TY - JOUR

T1 - A geochemical study of the Ediacaran discoidal fossil Aspidella preserved in limestones

T2 - Implications for its taphonomy and paleoecology

AU - Bykova, N.

AU - Gill, B. C.

AU - Grazhdankin, D.

AU - Rogov, V.

AU - Xiao, S.

N1 - © 2017 John Wiley & Sons Ltd.

PY - 2017/7/1

Y1 - 2017/7/1

N2 - The Ediacara biota features the rise of macroscopic complex life immediately before the Cambrian explosion. One of the most abundant and widely distributed elements of the Ediacara biota is the discoidal fossil Aspidella, which is interpreted as a subsurface holdfast possibly anchoring a frondose epibenthic organism. It is a morphologically simple fossil preserved mainly in siliciclastic rocks, which are unsuitable for comprehensive stable isotope geochemical analyses to decipher its taphonomy and paleoecology. In this regard, three-dimensionally preserved Aspidella fossils from upper Ediacaran limestones of the Khatyspyt Formation in the Olenek Uplift of northern Siberia offer a rare opportunity to leverage geochemistry for insights into their taphonomy and paleoecology. To take advantage of this opportunity, we analyzed δ13Ccarb, δ18Ocarb, δ13Corg, δ34Spyr, and iron speciation of the Khatyspyt Aspidella fossils and surrounding sediment matrix in order to investigate whether they hosted microbial symbionts, how they were fossilized, and the redox conditions of their ecological environments. Aspidella holdfasts and surrounding sediment matrix show indistinguishable δ13Corg values, suggesting they did not host and derive significant amount of nutrients from microbial symbionts such as methanogens, methylotrophs, or sulfide-oxidizing bacteria. δ13Ccarb, δ18Ocarb, and δ34Spyr data, along with petrographic observations, suggest that microbial sulfate reduction facilitated the preservation of Aspidella by promoting early authigenic calcite cementation in the holdfasts before matrix cementation and sediment compaction. Iron speciation data are equivocal, largely because of the low total iron concentrations. However, consideration of published sulfur isotope and biomarker data suggests that Aspidella likely lived in non-euxinic waters. It is possible that Aspidella was an opportunistic organism, colonizing the seafloor in large numbers when paleoenvironments were favorable. This study demonstrates that geochemical data of Ediacaran fossils preserved in limestones can offer important insights into the taphonomy and paleoecology of these enigmatic organisms living on the eve of the Cambrian explosion.

AB - The Ediacara biota features the rise of macroscopic complex life immediately before the Cambrian explosion. One of the most abundant and widely distributed elements of the Ediacara biota is the discoidal fossil Aspidella, which is interpreted as a subsurface holdfast possibly anchoring a frondose epibenthic organism. It is a morphologically simple fossil preserved mainly in siliciclastic rocks, which are unsuitable for comprehensive stable isotope geochemical analyses to decipher its taphonomy and paleoecology. In this regard, three-dimensionally preserved Aspidella fossils from upper Ediacaran limestones of the Khatyspyt Formation in the Olenek Uplift of northern Siberia offer a rare opportunity to leverage geochemistry for insights into their taphonomy and paleoecology. To take advantage of this opportunity, we analyzed δ13Ccarb, δ18Ocarb, δ13Corg, δ34Spyr, and iron speciation of the Khatyspyt Aspidella fossils and surrounding sediment matrix in order to investigate whether they hosted microbial symbionts, how they were fossilized, and the redox conditions of their ecological environments. Aspidella holdfasts and surrounding sediment matrix show indistinguishable δ13Corg values, suggesting they did not host and derive significant amount of nutrients from microbial symbionts such as methanogens, methylotrophs, or sulfide-oxidizing bacteria. δ13Ccarb, δ18Ocarb, and δ34Spyr data, along with petrographic observations, suggest that microbial sulfate reduction facilitated the preservation of Aspidella by promoting early authigenic calcite cementation in the holdfasts before matrix cementation and sediment compaction. Iron speciation data are equivocal, largely because of the low total iron concentrations. However, consideration of published sulfur isotope and biomarker data suggests that Aspidella likely lived in non-euxinic waters. It is possible that Aspidella was an opportunistic organism, colonizing the seafloor in large numbers when paleoenvironments were favorable. This study demonstrates that geochemical data of Ediacaran fossils preserved in limestones can offer important insights into the taphonomy and paleoecology of these enigmatic organisms living on the eve of the Cambrian explosion.

KW - Aspidella

KW - carbon isotopes

KW - Ediacaran fossils

KW - iron speciation

KW - Siberia

KW - sulfur isotopes

KW - NORTHWESTERN CANADA

KW - ARCTIC SIBERIA

KW - TRACE FOSSILS

KW - CAMBRIAN BOUNDARY

KW - OCEAN OXYGENATION

KW - SULFATE REDUCTION

KW - OLDEST EVIDENCE

KW - SOUTH CHINA

KW - SULFUR ISOTOPE FRACTIONATION

KW - MICROBIAL MATS

KW - Calcium Carbonate/chemistry

KW - Oxidation-Reduction

KW - Biota

KW - Fossils

KW - Animals

KW - Geologic Sediments/chemistry

UR - http://www.scopus.com/inward/record.url?scp=85017661253&partnerID=8YFLogxK

U2 - 10.1111/gbi.12240

DO - 10.1111/gbi.12240

M3 - Article

C2 - 28397387

AN - SCOPUS:85017661253

VL - 15

SP - 572

EP - 587

JO - Geobiology

JF - Geobiology

SN - 1472-4677

IS - 4

ER -