J.J. Villalaín, P. Calvín, M. F. Bógalo, I. Falcón, and A. M. Casas Villalaí

n et a

l.

EGU 2020

Basque-

Cantabrian

BACKGROUND Widespread cretaceous remagnetizations

in inverted Mesozoic basins of the Iberia and North Africa

- Thick lower cretaceous syn-rift sediments in Iberia

- Thick lower Jurassic syn-rift sediments in Atlas ranges. Villa

laín e

t al.

EGU 2020

3

North Iberian cretaceous remagnetizations

ChRM

Systematic Normal polarity

E. Cameros Basin

Cabuérniga Basin

Aralar stratigraphic coordinates

Aralar

Polientes Basin

Organyà Basin

(Gong et al., 2008)

Iberian Range

Palencia, 2006

W. Cameros Basin

Iberian Ranges

Juarez, 1994

etc… Villa

laín e

t al.

EGU 2020

Timing of Iberian remagnetizations

AGE: - Pre basin-inversion (Oligocene) - Post- o syn- extensión - Post Aptian sediments - Normal polarity (K Superchron)

CRETACEOUS REMAGNETIZATION

Rem

agn

etiz

ed u

nit

s

TE

RT

IAR

Y

LA

TE

CR

ET

.

JUR

AS

SIC

EA

RL

Y C

RE

T.

CR

ET

AC

EO

US

T

RIA

SS

IC

LA

TE

J.

MID

. J.

EA

R. J

.

60

100

140

200

No

rmal

Cre

t.

Sup

erch

ron

Tect

on

ic s

ub

sid

ence

Ex

ten

sio

n

Tect

on

ic

inve

rsio

n

Villalaí

n et a

l.

EGU 2020

High Atlas cretaceous remagnetization

N

90

180

270

TILT CORR

(Lambert)

Down

Up

ChRM

Systematic Normal polarity

Villalaí

n et a

l.

EGU 2020

Dating from the Remagnetization Direction

nA

HYPOTHESIS

- If the different sites were remagnetized at

the same time.

- If the deflection of the magnetization is only due to tilting around the bedding

strike.

- The remagnetization direction is the intersection of the SC.

SC must intersect at the Remagnetization

direction Contours of A values

SCI REMAGNETIZATION DIRECTION

A min

- SC gives all possible original direction in a rotation of the magnetization around the strike.

Small Circle Intersection method (SCI)

Shipunov, 1997; Waldhor & Appel, 2006;

Callvín et al. 2017

Interfolding remagnetization

Small Circles Intersection (SCI) method

Villalaí

n et a

l.

EGU 2020

Aparent Polar Wander Path of Africa (APWP)

136 Ma

136 Ma 77 Ma 40 Ma

50º of cretaceous rotation

Systematic paleomagnetic studies in the Moroccan High Atlas

Expected directions in The High Atlas

Villalaí

n et a

l.

EGU 2020

Systematic paleomagnetic studies in the Moroccan High Atlas

Villalaí

n et a

l.

EGU 2020

Systematic paleomagnetic studies in the Central High Atlas (CHA)

Villalaí

n et a

l.

EGU 2020

NRM OF REMAGNETIZED JURASSIC LIMESTONE

The CHA cretaceous remagnetization has been observed in all these sites with the same magnetic properties: a viscous paleomagnetic component with maximum unblocking temperatures of 200-250ºC and the remagnetization normal polarity component up to 450–500ºC.

Villalaí

n et a

l.

EGU 2020

Magnetic properties: SD-SP uniaxial magnetite

Villalaí

n et a

l.

EGU 2020

Aiming to perform a 3D palinspastic restorations using interfolding remagnetizations a high resolution sampling has been made.

- 10.000 Km2

- 20 profiles - 600 paleomagnetic sites (calculating 600 paleobeddings)

0 100 km

Villalaí

n et a

l.

EGU 2020

All 526 sites

Before BC After total BC

After partial BC

Dec = 336.0° Inc = 43.7° η95 = 1.8 ° ζ 95 = 1.0 °

Direction of remagnetization from Small Circle Intersection Method over 526 sites

Very high accuracy Villalaí

n et a

l.

EGU 2020

Before BC After total BC

After partial BC

Dec = 336.0° Inc = 43.7° η95 = 1.8 ° ζ 95 = 1.0 °

All 526 sites

Exp

ecte

d p

aleo

mag

net

ic d

irec

tio

ns

at t

he

Hig

h A

tlas

DATING THE REMAGNETIZATIION

Villalaí

n et a

l.

EGU 2020

Sector east 77 sites

Central sector 257 sites

Sector west 118 sites

PALEOMAGNETIC DIRECTION AND LOCATION

Homogeneous direction (and age) in different areas

Villalaí

n et a

l.

EGU 2020

Bathonian and lower Cretaceous - 51 sites

Middle Jurassic 166 sites

Toarcian-Aalenian 89 sites

Lower Jurassic 89 sites

STRATIGRAPHIC UNITS

PALEOMAGNETIC DIRECTION AND STRATIGRAPHIC UNIT

Red-beds

Limestones

Limestones

Limestones

Homogeneous direction (and age) in different units of limestone

Villalaí

n et a

l.

EGU 2020

Red beds 51 sites

Carbonates 401 sites

PALEOMAGNETIC DIRECTION AND LITHOLOGIES

Villalaí

n et a

l.

EGU 2020

Timing of the remagnetization

The mechanism proposed for this type of this burial widespread remagnetizations in limestones is the generation of magnetite grains due to the heating related with burial. The homogeneous direction of the remagnetization seems to suggest an acquisition for a short event at 100 Ma. However, the extensional stage of these basins lasts tens of millions years keeping the necessary burial conditions for growth of magnetite grains covering several polarity chrons including the CNS.

AGE (Ma) 200 150 100 50 0

360 350 340 330 320 310 300

DEC

LIN

ATI

ON

(º)

6

Burial timing

6 km

0 km

Villalaí

n et a

l.

EGU 2020

Progressive or

punctual?

In this work we address the question of timing under with these processes happened, i.e. short vs. long remagnetization periods.

? Villa

laín e

t al.

EGU 2020

Punctual thermal event

model

Magnetic moment of SSD magnetite grains shows all Normal polarity It can explain the homogeneous direction and age of remagnetization

Villalaí

n et a

l.

EGU 2020

𝑀 = 𝑚𝑖

Progressive model for acquisition of remagnetization of limestones in deep sedimentary basins

Progressive generation of

magnetite during deep basin condition

Magnetite grow blocking the magnetic moment at Vc.

Two population of N and R SSD

magnetite grains

SP V>Vc

t <<

SSD V>Vc Blocked

magnetic moment

We propose the hypothesis that the ca. 100 Ma paleomagnetic direction shows by the remagnetization is just the average of magnetic moments of the entire SSD magnetite population that grow from the Middle Jurassic up to the Cenozoic. Grains block the magnetic moments when they grow above their critical volume, keeping the magnetic polarity generating over time a distribution of grains in normal and reverse polarity groups.

Villalaí

n et a

l.

EGU 2020

160-84 Ma

SM = 33,6 u.a.

SIMULATION model for calculating remagnetization direction as sum of magnetic moments of grains with different directions and polarities.

For each time interval ∆𝑡𝑖 the corresponding magnetic moment is calculated with polarity from GPTS (Gradstein et al., 2004) and direction from the GAPWP (Torsvik et al., 2012).

𝑀 = 𝑚𝑖 = 𝑘∆𝑡𝑖 𝑢𝑖

Villalaí

n et a

l.

EGU 2020

160-84 Ma

SM = 33,6 u.a.

SM = 38,0 u.a.

120-65 Ma

Villalaí

n et a

l.

EGU 2020

160-84 Ma

SM = 33,6 u.a.

SM = 38,0 u.a.

120-65 Ma

SM = 41,4 u.a.

160-65 Ma

The Progressive model allows to explain the homogeneity in the directions of remagnetization.

Villalaí

n et a

l.

EGU 2020

OBJETIVE: Quantify the effectiveness of the SSD magnetite grains contributing to the NRM

METHOD Sequence: - AF demagnetization of NRM - ARM acquisition - AF demagnetization of ARM - ARM acquisition in progressive DC field

Puntual thermal event (one

population of SSD magnetite)

Progresive model (two N and R population of

SSD magnetite)

vs

EXPERIMENT to test the presence of SSD magnetite grains with opposed magnetic moments.

Villalaí

n et a

l.

EGU 2020

Sequence: AF-ARM-AF

Comp. A

VRM

A. F.

20mT 80mT

140mT

N

Thermal

450ºC 300ºC

VRM

Comp. A

Villalaí

n et a

l.

EGU 2020

Sequence: AF-ARM-AF Two components: A: Cretaceous Remagnetization VRM: Viscous Normal Brunes component

Comp. A

VRM

A. F.

20mT 80mT

140mT

N

Thermal

450ºC 300ºC

VRM

Test the effectiveness: NRM VS ARM 0-20 mT fraction (paralels) 20-80 mT fraction (antiparaleles??)

0

0.2

0.4

0.6

0.8

1

1.2

0 50 100 150 200

ARM DEM / ARM AQ / NRM DEM

ARM DEMAG

ARM AQ

NRM DEMAG

Comp. A

Villalaí

n et a

l.

EGU 2020

Sequence: AF-ARM-AF

0

0.2

0.4

0.6

0.8

1

1.2

0 50 100 150 200

ARM DEM / ARM AQ / NRM DEM

ARM DEMAG

ARM AQ

NRM DEMAG

DT38-5B

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

0.05

-20 30 80 130 180

D ARM /DB D NRM / DB

D ARM /DB

D-NRM/DB

Type 1

y = -0.9173x + 0.9109

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.2 0.4 0.6 0.8 1

Arai diagram

ARM gained/ARMmax N

RM

left

/NR

Mo

-0.03

-0.025

-0.02

-0.015

-0.01

-0.005

0

0.005

0.01

0.015

0.02

-20 30 80 130 180

D ARM -D NRM / D B

Comp. A

VRM

Comp. A VRM

40 mT

20 mT

10 mT

70 mT

110 mT

170 mT

y = -0.573x + 0.6443 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.5 1

Arai diagram (20-70 mT)

20 mT

70 mT

comparing the NRM -ARM signal through the pseudo-Thellier approach

Villalaí

n et a

l.

EGU 2020

0

0.2

0.4

0.6

0.8

1

1.2

0 50 100 150 200

ARM DEM / ARM AQ / NRM DEM

ARM DEMAGARM AQNRM DEMAG

Sequence: AF-ARM-AF Type 1

y = -0.8358x + 0.8624

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.2 0.4 0.6 0.8 1

Arai diagram

y = -0.3959x + 0.5439

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.5 1

Arair diagram (20-70 mT)

0

0.01

0.02

0.03

0.04

0.05

0.06

-20 30 80 130 180

D ARM /DB D NRM / DB

D ARM /DB

D-NRM/DB

-0.05

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

-20 30 80 130 180

D ARM -D NRM / D B

40 mT 20 mT

10 mT

70 mT

110 mT

170 mT

Comp. A

VRM

Comp. A VRM

Villalaí

n et a

l.

EGU 2020

Sequence: AF-ARM-AF Tipo 2

0

0.2

0.4

0.6

0.8

1

1.2

0 50 100 150 200

ARM DEM / ARM AQ / NRM DEM

ARM DEMAG

ARM AQ

NRM DEMAG

y = -0.9707x + 1.0073

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.2 0.4 0.6 0.8 1

Arai diagram y = -0.9856x + 1.0203

0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1

Arai diagram (20-70 mT)

0

0.005

0.01

0.015

0.02

0.025

0.03

-20 30 80 130 180

D ARM /DB D NRM / DB

D ARM /DB

D-NRM/DB

-0.012

-0.01

-0.008

-0.006

-0.004

-0.002

0

0.002

0.004

0.006

0.008

-20 30 80 130 180

D ARM -D NRM / D B

DT33-1B

ARM gained/ARMmax

NR

M le

ft/N

RM

o

Villalaí

n et a

l.

EGU 2020

Sequence: AF-ARM-AF

0

0.2

0.4

0.6

0.8

1

0 0.5 1

Arai diagram

0

0.2

0.4

0.6

0.8

1

0 0.5 1

Arai diagram

ARM gained/ARMmax

NR

M le

ft/N

RM

o

ARM gained/ARMmax

NR

M le

ft/N

RM

o

Type 2 Type 1

Consistent with progressive model (several polarities)

Consistent with Punctual thermal event model (one polarity)

Villalaí

n et a

l.

EGU 2020