Mahenge Formation
{{short description|Geological formation in Tanzania}}
{{Infobox rockunit|name=Mahenge Formation|image=|caption=|type=Sedimentary|age={{fossilrange|46.3|45.7|Middle Eocene (Lutetian)}}|prilithology=Mudstone, shale|otherlithology=|namedfor=Mahenge|namedby=|region=|country=Tanzania|coordinates={{coord|4.8|S|34.3|E|display=inline,title}}|unitof=|subunits=|underlies=|overlies=Precambrian basement (Nyanzian Belt)|thickness=|extent=|area=|map={{Location map+ | Tanzania
| relief = 1
| width = 250
| float = center
| places =
{{Location map~ | Tanzania
| lat_deg = -4.8
| lon_deg = 34.3
| mark = Lightgreen pog.svg
| marksize = 10
}}
}}|map_caption=|period=Lutetian|paleocoordinates={{coord|18.0|S|33.0|E|display=inline}}}}The Mahenge Formation{{Cite journal |last1=McMahan |first1=Caleb D. |last2=Chakrabarty |first2=Prosanta |last3=Sparks |first3=John S. |last4=Smith |first4=W. M. Leo |last5=Davis |first5=Matthew P. |date=2013 |title=Temporal patterns of diversification across global cichlid biodiversity (Acanthomorpha: Cichlidae) |journal=PLOS ONE |volume=8 |issue=8 |pages=e71162 |doi=10.1371/journal.pone.0071162 |doi-access=free |issn=1932-6203 |pmc=3747193 |pmid=23990936|bibcode=2013PLoSO...871162M }} is a Middle Eocene-aged geological formation and Konservat-Lagerstätte from Tanzania.{{Cite journal |last1=Uhl |first1=Dieter |last2=Wuttke |first2=Michael |last3=Smith |first3=Krister T. |last4=Wedmann |first4=Sonja |last5=Lehmann |first5=Thomas |date=2024-12-01 |title=Pre-Quaternary maar lakes/volcanogenic lakes as Konservat Lagerstätten—Messel and beyond |url=https://link.springer.com/article/10.1007/s12549-024-00636-z |journal=Palaeobiodiversity and Palaeoenvironments |language=en |volume=104 |issue=4 |pages=753–761 |doi=10.1007/s12549-024-00636-z |bibcode=2024PdPe..104..753U |issn=1867-1608|url-access=subscription }} It contains a high variety of exceptionally-preserved fossils, including many of the earliest fossil records of dominant freshwater fish groups found in Africa today. It represents one of the most comprehensive Paleogene-aged African fossil deposits south of the Sahara. Based on fossil plant remains found in the formation, the Mahenge lake was situated within legume-dominated woodlands reminiscent of modern miombo forests.{{Cite journal |last1=Kaiser |first1=Thomas M. |last2=Ansorge |first2=Jörg |last3=Arratia |first3=Gloria |last4=Bullwinkel |first4=Volker |last5=Gunnell |first5=Gregg F. |last6=Herendeen |first6=Patrick S. |last7=Jacobs |first7=Bonnie |last8=Mingram |first8=Jens |last9=Msuya |first9=Charles |last10=Musolff |first10=Andreas |last11=Naumann |first11=Rudolf |last12=Schulz |first12=Ellen |last13=Wilde |first13=Volker |date=2006-09-01 |title=The maar lake of Mahenge (Tanzania) unique evidence of Eocene terrestrial environments in sub-Sahara Africa |url=http://www.schweizerbart.de/papers/zdgg/detail/157/55495/The_maar_lake_of_Mahenge_Tanzania_unique_evidence_?af=crossref |journal=Zeitschrift der Deutschen Gesellschaft für Geowissenschaften |language=en |volume=157 |issue=3 |pages=411–431 |doi=10.1127/1860-1804/2006/0157-0411 |bibcode=2006ZDGG..157..411K |issn=1860-1804|url-access=subscription }}
It was deposited within a former maar lake formed from a volcanic intrusion into the Precambrian bedrock via a kimberlite pipe.{{Citation |last1=Harrison |first1=Terry |title=Paleontological Investigations at the Eocene Locality of Mahenge in North-Central Tanzania, East Africa |date=2001 |work=Eocene Biodiversity: Unusual Occurrences and Rarely Sampled Habitats |pages=39–74 |editor-last=Gunnell |editor-first=Gregg F. |url=https://link.springer.com/chapter/10.1007/978-1-4615-1271-4_2 |access-date=2025-05-02 |place=Boston, MA |publisher=Springer US |language=en |doi=10.1007/978-1-4615-1271-4_2 |isbn=978-1-4615-1271-4 |last2=Msuya |first2=Charles P. |last3=Murray |first3=Alison M. |last4=Jacobs |first4=Bonnie Fine |last5=Báez |first5=Ana Maria |last6=Mundil |first6=Roland |last7=Ludwig |first7=Kenneth R.|url-access=subscription }} It has been dated to the Lutetian, roughly 46.0 million years ago. Unusually, relatively few fossil insect remains are known from the lake, unlike with other maar deposits. It is thought that the high diversity of fish in the lake may have led to most insects being consumed before they could be fossilized.
