Palynological Content Research Articles

Palynological variability within the Permian (Changhsingian) Umm Irna Formation (Jordan): implications for biostratigraphy and fluid-flow character in alluvial formations

The Permian (Changhsingian) Umm Irna Formation (Jordan) yields important plant fossils that have influenced our understanding of the early evolution of plants that later dominated the vegetation of the Mesozoic. The formation was deposited in a fluvial regime characterised by the co-occurrence of stacked small-scale braided channels and of larger, higher-sinuosity channels with deposition on point bars, all intercalated into a heterogeneous background sedimentation of finer-grained floodplain deposits, including stacked crevasse-splay deposits, interspersed abandoned-channel and oxbow-lake fills, and lenses of peaty back-swamp deposits. Here, we document the remarkable compositional variability expressed in 124 palynomorph assemblages that were recovered from different argillaceous deposits in the Umm Irna Formation within a ∼2 km2 outcrop area around a major meandering channel. Our results reveal lateral and vertical variation within individual argillaceous units, as well as lateral variation between different argillaceous units in the same sedimentary complex at similar stratigraphic levels. When combined with plant macrofossil data, the results show that variability in the palynological content may be influenced mainly by two factors. The first is connectedness to the major channel; the drainage system carried a mixture of palynomorphs from across the floodplain but also from a large hinterland of tributaries draining higher parts of the floodplain and uplands beyond to the south and east. The second is the influence of local vegetation communities on the floodplain which would likely be more marked in less connected parts of the floodplain. These findings have implications for the palynological study of alluvial sequences of the Palaeozoic and Mesozoic, and for understanding the ability to identify mudstone units via palynological fingerprinting. Such individual units are of great importance as baffles to fluid flow in reservoirs that might be used for oil and gas, low-temperature geothermal energy storage, carbon capture and storage, and hydrogen storage in alluvial successions.

Geochemical constrains for unravelling the condition of sedimentation, provenance, paleoclimate variation, and metallogenic implication of the cretaceous deposits of Mayo Oulo Basin (North Cameroon, Africa)

The sediments from the Mayo Oulo intracontinental Basin, along the N–S cross section between the Gadavou and Lombel localities in central part of the basin, were investigated through major and trace elements geochemistry associated with palynological analysis to determine their condition of sedimentation, paleoclimate evolution and metallogenic implication along the Cretaceous sequence from the N–S cross section of the central part of this basin. From bottom to top of this sequence there are various types of facies with various concentrations of carbonate. Based on their major oxides compositions, the sediments were classified as Shales associated with Fe-shales, Fe-sands, Wacke and Litharenite. The CIX (Chemical Index of Alteration, 62.65 to 98.14) and PIX (Plagioclase Index of Alteration, 65.00 to 99.13) sediments underwent a various chemical weathering; little chemical weathering in the middle to the upper part of the sequence and moderate to high chemical weathering in the lower part. The discriminant function-based multidimensional tectonic diagrams indicate mainly and respectively arc-collisional and Island arc-active continental margin settings which are consistent with the Precambrian geological history of the study area. The SiO2 vs. Al2O3+K2O + Na2O, C-values, associated with trace elements plots such as Sr/Ba, and Rb/Sr, and palynological content (continental or terrestrial species exclusively, dominated by Gymnosperm pollens such as. Inaperturopollenites sp., Araucariacites sp. and Classopollis sp, associated with spores such as Cicatricosisporites sp) indicate mainly arid to semi-arid climate with periodic humid to semi-humid conditions. The Sr/Ba values ranging from 0.084 to 6.408 suggest a fluctuating and sometimes high salinity (Hypersaline milieu). The rare earth elements data show high LREE/HREE ratios (2.86–13.31); high negative and positive Eu anomaly (Eu/Eu∗ = 0.33 to 1.38) and no Ce anomaly (Ce/Ce∗ = 0.94 to 1.02); these features, together with mixed major and trace element ratios and plots such as, Al2O3/TiO2 ratios (14.31–54.26); Th/Co ratios (0.30–14.58); Ce vs La/Yb, Zr vs TiO2 and La/Sc vs Th/Co plots, indicate that the sediments are derived mainly from felsic to intermediate or mafic rock composition. Ni/Co (1.86–3.59) and U/Th (0.03–0.76) ratios are consistent with oxic conditions from bottom to top of the sequence. The Al/Si ratio shows positive correlation with CIA, Th, Zr, Hf, Na, K and negative correlation with Ca and Mg. The positive correlation with K, Hf, Na, Zr, and Th from detrital origin and negative correlation with Ca and Mg from chemical origin could suggest the geochemical composition control of grain size. According to the ternary Al–Fe–Mn diagram metallogenic classification, the studied samples are essentially terrigenous and partially weakly metalliferous, close to those from the Babouri –Figuil and Mamfe Basins (Cameroon) and contrary to those from the Sob area (Polar Urals). No marine or transitional fossil species are recorded. The presence of numerous tetrads to dyads indicate a lacustrine or swampy environment surrounded by vegetation.

Palynological, palynofaciological and organic geochemistry analysis of oligocene microclastics sediments from the tremembé formation - São Paulo State, Brazil

Samples of outcrops from the mining companies Extrativa Santa Fé Ltda and Aligra - Indústria e Comércio de Argila Ltda provided the base material for this investigation into palynological, palynofaciological and organic geochemistry analyses of the Taubaté Basin, São Paulo State. The sediments belong to the Tremembé Formation and comprise microclastic rocks. The Tremembé Formation is known for its rich fossil record and clay mineral content, widely used as raw material for various industrial processes. The generating potential of the sediments was evaluated through qualitative and quantitative analyses of organic content, percentage of total organic carbon (TOC), and Rock-Eval pyrolysis.Furthermore, using transmitted light optical microscopy, observation of the palynological content allowed the identification of characteristic species in terms of age and thermal maturation through the Spore Color Index (SCI) and depositional paleoenvironment.Palynofacies were individualized via reflected light optical microscopy, and together with Rock-Eval pyrolysis data, the quality and type of kerogen were determined. The organic content of the two mining companies shows a predominance of amorphous, globose, and dispersed organic matter of lacustrine origin. Moreover, it is composed mainly of the genera Botryococcus and Pediastrum algae. Palynological associations allowed the section to be temporally positioned in the Oligocene.The abundance of bisaccate pollen grains attributable to conifers, represented mainly by the species Podocarpidites marwickii and Dacrydiumites florinii, combined with the presence of spores, suggests a temperate paleoclimate with humid niche conditions. The pyrolysis results and microscopic observation of the organic content in fluorescence mode show that deposition occurred under anoxic conditions, allowing better preservation of organic matter with high potential for generating hydrocarbons.

Depositional system and plant ecosystem responses to long-term low tempo volcanism, the Interbasaltic Formation, Antrim Lava Group

Abstract The Antrim Lava Group of NE Ireland comprises a volcanic sequence dominated by basaltic lava flows. Including subsidiary sedimentary interlayers and some evolved lavas and intrusions, the overall sequence reaches a cumulative thickness of ∼800 m. The tempo of eruption of the Antrim Lava Group is poorly constrained but can be evaluated via weathering patterns and environmental reconstructions derived from lava-flow interbeds. In this contribution, we present palynology from a newly identified and well-developed 2.0–2.5 m thick sedimentary sequence (interbed) at Ross's Quarry, Ballycastle, Co. Antrim, that helps elucidate the contemporary development of environments in a setting subject to periodic basaltic volcanism. The interbed is subdivided into geologically distinct subunits of cross-bedded and parallel-bedded sandstones and sandy siltstones, all rich in visible organic remains such as rootlets and fragments of wood and bark. A total of 19 samples was collected from the sequence and subsequently analysed for palynological content. The palynomorph data point toward a diversity of inputs ranging from estuaries, chalky soils, dry soils, swamps, lakes, floodplains, sand bars, wet soils, established bogs and fenlands. In contrast to current understanding, the palynological data and their inferred environments collectively reveal the presence of flora that favour a temperate climate rather than the subtropical climate that has previously been inferred from the lateritic interbeds of the Antrim Lava Group. By combining the Ross's Quarry observations with palynological data from other quarry sites and boreholes in Antrim, we provide new insights into the climate, weathering systems and eruptive history of the Antrim Lava Group.

Paleoenvironmental reconstruction of the Berriasian organic-rich interval of the Vaca Muerta Formation (Neuquén Basin, Argentina): Insights for the characterization of unconventional hydrocarbon shale reservoirs

The 50 m-thick Berriasian organic-rich interval (BORI) of the Vaca Muerta Formation (Neuquén Basin, Argentina) represents one of the most attractive stratigraphic intervals for unconventional hydrocarbon exploration in the unit. Nevertheless, little is known about the environmental conditions prevailing during the accumulation of the sediments. To unravel the causes that favored the preservation of the organic matter (OM) in the BORI, a detailed multiproxy sedimentological approach was conducted. The study included the analyses of microfacies, palynological content, calpionellid-calcisphere dinocysts, mineralogy, spectral gamma-ray, inorganic geochemistry, Rock-Eval pyrolysis and stable carbon isotopes of whole rock carbonate (δ13Ccarb), and associated OM (δ13Corg). The BORI presents a late Early to early Late Berriasian age and is subdivided into a lower and upper interval. The lower interval (25.6 m-thick) is primarily formed by radiolaritic wackestones and presents higher total organic carbon (TOC) content (4.2 wt% on average), mainly in the form of amorphous OM (AOM), with variable contribution of phytoclasts. The geochemical analyses (Si, Ni, Cu, Mo, U, V) indicate high productivity of the water column and overall sea bottom anoxia. Oppositely, the upper interval (24.4 m-thick) is mostly constituted by peloidal packstones/grainstones and presents a lower TOC content (1.5 wt% on average) mainly constituted by phytoclasts, with variable contribution of AOM. A decrease of the productivity and an increase of sea bottom oxygenation is recorded based on the geochemical analyses. The high OM content of the BORI responds to the combination of high productivity of the water column and sea bottom anoxia in response to the Berriasian transgression and a worldwide paleoclimatic change towards more humid conditions. The results of our study position the BORI as an attractive interval for unconventional hydrocarbon production due to its high TOC, low bulk clay mineral and high biogenic quartz content, granting an adequate geomechanical behavior.

New palynological record for the Puesto Albornoz Formation (Golfo San Jorge basin, Argentina): Stratigraphic and paleoenvironmental implications

Palynomorph assemblages were recovered from the Puesto Albornoz Formation (Golfo San Jorge Basin, Southern Argentina) at its type locality. The scarcity of outcrops with a continental Lower Cretaceous sedimentary record in this basin, and its marginal position in the western sector of the studied area, make Puesto Albornoz a unique and key locality for determining the timing of the basin evolution during the Cretaceous. The palynological content includes thirty-five spore species, twenty-one pollen taxa, and two algae. Among the fifty-eight species identified, forty-eight were identified for the first time for the unit. Based on the previous records of the analyzed taxa, a late Valanginian to Barremian, and more probably late Valanginian to Hauterivian age is inferred for the studied palynoflora. The palynological assemblages studied here closely resemble the Interulobites-Foraminisporis Zone (late Valangian-Hauterivian) of the Argentinian Patagonia, and the Cyclusphaera psilata-Classopollis association (late Valanginian-Barremian) of the Neuquén Basin.

Palynology and palynofacies studies in the lowermost Jurassic of the Lusitanian Basin (Pereiros Formation of the Silves Group), Portugal: evidence of the first transgressive episode

The Silves Group of the Lusitanian Basin in Portugal represents the initial infill of the continental rifting basins that formed during the breakup of northern Pangaea regions. Evaporites, especially halite, mark the transition from continental to marine settings and the beginning of the deposition in passive margin basins. This work presents the results of the palynostratigraphic and palynofacies analysis of two partial sections from the Pereiros Formation at the top of the Silves Group. The two sections are composed of sandstones, mudstones and dolostones interpreted as deposited in fluvial and lacustrine settings without apparent marine influence. The palynological content is diverse and wellpreserved, dating both sections to the early Hettangian (Lower Jurassic), indicated by the presence of spores Ischyosporites variegatus, Kraeuselisporites reissingeri, Porcellispora longdonensis and the pollen grains Perinopollenites elatoides and Pinuspollenites minimus. The palynological content of one of the sections (Lamas I) is noticeable by microforaminifera linings, suggesting evidence for a hitherto marine incursion at this age in the Silves Group stratigraphy. The beds that yielded the microforaminifera linings are interpreted as having been deposited in an estuarine-type setting, created by the first and short-lived marine transgressive event in the Lusitanian Basin during the early Hettangian.

Dinoflagellate cyst and pollen assemblages as tracers for marine productivity and river input in the northern Gulf of Mexico

Abstract. Both marine dinoflagellate cysts and terrestrially derived pollen and spores are abundant in coastal sediments close to river mouths, making sediment records from such settings ideal to simultaneously study land–ocean climate interactions, marine productivity patterns and freshwater input over time. However, few studies consider the combined calibration of these palynological proxies in modern coastal sediments offshore from rivers, which is needed to strengthen the interpretation of paleoreconstructions. Here, we analyze the palynological content of marine surface sediments along land–sea transects off the Mississippi and Atchafalaya river mouths in the northern Gulf of Mexico (GoM) and test three palynological indices which are often employed in the paleo-domain: (i) the abundance of cysts of heterotrophic and autotrophic dinoflagellates (dinocysts) as a tracer for primary productivity (H/A ratio) and (ii) the ratio between non-bisaccate pollen and bisaccates (P/B) as well as (iii) the ratio between pollen (excluding bisaccates) and dinocysts (P/D), which are both tracers for river input and distance to the coast. Our results show that dinoflagellate cysts are most abundant on the shelf, where heterotrophic dinocyst species dominate coastal assemblages in reach of the river plume, while autotrophic taxa are more present in the oligotrophic open ocean. This is clearly reflected in decreasing H/A values further offshore. Individual dinocyst taxa also seem to inhabit specific niches along an onshore–offshore transect, linked to nutrient availability and proximity to the turbid river plume. The highest pollen concentrations are found close to the Mississippi river mouth and mostly represent a mixture of local coastal and upstream vegetation, whereas bisaccate pollen was most abundant further offshore of the Mississippi river. Multivariate redundancy analysis (RDA) performed on both pollen and dinocyst assemblages, a set of environmental parameters, and the three palynological ratios showed that net primary productivity was the most important variable influencing the dinocyst assemblages, likely as the result of nutrient input. Additionally, the RDA confirmed that the H/A ratio indeed seems to track primary productivity, while the P/B ratio results in a robust indicator for distance to the coast, and the P/D ratio better reflects river input. Together, our data confirm and further specify the suitability of these three palynological ratios in river-dominated coastal margins as proxies for (past) marine productivity and distance to the coast and river.

Past beaked whale diversity in the North Sea: reappraisal through a new Miocene record and biostratigraphic analyses

Extant beaked whales (family Ziphiidae) are deep diving suction feeders and none of them can be considered as a permanent resident of the shallow southern North Sea. The rich fossil record of ziphiids from Neogene deposits of this area is thus surprising. However, chronostratigraphic intervals of most recorded taxa remain poorly constrained, preventing from assessing the evolution of their local diversity. In this work, we describe a new ziphiid cranium from the Neogene of Antwerp (north of Belgium), which is attributed to Caviziphius aff. C. altirostris. Sediment samples were extracted from 15 fossil ziphiid cranial remains from this area (including the one described herein), referred to eight species. The samples were analysed for their palynological content, leading to improved chronostratigraphic ranges for several species. Seven to eight ziphiid species from the southern North Sea, all from the Messapicetus clade, are proposed to originate from a Serravallian to Tortonian (late Middle to early Late Miocene) interval, and three to six more precisely from the mid- to late Tortonian. Added to the fossil record of other regions, these results point to a Late Miocene radiation of members of the Messapicetus clade, possibly related to the synchronous worldwide decline of several hyper-longirostrine dolphin clades.

Multi-proxy reconstruction of climate changes in the Lower St. Lawrence Estuary, Canada, during the Middle and Late-Holocene

The micropaleontological and palynological content, and geochemical and isotopic composition of a marine sediment core collected off Pointe-des-Monts in eastern Québec, Canada, reveal regional palaeoclimatic and paleoceanographic conditions in the Lower St. Lawrence Estuary over the last ~8200 years. The pollen and spore content allows comparison with the terrestrial palynostratigraphy, whereas dinoflagellate cysts and benthic foraminifera are used to reconstruct sea-surface conditions and bottom water properties, respectively. The dinocyst-based reconstructions indicate shifts between estuarine and oceanic conditions with important changes in sea-surface temperature, salinity, and primary productivity. Both the dinocyst assemblages and the quantitative sea-surface estimates highlight a distinct transition at ca. 4200 cal years BP. It is notably marked by a change towards higher salinity, which suggests reduced freshwater discharge, hence lower precipitation in the watershed, during the Late-Holocene. The isotopic composition (δ18O and δ13C) and assemblages of the benthic foraminifera indicate centennial to millennial frequency variability of bottom water properties, over a general trend towards decreasing temperatures and increasing ventilation from the beginning of the Middle Holocene until the last century. Since then, reverse trends with abrupt warming and decreasing dissolved oxygen content in bottom water have been observed.

New paleoenvironmental and palynostratigraphic data from Solimões Formation (Solimões Basin, Amazonas, Brazil)

The Western Amazon was affected by tectonic events of great impacts, such as the uplift of the Andes during the Neogene. Such events promoted significant changes in the fluvial drainage system, in the climate, as well as in the ecosystems, triggering great irradiation of the Amazonian biota. Marine evidence recorded in the region also influenced the radiation of the biota. Despite advances in the paleoenvironmental and age models proposed for the Western Amazon deposits, we still observe conflicting results and interpretations on these aspects. Thus, here were analyzed the palynological content of three cores aimed to contribute with new paleoenvironmental and biostratigraphic data of the Solimões Formation. We presented new paleobotanical data from the 1AS-5-AM, 1AS-7D-AM, and 1AS-8-AM cores and correlated the biostratigraphic data already published with the data obtained here; were recognized five palynozones (Verrutricolporites, Psiladiporites, Crassoretitriletes, Grimsdalea, and Asteraceae), reaching a range from the early to the late Miocene. The vegetation throughout the sequences studied includes elements of dryland forest next to zones of wetlands vegetation, including flooded forests and swamps; the floristic composition changed over time, predominating flooding vegetation during the early and part of the middle Miocene.

Continental influence on the fertilization of marine waters during the late quaternary in the south of the Brazilian continental margin

This study sought to understand the role of continental influence on ocean productivity along the late Quaternary based on the comparison between continental palynomorphs and paleoproductivity proxies from the marine sediment core SIS188. Retrieved from the slope of the Pelotas Basin at a depth of 1,514 m, the core documents the time interval between 47.8 and 7.4 cal ka BP, including the Marine Isotope Stages (MIS) 3, 2 and 1. The palynological content found in the core SIS188 indicates a typical flora of the southern Brazil highlands, which is at the same latitude as the core. Thus, continental input sources, such as wind-borne dust and discharges from the Mampituba and Araranguá rivers, would more likely account for the palynological content than the Brazilian Coastal Current (BCC). During the glacial intervals (MIS 3 and MIS 2), paleoproductivity (indicated by the proxies coccolith numbers, N Ratio, and TOC content) suggest the intensification of upwelling and transport of wind dust, the latter of which may have transported pollen grains to the core region. There is a concentration decrease of continental palynomorphs at the end of MIS 2, which is accentuated during MIS 1 when the sea level is higher. Paleoproductivity was high during MIS 1, especially from the Holocene onwards, although the concentration of continental-derived palynomorphs decreases sharply, showing that the rise in sea level interferes with the fertilization of marine waters far from the coast by continental input.

The signal of climate changes over the last two millennia in the Gulf of St. Lawrence, eastern Canada

AbstractClimate changes over the past two millennia in the central part of the Gulf of St. Lawrence are documented in this paper with the aim of determining and understanding the natural climate variability and the impact of anthropogenic forcing at a regional scale. The palynological content (dinocysts, pollen, and spores) of the composite marine sediment core MSM46-03 collected in the Laurentian Channel was used to reconstruct oceanographic and climatic changes with a multidecadal temporal resolution. Sea-surface conditions, including summer salinity and temperature, sea-ice cover, and primary productivity, were reconstructed from dinocyst assemblages. Results revealed a remarkable cooling trend of about 4°C after 1230 cal yr BP (720 CE) and a culmination with a cold pulse dated to 170–40 cal yr BP (1780–1910 CE), which likely corresponds to the regional signal of the Little Ice Age. This cold interval was followed by a rapid warming of about 3°C. In the pollen assemblages, the decrease ofPinusabundance over the past 1700 yr suggests changes in wind regimes, likely resulting from increased southerly incursions of cold and dry Arctic air masses into southeastern Canada.

Miocene paleoenvironments and paleoclimatic reconstructions based on the palynology of the Solimões Formation of Western Amazonia (Brazil)

The Neogene was a critical interval in the establishment of the modern geography and biotic composition of Amazonia. Because the region is covered with rainforest vegetation and lacks extensive outcrops, most of the understanding of its geological and evolutionary history relies on the study of rock cores. We studied the Miocene paleoenvironments and paleoclimate of borehole 1-AS-15-AM, drilled in western Amazonia, by analyzing the palynological content of 107 samples from the Solimões Formation. Graphic correlation indicates that the borehole spans palynological zones T13 to T16 (middle to late Miocene). We found 342 morphospecies of pollen and spores, including 280 angiosperm taxa and 62 pteridophyte taxa. Sixteen new species are described: 12 angiosperms and four pteridophytes. Pollen counts are dominated by elements associated with aquatic grasses, palms and ferns that can be associated with the Pebas ecosystem. We also found 11 morphospecies of dinoflagellate cysts and microforaminiferal linings between 115.4 m and 118.95 m that correlate with the middle Miocene marine flooding event of western Amazonia. Average Miocene temperature was estimated to be 24.9 °C (min = 14.40, max = 27.30) while precipitation was 1946 mm/y (min = 1,080, max = 3000), not significantly different from Holocene estimates.

What happened to the organic matter from the Upper Cretaceous succession in Guatemala, Central America?

Organic palynological content in rocks, which commonly occurs in aquatic and terrestrial sediments, is essential for sediment dating, palaeoenvironmental reconstructions and determination of hydrocarbon potential. Unfortunately, the palynological signal may be blurred or even completely destroyed by intra- and post-depositional diagenetic processes. Fossil shells of foraminifera constitute another tool for dating and/or palaeoenvironmental reconstructions and, unlike palynological matter, they are not affected by post-depositional oxidation or thermal alteration. Herein, we present a preliminary palynological study of Upper Cretaceous formations in northern and central Guatemala and we compare it to foraminiferal data. Rocks that are often full of foraminifera, visible without magnification, yielded monotonous palynofacies dominated by black-opaque equidimensional phytoclasts. The palynological signal may potentially be explained by: (i). unfavourable aquatic conditions and habitat; (ii). a high-sedimentation rate combined with organic matter dilution; (iii). organic matter oxidation related to subaerial exposure; (iv). post-depositional weathering and oxidation; (v). thermal conversion of organic matter during burial and/or interaction with volcanic intrusions. Due to the complicated tectonic history of the Yucatán region, all of these factors need more extensive discussion.

Dinoflagellate cyst biostratigraphy of Upper Cretaceous turbiditic deposits from a part of the Bąkowiec section in the Skole Nappe (Outer Carpathians, southern Poland)

Dinoflagellate cysts from turbiditic deposits of the Ropianka Formation in an interval of the Bąkowiec section (Skole Nappe, Outer Carpathians, southern Poland) have been analyzed. This interval, previously attributed to the Cretaceous–Paleogene boundary transition based on planktic and benthic foraminifera, contains organic-walled dinoflagellate cysts (dinocysts) of a latest Campanian age. The difference in age, revealed here between foraminifera and dinocyst findings, is considered as an unresolved dilemma, which is pending some explanations, probably on the basis of further multidisciplinary studies envisaged in the same outcrop. The palynological content is well preserved and rich in dinocyst cyst taxa, including 37 upper Campanian index species among 92 species in total. The dinocyst assemblages observed in this interval are similar to those previously recognized in biostratigraphically well-calibrated sections of Western Europe. The dinocyst marker events enabled a correlation of the studied interval with the Samlandia mayi dinocyst Zone of Slimani (2001a), which is an equivalent to the Belemnitella minor Zone in the northwestern Europe. These dinocyst events include the first occurrences (FOs) of Kleithriasphaeridium truncatum, Nematosphaeropsi philippotii, Samlandia carnarvonensis, Samlandia mayi and last occurrences (LOs) of Corradinisphaeridium horridum, Raetiadinium truncigerum, Odontochitina operculata and Xenascus ceratioides subsp. ceratioides. The palynological content shows significant reworking of Campanian dinocyst taxa and a richness in palynodebris of continental origin, which are likely related to deposition by turbiditic currents.

Marine-lacustrine systems during the Eocene in northern South America – Palynological evidence from Colombia

The Neotropics have experienced a series of marine incursions and the development of lacustrine systems at different intervals during the Cenozoic. One of these events occurred during the middle-late Eocene, an interval of time related to one of the most prolific oil reservoirs in Colombia, the Mirador Formation. Previous studies have identified marginal and marine environments during the late Eocene, especially in the Putumayo basin and the central Llanos foothills of Colombia. However, it is still not clear if the marine incursion is restricted to the late Eocene, or if the incursion started early. To investigate this, we analyzed a stratigraphic section located in the Llanos Foothills of Colombia. We studied the palynological content of 57 samples to stablish a temporal framework for the interval and to estimate the degree of marine, terrestrial and/or lacustrine influence during the deposition. The marine influence is especially marked during the middle Eocene and show a decreasing trend that finally reach values close to zero in the early Oligocene. Differences in the contribution of microforaminifera, dinoflagellate cysts, and freshwater algae are evident throughout the section. The corridor proposed to explain the marine incursion during the late Eocene, was active at least since the middle Eocene.

A New Age Interpretation For The Meluhu Formation In Toronipa Peninsula, The Southeast Arm Of Sulawesi, Indonesia

The offshore area in the northeast of Kendari city, the southeast arm of Sulawesi, is an area with favourable hydrocarbon prospectivity shown by numerous oil and gas seeps in the surrounding coastal area. It is a frontier basin in eastern Indonesia, known as the Manui Basin. An exploration well named Abuki-1 was drilled in 1990 suggested a Miocene transgressive sequence as a potential reservoir and source rock at this basin. However, this unit has no analogous exposure in the onshore area resulting in the lack of study and knowledge of this potential Miocene unit. Therefore, we revisit the sedimentary rocks exposure nearby Abuki-1 well in the Toronipa peninsula to study about its sedimentary facies and palynological contents. These outcrops by previous researchers were included in Toronipa Member of Meluhu Formation, and a Triassic age was suggested for this unit. By contrast, our result shows that these exposures are Middle to Late Miocene in age as indicated by the occurrence of the Florschuetzia group pollens (Florschuetzia trilobata, F. levipoli, and F. meridionalis). The absence of Plio-Pleistocene pollen and spores index fossils (Stenochlaena milnei group, Dacrycarpus imbricatus, and Phyllocladus) supports the Middle to Late Miocene age interpretation. A wave-dominated estuary depositional model is proposed based on the presence of river-dominated, mixed-energy, and wave-dominated facies associations. We suggest that the studied sediments are the outcrop analogues for the Middle to Late Miocene transgressive sequence found in Abuki-1 well. Furthermore, we recommend that these Miocene estuary-fill complexes should have excellent hydrocarbon potential. The reservoir potential is the sand deposits of the fluvial, tidal, washover, and shoreface facies with moderately to well-sorted characteristics. The source rocks candidate is the mud of lagoon, tidal flat, floodplain, and marine offshore facies. Moreover, the Manui Basin, with its Miocene estuarine deposits, requires further study to reveal its hydrocarbon accumulation potential.

Natural variability of the Arctic Ocean sea ice during the present interglacial

The impact of the ongoing anthropogenic warming on the Arctic Ocean sea ice is ascertained and closely monitored. However, its long-term fate remains an open question as its natural variability on centennial to millennial timescales is not well documented. Here, we use marine sedimentary records to reconstruct Arctic sea-ice fluctuations. Cores collected along the Lomonosov Ridge that extends across the Arctic Ocean from northern Greenland to the Laptev Sea were radiocarbon dated and analyzed for their micropaleontological and palynological contents, both bearing information on the past sea-ice cover. Results demonstrate that multiyear pack ice remained a robust feature of the western and central Lomonosov Ridge and that perennial sea ice remained present throughout the present interglacial, even during the climate optimum of the middle Holocene that globally peaked ∼6,500 y ago. In contradistinction, the southeastern Lomonosov Ridge area experienced seasonally sea-ice-free conditions, at least, sporadically, until about 4,000 y ago. They were marked by relatively high phytoplanktonic productivity and organic carbon fluxes at the seafloor resulting in low biogenic carbonate preservation. These results point to contrasted west-east surface ocean conditions in the Arctic Ocean, not unlike those of the Arctic dipole linked to the recent loss of Arctic sea ice. Hence, our data suggest that seasonally ice-free conditions in the southeastern Arctic Ocean with a dominant Arctic dipolar pattern, may be a recurrent feature under "warm world" climate.

The palynology of the Nayband Formation (Upper Triassic) of the Tabas Block, Central Iran

Palynological study of the Upper Triassic Bidestan and Howz-e-Sheikh members of the Nayband Formation of the Tabas Block, Central Iran, revealed relatively diverse and well-preserved assemblages of palynoflora dominated by dinoflagellate cysts and miospores. The two well-known interval dinoflagellate cysts zones of Hebecysta balmei Interval Zone and Rhaetogonyaulax rhaetica Interval Zone were differentiated based on the index dinoflagellate cysts recorded and confirmed the middle Norian-Rhaetian age for the members. The palynological content of these dinoflagellate cyst zones are quite comparable to the Upper Triassic zones of Australia. Biogeographically, the recorded palynomorphs are a mixture of both Eurasian and Gondwanan elements but the middle Norian to earliest Rhaetian elements are more closely related to Gondwanic flora. The co-occurrence of marine and terrestrial elements suggests a shallow marine environment for the members studied.