Non-opaque Phytoclasts Research Articles

Palynofacies analysis of a lacustrine succession: The Maracangalha Formation (Lower Cretaceous), Recôncavo Basin, Brazil

A palynofacies analysis was carried out using samples collected from the Manguinhos, Gameleira, Praia da Falha and Penha outcrops of the Lower Cretaceous Maracangalha Formation, Recôncavo Basin, NE Brazil. Qualitative and quantitative analysis of the organic particles, as well as grouping analysis based on the characteristics of the particles found, were conducted to establish the present database. The organic particles were grouped into amorphous organic matter (AOM); opaque phytoclasts; non-opaque phytoclasts and palynomorphs and four distinct palynofacies were recognized. The palynofacies I (P I), present in the Praia da Falha outcrop, is composed of a high abundance of non-opaque phytoclasts (51.22%), followed by palynomorphs (23.61%). The palynofacies II (P II), occurring in the Penha outcrop, shows a high abundance of non-opaque phytoclasts (71.67%), followed by opaque phytoclasts (12%). The palynofacies III (P III), occurring in the Manguinhos outcrop, consists of a high abundance of AOM (48.07%), followed by opaque phytoclasts (32,6%). The palynofacies IV (P IV), occurring in the Gameleira outcrop, also has a high abundance of AOM (47.05%), followed by non-opaque phytoclasts (28.76%). According to the associations of sedimentary organic matter, essentially represented by particles of continental origin, a lacustrine setting is well characterized, corroborating what has been previously suggested in the literature. The palynofacies interpretation also indicates deposition strongly controlled by fluvio-deltaic input. Overall, the Praia da Falha and Penha outcrops suggest proximity to the depositional source in a high-energy environment. In these localities, the predominance of non-opaque phytoclasts indicates deposition under oxic conditions probably near the lake shore. On the other hand, in the Gameleira and Manguinhos outcrops, the predominance of AOM suggests deposition away from the sediment source in a more distal, low-energy environment, with prevalence of suboxic-to-anoxic conditions.

Multidisciplinary approach as a key for paleoenvironmental interpretation in a Weichselia-dominant interval from the late Aptian Codó Formation (Parnaíba Basin, Brazil)

The presence of the fern Weichselia in a restricted sedimentary interval of a drilling core in the Parnaíba Basin (Brazil) was used as a lead for paleoenvironmental interpretation integrating paleobotanical, palynofacies, palynological, organic petrography and clay mineralogy analyses. The fern paleobiogeography was amplified and its association with terrestrial bryophyte gametophytes (Muscites) indicated depositional conditions corresponding to marginal areas of freshwater bodies subjected to frequent flooding under the general fluvial-deltaic conditions so far accepted for the intermediary portion of the Codó Formation. The high dominance of non-opaque phytoclasts and very scarce autochthonous non-marine palynomorphs pointed to a shallow water body linked to marginal areas of fluvial systems in the river outlets, channel margins in estuarine systems, and/or shallow floodplain lakes connected/open to fluvial canals. The very scarce marine palynomorphs (dinoflagellate cysts) suggest a limited influence from unstable environments on coastal margins or estuarine canals. The terrestrial vegetation surrounding the depositional setting, deciphered by palynological analysis, reflected distinct environmental conditions prevailing simultaneously in 1) humid areas dominated by fern communities, and 2) dry-xerophytic areas dominated mainly by Araucariaceae and Cheirolepidiaceae gymnosperms, both as components of a wider Aptian paleoenvironment within the periequatorial latitudes in South America. The results were supported by clay mineralogy that showed abundance of detrital kaolinite over montmorillonite and suggest the dominance of a climatic humidification process and a less expressive semiarid climate in a regional context.

Kerogen assemblages and δ13CKerogen of the uppermost Pliensbachian–lower Toarcian succession of the Asturian Basin (northern Spain)

The Toarcian Oceanic Anoxic Event (TOAE) is characterised by a perturbation of the global carbon cycle and the widespread deposition of organic matter (OM)-rich strata/sediments in the northern areas of the West Tethys Shelf, in several northern European epicontinental basins. Contrariwise, in the southern areas of the West Tethys Shelf such as western and southern Iberian, and northern Gondwana margins, OM-rich strata/sediments are spatially and temporally restricted. To better understand the relationship between OM production, depositional conditions, and palaeoceanographic controls on the occurrence of OM-rich facies in the northern Iberian margin, we collected and analysed 18 samples from the Rodiles section (Asturian Basin) for geochemical (total organic carbon-TOC, total sulfur-TS, δ13CKerogen, and δ13CWood) and palynofacies analysis.The studied upper Pliensbachian–lower Toarcian succession has TOC values reaching up to 2.9 wt%. The relative dominance of non-opaque phytoclasts and the δ13CKerogen values (average of ~ −24‰) in the lowermost Toarcian (Tenuicostatum Zone) agrees with previous interpretations indicating that this area was located in a dominantly winter-wet climate zone. A change in the kerogen assemblages is observed at the Tenuicostatum/Serpentinum zones boundary (onset of TOAE), related to an increase in amorphous OM (AOM). A slight increase in non-opaque phytoclasts and terrestrial palynomorphs, and a negative δ13CKerogen excursion (reaching −31.5‰) is recorded in the same interval. These observations suggest a increase in continental weathering and fluvial runoff associated with more humid conditions, likely resulting in increased superficial productivity and deposition and preservation of OM under, at least, suboxic conditions. Above the TOAE interval, the δ13CKerogen record (values around −24‰) and the drastic drop in TOC and AOM content indicate that bottom water oxygenation improved after the TOAE.Our results demonstrate a link between early Toarcian climate dynamics and the deposition of OM-rich strata/sediments.

An integrated analysis of palynofacies and diatoms in the Jucuruçu River valley, northeastern Brazil: Holocene paleoenvironmental changes

This study demonstrates the usefulness of palynofacies as a tool for characterizing the origin, transport, and settling of particulate organic matter preserved in fluvial plain sediments and its integration with diatoms for inferring past depositional environments. Palynofacies, diatoms, and organic geochemistry (S, C/S) data from a sediment core (PR07) collected from the Jucuruçu River valley in coastal southern Bahia, northeastern Brazil were used to better understand ecosystem changes that occurred in the region during the last ~7.5k years. Elemental values (S: 0.15–5.9%; C/S: 0.12–41.5) suggest marine and fluvial influences in the valley during the Holocene, and organic matter was derived from freshwater and marine phytoplankton. The presence of heterolithic deposits, brackish/marine diatoms, predominance of amorphous group, non-opaque phytoclasts, pyrite crystals, and marine microfossils suggests that a tidal flat formed during a mid-Holocene sea-level highstand. A fluvial plain developed in the last 5k years, due to marine regression and an increase in fluvial sediment supply to the region.

Organic geochemical, palynofacies, and petrographic analyses examining the hydrocarbon potential of the Kharita Formation (Albian) in the Matruh Basin, northwestern Egypt

A recent study of selected samples from the Cretaceous (Albian) Kharita Formation of Egypt revealed very good to excellent source rock (SR) potential for six intraformational, organic-rich intervals. This work investigates the SR potential of the entire Kharita Formation across the Matruh Basin, using samples from two wells: the Abu Tunis 1X well from the central part of the basin, and the Siqeifa 1X well drilled on the eastern margin of the basin. More strongly reducing conditions were developed in the centre of the basin, and resulted in the deposition of more organic-rich shales by comparison to the less reducing conditions that prevailed on the eastern basin margin, where the shales contain less organic matter. Deltaic intraformational shales and carbonates in the Kharita Formation of Abu Tunis 1X constitute a significant 120 m net of the potential SR. The lower Kharita Formation contains 34 m net shale SR of good to very good/excellent organic richness, yielding values of 1.14–11.59 wt % total organic carbon (TOC). The organic matter has low Hydrogen Index (HI) values (184–389 mg HC/g TOC) and amorphous organic matter (AOM) and relatively high non-opaque phytoclast frequencies indicating mainly gas/oil-prone organofacies (kerogen Types III/II). The upper Kharita is rather important, containing 86 m net shale/carbonate SR that has fair to good organic richness (0.8–1.8 wt % TOC), and lower HI (126–250 mg HC/g TOC), a dominance of non-opaque phytoclasts, and subordinate AOM frequencies, which together indicate gas/oil-prone organofacies (kerogen III/II). In the Siqeifa 1X well, Kharita deltaic intraformational shales and shaley dolostones comprise 80 m net SR, which has mainly fair to good to less very good organic richness (0.8–2.1 wt % TOC), whilst low HI (93–220 mg HC/g TOC), dominance of non-opaque phytoclasts and subordinate AOM indicate gas-prone organofacies (kerogen Type III). A relative upward increase in deposition of lignite and coaly carbonaceous material supports a gas-prone organofacies. Whilst thermal maturity indices only point to immature to early mature (pre- to early oil-window) SRs in both the Abu Tunis 1X and Siqeifa 1X wells, hydrocarbon exploration focussing on this potential source rock may be justified in areas to the southeast of the Matruh Basin, where modelling indicates this unit may have reached the late mature oil- to main gas-generation windows.

Sedimentary organic matter and δ13CKerogen variation on the southern Iberian palaeomargin (Betic Cordillera, SE Spain) during the latest Pliensbachian–Early Toarcian

The Early Toarcian Oceanic Anoxic Event (T-OAE) is characterised by major palaeoenvironmental and palaeoceanographical changes (ocean anoxia, global warming, ocean acidification, among other), and a severe perturbation of the global carbon cycle. Although widespread oceanic anoxia was a significant control on the occurrence of organic-rich facies during the T-OAE in several locations of the northern Tethyan margin, the effects of anoxia, oceanic productivity, and dilution are poorly understood in other worldwide locations, such as the southern Tethyan and Iberian margins.In this study, we report new geochemical [total organic carbon (TOC), total sulphur (TS), total carbonate content (CaCO3), δ13C from kerogen isolates (δ13CKerogen)], palynofacies and thermal maturation data from the Upper Pliensbachian–Lower Toarcian successions in La Cerradura and Fuente Vidriera, External Subbetic domain, Betic Cordillera (SE Spain). The obtained results indicate that these successions have low TOC contents (~ 0.3 wt.%), with TOC reaching up to 0.46 wt.% around the Polymorphum–Serpentinum ammonite zone boundary in La Cerradura. δ13CKerogen negative carbon isotope excursions (CIE) are observed at the base of the Polymorphum Zone, the Pliensbachian–Toarcian Event (Pl-Toa), and base of the Serpentinum Zone (T-OAE). Overall, the low maturity kerogen assemblages are dominated by terrestrial OM and with a minor marine component. Small increments in terrestrial OM, non-opaque phytoclasts, and palynomorphs are observed just before and during the T-OAE in the studied area.During the Early Toarcian, in the External Subbetic domain, accumulation and preservation of OM was low and with a significant terrestrial contribution, similarly to other locations around the southern margins of Iberia and Tethys. The dominance of the opaque phytoclast subgroup, the occurrence of Classopollis, and the relatively more positive δ13C of terrestrial kerogen suggest that OM was mostly sourced from an area characterised by a semi-arid climate (i.e. with pronounced arid periods) during most of the Polymorphum Zone. The T-OAE negative CIE is accompanied by an increase in terrestrial OM, with a slight increase in the non-opaque phytoclast subgroup and terrestrial palynomorph subgroup. The increase of non-opaque phytoclast and terrestrial palynomorphs are in line with the posited enhancements of the hydrological cycle and export of terrestrial OM into marine environments during the T-OAE. This study suggests a link between 13C fractionation during photosynthesis in C3 plants and climate during the Early Toarcian. This link suggests coupling of the water and terrestrial carbon cycles before and during the T-OAE.

Inferências paleoambientais a partir de análise de palinofácies da Formação Hidden Lake (Coniaciano, Cretáceo), Bacia Larsen, Ilha James Ross, Antártica

The James Ross Sub-basin has one of the most complete sedimentary sequences deposited in the Southern Hemisphere. This work aims to characterize the sedimentary organic matter of 32 samples recovered from HL-1 (64 m) and HL-2 (59 m) sections, assigned to Hidden Lake Formation (Coniacian), thus to identify the paleoenvironmental changes. The Amorphous, Phytoclasts and Palynomorphs groups were identified. The sedimentary organic matter was grouped into amorphous material, opaque phytoclasts, non-opaque phytoclasts, continental palynomorphs and marine palynomorphs. The stratigraphic distribution of the groups revealed three intervals (I–III) for HL-1 section and four for HL-2 (A–D). The paleoenvironmental changes were supported based on facies association (AF-1-AF3), continental/marine ratio and principal components analysis. The two sections were correlated as follow: I/A, II/B and III-C-D. The Interval I/A is characterized by high values of woody material. The Interval II/B continues with high values of woody material; however, the highest peak of amorphous organic matter is recorded in HL-1 section, and the lowest abundance of non-opaque in the HL-2. In the III/C-D is recorded a conspicuous increase in marine elements in both sections. A fan-delta paleoenvironment is suggested for both sections. In section HL-1, a large amount of phytoclasts and volcanoclastic detritus suggests more proximal position in the sedimentary body. In the HL-2 section, a large amount of marine elements suggests normal marine removed from active terrigenous inputs.

The Mesozoic–Cenozoic organic facies in the Lower Tagus sub-basin (Lusitanian Basin, Portugal): Palynofacies and organic geochemistry approaches

Studies of the Mesozoic and Cenozoic sequence crossed by the Barreiro-4 borehole provide an improved understanding of the organic matter deposited in the Lower Tagus sub-basin (Lusitanian Basin, Portugal) and the implications for the potential source rock and depositional environment. This study focused on 43 samples (Middle Jurassic to Neogene) that were subjected to palynofacies and organic geochemistry analyses (Total Organic Carbon, Rock-Eval pyrolysis and molecular biomarker analysis). The palynofacies data indicate that the sequence contains mainly phytoclasts (non-opaque phytoclasts). However, the Middle Jurassic samples are dominated by Amorphous Organic Matter (AOM). Continental and/or marine palynomorphs are present in all the samples. The Cretaceous samples are characterized by small amounts of kerogen that have high contents of solid bitumen. The Total Organic Carbon (TOC) content is generally less than 1 wt.%. The Rock-Eval S1 and S2 parameters vary from 0.01 to 3.50 mgHC/g rock and 0.15 to 34.03 mgHC/g rock, respectively, with the highest values corresponding to the Cretaceous samples. The hydrogen index (HI) and oxygen index (OI) values range from 35 to 552 mgHC/g TOC and 4 to 180 mgHC/g TOC, respectively. The Tmax values range from 416 to 437 °C. The biomarker analysis showed that n-alkanes with 15–30 carbon atoms are present and usually have a unimodal distribution with a predominance of low to medium molecular weight compounds. The CPI values range between 0.63 and 3.65, and the pristane/phytane ratios vary between 0.48 and 1.64, indicating alternation of oxic–anoxic conditions along the sequence. The distribution of terpanes shows small amounts of tricyclic and tetracyclic terpanes in most of the samples (except for some Cretaceous samples) and a predominance of pentacyclic terpanes. The amount of 17α (H),22,29,30-trisnorhopane (Tm) usually exceeds the amount of 18α (H),22,29,30-trinorneohopane (Ts). The 20S/(20S + 20R) and αββ/(ααα + αββ) ratios of the C29 steranes generally have values below the range of equilibrium, indicating an immature stage of the OM.

Palynofacies and stable C and N isotopes of Holocene sediments from Lake Macuco (Linhares, Espírito Santo, southeastern Brazil): Depositional settings and palaeoenvironmental evolution

Particulate organic matter in sediments constitutes a valuable proxy for paleoenvironmental reconstructions. A 192cm lacustrine sediment core (~7521calyr. 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 106cm, ~7521calyr. B.P. to ~7054calyr. 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 65cm, ~7054calyr. B.P.—interpolated age to ~4847calyr. 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 27cm, ~4847calyr. B.P. to ~3800calyr. 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 0cm, <~3800calyr. 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.

Organic facies of the Oligocene lacustrine system in the Cenozoic Taubaté basin, Southern Brazil

Abstract A quantitative study of palynofacies and organic facies was carried out in the Cenozoic sedimentary succession of the Taubate basin. The palaeoenvironmental distributions of particulate organic components were examined in relation to various potential controlling factors (lithology, depositional environment, and stratigraphic sequence). About 30 samples were analyzed from a single borehole drilled in Sao Paulo State. This involved rigorous kerogen counts supported by 30 TOC and sulphur, 20 Rock-Eval pyrolysis and 20 biochemistry analyses. In the studied area the Oligocene deposits are approximately 600 m thick. Data was obtained by counting 300 to 500 kerogen particles per sample, and then recalculating the percentages of the different constituent groups (phytoclast, palynomorph, and amorphous organic matter — AOM). The kerogen assemblage is palynomorph-dominated (> 70%), consisting mainly of freshwater lacustrine algae ( Pediastrum and Botryococcus ). Non-opaque phytoclasts predominate in most of the kerogen samples. However, significant variations in the proportion of biostructured and non-biostructured brown phytoclasts occur in some intervals. The fluorescent AOM content occurs in some levels and is composed of two main components: an intensively fluorescing structureless organic matter, which also has high lipid and protein content indicating a probable bacterial origin for the organic matter (microbial mats); and terrestrially-derived amorphous organic matter, which has been reworked to a different extent exhibiting a high content of carbohydrates. Comparison of the mean kerogen assemblages from different lithologies revealed that the finer-grained lithologies generally have higher palynomorph percentages, whereas coarser-grained lithologies present higher percentages of phytoclasts, emphasizing the important role of grain size in organic-matter distribution. The TOC content is generally less than 10%, but reaches as high as 44% in some intervals, due mainly to the presence of coaly seams. The T max , Spore Coloration Index, and spectral fluorescence measurement values obtained from these samples indicate a low maturity stage. The integration of these results, together with the organic facies parameters, indicate that the analyzed sedimentary section represents a variation from a freshwater lacustrine environment with an oxidant regime to a restricted saline, lacustrine environment with a dysoxic–anoxic regime. There was an excellent correlation between the optical and geochemical parameters.

PALINOFÁCIES E PROCESSOS DEPOSICIONAIS EM SEDIMENTOS DE FUNDO DA LAGOA DOS QUADROS, PLANÍCIE COSTEIRA DO RIO GRANDE DO SUL, BRASIL

This study is based on the qualitative and quantitative characterization of particulate organic matter (palynomorphs, opaque phytoclasts, non-opaque phytoclasts and amorphous organic matter-AOM) and statistic methods of analysis from bottom sediments of Quadros Lake, of Rio Grande do Sul Coastal Plain. These data provided the identification of five palynofacies, with paleoenvironmental significance. Palynofacies A, with equivalent particulate organic matter among the four groups is associated to processes of gradational suspension; Palynofacies B and C represent fluvial influx control, with percentual differences between the groups; Palynofacies D, predominantly comprised of AOM and opaque phytoclasts is correlated to suspension and traction processes; suspension processes are attributed to Palynofacies E, with AOM and palynomorphs predominance. The results have shown the potential of palynofacies analysis through the interpretation and reconstitution of environments.

Análise de palinofácies em sedimentos holocênicos da lagoa dos Quadros, Rio Grande do Sul, Brasil

n PALYNOFACIES ANALYSIS IN HOLOCENIC SEDIMENTS OF QUADROS LAGOON, RIO GRANDE DO SUL PLAIN, BRAZIL. The interpretation of environmental changes during the Holocene on the North Rio Grande do Sul Coastal Plain, is based on the core QU-RS-B09 of Quadros lagoon record. The palynofacies analysis was carried out in 41 sedimentary samples along the 405 cm of the core, dated of 6.700 - 40 years BP at 375 cm deep and in 4.870 - 40 years BP 75 cm deep. Q-mode cluster analysis provided the identification of six groupings which stratigraphically plotted allowed the characterization of three intervals with palynofacies features corresponding to different environments in the holocenic evolution of the lagoon. Interval 1A, characterized by a palynofacies predominantly comprised of Amorphous Organic Matter (AOM), opaque and non-opaque phytoclasts, is associated to a Lagoon System in a Transgressive Phase. Interval 1B, whose palynofacies corresponds to opaque phytoclasts, MOA and non-opaque phytoclasts characterizes the Lagoon System and the Lagoon Maximum Transgressive (PGMT). Interval 2, predominantly comprised of AOM and Botryococcus braunii, characterizes the Lagoon System in a Regressive Phase, having an increase of pollen grains and spore percents towards the top, which characterizes conditions similar to the present coastal lake.