3 (a-d and f, central area) and 1 (e, NW area). Well 3 examples correspond to the Unit 1
of Sattler et al. (2016). a)Massive (McM, MmM) to diffusely laminated (McL) mudstone beds. The lower bed is characterized by
a basal tuffaceous mud (V, orange arrows). Soft-sediment deformation structures are associated to bed boundaries (E). b) FMFd
with clear flow fluctuations (normal-inverse grading trends). Beds limits (E) are defined by intrabasinal calcareous mud (i) mainly
composed of skeletal grains and microfossils (Fig. 7). c) FMFd with high content of intrabasinal materials (carbonate grains, i).
Towards the top, pyrite concentrations define beds boundaries (Py, yellow arrows). d) FMFd characterized by normally-graded
beds over a basal erosional/sharp contact. Pyrite concentrations are associated to erosional boundaries. e) FMFd from the NW
area. Bed boundaries are defined by pyrite intervals and occasionally soft-sediment deformation structures. f)FMFd displaying a
mixture of intrabasinal (i) and extrabasinal (e) components.
IAPG Instituto Argentino del Petróleo y el Gas
80 Simposio de Recursos No Convencionales: Hacia una Nueva Convención
mud (Fig. 9a). The occurrence of both carbonate and tuffaceous materials towards the base of
FMFd could be explained by the erosional nature of muddy hyperpycnal flows. During their
travel basinward, muddy hyperpycnal flows would be able to erode and incorporate any available
type of unconsolidated fine-grained materials laying at the seafloorinto theirprimary extrabasinal
sedimentary load. This could be the case of thin levels of volcanic ash materials originally settled
out through the water column during the course of volcanic eruptions.
The same assumption can be made for the organic matter content of muddy hyperpycnites,
which can be characterized by both intrabasinal (type II) and extrabasinal (type III) organic matter
content. TOC in FMFd within the studied wells are generally over 2 %, reaching in some instances
more than 10 % TOC in inner basin areas (Fig. 7). The presence of the highest TOC contents in
distal system positions is related to the organic matter sequestration from the main production
area (shelfal environments) by fluid mud flows, accumulating it far off-shore in terminal turbiditic
muddy lobe-complexes (accumulation zone).
However, as mentioned before, when FMFd are characterized by normally-graded beds
accumulated over an erosional surface, the distinction between muddy hyperpycnites and other
type of fluid mud flows deposits becomes challenging (Mulder and Alexander 2001, Mulder
et al. 2003, Bhattacharya and MacEachern 2009, Wilson and Schieber 2014, Schieber 2016).
In these situations where FMFd internal stacking pattern is not distinctive of any flow type,
complementary studies are needed to accurate the deposit origin (e.g. petrography, SEM,
palynology, geochemistry).
Besides hyperpycnal flow events, basinward mud transportation could be possible by surge-
type muddy turbidity currents developed close to the shelf-break (Fig. 11). Unfortunately, the only
studied core interval that match within well-defined foresets of high-angle prograding clinoforms
is the Well 2 core (Fig. 2), where syn-depositional deformational structures are clearly recognizable
(Fig. 10). Deposits associated to intrabasinal sediment gravity flow processes are well known within
high angle slope settings of the Vaca Muerta mixed system (Arregui 2014, Pose et al. 2014, Otharán
et al. 2017b, Reijenstein et al. 2017).
Flume experiments performed by Gerber et al. (2008) proposed that intrabasinal fluid mud
flows could be responsible for the origin and progradation of clinoform morphologies. This
autocyclic mechanism for clinoform growth and evolution by slope-flow feedback could give
a possible explanation for the origin of the Vaca Muerta Formation prograding clinoforms. If
this hypothesis is valid and muddy turbidites are the primary building blocks of Vaca Muerta
clinoforms, then distinct stratal patterns should be recognizable in the fine-scale stratigraphic
architecture. Future integrated sedimentological and seismic-stratigraphic analyses focused on the
foresets segments of the Vaca Muerta Formation clinoforms are going to provide enough evidence
to answer these remaining questions aboutclinoform origin.
IAPG Instituto Argentino del Petróleo y el Gas 81
The role of fluid mud flows in the accumulation of organic-rich shales.
The upper jurassic-lower cretaceus Vaca Muerta Formation, Neuquén Basin, Argentina
DISCUSSION AND CONCLUSION
The accumulation of organic-rich mudstones was historically associated to low energy
depositional environments with anoxic bottom waters, where mudstone deposition was mainly
related to gradual and continuous fallout of mud from dilute buoyant plumes (Pettijohn 1975,
O´Brein and Slatt 1990, Boggs 2001, Potter et al. 2005). Based on this, basin inner zones were
considered as unsuitable environments for source rock deposition due to the generally low
concentrations of organic matter resulting from both low inputs and production, adding an
intense organic matter degradation during its transit time through the large water column (Arthur
et al. 1984, Stow et al. 2001).
This study documents the participation of fluid mud flows in the accumulation of Vaca
Muerta organic-rich shales in different system positions. The origin of fluid mud flows can be either
related to hyperpycnal river discharges (Fig. 6) or intrabasinal surge-type sediment gravity flows
developed close to the shelf-break (Fig. 11). Distinguishing between extrabasinal (hyperpycnal)
and intrabasinal (surge-type) muddy turbidites can be important since the organic matter content
of these FMFd seem to be different. In agreement with Reijenstein et al. (2017) and Notta et al.
(2017), the studied intrabasinal FMFd within the Vaca Muerta Formation are relativelydepleted
in TOC content, at least in the foresets segments of high-angle clinoforms. On the other hand,
muddy hyperpycnites are generally associated to high TOC content (Figs. 7 and 8). However,
muddy hyperpycnites have been recently documented within different organic-rich mudstones
(Abouelresh and Slatt 2011, Wilson and Schieber 2014, 2015) as well as in organic lean mudstones
(Soyinka and Slatt 2008, Bhattacharya and MacEachern 2009). These discrepancies in the TOC
content of ancient muddy hyperpycnites caused a great confusion about the hydrocarbon potential
of hyperpycnal deposits.
Nevertheless, recent oceanographic campaigns in deep-marine turbidite systems have
demonstrated that hyperpycnal flows are really efficient in the accumulation and rapid burial of
organic-rich sediments (Baudin et al. 2010, 2017a, b, Biscara et al. 2011, Stetten et al. 2015, Mignard
et al. 2017). Thus, the rapid and direct basinward transfer of organic matter by hyperpycnal flows
would have avoided its dilution and degradation in shallow marine environments. Finally, the
Figure 11. Intrabasinal muddy-turbidity currents associated to slope instabilitiescaused by the progressive clinoform growth and
consequent foresets angle increase. In contrast with muddy hyperpycnal flows, intrabasinal muddy turbidity currents need the
presence of high-gradient systems with a well-defined shelf-break configuration.
IAPG Instituto Argentino del Petróleo y el Gas
82 Simposio de Recursos No Convencionales: Hacia una Nueva Convención
arrival of extinguishing hyperpycnal flows to the basin inner zones would have provided a fast
deposition and burial of high quantities oforganic matter in terminal turbiditic muddy lobe
complexes, favoring its preservation (Fig. 12).
Figure 12. Block diagram illustrating the origin of intrabasinal (surge-type) and extrabasinal (hyperpycnal) fluid mud flows.
Particularly, muddy hyperpycnal flows are believed to play an important role in the transference of organic matter from the
production zone towards inner basin areas, where it is efficient buried and preserved in organic-rich muddy lobe complexes
(storage zone). OM: organic matter.
Muddy hyperpycnal flows should be further considered for the exploration of Vaca Muerta
and other unconventional resource shales, since they constitute a major pathway for organic
matter transferfrom the main production area (shelf/ramp environments) towards the storage
zone (basinal settings). This mud transport mechanism could explain why the highest TOC
contents are commonly found in unsuitable environments for organic matter production. The
future understanding of the complexity of fluid mud flows internal stacking pattern will be crucial
to identify long-term exploitable organic rich levels.
ACKNOWLEDGEMENTS
The authors deeply acknowledge the support of the Departamento de Geología of the
Universidad Nacional del Sur and the CONICET. Pampa Energía S.A. kindly provided the
financial support for core studies and authorizedthe publication of this contribution.
IAPG Instituto Argentino del Petróleo y el Gas 83
The role of fluid mud flows in the accumulation of organic-rich shales.
The upper jurassic-lower cretaceus Vaca Muerta Formation, Neuquén Basin, Argentina
REFERENCES CITED
Abouelresh, M.O. and R.M. Slatt, 2011,“Shale depo-
sitional processes: Example from the Paleozoic
Barnett Shale, Fort Worth Basin, Texas, USA”,
Open Geosciences 3 (4), p. 398-409.
Abouelresh, M.O. andR.M. Slatt, 2012,“Lithofacies
and sequence stratigraphy of the Barnett Shale
in east-central Fort Worth Basin, Texas”, AAPG
bulletin 96 (1), p. 1-22.
Allen, J.R.L., 1969,“Erosional current marks of weakly
cohesive mud beds”, Journal of Sedimentary Re-
search, 39 (2),p. 607-623.
Arthur, M.A.,W.E. DeanandD.A.V.Stow, 1984,“Mod-
els for the deposition of Mesozoic Cenozoic
fine-grained organic-carbon-rich sediment in the
deep sea”, Geological Society of London, Special
Publication, 15, p. 527-560.
Arregui, C., 2014,“Ciclos deposicionales de las Fms
Quintuco y Vaca Muerta: génesis y evolución”,
IX Congreso de Exploración y Desarrollo de Hi-
drocarburos, Trabajos Técnicos,2, p. 189-207.
Askenazi, A., P.Biscayart, M. Cáneva, S. Montenegro
andM. Moreno, 2013,“Analogía entre la Formación
Vaca Muerta y Shale Gas/Oil Plays de EEUU”, So-
ciety of Petroleum Engeneers (SPE), inédito, 20 p.
Azpiroz-Zabala, M.,M.J.Cartigny, P.J. Talling, D.R.
Parsons, E.J. Sumner, M.A. Clare, andE.L.Pope,
2017,“Newly recognized turbidity current structure
can explain prolonged flushing of submarine can-
yons”, Science advances, 3(10), 12 p., e1700200.
Baudin, F., J.R. Disnar, P. Martinez and B. Dennielou,
2010,“Distribution of the organic matter in the chan-
nel-levees systems of the Congo mud-rich deep-sea
fan (West Africa). Implication for deep offshore pe-
troleum source rocks and global carbon cycle”, Ma-
rine and Petroleum Geology, 27(5), p. 995-1010.
Baudin, F.,E.Stetten,J. Schnyder, K. Charlier, P. Marti-
nez, B. Dennielou andL.Droz, 2017a,“Origin and
distribution of the organic matter in the distal
lobe of the Congo deep-sea fan – A Rock-Eval
survey”, Deep-Sea Research Part II.
Baudin, F.,P. Martinez, B.Dennielou, K. Charlier, T.
Marsset, L. Drozand C.Rabouille, 2017b,“Organic
carbon accumulation in modern sediments of the
Angola basin influenced by the Congo deep sea
fan”, Deep Sea Research Part II: Topical Studies
in Oceanography.
Bhattacharya, J.P. and J.A. MacEachern, 2009,“Hyper-
pycnal rivers and prodeltaic shelves in the Cre-
taceous seaway of North America”, Journal of
Sedimentary Research, 79 (4), p. 184-209.
Biscara, L.,T. Mulder, P. Martinez, F. Baudin,
H. Etcheber, J.M. Jouanneau andT.Garlan,
2011,“Transport of terrestrial organic matter in
the Ogooué deep sea turbidite system (Gabon)”,
Marine and Petroleum Geology, 28(5), p. 1061-
1072.
Blanpied, C. andD.J.Stanley, 1981,“Uniform mud
(unifite) deposition in the Hellenic Trench, East-
ern Mediterranean”.
Boggs Jr., S., 2001,“The Oceanic (Deep-Water) Envi-
ronment”, in S.BoggsJr.(ed.), Principles of sedi-
mentology and stratigraphy,3rd edition, Pren-
tice-Hall,p. 349-364, Upper Saddle River, New
Jersey.
Bohacs, K.M., O.R. Lazar and T.M. Demko,
2014,“Parasequence types in shelfal mudstone
strata-Quantitative observations of lithofacies
and stacking patterns, and conceptual link to
modern depositional regimes”, Geology 42 (2),
p. 131-134.
IAPG Instituto Argentino del Petróleo y el Gas
84 Simposio de Recursos No Convencionales: Hacia una Nueva Convención
Chang, T.S. andS.S.Chun, 2012,“Micro-characteristics
of sustained, fine-grained lacustrine turbidites in
the Cretaceous Hwangsan Tuff, SW Korea”, Geo-
sciences Journal 16 (4), p. 409-420.
Desjardins, P., M. Fantín, F. González Tomassini, H.
Reijenstein,F. Sattler, F. Dominguez, D. Kietzmann,
H. Leanza, A. Bande, S. Benoit, M. Borgnia, F. Vittore,
T. Simoand D. Minisini,2016,“Capítulo 2: Estrati-
grafía Sísmica Regional”, in G. González, D. Vallejo, P.
Desjardins, F. Gonzalez-Tomassini, D. Kietzmann, L.
Rivarola, and F. Dominguez (eds.), Transecta Regional
de la Formación Vaca Muerta Integración de sísmica,
registros de pozos, coronas y afloramientos, p.5-22.
Dominguez, R.F.,H.Reijenstein, G. Köhler, F. Sattler,
M.J. Moreno, L. Gomez Rivarola and M. Borg-
nia, 2017,“Distribución regional de quiebres de
clinoformas del sistema Vaca Muerta-Quintuco”,
XX Congreso Geológico Argentino,Simposio
Geología de la Formación Vaca Muerta,p. 38-45.
Tucumán, Argentina.
Dżulyżski, S. andJ.E.Sanders, 1962, “Current marks on
firm mud bottoms”,Connecticut Acad. Arts and
Sci., Trans. 42, p. 57-96.
Einsele, G.,R. Overbeck, H.U. Schwarz, and G. Un-
söld, 1974,“Mass physical properties, sliding and
erodibility of experimentally deposited and dif-
ferentially consolidated clayey muds”, Sedimen-
tology 21 (3),p. 339-372.
Enos, P. andL.H.Sawatsky, 1981,“Pore networks in
Holocene carbonate sediments”, Journal of Sedi-
mentary Research, 51 (3),p. 961-985.
Galeazzi, S.,G. González, M. Santiago, D. García,
L.Maschio, R. González, and J.Ramírez Martínez,
2014,“Simposio de Recursos No Convencionales:
Ampliando el Horizonte Energético”, Instituto
Argentino del Petróleo y Gas (IAPG),1ª ed., 904 p.
Ciudad Autónoma de Buenos Aires.
Gerber, T.P., L.F. Pratson, M.A. Wolinsky,R. Steel, J.
Mohr, J.B. Swenson and C. Paola, 2008,“Clino-
form progradation by turbidity currents: model-
ing and experiments”, Journal of Sedimentary
Research, 78(3), p. 220-238.
González, G.,D. Vallejo, P. Desjardins, F. Gonzalez-
Tomassini, D. Kietzmann, L. Rivarola and F.
Dominguez, 2016,“Transecta Regional de la
Formación Vaca Muerta–Integración de sísmica,
registros de pozos, coronas y afloramientos”, In-
stituto Argentino de Petróleo y el Gas (IAPG),
publicación especial.
Goldhammer, R.K., 1997,“Compaction and decom-
paction algorithms for sedimentary carbonates”,
Journal of Sedimentary Research, 67 (1),p. 26-35.
Gulisano, C.A., 1981,“El ciclo Cuyano en el norte de
Neuquén y sur de Mendoza”, VIII Congreso Ge-
ológico Argentino, 3, p. 579–592, Buenos Aires,
Argentina.
Gulisano, C.A., A.R. Gutiérrez Pleimlingand R.E.
Digregorio, 1984, “Esquema estratigráfico de
la secuencia Jurásica del oeste de la provincia
del Neuquén”, IX Congreso Geológico Argen-
tino, 1,p. 236-259, San Carlos de Bariloche,
Argentina.
Hogg, S.L., 1993,“Geology and Hydrocarbon potential
of the Neuquén Basin”, Journal of Petroleum Ge-
ology,16, p. 383-396.
Iparraguirre, J., C. Zavala, M. Arcuri, M. Di Meglio
and A. Zorzano, 2016, “Litho 2: Enabling the
power of mobile devices and cloud computing
for creating comprehensive sedimentary logs
from outcrop, core and mud logging”, Interna-
tional Conference and Exhibition, Society of
Exploration Geophysicists and American As-
sociation of Petroleum Geologists, Barcelona,
Spain.
IAPG Instituto Argentino del Petróleo y el Gas 85
The role of fluid mud flows in the accumulation of organic-rich shales.
The upper jurassic-lower cretaceus Vaca Muerta Formation, Neuquén Basin, Argentina
Kietzmann, D.A., R.M. Palma, A.C. Riccardi, J. Mar-
tín-Chivelet and J. López-Gómez, 2014a, “Sedi-
mentology and sequence stratigraphy of a Titho-
nian–Valanginian carbonate ramp (Vaca Muerta
Formation): A misunderstood exceptional source
rock in the Southern Mendoza area of the Neu-
quén Basin, Argentina”, Sedimentary Geology
302, p. 64-86.
Kietzmann, D.A., A.L. Ambrosio, J. Suriano, S. Alon-
so, V. Vennari, B. Aguirre-Urreta, G. Depineand
D. Repol, 2014b,“Variaciones de facies de las
secuencias basales de la Formación Vaca Muerta
en su localidad tipo (Sierra de la Vaca Muerta),
Cuenca Neuquina”, IX Congreso de Explor-
ación y Desarrollo de Hidrocarburos, Trabajos
Técnicos,p. 299-318,Mendoza, Argentina.
Kietzmann, D.A., A.L. Ambrosio,J. Suriano, M.S.
Alonso, F.G. Tomassini, G. Depine and D. Re-
pol, 2016, “The Vaca Muerta–Quintuco system
(Tithonian–Valanginian) in the Neuquén Basin,
Argentina: A view from the outcrops in the Chos
Malal fold and thrust belt”, AAPG Bulletin 100
(5), p. 743-771.
Lash, G.G. and D. Blood, 2004,“Geochemical and
textural evidence for early (shallow) diagenetic
growth of stratigraphically confined carbonate
concretions, Upper Devonian Rhinestreet black
shale, western New York”, Chemical Geology,
206 (3), p. 407-424.
Lazar, R., K.M. Bohacs, J. Schieber, J. Macquaker,
andT.Demko, 2015a,“Mudstone Primer: Lithofa-
cies variations, diagnostic criteria, and sedimen-
tologic-stratigraphic implications at lamina to
bedset scale”, Society for Sedimentary Geology,
204 p. Oklahoma.
Lazar, O.R.,K.M. Bohacs, J.H.S Macquaker,J.Schieber,
andT.M.Demko, 2015b,“Integrated approach for
the nomenclature and description of the spec-
trum of fine-grained sedimentary rocks”, Journal
of Sedimentary Research, 85 (3), p. 230-246.
Leanza, H.A.,1973,“Estudio sobre los cambios faciales
de los estratos limítrofes Jurásico-Cretácicos entre
Loncopué y Picún Leufú, provincia del Neuquén,
República Argentina”, Revista de la Asociación
Geológica Argentina, 28 (2),p. 97-132.
Leanza, H.A., H.G. Marchese, and J.C.Riggi, 1977,“Es-
tratigrafía del Grupo Mendoza con especial refer-
encia a la Formación Vaca Muerta entre los Para-
lelos 35º y 40º ls Cuenca Neuquina-Mendocina”,
Revista de la Asociación Geológica Argentina, 32
(3),p. 190-208.
Leanza, H.A., C.A. Hugo, D. Repol and M. Salvarredy
Aranguren, 2003,“Miembro Huncal (Berriasiano
inferior): un episodio turbidítico en la Formación
Vaca Muerta, Cuenca Neuquina, Argentina”, Re-
vista de la Asociación Geológica Argentina, 58
(2), p. 248-254.
Leanza, H.A.,F. Sattler, R.S. Martinezand O.Carbone,
2011,“La Formación Vaca Muerta y equiva-
lentes (Jurásico Tardío – Cretácico Temprano)
en la Cuenca Neuquina”, in H.A.Leanza, C.
Arregui,O.Carbone,J.C.Danieli and J.M. Val-
lés (eds.), Relatorio del 18º Congreso Geológico
Argentino, Geología y Recursos Naturales de la
Provincia del Neuquén, p. 113-129.
Legarreta, L., 2002,“Eventos de desecación en la Cuen-
ca Neuquina: depósitos continentales y distribu-
ción de hidrocarburos”, V Congreso de Explor-
ación y Desarrollo de Hidrocarburos, p.1-20.
Legarreta, L.,E.Kozlowski, and A. Boll, 1981,“Esquema
estratigráfico y distribución de facies del Grupo
Mendoza en el ámbito surmendocino de la cuen-
ca Neuquina”, VIII Congreso Geológico Argen-
tino, 3, p. 389-409, San Luis, Argentina.
IAPG Instituto Argentino del Petróleo y el Gas
86 Simposio de Recursos No Convencionales: Hacia una Nueva Convención
Legarreta, L., and C.A. Gulisano, 1989, “Análisis es-
tratigráfico secuencial de la cuenca Neuquina
(Triásico superior-Terciario Inferior)”, X Congre-
so Geológico Argentino, p. 221-243, Tucumán,
Argentina.
Legarreta, L. and M.A. Uliana, 1991, “Jurassic-Cre-
taceous marine oscillations and geometry of
backarc basin fill, central Argentine Andes”, in
D.I.MacDonald (ed.), Sedimentation, Tectonics
and Eustasy: Sea level Changes at Active Plate
Margins, International Association of Sedimen-
tologists, Special Publication, 12,p. 429-450, Ox-
ford.
Legarreta, L. and H.J. Villar, 2015,“The Vaca Muerta
Formation (Late Jurassic – Early Cretaceous),
Neuquén Basin, Argentina: Sequences, Facies
and Source Rock Characteristics”, Unconven-
tional Resources Technology Conference, San
Antonio.
Li, Z.,J. Bhattacharya and J. Schieber, 2015,“Evaluating
alongżstrike variation using thinżbedded facies
analysis, Upper Cretaceous Ferron Notom Delta,
Utah”, Sedimentology 62 (7), p. 2060-2089.
Macquaker, J.,S. Bentley,K. Bohacs, R. Lazar, and R.
Jonk, 2010,“Advective Sediment Transport on
Mud-Dominated Continental Shelves: Processes
and Products”, AAPG Annual Convention and
Exhibition, New Orleans, Louisiana.
Marchal, D.,F. Sattlerand G. Köhler, 2016,“Capítulo
14: Sierra Chata”, in G. González, D. Vallejo,
P. Desjardins, F. Gonzalez-Tomassini, D. Ki-
etzmann, L. Rivarola, and F. Dominguez (eds.),
Transecta Regional de la Formación Vaca Muerta
Integración de sísmica, registros de pozos, coro-
nas y afloramientos, p.155-167.
Marshall, J.D. and D. Pirrie, 2013,“Carbonate concre-
tions-explained”, Geology Today, 29(2),p. 53-62.
McNeill, D.F., P.K. Swart, L.Rodríguez Blanco, M.
Tenaglia, R.J. Weger,B. Burke, L.E Rueda,C.
Kaiser,L. Yoder,J.S. Klaus, and G.P. Eberli,
2015,“Characterization of marine concretions
in a mixed system: Late Miocene Dominican
Republic and Late Jurassic/Cretaceous Neuquén
Basin Argentina”, Comparative Sedimentology
Laboratory (CSL), inédito, p. 71-74.
Mignard, S.L.A.,T. Mulder, P. Martinez, K.Charlier, L.
Rossignol and T. Garlan, 2017,“Deep-sea terrig-
enous organic carbon transfer and accumulation:
Impact of sea-level variations and sedimentation
processes off the Ogooue River (Gabon)”, Marine
and Petroleum Geology, 85, p. 35-53.
Mitchum, R.M. and M.A. Uliana, 1985,“Seismic stra-
tigraphy of carbonate depositional sequences,
Upper Jurassic-Lower Cretaceous, Neuquén Ba-
sin, Argentina”, inO. Berg and D. Woolverton
(eds.), Seismic Stratigraphy, II: an Integrated
Approach to Hydrocarbon Exploration, AAPG
Memoir 39,p. 255-274.
Mosquera, A.,J. Silvestro, V.A. Ramos, M. Alarcón,
and M. Zubiri, 2011,“La estructura de la Dor-
sal de Huincul”, VIII Congreso Geológico
Argentino, Actas, p. 385-397, San Luis, Ar-
gentina.
Mpodozis, C. and V. Ramos, 1989,“The Andes of Chile
and Argentina”, in G.E. Ericksen, M.TCañas Pi-
nochet and J.A.Reinemud (eds.), Geology of the
Andes and Its Relation to Hydrocarbon and Min-
eral Resources, Circumpacific Council for Ener-
gy and Mineral Resources, Earth Sciences Series,
Nº 11,p. 59-90. Houston.
Mulder, T. and J. Alexander, 2001,“The physical char-
acter of subaqueous sedimentary density flows
and their deposits”, Sedimentology, 48(2), p.
269-299.
IAPG Instituto Argentino del Petróleo y el Gas 87
The role of fluid mud flows in the accumulation of organic-rich shales.
The upper jurassic-lower cretaceus Vaca Muerta Formation, Neuquén Basin, Argentina
Mulder, T., J.P. Syvitski, S.Migeon, J.C. Faugeres, and
B. Savoye, 2003,“Marine hyperpycnal flows: ini-
tiation, behavior and related deposits. A review”,
Marine and Petroleum Geology, 20 (6), p. 861-882.
Mutti, E.,C.A.Gulisano and L. Legarreta, 1994,“Anom-
alous systems tracts stacking patterns within
third order depositional sequences (Jurassic-Cre-
taceous Back Arc Neuquén Basin, Argentine An-
des)”, Second High-Resolution Sequence Stratig-
raphy Conference, Abstracts,p. 137-143. Tremp.
Nakajima, T. 2006,“Hyperpycnites deposited 700 km
away from river mouths in the Central Japan Sea”,
Journal of Sedimentary Research 76 (1), p. 59-72.
Notta, R.,O.Davogustto, P. Desjardins and B. Williams,
2017,“Slump deposits identification in low angle
carbonate ramp settings, Cruz de Lorena (Neu-
quén Basin, Argentina): Towards an integrated
model explaining anomalous water recovery and
poor well performance”, XX Congreso Geológico
Argentino, Simposio Geología de la Formación
Vaca Muerta, p. 91-96,Tucumán, Argentina.
O’Brien, N. R. and R.M. Slatt, 1990, “Argillaceous
rock atlas”, Springer Science and Business Media:
141 p. New York.
Otharán, G.A. and C.A. Zavala, 2016,“Reconocimien-
to de turbiditas fangosas en la Formación Vaca
Muerta (Jurásico tardío-Cretácico temprano),
Neuquén, Argentina”, VI Simposio Argentino
del Jurásico, Actas, p.30, Malargüe, Argentina.
Otharán, G.A., Zavala, C.A. and M. Arcuri,
2017a,“Reevaluación de los procesos de acumu-
lación de lutitas bituminosas a partir del estudio
de intervalos cementados. Formación Vaca Muer-
ta (Tithoniano Temprano-Valanginiano Tempra-
no), Cuenca Neuquina”, XX Congreso Geológico
Argentino, Simposio Geología de la Formación
Vaca Muerta,p. 97-102,Tucumán, Argentina.
Otharán, G.A., C.A. Zavalaand M. Arcuri, 2017b,“Las
turbiditas de la Formación Vaca Muerta (Titho-
niano) en la Subcuenca de Picún Leufú, Cuenca
Neuquina, Argentina”, XX Congreso Geológico
Argentino, Simposio Geología de la Formación
Vaca Muerta, p. 103-109, Tucumán, Argentina.
Otharán, G.A. and C.A Zavala, 2018,“Muddy hyperpy-
cnal flows and organic-rich shales”, Workshop on
Deep Water Sedimentation, Nº 1,p. 10-11, Bahía
Blanca, Argentina.
Pettijohn, F.J., 1975,“Sedimentary Rocks, Third Edi-
tion”, Harper and Row, 628 p., New York.
Potter, P.E.,J.B Maynard andW.A. Pryor, 1980,“Sedi-
mentology of Shale”, Springer Verlag, 303p.,
New York.
Potter, P.E., J.B. Maynard and P.J. Depetris, 2005, “Mud
and mudstones: Introduction and overview”, Spring-
er Science and Business Media, 304 p, Germany.
Pose, F., A. Gangui and S. Galeazzi, 2014,“Estratigrafía
secuencial del intervalo Quintuco-Vaca Muerta
en el Engolfamiento Neuquino, Cuenca Neuqui-
na, Argentina”, IX Congreso de Exploración y
desarrollo de hidrocarburos, Simposio de recur-
sos no convencionales: Ampliando el horizonte
energético, p. 341-364.
Poyatos-Moré, M.,G.D.Jones, R.L. Brunt, D.M Hodgson,
R.J. Wild and S.S. Flint, 2016,“Mud-Dominated Ba-
sin-Margin Progradation: Processes and Implications”,
Journal of Sedimentary Research 86 (8),p. 863-878.
Reijenstein, H.,I. Lanusse,P. Oviedo, D.Licitra,D. Sote-
lo, F. Vittore, J.Quiroga, and F. González Tomassi-
ni, 2017,“¿Deslizamientos en Vaca Muerta? Obser-
vaciones e integración de datos sísmicos, pozos y
coronas en el yacimiento Loma Campana, Cuenca
Neuquina, Argentina”,XX Congreso Geológico Ar-
gentino, Simposio Geología de la Formación Vaca
Muerta, p. 122-129,Tucumán, Argentina.
IAPG Instituto Argentino del Petróleo y el Gas
88 Simposio de Recursos No Convencionales: Hacia una Nueva Convención
Rupke, N.A. and D.J Stanley, 1974,“Distinctive prop-
erties of turbiditic and hemipelagic mud layers in
the Algero-Balearic Basin, western Mediterranean
Sea”, Smithsonian contributions to the earth sci-
ences, Nº 1, 40 p.
Sanders, J.E., 1965,“Primary sedimentary structures
formed by turbidity currents and related sedi-
mentation mechanisms”, G.V.Middleton(ed.),
Primary sedimentary structures and their hydro-
dinamic interpretation, Soc. Econ. Paleontolo-
gists Mineralogists, Spec. Publ. 12, p. 192-219.
Sattler, F., R.F. Domínguez, M. Fantín, P. Desjar-
dins, H. Reijenstein, S. Benoit, M. Borgnia, F.
Vittore, F.González Tomassini, E. Feinstein,
D. Kietzmann, and D. Marchal, 2016,“Anexo
1”, inG. González, D. Vallejo, P. Desjardins,
F. Gonzalez-Tomassini, D. Kietzmann, L. Ri-
varola, and F. Dominguez (eds.), Transecta
Regional de la Formación Vaca Muerta Inte-
gración de sísmica, registros de pozos, coronas
y afloramientos.
Scasso, R.A.,M.S.Alonso, S. Lanés, H.J. Villar and H.
Lippai, 2002,“Petrología y geoquímica de una
ritmita marga-caliza del Hemisferio Austral: El
Miembro Los Catutos (Formación Vaca Muerta),
Tithoniano medio de la Cuenca Neuquina”, Re-
vista de la Asociación Geológica Argentina, 57
(2), p. 143-159.
Schieber, J., 1998, “Sedimentary features indicat-
ing erosion, condensation, and hiatuses in the
Chattanooga Shale of Central Tennessee: rel-
evance for sedimentary and stratigraphic evo-
lution”, inJ.Schieber, W. Zimmerle and P.Sethi
(eds.), Mudstones and Shales, vol. 1, Basin
Studies, Sedimentology and Paleontology,
Schweizerbart’sche Verlagsbuchhandlung,p.
187-215, Stuttgart.
Schieber, J. and G. Baird, 2001, “On the origin and
significance of pyrite spheres in Devonian black
shales of North America”, Journal of Sedimen-
tary Research 71 (1),p. 155-166.
Schieber, J., 2003,“Simple gifts and buried treasures-
implications of finding bioturbation and erosion
surfaces in black shales”, The Sedimentary Re-
cord 1 (2),p. 4-8.
Schieber, J.,J.B. Southard and K.G. Thaisen, 2007,“Ac-
cretion of mudstone beds from migrating floc-
cule ripples”, Sciences, 318 (5857), p. 1760-1763.
Schieber, J.and J.B. Southard, 2009, “Bedload trans-
port of mud by floccule ripples: direct observa-
tion of ripple migration processes and their im-
plications”, Geology 37 (6), p. 483-486.
Schieber, J. and Z. Yawar, 2009, “A new twist on mud
deposition: mud ripples in experiment and rock
record”, The Sedimentary Record, 7 (2), p. 4-8.
Schieber, J.,J.B.Southard, and A. Schimmelmann,
2010,“Lenticular shale fabrics resulting from in-
termittent erosion of water-rich muds: interpret-
ing the rock record in the light of recent flume
experiments”, Journal of Sedimentary Research
80 (1),p. 119-128.
Schieber, J.,J.B. Southard,P. Kissling,B.Rossman, and
R. Ginsburg, 2013,“Experimental deposition of
carbonate mud from moving suspensions: im-
portance of flocculation and implications for
modern and ancient carbonate mud deposition”,
Journal of Sedimentary Research, 83 (11),p.
1025-1031.
Schieber, J., 2016,“Mud-redistribution in epicontinen-
tal basins-Exploring likely processes”, Marine
and Petroleum Geology, 71,p. 119-133.
Slatt, R.,2011,“Important geological properties of un-
conventional resource shales”, Open Geoscienc-
es, 3 (4), p. 435-448.
IAPG Instituto Argentino del Petróleo y el Gas 89
The role of fluid mud flows in the accumulation of organic-rich shales.
The upper jurassic-lower cretaceus Vaca Muerta Formation, Neuquén Basin, Argentina
Soyinka, O.A. and R.M. Slatt, 2008,“Identification
and microżstratigraphy of hyperpycnites and tur-
bidites in Cretaceous Lewis Shale, Wyoming”,
Sedimentology, 55 (5),p. 1117-1133.
Stetten, E.,F.Baudin, J.L.Reyss, P. Martinez, K. Char-
lier, J. Schnyder, C. Rabouille, B. Dennielou,J.
Coston-Guariniand A. Pruski,2015,“Organic
matter characterization and distribution in sedi-
ments of the terminal lobes of the Congo deep-
sea fan: evidence for the direct influence of the
Congo River”, Marine Geology, 369, p. 182-195.
Stinco, L.P. and S.P Barredo, 2014,“Vaca Muerta For-
mation: An example of shale heterogeneities
controlling hydrocarbon accumulations”, Un-
conventional Resources Technology Conference
(URTeC), American Association of Petroleum
Geologists,Denver, United States.
Stipanicic, P.N., F.Rodrigo, O.L. Baulíes
andC.G.Martínez, 1968,“Las formaciones pre-
senonianas del denominado Macizo Nordpa-
tagónico y regiones adyacentes”, Revista de la
Asociación Geológica Argentina, 23 (2),p. 367-
388, Buenos Aires, Argentina.
Stow, D.A.V.,A.Y.Hucand P. Bertrand, 2001, “Depo-
sitional processes of black shales in deep water”,
Marine and Petroleum Geology 18, p. 491-498.
Vallejo, M.D. and G. González, 2016, “Capítulo 1: In-
troducción”, in G. González, D. Vallejo, P. Des-
jardins, F. Gonzalez-Tomassini, D. Kietzmann,
L. Rivarola, and F. Dominguez (eds.), Transecta
Regional de la Formación Vaca Muerta Inte-
gración de sísmica, registros de pozos, coronas y
afloramientos, p.1-4.
Vergani, G.D.,A.J. Tankard, H.J.Belotti, and H.J. Wel-
sink, 1995, “Tectonic evolution and paleoge-
ography of the Neuquén basin, Argentina”, in
A.J.Tankard, S.R. Suárez and H.J.Welsink (eds.),
Petroleum Basins of South America, AAPG Mem-
oir 62,p. 383-402.
Weaver, C., 1931,“Paleontology of the Jurassic and
Cretaceous from west central Argentina”, Uni-
versity of Washington, Memoir, Nº 1, p. 1-496.
Westphal, H., M.J. Head, and A. Munnecke, 2000,“Dif-
ferential diagenesis of rhythmic limestone alter-
nations supported by palynological evidence”,
Journal of Sedimentary Research 70 (3), p. 715-
725.
Wilson, R. and J. Schieber, 2014,“Muddy prodeltaic
hyperpycnites in the Lower Genesee Group of
Central New York, USA: Implications for mud
transport in epicontinental seas”, Journal of Sedi-
mentary Research 84 (10), p. 866-874.
Wilson, R. andJ. Schieber,2015,“Sedimentary Facies
and Depositional Environment of the Middle
Devonian Geneseo Formation of New York,
USA”, Journal of Sedimentary Research 85
(11),p. 1393-1415.
Zeller, M., S.B. Reid, G.P. Eberli, R.J. Weger and J.L.
Massaferro, 2015, “Sequence architecture and
heterogeneities of a field–Scale Vaca Muerta ana-
log (Neuquén Basin, Argentina)–From outcrop to
synthetic seismic”, Marine and Petroleum Geol-
ogy, 66, p. 829-847.
Zavala, C. and R. González, 2001,“Estratigrafía del
Grupo Cuyo (Jurásico inferior–medio) en la Si-
erra de la Vaca Muerta, Cuenca Neuquina”, Bo-
letín de Informaciones Petroleras, Tercera Época,
año XVII, Nº 65, p. 40-54.
Zavala, C., J.J.Ponce, M. Arcuri, D.Drittanti,
H.Freijeand M. Asensio, 2006,“Ancient lacus-
trine hyperpycnites: a depositional model from a
case study in the Rayoso Formation (Cretaceous)
of west-central Argentina”, Journal of Sedimen-
tary Research 76 (1), p. 41-59.
IAPG Instituto Argentino del Petróleo y el Gas
90 Simposio de Recursos No Convencionales: Hacia una Nueva Convención
Zavala, C., M.Arcuri, H. Gamero, C. Contreras and
M. Di Meglio, 2011,“A genetic facies tract for
the analysis of sustained hyperpycnal flow depos-
its”, inR.M. Slatt and C. Zavala (eds.), Sediment
Transfer from Shelf to Deep Water-Revisiting the
Delivery System, American Association Of Petro-
leum Geologists, Studies in Geology Vol. 61, p.
31-51.
Zavala, C., M. Arcuri, M. Di Meglio and A. Zorzano,
2014,“Depósitos de turbiditas intra y extracuencales:
Origen y Características distintivas”, IX Congreso de
Exploración y Desarrollo de Hidrocarburos, Trabajos
Técnicos (Tomo II), p. 225-244, Mendoza, Argentina.
Zavala, C. and M. Arcuri, 2016,“Intrabasinal and ex-
trabasinal turbidites: Origin and distinctive char-
acteristics”, Sedimentary Geology, 337, p. 36-54.
... preserves an almost uncompacted record of primary sedimentary structures, that is, the bedding-parallel, early-diagenetic carbonate concretions (Gómez Rivarola and Borgnia, 2018;Kietzmann et al., 2016;Otharán et al., 2018) formed near the sediment-water interface in response to microbial decay of organic carbon (LF 12 in Figure 5). ...
... Beyond muddy hyperpycnal flows, where an event bed internal stacking pattern is characterized by an overall normal grading trend (a basal massive/ rippled coarse-grained mudstone interval (McM) overlain by massive, fine-grained mudstone deposit (MfM)), its origin may be associated to waning, surge-type intrabasinal muddy turbidity currents ( Otharán et al., 2018). Intrabasinal muddy turbidity currents are products of episodic (non-steady) events triggered by slope instability or intense wave activity during storm events, effective processes delivering mud from the topset and foreset to the bottomset. ...
... Intrabasinal muddy turbidity currents are products of episodic (non-steady) events triggered by slope instability or intense wave activity during storm events, effective processes delivering mud from the topset and foreset to the bottomset. These waning flows progressively lose their capacity and competence and deposit their sediment load as normally graded mudstone beds in distal foresets and proximal bottomsets locally associated with mass transport complexes (Arregui, 2014;Pose et al., 2014;Reijenstein et al., 2017;Otharán et al., 2018). As these flows require the existence of a depositional gradient, it is likely that they originated along the steep western margin of the basin, close to the active volcanic arc, rather than along the eastern margin where low-angle ramps (0.2°-0.3°) characterized the basin, especially during deposition of Unit 1 and 2. ...
Chapter
This contribution integrates lithologic, mineralogical, geochemical, and geomechanical data from cores and outcrops, and emphasizes where and how sedimentology may help the exploration of self-sourced unconventional reservoirs. In fact, the activity in the unconventional, 2020, Sedimentology, depositional model, and implications for reservoir quality, in Daniel Minisini, Manuel Fantín, Iván Lanusse Noguera, and Héctor A. Leanza, eds., Integrated geology of unconventionals: The case of the Vaca Muerta play, Argentina: AAPG Memoir 121, p. 201-236.
... Interpretación: se interpreta que esta facies se habría acumulado a partir de altas tasas de decantación en flujos fluidos de fango (Otharán et al. 2018;2020). La existencia de cambios cíclicos en el tamaño de grano sugiere un flujo de fondo en movimiento, rasgos diagnósticos que los diferencian de la decantación pura en aguas calmas (Zavala et al., 2014). ...
... Figura 2.Mapa geológico y columna estratigráfica generalizada del área central de la Cuenca Neuquina (modificado deOtharán et al. 2018). ...
Thesis
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.
... In outcrops, the study of mud flow deposits is facilitated by making macroscopic polished slabs of early diagenetic carbonate concretions. Early diagenetic concretions are very important because they can preserve a "frozen" record of the original depositional muddy fabric (Otharán et al. 2018(Otharán et al. , 2020, often highly deformed by compaction (Schieber et al. 2010). ...
... A common characteristic of these muddy deposits is the existence of an impressive erosional basal boundary, which suggests basin bottom erosion by passing-by flows, with the associated incorporation of intrabasinal materials like microfossils and organic matter (Fig. 19). Consequently, the resulting deposits are often characterized by a complex mixture of intrabasinal and extrabasinal components (Zavala and Arcuri 2016;Otharán et al. 2018). The join occurrence of different paleodepth indicators in single beds is very common, and could be wrongly interpreted as indicative of a "transitional" environment with drastic changes in sea level. ...
Article
A hyperpycnal flow forms when a relatively dense land-derived gravity flow enters into a marine or lacustrine water reservoir. As a consequence of its excess of density, the incoming flow plunges in coastal areas, generating a highly dynamic and often long-lived dense underflow. Depending on the characteristics of the parent flow (flow duration and flow rheology) and basin salinity, the resulting deposits (hyperpycnites) can be very variable. According to flow duration, land-derived gravity flows can be classified into short-lived or long-lived flows. Short-lived gravity flows last for minutes or hours, and are mostly related to small mountainous river discharges, alluvial fans, collapse of natural dams, landslides, volcanic eruptions, jökulhlaups, etc. Long-lived gravity flows last for days, weeks or even months, and are mostly associated with medium- to large-size river discharges. Concerning the rheology of the incoming flow, hyperpycnal flows can be initiated by non-Newtonian (cohesive debris flows), Newtonian supercritical (lahars, hyperconcentrated flows, and concentrated flows) or Newtonian subcritical flows (pebbly, sandy or muddy sediment-laden turbulent flows). Once plunged, non-Newtonian and Newtonian supercritical flows require steep slopes to accelerate, allow the incorporation of ambient water and develop flow transformations in order to evolve into a turbidity current and travel further basinward. Their resulting deposits are difficult to differentiate from those related to intrabasinal turbidites. On the contrary, long-lived Newtonian subcritical flows are capable of transferring huge volumes of sediment, freshwater and organic matter far from the coast even along gentle or flat slopes. In marine settings, the buoyant effect of interstitial freshwater in pebbly and sandy hyperpycnal flows can result in lofting due to flow density reversal. Since the excess of density in muddy hyperpycnal flows is provided by silt-clay sediments in turbulent suspension, lofting is not possible even in marine/saline basins. Muddy hyperpycnal flows can also erode the basin bottom during their travel basinward, allowing the incorporation and transfer of intrabasinal sediments and organic matter. Long-lived hyperpycnal flow deposits exhibit typical characteristics that allow a clear differentiation respect to those related to intrabasinal turbidites. Main features include (1) composite beds with gradual and recurrent changes in sediment grain-size and sedimentary structures, (2) mixture of extrabasinal and intrabasinal components, (3) internal and discontinuous erosional surfaces, and (4) lofting rhythmites in marine/saline basins.
... In outcrops, the study of mud flow deposits is facilitated by making macroscopic polished slabs of early diagenetic carbonate concretions. Early diagenetic concretions are very important because they can preserve a "frozen" record of the original depositional muddy fabric (Otharán et al. 2018(Otharán et al. , 2020, often highly deformed by compaction (Schieber et al. 2010). ...
... A common characteristic of these muddy deposits is the existence of an impressive erosional basal boundary, which suggests basin bottom erosion by passing-by flows, with the associated incorporation of intrabasinal materials like microfossils and organic matter (Fig. 19). Consequently, the resulting deposits are often characterized by a complex mixture of intrabasinal and extrabasinal components (Zavala and Arcuri 2016;Otharán et al. 2018). The join occurrence of different paleodepth indicators in single beds is very common, and could be wrongly interpreted as indicative of a "transitional" environment with drastic changes in sea level. ...
Article
Full-text available
A hyperpycnal flow forms when a relatively dense land-derived gravity flow enters into a marine or lacustrine water reservoir. As a consequence of its excess of density, the incoming flow plunges in coastal areas, generating a highly dynamic and often long-lived dense underflow. Depending on the characteristics of the parent flow (flow duration and flow rheology) and basin salinity, the resulting deposits (hyperpycnites) can be very variable. According to flow duration, land-derived gravity flows can be classified into short-lived or long-lived flows. Short-lived gravity flows last for minutes or hours, and are mostly related to small mountainous river discharges, alluvial fans, collapse of natural dams, landslides, volcanic eruptions, jökulhlaups, etc. Long-lived gravity flows last for days, weeks or even months, and are mostly associated with medium- to large-size river discharges. Concerning the rheology of the incoming flow, hyperpycnal flows can be initiated by non-Newtonian (cohesive debris flows), Newtonian supercritical (lahars, hyperconcentrated flows, and concentrated flows) or Newtonian subcritical flows (pebbly, sandy or muddy sediment-laden turbulent flows). Once plunged, non-Newtonian and Newtonian supercritical flows require steep slopes to accelerate, allow the incorporation of ambient water and develop flow transformations in order to evolve into a turbidity current and travel further basinward. Their resulting deposits are difficult to differentiate from those related to intrabasinal turbidites. On the contrary, long-lived Newtonian subcritical flows are capable of transferring huge volumes of sediment, freshwater and organic matter far from the coast even along gentle or flat slopes. In marine settings, the buoyant effect of interstitial freshwater in pebbly and sandy hyperpycnal flows can result in lofting due to flow density reversal. Since the excess of density in muddy hyperpycnal flows is provided by silt-clay sediments in turbulent suspension, lofting is not possible even in marine/saline basins. Muddy hyperpycnal flows can also erode the basin bottom during their travel basinward, allowing the incorporation and transfer of intrabasinal sediments and organic matter. Long-lived hyperpycnal flow deposits exhibit typical characteristics that allow a clear differentiation respect to those related to intrabasinal turbidites. Main features include (1) composite beds with gradual and recurrent changes in sediment grain-size and sedimentary structures, (2) mixture of extrabasinal and intrabasinal components, (3) internal and discontinuous erosional surfaces, and (4) lofting rhythmites in marine/saline basins.
... Las lutitas carbonosas masivas se originarían a partir de altas tasas de decantación de la carga en suspensión, mientras que una disminución en la velocidad de decantación daría origen a los depósitos de lutitas carbonosas laminadas (Otharán et al. 2018). ...
... Las trazas fósiles son escasas, y mayormente integradas por el icnogénero Chondrites. Interpretación: Se interpreta que esta facies se habría acumulado por floculación y decantación de materiales finos desde aguas calmas o a partir de altas tasas de decantación en flujos fluidos de fango (Otharán et al. 2018). ...
Article
Full-text available
Cores recovered from PANG0001 and PANG0003 wells provide an exceptional record of the upper Paleozoic of the Ventania/Claromecó Basin. These wells are located at 90 km at the northeast of Sierra de la Ventana locality, reaching a depth of 958.30 and 901.66 meters, respectively. Two continuous sections of more than 700 m each were described. These cores show a succession of fine-grained sandstone interbedded with black claystone, carbonatic claystone, coal and fine tuff. The analyzed succession is included to the Tunas Formation based on lithology, age, thickness and stratigraphic position. Sixteen sedimentary facies and four facies sequences were recognized and interpreted as shelfal to prodelta shales, shelfal sandstone lobes, shelfal to mouth bars and fluvial to distributary channels, interdistributary swamps to alluvial plains. The sequence stratigraphic analysis allows to identify 8 main third-order depositional sequences (T1 to T8), which are in turn grouped into two megacycles or transgressive-regressive megasequences. Taking into account its lithological characteristics, internal arrangement, and ichnological content, a river-dominated deltaic environment is interpreted. Within this context, a dominantly sandy sequence would have been accumulated in delta plain to delta front areas, while heterolithic levels would represent prodelta and shelfal deposits. Coal levels appear associated with the lower sequences (T1 and T2) and correspond to floodplain to interdistributary swamp deposits related to fluvial systems.
... Diante dessas diferentes circunstâncias, nós sugerimos que os ofiuroides do grau A3 poderiam ter sido soterrados por sedimentos remobilizados tanto por fluxos hiperpicnais como por ondas de tempestades, além de uma combinação de ambos os processos. Mesmo assim, é bastante provável que fluxos hiperpicnais tenham tido uma influência dominante na geração dos leitos A3, levando em consideração que podem transportar grandes volumes de água doce intersticial (Figura 9C-D) e que são muito aptos em difundir lamas fluidas para zonas distais em bacias marinhas epicontinentais (Figura 9A) (Zavala et al. 2012;Zavala & Arcuri, 2016;Otharán et al., 2018;Zavala, 2020). Esse contexto deposicional é representado aqui pela alta proporção de ofiuroides do grau A3 preservados em leitos tipicamente maciços de argilito e siltito arenoso, (Müller, 1979). ...
Thesis
Due to the low preservation potential of their multi-elemental skeletons, articulated ophiuroid fossils can be used as an accurate taphonomic guide to exceptional fossilization conditions. Based on this principle, the objective of this work is to investigate the taphonomic history of ophiuroids-producing beds across three paleontological sites in eastern Paraná state, Brazil, where epicontinental Devonian sequences from the Ponta Grossa Formation are well represented. Through fieldwork, tomographic analysis, and description of 218 samples, five taphonomic grades were listed to represent the depositional histories of these ophiuroid beds in the Ponta Grossa Formation. Three high-order taphonomic grades (A1-A3) reflect ophiuroids suddenly buried in life. Grade A1 encompasses sparse skeletons of ophiuroids articulated and oriented in normal postures, parallel to the bedding planes. Grade A2 groups clusters of articulated ophiuroids oriented in specific horizons, sometimes with specimens in inverted postures. Grade A3 comprises complete to incomplete skeletons of ophiuroids in escape postures, inclined at low angles in the bedding planes, occasionally with evidence of autotomized arms. In turn, two lower-order taphonomic grades (B1-B2) include a limited number of disarticulated skeletons, reflecting ophiuroid specimens buried between hours to a few days after death. Grade B1 consists of disarticulated ophiuroids in a normal post-mortem degradation sequence, with arms tips absent or dissociated close in the sediment. Grade B2 combines ophiuroids in a selective disarticulation pattern, with the mixing of intact segments and dissociated portions in the sediment, suggesting macrobenthic disturbance of the carcasses. These records indicate that fluvial discharges were the primary burial mechanisms for ophiuroids in the Ponta Grossa Formation, as they can transport large loads of freshwater-rich sediment to distal zones of marine basins, favoring mass dormancy of errant echinoderms. Meanwhile, storms were probably only a subordinate burial process, given that they remobilize sediments without a key anesthetic. Furthermore, with the aid of scanning electron microscopy, carbonaceous compressions were recorded for the first time in fossil echinoderms, highlighting the kerogenization of visceral organs of the disk of some ophiuroids, apparently with associated pyritization. Considering the association with varied lithotypes and benthic communities, it is likely that ophiuroids have thrived in different seabeds along the Ponta Grossa Formation, although being preserved only under a restricted taphonomic window, especially in distal marine regions free from the interference of waves, currents, and bioturbators. This preservation window seems to have been potentiated in regressive systems due to the gradual increase in fluvial influence over the ancient epicontinental sea of the formation. Therefore, because of the presence of exceptionally articulated ophiuroids with preserved organic remains, the Ponta Grossa Formation can be adequately classified as a echinoderm Konservat-Lagerstätte from the Devonian of Brazil.
Article
The Songliao Basin in NE China is a large rift basin filled with Cretaceous terrestrial sediments. Lacustrine mudstones of the Nenjiang Formation form an important source rock in the Cretaceous Songliao Basin. These shales are commonly thought to have been deposited in deep, quiet, and anoxic environments. Samples obtained from the core of the SK‐2 scientific borehole provide critical insights to understand the hydrodynamic and hydroclimatic environments, which are, however, different from the traditional views regarding the deposition of these rocks. By following a mudstone description guide, five different mudstone lithofacies (LF) transported and deposited by muddy hyperpycnal flows and muddy debris flows were recognized. They are laminated fine mudstone (LF1), laminated medium mudstone (LF2), and laminated coarse mudstone (LF3) showing pairs of inverse grading (Ha) and normal grading (Hb) under the microscope, graded coarse mudstone (LF4) and massive coarse mudstone (LF5). We found that mudstones of the First Member of the Nenjiang Formation are dominated by siliciclastic detritus and argillaceous components and show frequent variations in grain size. Because large‐scale sub‐lacustrine channels travelling long distance (>80 km) were widely distributed in the Songliao palaeolake during the deposition of the Nenjiang Formation, fluctuations in mudstone grain size might have been caused by velocity fluctuations in flows. Sedimentary structures and textures preserved in mudstones of the First Member of the Nenjiang Formation indicate that the majority of these lithofacies were accumulated by muddy hyperpycnal flows and muddy debris flows. Therefore, a depositional model dominantly influenced by muddy hyperpycnal flows and debris flows is proposed. This work not only provides a new view for the depositional process of mudstones of the Songliao Basin, NE China, but also give insights to understand lacustrine palaeoenvironment and terrestrial palaeoclimate.
Article
Being the main oil-bearing basin of Argentina, the Neuquén Basin contains a well-documented stratigraphic record of continental and marine sedimentation during the Jurassic and Cretaceous in the western margin of Gondwana. Marine sedimentation started in the Early Jurassic with the deposition of the offshore to prodelta shales of the Los Molles Formation, the basal unit of the Cuyo Group. A palynological study of outcrop samples of the Los Molles Formation at two localities, Puente Picún Leufú, southern Neuquén Basin, and Cordillera del Viento, central basin area, is presented. The palynological evidence allows inferring two different palaeoceanographic contexts during the deposition of the Los Molles Fm. At Puente Picún Leufú and the lower part of the Cordillera del Viento localities, the record of acritarchs and prasinophytes suggests a stratified water column, suboxic-to-anoxic bottom conditions, and a reduced salinity within the photic zone, associated with a marginal marine environment under restricted oceanic circulation. These conditions would have last at least until the Early Bajocian. Conversely, at the middle and mainly the upper part of Cordillera del Viento locality, the predominance of dinocysts in the assemblages indicates a hydrographically unstable shelf (non-stratified water mass column) with well-oxygenated bottom waters developed under open-marine settings with non-restricted oceanic circulation. The abundance and diversity of dinocyst assemblages are comparable with those observed in the Late Callovian Lotena Formation. These evidences suggest an open oceanic circulation due to the establishment of different seaways in the Neuquén Basin, during the final accumulation of the Los Molles Formation (Early Callovian).
Article
Full-text available
The conventional sedimentological model suggests that the accumulation of organic-rich fine-grained sedimentary rocks (<62.5 μm) is uniquely associated with fallout processes in low energy depositional environments. This contribution analyzes organic-rich mudstones belonging to the lower section of the Vaca Muerta Formation at central areas of the Neuquén Basin (Arroyo Mulichinco, Tres Chorros and Río Neuquén localities). The studied interval is characterized by the highest organic matter content of the Vaca Muerta Formation (up to 8% TOC). The associated mudstone deposits are usually highly compacted, thus obscuring the recognition of the original fabric and the analysis of mudstone depositional processes. Nevertheless, the common occurrence of carbonate concretions within these highly compacted intervals provides an exceptional preservation of mudstone primary fabric. After macroscopic study of polished slabs and thin sections of these cemented beds, a series of facies genetically linked to muddy underflows were recognized. The origin of these deposits is related to long-lived muddy hyperpycnal flows (quasi-steady mud flows) triggered by extreme river discharges during rainfall humid periods. During their travel basinward, hyperpycnal flows, originally composed of detrital mud, would be able to go through very low gradient reliefs, incorporating the available intrabasinal components (including organic matter) to their extrabasinal sedimentary load. The rapid basinward transfer of organic-rich mud would have provided a fast deposition and efficient burial of organic matter, avoiding its potential degradation at seafloor. Muddy underflows constitute a rational mechanism to explain the common occurrence of bituminous mudstones at central areas of the Neuquén Basin.
Chapter
Full-text available
Este capítulo nació con el objetivo de establecer un acuerdo de esquema estratigráfico simple y práctico para el intervalo Tithoniano - Valanginiano inferior, elaborado a partir de las superficies cotidianamente interpretadas por los distintos grupos de trabajo en los diferentes ámbitos de la cuenca. Estas superficies se eligieron en base a esquemas antecedentes, a criterios de estratigrafía sísmica y a la relevancia petrolera, como base o techo de intervalos considerados objetivos prospectivos. Los resultados son un esquema estratigráfico funcional a las necesidades de los profesionales de la industria y un cuadro de equivalencias estratigráficas, un tipo de “Piedra de Rosetta”, que traduce entre algunos de los esquemas antecedentes y las clasificaciones utilizadas por los geólogos participantes en esta publicación.
Article
Full-text available
Seabed-hugging flows called turbidity currents are the volumetrically most important process transporting sediment across our planet and form its largest sediment accumulations. We seek to understand the internal structure and behavior of turbidity currents by reanalyzing the most detailed direct measurements yet of velocities and densities within oceanic turbidity currents, obtained from weeklong flows in the Congo Canyon. We provide a new model for turbidity current structure that can explain why these are far more prolonged than all previously monitored oceanic turbidity currents, which lasted for only hours or minutes at other locations. The observed Congo Canyon flows consist of a short-lived zone of fast and dense fluid at their front, which outruns the slower moving body of the flow. We propose that the sustained duration of these turbidity currents results from flow stretching and that this stretching is characteristic of mud-rich turbidity current systems. The lack of stretching in previously monitored flows is attributed to coarser sediment that settles out from the body more rapidly. These prolonged seafloor flows rival the discharge of the Congo River and carry ~2% of the terrestrial organic carbon buried globally in the oceans each year through a single submarine canyon. Thus, this new structure explains sustained flushing of globally important amounts of sediment, organic carbon, nutrients, and fresh water into the deep ocean.
Presentation
Full-text available
La Formación Vaca Muerta (Tithoniano – Valanginiano temprano) se compone mayoritariamente por sedimentitas marinas de grano fino ampliamente distribuidas en la Cuenca Neuquina. Si bien en áreas centrales incluye depósitos turbidíticos (Miembro Huncal), son escasas las menciones de turbiditas hacia el sur de la Dorsal de Huincul. Se relevaron cinco secciones estratigráficas (QS-01 – QS-05) de un intervalo arenoso reconocido en los afloramientos de la Formación Vaca Muerta en la Quebrada del Sapo. A partir de la correlación estratigráfica de estas secciones pueden reconocerse una serie de clinoformas progradantes al noreste, las cuales muestran una fuerte variación de espesor a lo largo de su extensión. El análisis de facies sugiere un origen turbidítico para estos depósitos, cuya acumulación parece estar vinculada a procesos de resedimentación en un medio de talud sujeto a frecuentes deslizamientos gravitacionales, de modo semejante al modelo propuesto para las turbiditas que componen el Miembro Huncal. Sin embargo, estas turbiditas son tithonianas, mientras que aquellas del Miembro Huncal corresponden al Berriasiano. Datos regionales indican que la acumulación de la Formación Vaca Muerta en esta área se habría desarrollado sobre un marcado relieve preexistente. La presencia de truncaciones de bajo ángulo sugiere la posible existencia de actividad tectónica sinsedimentaria durante el Tithoniano en áreas de la Dorsal de Huincul. Palabras clave: Quebrada del Sapo, procesos de resedimentación, deslizamientos gravitacionales, actividad tectónica sinsedimentaria.
Conference Paper
The accumulation of organic-rich mudstones was largely associated to low energy depositional environments with anoxic bottom waters, where mudstone deposition was mainly related to gradual and continuous mud fallout from dilute buoyant plumes. Based on this, basin inner zones were considered as unsuitable environments for source rock deposition due to the generally low concentration of OM resulting from both low inputs and production, adding an intense OM degradation during its transit time through the water column. Nevertheless, recent detailed sedimentological analyses in a variety of unconventional shales have revealed that the participation of fallout processes is probably subordinated to other still poorly known depositional processes, opening a new paradigm for source rocks origin. In Argentina, the Upper Jurassic-Lower Cretaceous Vaca Muerta Formation is composed of organic-rich mudstones and carbonates dominated by type II kerogen representing South America's main unconventional reservoir. New cores and excellent outcrops provide a great opportunity to study the depositional history of this unit. These deposits were previously interpreted as accumulated by fallout deposition in a quiet and anoxic deep marine environment. However, recent studies revealed that the Vaca Muerta Formation is a highly heterogeneous stratigraphic unit accumulated by different and poorly know depositional processes. In fact, the formation displays distinct lithofacies alternating at centimeter to millimeter scale having variable organic matter content (up to 14% TOC), features that influence the reservoir quality and performance. High resolution sedimentological analysis were performed on relatively uncompacted intervals preserved in early diagenetic calcareous concretions collected from the basal deposits of the Vaca Muerta Formation in basinal settings. Evidences found in concretions suggest a deposition related to fluid mud flows instead of the classic model of "normal fallout". The triggered mechanisms for the origin of the recognized fluid mud flow deposits are mainly associated to direct river discharges during flood events. Each flood event would be capable of generating quasi-steady muddy hyperpycnal flows that may be sustained for days, weeks, or even months. These long-lasting events would be able to transfer significant volumes of organic matter and fine-grained sediments for long distances towards distal basinal settings. The erosion capacity of muddy hyperpycnal flows enables the incorporation of intrabasinal components (e.g. marine microfossils, carbonate mud, type II OM) which are transported together with the primary extrabasinal sedimentary load (e.g. detrital 10
Book
Fabric analysis techniques x-radiography, petrography and scanning electron microscopy descriptions miscellaneous features in argillaceous rocks case studies of specific distinctive features case study of fabric analysis in evaluating sedimentary processes and environments formation of shale by compaction of flocculated clay-A model fabrics of some hydrocarbon source rocks and oil shales fabric of geopressured shale composition of argillaceous rocks.
Article
Sedimentary, isotopic and bulk geochemical proxies measured in sediment samples of five gravity cores collected in the distal part of the Ogooue turbidite system (around 4000 m-depth) were used to develop a conceptual model to describe the accumulation of terrigenous organic matter (OM) during the last 200,000 yrs BP in the eastern part of the Gulf of Guinea. This model takes into account the influence of the different depositional processes (turbiditic vs hemipelagic sedimentation), geomorphological features and sea-level variations.
Article
The Congo River, the second largest river in the world, is a major source of organic matter for the deep Atlantic Ocean because of the connection of its estuary to the deep offshore area by a submarine canyon which feeds a vast deep-sea fan. The lobe zone of this deep-sea fan is the final receptacle of the sedimentary inputs presently channelled by the canyon and covers an area of ~2500 km². The quantity and the source of organic matter preserved in recent turbiditic sediments from the distal lobe of the Congo deep-sea fan were assessed using Rock-Eval pyrolysis analyses. Six sites, located at approximately 5000 m water-depth, were investigated. The mud-rich sediments of the distal lobe contain high amounts of organic matter (~3.5 to 4% Corg), the origin of which is a mixture of terrestrial higher-plant debris, soil organic matter and deeply oxidized phytoplanktonic material. Although the respective contribution of terrestrial and marine sources of organic matter cannot be precisely quantified using Rock-Eval analyses, the terrestrial fraction is dominant according to similar hydrogen and oxygen indices of both suspended and bedload sediments from the Congo River and that deposited in the lobe complex. The Rock-Eval signature supports the 70% to 80% of the terrestrial fraction previously estimated using C/N and δ¹³Corg data. In the background sediment, the organic matter distribution is homogeneous at different scales, from a single turbiditic event to the entire lobe, and changes in accumulation rates only have a limited effect on the quantity and quality of the preserved organic matter. Peculiar areas with chemosynthetic bivalves and/or bacterial mats, explored using ROV Victor 6000, show a Rock-Eval signature more or less similar to background sediment. This high organic carbon content associated to high sedimentation rates (> 2 to 20 mm.yr⁻¹) in the Congo distal lobe complex implies a high burial rate for organic carbon. Consequently, the Congo deep-sea fan represents an enormous sink of terrestrial organic matter when compared to other turbiditic systems over the world.
Article
Geochemical data (total organic carbon-TOC content, δ¹³Corg, C:N, Rock-Eval analyses) were obtained on 150 core tops from the Angola basin, with a special focus on the Congo deep sea fan. Combined with the previously published data, the resulting dataset (322 stations) shows a good spatial and bathymetric representativeness. TOC content and δ¹³Corg maps of the Angola basin were generated using this enhanced dataset. The main difference in our map with previously published ones is the high terrestrial organic matter content observed downslope along the active turbidite channel of the Congo deep sea fan till the distal lobe complex near 5,000 m of water-depth. Interpretation of downslope trends in TOC content and organic matter composition indicates that lateral particle transport by turbidity currents is the primary mechanism controlling supply and burial of organic matter in the bathypelagic depths.