PHANEROZOIC BURIAL, UPLIFT AND DENUDATION OF THE EQUATORIAL ATLANTIC MARGIN OF SOUTH AMERICA JAPSEN, Peter1, BONOW, Johan M.2, GREEN, Paul F3., DALL’ASTA, Massimo4, ROIG, Jean-Yves5 1: Geological Survey of Denmark and Greenland (GEUS), 1350 Copenhagen, Denmark (
[email protected]); 2: Geovisiona AB, Järfälla, Sweden; 3: Geotrack International, Melbourne, Australia; 4: Total Research and Development, Pau, France; 5: BRGM, Orleans, France
Field work 2016
N
1
Elevation (m)
Cayenne
150 m
Near
50 km
Base
Base Tertiary
Albia
-2
n
N-S profile across the northern margin of the Guiana Shield and the southern margin of the Guyana Basin along ~55.5˚W (cf.Wong et al. 1998).Tilted and truncated Lower Cretaceous strata rest on Precambrian basement (Sapin et al. 2016).
2 Suriname’s coastal plain. Bauxite in Eocene sediments below a regional Oligocene hiatus.
Profile B
S Well A
500 m
Integrated studies of burial, uplift and denudation Tafelberg up to 1 km above sea level. Roraima Group Paleoproterozoic sandstone.
Well B
Quaternary
Cretaceous Permian
Base-Cretaceous unconformity
Integration of information from multiple disciplines is key to the approach. Without the AFTA data, the landscape analysis would have yielded only a relative event chronology and amounts of exhumation would have remained unknown. Without the landscape analysis, important information about when plateau surfaces were formed as the result of prolonged denudation could not have been used as constraints in the reconstruction of the burial and exhumation history. Identification of sedimentary remnants provides additional detail on periods of surface exposure.
-2
-4
a m
Ordovician
50 km
n o z
Belem
Profile C W
Well E
Well F
Quaternary
Permian
4
Elf report (1970)
Cretaceous
Well G
250 km Vast sub-horizontal surfaces (peneplains) at distinct levels characterize the landscape of the Guiana Shield. Profile A
Study area
Cenozoic Cretaceous Palaeozoic Precambrian
Miocene 0
ld
Profile B
Profile C
Elf report (1970) -6
This configuration suggests that major exhumational events affected the region during Triassic to Early Cretaceous times. A Devonian outlier on basement ~125 km SE of Cayenne (van Boekel 1967) documents that parts of the Guiana Shield already were exposed in Palaeozoic time. We will be testing the possibility that significant thicknesses of Proterozoic, Paleozoic, Mesozoic and or Cenozoic sections have been removed over a wider area during this period.
These observations are in good agreement with our initial AFTA data from the margin of the Guiana Shield. The data seem to show three phases of denudation (Triassic-Jurassic, Cretaceous and Cenozoic).The conclusion is also in agreement with the results of Theveniaut and Freyssinet (2002) who used palaeomagnetic data to conclude that bauxitic surfaces across basement at up to 400 m a.s.l. on the Guiana Shield formed during the Palaeogene. However, according to their interpretation, plains above that elevation may be Mesozoic.
50 m high cliffs of the Cretaceous Alter do Chão Formation along the Tapajós river.
Elevation of the northern parts of South America.The focus of the SAEAM study is the Guiana Shield north of the Amazon. Previously Japsen et al. (2012) studied the burial and exhumation history of NE Brazil.
Geology of the study area. On the northern margin of the Guiana Shield, Cretaceous and Cenozoic strata rest on basement. On the southern margin, Palaeozoic strata rest on basement.
References Green, Lidmar-Bergström, Japsen, Bonow & Chalmers 2013: Stratigraphic landscape analysis, thermochronology and the episodic development of elevated passive continental margins. GEUS Bulletin. Japsen, Green, Bonow & Erlström 2016: Episodic burial and exhumation of the southern Baltic Shield: Epeirogenic uplifts during and after break-up of Pangea. Gondwana Research. Japsen, Bonow, Green, Cobbold, Chiossi et al. 2012: Episodic burial and exhumation history of NE Brazil after opening of the South Atlantic. GSA Bulletin. Sapin, Davaux, dall'Asta et al. 2016: Post-rift subsidence of the French Guiana hyper-oblique margin: from rift-inherited subsidence to Amazon deposition effect. Geol. Soc. Spec. Publ. Theveniaut & Freyssinet 2002: Timing of lateritization on the Guiana Shield: synthesis of paleomagnetic results from French Guiana and Suriname. 3 x Palaeo. van Boekel, N.M. 1967: Nova localidade fossilífera do Devoniano no Amapá. Anais da Academia Brasileira de Ciências 39. Wong, T.E., Krook, L. & Zonneveld, J. 1998: Investigations in the coastal plain and offshore area of Suriname. The History of Earth Sciences in Suriname. Royal Netherlands Academy of Arts and Sciences & Netherlands Institute of Applied Geoscience TNO, Amsterdam 73, 100.
-2
-5
N-S and E-W profiles (B and C) across the Amazon Basin illustrating the erosional unconformity of the Palaeozoic strata below the Aptian–Maastrichtian succession (Alter do Chão Formation).
Japsen et al. 2012
-1
Lower -3 Cret. -4
4 ie h S a n a i u G
-5
E
Palaeogene
50 km
Serra Azul, north of the Amazon. Mountains up to ~600 m a.s.l. in Ordovician Trombetas sandstone.
-1
200 Ma intrusion (CAMP)
Ordovician
Physics: Palaeo-thermal (AFTA,VR) and paleo-burial (sonic) data
0
-3
A
3
Well C Well D
Precambrian
3
Evidence of removed covers
-3
250 m N
Geology: Rocks deposited at the surface of the Earth
-1
The lowermost of the sub-horizontal planation surfaces across the basement of the Guiana Shield continues across the coastal plain of Suriname without significant change in elevation. This sub-horizontal plain truncates the tilted, sub-Cretaceous basement surface along the Atlantic margin, and this configuration indicates that this plain was formed in the Cenozoic. We will investigate the age and the nature of the sub-horizontal plains across the Guiana Shield.
350 m
Evidence of surface processes Stratigraphic landscape analysis: End-result of uplift and denudation
0
Base Neogene unconformity
Oligocene absent Oligocene thin or absent Weathered basement
Paramaribo
2
Coast
Altitude (km)
The study will thus combine the thermal history from AFTA data with the denudation history from stratigraphic landscape analysis to provide magnitudes and timing of vertical movements (Japsen et al. 2012, 2016).
S
Lowermost planation surface
The study investigates the history of burial, uplift and denudation of the South American Equatorial Atlantic Margin (SAEAM) including the Guiana Shield. The study combines apatite fission-track analysis (AFTA) and vitrinite reflectance data from samples of outcrops and drillcores, sonic velocity data from drill holes and stratigraphic landscape analysis (mapping of peneplains) – all constrained by geological evidence, following the methods of Green et al. (2013).
Profile A
Altitude (km)
1
Altitude (km)
The SAEAM Uplift study
