Conference PaperPDF Available

Hyperpycnal Flows and Deposits

Abstract

A hyperpycnal flow forms when a relatively dense land derived gravity flow enters in a marine or lacustrine water reservoir. As a consequence of its excess in density, the flow plunges in coastal areas generating a highly dynamic and often long-lived dense underflow. Depending on the 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 in 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 to 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 (bedload, sandy or muddy dominated 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 to evolve into a turbidity current and travel 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 transfer 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 bedload and sandy dominated hyperpycnal flows can result in lofting due to 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 dominated hyperpycnal flows can also erode the basin bottom during its 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) complex 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.
4th INTERNATIONAL CONFERENCE
of PALAEOGEOGRAPHY
ABSTRACTS
Beijing, China
September, 2019
31
Lisco Stefania Nunzia1, Acquafredda Pasquale1, Gallicchio Salvatore1, Sabato Luisa2, Bonifazi
Andrea3, Cardone Frine2, Corriero Giuseppe2, Gravina Maria Flavia2, Pierri Cataldo2 and Moretti
Massimo1
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Sabellaria alveolataLinnaeus1767O会丽丽
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停五云产LSabellaria alveolata 
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Ostia-O产 Sabellaria alveolata 产云L
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产云产L
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Sabellaria alveolata云O云

K-12
Hyperpycnal Flows and Deposits
Carlos Zavala1,2
(1. Departamento de Geología, Universidad Nacional del Sur, San Juan 670, 8000 Bahía Blanca,
Argentina,. 2.GCS Argentina SRL, Molina Campos 150, 8000 Bahía Blanca, Argentina)
Abstract: A hyperpycnal flow forms when a relatively dense land derived gravity flow
enters in a marine or lacustrine water reservoir. As a consequence of its excess in
density, the flow plunges in coastal areas generating a highly dynamic and often long-
lived dense underflow. Depending on the 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 in 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 to medium
to large size river discharges. Concerning the rheology of the incoming flow,
32
hyperpycnal flows can be initiated by non-Newtonian (cohesive debris flows),
Newtonian supercritical (lahars, hyperconcentrated flows, and concentrated flows) or
Newtonian subcritical flows (bedload, sandy or muddy dominated 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 to evolve into a turbidity current and travel 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
transfer 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 bedload and sandy dominated hyperpycnal flows can result in lofting due
to 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 dominated hyperpycnal flows can also erode the basin
bottom during its 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) complex 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.
Keywords: Hyperpycnal flows, hyperpycnites, turbidites, sediment gravity flows

Carlos Zavala

S产丝L五
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33
作五()些(
)些(r产东)
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云L五产东(
产/亭云L
L
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与3O产4O/亭产L
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
K-13
Growth and form of Conophyton (Maslov) A radical
reinterpretation inspired by occurrences of Mg Silicates in the
modern microbialites of Lakes Clifton and Preston, Western
Australia
Robert V. Burne 1, 2
(1. Research School of Earth Sciences, Australian National University, Canberra, ACT
Australia
2. School of Earth and Environmental Science, University of Queensland, St Lucia,
Australia)
AbstractSConophyton (Maslov) is a stromatolite form composed of cylindroidal colonies
of nested conical laminae. The majority of fossil Conophytons are dolomitic. The
remains of the microbial communities responsible for their construction are rarely
found, but, where present, there are virtually always in areas of chert within the
Conophyton. Well-preserved Conophytons, up to 4m tall and with basal diameters of
up to 50cm are exposed in the Proterozoic Atar Formation of Mauritanea. Here
many occur in growth position as fields of individual columns spaced between 5
... Hyperpycnal flows are river-derived, quasi-steady underflows that are capable of transfer huge volumes of sediments from the land to the shelf and potentially further to deep-basins (Bates, 1953;Wright et al., 1988;Mulder and Syvitski, 1995;Mutti et al., 2009), which play an import role in sediment transport from source to sink and deep-water sediment partitioning (Mulder et al., 2003;Sømme et al., 2009). Deposits from hyperpycnal flows host relative complete and high-precision information of climate changes compared to on-shore records and constitute important targets in deep-water petroleum exploration as well (Warrick and Milliman, 2003;Zhang et al., 2014;Xian et al., 2018a;Liu et al., 2020;Chen et al., 2021), which have drawn increasing attention in recent years and the origination, transport mechanism and depositional process of which are still topics on debate (Lamb et al. 2010;Talling, 2014;Zavala and Arcuri, 2016;Xian et al., 2018a;Shanmugam, 2018;Zavala and Pan, 2018;Zavala, 2019;van Loon et al., 2019). ...
Article
There has been an increased attention on hyperpycnal flows due to its importance in delivering large volumes of sediments into deep-water. The process and products of hyperpycnal flow in tectonically-active margins are still poorly understood, and potentially constitute one of the most important deep-water mechanisms in rift basins. This study integrates core data, well-logging and 3D seismic data to investigate the hyperpycnal flow process and dispersal pattern on the Eocene Dongying rift margin. 17 facies, including 5 conglomerate facies, 9 sand facies and 3 mud facies are identified, interpreted as the product of debris flows, traction currents, turbidity currents, transitional flows and lofting plumes, and suggesting the complex blend in flood-triggered hyperpycnal flow on rift margin. Two different hyperpycnal flow types are identified and a related process model is proposed based on facies sequence, distribution, transport mechanism and flood discharge analysis, including seasonal-flood triggered hyperpycnal flow (SHF) and outburst-flood triggered hyperpycnal flow (OHF). The evolution of the hyperpycnal system suggests two dispersal styles, including proximal sublacustrine fan dominated by OHF and distal sublacustrine fan dominated by SHF, respectively. Climate and tectonic movements are suggested to be the main factors controlling hyperpycnal flow generation and deposition on rift margins. The relatively arid climate enhanced seasonal-flood activity and associated sustained and stable SHF, which further prompt distal sublacustrine fan development during a weak rifting period. On the other hand, the generation of outburst-floods can be attributed to the enhanced fault activity, which corresponds to the periodical tectonic movements in the basin. As a result, proximal sublacustrine fans tend to develop in near-shore topographic lows down-dip of syn-depositional faults due to increased tectonic activities, accommodation and enhanced OHF. A deep-water depositional model is proposed for hyperpycnal systems on rift margins by emphasizing the variety in sedimentary process and dispersal patterns controlled by climate and tectonics forces, which may provide new insights into hyperpycnal flow theories and deep-water exploration in world rift basins.
Article
Full-text available
It is well recognized that dam construction aggravates eutrophication and hypoxia in river reservoirs, but the interaction between oxygen dynamics and carbon cycling is often unclear. Here we investigated the external and internal controls on oxygen consumption and effects of hypoxia on carbon dioxide (CO2) emission in a subtropical reservoir in southeast China based on detailed field measurements during 2017 and 2018. Hypoxia lasted 4 months starting in mid-July and expanded from the bottom to near surface water. Rainstorm hyperpycnal flow and unusual hydraulics (outflow exit 40 m from the bottom) resulted in two thermoclines and enhanced the oxygen deficit in deeper water. Microbial respiration accounted for 67.4%–96.5% of total oxygen consumption in the bottom water. The increased supply of organic matter from storm runoff and to a lesser extent primary production in summer enhanced subsequent oxygen consumption. We observed an imbalance between excess CO2 production and oxygen depletion in summer and winter which was likely associated with other processes in the hypolimnion (e.g., chemoautotrophy, anaerobic degradation of organic matter, proton buffering, and nitrification). The water-air CO2 fluxes suggest that the surface reservoir usually served as a CO2 source, but was a sink in summer due to high primary productivity. CO2 was always oversaturated in the hypolimnion; this layer was at the depth of the dam outflow and ultimately released 68% of annual CO2 efflux to the atmosphere. This research confirmed that construction of a hydropower dam has substantially altered reservoir metabolism and regulated the CO2 emission pathway.
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