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Magnetostratigraphy and carbon isotopes of the Ediacaran Avellaneda Formation, Rio de La Plata Craton, Argentina

1 1 2,3 2,3 3,4 3,4Jhon Afonso ; Ricardo Trindade ; Pablo Franceschinis , Augusto Rapalini , M. J. Arrouy , D. Poiré 1 - Institute of Astronomy, Geophysics and Atmospheric Sciences, Departament of Geophysics, University of São Paulo, Brazil (jhon.afonso@iag.usp.br)2 - Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires (IGEBA), Departamento de Ciencias Geológicas, Facultad de Ciencias Exactas y Naturales, Buenos Aires, Argentina3 - Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina4 - Centro de Investigaciones Geológicas, Facultad de Ciencias Naturales y Museo, La Plata, Argentina

1 - INTRODUCTION

Brasil

Uruguay

Paraguay

Chile

Argentina

300 km

South Atlantic Ocean

48

40

32

24

80

72

24

64

56

48

Buenos Aires Complex

Villa MónicaFormation

Colombo Fm

Cerro LargoFormation

Olavarría Formation

Loma NegraFormation

AliciaFormation

Cerro NegroFormation

Sie

rras

Baya

s G

rupo

La P

rovi

denci

a G

rup

HALLMARK STRATIGRAPHY

1150 Ma

~560 - 550 Ma

2.2 Ga

~600 Ma

13δ C -2 to +2‰

Barker Surface13δ C +2 to +4‰

Piedra AmarillaSurface

0.7068-0.707087 86( Sr/ Sr)

0.7064-0.708287 86( Sr/ Sr)

~590 - 580 Ma

Ediacaran acritarchs

40 km

Crystalline rock Dolostone

Diamictite Limestone

Marls

Mudstone

Shale

Siltstone

Sandstone

Iron level

N

37°0

0'

38°0

0'

60°00' 58°00'

Buenos Aires Complex

HALLMARK STRATIGRAPHY

~560 - 550 Ma

~600 Ma

13δ C -2 to +2‰

Barker Surface13δ C +2 to +4‰

0.7064-0.708287 86( Sr/ Sr)

~590 - 580 Ma

Ediacaran acritarchs

(Aspidella sp.)

LITHOLOGY

Major fault Fault

STRUCTURES

Cities

LOCALITIES

Studied area

Ordovician-Silurian

Neoproterozoic sedimentary cover

Paleo-mesoproterozoic basement

MAP LEGEND

National capital

Studied area

Paleomagnetic data from the Ediacaran (635-542 Ma) indicate rapid flips in polarity

of the Earth magnetic field (Meert et al., 2016). This unusual behavior provides a

powerful tool for high resolution markers. Correlation of these reversals to a

geomagnetic polarity time scale yeld an important geochronological methods that

facilitates precise stratigraphic correlation and arrange global geological events.

Here, we present a magnetostratigraphy study combined with carbon isotopes

curves from the Avellenada Formation (580-560 Ma).

2 - GEOLOGICAL BACKGROUND

The Avellaneda Formation is exposed in the the Tandilia System, located on Rio de La

Plata Craton, Argentina (Fig. 1A). This is unit can reach up to 20 meters of thick

including massive to laminated marls and very fine-grained siliciclastic rocks likely

formed in shallow marine subtidal environments (Arrouy et al., 2015). Geochemical

data from the Loma Negra Formation (Fig. 1B) and soft-bodied taxon Aspidella

remains founded in Cerro Negro Formation (Fig. 1B), settle the Avellaneda Formation

likely age between 580 and 560 Ma (Arrouy et al., 2016).

3 - MATERIALS AND METHODS

Two drill cores (TSE-34 and TSE-07) recovered from Avellaneda Formation near the city of Olavarria were sampled and described. Oriented samples for 3paleomagnetic measurements were collected every 0.3–0.5 meters. At least two cylindrical cores measuring 2.2 cm were extracted from each sample. The two

drill cores provided 178 cylindrical specimens. All individual specimens were subjected to thermal demagnetization treatments. Measurements of the natural

remanent magnetization (NRM) were made using a three-axis 2G cryogenic magnetometer, housed in a magnetically shielded room in the Laboratório de

Paleomagnetismo at the Universidade de São Paulo (USPmag). Measurements were processed using the Remasoft 3.0 software. Carbon isotope analyses were

prepared using a powders drill and analysed in Laboratório de Isótopos Estáveis (LES) at the Universidade de São Paulo.

N

E

S

W

S

N

EW

N

E

S

W

Up

E

Down

W

N

E

S

W

Up

E

Down

W

M/M

max

0.2

0.4

0.6

0.8

0

1.0

0 100 200 300 400 500 600 (T°C)

0.2

0.4

0.6

0.8

0

1.0

0 100 200 300 400 500 600

M/M

max

(T°C)

N

E

S

W

N

E

S

W

Up

E

Down

W

0 100 200 300 400 500 600 (T°C)

M/M

max

0.2

0.4

0.6

0.8

0

1.0

TSE-07-11A

TSE-07-26E

TSE-34-2C

Down

Up

Horizontal

Vertical

4 - RESULTS

Sedimentary rocks described in both drill cores are similar (Fig. 2). Grey to redish marls and very-fine grained siliciclastic sediments are main constituents

of drill cores (Fig. 2A and 2B). Thermal desmagnetization treatment revealed a stable high-temperature component (HTC) above ~300-575°C or 620°C

depending on samples (Fig. 3). HTC show positive and negative inclination. Plot the inclination versus stratigraphic position allow the recognition of 13

correlatable magnetozones (Fig. 4A). Stable carbon isotope ratio (δ Ccarb) provide an independent tool and support for magnetostratigraphic 13 18

correlations. δ Ccarb against δ Ocarb suggest a primary C isotope curve (Fig. 4B).

Fig. 1 - Geological context. (A) Schematic map of the Tandilla System. (B) Stratigraphic column

for the area.

AvellanedaFormation

Lo

ma

Ne

gra

Fm

Ave

lla

ne

da

Fm

Box - 29 Box - 27 Box - 18 TOP

Ave

lla

ne

da

Fm

Ali

cia

Fm

Box - 19

BASE

Box - 12 TOPBox - 10 Box - 09 Box - 07

Ave

llan

ed

a F

mC

erro

Ne

gro

Fm

Lo

ma

Ne

gra

Fm

Ave

llan

ed

a F

m

BASE

Fig. 1 - Geological context. (A) Schematic map of the Tandilla System. (B) Stratigraphic column for the area. Fig. 2B column

were compiled of previous studies of Arrouy et al., (2016) and Gómez-Peral et al., (2019).

Fig. 2 - Photography of drill cores samples from Avelleneda Formation. In the left site samples from core TSE-34. Samples obtained

from core TSE-07 appear on the right. Red arrow indicate the lower and upper boundaries of the Avellenda Formation.

TSE-34-10A

N

E

S

W

N

E

S

W

Up

E

Down

W

0 600300 400 500100 200 700

M/M

max

0.2

0.4

0.6

0.8

0

1.0

(T°C)

Fig. 3 - Representative thermal demagnetization data. Data are in stratigraphic coordinates and are plotted in vector-endpoint

diagrams (Zijderveld, 1967), equal-area stereographic projection and magnetization intensity versus temperature curves. The

characteristic remanent magnetizations were determined by principal component analysis (Kirschvink, 1980). Blue and red

arrows showing horizontal and vertical components, respectively.

5 - DISCUSSION

13δ C

TSE - 34

82

83

84

85

86

87

88

89

90

91

Loma Negra Formation

(~ 590-580 Ma)

Ave

lla

ne

da

Fo

rma

tio

n

Alicia Formation

(~560-550 Ma)

E34-10

E34-12

E34-11

E34-9

E34-8

E34-7

E34-6

E34-5E34-4

E34-3

E34-1

E34-2

Polarity13δ C

-5.0 0 5.0 -90 -45 0 45 90

I (°)

13δ C (+2 to +4%)87 86Sr/ Sr (07064 - 07082)

E34-13

E34-14

E34-15

E34-16

PolarityTSE - 7

40

41

42

43

44

45

46

47

48

49

50

51

52

53

54

55

56

57

E7-26

E7-25

E7-24

E7-23

E7-22

E7-21

E7-20

E7-19

E7-18

E7-17

E7-16

E7-15

E7-14

E7-11

E7-12

E7-13

Loma Negra Formation

(~ 590-580 Ma)

13δ C

-5.0 0 5.0

E7-36

E7-37

E7-38

E7-39

E7-40

E7-42

E7-41

E7-43

E7-44

E7-45

E7-46

-90 -45 0 45 90

I (°)

13δ C (+2 to +4%)

87 86Sr/ Sr (07064 - 07082)

-3 -2 -1 0 1 2 3 4 5-16

-15

-14

-13

TSE-07

TSE-34

18δ

O

Mudstone

Marls

Claystone

Limestone

Shale

Reverse polarity

Normal polarity

E7/E34 Sample

Acritharcs

Aspidella sp.

LITHOLOGY POLARITY

FOSSILS

Fig. 4 - Correlation of the drill cores from Avellanade Formation. (A) Carbon isotope curves and magnetostratigraphic frames including variations of lithology, inclinations, and 13 18polarity along depths. (B) Plot δ Ccarb versus δ Ocarb (arrow indicate the diagentic trends).

6 - CONCLUSIONS

Magnetostratigraphy coupled with carbon isotopes data from Ediacaran Avellenada Formation provide a reliable tool to perform high precise correlations.

The detailed paleomagnetic investigations show the presence of multiple geomagnetic polarities in the Ediacaran.

In the future, we hope provide robust magnetostratigraphic data able to extend correlation with worldwide Ediacaran successions

REFERENCES

Arrouy, M.J., Poiré, D., Gómez Peral, L.E., Canalicchio, J.M., 2015. Sedimentología y estratigrafía del grupo La Providencia (nom. nov.): cubierta superior neoproterozoica, Sistema de Tandilia, Argentina. Latin American Journal of Sedimentology and Basin Analysis. 22, 171–189.

Meert J.G., Levashova N.M., Bazhenov M.L., Landing E. 2016. Rapid changes of magnetic Field polarity in the late Ediacaran: Linking the Cambrian evolutionary radiation and increased UV-B radiation. Gondwana Research, 34:149-157.

Gómez Peral, L.E., Julia, M., Poiré, D.G., Cavarozzi, C.E., 2019. Redox-sensitive trace element distribution in the Loma Negra Formation in Argentina: The record of an Ediacaran oxygenation event. Precambrian Research. 332, 105384.

Arrouy, M.J., Warren, L. V., Quaglio, F., Poiré, D.G., Simões, M.G., Rosa, M.B., Peral, L.E.G., 2016. Ediacaran discs from South America: Probable soft-bodied macrofossils unlock the paleogeography of the Clymene Ocean. Scientific Reports. 6, 1–10.

Studied area

Fig. 1A Fig. 1B

Fig. 2A Fig. 2B

Fig. 4A

Fig. 4B

Acknowledgment:

We are especially grateful to Cementos Avellaneda S/A for logistical support and for allowing access to drill cores.