Neoproterozoic microbial processes in chemical sediment diagenesis

evidence from the Aberfeldy barite deposits

Norman Moles, Adrian Boyce

Research output: Contribution to conferenceAbstractResearchpeer-review

Abstract

Microbial- and diffusion-controlled diagenetic processes were significant in the formation of sulfide-, sulfate- and carbonate-rich stratiform mineralization hosted by Neoproterozoic graphitic metasediments near Aberfeldy in Perthshire, Scotland. In 1-10m thick beds of barite rock, barite δ34S of +36 ±1.5 ‰ represents the isotopic composition of contemporaneous seawater sulfate. Pronounced vertical variations in δ34S (+30 to +41 ‰) and δ18O (+8 to +21 ‰) occur on a decimetre-scale at bed margins. These excursions are attributed to early diagenetic alteration, while the barite sediment was fine-grained and porous, due to pulsed infiltration of isotopically diverse porefluids into the marginal barite. Fluid-mediated transfer of barium and sulfate into adjacent sediments contributed to barium enrichment and growth of millimetric sulfate crystals cross-cutting sedimentary lamination. Witherite, barytocalcite and norsethite occur only as small inclusions within crystals of pyrite. Barium carbonate formation is ascribed to early diagenetic processes that generated very low sulfate activity in pore waters. Subsequently, sulfidation reactions produced secondary barite + non-barium carbonates in the rock matrix. Comparatively low δ34S (+16 to +22 ‰) in secondary barite indicate sulfur derived from reduced sulfide. Similar sulfide δ34S ratios in the host sediments are consistent with microbial reduction of seawater/ porewater sulfate.
Original languageEnglish
Pages1413-1416
Number of pages4
Publication statusPublished - 27 Aug 2019
Event15th SGA Biennial Meeting 2019 - Glasgow University, Glasgow, United Kingdom
Duration: 27 Aug 201930 Aug 2019
https://www.sga2019glasgow.com/

Conference

Conference15th SGA Biennial Meeting 2019
CountryUnited Kingdom
CityGlasgow
Period27/08/1930/08/19
Internet address

Fingerprint

barite
diagenesis
sulfate
barium
sediment
sulfide
carbonate
porewater
crystal
seawater
lamination
fine grained sediment
metasediment
rock
chemical
pyrite
isotopic composition
infiltration
sulfur
mineralization

Cite this

Moles, N., & Boyce, A. (2019). Neoproterozoic microbial processes in chemical sediment diagenesis: evidence from the Aberfeldy barite deposits. 1413-1416. Abstract from 15th SGA Biennial Meeting 2019, Glasgow, United Kingdom.
Moles, Norman ; Boyce, Adrian. / Neoproterozoic microbial processes in chemical sediment diagenesis : evidence from the Aberfeldy barite deposits. Abstract from 15th SGA Biennial Meeting 2019, Glasgow, United Kingdom.4 p.
@conference{fdc513b1e623466f91f9286f64a7af63,
title = "Neoproterozoic microbial processes in chemical sediment diagenesis: evidence from the Aberfeldy barite deposits",
abstract = "Microbial- and diffusion-controlled diagenetic processes were significant in the formation of sulfide-, sulfate- and carbonate-rich stratiform mineralization hosted by Neoproterozoic graphitic metasediments near Aberfeldy in Perthshire, Scotland. In 1-10m thick beds of barite rock, barite δ34S of +36 ±1.5 ‰ represents the isotopic composition of contemporaneous seawater sulfate. Pronounced vertical variations in δ34S (+30 to +41 ‰) and δ18O (+8 to +21 ‰) occur on a decimetre-scale at bed margins. These excursions are attributed to early diagenetic alteration, while the barite sediment was fine-grained and porous, due to pulsed infiltration of isotopically diverse porefluids into the marginal barite. Fluid-mediated transfer of barium and sulfate into adjacent sediments contributed to barium enrichment and growth of millimetric sulfate crystals cross-cutting sedimentary lamination. Witherite, barytocalcite and norsethite occur only as small inclusions within crystals of pyrite. Barium carbonate formation is ascribed to early diagenetic processes that generated very low sulfate activity in pore waters. Subsequently, sulfidation reactions produced secondary barite + non-barium carbonates in the rock matrix. Comparatively low δ34S (+16 to +22 ‰) in secondary barite indicate sulfur derived from reduced sulfide. Similar sulfide δ34S ratios in the host sediments are consistent with microbial reduction of seawater/ porewater sulfate.",
author = "Norman Moles and Adrian Boyce",
year = "2019",
month = "8",
day = "27",
language = "English",
pages = "1413--1416",
note = "15th SGA Biennial Meeting 2019 ; Conference date: 27-08-2019 Through 30-08-2019",
url = "https://www.sga2019glasgow.com/",

}

Moles, N & Boyce, A 2019, 'Neoproterozoic microbial processes in chemical sediment diagenesis: evidence from the Aberfeldy barite deposits' 15th SGA Biennial Meeting 2019, Glasgow, United Kingdom, 27/08/19 - 30/08/19, pp. 1413-1416.

Neoproterozoic microbial processes in chemical sediment diagenesis : evidence from the Aberfeldy barite deposits. / Moles, Norman; Boyce, Adrian.

2019. 1413-1416 Abstract from 15th SGA Biennial Meeting 2019, Glasgow, United Kingdom.

Research output: Contribution to conferenceAbstractResearchpeer-review

TY - CONF

T1 - Neoproterozoic microbial processes in chemical sediment diagenesis

T2 - evidence from the Aberfeldy barite deposits

AU - Moles, Norman

AU - Boyce, Adrian

PY - 2019/8/27

Y1 - 2019/8/27

N2 - Microbial- and diffusion-controlled diagenetic processes were significant in the formation of sulfide-, sulfate- and carbonate-rich stratiform mineralization hosted by Neoproterozoic graphitic metasediments near Aberfeldy in Perthshire, Scotland. In 1-10m thick beds of barite rock, barite δ34S of +36 ±1.5 ‰ represents the isotopic composition of contemporaneous seawater sulfate. Pronounced vertical variations in δ34S (+30 to +41 ‰) and δ18O (+8 to +21 ‰) occur on a decimetre-scale at bed margins. These excursions are attributed to early diagenetic alteration, while the barite sediment was fine-grained and porous, due to pulsed infiltration of isotopically diverse porefluids into the marginal barite. Fluid-mediated transfer of barium and sulfate into adjacent sediments contributed to barium enrichment and growth of millimetric sulfate crystals cross-cutting sedimentary lamination. Witherite, barytocalcite and norsethite occur only as small inclusions within crystals of pyrite. Barium carbonate formation is ascribed to early diagenetic processes that generated very low sulfate activity in pore waters. Subsequently, sulfidation reactions produced secondary barite + non-barium carbonates in the rock matrix. Comparatively low δ34S (+16 to +22 ‰) in secondary barite indicate sulfur derived from reduced sulfide. Similar sulfide δ34S ratios in the host sediments are consistent with microbial reduction of seawater/ porewater sulfate.

AB - Microbial- and diffusion-controlled diagenetic processes were significant in the formation of sulfide-, sulfate- and carbonate-rich stratiform mineralization hosted by Neoproterozoic graphitic metasediments near Aberfeldy in Perthshire, Scotland. In 1-10m thick beds of barite rock, barite δ34S of +36 ±1.5 ‰ represents the isotopic composition of contemporaneous seawater sulfate. Pronounced vertical variations in δ34S (+30 to +41 ‰) and δ18O (+8 to +21 ‰) occur on a decimetre-scale at bed margins. These excursions are attributed to early diagenetic alteration, while the barite sediment was fine-grained and porous, due to pulsed infiltration of isotopically diverse porefluids into the marginal barite. Fluid-mediated transfer of barium and sulfate into adjacent sediments contributed to barium enrichment and growth of millimetric sulfate crystals cross-cutting sedimentary lamination. Witherite, barytocalcite and norsethite occur only as small inclusions within crystals of pyrite. Barium carbonate formation is ascribed to early diagenetic processes that generated very low sulfate activity in pore waters. Subsequently, sulfidation reactions produced secondary barite + non-barium carbonates in the rock matrix. Comparatively low δ34S (+16 to +22 ‰) in secondary barite indicate sulfur derived from reduced sulfide. Similar sulfide δ34S ratios in the host sediments are consistent with microbial reduction of seawater/ porewater sulfate.

UR - https://www.sga2019glasgow.com/

M3 - Abstract

SP - 1413

EP - 1416

ER -

Moles N, Boyce A. Neoproterozoic microbial processes in chemical sediment diagenesis: evidence from the Aberfeldy barite deposits. 2019. Abstract from 15th SGA Biennial Meeting 2019, Glasgow, United Kingdom.