Cross-examining Earth's oldest stromatolites: Seeing through the effects of heterogeneous deformation, metamorphism and metasomatism affecting Isua (Greenland) ∼3700 Ma sedimentary rocks

Allen P. Nutman, Vickie C. Bennett, Clark R.L. Friend, Martin Van Kranendonk, Leo Rothacker, Allan R. Chivas

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

The ∼3700 Ma and 3800 Ma meta-volcanic and -sedimentary rocks in the Isua supracrustal belt (Greenland) were affected by heterogeneous ductile deformation under amphibolite facies conditions (∼500–650 °C), and variably modified by secondary silica and carbonate mineralisation deposited from diagenetic and metasomatic fluids. Rare low-deformation areas preserve original volcanic features – submarine basaltic pillows and sedimentary features – including bedding. These are best-preserved in two dimensions on flat- to moderately-inclined outcrop surfaces, but invariably are tectonically-stretched along a steeply-plunging third dimension, through stretching in the direction of fold axes; a style of deformation found throughout Earth's history. There is a debate about whether rare relicts of ∼3700 Ma stromatolites preserved in metadolomites that formed in a shallow marine setting (Nutman et al., 2016) represent bona fide biogenic primary structures fortuitously preserved in low deformation, or whether these structures are manifestations of deformation combined with non-biogenic deposition of secondary carbonate (Allwood et al., 2018). Here, we critically test the primary nature of the sedimentary rocks hosting the proposed stromatolites and also the veracity of the proposed stromatolites, by addressing the following questions: (i) Are the rocks an in situ outcrop of known age, or displaced blocks of unknown age or origin?; (ii) How much of the carbonate is of an originally sedimentary versus a secondary (i.e., metasomatic – introduced) origin?; (iii) Is the seawater-like REE + Y (rare earth element and yttrium) trace element signature carried definitely by carbonate minerals and therefore diagnostic of a cool, surficial sedimentary system?; (iv) Are the proposed stromatolites consistent with biogenicity in terms of their geometry and fine-scale layering, or could they be the product of soft sediment or structural deformation (compression in folding)? The answers to these questions, which combine diverse observations from geologic context, geochemistry and stromatolite morphology show that the weight of evidence is consistent with a biogenic origin for the stromatolites formed in a shallow water setting and are inconsistent with formation entirely through inorganic processes.

Original languageEnglish
Article number105347
JournalPrecambrian Research
Volume331
DOIs
Publication statusPublished - Sep 1 2019
Externally publishedYes

Fingerprint

Sedimentary rocks
metasomatism
sedimentary rock
metamorphism
Earth (planet)
Carbonates
carbonate
outcrop
rare earth element
volcanic feature
stromatolite
sedimentary feature
yttrium
Carbonate minerals
ductile deformation
Yttrium
Geochemistry
amphibolite facies
Trace Elements
folding

Keywords

  • Dolomite
  • Early life
  • Eoarchean
  • Isua
  • Stromatolites

ASJC Scopus subject areas

  • Geology
  • Geochemistry and Petrology

Cite this

Cross-examining Earth's oldest stromatolites : Seeing through the effects of heterogeneous deformation, metamorphism and metasomatism affecting Isua (Greenland) ∼3700 Ma sedimentary rocks. / Nutman, Allen P.; Bennett, Vickie C.; Friend, Clark R.L.; Van Kranendonk, Martin; Rothacker, Leo; Chivas, Allan R.

In: Precambrian Research, Vol. 331, 105347, 01.09.2019.

Research output: Contribution to journalArticle

@article{c4fd1915857a4ae79c32a3c820c5c866,
title = "Cross-examining Earth's oldest stromatolites: Seeing through the effects of heterogeneous deformation, metamorphism and metasomatism affecting Isua (Greenland) ∼3700 Ma sedimentary rocks",
abstract = "The ∼3700 Ma and 3800 Ma meta-volcanic and -sedimentary rocks in the Isua supracrustal belt (Greenland) were affected by heterogeneous ductile deformation under amphibolite facies conditions (∼500–650 °C), and variably modified by secondary silica and carbonate mineralisation deposited from diagenetic and metasomatic fluids. Rare low-deformation areas preserve original volcanic features – submarine basaltic pillows and sedimentary features – including bedding. These are best-preserved in two dimensions on flat- to moderately-inclined outcrop surfaces, but invariably are tectonically-stretched along a steeply-plunging third dimension, through stretching in the direction of fold axes; a style of deformation found throughout Earth's history. There is a debate about whether rare relicts of ∼3700 Ma stromatolites preserved in metadolomites that formed in a shallow marine setting (Nutman et al., 2016) represent bona fide biogenic primary structures fortuitously preserved in low deformation, or whether these structures are manifestations of deformation combined with non-biogenic deposition of secondary carbonate (Allwood et al., 2018). Here, we critically test the primary nature of the sedimentary rocks hosting the proposed stromatolites and also the veracity of the proposed stromatolites, by addressing the following questions: (i) Are the rocks an in situ outcrop of known age, or displaced blocks of unknown age or origin?; (ii) How much of the carbonate is of an originally sedimentary versus a secondary (i.e., metasomatic – introduced) origin?; (iii) Is the seawater-like REE + Y (rare earth element and yttrium) trace element signature carried definitely by carbonate minerals and therefore diagnostic of a cool, surficial sedimentary system?; (iv) Are the proposed stromatolites consistent with biogenicity in terms of their geometry and fine-scale layering, or could they be the product of soft sediment or structural deformation (compression in folding)? The answers to these questions, which combine diverse observations from geologic context, geochemistry and stromatolite morphology show that the weight of evidence is consistent with a biogenic origin for the stromatolites formed in a shallow water setting and are inconsistent with formation entirely through inorganic processes.",
keywords = "Dolomite, Early life, Eoarchean, Isua, Stromatolites",
author = "Nutman, {Allen P.} and Bennett, {Vickie C.} and Friend, {Clark R.L.} and {Van Kranendonk}, Martin and Leo Rothacker and Chivas, {Allan R.}",
year = "2019",
month = "9",
day = "1",
doi = "10.1016/j.precamres.2019.105347",
language = "English",
volume = "331",
journal = "Precambrian Research",
issn = "0301-9268",
publisher = "Elsevier",

}

TY - JOUR

T1 - Cross-examining Earth's oldest stromatolites

T2 - Seeing through the effects of heterogeneous deformation, metamorphism and metasomatism affecting Isua (Greenland) ∼3700 Ma sedimentary rocks

AU - Nutman, Allen P.

AU - Bennett, Vickie C.

AU - Friend, Clark R.L.

AU - Van Kranendonk, Martin

AU - Rothacker, Leo

AU - Chivas, Allan R.

PY - 2019/9/1

Y1 - 2019/9/1

N2 - The ∼3700 Ma and 3800 Ma meta-volcanic and -sedimentary rocks in the Isua supracrustal belt (Greenland) were affected by heterogeneous ductile deformation under amphibolite facies conditions (∼500–650 °C), and variably modified by secondary silica and carbonate mineralisation deposited from diagenetic and metasomatic fluids. Rare low-deformation areas preserve original volcanic features – submarine basaltic pillows and sedimentary features – including bedding. These are best-preserved in two dimensions on flat- to moderately-inclined outcrop surfaces, but invariably are tectonically-stretched along a steeply-plunging third dimension, through stretching in the direction of fold axes; a style of deformation found throughout Earth's history. There is a debate about whether rare relicts of ∼3700 Ma stromatolites preserved in metadolomites that formed in a shallow marine setting (Nutman et al., 2016) represent bona fide biogenic primary structures fortuitously preserved in low deformation, or whether these structures are manifestations of deformation combined with non-biogenic deposition of secondary carbonate (Allwood et al., 2018). Here, we critically test the primary nature of the sedimentary rocks hosting the proposed stromatolites and also the veracity of the proposed stromatolites, by addressing the following questions: (i) Are the rocks an in situ outcrop of known age, or displaced blocks of unknown age or origin?; (ii) How much of the carbonate is of an originally sedimentary versus a secondary (i.e., metasomatic – introduced) origin?; (iii) Is the seawater-like REE + Y (rare earth element and yttrium) trace element signature carried definitely by carbonate minerals and therefore diagnostic of a cool, surficial sedimentary system?; (iv) Are the proposed stromatolites consistent with biogenicity in terms of their geometry and fine-scale layering, or could they be the product of soft sediment or structural deformation (compression in folding)? The answers to these questions, which combine diverse observations from geologic context, geochemistry and stromatolite morphology show that the weight of evidence is consistent with a biogenic origin for the stromatolites formed in a shallow water setting and are inconsistent with formation entirely through inorganic processes.

AB - The ∼3700 Ma and 3800 Ma meta-volcanic and -sedimentary rocks in the Isua supracrustal belt (Greenland) were affected by heterogeneous ductile deformation under amphibolite facies conditions (∼500–650 °C), and variably modified by secondary silica and carbonate mineralisation deposited from diagenetic and metasomatic fluids. Rare low-deformation areas preserve original volcanic features – submarine basaltic pillows and sedimentary features – including bedding. These are best-preserved in two dimensions on flat- to moderately-inclined outcrop surfaces, but invariably are tectonically-stretched along a steeply-plunging third dimension, through stretching in the direction of fold axes; a style of deformation found throughout Earth's history. There is a debate about whether rare relicts of ∼3700 Ma stromatolites preserved in metadolomites that formed in a shallow marine setting (Nutman et al., 2016) represent bona fide biogenic primary structures fortuitously preserved in low deformation, or whether these structures are manifestations of deformation combined with non-biogenic deposition of secondary carbonate (Allwood et al., 2018). Here, we critically test the primary nature of the sedimentary rocks hosting the proposed stromatolites and also the veracity of the proposed stromatolites, by addressing the following questions: (i) Are the rocks an in situ outcrop of known age, or displaced blocks of unknown age or origin?; (ii) How much of the carbonate is of an originally sedimentary versus a secondary (i.e., metasomatic – introduced) origin?; (iii) Is the seawater-like REE + Y (rare earth element and yttrium) trace element signature carried definitely by carbonate minerals and therefore diagnostic of a cool, surficial sedimentary system?; (iv) Are the proposed stromatolites consistent with biogenicity in terms of their geometry and fine-scale layering, or could they be the product of soft sediment or structural deformation (compression in folding)? The answers to these questions, which combine diverse observations from geologic context, geochemistry and stromatolite morphology show that the weight of evidence is consistent with a biogenic origin for the stromatolites formed in a shallow water setting and are inconsistent with formation entirely through inorganic processes.

KW - Dolomite

KW - Early life

KW - Eoarchean

KW - Isua

KW - Stromatolites

UR - http://www.scopus.com/inward/record.url?scp=85067387094&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85067387094&partnerID=8YFLogxK

U2 - 10.1016/j.precamres.2019.105347

DO - 10.1016/j.precamres.2019.105347

M3 - Article

AN - SCOPUS:85067387094

VL - 331

JO - Precambrian Research

JF - Precambrian Research

SN - 0301-9268

M1 - 105347

ER -