The Coniacian–Santonian sedimentary record in southern Tanzania (Ruvuma Basin, East Africa): Planktonic foraminiferal evolutionary, geochemical and palaeoceanographic patterns

Abstract

A 101 m thick stratigraphically complete late Coniacian-early Santonian (ca 89 to 83 Ma) sedimentary sequence drilled in Tanzania (Tanzania Drilling Project Site 39) allows, for the first time, examination of the planktonic foraminiferal biostratigraphy and evolution, the depositional history, and geochemical patterns of the subtropical-tropical Indian Ocean region. The sedimentary succession corresponds to an outer shelf to upper slope setting and is dominated by calcareous clayey siltstones and mudstones. The occurrences of Tethyan marker species enable application of the tropical biozonation including identification of the Dicarinella concavata and Dicarinella asymetrica Zones. In addition, Tanzania Drilling Project Site 39 is proposed as reference section for the Coniacian/Santonian boundary in the Indian Ocean with the boundary placed at the lowest occurrence of Globotruncana linneiana in agreement with the Global Stratotype Section and Point (Spain). The record at Tanzania Drilling Project Site 39 provides a unique opportunity to document the planktonic foraminiferal evolution in a subtropical marginal sea environment during a key period in their evolutionary history characterized by a major radiation among the deep-dwelling taxa. Combined documentation of lithological and geochemical changes (%CaCO 3 , %C org , d 13 C carb and d 18 O carb ) reveals a setting influenced by continental-derived nutrients in the Dicarinella concavata Zone (Lindi Formation) with a change to higher carbonate production and reduced surface water primary productivity in the overlying Dicarinella asymetrica Zone (Nangurukuru Formation). Planktonic foraminiferal assemblage changes mirror the depositional and geochemical trends and indicate a progressive shift from a more eutrophic to a more oligotrophic regime through time. At the local scale, this palaeoceanographic scenario is consistent with the deepening of coastal Tanzania in response to the Late Cretaceous marine transgression registered in south-east Tanzania. Because the tectonic evolution and sea-level rise along the East Africa continental margin is superimposed on the Coniacian-Campanian global long-term sea-level high, this study hypothesizes that 252

Coniacian-late Campanian Planktonic Events in the Duwi Formation, Red Sea Region, Egypt

“…Remarks: According to the diverse of shell shapes as marginotruncanids, dicrinellids and concvatotruncanids groups evolved from Praeglobotrucana [50,51], cited concavata species within the genus Dicarinella where the species of Dicarinella have an umbilically convex shell with closely positioned keels near the dorsal side. The extinction of C. concavata within the nearly lowest appearance of Dicarinella asymertrica correlates with observations of Petrizzo [52] in southern Tanzania, South Spain, Petrizzo [53] in Exmouth Plateau, Indian Ocean, in the Tethyan Tunisia [54] and in southern Tibet [55].…”

“…Premoli Silva and Sliter [7,46] and others accepted the first appearance of Dicarinella asymetrica as a zonal marker of the Santonian Stage in low latitude globotruncanid zonal schemes. The disappearance of Concavotruncana concavata is reported at the same level of the first appearance of Dicarinella asymetrica but the highest occurrence of C. concavata cannot be used as marker event for the Asymetrica event [52].…”

Mesozoic climates and oceans – a tribute to Hugh Jenkyns and Helmut Weissert

“…de Winter & Claeys, ), and reconstructions of local palaeoceanographic conditions from sedimentological, geochemical and palaeontological data sets (e.g. Petrizzo et al ., ).…”

Late Cretaceous Paleoceanographic Evolution and the Onset of Cooling in the Santonian at Southern High Latitudes (IODP Site U1513, SE Indian Ocean)

“…The interval from the LO of G. linneiana to the top of the Cretaceous sediments is assigned to the G. linneiana Zone (Petrizzo et al., 2020), and registers a sequence of appearances ( Globotruncana bulloides at 97.26 m CCSF, Archaeoglobigerina cretacea at 75.29 m CCSF, and Globotruncana hilli at 70.43 m CCSF) and the disappearance of P. papula (77.60 m CCSF) that show similar stratigraphic distributions at low and mid‐latitudes (e.g., Petrizzo, 2019; Petrizzo et al., 2017; Premoli Silva & Sliter, 1995).…”