Exceptionally well-preserved Cretaceous microfossils reveal new biomineralization styles

Abstract

Calcareous microplankton shells form the dominant components of ancient and modern pelagic sea-floor carbonates and are widely used in palaeoenvironmental reconstructions. The efficacy of these applications, however, is dependent upon minimal geochemical alteration during diagenesis, but these modifying processes are poorly understood. Here we report on new biomineralization architectures of previously unsuspected complexity in calcareous cell-wall coverings of extinct dinoflagellates (pithonellids) from a Tanzanian microfossil-lagerstätte. These Cretaceous 'calcispheres' have previously been considered biomineralogically unremarkable but our new observations show that the true nature of these tests has been masked by recrystallization. The pristine Tanzanian fossils are formed from fibre-like crystallites and show archeopyles and exquisitely constructed opercula, demonstrating the dinoflagellate affinity of pithonellids, which has long been uncertain. The interwoven fibre-like structures provide strength and flexibility enhancing the protective function of these tests. The low-density wall fabrics may represent specific adaptation for oceanic encystment life cycles, preventing the cells from rapid sinking.

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

“…The Upper Cretaceous sediments from south‐east Tanzania have been interpreted as having been deposited in an outer shelf to upper slope environment below the storm‐wave base and influenced by relatively low‐energy conditions. This interpretation was based on the abundance of open‐ocean taxa (common planktonic microfossils and sporadic occurrences of ammonites and bivalves), as well as the predominance of lithologies dominated by clay‐sized and silt‐sized particles, and on the overall scarcity of sedimentary structures especially those indicating traction transport (Jiménez Berrocoso et al ., , , ; Petrizzo et al ., ; Falzoni et al ., ; Wendler & Bown, ; Wendler et al ., ; Haynes et al ., , ). Superimposed on these low‐energy depositional conditions, cores 30 to 29 from TDP Site 39 record one of the main lithological shifts in the subsurface of this region: the transition from the Lindi Formation into the Nangurukuru Formation near the boundary of the D. concavata and D. asymetrica zones (Fig.…”

The Lindi Formation (upper Albian–Coniacian) and Tanzania Drilling Project Sites 36–40 (Lower Cretaceous to Paleogene): Lithostratigraphy, biostratigraphy and chemostratigraphy

“…Since 2002, a major focus of the Tanzania Drilling Project (TDP) has been to study Late Cretaceous-Neogene climates using outcrop and cored sediment samples from southeastern Tanzania (Fig. 1), a well-known province for the occurrence of calcareous microfossils with excellent preservation (Pearson et al, 2001Bown, 2005a;Lees, 2007;Bown et al, 2008;Jiménez Berrocoso et al, 2010Falzoni and Petrizzo, 2011;Petrizzo et al, 2011;Wendler et al, 2011Falzoni et al, 2013;MacLeod et al, 2013;Wendler and Bown, 2013;Huber and Petrizzo, 2014;Haynes et al, 2015;Lees and Bown, 2014). The excellent preservation of microfossils has been attributed to shallow burial of sediments that are clay rich and relatively impermeable (e.g., Pearson et al, 2004Pearson et al, , 2006Nicholas et al, 2006Nicholas et al, , 2007.…”

Southeastern Tanzania depositional environments, marine and terrestrial links, and exceptional microfossil preservation in the warm Turonian

“…The excellent preservation of foraminifera and other calcareous microfossils at TDP Site 31 is well documented (e.g., Wendler et al, 2011Wendler et al, , 2016MacLeod et al, 2013;Wendler and Bown, 2013;Huber and Petrizzo, 2014). Palynomorphs extracted from these sections are some of the best preserved from Late Cretaceous strata worldwide, and they far surpass preservation in equivalent strata from Colom bia and Canada (e.g., Sweet and McIntyre, 1988;Garzon et al, 2012;Akyuz et al, 2015).…”