Mesozoic biostratigraphic, paleoenvironmental, and paleobiogeographic synthesis, equatorial Atlantic

Cretaceous sediments from Ocean Drilling Program Leg 159 on the Côte d’Ivoire-Ghana Marginal Ridge (CIGMR), eastern equatorial Atlantic, are characterized by distinct stratigraphic changes in sedimentary facies associated with changes in the composition of the clayey and organic fractions, as well as of the calcareous nannofossil, radiolarian, foraminiferal, and palynomorph assemblages. In the absence of reliable magnetostratigraphic information, an integrated biostratigraphy provides the only means used to calibrate the geologic history of the Leg 159 area. The existence of marine depositional environments as early as the late Aptian to early Albian close to the Leg 159 drill sites puts constraints on the timing of the opening of the equatorial Atlantic gateway. Marine sedimentation on the ridge suggests that the West African and South American cratons were largely detached at this segment of the margin by the middle to late Albian. During the Cenomanian to Coniacian the ridge appears to have remained in an elevated position with concurrent low deposition or condensation (Site 959), high carbonate debris accumulation (Site 960), and even erosion (Site 962). Total organic Carbon measurements and microfaunal data lead us to suggest that, following the early opening of the seaway during the Albian, circulation remained restricted in the fragmented sub-basins of the CIGMR. It probably was not until the Santonian that a deep-water connection and circulation system became established between the Central and the South Atlantic. The sedimentary and faunal record at Site 959 show that a rapid subsidence occurred during the Santonian, with sub-calcite compensation depth conditions maintained until and beyond the Cretaceous/Tertiary boundary

Bedrock and Detrital Zircon Thermochronology to Unravel Exhumation Histories of Accreted Tectonic Blocks: An Example from the Western Colombian Andes

The Northern Andes are the result of multiple tectonic phases, which include extensional and compressional volcanic arcs, strike-slip fragmentation, and accretion of exotic terranes. The alternations of these tectonic settings have overprinted and fragmented the geological record, which has hindered precise paleogeographic and tectonic reconstructions. In the western segment of the Colombian Andes, the oceanic-cored Western Cordillera (WC) and the continental Central Cordillera (CC) are separated by the Romeral Fault Zone (RFZ). This segment of the Andes preserves the record of Cretaceous back-arc extension, the onset of compression, and the accretion of the Caribbean plateau during the Late Cretaceous-Paleocene. To refine the tectonic evolution of the Western Colombian Andes, this study documents new detrital zircon fission-track (ZFT) data from the Meso-Cenozoic sedimentary cover in the CC, the RFZ, and the WC; new ZFT and zircon helium (ZHe) bedrock data from the CC and the RFZ; and new U–Pb detrital data from the Miocene sedimentary cover of the RFZ. Within the RFZ, we obtained bedrock ZFT ages of 239.0 ± 11.0 Ma and 111.1 ± 4.3 Ma, and detrital ZFT data from the Abejorral Formation are interpreted as the result of post-magmatic cooling and Cretaceous rifting. Late Cretaceous to Eocene ZFT and ZHe ages (~61–50 Ma) in the CC and detrital ZFT data in the WC record exhumation and deformation of the CC during and after the collision of the Caribbean plateau with the continental margin. Finally, detrital U–Pb and ZFT data from the Amagá Formation record the formation of a Miocene intermountain basin. This study reconstructs the basin geometries and the deformation patterns before, during, and after the collision of the Caribbean plateau with the South American margin. We highlight that in accretionary orogens, in which prolonged deformation and erosion have removed the sedimentary cover, the quantification of differential basement exhumation is key to reconstruct thick-skin deformation and to define major tectonic boundaries

Palynofacies and Stable C and N Isotopes of Holocene Sediments from Lake Macuco (Linhares, Espirito Santo, Southeastern Brazil): Depositional Settings and Palaeoenvironmental Evolution

Particulate organic matter in sediments constitutes a valuable proxy for paleoenvironmental reconstructions. A 192 cm lacustrine sediment core (~ 7521 cal yr. B.P.) from the northern coast of the State of Espírito Santo, southeastern Brazil, was radiocarbon dated and then analyzed for palynofacies, stable isotopes (C and N), and grain size. The values for total organic carbon -- TOC (1.91% to 20.89%), total nitrogen -- TN (0.08% to 1.1%), δ13C (− 27.10‰ to − 29.01‰), δ15N (1.92‰ to 5.09‰) and C/N (12.87 to 50.11) suggest predominance of C3 plants and changing mixtures of terrestrial and aquatic organic matter in the sediments. Palynofacies and cluster analyses were used to identify four palynofacies associations that reflect different phases in the Lake Macuco evolution. Palynofacies 1 (192 to 106 cm, ~ 7521 cal yr. B.P. to ~ 7054 cal yr. B.P.—interpolated age) is characterized mainly by amorphous organic matter (AOM), non-opaque phytoclasts (NOPs), mangrove pollen grains (Rhizophora sp. L. 1753 and Avicennia sp. L. 1753), and foraminiferal test linings. Palynofacies 2 (106 to 65 cm, ~ 7054 cal yr. B.P.—interpolated age to ~ 4847 cal yr. B.P.) is dominated by NOPs and AOM, with an increase in the values of mangrove pollen grains relative to Palynofacies 1. Both palynofacies reflect marine and fluvial influences in a depositional environment related to the development of an estuarine system during the mid-Holocene transgressive stage. Palynofacies 3 (65 to 27 cm, ~ 4847 cal yr. B.P. to ~ 3800 cal yr. B.P.—interpolated age) comprises high abundances of fluvial elements (NOP and opaque phytoclasts—OP) and low values of AOM. The depositional environment is interpreted as being an estuary during the marine regression, with the displacement of the estuarine basin and mangroves towards the sea. Palynofacies 4 (27 to 0 cm, \u3c ~ 3800 cal yr. B.P.) is characterized by the predominance of AOM and NOP, increase in the values of freshwater algae, and no evidence of marine influence. This last phase reflects the beginning of the establishment of Lake Macuco and floodplain of the Barra Seca River under conditions similar to the present-day. Particulate organic matter in sediments constitutes a valuable proxy for paleoenvironmental reconstructions. A 192 cm lacustrine sediment core (~ 7521 cal yr. B.P.) from the northern coast of the State of Espírito Santo, southeastern Brazil, was radiocarbon dated and then analyzed for palynofacies, stable isotopes (C and N), and grain size. The values for total organic carbon -- TOC (1.91% to 20.89%), total nitrogen -- TN (0.08% to 1.1%), δ13C (− 27.10‰ to − 29.01‰), δ15N (1.92‰ to 5.09‰) and C/N (12.87 to 50.11) suggest predominance of C3 plants and changing mixtures of terrestrial and aquatic organic matter in the sediments. Palynofacies and cluster analyses were used to identify four palynofacies associations that reflect different phases in the Lake Macuco evolution. Palynofacies 1 (192 to 106 cm, ~ 7521 cal yr. B.P. to ~ 7054 cal yr. B.P.--interpolated age) is characterized mainly by amorphous organic matter (AOM), non-opaque phytoclasts (NOPs), mangrove pollen grains (Rhizophora sp. L. 1753 and Avicennia sp. L. 1753), and foraminiferal test linings. Palynofacies 2 (106 to 65 cm, ~ 7054 cal yr. B.P.—interpolated age to ~ 4847 cal yr. B.P.) is dominated by NOPs and AOM, with an increase in the values of mangrove pollen grains relative to Palynofacies 1. Both palynofacies reflect marine and fluvial influences in a depositional environment related to the development of an estuarine system during the mid-Holocene transgressive stage. Palynofacies 3 (65 to 27 cm, ~ 4847 cal yr. B.P. to ~ 3800 cal yr. B.P.--interpolated age) comprises high abundances of fluvial elements (NOP and opaque phytoclasts--OP) and low values of AOM. The depositional environment is interpreted as being an estuary during the marine regression, with the displacement of the estuarine basin and mangroves towards the sea. Palynofacies 4 (27 to 0 cm, \u3c ~ 3800 cal yr. B.P.) is characterized by the predominance of AOM and NOP, increase in the values of freshwater algae, and no evidence of marine influence. This last phase reflects the beginning of the establishment of Lake Macuco and floodplain of the Barra Seca River under conditions similar to the present-day

Dinoflagellate cysts from the Cretaceous–Paleogene boundary at Ouled Haddou, southeastern Rif, Morocco: biostratigraphy, paleoenvironments and paleobiogeography

A palynological investigation of a section dated by foraminifera, at Ouled Haddou, south-eastern Rifian Corridor, northern Morocco, revealed a rich and well-preserved dinoflagellate cyst assemblage that allowed a palynological separation of Maastrichtian from Danian deposits. The gradual change of the dinoflagellate cyst assemblages and the biostratigraphic resolution attained, suggest that the studied Maastrichtian-Danian section is continuous. The recognition of the latest Maastrichtian and earliest Danian is based on global dinoflagellate cyst events, including the first occurrence of the latest Maastrichtian species Disphaerogena carposphaeropsis, Glaphyrocysta perforata, and Manumiella seelandica, the latest Maastrichtian acme of Manumiella seelandica, and the first occurrence of the earliest Danian markers Carpatella cornuta, Damassadinium californicum, Eisenackia circumtabulata, Membranilarnacia tenella and Senoniasphaera inornata. The Cretaceous-Paleogene boundary is placed above the latest Maastrichtian events, mainly immediately above the acme of M. seelandica and below the earliest Danian events, particularly below the first occurrences of C. cornuta and D. californicum. The biostratigraphic interpretations are based on a comparison with calibrated dinoflagellate cyst ranges from several reference sections, mainly in the Northern Hemisphere middle latitudes. The Cretaceous-Paleogene boundary is not marked by a mass extinction of dinoflagellate cyst species, but shows important changes in the relative abundances of different species or groups of morphologically related species. These changes are paleoenvironmentally controlled. The peridinioid assemblage suggests deposition in a subtropical to warm temperate province. One dinoflagellate cyst species, Phelodinium elongatum, is formally described