Geochemical proxies and hiatuses in contourites of the Gulf of Cadiz

Zeinab Smillie, Dorrik Stow, F. J. Sierro, Francisco J. Jiménez-Espejo, Emmanuelle Ducassou, Montserrat Alonso Garcia, Jim Buckman

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Regional unconformities are common and significant features of contourite depositional systems worldwide. They are caused by accelerated bottom currents that erode and winnow the seafloor or prevent deposition from occurring. Such episodes of increased bottom current activity may be linked with major tectonic and/or climatic events, as well as to changes in flow pathways and sedimentation patterns. In the Gulf of Cadiz, hiatuses are recorded at all six sites, under the influence of the Mediterranean Outflow Water, that were drilled during IODP Expedition 399. They are expressed either by a marked gap in sedimentation, or as a much condensed succession. The two most significant hiatuses in the sedimentary record after the Miocene–Pliocene boundary unconformity, are the late Pliocene Discontinuity (LPD, 3–3.2 Ma) and the early Quaternary Discontinuity (EQD, 2–2.4 Ma). We evaluated the nature of changes in the patterns of sedimentation, elemental distribution and microfauna across both these hiatuses. At sites U1387 and U1391, there is extensive development of fine dolomite crystals within the sediment, at the expense of both biogenic and lithogenic components. This is combined with framboidal pyrite formation and an extensive network of iron sulphide filled Trichichnus trace fossil filaments. The original composition of the contourite around the hiatuses may have been overprinted by the carbonate authigenesis. However, the distribution of grain size and stable heavy minerals remain largely unaffected. The LPD and EQD at the sites of investigation are associated with significant increase in current velocities as evident from the high Zr % and Zr/Al ratio and the increase in main grain size. Foraminiferal analyses showed marked changes in the deep-water oxygenation status from the late Pliocene towards the early Quaternary. This is particularly evident at site U1387 where the LPD and EQD hiatuses run together as one longer hiatus of around 1 My duration. Our results suggest that the dolomitisation along the unconformity surface is linked with fluid seepage from depth. These fluids encountered a partially calcite-cemented baffle to flow, which was originally due to incipient hardground formation at the seafloor, and this provided the calcite template for replacement by dolomite.
LanguageEnglish
Title of host publication20th International Sedimentological Congress
Publication statusAccepted/In press - 26 Apr 2018
Event20th International Sedimentological Congress 2018 - Québec, Canada
Duration: 13 Aug 201817 Aug 2018

Conference

Conference20th International Sedimentological Congress 2018
Abbreviated titleISC 2018
CountryCanada
CityQuébec
Period13/08/1817/08/18

Fingerprint

contourite
unconformity
Pliocene
bottom current
sedimentation
dolomite
discontinuity
calcite
seafloor
grain size
authigenesis
fluid
iron sulfide
dolomitization
oxygenation
trace fossil
hiatus
heavy mineral
seepage
pyrite

Cite this

Smillie, Z., Stow, D., Sierro, F. J., Jiménez-Espejo, F. J., Ducassou, E., Alonso Garcia, M., & Buckman, J. (Accepted/In press). Geochemical proxies and hiatuses in contourites of the Gulf of Cadiz. In 20th International Sedimentological Congress
Smillie, Zeinab ; Stow, Dorrik ; Sierro, F. J. ; Jiménez-Espejo, Francisco J. ; Ducassou, Emmanuelle ; Alonso Garcia, Montserrat ; Buckman, Jim. / Geochemical proxies and hiatuses in contourites of the Gulf of Cadiz. 20th International Sedimentological Congress. 2018.
@inproceedings{bc40f8cf942743eab80afd65463b235e,
title = "Geochemical proxies and hiatuses in contourites of the Gulf of Cadiz",
abstract = "Regional unconformities are common and significant features of contourite depositional systems worldwide. They are caused by accelerated bottom currents that erode and winnow the seafloor or prevent deposition from occurring. Such episodes of increased bottom current activity may be linked with major tectonic and/or climatic events, as well as to changes in flow pathways and sedimentation patterns. In the Gulf of Cadiz, hiatuses are recorded at all six sites, under the influence of the Mediterranean Outflow Water, that were drilled during IODP Expedition 399. They are expressed either by a marked gap in sedimentation, or as a much condensed succession. The two most significant hiatuses in the sedimentary record after the Miocene–Pliocene boundary unconformity, are the late Pliocene Discontinuity (LPD, 3–3.2 Ma) and the early Quaternary Discontinuity (EQD, 2–2.4 Ma). We evaluated the nature of changes in the patterns of sedimentation, elemental distribution and microfauna across both these hiatuses. At sites U1387 and U1391, there is extensive development of fine dolomite crystals within the sediment, at the expense of both biogenic and lithogenic components. This is combined with framboidal pyrite formation and an extensive network of iron sulphide filled Trichichnus trace fossil filaments. The original composition of the contourite around the hiatuses may have been overprinted by the carbonate authigenesis. However, the distribution of grain size and stable heavy minerals remain largely unaffected. The LPD and EQD at the sites of investigation are associated with significant increase in current velocities as evident from the high Zr {\%} and Zr/Al ratio and the increase in main grain size. Foraminiferal analyses showed marked changes in the deep-water oxygenation status from the late Pliocene towards the early Quaternary. This is particularly evident at site U1387 where the LPD and EQD hiatuses run together as one longer hiatus of around 1 My duration. Our results suggest that the dolomitisation along the unconformity surface is linked with fluid seepage from depth. These fluids encountered a partially calcite-cemented baffle to flow, which was originally due to incipient hardground formation at the seafloor, and this provided the calcite template for replacement by dolomite.",
author = "Zeinab Smillie and Dorrik Stow and Sierro, {F. J.} and Jim{\'e}nez-Espejo, {Francisco J.} and Emmanuelle Ducassou and {Alonso Garcia}, Montserrat and Jim Buckman",
year = "2018",
month = "4",
day = "26",
language = "English",
booktitle = "20th International Sedimentological Congress",

}

Smillie, Z, Stow, D, Sierro, FJ, Jiménez-Espejo, FJ, Ducassou, E, Alonso Garcia, M & Buckman, J 2018, Geochemical proxies and hiatuses in contourites of the Gulf of Cadiz. in 20th International Sedimentological Congress. 20th International Sedimentological Congress 2018, Québec, Canada, 13/08/18.

Geochemical proxies and hiatuses in contourites of the Gulf of Cadiz. / Smillie, Zeinab; Stow, Dorrik; Sierro, F. J.; Jiménez-Espejo, Francisco J.; Ducassou, Emmanuelle; Alonso Garcia, Montserrat; Buckman, Jim.

20th International Sedimentological Congress. 2018.

Research output: Chapter in Book/Report/Conference proceedingConference contribution

TY - GEN

T1 - Geochemical proxies and hiatuses in contourites of the Gulf of Cadiz

AU - Smillie, Zeinab

AU - Stow, Dorrik

AU - Sierro, F. J.

AU - Jiménez-Espejo, Francisco J.

AU - Ducassou, Emmanuelle

AU - Alonso Garcia, Montserrat

AU - Buckman, Jim

PY - 2018/4/26

Y1 - 2018/4/26

N2 - Regional unconformities are common and significant features of contourite depositional systems worldwide. They are caused by accelerated bottom currents that erode and winnow the seafloor or prevent deposition from occurring. Such episodes of increased bottom current activity may be linked with major tectonic and/or climatic events, as well as to changes in flow pathways and sedimentation patterns. In the Gulf of Cadiz, hiatuses are recorded at all six sites, under the influence of the Mediterranean Outflow Water, that were drilled during IODP Expedition 399. They are expressed either by a marked gap in sedimentation, or as a much condensed succession. The two most significant hiatuses in the sedimentary record after the Miocene–Pliocene boundary unconformity, are the late Pliocene Discontinuity (LPD, 3–3.2 Ma) and the early Quaternary Discontinuity (EQD, 2–2.4 Ma). We evaluated the nature of changes in the patterns of sedimentation, elemental distribution and microfauna across both these hiatuses. At sites U1387 and U1391, there is extensive development of fine dolomite crystals within the sediment, at the expense of both biogenic and lithogenic components. This is combined with framboidal pyrite formation and an extensive network of iron sulphide filled Trichichnus trace fossil filaments. The original composition of the contourite around the hiatuses may have been overprinted by the carbonate authigenesis. However, the distribution of grain size and stable heavy minerals remain largely unaffected. The LPD and EQD at the sites of investigation are associated with significant increase in current velocities as evident from the high Zr % and Zr/Al ratio and the increase in main grain size. Foraminiferal analyses showed marked changes in the deep-water oxygenation status from the late Pliocene towards the early Quaternary. This is particularly evident at site U1387 where the LPD and EQD hiatuses run together as one longer hiatus of around 1 My duration. Our results suggest that the dolomitisation along the unconformity surface is linked with fluid seepage from depth. These fluids encountered a partially calcite-cemented baffle to flow, which was originally due to incipient hardground formation at the seafloor, and this provided the calcite template for replacement by dolomite.

AB - Regional unconformities are common and significant features of contourite depositional systems worldwide. They are caused by accelerated bottom currents that erode and winnow the seafloor or prevent deposition from occurring. Such episodes of increased bottom current activity may be linked with major tectonic and/or climatic events, as well as to changes in flow pathways and sedimentation patterns. In the Gulf of Cadiz, hiatuses are recorded at all six sites, under the influence of the Mediterranean Outflow Water, that were drilled during IODP Expedition 399. They are expressed either by a marked gap in sedimentation, or as a much condensed succession. The two most significant hiatuses in the sedimentary record after the Miocene–Pliocene boundary unconformity, are the late Pliocene Discontinuity (LPD, 3–3.2 Ma) and the early Quaternary Discontinuity (EQD, 2–2.4 Ma). We evaluated the nature of changes in the patterns of sedimentation, elemental distribution and microfauna across both these hiatuses. At sites U1387 and U1391, there is extensive development of fine dolomite crystals within the sediment, at the expense of both biogenic and lithogenic components. This is combined with framboidal pyrite formation and an extensive network of iron sulphide filled Trichichnus trace fossil filaments. The original composition of the contourite around the hiatuses may have been overprinted by the carbonate authigenesis. However, the distribution of grain size and stable heavy minerals remain largely unaffected. The LPD and EQD at the sites of investigation are associated with significant increase in current velocities as evident from the high Zr % and Zr/Al ratio and the increase in main grain size. Foraminiferal analyses showed marked changes in the deep-water oxygenation status from the late Pliocene towards the early Quaternary. This is particularly evident at site U1387 where the LPD and EQD hiatuses run together as one longer hiatus of around 1 My duration. Our results suggest that the dolomitisation along the unconformity surface is linked with fluid seepage from depth. These fluids encountered a partially calcite-cemented baffle to flow, which was originally due to incipient hardground formation at the seafloor, and this provided the calcite template for replacement by dolomite.

M3 - Conference contribution

BT - 20th International Sedimentological Congress

ER -

Smillie Z, Stow D, Sierro FJ, Jiménez-Espejo FJ, Ducassou E, Alonso Garcia M et al. Geochemical proxies and hiatuses in contourites of the Gulf of Cadiz. In 20th International Sedimentological Congress. 2018