54943194
The Lindi Formation (upper Albian–Coniacian) and Tanzania Drilling Project Sites 36–40 (Lower Cretaceous to Paleogene): Lithostratigraphy, biostratigraphy and chemostratigraphy
The 2009 Tanzania Drilling Project (TDP) expedition to southeastern Tanzania cored a total of 572.3 m of sediments at six new mid-Cretaceous to mid-Paleocene boreholes (TDP Sites 36, 37, 38, 39, 40A, 40B). Added to the sites drilled in 2007 and 2008, the new boreholes confirm the common excellent preservation of planktonic and benthic foraminifera and calcareous nannofossils from core samples that will be used for biostratigraphy, evolutionary studies, paleoceanography and climatic reconstructions from the Tanzanian margin, with implications elsewhere. The new sites verify the presence of a relatively expanded Upper Cretaceous succession in the region that has allowed a new stratigraphic unit, named here as the Lindi Formation (Fm), to be formally defined. The Lindi Fm (upper Albian to Coniacian), extending ∼120 km between Kilwa and Lindi, comprises a 335-m-thick, outer-shelf to upper-slope unit, consisting of dark gray claystone and siltstone interbeds, common finely-laminated intervals, minor cm-thick sandstones and up to 2.6% organic carbon in the Turonian. A subsurface, composite stratotype section is proposed for the Lindi Fm, with a gradational top boundary with the overlying Nangurukuru Fm (Santonian to Maastrichtian) and a sharp bottom contact with underlying upper Albian sandstones.

The section cored at TDP Sites 36 and 38 belongs to the Lindi Fm and are of lower to middle Turonian age (planktonic foraminifera Whiteinella archaeocretacea to Helvetoglobotruncana helvetica Zones and nannofossils subzones UC6b ± UC7). The lower portion of TDP Site 39 (uppermost part of the Lindi Fm) is assigned to the lower to upper Coniacian (planktonic foraminifera Dicarinella concavata Zone and nannofossils zone UC 10), while the remaining part of this site is attributed to the Coniacian–Santonian transition and younger Santonian (planktonic foraminifera D. asymetrica Zone and upper part of nannofossils zone UC10). TDP Site 37 recovered relatively expanded (150 m thick), monotonous calcareous claystones from the lower to upper Maastrichtian (planktonic foraminifera Pseudoguembelina palpebra to Abathomphalus mayaroensis Zones and nannofossils zones UC19 to UC20aTP) that were separated by a hiatus and/or a faulted contact from overlying brecciated carbonates of the Selandian (middle Paleocene: PF Zone P3 and nannofossil zone NP5). The lower portion of TDP Sites 40A and 40B recovered sandstones and conglomerates barren of microfossils. Their overlying parts were assigned to incomplete sections of the nannofossil zones NC6A to NC8 (uppermost Barremian to lower Albian). Benthic foraminiferal assemblages allowed the Barremian to lower Aptian to be identified in TDP Sites 40A and 40B, while the upper Aptian to middle Albian (Hedbergella trocoidea to Ticinella primula Zones) were assigned using planktonic foraminifera. Cores recovered at TDP 39 (Coniacian–Santonian) and at TDP Sites 40A and 40B (Barremian–middle Albian) represent the first time that these two intervals have been continuously cored and publicly documented in Tanzania.

Bulk sediment isotope records generated for the new sites show lower δ18Ocarb values in the Turonian and Santonian (∼−3.5‰ to −5‰) than in the Maastrichtian (∼−3‰), a situation consistent with extreme global warmth in the older intervals and cooling toward the end of the Cretaceous. Also, similar to Turonian sites from previous TDP expeditions, a negative δ13Corg excursion was detected across the W. archaeocretacea–H. helvetica boundary of TDP Site 36 (close to, but above, the Cenomanian-Turonian boundary). This excursion probably responded to local processes in the region, but it is unknown whether they were related to the recovery phase from Ocean Anoxic Event 2.
4344258
Warm tropical sea surface temperatures in the Late Cretaceous and Eocene epochs
Climate models with increased levels of carbon dioxide predict that global warming causes heating in the tropics, but investigations of ancient climates based on palaeodata have generally indicated cool tropical temperatures during supposed greenhouse episodes. For example, in the Late Cretaceous and Eocene epochs there is abundant geological evidence for warm, mostly ice-free poles, but tropical sea surface temperatures are generally estimated to be only 15–23 °C, based on oxygen isotope palaeothermometry of surface-dwelling planktonic foraminifer shells. Here we question the validity of most such data on the grounds of poor preservation and diagenetic alteration. We present new data from exceptionally well preserved foraminifer shells extracted from impermeable clay-rich sediments, which indicate that for the intervals studied, tropical sea surface temperatures were at least 28–32 °C. These warm temperatures are more in line with our understanding of the geographical distributions of temperature-sensitive fossil organisms and the results of climate models with increased CO2 levels.
129872823
A Paleogene calcareous microfossil Konservat-Lagerstätte from the Kilwa Group of coastal Tanzania
Microfossil assemblages and their shell geochemistry are widely used in paleocean-ography, but they can be significantly altered by subtle variations in preservation state. Clay-rich, hemipelagic sediments of the Paleogene Kilwa Group of coastal Tanzania host calcareous microfossils that are exceptionally preserved, as evidenced by morphological, taxonomic, and geochemical data. The planktonic foraminifera are preserved as glassy, translucent tests with original microgranular wall textures that resemble well-preserved modern specimens, and they arguably yield geochemical values that are relatively unaffected by recrystallization. The calcareous nannofossils are extraordinarily diverse and represented by unique assemblage compositions that include dissolution-susceptible taxa, especially holo-coccoliths and rhabdoliths, and fragile and very small (< 3-mu m) heterococcoliths, many of which are new taxa. Notably, the extant, deep-photic-zone taxon Gladiolithus is documented for the first time in the pre-Quaternary fossil record. The Kilwa Group calcareous nannofossil diversities are consistently higher than all coeval assemblages and provide a benchmark against which to compare other Paleogene biodiversity data. Highest diversities are preserved in hemipelagic, clay-rich lithologies and the greatest losses occur in lithified, carbonate-rich sediments. Most of the lost diversity, however, is confined to distinct taxonomic groups (holococcoliths and Syracosphaerales), and in general the preservational potential of Paleogene coccolithophores was greater than in the modern oceans because a larger proportion of the biodiversity fell within the larger size fractions. For both foraminifera and coccolithophores, incorporation into impermeable clay-rich sediments that have never been deeply buried appears to have been critical in producing this Konservat-Lagerstatte preservation.
26188753
Lithostratigraphy, biostratigraphy and chemostratigraphy of Upper Cretaceous sediments from southern Tanzania: Tanzania drilling project sites 21–26
The 2007 drilling season by the Tanzania drilling project (TOP) reveals a much more expanded Upper Cretaceous sequence than was recognized previously in the Lindi region of southern Tanzania. This TDP expedition targeted recovery of excellently preserved microfossils (foraminifera and calcareous nannofossils) for Late Cretaceous paleoclimatic, paleoceanographic and biostratigraphic studies. A total of 501.17 m of core was drilled at six Upper Cretaceous sites (TDP Sites 21, 22, 23, 24, 24B and 26) and a thin Miocene-Pleistocene section (TDP Site 25). Microfossil preservation at all these sites is good to excellent, with foraminifera often showing glassy shells and consistently good preservation of small and delicate nannofossil taxa. In addition to adding to our knowledge of the subsurface geology, new surface exposures were mapped and the geological map of the region is revised herein.TDP Sites 24, 24B and 26 collectively span the upper Albian to lower-middle Turonian (planktonic foraminiferal Planomalina buxtorfi-Whiteinella archaeocretacea Zones and calcareous nannofossil zones UC0a-UC8a). The bottom of TOP Site 21 is barren, but the rest of the section represents the uppermost Cenomanian-Coniacian (W. archaeocretacea-Dicarinella concavata Zones and nannofossil zones UC5c-UC10). Bulk organic delta C-13 data suggest recovery of part of Ocean Anoxic Event 2 (OAE2) from these four sites. In the upper part of this interval, the lower Turonian nannofossil zones UC6a-7 are characterized by a low-diversity nannoflora that may be related to OAE2 surface-water conditions. TDP Site 22 presents a 122-m-thick, lower-middle Turonian (W. archaeocretacea-Helvetoglobotruncana helvetica Zones) sequence that includes the nannofossil zones UC6a(-7?), but invariable isotopic curves. Further, a lower to upper Campanian (Globotruncana ventricosa-Radotruncana calcarata Zones and nannofossil subzones UC15b(TP)-UC15d(TP)) succession was drilled at TDP Site 23. Lithologies of the new sites include thin units of gray, medium to coarse sandstones, separating much thicker intervals of dark claystones with organic-rich laminated parts, irregular silty to fine sandstone partings, and rare inoceramid and ammonite debris. These lithofacies are interpreted to have been deposited in outer shelf and upper slope settings and indicate relatively stable sedimentary conditions during most of the Late Cretaceous on the Tanzanian margin. (C) 2009 Elsevier Ltd. All rights reserved.
83946238
TAXONOMIC OVERVIEW AND EVOLUTIONARY HISTORY OF GLOBOTRUNCANITA INSIGNIS (GANDOLFI, 1955)
Globotruncanita insignis (Gandolfi, 1955) is a planktonic species commonly recognized in Late Cretaceous foraminiferal assemblages, but uncertainty about its morphologic variability and phyletic relationships have led to different interpretations of it. The taxon was considered to be morphologically and evolutionary related to Globotruncana rosetta (Carsey, 1926), phyletically linked to Globotruncanita elevata (Brotzen, 1934), or a junior synonym of the latter species. In addition, the neotype that replaced the lost holotype caused a taxonomic debate and compromised the identification of G. insignis , which has been assigned to both Globotruncanita and Globotruncana. This study resolves the taxonomic problems and reconstructs the phyletic lineage of this species on the basis of a continuous sequence of exceptionally well preserved and highly diversified planktonic foraminiferal assemblages in the Contusotruncana plummerae and Radotruncana calcarata zones, recently recovered from southeastern Tanzania drillholes. In addition to common G. insignis that characteristically have a strongly convex umbilical side, we recognized succession of morphotypes intermediate between Globotruncanita stuartiformis and G. insignis that demonstrates an ancestor–descendant relationship between the two taxa and further validates the assignment of G. insignis to Globotruncanita . Moreover, our results confirm that the neotype falls in the same phyletic lineage, but it represents a primitive form of G. insignis .
129852075
Identification of the base of the lower-to-middle Campanian Globotruncana ventricosa Zone: Comments on reliability and global correlations
The reliability of the first appearance datum of Globotruncana ventricosa as biozonal marker for the Campanian is discussed. The taxonomy and species concept of G. ventricosa and of Globotruncana tricarinata, that has been either regarded as junior synonym of Globotruncana linneiana or of G. ventricosa, are examined to avoid misidentifications, and one species is here formally described as new, Globotruncana neotricarinata nov. sp. The tropical and subtropical planktic foraminiferal assemblages from the Bottaccione section (Gubbio, Italy), from Deep Sea Drillig Project (DSDP) Site 146 (Caribbean Sea, central Atlantic Ocean), and from Ocean Drilling Program (ODP) Hole 1210B (Shatsky Rise, northwestern Pacific Ocean) are analyzed for the presence of biostratigraphic markers. Lowest and highest occurrence data have been checked in thin sections and washed residues in the Bottaccione section. The comparative biostratigraphic analysis of the planktic foraminiferal distribution highlights: 1) the absence of G. ventricosa at the stratigraphic level at which it is supposed to first occur in the Tethyan area, 2) the presence of transitional specimens resembling G. ventricosa and thus erroneously used to identify the base of the G. ventricosa Zone, 3) the presence of a good sequence of bioevents that appear to be promising for regional and global correlations such as the appearance of Globotruncanita atlantica, Contusotruncana plummerae and the disappearance of Hendersonites carinatus. The correlation potential of these bioevents has been verified across latitudes by studying the Campanian planktic foraminiferal assemblage in pelagic sediments drilled on coastal Tanzania (western Indian Ocean), and at the deep-sea ODP Hole 762C (Exmouth Plateau, western Indian Ocean), that were located at 30°S and 47°S in the Late Cretaceous, respectively. Besides the known diachronous first appearance of G. ventricosa in the Southern Ocean sites, results confirm the difficulty in using G. ventricosa as zonal marker in the tropical and subtropical areas, and the validity of the first appearance datum of C. plummerae for regional and global correlations.
129832563
Santonian–Campanian planktonic foraminifera from Tanzania, Shatsky Rise and Exmouth Plateau: Species depth ecology and paleoceanographic inferences
Abstract The Santonian–Campanian interval is of particular interest as it encompasses a cooling trend after the Late Cretaceous greenhouse maximum warmth of the Turonian as well as a possibly related major faunal turnover among planktonic foraminifera. The recovery of pristinely preserved planktonic foraminifera from Santonian–Campanian sequences in southeastern Tanzania allows examination of faunal changes and documentation of species-specific stable isotope (δ 13 C and δ 18 O) signatures. These isotopic data are ideal for inferring species paleoecological preferences and for tracing major paleoceanographic changes. This study reports the first δ 18 O and δ 13 C data generated on “glassy” specimens of Marginotruncana coronata , M. undulata , M. marginata , and M. pseudolinneiana and Sigalia carpatica . Additional results from Shatsky Rise (Ocean Drilling Program Leg 198, Hole 1210B) and Exmouth Plateau (ODP Leg 122, Hole 762C) provide geographic control on species habitat preferences and paleoceanographic context. Isotopic analyses suggest that double-keeled species, including Globotruncana bulloides , Contusotruncana fornicata , C. plummerae and probably marginotruncanids, inhabited the surface mixed layer, whereas the biserial Gublerina rajagopalani was a permanent thermocline dweller. Thus, our study confirms recent suggestions that the depth-distribution models based on shell morphology and analogies with modern taxa are not applicable. At all the examined localities, changes in planktonic foraminiferal assemblages are used to define several ecological intervals, each one characterized by a distinctive taxonomic composition and/or increasing/decreasing species diversity. Combined geochemical and paleontological observations suggest that, by the middle–late Campanian, a stratified upper water column developed in Tanzania while less stratified and/or mesotrophic conditions prevailed at Shatsky Rise and Exmouth Plateau.
131091954
A stable and hot Turonian without glacial δ18O excursions is indicated by exquisitely preserved Tanzanian foraminifera
A shift from the icehouse climate in which humans evolved to a Late Cretaceous–like greenhouse climate is an often-repeated cautionary prediction of the consequences of continued anthropogenic CO 2 emissions. The corollary, that understanding the past might help predict the future, has justified many Late Cretaceous studies, but important questions remain about climate stability and sensitivity. New δ 18 O measurements of more than 1000 samples of exceptionally well preserved foraminifera (8 planktic and 11 benthic taxa) from two sites in Tanzania indicate that hot and remarkably stable conditions prevailed in the region during the Turonian, including during a proposed greenhouse glacial event. Planktic taxa have δ 18 O values largely between –4.0‰ and –5.0‰, suggesting surface-water temperatures between 30 and 35 °C. Estimates for seafloor temperatures are between 18 and 25 °C. No parallel shifts in δ 18 O values are observed among planktic and benthic taxa, contradicting an often-cited line of evidence for greenhouse glaciations and supporting an effectively ice-free Turonian world.
6940985
Exceptionally well-preserved Cretaceous microfossils reveal new biomineralization styles.
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.
35583776
Paleogene and Cretaceous sediment cores from the Kilwa and Lindi areas of coastal Tanzania: Tanzania Drilling Project Sites 1-5
Initial results of scientific drilling in southern coastal Tanzania are described.A total of five sites was drilled (mostly using 
continuous coring) by the Tanzania Drilling Project for paleoclimate studies.The sediments are predominantly clays and claystones 
deposited in a deep marine shelf environment and often contain excellently preserved microfossils suitable for geochemical analysis. 
The studies reported here include summaries of the lithostratigraphy, biostratigraphy (planktonic foraminifers, calcareous nannofossils, 
benthic foraminifers, and palynology), magnetostratigraphy, and organic geochemistry. 
TDP Site 1 was drilled near Kilwa Masoko airstrip (8�54.5160S, 39�30.3970E).It yielded 8.55 m of barren blue-grey clays that may 
be Miocene in age, followed by 1.2 m of greenish-black to dark greenish-grey clay probably of the same age. The remainder of the 
hole cored 62.35 m of lower Oligocene sediments (nannofossil Zone NP23), which are predominantly greenish-black to dark 
greenish-grey clays.Total penetration was 74.10 m.The coring represents the first report of a thick Oligocene clay formation in the 
area. 
TDP Site 2 was drilled near Kilwa Masoko prison (8�55.2770S, 39�30.2190E).It yielded 92.78 m of predominantly dark greenishgrey 
clay with occasional allochthonous limestone beds that consist mostly of redeposited larger foraminifers.The site encompasses 
lower to middle Eocene planktonic foraminifer Zones P8/9 to P11 and nannofossil Subzones NP14b to NP15c.It encompasses a 
rarely cored interval across the Ypresian–Lutetian transition. 
TDP Site 3 was drilled near Mpara in the Kilwa area (8�51.5850S, 39�27.6550E).It yielded 56.4 m of predominantly dark greenishgrey 
clays and claystones.The site is assigned to lower Eocene planktonic foraminifer Zone P6 and nannofossil Zone NP11. 
TDP Site 4 was drilled near Ras Tipuli on the northwest side of Lindi creek (9�56.9990S, 39�42.9850E).It yielded 19.8 m of 
predominantly dark greenish-grey clay with allochthonous limestone interbeds.The site encompasses middle Eocene planktonic 
foraminifer Zones P12–P14 and nannofossil Zone NP17. 
TDP Site 5 was drilled at Machole, near Lindi, south of Kitulo Hill (10�01.6460S, 39�41.3750E).It yielded 31.6 m of predominantly 
greenish-black to dark greenish-grey clay assigned to the upper Cretaceous Globotruncana falsostuarti planktonic foraminifer 
zone and nannofossil zones UC15e–UC17 (upper Campanian–lower Maastrichtian).Paleomagnetic analysis suggests that the site 
straddles two magnetic reversals, between Chrons C32r.2r and C32r.1n. 
Samples from TDP Sites 1–5 yielded dinocyst and miospore assemblages that are integrated with the calcareous stratigraphy. 
Organic geochemical analyses of samples from each of the cores revealed biomarkers of predominantly terrestrial origin and an unusually low degree of thermal maturity, suggesting shallow burial depths.X-ray diffraction studies suggest that much of the 
Paleogene clay may be reworked from eroded Mesozoic formations.
56118002
Further Paleogene and Cretaceous sediment cores from the Kilwa area of coastal Tanzania: Tanzania Drilling Project Sites 6-10
Initial results from scientific drilling in southern coastal Tanzania are described. In a field season in 2003, a total of five sites was 
drilled (mostly using continuous coring) by the Tanzania Drilling Project for paleoclimate studies. The sediments are predominantly marine 
clays and claystones deposited in an outer shelf or slope environment and often contain excellently preserved microfossils suitable for 
geochemical analysis. The studies reported here include summaries of the lithostratigraphy, biostratigraphy (planktonic foraminifers, 
calcareous nannofossils, benthic foraminifers, and palynology) and organic geochemistry. 
TDP Site 6 was drilled near Kilwa Masoko (UTM 37L 555752, 9014922), 350 m to the south-east of a previous site, TDP Site 1. The 
top 59.58 m, which was mostly drilled without coring, consists of an Oligocene clay formation belonging to nannofossil Zone NP23. The 
rest of the hole, to a total depth of 61.25 m, consists of a fault zone in which the Oligocene sediments are intermixed with middle Eocene 
clays of planktonic foraminifer Zone E9 and nannofossil Subzone NP15b. 
TDP Site 7 consists of two holes (Hole TDP7A: UTM 37L 547126, 9030142; Hole TDP7B: UTM 37L 0547130, 9030140) drilled just 
5 m apart at Kwamatola, a creek to the south of Kilwa Kivinje. Underneath approximately 20 m of unconsolidated sands and gravels, 
claystones and siltstones were recovered to a total depth of 128.00 m. The site spans lower Eocene planktonic foraminifer Zones E1, E2 
and E3 and nannofossil Subzones NP 9b and NP10. The bottom of Hole TDP7B approaches the Paleocene–Eocene boundary but no 
unambiguously Paleocene sediments were recovered. 
TDP Site 8 was drilled to the south-east of Singino Hill (UTM 37L 548033, 9025811). Below a covering of surface gravels, it yielded 
predominantly dark greenish-grey claystones to a total depth of 22.95 m. The sediments are from the lower Eocene and span the boundary 
between planktonic foraminifer Zones E3 and E4 and fall within nannofossil Zone NP10. 
TDP Site 9 was drilled near Nangurukuru junction (UTM 37L 538987, 9027049). It yielded predominantly dark greenish-grey siltstones 
to a total depth of 88.80 m. Thin siliciclastic beds with trace fossils of the Nereites ichnofacies are common in the lower third 
of the site. These sediments span the Campanian–Maastrichtian stage boundary and are assigned to the Globotruncanella havanensis 
to Gansserina gansseri planktonic foraminifer zones and nannofossil Subzones UC15eTP to UC17. 
TDP Site 10 was drilled to the west of Singino Hill, adjacent to the main Kilwa road (UTM 37L 0541243, 9028791). Below a superficial 
covering of gravel, it yielded predominantly dark greenish-grey silty claystones to a total depth of 100.80 m. These sediments are 
assigned to Paleocene planktonic foraminifer Zone P4c–P5 and nannofossil Subzone NP9b. 
Organic geochemical analyses from all the sites revealed biomarkers of predominantly terrestrial origin and collectively indicate an 
unusually low degree of thermal maturity for the area, suggesting shallow maximum burial depths. Traces of migrated hydrocarbons 
were found in TDP Sites 7 and 10.
130300585
Stratigraphy and sedimentology of the Upper Cretaceous to Paleogene Kilwa Group, southern coastal Tanzania
Abstract The geology of southern coastal Tanzania has remained poorly understood since the first comments on its stratigraphy were made over 100 years ago. However, new field surveys combined with shallow drilling along the coast between Kilwa and Lindi are beginning to resolve the depositional history and structural evolution of this region over the past 85 Ma. Here we present the first attempt to synthesize the results of these studies to provide a coherent sedimentological, litho- and sequence stratigraphic framework, including new geological maps, for the Upper Cretaceous and Paleogene of the coastal zone. Santonian to Oligocene sediments crop out along a broad coastal belt south of the Rufiji River from the Kilwa peninsula to Lindi Creek in southern Tanzania. During ∼55 Ma, over 1 km of a broadly homogeneous, mid to outer shelf clay-dominated succession was deposited across the passive margin, which we define here as the Kilwa Group. This lies disconformably across the shelf on Albian marls and is itself unconformably overlain by shallow water Miocene clays and more recent limestones, sands and gravels. Four formations can be identified within the Kilwa Group on the basis of characteristic secondary lithologies and facies, described here for the first time; the Nangurukuru, Kivinje, Masoko and Pande Formations. These formations include conformable stratigraphic intervals through both the Paleocene–Eocene and Eocene–Oligocene boundaries. Within the Kilwa Group, 12 sequence stratigraphic cycles can be identified at present, demonstrating relatively uniform and continual subsidence across the margin from Santonian to Early Oligocene time. A further major bounding surface is present between the Upper Cretaceous and Paleogene, but this may become partly conformable in the Lindi area. Although the principal lithology in all formations is clay or claystone, there are more permeable intervals containing pervasive coarser siliciclastic sediments and these have yielded traces of crude oil which is likely to have migrated from lower in the succession. The Kilwa Group thus also provides important new evidence for petroleum play development in the southern coastal zone.
85453193
Lithostratigraphy, biostratigraphy and chemostratigraphy of Upper Cretaceous and Paleogene sediments from southern Tanzania: Tanzania Drilling Project Sites 27–35
The 2008 Tanzania Drilling Project (TDP) expedition recovered common planktonic foraminifera (PF), calcareous nannofossils (CN) and calcareous dinoflagellates with extraordinary shell preservation at multiple Cenomanian–Campanian sites that will be used for paleoclimatic, paleoceanographic, and biostratigraphic studies. New cores confirm the existence of a more expanded and continuous Upper Cretaceous sequence than had previously been documented in the Lindi and Kilwa regions of southeastern coastal Tanzania. This TDP expedition cored 684.02 m at eight Upper Cretaceous sites (TDP Sites 28–35) and a thin Paleocene section (TDP Site 27). 
 
TDP Sites 29, 30, 31 and 34 together span the lowermost Turonian to Coniacian (PF Whiteinella archaeocretacea to Dicarinella concavata Zones and CN Zones UC6a–9b), with TDP Site 31 being the most biostratigraphically complete Turonian section found during TDP drilling. A discontinuous section from the Santonian–upper Campanian (PF D. asymetrica to Radotruncana calcarata Zones and CN Zones UC12–16) was collectively recovered at TDP Sites 28, 32 and 35, while thin sequences of the lower Cenomanian (PF Thalmanninella globotruncanoides Zone and CN subzones UC3a–b) and middle Paleocene (Selandian; PF Zone P3a and CN Zone NP5) were cored in TDP Sites 33 and 27, respectively. Records of δ13Corg and δ13Ccarb from bulk sediments generated for all the Cretaceous sites show largely stable values through the sections. Only a few parallel δ13Corg and δ13Ccarb shifts have been found and they are interpreted to reflect local processes. The δ18Ocarb record, however, is consistent with Late Cretaceous cooling trends from the Turonian into the Campanian. Lithologies of these sites include thick intervals of claystones and siltstones with locally abundant, finely-laminated fabrics, irregular occurrences of thin sandstone layers, and sporadic bioclastic debris (e.g., inoceramids, ammonites). Minor lithologies represent much thinner units of up to medium-grained, massive sandstones. The %CaCO3 (∼5–40%) and %Corg (∼0.1–2%) are variable, with the highest %CaCO3 in the lower Campanian and the highest %Corg in the Turonian. Lithofacies analysis suggests that deposition of these sediments occurred in outer shelf-upper slope, a setting that agrees well with inferences from benthic foraminifera and calcareous dinoflagellates.
129916473
Miocene tropical Indian Ocean temperatures: evidence from three exceptionally preserved foraminiferal assemblages from Tanzania
Early to Middle Miocene tropical sea surface temperatures (SSTs) in the equatorial Pacific and Indian oceans have been previously estimated using oxygen isotope palaeothermometry with the shells of surface-dwelling planktonic foraminifera. These estimations are generally lower than in the present day oceans. However, they could be flawed if the foraminiferal tests used for isotopic analysis have been diagenetically altered during shallow burial on the sea floor. This paper presents new isotopic data from three exceptionally well-preserved assemblages from the clay-rich sediments of coastal Tanzania, which constitute a more stringent test for the theory of cool Miocene tropical temperatures. Multiple planktonic and benthic foraminifera morphospecies are analysed for oxygen and carbon isotopes, representing various ecological habitats and isotopic fractionations. 
 
The isotopic data are used to determine Indian Ocean tropical sea surface and outer-shelf bottom water temperatures. Oxygen isotope data from the Early Miocene equivalent biozone M1b (22.35 Ma ± 0.85), imply tropical SSTs of approximately 30 °C, while isotope data from Middle Miocene equivalent biozones M9 (12.2 Ma ± 0.3) and M11 (11.55 Ma ± 0.15), suggest SSTs of 27–29 °C. For the assemblage from biozone M1b, isotopic data are used to calculate a shelf bottom water temperature of 21.3 °C, while for biozones M9 and M11–12, bottom water temperatures of 14–15 °C. These palaeotemperature estimates are similar to the modern sea surface and bottom water temperatures in the western Indian Ocean, yet are ∼10 °C higher than palaeotemperatures previously calculated for similar time intervals. These new data compliment recent studies using exceptionally-preserved Cretaceous and Palaeogene foraminiferal assemblages from clay-rich sediments and provide further evidence that micrometer-scale diagenesis can have a significant influence on isotopic ratios in foraminifera shells.
127384454
New Paleogene calcareous nannofossil taxa from coastal Tanzania: Tanzania Drilling Project Sites 11 to 14.
New calcareous nannofossil taxa are described from well-preserved and diverse Late Paleocene-Early Oligocene nannofossil assemblages from new onshore drilling sites in southern Tanzania. One new genus, Leesella, 30 new species, Blackites flammeus, B. furvus, B. gracilentus, B. ornatus, B. singulus, B. spiculiformis, B. tortilis, Bomolithus supremus, Calcidiscus? gerrardii, Calciosolenia alternans, Daktylethra probertii, D. unitatis, Discoaster spinescens, Hayella simplex, Holodiscolithus catellus, H. fabaceus, Leesella procera, Micrantholithus minimus, Neochiastozygus pusillus, Orthozygus sudis, O. suggrandis, Pemma? triquetra, P.? uncinata, Sphenolithus runus, S. strigosus, Varolia boomeri, V. macleodii, V. sicca, Youngilithus pyxis and Zygodiscus multiforus, one new combination, Zygodiscus cearae, and two indeterminate nannoliths are described and illustrated.
129096951
Large terrestrial and marine carbon and hydrogen isotope excursions in a new Paleocene/Eocene boundary section from Tanzania
Recent onshore drilling expeditions in Tanzania have yielded sediments spanning much of the Late Cretaceous and Paleogene which show exceptionally good preservation of both calcareous microfossils and organic matter. The interval of the Paleocene–Eocene Thermal Maximum (PETM) was recovered at Tanzania Drilling Project (TDP) Site 14, in 2004. The PETM interval was identified using planktonic foraminifer and nannofossil biostratigraphy. Carbon isotopic measurements of planktonic foraminifera from the genus Subbotina show a maximum measured negative shift in δ13C values of approximately 4.5‰, which is significantly larger than has been observed for most deep sea foraminifer records. Higher plant derived n-alkanes yield a ca. 6.5‰ negative shift through the same interval. As carbon isotope fractionation in higher plants varies amongst taxa and is influenced by humidity, it is possible that this remarkably large shift in the n-alkane δ13C values records environmental and vegetation changes as well as changes in the δ13C value of the ocean–atmosphere reservoir. However, dramatic increases in humidity appear to be unlikely as higher plant biomarker δD values shift to higher rather than lower values. Taken together, the records suggest that the magnitude of the carbon isotope excursion (CIE) in the ocean–atmosphere reservoir may have been larger than has generally been accepted. This has important implications for the source and quantity of 13C-depleted carbon released at the PETM.
129669832
Planktonic foraminiferal turnover, diversity fluctuations and geochemical signals across the Eocene/Oligocene boundary in Tanzania
A major turnover in planktonic foraminifera occurred across the Eocene/Oligocene (E/O) boundary. New drill holes through the E/O boundary in southern Tanzania contain extremely well-preserved and diverse assemblages of planktonic foraminifera. Here we document a 1.2 million year record of assemblages, diversity and stable isotope fluctuations through this critical interval, which is often dissolved and/or recrystallised in carbonate-rich facies. The E/O boundary is marked by the abrupt extinction of all five remaining species of the family Hantkeninidae and a distinct size reduction in the genus Pseudohastigerina. The boundary is preceded over a short stratigraphic interval by the extinction of Turborotalia cerroazulensis, Turborotalia cocoaensis and Turborotalia cunialensis. Quantitative analysis of planktonic foraminiferal assemblages reveals significant changes in the abundance of certain species and the composition of the assemblages. We compare diversity fluctuations to the stable isotope record of Pseudohastigerina naguewichiensis and use multispecies stable isotope analyses to determine the life habitats of the most important species. A major shift in the evenness occurs at ~ 33.8 Ma associated with the extinction of the T cerroazulensis group suggesting acute ecological disturbance. We propose that the extinction of the T. cerroazulensis group at ~ 33.8 Ma was directly related to cooling of sea surface temperatures, while the extinction of Hantkeninidae was due to modifications in the thermal structure of the oceans and associated productivity changes. After the extinctions, renewed origination and diversification occurred, leading to a characteristic Oligocene planktonic foraminifer assemblage.
129536558
Calcareous plankton evolution and the Paleocene/Eocene thermal maximum event: new evidence from Tanzania
The biotic response of calcareous microplankton at the Paleocene/Eocene thermal maximum (PETM) climate event principally comprised poleward migrations, the appearance of excursion taxa and elevated turnover in calcareous nannoplankton. Here we examine whether this relatively muted evolutionary signal may be due to the quality of the stratigraphic and fossil record by analysing exceptionally well preserved microfossils from an expanded, hemipelagic PETM section in southern Tanzania (TDP Site 14). Both nannofossils and planktonic foraminifera show major abundance declines at the onset of the PETM that are not explained by dilution or dissolution. The PETM onset is also marked by the extinction of eight nannofossil species, possibly as many as 12, and the intra-PETM assemblages are quite distinct from background, and dominated by Coccolithus including the excursion taxon C. bownii. This biotic response is not clearly biased in favour of particular ecological groups, although the nannofossil excursion taxa were all warm-water favouring, and there was a net diversity loss within cool-water-favouring eutrophic groups. A shift from Toweius- to Coccolithus-dominated assemblages is suggestive of increased oligotrophy, although the presence of abundant Gladiolithus indicates upper photic zone oligotrophy throughout the time interval represented by the TDP Site 14 section. The significant plankton assemblage shifts, diversity decline and possible reduction of calcareous plankton production and/or export suggest the rapid onset of highly disruptive environmental change at the PETM onset. This change must have included rapid temperature increase, and heat stress may have played a role in shaping the PETM assemblage compositions, causing a limited number of extinctions and favouring taxa from warmer areas of the groups' ecological range. However, the muted evolutionary response in these plankton groups indicates that they were highly resilient to this environmental change and through adaptation to the new conditions (e.g. the excursion taxa), but probably principally through range shifts (i.e. migration) or simply the ability to acclimatize, the vast majority of the biodiversity survived and thrived again once conditions returned to normal.
129711132
Extinction of larger benthic foraminifera at the Eocene/Oligocene boundary
A number of long-ranging and widespread larger benthic foraminiferal taxa are known to have become extinct during the Eocene–Oligocene transition. However, detailed records through the transition are rare, and few complete sections are known. Here we study an apparently complete section from Tanzania from three drill cores across the Eocene/Oligocene boundary in a hemipelagic clay succession. Within these, larger benthic foraminifera occur dispersed in the clays and concentrated in limestones which occur as secondary debris flow deposits. These cores allow the larger benthic foraminiferal stratigraphy to be tied to planktonic foraminifera and nannofossil biostratigraphy and stable isotope (δ18O, δ13C) stratigraphy. These records show that all of the larger benthic foraminifera extinction events occur close to the Eocene/Oligocene boundary as recognised by the extinction of the planktonic foraminiferal Family Hantkeninidae, rather than at the prominent oxygen isotope excursion in the lower Oligocene that signifies maximum ice growth and global sea-level fall. This correlation raises questions about the mechanism responsible for the extinctions and has implications for global larger benthic foraminiferal stratigraphy.
128957568
Development of the Mozambique and Ruvuma sedimentary basins, offshore Mozambique
Two major sedimentary basins have been identified on the continental margin of Mozambique—Mozambique Basin and Ruvuma Basin. The formation of the basins is related to the break-up of Gondwana and opening of the western part of the Indian Ocean. The basins are relatively young, having developed discordantly to the structural plan of Gondwana sedimentary basins. 
 
The history of the formation of the East African continental margin sedimentary basins within Mozambique has been studied on the basis of the present-day concept of Gondwana break-up and Madagascar's drift with respect to Africa. Two stages in the history of the East African basins can be recognized: late-Gondwana and post-Gondwana. 
 
The late-Gondwana stage (303-157 Ma) is typified by sedimentary and volcanogenic rocks of the Karoo Group. 
 
The post-Gondwana stage (157-0 Ma) corresponds to the period of active Gondwana break-up and the formation of Indian Ocean marginal basins. 
 
The Mozambique Basin occupies both central and southern parts of the coastal plain of Mozambique, extending onto the continental shelf and slope. The sedimentary fill is composed of Upper Jurassic, Cretaceous and Cenozoic rocks which discordantly overly the Karoo basalts. The Upper Jurassic occurs as continental red-beds, mostly distributed within buried grabens. Cretaceous rocks occur as terrigenous sediments of continental and marine genesis. Cenozoic deposits are of predominantly marine and deltaic origin. 
 
The Ruvuma Basin, situated in the north of Mozambique, is part of an extended East African marginal basin which includes parts of the coastal plains and continental margins of Tanzania and Kenya. The basement of the basin is composed of crystalline and metamorphic rocks of pre-Cambrian age. The sedimentary fill is represented by continental terrigenous Karoo sediments, marine and lagoonal Jurassic deposits, and marine and deltaic rocks of Cretaceous and Cenozoic age. 
 
The main difference between the sedimentary fill of the Mozambique and Ruvuma basins is related to the changing sedimentary environment in the period of Gondwana break-up, Jurassic and Early Cretaceous, when the drift of Madagascar and sea-floor spreading took place and the marine basin gradually extended southwards between the East African margin and Madagascar. 
 
From the Late Cretaceous on, the sedimentary environment within both basins was similar, the Mozambique and Ruvuma basins forming a single system on the East African continental margin. 
 
The main stages of the basins' development are illustrated by a series of palaeogeographic reconstruction maps.
128539979
Mesozoic Karoo and post-Karoo formations in the Kilwa area, southeastern Tanzania - a stratigraphic study based on palynology, micropaleontology and well log data from the Kizimbani Well
The Kizimbani exploration well, drilled by Agip (Africa) Ltd. in the Kilwa area of southeastern Tanzania in 1979, has provided new information on the Karoo basin in the coastal region of Tanzania and its post-Karoo geohistory. The sediments can be divided into four major lithostratigraphic units which have been dated on palynological and micropalaeontological evidence: The Ngerengere(?) Beds, of Early Jurassic age, are resting on metamorphic basement (reached at 2612 m depth) and consist of approximately 700 m of continental conglomerates, sandstones and clays representing the youngest Karoo. Succeeding these beds are three post-Karoo units which are correlatable with lithostratigraphic units previously described from outcrops. These start with the Middle Jurassic Matumbi Series (600 m of clays and limestones) followed by the Middle(?) to Late Jurassic Pindiro Shales and Evaporites (1100 m) and terminate with the mid-Cretaceous Kingongo and Kihuluhulu marls (250 m). The evaporites are assigned a Late Jurassic age in contrast to earlier interpretation of another well (Mandawa No. 7) which had placed them in the upper part of the Karoo sequence (Triassic - ?Early Jurassic). A geohistory diagram has been constructed for the Kizimbani Well and a reinterpretation is offered for the Mandawa No. 7 Well.
129722233
Gravity modelling along a seismic line across the Mandawa basin, southeastern Tanzania
Abstract Gravity data is modelled from the onshore Mandawa basin, a salt basin forming an isolated arm of a Mesozoic rift system situated along the sheared continental margin of East Africa. The main purpose is to verify that the Pande high, constituting the eastern rim of the Mandawa basin, contains a sedimentary sequence thick enough to allow future hydrocarbon exploration. The Bouguer anomaly response, incorporating an elevation and a terrain correction, has been used to constrain the modelling results. A regional trend is established by assuming the presence of two constrasting density bodies at a depth of 8 to 12 kilometres. Seven seismic markers have been mapped, coinciding with significant density contrasts; the shallow horizons are calibrated by the surface geology. Uncertainty on the deeper markers is high as only three deep wells penetrate the deeper sequences. The densities of the units are based on the results of these deep wells together with additional shallow hole data. The modelling results are in line with the existing seismic interpretation and hence leave scope for a sedimentary pile on the Pande basement high. The difference between the calculated model and the residual gravity field generally does not exceed 1.5 mgal. This modelling exercise illustrates that gravity data provide valuable constraints on the structural configuration of little explored basins, especially when the seismic data are of poor quality.
126468748
Geological development of the East African coastal basin of Tanzania
The East African coastal basin of Tanzania, which is characterised by an extensional tectonic style, is located along the passive continental margin of the western Indian Ocean. The present study is concerned with the Mafia Island and the Mafia Channel which together form a subbasin within the north-south elongated coastal sedimentary basin of Tanzania. In the time interval from late Paleozoic to Recent, the passive margin of the region was subjected to a three-fold geological development, namely the Karoo rifting phase (1) which is characterised by extensional tectonics, the Gondwana break-up and opening of the Somali basin (2) which was contemporaneous with the movement of Madagascar off the east African coast in the Mesozoic, and the Cenozoic East African rift system (3). This structural framework made provision to the basin deposition history. The development started with the deposition of the continental, terrigenous, Karoo sequence in the Upper Permian to Lower Jurassic. The Karoo deposition was followed by a series of transgressions and regressions under full marine conditions which started in the Middle Jurassic and continued into the Tertiary. The deposits include marine marls, detrital limestones, fossiliferous shales and calcareous sandstones, reaching in places thicknesses of more than 4000 m of Mesozoic, and more than 6000 m of Cenozoic, sediments. Seismostratigraphic techniques applied in the Mafia Channel and Island identified five deposition sequences separated by regional unconformity surfaces i.e. sequence boundaries. Including the pre-Upper Cretaceous sequence they are; the Upper Cretaceous to Middle Eocene sequence (DS I), the Middle Eocene to Lower Miocene sequence (DS II), the Lower Miocene to Pliocene sequence (DS III), and the Pliocene to Recent sequence (DS IV). In the Mafia Channel up to 6000 m of sediments are present. Their ages range from Middle Eocene to Quaternary. The deposits start with marine shales which are overlain by carbonate rocks of Upper Eocene . These carbonates are in the present investigation regarded as the acoustic basement in the central and northern parts of the study area. On top of Upper Eocene carbonates, deltaic and shallow marine sediments are deposited. Southwards in the Channel, the sequences are located at shallower depths which makes it possible to trace also the Upper Cretaceous sequence with confidence. On the Mafia Island, the deposition on top of the Upper Cretaceous (Campanian) acoustic basement mainly includes deltaic sandstones, followed by intercalations of carbonate and argillaceous rocks. The structural framework reflects the different tectonic regimes which prevailed in the area. Above the acoustic basement structural elements of Mafia Channel and Island are interpreted as originating from the superimposition of the Cenozoic East African rifting event, and from the uplifts of the mainland coast and Mafia Island during Late Eocene time. As a result the central part collapsed and formed an asymmetric sag structure in the channel. These elements are seismically identified and subdivided as (from northwest to southeast), the Dar-es-Salaam Platform Offshore, the Central Mafia Channel and the Mafia Island Rise. These domains are separated by respective NE-SW major faults (MF1, MF2 and MF3) and can be demonstrated in the profiles which run in a NW-SE direction. With respect to petroleum potential, the Mafia Channel and Island indicate a considerable content. Three hydrocarbon plays are introduced, namely; 1) the Neocomian regressive sands of Songosongo play 2) the Upper Eocene limestone and 3) the Upper Oligocene turbidites.
129319353
Tectonic and sedimentary evolution of the coastal basin of Tanzania during the mesozoic times
The present paper reviews and updates the stratigraphy and tectonic evolution of the coastal basin of Tanzania during the Mesozoic times based on the interpretation of existing palaeontological and stratigraphical information and supplemented by recent fieldwork investigations by the author. 
Tectonic events largely controlled the evolution of the coastal basin of Tanzania and the Indian Ocean. These included the Karoo rifting during Permo-Triassic, the break up of the Gondwana Supercontinent, which started with rifting in the Triassic period, the opening of the Somali basin in the Middle Jurassic, and the Cenozoic rifting along the East African rift system. The Karoo rifting created a zone of weakness that led to the fragmentation of the Gondwana Supercontinent. 
The Early Jurassic continental sediments developed in the graben-like structure with occasional marine incursions reflecting ancient seaways on the ocean side. The early Middle Jurassic oolitic limestones developed along the shoreline forming the marine carbonate platform. During these times, the area was periodically under fresh water influence. During Bajocian-Bathonian times, the whole of Tanzanian coast was completely under marine conditions though restricted to shallow sea in which coral reefs could grow. It was during these times that a stable continental shelf developed. However, the stability of the shelf was later affected by the reactivation of the Tanga Fault pattern. As a result, the sediments from the provenance including the Bajocian-Bathonian coral reefs were reworked and transported by means of gravity flow and fluvial influence, and deposited in a fault controlled shallow basin at Msolwa to form sub-marine fans. From the Callovian to Kimmeridgian, the main facies included the transgressive low energy shale and septarian marls rich in fossils, particularly ammonites. During this period, an open marine environment was predominant. This transgressive episode was succeeded by a regressive phase during Lower Cretaceous in which sandstone deposits were predominant. The Upper Cretaceous transgressive sediments (shales and marls) lie unconformably over the regressive older deposits, marking the topmost part of the Mesozoic sequence in the study area. Tanz. J. Sci. Vol.29(1) 2003: 1-16
140674642
Revised lithostratigraphy of the Mesozoic-Cenozoic succession of the onshore Rovuma Basin, northern coastal Mozambique
A revised formal lithostratigraphy for the Mesozoic to Cenozoic succession of the onshore portion of the Rovuma Basin in northern Mozambique replaces a previous mixture of informal lithostratigraphical and biostratigraphical names. The following nine formations are formally described: Rio Mecole Formation (Jurassic? age), N’Gapa Formation (Jurassic? age), Pemba Formation (late Jurassic and early Cretaceous age), Macomia Formation (Aptian-Albian age), Mifume Formation (Albian (offshore)/Campanian (onshore)-Maastrichtian age), Alto Jingone Formation (Paleocene-Eocene age), Quissanga Formation (middle Eocene-Oligocene age), Chinda Formation (Neogene age) and Mikindani Formation (Neogene age). The basin’s geology records the temporal development of the coastline of northern Mozambique and southern Tanzania over the last c . 200 million years. Intracratonic rift-basins formed during the early Jurassic Period developed into a south-facing gulf prior to complete separation of eastern Africa from the rest of eastern Gondwana in early Cretaceous times. Concomitant with the lateral crustal movements, vertical isostatic and locally fault-controlled, uplift was a major influence on sedimentation in eastern Africa. This led to erosion with high-energy, fluvial sedimentation into the rift-basins and the establishment of a marine basin throughout the Cretaceous Period. Reduced sedimentation rates during the Paleocene and Eocene were followed by regenerated river-transported sedimentation due to doming and erosion of eastern Africa associated with the development of the East African Rift System since the Oligocene. The major onshore faults that control the shape of the Rovuma Basin and which have been intermittently active since the Jurassic cut across the east-northeast to west-southwest structural grain of the underlying Precambrian crystalline rocks of the East African Orogen. However, some of the east-northeast to west-southwest transfer faults identified in the offshore part of the Rovuma Basin may represent, in part, reactivated Pan African ductile shears
130458121
A revised Cenozoic geochronology and chronostratigraphy
Since the publication of our previous time scale (Berggren and others, 1985c = BKFV85) a large amount of new magneto- and biostratigraphic data and radioisotopic ages have become available. An evaluation of some of the key magnetobiostratigraphic calibration points used in BKFV85, as suggested by high precision 40 Ar/ 39 Ar dating (e.g., Montanari and others, 1988; Swisher and Prothero, 1990; Prothero and Swisher, 1992; Prothero, 1994), has served as a catalyst for us in developing a revised Cenozoic time scale. For the Neogene Period, astrochron- ologic data (Shackleton and others, 1990; Hilgen, 1991) required re-evaluation of the calibration of the Pliocene and Pleistocene Epochs. The significantly older ages for the Pliocene-Pleistocene Epochs predicted by astronomical calibrations were soon corroborated by high precision 40 Ar/ 39 Ar dating (e.g., Baksi and others, 1992; McDougall and others, 1992; Tauxe and others, 1992; Walter and others, 1991; Renne and others, 1993). At the same time, a new and improved definition of the Late Cretaceous and Cenozoic polarity sequence was achieved based on a comprehensive evaluation of global sea-floor magnetic anomaly profiles (Cande and Kent, 1992). This, in turn, led to a revised Cenozoic geomagnetic polarity time scale (GPTS) based on standardization to a model of South Atlantic spreading history (Cande and Kent, 1992/1995 = CK92/95). This paper presents a revised (integrated magnetobiochronologic) Cenozoic time scale (IMBTS) based on an assessment and integration of data from several sources. Biostratigraphic events are correlated to the recently revised global polarity time scale (CK95). The construction of the new GPTS is outlined with emphasis on methodology and newly developed polarity history nomenclature. The radioisotopic calibration points (as well as other relevant data) used to constrain the GPTS are reviewed in their (bio)stratigraphic context. An updated magnetobiostratigraphic (re)assessment of about 150 pre-Pliocene planktonic foraminiferal datum events (including recently avail- able high southern (austral) latitude data) and a new/modified zonal biostratigraphy provides an essentially global biostratigraphic correlation framework. This is complemented by a (re)assessment of nearly 100 calcareous nannofossil datum events. Unrecognized unconformities in the stratigraphic record (and to a lesser extent differences in taxonomic concepts), rather than latitudinal diachrony, is shown to account for discrep- ancies in magnetobiostratigraphic correlations in many instances, particularly in the Paleogene Period. Claims of diachrony of low amplitude (<2 my) are poorly substantiated, at least in the Paleocene and Eocene Epochs. Finally, we (re)assess the current status of Cenozoic chronostratigraphy and present estimates of the chronology of lower (stage) and higher (system) level units. Although the numerical values of chronostratigraphic units (and their boundaries) have changed in the decade since the previous version of the Cenozoic time scale, the relative duration of these units has remained essentially the same. This is particularly true of the Paleogene Period, where the Paleocene/Eocene and Eocene/Oligocene boundaries have been shifted ~2 my younger and the Cretaceous/Paleogene boundary ~1 my younger. Changes in the Neogene time scale are relatively minor and reflect primarily improved magnetobiostratigraphic calibrations, better understanding of chronostratigraphic and magnetobiostratigraphic relationships, and the introduction of a congruent astronom- ical/paleomagnetic chronology for the past 6 my (and concomitant adjustments to magnetochron age estimates).
55753338
Cretaceous Nannoplankton Biostratigraphy and Oceanography of the Northwestern Atlantic Ocean
A tentative Cretaceous nannoplankton zonation is given and the biostratigraphic extent of classical European and newly proposed oceanic stages as well as radiometric ages for important paleontological events and geochronologic boundaries are presented. Calcareous nannoplankton distribution at Sites 390 and 391 is discussed. The evolutionary lineage of Lithraphidites carniolensis-L. praequadratus-L. quadratus is used for the biostratigraphic subdivision of the uppermost Bermudan Stage. A working hypothesis of Cretaceous nannoplankton evolution and oceanography of the Cretaceous oceans is discussed. One new genus (Haqius) and two new species (Lithraphidites praequadratus and Cyclagelosphaera bergeri) are proposed. The evolution of Retecapsa during the Early Cretaceous is discussed and light micrographs are provided for/?, neocomiana, R. angustiforata, and/?, brightonii.
130028100
A revised tropical to subtropical Paleogene planktonic foraminiferal zonation
New biostratigraphic investigations on deep sea cores and outcrop sections have revealed several shortcomings in currently used tropical to subtropical Eocene plank­ tonic foraminiferal zonal schemes in the form of: 1) mod­ ified taxonomic concepts, 2) modifiel:l/different ranges of taxa, and 3) improved calibrations with magnetostratig­ raphy. This new information provides us with an op­ portunity to make some necessary improvements to ex­ isting Eocene biostratigraphic schemes. At the same time, we provide an alphanumeric notation for Paleo­ gene zones using the prefix 'P' (for Paleocene), 'E' (for Eocene) and '0' (for Oligocene) to achieve consistency with recent short-hand notation for other Cenozoic zones (Miocene ['M'], Pliocene [PL] and Pleistocene [PTD. Sixteen Eocene (E) zones are introduced (or nomen­ claturally emended) to replace the 13 zones and subzones of Berggren and others (1995). This new zonation serves as a template for the taxonomic and phylogenetic studies in the forthcoming Atlas of Eocene Planktonic Forami­ nifera (Pearson and others, in press). The 10 zones and subzones of the Paleocene (Berggren and others, 1995) are retained and renamed and/or emended to reflect im­ proved taxonomy and an updated chronologic calibra­ tion to the Global Polarity Time Scale (GPTS) (Berggren and others, 2000).' The PaleocenelEocene boundary is correlated with the lowest occurrence (LO) of Acarinina sibaiyaensis (base of Zone El), at the top of the trun­ cated and redefined (former) Zone P5. The five-fold zonation of the Oligocene (Berggren and others, 1995) is modified to a six-fold zonation with the elevation of (former) Subzones P21a and P21b to zonal status. The Oligocene (0) zomil' components are re­ named and/or nomenclaturally emended.
140657070
New high resolution calcareous nannofossil analysis across the Danian / Selandian transition at the Zumaia section: comparison with South Tethys and Danish sections
A high resolution calcareous nannofossil biostratigraphic analysis was carried out across the Danian/Selandian transition at the Zumaia section (western Pyrenees). In the studied interval, spanning Varol’s Subzone NTp7a to Zone NTp9, a sequence of 10 distinct calcareous nannofossil events is identified. The recognition of these bioevents confirms the continuous and expanded character of the Zumaia section and allows an accurate biostratigraphic correlation of the D/S transition between Zumaia, the Danish reference sections and the more southerly Tethys sections. According to this correlation, the abrupt transition from the upper Danian limestones (the calcisiltite unit) to the Lellinge Greensand that marks the D/S boundary in the type area correlates with the lithological change from the Aitzgorri Limestone Formation to the Itzurun Formation in Zumaia. The calcareous nannofossil bioevents recorded in connection with the organic-rich layer used to mark the base of the Selandian in the Tethys region were detected in Zumaia ~10 m below the top of the Aitzgorri Limestone Formation. This finding suggests that the organic-rich layer is considerably older than the Danian/Selandian (D/S) boundary at Zumaia and the type area, and thus using it to mark the D/S boundary in Tethys is not appropriate. According to a counting of limestone/marl couplets, which are demonstrated to be the stratigraphic expression of precession cycles throughout the Zumaia section, the organic-rich layer in the Tethys region is ~546 kyr older than the D/S boundary at the type area.
14637675
PLANKTIC FORAMINIFERAL SPECIES TURNOVER ACROSS DEEP-SEA APTIAN/ ALBIAN BOUNDARY SECTIONS
A major planktic foraminiferal species turnover accompanied by a dramatic reduction in shell size, a fundamental change in shell architecture, and a precipitous drop in the abundance of planktic relative to benthic species occurs across the Aptian/Albian boundary interval (AABI) at globally distributed deep-sea sections. Extinction of the large and distinctive planktic foraminifer Paraticinella eube-jaouaensis , used to denote a level at or near the Aptian/ Albian boundary, coincides with the extinctions of relatively long-ranging Aptian species of Hedbergella and Globiger-inelloides . At Deep Sea Drilling Project (DSDP) Site 511 (southern South Atlantic), which is the most complete and best preserved of the studied AABI sections, the Aptian assemblage is of low diversity and species are replaced by initially one and then two very small, smooth-surfaced, thin-walled species of Microhedbergella n. gen. The oldest species of this genus, Mi. miniglobularis n. sp., probably descended from Hedbergella praelippa n. sp. and is the nominate taxon for a new lowermost Albian interval zone and is considered ancestral to several small, gradually evolving microperforate species, including Mi. praeplanispira n. sp., Mi. pseudopla-nispira n.sp., and Mi. pseudodelrioensis n. sp., which range into the middle and upper Albian. The small hedbergellids that characterize the Mi. miniglobularis Interval Zone at Site 511 have also been identified from samples taken just above the Kilian black shale level in the Vocontian Basin of southeast France. The Albian record at Site 511 reveals a gradual increase in planktic foraminifera shell size and assemblage dominance, as well as the gradual evolution during the middle Albian of species characterized by a finely perforate, pustulose test. Taxa with this shell infrastructure are included in Muricohedbergella n. gen. A new “ Ticinella yezoana ” Partial Range Zone is erected at Site 511 for correlation of the middle-upper Albian at high latitudes. At Ocean Drilling Program (ODP) Site 1049 (western North Atlantic), which also yields well-preserved foraminifera across the AABI, Aptian species of Hedbergella , Globiger-inelloides , and Pseudoguembelitria blakenosensis n. gen., n. sp. are replaced by lower Albian assemblages composed only of two minute species of Microhedbergella . However, this boundary section is considered incomplete because of the absence of the Mi. miniglobularis Zone. A new upper lower Albian Ti. madecassiana Zone is defined at Site 1049 for the interval between the lowest occurrence (LO) of the nominate taxon and the LO of Ti. primula , the nominate species of the middle Albian Ti. primula Zone. The AABI at DSDP Site 545 (eastern North Atlantic) has a major unconformity spanning the uppermost Aptian through the upper Albian. A black shale sequence previously placed in the lower Albian and designated as Oceanic Anoxic Event 1b is now determined to be latest Aptian in age. The AABI at ODP Site 763 (southeast Indian Ocean) is also marked by an unconformity between the upper Aptian Pa. eubejouaensis Zone and the lower Albian Mi. rischi Zone. This site needs further study to resolve whether overlap of species from both zones is the result of downslope reworking or an exception to the pattern of abrupt species turnover observed at the other deep-sea sites. The dramatic changes in planktic foraminiferal assemblages across the AABI suggest major changes in carbonate chemistry, vertical stratification, or productivity in the surface mixed layer occurred during the last 1 myr of the Aptian. Understanding the cause or causes for these changes will require much further investigation.
129425719
Abrupt planktic foraminiferal turnover across the Niveau Kilian at Col de Pré-Guittard (Vocontian Basin, southeast France): new criteria for defining the Aptian/Albian boundary
A detailed and quantitative study of foraminiferal assemblages across the Niveau Kilian in the Col de Pre-Guittard section (Vocontian Basin, southeast France) ably documents the planktic foraminiferal turnover across the Aptian - Albian boundary interval. The latest Aptian assemblage is dominated by few long-ranging Hedbergella and large-sized Paraticinella that completely disappear near the base of the Niveau Kilian organic-rich level. Planktic foraminiferal assemblages from across the Niveau Kilian to the top of the studied section are composed of minute, but very distinctive smooth-surfaced species of Microhedbergella miniglobularis and Mi. renilaevis. The appearance of Mi. renilaevis in the middle part of the Niveau Kilian represents a major step in the evolution and diversification of the Albian planktic fauna. The lowest occurrence of this taxon is recorded immediately above the extinction level of the Aptian hedbergellids and corresponds with a dramatic decrease in the number of planktic and benthic foraminifera specimens, with a 1 ‰ negative δ13C excursion in bulk carbonate, and evidence for regional rise in sea-surface temperature. Our careful study of the species composition permits refinement of the previous biozonation by using the appearance datum of Mi. renilaevis as a zonal boundary event. Changes include redefinition of the top of the Microhedbergella miniglobularis Zone and designation of a new Microhedbergella renilaevis Zone. The same sequence of events was reported from several deep-sea sites in the Atlantic and Indian Oceans. Therefore, documentation of the planktic foraminiferal turnover, combined with the carbon-isotope stratigraphy in the Col de Pre-Guittard section, provide new criteria for defining the Global Boundary Stratotype Section and Point for the base of the Albian Stage in a stratigraphically complete succession.
129425719
Abrupt planktic foraminiferal turnover across the Niveau Kilian at Col de Pré-Guittard (Vocontian Basin, southeast France): new criteria for defining the Aptian/Albian boundary
A detailed and quantitative study of foraminiferal assemblages across the Niveau Kilian in the Col de Pre-Guittard section (Vocontian Basin, southeast France) ably documents the planktic foraminiferal turnover across the Aptian - Albian boundary interval. The latest Aptian assemblage is dominated by few long-ranging Hedbergella and large-sized Paraticinella that completely disappear near the base of the Niveau Kilian organic-rich level. Planktic foraminiferal assemblages from across the Niveau Kilian to the top of the studied section are composed of minute, but very distinctive smooth-surfaced species of Microhedbergella miniglobularis and Mi. renilaevis. The appearance of Mi. renilaevis in the middle part of the Niveau Kilian represents a major step in the evolution and diversification of the Albian planktic fauna. The lowest occurrence of this taxon is recorded immediately above the extinction level of the Aptian hedbergellids and corresponds with a dramatic decrease in the number of planktic and benthic foraminifera specimens, with a 1 ‰ negative δ13C excursion in bulk carbonate, and evidence for regional rise in sea-surface temperature. Our careful study of the species composition permits refinement of the previous biozonation by using the appearance datum of Mi. renilaevis as a zonal boundary event. Changes include redefinition of the top of the Microhedbergella miniglobularis Zone and designation of a new Microhedbergella renilaevis Zone. The same sequence of events was reported from several deep-sea sites in the Atlantic and Indian Oceans. Therefore, documentation of the planktic foraminiferal turnover, combined with the carbon-isotope stratigraphy in the Col de Pre-Guittard section, provide new criteria for defining the Global Boundary Stratotype Section and Point for the base of the Albian Stage in a stratigraphically complete succession.
128745002
Paraticinella rohri () as the valid name for the latest Aptian zonal marker species of planktonic foraminifera traditionally called bejaouaensis or eubejaouaensis
Abstract The planktonic foraminiferal taxon Ticinella bejaouaensis Sigal, 1966 had long been an important zonal biomarker for the latest Aptian characterized by its large test, numerous (8–10) final-whorl chambers, and rugose test surface, usually with an umbilical cover-plate. Upon confirmation that Sigal's Madagascan holotype was actually from the upper Albian, this species was renamed as T. eubejaouaensis Randrianasolo and Anglada, 1998 using Sigal's Tunisian bejaouaensis paratype, which is late Aptian in age, as the new holotype. Following emendation of the genus, Paraticinella eubejaouaensis has recently become the standard usage. However, the validity of this species is still uncertain because the original designation was given in very obscure publication(s). Meanwhile, albeit tenuous, a presumable senior name “ Paraticinella rohri ( Bolli, 1959 )” has recently been proposed in place of eubejaouaensis . Rigorous assessment of the original species designation of T. eubejaouaensis ascertains that the method of publication used does not comply with the criteria required in the International Code of Zoological Nomenclature, thereby making this species an invalid name, or nomen nudum . New backscattered scanning electron microscopic observations of the primary types of Praeglobotruncana rohri Bolli, 1959 reveal that this hitherto unattended species is indeed synonymous to “ T. eubejaouaensis ” particularly by exhibiting equatorially aligned rugosities on the wall surface, and that the holotype is sufficiently preserved and well qualified as the name-bearing type. The latest Aptian age of the rohri type level is robustly established by its co-occurrence with Pseudoplanomalina cheniourensis ( Sigal, 1952 ) and Hedbergella trocoidea ( Gandolfi, 1942 ) (= another rohri paratype). Upon confirmation of the absence of any potential nomenclatural acts for conservation of the junior name “[ eu ] bejaouaensis ,” we are obliged to provide formal redescription and establish the valid, objective senior name Paraticinella rohri ( Bolli, 1959 ), the binomen that should be of mandatory use henceforth. Accordingly, the uppermost Aptian “[ eu ] bejaouaensis ” Zone should be referred to as the “ Pt. rohri Zone.” Having reviewed the supraspecific taxonomy, herein the type species of the genus Paraticinella is redefined as Pt. rohri , and the subfamily Pseudoplanomalininae is proposed.
129316727
Early to mid-Cretaceous calcareous nannoplankton from the northwest Pacific Ocean, Leg 198, Shatsky Rise
During Ocean Drilling Program Leg 198, Sites 1207, 1208, 1212, 1213, and 1214 were drilled on Shatsky Rise, coring Lower to mid-Cretaceous successions of nannofossil chalk, porcellanite, and chert. Although recovery was poor, these sites yielded an outstanding record of calcareous nannoplankton, providing valuable data concerning the evolutionary succession and paleobiogeography of the largest Cretaceous marine habitat. Mid-Cretaceous sections (Aptian-Cenomanian) were recovered at all sites, and Site 1213 includes an apparently complete Berriasian-Hauterivian section. Biostratigraphic dating is problematic in places because of the absence or rarity of zonal fossils of both Boreal and Tethyan affinity. The majority of nannofossil assemblages are relatively typical of this age, but there are clear differences that set them apart from coeval epicontinental assemblages: for example, Lithraphidites carniolensis is common to abundant throughout and was most likely an oceanic-adapted taxon; the cold- to temperate-water species Crucibiscutum salebrosum, Repagulum parvidentatum, and Seribiscutum primitivum are entirely absent, indicating the persistence of tropical, warm surface water temperatures; and the warm-water species Hayesites irregularis is common. Most striking, however, is the virtual absence of Nannoconus and Micrantholithus, both taxa that were conspicuous and often common components of many Tethyan and Atlantic nannofloras. These forms were almost certainly neritic adapted and usually absent in deep open-ocean settings away from guyots and platforms. Other Tethyan taxa are also absent or rare and sporadically distributed (e.g., Calcicalathina oblongata, Conusphaera spp., Tubodiscus verenae, and Lithraphidites bollii), and factors related to neritic environments presumably controlled their distribution. Site 1213 also records extended Early Cretaceous ranges for species previously thought to have become extinct during the Late Jurassic (e.g., Axopodorhabdus cylindratus, Hexapodorhabdus cuvillieri, and Biscutum dorsetensis), suggesting these species became Pacific-restricted prior to their extinction. Watznaueria britannica may also have been a species with Pacific affinities before reexpansion of its biogeography in the early Aptian. One new genus (Mattiolia) and thirteen new species (Zeugrhabdotus clarus, Zeugrhabdotus petrizzoae, Helicolithus leckiei, Rhagodiscus amplus, Rhagodiscus robustus, Rhagodiscus sageri, Rhagodiscus adinfinitus, Tubodiscus bellii, Tubodiscus frankiae, Gartnerago ponticula, Haqius peltatus, Mattiolia furva, and Kokia stellata) are described from the Shatsky Rise Lower Cretaceous section.
128765239
Nannofossils and superplumes: The Early Aptian “nannoconid crisis”
A group of calcareous nannoplankton named nannoconids experienced a crisis in the early Aptian and recovered only later in the late Aptian after a period of virtual absence. Although no extinctions occurred, the widespread nature of the “nannoconid crisis” suggests a global causal factor. This crisis is recorded within the Chiastozygus litterarius nannofossil and Globigerinelloides blowi planktonic foraminiferal zones, postdates magnetic chronozone M0 by approximately 300 kyr, and precedes the oceanic anoxic subevent 1a and associated δ13C anomaly by some 40–100 kyr. Selective dissolution and anoxia cannot explain the crisis, because nannoconids are dissolution-resistant forms and their crisis clearly precedes the deposition of anoxic sediments. At least 1 m.y. prior to the “nannoconid crisis,” the onset of a nannoplankton speciation event may be the response of nannofloras to a major rise in relative sea level. The “nannoconid crisis” seems to be synchronous with the early Aptian volcanic eruptions in the Pacific Ocean. Hence calcareous nannoplankton were severely affected by the “superplume” volcanic episode. The coccolithophorid bloom/nannoconid crisis was possibly induced by the excessive CO2 levels in the atmosphere and/or caused by changes in nutrient content of oceanic surface waters. Fertility was enhanced by rapid turnover of nutrients due to the abnormal volcanic activity and accelerated transfer of nutrients from the continents into the oceans under warm and humid conditions of the mid-Cretaceous greenhouse climate. The “nannoconid crisis” may represent a competition between phytoplankton groups for nutrients or, more likely, competition between different calcareous nannoplankton. The biologic affinity and mode of life of Nannoconus are unknown, because there is no modern analog of this genus. However, comparison of Lower Cretaceous nannofossil assemblages with modern nannoplankton cummunities suggests that nannoconids, like extant Florisphaera profunda, possibly inhabited the lower photic zone. Concentrations of nutrients in the upper euphotic zone may have triggered blooms of coccolithophorids and nannoconid depletion. This model implies that the “nannoconid crisis” is the result of an abrupt, major change in the structure of surface waters caused directly or indirectly by the “superplume.” The adjustments of the biosphere to the new paleoceanographic and climatic conditions required some 40–100 kyr before changing into abnormally high primary productivity and deposition of organic carbon-rich sediments with dinoflagellates outcompeting nannoplankton.
53664915
Black shale deposition, atmospheric CO2 drawdown, and cooling during the Cenomanian-Turonian Oceanic Anoxic Event
[1] Oceanic Anoxic Event 2 (OAE2), spanning the Cenomanian-Turonian boundary (CTB), represents one of the largest perturbations in the global carbon cycle in the last 100 Myr. The δ13Ccarb, δ13Corg, and δ18O chemostratigraphy of a black shale–bearing CTB succession in the Vocontian Basin of France is described and correlated at high resolution to the European CTB reference section at Eastbourne, England, and to successions in Germany, the equatorial and midlatitude proto-North Atlantic, and the U.S. Western Interior Seaway (WIS). Δ13C (offset between δ13Ccarb and δ13Corg) is shown to be a good pCO2 proxy that is consistent with pCO2 records obtained using biomarker δ13C data from Atlantic black shales and leaf stomata data from WIS sections. Boreal chalk δ18O records show sea surface temperature (SST) changes that closely follow the Δ13C pCO2 proxy and confirm TEX86 results from deep ocean sites. Rising pCO2 and SST during the Late Cenomanian is attributed to volcanic degassing; pCO2 and SST maxima occurred at the onset of black shale deposition, followed by falling pCO2 and cooling due to carbon sequestration by marine organic productivity and preservation, and increased silicate weathering. A marked pCO2 minimum (∼25% fall) occurred with a SST minimum (Plenus Cold Event) showing >4°C of cooling in ∼40 kyr. Renewed increases in pCO2, SST, and δ13C during latest Cenomanian black shale deposition suggest that a continuing volcanogenic CO2 flux overrode further drawdown effects. Maximum pCO2 and SST followed the end of OAE2, associated with a falling nutrient supply during the Early Turonian eustatic highstand.
55903093
Secular variation in Late Cretaceous carbon isotopes: a new δ13C carbonate reference curve for the Cenomanian–Campanian (99.6–70.6 Ma)
Carbon stable-isotope variation through the Cenomanian–Santonian stages is characterized using data for 1769 bulk pelagic carbonate samples collected from seven Chalk successions in England. The sections show consistent stratigraphic trends and δ13C values that provide a basis for high-resolution correlation. Positive and negative δ13C excursions and inflection points on the isotope profiles are used to define 72 isotope events. Key markers are provided by positive δ13C excursions of up to +2‰: the Albian/Cenomanian Boundary Event; Mid-Cenomanian Event I; the Cenomanian/Turonian Boundary Event; the Bridgewick, Hitch Wood and Navigation events of Late Turonian age; and the Santonian/Campanian Boundary Event. Isotope events are isochronous within a framework provided by macrofossil datum levels and bentonite horizons. An age-calibrated composite δ13C reference curve and an isotope event stratigraphy are constructed using data from the English Chalk. The isotope stratigraphy is applied to successions in Germany, France, Spain and Italy. Correlation with pelagic sections at Gubbio, central Italy, demonstrates general agreement between biostratigraphic and chemostratigraphic criteria in the Cenomanian–Turonian stages, confirming established relationships between Tethyan planktonic foraminiferal and Boreal macrofossil biozonations. Correlation of the Coniacian–Santonian stages is less clear cut: magnetostratigraphic evidence for placing the base of Chron 33r near the base of the Upper Santonian is in good agreement with the carbon-iso-tope correlation, but generates significant anomalies regarding the placement of the Santonian and Campanian stage boundaries with respect to Tethyan planktonic foraminiferal and nannofossil zones. Isotope stratigraphy offers a more reliable criterion for detailed correlation of Cenomanian–Santonian strata than biostratigraphy. With the addition of Campanian δ13C data from one of the English sections, a composite Cenomanian–Campanian age-calibrated reference curve is presented that can be utilized in future chemostratigraphic studies. The Cenomanian–Campanian carbon-isotope curve is remarkably similar in shape to supposedly eustatic sea-level curves: increasing δ13C values accompanying sea-level rise associated with transgression, and falling δ13C values characterizing sea-level fall and regression. The correlation between carbon isotopes and sea-level is explained by variations in epicontinental sea area affecting organic-matter burial fluxes: increasing shallow sea-floor area and increased accommodation space accompanying sea-level rise allowed more efficient burial of marine organic matter, with the preferential removal of 12C from the marine carbon reservoir. During sea-level fall, reduced seafloor area, marine erosion of previously deposited sediments, and exposure of basin margins led to reduced organic-carbon burial fluxes and oxidation of previously deposited organic matter, causing falling δ13C values. Additionally, drowning of carbonate platforms during periods of rapid sea-level rise may have reduced the global inorganic relative to the organic carbon flux, further enhancing δ13C values, while renewed platform growth during late transgressions and highstands prompted increased carbonate deposition. Variations in nutrient supply, changing rates of oceanic turnover, and the sequestration or liberation of methane from gas hydrates may also have played a role in controlling carbon-isotope ratios.