The Tendaguru Formation, or Tendaguru Beds are a highly fossiliferous formation and Lagerstätte located in the Lindi Region of southeastern Tanzania. The formation represents the oldest sedimentary unit of the Mandawa Basin, overlying Neoproterozoic basement, separated by a long hiatus and unconformity. It reaches a total sedimentary thickness of more than 110 metres (360 ft). The formation ranges in age from the late Middle Jurassic to the Early Cretaceous, Oxfordian to Hauterivian stages, with the base of the formation possibly extending into the Callovian. The Tendaguru Formation is subdivided into six members; these are from oldest to youngest the Lower Dinosaur Member, the Nerinella Member, the Middle Dinosaur Member, the Indotrigonia africana Member, the Upper Dinosaur Member, and the Rutitrigonia bornhardti-schwarzi member. The succession comprises a sequence of sandstones, shales, siltstones, conglomerates with minor oolitic limestones, deposited in an overall shallow marine to coastal plain environment, characterized by tidal, fluvial and lacustrine influence with a tsunami deposit occurring in the Indotrigonia africana member. The climate of the Late Jurassic and Early Cretaceous was semi-arid with seasonal rainfall and the eustatic sea level was rising in the Late Jurassic from low levels in the Middle Jurassic. Paleogeographical reconstructions show the Tendaguru area was located in the subtropical southern hemisphere during the Late Jurassic. The Tendaguru Formation is considered the richest Late Jurassic strata in Africa. The formation has provided a wealth of fossils of different groups; early mammaliaforms, several genera of dinosaurs, crocodyliforms, amphibians, fish, invertebrates and flora. More than 250 tonnes (250 long tons; 280 short tons) of material were shipped to Germany during excavations in the early 20th century. The faunal assemblage of the Tendaguru is similar to the Morrison Formation of the central-western United States, with an additional marine interbed fauna not present in the Morrison. The dinosaur fauna found in the formation is similar to that of other highly fossiliferous stratigraphic units of the Late Jurassic; among others the Kimmeridge and Oxford Clays of England, the Sables de Glos, Argiles d'Octeville, Marnes de Bléville of France, the Alcobaça, Guimarota and Lourinhã Formations of Portugal, the Villar del Arzobispo Formation of Spain, the Shishugou, Kalazha and Shangshaximiao Formations in China, the Toqui Formation of Chile and Cañadón Calcáreo Formation and the Morrison Formation, with the presence of dinosaurs with similar counterparts, e.g., Brachiosaurus and Stegosaurus in the Morrison, and Giraffatitan and Kentrosaurus in the Tendaguru.
Description
The Tendaguru Formation represents the oldest sedimentary unit in the Mandawa Basin, directly overlying Neoproterozoic basement consisting of gneiss. The contact contains a large hiatus, a missing sequence of stratigraphy, spanning the Paleozoic, Triassic and Early Jurassic. The formation is unconformably overlaid by late Early Cretaceous sediments of the Makonde Formation that forms the top of several plateaus; Namunda, Rondo, Noto, and Likonde-Kitale. Based on extended geological and paleontological observations, the "Tendaguruschichten" (Tendaguru Beds) were defined by Werner Janensch as expedition leader and Edwin Hennig in 1914 referring to a sequence of Late Jurassic to Early Cretaceous strata, exposed in the Tendaguru area, which is named after the Tendaguru Hill.
Stratigraphy The Tendaguru is divided into 6 members, which represent different depositional environments, with the 'Dinosaur Beds' representing terrestrial facies while the beds with genus/species names represent marine interbeds with shallow marine to lagoonal facies. In ascending order these are: the Lower Dinosaur Member, the Nerinella Member, the Middle Dinosaur Member, Indotrigonia africana Member, the Upper Dinosaur Member, and the Rutitrigonia bornhardti-schwarzi Member. The units of the Tendaguru are known to interfinger with each other.
Paleogeography and depositional environment
Paleogeography
The Tendaguru Formation was deposited in the Mandawa Basin, a post-Karoo, Mesozoic rift basin located between the Ruvu Basin and Rufiji Trough to the north and the Ruvuma Basin to the south. To the west of the basin, Archean and Early Proterozoic basement rocks crop out. The main rift phase in present-day southeastern Africa led to the separation of Madagascar and the then-connected Indian subcontinent that happened during the Early Cretaceous. The Songo Songo and Kiliwani gas fields are located just offshore the basin. At time of deposition the area was undergoing a semi-arid climate with coastal influences that maintained somewhat higher moisture levels than seen inland. The upper parts of the formation, the Middle Dinosaur and Rutitrigonia bornhardti-schwarzi Members in particular, showed prevailing semiarid conditions with pronounced dry seasons, based on palynologic analysis. The Tendaguru fauna was stable through the Late Jurassic. During the Late Jurassic and Early Cretaceous, the Gondwana paleocontinent was breaking up and the separation of the Laurasian and Gondwana supercontinents resulted from the connection of the Tethys Ocean with the proto-Atlantic and the Pacific Ocean. In addition, the South Atlantic developed towards the end of the Late Jurassic with the separation of South America and Africa. Africa became increasingly isolated from most other continents by marine barriers from the Kimmeridgian into the Early Cretaceous, but retained a continental connection with South America. Global sea levels dropped significantly in the Early Jurassic and remained low through the Middle Jurassic but rose considerably towards the Late Jurassic, deepening the marine trenches between continents.
Depositional environment
The sedimentary rocks and fossils record a repeated shift from shallow marine to tidal flat environments indicating that the strata of the Tendaguru Formation were deposited near an oscillating strandline which was controlled by sea level changes. The three dinosaur-bearing members are continental to marginal marine and the three sandstone-dominated members are marginal marine in origin.
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