Wenchit River Valley
North Shewa Zone, Amhara Region, Ethiopia
“Tertiary Sediments” (23-16 Ma)
Longwave UV (365nm)
Spec. A (Marcasite): 11.2g / 27x20x31mm (in image)
Spec. B (Large Yellow): 8.0g / 41x30x20mm
Spec. C (Flow Lines): 8.4g / 34x31x20mm
Spec. D (Run [Large Half]): 5.3g / 24x21x17mm
Spec. E (Run [Small Half]): 2.8g / 23x19x14mm
Spec. F (Green Flow): 5.7g / 26x25x20mm
Spec. G (Green Angular): 3.1g / 27x20x15mm
Spec. H (Umber [Large Half]): 3.3g / 26x18x17mm
Spec. I (Umber [Small Half]): 2.2g / 22x12x12mm
*With the exception of Specimens D and E, all present slight matrix on the exterior, consisting primarily of siltstone. Specimen A has a large cluster of iron sulfide mineral concretions on its rear side, accounting for the majority of the piece's weight.
While there are several other amber and copal deposits on the African continent, Ethiopian amber deposits discovered back in 2010 have proven to be the most productive: on average, at least 20kg is mined by the locals every year. The amber is hard, and ranges in color from dark brown, red, and yellow, as well as varying shades of green; the green coloration is a natural base color, although a green fluorescence can be seen in some Ethiopian material when exposed to high-intensity LED light or sunlight: similar green fluorescent response is seen in some Dominican, Mexican, and Myanmar ambers. The green base coloration seen in some Ethiopian amber was likely caused by significant pressure and heat: volcanic layers of basalt of varying thickness overlie and underlie the deposits, and acted as a natural autoclave. The size of recovered amber specimens ranges anywhere from 5-25cm in size.
Geology and Age of Deposits:
Amber is found in sandstone and siltstone layers along the valley walls of the Wenchit, Jemma, and Mugher rivers; the amber-bearing layers were originally attributed to the Debre Libanos Sandstone, a Cretaceous geological Formation within the Blue Nile Basin 200-500m thick: this assignment was based on local observations, a geological map, and fossil spore identification. However, due to incorrectly-dated and some then-unidentified fossil spores, as well as arthropod and plant inclusions from genera with living relatives, the amber is believed to be Early Miocene in age. The amber occurs not in the Debre Libanos Sandstone, but in Tertiary sediments comprised of siltstone and sandstone situated between basalt layers, which often display columnar jointing. These basalt flows vary in age from Early Oligocene (~30 Ma) to Quaternary (2.58 Ma to Recent).
Inclusions, Botanical Source:
Ethiopian amber is frequently rich in inclusions, especially bacteria and fungal spores; plant inclusions include liverworts, various angiosperms, and rare examples of mosses and lichens; arthropods are abundant, including mites, spiders, and over 13 families of hexapods (e.g., beetles, flies, ants, etc.). Comparing the spectrographic results of Ethiopian amber with Dominican and Mexican ambers, has shown that this is a Class Ic resin, most likely produced by a member of the Fabaceae family; fossil leaves and flower parts of trees belonging to the Hymenaea genus have been found in this amber, adding weight to the chemical analysis’ findings.
“A review of copal and amber occurrences in Africa and their paleontological significance.”; Bulletin de la Société géologique de France, 2020, 191 (1), p. 17; Valentine Bouju, Vincent Perrichot
“On the ages of flood basalt events Sur l’âge des trapps basaltiques”; Comptes Rendus Geoscience, Volume 335, Issue 1, pp. 113-140; Courtillot, Renne 2003
“Stratigraphic and structural evolution of the Blue Nile Basin, Northwestern Ethiopian Plateau”; Geological Journal Issue 44, pp. 44, 47-50; N. Gani, et. al. 2008