Integrated heavy mineral study of Jurassic to Paleogene sandstones in the Mandawa Basin, Tanzania: Sediment provenance and source-to-sink relations

Abstract

This paper concerns the heavy mineral composition of Jurassic, Cretaceous and Paleogene sedimentary successions in the Mandawa Basin. The nature of the heavy mineral assemblages in 38 samples was investigated to assess changes in sediment provenance through time. Further, the geochemistry of detrital amphiboles and garnets and the detrital zircon populations were used to determine possible sediment source terranes. Based on the heavy mineral compositions the sandstones were grouped into four heavy mineral assemblages: garnetdominated, amphibole-dominated, epidote-dominated and zircon-dominated. Garnet-dominated sandstones are abundant in most Middle Jurassic to Middle Eocene samples and represent the main sediment input into the Mandawa Basin. Amphibole-dominated sandstones occur in a few Lower Cretaceous samples deposited in close proximity to their sediment source in the Masasi Spur area. A change in provenance is observed in the epidotedominated sandstones of Middle Eocene and Early Oligocene age. This change coincides with a climatic shift towards a wetter and cooler climate associated with an uplift phase in East Africa. The detrital zircon population in the investigated samples share the same age fractions and are indistinguishable within analytical error. Mineral chemistries and zircon ages imply that the sediments deposited in the Mandawa Basin were mainly derived from several high-grade sources within the Neoproterozoic Mozambique Belt to the west of the basin.

A multidisciplinary approach for the quantitative provenance analysis of siltstone: Mesozoic Mandawa Basin, southeastern Tanzania

“…The latter indicates from metamafic lithologies through time. Although in different proportions, garnet types are in agreement to those reported inFossum et al (2018). Such differences can either be attributed grain-size (cfr.Krippner et al 2016) or broader sediment routing system for silty sediments.…”

“…The source weight for the 3-ways MDS including garnet, detrital zircon (DZ) and heavy mineral database display a configuration in which DZ and garnet weights determine the difference between Jurassic and Cretaceous samples (Figure 7). However, the fact that the Fossum et al (2018) propose an unchanged sediment routing system between the Jurassic and the Eocene, our dataset support a broadening of the drainage system in the Cretaceous that increasingly extended as far as the Archean Craton and the Usagran-Ubendian and Kiraban-Urumide belts. Such differences are not necessarily related to data quality and/or interpretation but, more probably, to grain-size and hydraulic sorting controlled compositional features for heavy minerals, zircon and garnet.…”

“…On the other hand, source weights variations along the Y axis highlight the difference in DZ ages and garnet types between Jurassic and Cretaceous samples due to (i) increasing contribution from older terranes (UUB and Tanzanian Archean Craton) through time and (ii) garnet types changing in composition from dominantly A-Bi-Bii types to mostly A-Ci-Cii types. Compositional signatures included in this study are the same of those ofFossum et al 2018. However, proportions between U-Pb age distribution and garnet end-members are different and lead to different conclusions.…”

Hybrid turbidite-drift channel complexes: An integrated multiscale model

“…Albian transgression resulted in the development of the extensive deep-marine deposits that are the focus of this study. Major river systems drained the African continent and supplied fine-grained sediment, while additional sediment was shed from uplifted rift shoulders along the paleocoastline (Smelror et al, 2008;Fossum et al, 2019).…”

Large-scale mass wasting in the western Indian Ocean constrains onset of East African rifting

“…Sediment supply towards the Indian Ocean had been increasing since the Eocene 41 due first to prerift doming and then rift-flank uplift and volcanic topographic changes, leading to the progradation of the Rufiji and Rovuma River deltas and the over-steepening of the slope, as suggested by the architecture of the turbidite channels 43 . A change in provenance in the epidote-dominated sandstones of the Mandawa Basin has been documented between the middle Eocene and the Oligocene 53 23,33 . Earthquake and fault patterns provide additional constraints on the cause of the Mafia mega-slide.…”