The Geology of Early Humans in the Horn of Africa

Magnetostratigraphy of the eastern Hadar Basin (Ledi-Geraru research area, Ethiopia) and implications for hominin paleoenvironments
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Published:December 01, 2008
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Guillaume Dupont-Nivet, Mark Sier, Christopher J Campisano, J Ramón Arrowsmith, Erin DiMaggio, Kaye Reed, Charles Lockwood, Christine Franke, Silja Hüsing, 2008. "Magnetostratigraphy of the eastern Hadar Basin (Ledi-Geraru research area, Ethiopia) and implications for hominin paleoenvironments", The Geology of Early Humans in the Horn of Africa, Jay Quade, Jonathan G. Wynn
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To date and characterize depositional environments of the hominin-bearing Hadar Formation, lacustrine sediments from the eastern part of the Hadar Basin (Ledi-Geraru research area) were studied using tephrostratigraphy and magnetostratigraphy. The Sidi Hakoma Tuff, Triple Tuff-4, and the Kada Hadar Tuff, previously dated by 40Ar/39Ar in other parts of the basin, were identified using characteristic geochemical composition and lithologic features. Paleomagnetic samples were collected every 0.5 m along an ~230-m-thick composite section between the Sidi Hakoma Tuff and the Kada Hadar Tuff. A primary detrital remanent magnetization mostly carried by (titano-) magnetites of basaltic origin was recognized. Consistent with existing data of the Hadar Basin, paleomagnetic directions show a postdepositional counterclockwise vertical-axis tectonic rotation (~5°–10°) and shallowing of paleomagnetic inclination (~5°–10°) related to sedimentation and compaction. Two normal-polarity intervals (chrons 2An.3n and 2An.2n) are recorded bracketing a reversed interval identified as the Mammoth event (chron 2An.2r). Resulting sediment accumulation rates (~90 cm/k.y.) are high compared to existing accumulation-rate estimates from the more western part of the Hadar Basin. The resulting eastward increasing trend suggests that deposition took place in an eastward-tilting basin. Sediment accumulations were constant throughout the basin from ca. 3.4 to 3.2 Ma. At 3.2 Ma, a regional and relatively short-lived event is indicated by significant change in depositional conditions and a large increase in accumulation rate. This disruption may have been related to increased climate variability due to astronomical climate forcing. It provides a possible explanation for changes in the Hadar faunal community and Australopithecus afarensis in particular.
- Africa
- Australopithecinae
- Australopithecus
- Australopithecus afarensis
- biologic evolution
- Cenozoic
- chemical composition
- Chordata
- East Africa
- Ethiopia
- Eutheria
- Hadar
- Hadar Formation
- Hominidae
- igneous rocks
- lacustrine environment
- lithostratigraphy
- magnetostratigraphy
- Mammalia
- Neogene
- paleoenvironment
- paleomagnetism
- Pliocene
- Primates
- pyroclastics
- sedimentation
- sedimentation rates
- tectonics
- Tertiary
- Tetrapoda
- Theria
- tuff
- Vertebrata
- volcanic rocks