Tephrostratigraphy and depositional environment of young (<2.94 Ma) Hadar Formation deposits at Ledi-Geraru, Afar, Ethiopia

Erin N. Dimaggio, J. Ramón Arrowsmith, Christopher J. Campisano, Roy Johnson, Alan L. Deino, Mark Warren, Shimeles Fisseha, Andrew S. Cohen

Research output: Contribution to journalArticle

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Abstract

The Pliocene Hadar Formation, exposed throughout the lower Awash Valley, Ethiopia, chronicles the evolution and paleoenvironmental context of early hominins. Deposition of the Hadar Formation continued until at least 2.94 Ma, but what transpired in the Hadar Basin after this time remains poorly documented due to an erosional event that truncated the formation throughout much of the valley. Here we present geologic mapping and stratigraphic analysis of a 26 m-thick section of sedimentary rocks and tephras exposed in the Ledi-Geraru project area in the region of Gulfaytu. The section contains Hadar Formation strata younger than 2.94 Ma, and sediments that we interpret are Busidima Formation in age, <2.7 Ma. We use this record to place additional constraints on depositional environments and the tectonic and paleogeomorphic history of the region. The lower ~20 m of section contains lacustrine deposits that conformably overly a 2.94 Ma marker bed (BKT-2U) that previously served as the uppermost dated tephra in the Hadar Formation. We identified seven post-BKT-2U tephras; three were analyzed for glass chemistry, and one yielded an 40Ar/39Ar age of 2.931 ± 0.017 Ma (1σ). Based on these analyses, the newly mapped deposits at Gulfaytu extend the top of the Hadar Formation, representing ca. 20 kyr of post-BKT-2 sedimentation. The Hadar Basin remained depositional following the BKT-2 eruptions, and paleolake Hadar was present at Gulfaytu at this time. An erosional surface marked by a conglomerate truncates the Hadar strata suggesting that the Gulfaytu region was also was influenced by significant changes to basin architecture well-documented elsewhere in the lower Awash Valley. In addition, geophysical models suggest that central Ledi Geraru hosts a thick subsurface lacustrine sedimentary record within the Hadar Basin. The results of this paper provide the outcrop and near surface characterization for the Hominin Sites and Paleolakes Drilling Project (HSPDP) effort at Gulfaytu.

Original languageEnglish (US)
Pages (from-to)234-250
Number of pages17
JournalJournal of African Earth Sciences
Volume112
DOIs
StatePublished - Dec 1 2015

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depositional environment
basin
valley
marker bed
tephra
conglomerate
lacustrine deposit
sedimentary rock
Pliocene
outcrop
volcanic eruption
glass
drilling
sedimentation
tectonics
young
history
sediment
project

All Science Journal Classification (ASJC) codes

  • Geology
  • Earth-Surface Processes

Cite this

Dimaggio, Erin N. ; Arrowsmith, J. Ramón ; Campisano, Christopher J. ; Johnson, Roy ; Deino, Alan L. ; Warren, Mark ; Fisseha, Shimeles ; Cohen, Andrew S. / Tephrostratigraphy and depositional environment of young (<2.94 Ma) Hadar Formation deposits at Ledi-Geraru, Afar, Ethiopia. In: Journal of African Earth Sciences. 2015 ; Vol. 112. pp. 234-250.
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abstract = "The Pliocene Hadar Formation, exposed throughout the lower Awash Valley, Ethiopia, chronicles the evolution and paleoenvironmental context of early hominins. Deposition of the Hadar Formation continued until at least 2.94 Ma, but what transpired in the Hadar Basin after this time remains poorly documented due to an erosional event that truncated the formation throughout much of the valley. Here we present geologic mapping and stratigraphic analysis of a 26 m-thick section of sedimentary rocks and tephras exposed in the Ledi-Geraru project area in the region of Gulfaytu. The section contains Hadar Formation strata younger than 2.94 Ma, and sediments that we interpret are Busidima Formation in age, <2.7 Ma. We use this record to place additional constraints on depositional environments and the tectonic and paleogeomorphic history of the region. The lower ~20 m of section contains lacustrine deposits that conformably overly a 2.94 Ma marker bed (BKT-2U) that previously served as the uppermost dated tephra in the Hadar Formation. We identified seven post-BKT-2U tephras; three were analyzed for glass chemistry, and one yielded an 40Ar/39Ar age of 2.931 ± 0.017 Ma (1σ). Based on these analyses, the newly mapped deposits at Gulfaytu extend the top of the Hadar Formation, representing ca. 20 kyr of post-BKT-2 sedimentation. The Hadar Basin remained depositional following the BKT-2 eruptions, and paleolake Hadar was present at Gulfaytu at this time. An erosional surface marked by a conglomerate truncates the Hadar strata suggesting that the Gulfaytu region was also was influenced by significant changes to basin architecture well-documented elsewhere in the lower Awash Valley. In addition, geophysical models suggest that central Ledi Geraru hosts a thick subsurface lacustrine sedimentary record within the Hadar Basin. The results of this paper provide the outcrop and near surface characterization for the Hominin Sites and Paleolakes Drilling Project (HSPDP) effort at Gulfaytu.",
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Tephrostratigraphy and depositional environment of young (<2.94 Ma) Hadar Formation deposits at Ledi-Geraru, Afar, Ethiopia. / Dimaggio, Erin N.; Arrowsmith, J. Ramón; Campisano, Christopher J.; Johnson, Roy; Deino, Alan L.; Warren, Mark; Fisseha, Shimeles; Cohen, Andrew S.

In: Journal of African Earth Sciences, Vol. 112, 01.12.2015, p. 234-250.

Research output: Contribution to journalArticle

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T1 - Tephrostratigraphy and depositional environment of young (<2.94 Ma) Hadar Formation deposits at Ledi-Geraru, Afar, Ethiopia

AU - Dimaggio, Erin N.

AU - Arrowsmith, J. Ramón

AU - Campisano, Christopher J.

AU - Johnson, Roy

AU - Deino, Alan L.

AU - Warren, Mark

AU - Fisseha, Shimeles

AU - Cohen, Andrew S.

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N2 - The Pliocene Hadar Formation, exposed throughout the lower Awash Valley, Ethiopia, chronicles the evolution and paleoenvironmental context of early hominins. Deposition of the Hadar Formation continued until at least 2.94 Ma, but what transpired in the Hadar Basin after this time remains poorly documented due to an erosional event that truncated the formation throughout much of the valley. Here we present geologic mapping and stratigraphic analysis of a 26 m-thick section of sedimentary rocks and tephras exposed in the Ledi-Geraru project area in the region of Gulfaytu. The section contains Hadar Formation strata younger than 2.94 Ma, and sediments that we interpret are Busidima Formation in age, <2.7 Ma. We use this record to place additional constraints on depositional environments and the tectonic and paleogeomorphic history of the region. The lower ~20 m of section contains lacustrine deposits that conformably overly a 2.94 Ma marker bed (BKT-2U) that previously served as the uppermost dated tephra in the Hadar Formation. We identified seven post-BKT-2U tephras; three were analyzed for glass chemistry, and one yielded an 40Ar/39Ar age of 2.931 ± 0.017 Ma (1σ). Based on these analyses, the newly mapped deposits at Gulfaytu extend the top of the Hadar Formation, representing ca. 20 kyr of post-BKT-2 sedimentation. The Hadar Basin remained depositional following the BKT-2 eruptions, and paleolake Hadar was present at Gulfaytu at this time. An erosional surface marked by a conglomerate truncates the Hadar strata suggesting that the Gulfaytu region was also was influenced by significant changes to basin architecture well-documented elsewhere in the lower Awash Valley. In addition, geophysical models suggest that central Ledi Geraru hosts a thick subsurface lacustrine sedimentary record within the Hadar Basin. The results of this paper provide the outcrop and near surface characterization for the Hominin Sites and Paleolakes Drilling Project (HSPDP) effort at Gulfaytu.

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