Palynofacies Assemblages Research Articles

Palynostratigraphy of the Mississippian-Pennsylvanian boundary in the Tyler Formation, Williston Basin, USA: Implications for organic matter-rich source rocks and paleoenvironmental reconstruction

The Carboniferous was a period of intense environmental perturbations, climate changes between greenhouse and icehouse, eustatic sea level change, and accumulation of organic carbon-rich sediments. At this time, the Tyler Formation was deposited in the midcontinent USA. A detailed palynological analysis of the Tyler Formation revealed a highly diverse assemblage of spores with minor pollen content, represented by 100 species belonging to 51 genera. Stratigraphically constrained spores and pollen grains were used to construct three interval zones of middle-late Chesterian (late Viséan-Serpukhovian) to early Morrowan (middle Bashkirian) ages. The stratigraphic position of the Mississippian-Pennsylvanian boundary was determined in the lower Tyler Formation based on the last appearance of typical forms of the late Chesterian, including Tripartites vetustus, Knoxisporites triradiatus, Knoxisporites stephanephorus, Densosporites diatretus, and Schopfipollenites acadiensis, compared to the first appearance of early Morrowan Crassispora kosankei, Cirratriradites saturnii, Radiizonates aligerens, and Raistrickia saetosa. Palynofacies analysis and statistical clustering of the Tyler Formation showed three palynofacies assemblages. PFA-1 showed moderate relative abundances of phytoclasts and AOM, suggesting deposition close to fluvio-deltaic and shallow marine environments, while PFA-2 exhibited high abundances of phytoclasts, mostly of opaque wood, reflecting deposition in active river-dominated delta plains. PFA-3 showed the highest abundances of AOM, suggesting deposition in a shallow marine environment. Organic petrography and geochemistry data indicate that the Tyler Formation is one of the best source rock intervals throughout the midcontinent USA. Based on organic matter richness, the Tyler Formation is subdivided into three groups. The first group has TOC contents higher than 10 wt% of kerogen Types III, mixed II/III, and II with excellent hydrocarbon generation potential. The second group has TOC content in the range of 2–10 wt% of kerogen Types III, mixed II/III, and II, and fair to excellent hydrocarbon generation potential. The third group shows organic matter richness with TOC content below 2 wt% with good organic matter richness and kerogen Types III to IV, and poor to fair hydrocarbon generation potential. The organic matter thermal maturity is evaluated based on Tmax and VRo% values, suggesting that all samples of Tyler Formation are in the early to late stages of the oil window. However, care should be considered when assessing a mature source rock because the kerogen typing and generation is based on present-day TOC, S2, and HI rather than their original values.

The Early Aptian Oceanic Anoxic event (OAE-1a) of the uppermost M'Cherga formation of northern Tunisia: Geochemical characterization and inferred petroleum potential

The Early Aptian organic-rich deep marine deposits of the upper Member of the M'Cherga Formation (Valanginian-Aptian) of northern Tunisia were studied based on a multidisciplinary approach including biostratigraphy, sedimentology and organic geochemistry. This study is based on the analysis of 128 samples collected from three sections (Oued Bazina, Djebba and Tel Ghozlene) selected from the salt dome zone (SDZ) and one section of Jebel Oust, situated westward of the Tunisian range. This work is supplemented by previous research undertaken on Oued Zarga and Jebel Ammar sections. Taxonomic analysis of previous and new data (ammonites and planktonic foraminifera) indicate that three informal lithological units rich in organic matter (U1, U2 and U3) are of Early Aptian age, covering both Blowiella blowi and Leupoldina cabri planktonic foraminiferal zones and indiscriminate Lowermost Aptian to the Deshayesites deshayesi – Dufrenoyia furcata ammonite Zones interval.The Rock-Eval analytical results indicate that the studied Early Aptian strata are relatively rich in total organic carbon (TOC) content with values reaching 4.6 % within the U3 (Leupoldina cabri biozone). The latter occurring in the different studied sections constitutes an important deepening phase related to a global sea-level rise testified by the development of well laminated platy limestones containing abundant ammonites and radiolaria. This unit (U3), covering Leupoldina cabri planktonic foraminiferal zone and Deshayesites deshayesi to Dufrenoyia furcata ammonite Zones interval records the Oceanic Anoxic Event -1a (OAE-1a).The palynofacies assemblages show that the organic matter is mainly represented by amorphous particles. The Tmax values ranging from 437 °C to 456 °C (Mean Tmax: 446 °C) and the measured vitrinite reflectance ranging from 0.79 to 1.03 %, indicate that most samples are early mature except for those of the Tel Ghozlene (TG) section which are within the peak oil-generation-window. Lateral facies and thickness variation, in addition to the organic matter distribution throughout the studied domains, strongly suggest the imprint of salt tectonics both on the sedimentological pattern and associated anoxia during the Aptian. Maturation of the organic-rich facies occurred during the Upper Cretaceous-Paleogene compressional phase and associated salt dome remobilization. Source rocks, developed in the Upper Member of the M'Cherga Formation, are attributed to the OAE1a Event and should be considered when reviewing the petroleum potential of conventional and unconventional resources in northern Tunisia.

Late Albian-Cenomanian paleoenvironmental and paleoclimatic reconstructions in northeastern Gondwana: Palynological perceptions

The late Albian-Cenomanian (100.5–93.9 Ma) is considered a greenhouse world without permanent ice caps and with high eustatic sea levels. The high sea-level led to the flooding of low-lying coastal plains and the formation of extensive shallow shelf seas. Depositional conditions and ecosystems at these marginal and shallow shelf settings were affected by changes in environmental conditions, such as climate and vegetational ecosystems in surrounding regions. This study conducts palynomorph and palynofacies and lithofacies analysis of fifty-nine cutting samples from the North Qarun-1x well in the Gindi Basin (North Western Desert, Egypt) to assess the evolution of depositional and paleoenvironmental conditions as well as paleo-vegetation pattern in response to changes in climate and sea level. The sediment succession comprises the upper Albian to Cenomanian upper Kharita and Bahariya formations and Abu Roash G Member. Biostratigraphic analysis of palynomorph composition led to define seven interval zones of upper Albian-Cenomanian. At this time, Egypt was inundated by the southern margin of the Tethys Ocean, which led to the deposition of thick siliciclastic and carbonate facies in a marginal marine depositional environment. Statistical cluster analysis of particulate organic matter (POM) allowed three palynofacies assemblages (PFA-1 to PFA-3) to be recognized, indicating oscillating depositional conditions that shifted between fluvio-deltaic to marginal shallow marine, proximal, and distal inner neritic shelf environments. PFA-1 comprises the highest proportions of total phytoclasts, indicating fluvio-deltaic to marginal shallow marine conditions. PFA-2 is dominated by moderate abundances of AOM and phytoclasts, characterizing a proximal inner neritic shelf environment. PFA-3 consists of a slightly higher concentration of AOM compared to phytoclasts, indicating a distal inner neritic shelf environment with diminished terrestrial input and increased abundances of marine microplankton. Organic palynomorphs are abundant in mid-Cretaceous strata of northern Egypt. Abundant records of humidity indicators, mainly fern spores, along with other gymnosperms (mainly Taxodiaceae and Araucariaceae) compared to low aridity indicators of gnetalean Elaterates and Ephedroids along with non-gnetalean Classopollis suggest predominantly warm and humid conditions. Two intervals in the lower part of the Bahariya Formation and in the middle part of the Abu Roash G Member showed moderate to high abundances of aridity indicators and thus, warm arid to semi-arid climate events during the early and late Cenomanian.

Depositional environments and plant communities in the exceptional context of the Kungurian megacaldera of the Athesian Volcanic Group (Southern Alps, N-Italy)

We used a combined approach (lithofacies and palynology) and multivariate analyses to reconstruct the different depositional environments and changes in the plant communities throughout the middle to late Kungurian in the tropical Pangea. The late Paleozoic terrestrial biotas underwent changes under the pressure of a general aridification trend and a warming event that changed biota composition favoring drought-tolerant taxa during the Artinskian. Few studies integrate the different terrestrial ecosystem components to reconstruct palaeoenvironments and climate changes throughout the Cisuralian (early Permian). We analyzed several sedimentary successions of different stratigraphic positions intercalated in well-dated volcanic units of the megacaldera of the Athesian Volcanic Group (Southern Alps, northern Italy). The obtained palynofacies and quantitative sporomorph records with an exceptional high resolution (∼10 Ma) evidence a palaeoenvironmental/climatic change in the plant communities from the middle to the late Kungurian. The late Kungurian shows a higher diversity in the plant communities with a dominance of seed ferns and a higher relative abundance of xeromorphic-hygromorphic sporomorph taxa. This suggests the presences of more stable and putatively more humid environmental conditions in respect to the middle Kungurian. Furthermore, a direct comparison between lithofacies and all primary components of the palynofacies assemblages permits to characterize lacustrine and alluvial depositional environments since these studies are underrepresented for terrestrial environments.

Upper Cretaceous (Cenomanian) palynostratigraphy and palynofacies of the Shushan Basin, North Egypt

This study provides an updated quantitative analysis and prospective paleoenvironment reconstruction of the Tut oilfield, Shushan Basin, North Egypt to evaluate the hydrocarbon reservoirs in space and times for further development plans and modeling in the Tethyan region. Two sporomorph interval zones (Classopollis brasiliensis and Afropollis jardinus), and one total foraminiferal Range Zone (Thomasinella punica) are proposed. Three palynofacies assemblages are differentiated using cluster analysis of the different palynofacies parameters. The paleoenvironmental conditions during the Cenomanian were reconstructed. Palynofacies assemblage I of the Baharyia Formation suggests a marginally dysoxic-oxic basin environment with a common occurrence of ostracods and terrestrial organic matter, while palynofacies assemblage II reflects the high abundance of dinoflagellate cysts, suggesting a suboxic-anoxic middle neritic environment. Palynofacies assemblage III of the upper part of the Abu Roash G Member represents a relatively deep water inner-middle neritic environment. Three 3rd order significant sequences separated by two hiatus surfaces (Ce3 and Ce4) are described and correlated with the global eustatic sea-level. The hydrocarbon evaluation results show that the samples from the Abu Roash G Member contain oil-prone material of kerogen type II, while the samples of the Baharyia Formation are characterized by kerogen type III (gas-prone). Spore coloration analysis reveals that the samples from the studied units are too immature to produce gas or oil and are ineffective as sources of hydrocarbons.

The Bowland Shale Formation in the Blacon Basin: palaeoecology and resource potential

Abstract We evaluated the unconventional hydrocarbon potential of the Holywell Shale Formation, a lateral equivalent of the Bowland Shale Formation deposited in the Blacon Basin. Two cores with Arnsbergian–Chokierian and Kinderscoutian (Namurian, Late Mississippian–Early Pennsylvanian) ages from the Ellesmere Port 1 borehole were sampled for palynological, stable isotope, Rock-Eval 6 pyrolysis and ichnofacies analyses. The study was designed to provide boundary conditions for parameters that are under-represented in the public domain and hamper accurate resource assessments: thermal maturity (through mean random vitrinite reflectance, R r ), present-day organic matter content, kerogen type, original hydrogen index and original organic matter content. Our results show that the Arnsbergian Core 2 has been buried to a depth equivalent to the bottom of the oil window to the top of the gas window (% R r = 1.15%–1.29%). The Kinderscoutian Core 1 is too immature to have generated any natural gas (% R r = 0.91–1.03%). Furthermore, kerogen typing and ichnofacies analysis show that the Bowland Shale Formation is very heterogeneous, with organic matter originating from terrestrial and marine sources. Five palynofacies assemblages are described that range in basin setting from proximal and oxic to distal and anoxic with evidence of episodic connections to the open ocean. The combination of heterogeneity and low thermal maturity restricts the thickness of the Bowland Shale Formation in the Blacon Basin that is prospective for unconventional hydrocarbons. Our results show that these Carboniferous mudstones should not be treated as uniform units with uniform composition and maturity in basin modelling and resource estimates. This undoubtedly has repercussions for future exploration because the contrasting composition and density of the materials making up the Bowland Shale Formation may complicate extraction, while the thermal maturity window significantly narrows the prospective interval.

Newly discovered Botryococcus-rich source rocks in the western Qaidam Basin, NW China and their implications for shale oil exploration in saline lacustrine basins

Owing to the high hydrocarbon content and photosynthetic efficiency of phytoplankton, planktonic microalgae account for the main source of petroleum hydrocarbons in marine and continental petroliferous basins. Therefore, the presence of algal residues in such basins is considered an important indicator of high-quality hydrocarbon source rocks. The southwestern region of the Qaidam Basin, characterized by lacustrine deposits from the Paleogene, has substantial petroleum resources. However, studies on the development of source rocks and the mechanisms involved in their organic matter enrichment are insufficient, thus hampering ongoing shale oil exploration efforts. Herein, abundant Botryococcus fossils were discovered in the main source rocks of the upper member of Xiaganchaigou Formation of Paleogene in Southwest Qaidam, accounting for >50 % of the total organic matter content. The palynofacies assemblages reflected relatively distal and oxygen-rich sedimentary environments. The algae-rich rocks usually exhibited distinctive laminated structures alternately composed of quartz-feldspathic, clay and carbonate laminae, indicating periodic climate fluctuations. The Botryococcus, which was mainly preserved in the coarse-grain quartz-feldspathic laminae, probably reflected heavy precipitation conditions and subsequently high nutrient inputs. Finally, the oxygen-rich, low salinity and eutrophic water was likely taking form which benefit the growth of these hydrobiontic algae. These algal-rich shales exhibited typically high hydrogen index (IH) and total organic carbon (TOC) values, indicating their high hydrocarbon-generation potential. Thus, they are important marker beds for high-quality source rocks in petroliferous basins. Concurrently, the coarse-grained detrital mineral laminae displayed excellent reservoir physical properties, probably providing sufficient reservoir space for planktonic algae-derived liquid hydrocarbon. Therefore, these Botryococcus-rich source rocks might represent important targets for ongoing shale oil exploration.

Deciphering the laminated botryococcus-dominated shales in saline lacustrine basin, Western Qaidam Basin, NW China: Implications for shale oil potential

Given the high lipid content and potentially huge biomass, the explosive occurrence Botryococcus is regarded as a significant marker of high-quality oil source rocks in petroliferous basins. However, they are rarely discovered in saline lacustrine source rocks, and the formation mechanism of these alga-rich shales remains uncertain. In this study, abundant Botryococcus fossils were firstly found, accounting for an average of 43.5% of the total organic debris from the upper Xiaganchaigou Formation in the Yingxiongling and Zhahaquan hydrocarbon-rich sags of the western Qaidam Basin. The Botryococcus-dominated palynofacies assemblages were usually interpreted as derived from a distal oxic shelf environment. These Botryococcus-dominated sediments were characterized by a perfect laminated texture and composed of detrital, carbonate, and clay laminae. The Botryococcus fossils exclusively occur in the detrital laminae with large-grained quartz and feldspar and low carbonate content, possibly reflecting increased river input under relatively heavy precipitation. The cyclothymic deposition between these Botryococcus-rich detrital laminae and other laminae probably indicates that sufficient terrestrial nutrient inputs and lake salinity decreases driven by periodic heavy precipitation result in Botryococcus bloom under fresh or brackish water environments. These Botryococcus-dominated shales in the western Qaidam Basin usually have a high oil-prone hydrocarbon generation potential, as evidenced by their organic geochemistry parameters. These sediments have biomarker features extremely similar to crude oil with a high relative abundance of C20–C24 tricyclic terpanes, phytane, C27ααR sterane, and a unimodal distribution of n-alkanes with the maximum at n-C18. Therefore, these Botryococcus-dominated shales are possibly important oil sources of these prolific oil sags. Additionally, these high-quality source rock sequences can reach a few tens of meters in thickness and evidently have significance for future shale oil resources.

Non-pollen palynomorph and palynofacies assemblages from the Lower Cretaceous of Iraq: A glimpse into palaeobiology and palaeoenvironment

Non-pollen palynomorph and palynofacies assemblages from the Lower Cretaceous of Iraq: A glimpse into palaeobiology and palaeoenvironment

Organic Matter Assessment and Paleoenvironmental Changes of the Middle Jurassic Main Source Rocks (Khatatba Formation) in the North Western Desert, Egypt: Palynofacies and Palynomorph Perspectives

The Middle Jurassic in the north Western Desert, Egypt, was a time of complex tectonics and increased environmental perturbations attributed to the predominant sedimentation of organic carbon-rich fine siliciclastic and carbonate deposits of the Khatatba Formation. Although some studies have addressed the hydrocarbon potential and source rock characteristics of the Khatatba Formation, a regional-scale investigation of the prevalent paleoenvironmental conditions and organic matter characteristics is still necessary. In this study, the Khatatba Formation is investigated for detailed palynofacies analysis and palynomorph composition to assess organic matter kerogen types and reconstruct the depositional paleoenvironmental patterns on a regional scale. For this purpose, 116 drill cuttings were collected from five wells in the Matruh, Shushan, and Dahab-Mireir Basins. Moderately diverse assemblages of spores, pollen, and dinoflagellate cysts are reported. Age-diagnostic dinoflagellate cysts, including Adnatosphaeridium caulleryi, Dichadogonyaulax sellwoodii, Korystocysta gochtii, Wanaea acollaris, and Pareodinia ceratophora, along with occasional records of Systematophora areolate and Systematophora penicillate, defined a Bajocian–Callovian age. Based on particulate organic matter (POM) composition, four palynofacies assemblages (PFAs) are identified. PFA-1 is the most common within the Khatatba Formation in the five studied wells. It contains high proportions of phytoclast fragments versus low contents of amorphous organic matter (AOM) and palynomorphs and is defined by a gas-prone kerogen Type III. PFA-2 is comprised of moderate abundances of AOM and phytoclast characteristics of oil-prone kerogen Type II. PFA-3 is dominated by phytoclasts and moderate to low proportions of AOM and palynomorphs of kerogen Type III, whereas PFA-4 consists of AOM and palynomorphs defining kerogen Type II. PFA-1 indicates predominant deposition in proximal active fluvio-deltaic sources to marginal marine conditions with enhanced contributions of terrestrial/riverine influx. PFA-2 and PFA-3 reveal deposition under an enhanced dysoxic to anoxic proximal inner neritic shelf due to the abundant occurrences of spores and coastal to shallow marine dinoflagellate cysts. PFA-4 suggests deposition under enhanced suboxic to anoxic distal inner neritic conditions because of enhanced AOM and abundant proximate and some chorate dinoflagellate cysts. Thus, the Middle Jurassic experienced a predominantly marginal to shallow water column in this part of the southern margin of the Tethyan Ocean where the Matruh, Shushan, and Dahab-Mireir Basins were located.

Palynostratigraphy and paleoenvironmental inferences of the Jurassic successions, Darag Basin, Gulf of Suez, Egypt

The present study shows the advantage of the palynostratigraphy and paleoenvironmental inferences concepts in subdividing and interpreting the depositional environment of the Jurassic rocks, depending on two sections in two boreholes drilled in the Darag Basin, Egypt. Six Jurassic rock units representing the mixed siliciclastic and carbonate sediments were recognized from top to base; the Tauriat, Arousiah, Kehailia, Safa, Shusha and Rajabiah formations. The palynomorph assemblage associated with moderately diversified dinoflagellate cysts and fewer sporomorphs, show poor to fair preservation. About 20 dinoflagellate cysts, 8 pollen, and 3 pteridophytic spore species have been recorded. The Jurassic rocks are originated from the late Jurassic (early Oxfordian) and early (Toarcian - Aaleneian) based on the recovered marker taxa. The studied sections are differentiated into six biozones, Systematophora sp. (Callovian-Oxfordian), Gonyaulacysta jurassica (Callovian), Dichadogonyaulax sellwoodii (Late Bathonian), Sentusidinium sp. (Early Bathonian), Pareodinia ceratophora (Bajocian) and Psilate spores, Classopollis and Sphaeripollenites Acme Zone (Toarcian-Aalenian).According to the Particulate Organic Matter (POM) composition in the studied wells, the palynofacies assemblages led to identifying three depositional settings, the palynofacies −1 (PFA-1), which is characterized by opaque phytoclasts and high volume of spores and pollen grains was deposited in a marginal shallow-marine environment during a relative sea-level fall. The PFA-2 is composed of brown phytoclasts, moderate Amorphous Organic Matter (AOM) with pollen grains and dominated dinocysts. It was deposited during a slight sea level rise in a proximal inner neritic environment. Simultaneously, the PFA-3, which was dominated by AOM and dinoflagellate cysts with moderate brown phytoclast content, was deposited as a distal inner neritic environment during a relatively high relative sea level.

Paleoenvironmental, paleoclimatic, and organic matter assessment of the hybrid Kharita Formation (Albian) in the Abu Gharadig Basin, Egypt: Integration between palynology, organic petrography, and organic geochemistry

The Early Cretaceous (Albian) was a time of equatorial to polar temperature warming and increased environmental perturbations of the global carbon cycle and oceanic anoxia, which resulted in the widespread accumulation of organic carbon-rich sediments. During the Albian, the southern margin of the Tethys Ocean was characterized by marginal to shallow water conditions with minor phases of enhanced stratification and bottom water anoxia in northern Egypt. At this time, accumulation of the thick siliciclastic succession of sandstones versus shale intercalations of the Kharita Formation took place in the Abu Gharadig Basin. The Kharita Formation is investigated for palynological composition and palynofacies analysis, organic matter characterization, hydrocarbon generation potential, and thermal maturity assessment based on 30 and 26 drill cuttings samples from the BED2-3 and BED2-1x wells, respectively. A rich palynological assemblage of herbaceous hygrophilous plants, including pteridophyte spores and water ferns, along with Elaterates and Afropollis pollen indicated warm humid climate conditions. Furthermore, abundant occurrences of Araucariaceae and Cheirolepidiaceae, including Araucariacites, Inaperturopollenites, and Classopollis, reinforcing warm climatic conditions and their climax in areas near coastal vegetation. Statistical cluster analysis identified two palynofacies assemblages (PFA) based on stratigraphic variation in the particulate organic matter (POM). The PFA-1 characterized all samples of the BED2-3 and some intervals of the BED2-1x wells and comprised moderate abundances of phytoclasts and amorphous organic matter (AOM) that defined a kerogen Type II, whereas the PFA-2 was recorded only in the BED2-1x well and is dominated by phytoclast fragments of kerogen Type III. The geochemical screening revealed, based on the low average values of TOC (1.2 wt%), S2 (1.8 mg HC/g rock), and HI (146 mg HC/g TOC), that the Kharita Formation is characterized by a kerogen Type III of gas-prone hydrocarbon but with low generation potential. Tmax and vitrinite reflectance measurements along with greenish-to golden-yellow liptinite macerals indicated that the thermal maturity of preserved organic matter is still in the immature to the early mature stage of the oil window. Inconsistency in kerogen types between PFA-1 and geochemical deductions was interpreted in terms of microscopic investigations of the recovered AOM. Morphologic characteristics observed that most AOM particles were of terrigenous origin due to the impact of biodegradation and transformation of phytoclast particles into AOM, confirming a kerogen Type III of gas-prone hydrocarbons instead of Type II that was elucidated by palynofacies ternary diagrams. The occurrence of coaly matter in the BED2-1x infers closer proximity to fluvio-deltaic sources during deposition of the lower part of the Kharita Formation than in the BED2-3.

Palynomorph composition and palynofacies analysis of the Cenomanian Bahariya Formation in the north Western Desert of Egypt: Depositional palaeoenvironment and sequence stratigraphic implications

Abstract This study investigates the Bahariya Formation using 39 rock-cutting samples from the Abu Gharadig Basin in the north Western Desert, Egypt. An approach combining palynomorph composition and palynofacies analysis with lithological composition and geophysical gamma ray log values is used to assess biostratigraphic age constraints, prevalent depositional palaeoenvironments, and relative sea level changes. A moderately diverse assemblage comprised mainly of terrestrial palynomorphs versus minor content of marine palynomorphs is identified. Marker spore and pollen taxa are used to name three interval zones of early Cenomanian, and early-middle Cenomanian ages. Quantitative distribution of particulate organic matter using cluster analysis reveals two palynofacies assemblages: an older assemblage dominated by phytoclasts (mainly wood particles); and a younger assemblage characterised by moderate abundances of amorphous organic matter and phytoclasts. Palynofacies analysis suggests deposition of the Bahariya Formation in fluvio-deltaic to inner neritic shelf environments. Based on the pronounced stratigraphic variations in the particulate organic matter composition, including terrestrial:marine palynomorph ratio, lithological and gamma-ray log data, three complete transgressive-regressive sequences and one incomplete sequence and their systems tracts are defined. The transgressive-regressive trends reflect 3rd order sequences. Additionally, successive changes in relative sea level indicate a continuous rise at the topmost part of the succession.

Depositional setting and organic matter characterization of the Upper Devonian Antrim Shale, Michigan Basin: Implications for hydrocarbon potential

During the Late Devonian, the Michigan Basin in the Eastern Interior Seaway was characterized by phases of well-developed bottom water anoxia, triggering extensive accumulation of organic matter-rich black shales. Palynological analysis for paleoenvironmental reconstruction and biostratigraphy of the Upper Devonian rocks has been previously performed in other basins of eastern North America, but it is lacking in the Michigan Basin. Here, the Upper Devonian Antrim Shale Formation is investigated for biostratigraphic, paleoenvironmental, and sea level reconstructions, organic matter characterization, and source rock potential. 35 core samples from three drill holes across the Michigan Basin spanning the Norwood, Paxton, Lachine, and Upper members. Palynological analysis showed a moderately diverse assemblage of 31 genera represented by 53 species of relatively well-preserved prasinophyte phycomata and acritarchs, with sparse records of plant spores and freshwater algae. Based on marker prasinophytes and acritarchs, an age of late Frasnian was assigned to the Norwood and Paxton members, while an early Famennian age was proposed to the Lachine and Upper members of the Antrim Shale. Two palynofacies assemblages (PFA) were identified from the variation in the particulate organic matter (POM) composition, both of which indicate deposition in a distal inner neritic shelf environment, but the PFA-2 took place in slightly shallower conditions than the PFA-1. Geochemical screening indicated high organic matter content (up to 25 wt%, avg. 8.5 wt%) and excellent hydrocarbon generating potential of kerogen Type II for the Norwood, Lachine, and Upper members. Only the Paxton Member was dominated by poor to fair organic richness (<0.6 wt%) and low hydrocarbon potential with a mixed Type II/III kerogen. Organic petrography indicated that the dominant organic matter assemblage consists mainly of unicellular marine Tasmanites telalginite and Leiosphaeridia, followed by solid bitumen of the initial oil type. Thermal maturity, determined from VRo-eq and Tmax, indicated that all samples are in the oil window, except for some intervals in the Paxton Member.

The palynology of the Kimmeridge Clay and Carstone Formations (Upper Jurassic–Lower Cretaceous) at Middlegate Quarry, North Lincolnshire, UK, and its biostratigraphical and palaeoenvironmental significance

At Middlegate Quarry, the Carstone Formation is a c. 0.8 m thick unit of oolitic ferruginous sandstone. It rests unconformably on the lower Kimmeridge Clay Formation (KCF) and is overlain by the Hunstanton Formation (Red Chalk) with an apparently gradational junction. Marine dinoflagellate cysts (dinocysts) are present at a concentration of 9520 to 13 600 specimens per gram in the 0.15 m of KCF below the unconformity, and include taxa that confirm ammonite evidence for the intra-Lower Kimmeridgian Substage (Upper Jurassic, Cymodoce Ammonite Zone). A rich recovery of well-preserved Lower Cretaceous palynomorphs is reported for the first time from the overlying Carstone. Reworking of mudstone from the KCF into the formation appears to have provided a local argillaceous preservation matrix at Middlegate. The basal 0.15 m is dominated by palynomorphs derived from the KCF but the interval from 0.15 to 0.55 m above the unconformity mainly contains indigenous Lower Cretaceous palynomorphs. Dinoflagellate cysts are present in the Carstone at an average concentration of 454 specimens per gram, and include taxa that probably have stratigraphical range bases above the Aptian–Albian stage boundary: Cyclonephelium compactum, Cyclonephelium intonsum, Endoscrinium heikeae , Leptodinium cancellatum (consistent), Stephodinium coronatum and Stephodinium spinulosum . The additional presence of taxa with range tops/event tops in the Lower Albian Tardefurcata Ammonite Zone (common Cauca parva , frequent Canninginopsis monile and Kleithriasphaeridium eoinodes , and rare Dingodinium albertii, Discorsia nannus and Kiokansium prolatum ) indicate probable assignment to this zone. The new palynological data support previous macrofossil (brachiopod) study of the Carstone at Middlegate and nearby Melton Bottom Quarry which tentatively assigns its highest part to the Tardefurcata Zone. The palynological and palynofacies assemblages are interpreted to confirm a relatively proximal to shoreline site of deposition, possibly inner to middle neritic. Supplementary material: Quarry photographs and a palynological distribution chart are available at https://doi.org/10.6084/m9.figshare.c.5538977

Late Jurassic-Early Cretaceous palynostratigraphy and palaeoclimate in the Andigama Basin, Sri Lanka

Sri Lanka consists of only ten percent of sedimentary rocks, and high-grade metamorphic rocks underlie the rest. Most of these sedimentary terrains are post-Gondwanic and such formations help to understand the geological history of the island. We report the first record of an age diagnostic (Late Jurassic-Early Cretaceous) palynological assemblage of the sedimentary rocks in the Andigama Basin (borehole AND BH01) Sri Lanka. The study was undertaken to assess the palaeoenvironmental settings in this basin based on palynological and palynofacies investigations. A palynofloral study suggests luxuriant gymnospermous forests proliferation in the Andigama Basin during this time. The palynological assemblage is characterized by the predominance of coniferous pollen grains of Araucariacites spp., Callialasporites spp. along with some stratigraphically significant taxa viz., Cicatricosisporites spp., Aequitriradites verrucosus, Triporoletes sp., Impardecispora indica, Concavissimisporites verrucatus, Distaltriangulisporites perplexus, Verrucosisporites verrucosus, and Contignisporites fornicates of Tithonian-Berriasian time. Palynofacies records suggest three distinct Palynofacies Assemblages (PF 1–3). PF 1 indicates the forest swamp; PF 2 represents the mixed assemblage of forest swamp and reed marshes, while PF 3 suggests reed marshes/lakeshore deposits under oxic-anoxic environments. These palynofacies assemblage along with variable lithological counterparts varying from carbonaceous shale laminae interlayered with calcareous sandstone to brown shale and carbonaceous shale strata reflects diverse hydrodynamic conditions. Palynofloral and palynofacies records of the present study denote the warm and humid climatic conditions, which directly corroborates with global oxygen isotopic studies of the Late Jurassic-Early Cretaceous sediments.

Depositional paleoenvironment and source rock characterization across the Toarcian Oceanic Anoxic Event from the eastern Tethys, Tibet, SW China

An integrated approach based on organic petrographic and geochemical proxies along with palynological and palynofacies analysis were employed using 24 rock samples representing the upper part of the Quse and Sewa formations in the southern Qiangtang Basin, Tibetan Plateau, SW China. This interval was deposited during the Early Jurassic Toarcian Oceanic Anoxic Event (T-OAE) and is investigated to assess the biostratigraphic age control based on palynomorphs composition. The current approach allows for the interpretation of the local paleoenvironmental response to T-OAE climate variability that still unraveled based on palynofacies analysis of the Bilong co succession. Visual palynofacies analysis, vitrinite reflectance (VRo), and total organic carbon (TOC)/Rock-Eval pyrolysis parameters enables a detailed assessment of probable source rock characterization.The palynomorph content comprises mainly terrestrially-derived land-plants, mostly sphaeromorphs pollen grains, with minor content of marine dinoflagellate cysts (dinocysts). Marker dinocysts and pollen taxa allow the subdivision of the studied succession into two age-distinctive units of early Toarcian and late Bajocian-Bathonian. Additionally, carbon isotope profile of the studied succession observed a large negative carbon isotope excursion (CIE) within the lower Toarcian oil shale interval, which is compatible with regional δ13Corg records from adjacent basins at this time. The regional TOC contents of lower Toarcian reached up to 21 wt% in areas of the eastern Tethys compared to lower values in the western Tethys and Boreal (ca. 3 wt%). Two palynofacies assemblages revealed deposition of these deposits in distal inner neritic to fluvio-deltaic environment and to some extent in brackish marginal marine setting. Geochemical screening indicated that most samples were dominated by very good to excellent organic matter richness of kerogen Type II and mixed Type II/III with very good to excellent hydrocarbon generation. The calculated VRo-eq from Rock-Eval Tmax and measured VRo values are in good agreement and showed that the organic matter of the studied interval is in the early to middle stages of the oil window.

Palynomorph biostratigraphy, palynofacies, thermal maturity and paleoenvironmental interpretation of the Bajocian–Aptian succession in the OBA D-8 Well, Matruh Basin, Egypt

A palynological study of 35 cutting samples from the Middle Jurassic–Lower Cretaceous section encountered in the OBA D-8 Well in the north Western Desert of Egypt yielded palynomorphs and particulate organic matter used to interpret the biostratigraphy, palynofacies, paleoenvironment, thermal maturation, and hydrocarbon potential of the Matruh Basin. The stratigraphically significant dinoflagellate cyst and sporomorph taxa recovered, which include Murospora florida, Aequitriradites spinulosus, Pilosisporites trichopapillosus, Callialasporites trilobatus, Tenua anaphrissa, Muderongia simplex, Systematophora sp., Gonyaulacysta jurassica, Korystocysta gochtii, Pareodinia ceratophora, and Dissiliodinium sp., permit an age assignment of the studied section as Bajocian to Aptian. Seven formal dinoflagellate cyst zones and four formal sporomorph zones are proposed for this time interval, in addition to differentiating four palynofacies assemblages and using the Rock-Eval Pyrolysis method to visually and geochemically evaluate the source rock potential. The 0.45–2.82 wt% TOC values of the studied samples indicate fair to good source rocks. An inner neritic depositional environment due to relatively high sea level is deduced for the Khatatba and Masajid formations using palynological proxies, as reflected in the lower percentages of sporomorphs relative to dinoflagellate cysts. During the Lower Cretaceous, a predominance of terrestrial sporomorphs in the Alam-El Bueib Formation suggests the advance of a fluvio-deltaic environment, possibly related to a significant sea level fall and regressive phase.

Palynofacies analysis and depositional environments of Upper Cretaceous sediments in the ST‐9H well, offshore South Tano Basin, Western Ghana

Palynofacies analyses were carried out on 43 cutting samples from the ST 9H well in the Tano Basin, with the view of reconstructing the palaeoenvironment of the Upper Cretaceous sediments in the well. The stratigraphic distribution of the palynofacies assemblages defined four palynofacies units. Palynofacies PA reflects deposition in near shore/shallow marine (inner neritic) environment under distal dysoxic‐anoxic shelf condition. Palynofacies PB was deposited in an inner–middle neritic environment under mud‐dominated oxic shelf conditions, Palynofacies PC in an open marine (outer neritic) environment under distal suboxic‐anoxic basin conditions, and Palynofacies PD in a proximal–marginal marine environment under dysoxic‐anoxic basin conditions. These palynofacies assemblages (PA–PD) are characterized by kerogen types II (oil prone), III‐IV (gas prone), II &gt; I (oil prone), and III (gas prone), respectively. Marker dinoflagellate and miospore assemblages recovered from the sediments –are indicative of a Campanian–Maastrichtian age. The palaeofloral association and the perideanacean dinocysts assemblage are typical of Senonian Palme Province and the Malloy suite, respectively. These assemblages are indicative of a warm and humid tropical‐subtropical climatic condition.

Palynostratigraphic and palynofacies analysis of x and y wells, offshore Niger Delta, Nigeria

A detailed palynostratigraphic and palynofacies study was carried out on two shallow offshore wells, codenamed Well X and Well Y, from the Niger Delta Basin, Nigeria. The study is aimed at establishing the age and palaeoenvironment of the sedimentary sequences penetrated by the wells. Standard palynological/palynofacies laboratory procedures were used to free the palynomorphs and palynomacerals from the embedding matrices.Prepared palynological slides were studied using the Leitz Ortholux II transmitted light microscope. The palynofloral assemblages recorded from the two well sequences include well-preserved palynomorphs such as Zonocostites ramonae, Monoporites annulatus, Retitricolporites irregularis, Cyperaceaepollis sp., Echitricolporites spinosus and Nymphaeapollis clarus among others. The recognition of diagnostic pollen of Cyperaceaepollis sp. and Nymphaeapollis clarus as well as the associated palynomorph assemblage aided the delineation of the well sequences into the P830, P840-P850 and P860 subzones of the P800 palynological zone in the late Miocene. The relative abundance of particulate organic matter (Amorphous Organic Matter (AOM), Phytoclasts and Palynomorphs) revealed the delineation of three palynofacies assemblages, PF-A, PF-B and PF-C, suggesting three distinct paleoenvironments of deposition. These paleoenvironments range from distal shelf through marginal to proximal with varying conditions from oxic, suboxic to anoxic, thus suggesting marginal marine to coastal deltaic environments of deposition for the sedimentary sequences penetrated by the two wells.&#x0D; Keywords: Late Miocene, Niger Delta, Paleoenvironment, Palynostratigraphy, Palynofacies.