THE GEOMAGNETIC POLARITY TIME SCALE FOR EARY PALEOZOIC: DATA AND SYNTHESE

1 2Vladimir Pavlov and Yves Gallet1 Institute of Physics of the Earth, Russian Academy of Sciences

2 Institut de Physique

Late Ediacarian - Hyperactivity of the Earth magnetic field?

White sea area, Arkhangelsk region, Late Ediacarian, 558-555 Ma, siltstone and claystone,

about 60 reversals in 420 m,-1 estimated revrsal rate ~ 20 RMa

South Urals, Late Ediacarian, 545-550 Masiltstone and sandstone, 40 polarity zones

-1 in 110 m, estimated revrsal rate ~ 20-25 RMa

Southwestern Siberian platform, Late Ediacarian, ~550 Ma, siltstone and sandstone, 58 polarity zones

-1 in 60 m, estimated reversal rate > 30 RMa

Available data indicate that on the eve of and around the Precambrian-Phanerozoic transition geodinamo had operated in a hyper-activity reversing mode (Gallet and Pavlov, 2016) characterized by an extreme geomagnetic reversal frequency.

INTRODUCTION

Constructing the Geomagnetic Polarity Time Scale (GPTS) through the geological history is of crucial importance to address several major issues in Earth sciences, as for instance the long-term evolution of the geodynamo. The GPTS is also an important chronological tool allowing one to decipher the age and duration of various geological processes. Moreover, GPTS is widely used in prospecting for commercial minerals and in petroleum geology

. The chronology of the geomagnetic polarity reversals since the Upper Jurassic is rather well known thanks to the magnetic

anomalies recorded in the sea floor. For more ancient epochs our knowledge of the GPTS is still very fragmentary and much more uncertain. However significant information has been obtained for several time intervals, in particular for the Triassic and the beginning of the Phanerozoic.

We will focus our presentation on recent developments made in the determination of the GPTS during the Early Paleozoic (Cambrian and Ordovician).

Upper Cambrian

Kulumbesection

Khorbusuonka section

May

an s

tage

Mid

dle

Cam

bria

n

An

om

oca

rioid

es l

imb

ata

eform

isL

.laev

igata

- A

.tru

nca

ta

Ep

och

3

Mid

dle

Cam

bri

an

Am

ga s

tage

Toy

on s

tage

Bot

oma

T.g

ibbu

sT

.fis

sus

- P

.sach

eri

Ku

onam

- k

ites

Ory

ctoc

ara

Low

er C

amb

rian

Ep

och

2E

poc

h 3

Am

ga s

tage

Mayan

sta

ge

Mid

dle

Cam

bri

an

An

om

oca

rioid

es l

imb

ata

eform

isC

.per

fora

tus-

A.h

enri

ciT

.fis

sus-

P.s

ach

eri

T.g

ibbu

s

Ep

och

3

Cordylodusangulatus

Cordylodusangulatus

Cordyloduslindstromi

Cordyloduslindstromi

Cordylodusprolindstromi

Hirsutodontussimplex

Cordylodusproavus

Cordylodusproavus

H.discretus

H.appresus

H.resimus

Teridontusnakamurai

Pro

conodontu

s

Post

ero

-co

statu

sM

ulle

ri

Eoco

nodontu

s

C.minutus

P.muelleri

P.postero-costatus

P.tenui-serratus

Nya

yan

Loparian

Mansi

Black Mountain,

Australia Dayangcha,

Kulumbe

NW China

NW Siberia

C-

C-

D+

D+

D+

E-

E-

F1+

F1+

F1+

F2-

F3+

F3+

F3+

G1-

G2+

G3-

G4+

G5-

H+

H+

H+

G-

A-

B2-

B+

Ripperan and Kirschvink, 1992

Ripperdan et al

Gallet and Pavlov, 1998

., 1993

Ke

tyia

nY

ura

kia

nE

nts

ian

Тр

ем

ад

ок

Ар

ени

г

C.proavus

C.intermedius

C.angulatus

C.herfurhi

S.quadra-plicatus

Tangchan,Northern China

Eoconodontus (E.)notchpeakensis

Hirsutodontus ani

Drepanoistodus delfiter

Pro

toco

nodo

ntus

C.primitivus

Eoconodontus (E.)alisonae

Westergaardodinaamplicava

Eoconodontu

s

Paroistodusproteus

?

Rak

hmet

Aks

ay

Cordylodus proavus

Cordylodus intermedius

Cordylodus lindstromi

P.dahlmani-P.memorabilis

Sak

sB

atyr

bay

Ung

urA

ktay

Stages

Are

nig

(F

loia

n-D

arr

iwili

an)

Tre

madoc

Upper

Cam

brian

F1+

F3+G2+

H+

D+

B1+

B3+

B1+

B3+

I+

J+

J+

I+

I+

Madyian

Tavgian

Nganasanian

Ayus

okka

n

Yang et al., 2002

Mid

dle

cam

brian

Upper Cambrian - lowermost OrdovicianComparison of magnetostratigraphy of sections

from Siberia, Australia and China Composite

section

Kulumbe section: Uppermost Middle Cambrian- Lowermost Ordovician

Magnetostratigraphy from the Middle Cambrian through the Middle Ordovician Ordovician

The Middle Cambrian was mostly characterized by very high reversal frequency. Beginning from the end of the Middle Cambrian through Early Ordovician (Trema-doc) the geodinamo was in its “normal reversing mode” (Gallet and Pavlov, 2016) with medium to low reversal frequency. Between the Late Tremadocian and the Middle Llandeilian (begiining of the Sandbian age) the superchron Moyero occurred. This superchron of reversed polarity would have a duration of ~20 Myr.

Няй

ски

йУ

гор

ски

йК

им

ай

ски

йМ

укте

йск

ий

Вол

гинск

ий

Ки

ре

нск

о-

куд

ри

нск

ий

Ар

ен

иг

Лл

ан

ви

рн

Лл

ан

ви

рн

Лл

ан

ви

рн

Лл

ан

дей

ло

Ва

ра

нгу

Хун

небе

ргВ

ол

хов

Кун

да

ЛМГ

Уха

куК

укрус

е

Тр

ем

ад

ок

Ар

ен

иг

Лл

ан

ви

рн

Лл

ан

дей

ло

Азе

ри

Би

лл

инге

н

Composite section

Moyero

Kulumbe

Rozhkova

Tosna(Smethurst et al., 1998)

Lava(Smethurst et al., 1998)

South Sweden(Torsvik and Trench, 1991a)

Magnetostratigraphy of the Arenig and the Llanvirn

Ви

хор

евск

ий

Tre

mad

oc

Flo

ian

Siberia Europe

Dap

ing

ian

Dap

rriw

ilia

nS

an

db

ian

Flo

ian

Dap

ing

ian

Dap

rriw

ilia

nS

an

db

ian

Kudri

nsk

yC

he

rto

vsky

Volg

insk

y

Lla

ndeilo

Cara

doc

Sandbia

n

Llan

virn

Kir

ensk

y

Kulumbe

Stolbovaya

?

?

?

?

?

?

?

?

Kudrino,Rodionov et al.,2001;This study

Polovinka,Pavlov et al.,2000

Profile 2 Profile 1

?

Moyero,Gallet and Pavlov, 1996.

Alexeevka,this study

Gullhogen,Trench and Torsvik, 1991

Hallekis,Trench and Torsvik, 1991

Lena, 59.8N, 118.1E,Torsvik et al.,1995

Lla

ndeilo

Lla

nvirn

Cara

doc

Re

gio

sta

ge

Se

rie

Siberian platform East-European platformComposite Scale

Magnetostratigraphy of the Middle Ordovician

Re

gio

sta

ge

Se

rie

Gra

pto

lite

zo

ne

s

Uhaku

Kukru

se

Cara

doc

Lla

ndeilo

Lla

nvirn

N.g

racilis

G.t

ere

tiu

scu

lus

N.g

racili

sG

.te

retiu

scu

lus

Gra

pto

lite

zo

ne

s

Darr

iwili

an

Sandbia

nD

arr

iwili

an

Tom

mo

tA

tda

ba

n

Te

rre

ne

uvi

an

Ep

och

2

Ea

rly

Ca

mb

ria

n

525 Ma

516 Ma

509 Ma

Bo

tom

a -

To

yon

Mo

de

rate

(h

igh

?)

rev

ers

al

fre

qu

en

cy

Tom

mo

tA

tda

ba

nB

oto

ma

- T

oyo

n

Terr

en

eu

via

nE

po

ch 2

Ea

rly

Ca

mb

ria

n

Lo

w (

ve

ry l

ow

?)

rev

ers

al

fre

qu

en

cy

NN

S30°

S60°

экватор Е150°Е90°E30°

Kirschvink’s pole

Khramov’s pole

P-T

D3-C1

O2-O3

Cm3-O1

Cm2

Siberian APWP

N

NN

EARLY CAMBRIAN:

LONG STANDING CONROVERSY:

TWO PRIMARY POLES FOR ONE SIBERIAN PLATFORM?Kirschvink and Rozanov, 1984

Khramov et al., 1982

NN

N

SYNTHES: both directions are primary(i.e. have been recorded either during the formation of rocks or soon after).

But observed data can't be reconciled in the framework of the Geocentric Axial Dipole hypothesis!

Kirschvink’s direction Khramov’s direction?OR

Kirschvink and Rozanov, 1984

Pisarevsky et al., 1997

Pavlov et al., 2018

Pavlov et al.,unpubl.

To explain seemingly contradictory outcomes of the numerous paleomagnetic studies we consider a hypothesis of anomalous non-uniformitarian geomagnetic field during Early Camb- rian. In this case the geomagnetic field could be characterized by occurrence of two quasi-stable generation modes, which replaced each other in turn. The first mode would correspond to prolonged period during which an axial mostly mono-polar dipole field predominated. The second mode would correspond to relatively short epochs when a reversing circumpolar or midlatitude dipole predominated.

By the beginning of the Sandbian age (Late Llandeilo-Early Caradoc) geody-namo returns to “normal reversing state”, however, soon, the new long magnetic polarity interval (but of normal polarity) is, probably, established. Existence of this Late Ordovician - Early Silurian superchron would be in a good aggrement, with the hypothesis of “double - superchron” of Algeo (1996) and with the hypothesis of sudden transitions between geodynamo operation modes (Gallet and Pavlov, 2016). Further studies are needed to check these hypotheses.

Upper

Ord

ovi

cian

Cara

doc

Ash

gill

Hirnantia

n

Chert

ovs

kian

Baks

ania

n

Kudrino(Siberia)

Dolb

orian

Rozhkova(Siberia)

Almaly(Tienshan)

Gullhogen(Sweden)

Moyero(Siberia)

Botmoynak(Tianshan)

Khondelen (Siberia)

Toluk(Tianshan)

Regio

sta

ge

Series

Katia

nS

andbia

nM

ayan

Floi

an

Dopi

ngia

nDa

rriw

ilian

Sand

bian

Kat

ian

Hirn

an-

tian

Upper Cambrian

Mid

dle

Cam

bri

an

Mid

dle

Ord

ovic

ian

Am

gian

Toy

onA

tdab

anB

otom

aT

omm

ot

Low

er C

amb

rian

Silurian

Up

per

Ord

ovic

ian

Car

adoc

Low

er O

rdov

icia

n

Tre

mad

oc

Up

per

Cam

bri

an

Are

nig

Lla

nvi

rn

Lla

nd

eilo

Ash

gill

Rak

hm

etA

kta

yU

ngu

rB

atyr

bay

Ak

say

Sak

sA

yuso

kk

an526

510

499

499

Ma

485.4

477.7

443.8Ma

Superchron“Moyero”

Normalpolarity

Reversedpolarity

Anomalousinterval

Early Paleozoic Geomagnetic polarity time scale: tentative compilation

Ediacarian Middle Cambrian

458.4

Normal Reversing mode

Superchron mode

Hyper-Active Reversing mode

? ??

no data

?

0

2

4

6

8

10

0 100 200 300 400 500 600

Magnetic r

eve

rsal fr

equency

(re

v/M

yr)

Time (Ma)

Three Distinct Reversing Modes in the Geodynamo (Gallet and Pavlov, 2016)

The geodynamo operates in three distinct reversing modes: (i) a “normal” reversing mode generatinggeomagnetic polarity reversals according to a stationary random process, with on average a reversal rateof ~3 rev./Myr; (ii) a non-reversing “superchron” mode characterizing long time intervals without reversal;(iii) a hyper-active reversing mode characte-rized by an extreme geomagnetic reversal frequency. The transitions between the different reversing modes would be sudden, i.e. on the Myr time scale. We suggest that in the past, the occurrence of these transitions has been modulated by therma conditions at the core-mantle boundary governed by mantle dynamics.

Baykal Lake

Olekm

aLenaAngara

Ole

nek L

ena

Viluy

Viluy

Markha

Popigay

Fomich

Djogdjo

Magan

Pyas

ina

Kheta

Eni

sey

Kot

uy

Kotuykan

Nijnyaya TunguskaPodkamennaya Tunguska

Enisey Vitim

Aldan

Cretaceous

Jurassic

Permian and Triassic

Paleozoic

o70

o60

0100

0120

Precambrian

Turukhanskregion

Uchur-Mayaregion

EniseyRidge

Our sampling in the Siberian platform

Baykal Lake

Olekm

aLenaAngara

Ole

nek L

ena

Viluy

Viluy

Markha

Popigay

Fomich

Djogdjo

Magan

Pyas

ina

Kheta

Eni

sey

Kot

uy

Kotuykan

Nijnyaya TunguskaPodkamennaya Tunguska

Enisey Vitim

Aldan

Cretaceous

Jurassic

Permian and Triassic

Paleozoic

o70

o60

0100

0120

Precambrian

Kulumbe

Kudrino

Moyero

Rozhkova

Khorbusuonka

Location of main studied sections (Siberian platform)

Polovinka

Middle Lena

Khorbusuonka river section