Magnetostratigraphy and carbon isotopes of the Ediacaran Avellaneda Formation, Rio de La Plata Craton, Argentina 1 1 2,3 2,3 3,4 3,4 Jhon 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 ([email protected]) 2 - Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires (IGEBA), Departamento de Ciencias Geológicas, Facultad de Ciencias Exactas y Naturales, Buenos Aires, Argentina 3 - Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina 4 - 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 Mónica Formation Colombo Fm Cerro Largo Formation Olavarría Formation Loma Negra Formation Alicia Formation Cerro Negro Formation Sierras Bayas Grupo La Providencia Grup 1150 Ma ~560 - 550 Ma 2.2 Ga ~600 Ma 13 δ C -2 to +2‰ Barker Surface 13 δ C +2 to +4‰ Piedra Amarilla Surface 0.7068-0.7070 87 86 ( Sr/ Sr) 0.7064-0.7082 87 86 ( Sr/ Sr) ~590 - 580 Ma Ediacaran acritarchs 40 km Crystalline rock Dolostone Diamictite Limestone Marls Mudstone Shale Siltstone Sandstone Iron level N 37°00' 38°00' 60°00' 58°00' Buenos Aires Complex HALLMARK STRATIGRAPHY ~560 - 550 Ma ~600 Ma 13 δ C -2 to +2‰ Barker Surface 13 δ C +2 to +4‰ 0.7064-0.7082 87 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 3 paleomagnetic 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 E W N E S W Up E Down W N E S W Up E Down W M/Mmax 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/Mmax (T°C) N E S W N E S W Up E Down W 0 100 200 300 400 500 600 (T°C) M/Mmax 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 Avellaneda Formation Loma Negra Fm Avellaneda Fm Box - 29 Box - 27 Box - 18 TOP Avellaneda Fm Alicia Fm Box - 19 BASE Box - 12 TOP Box - 10 Box - 09 Box - 07 Avellaneda Fm Cerro Negro Fm Loma Negra Fm Avellaneda Fm 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 0 600 300 400 500 100 200 700 M/Mmax 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 13 δ C TSE - 34 82 83 84 85 86 87 88 89 90 91 Loma Negra Formation (~ 590-580 Ma) Avellaneda Formation Alicia Formation (~560-550 Ma) E34-10 E34-12 E34-11 E34-9 E34-8 E34-7 E34-6 E34-5 E34-4 E34-3 E34-1 E34-2 Polarity 13 δ C -5.0 0 5.0 -90 -45 0 45 90 I (°) 13 δ C (+2 to +4%) 87 86 Sr/ Sr (07064 - 07082) E34-13 E34-14 E34-15 E34-16 Polarity TSE - 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) 13 δ 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 (°) 13 δ C (+2 to +4%) 87 86 Sr/ Sr (07064 - 07082) -3 -2 -1 0 1 2 3 4 5 -16 -15 -14 -13 TSE-07 TSE-34 18 δO 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 18 polarity 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.
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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 ([email protected])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.
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