Palynofacies Data Research Articles

Coastal ecosystem responses to late stage Deccan Trap volcanism: the post K–T boundary (Danian) palynofacies of Mumbai (Bombay), west India

The Deccan Trap continental flood basalt eruptions of India occurred c. 67–63 Ma, thus spanning the Cretaceous–Tertiary boundary (65 Ma). Deccan eruptions were coeval with an interval of profound global environmental and climatic changes and widespread extinctions, and this timing has sparked controversy regarding the relative influence of Deccan volcanism upon end-Cretaceous catastrophic events. If Deccan Trap activity was capable of affecting global ecosystems, evidence should be present in proximal Indian sedimentary facies and their palaeontological contents. The impact of late stage Deccan volcanism upon biota inhabiting Mumbai (Bombay) Island's post K–T boundary lagoonal systems is documented here. Sediments (or “intertrappeans”) which accumulated within these lagoons are preserved between Trap lavas that characterise the closing stages of this flood basalt episode.Mumbai Island Formation intertrappean faunal and floral communities are conspicuously distinct from those common to many pre K–T boundary, late Maastrichtian intertrappeans across the Deccan province. The latter sedimentary intercalations mostly developed in cognate semiarid, palustrine ecosystems; by contrast, those around Mumbai evolved in sheltered, peripheral marine settings, within subsiding continental margin basins unique to this late Deccan stage, and under an increasingly humid Danian climate. Geochemical analyses reveal that Mumbai sedimentation and diagenesis were intimately related to local explosive volcanic and regional intrusive activity at c. 65–63 Ma. Although tectonic and igneous events imprinted their signatures throughout these sedimentary formations, organisms usually sensitive to environmental perturbations, including frogs and turtles, thrived. Critically, palynofacies data demonstrate that, whilst plant material deposition was responsive to environmental shifts, there were no palpable declines in floral productivity following Mumbai pyroclastic discharges. Therefore, it is implausible that this late stage explosive volcanism influenced major ecosystem collapses globally.

Lithofacies, palynofacies, and sequence stratigraphy of Palaeogene strata in Southeastern Nigeria

Integrated sedimentologic, macrofossil, trace fossil, and palynofacies data from Paleocene-Middle Eocene outcrops document a comprehensive sequence stratigraphy in the Anambra Basin/Afikpo Syncline complex of southeastern Nigeria. Four lithofacies associations occur: (1) lithofacies association I is characterized by fluvial channel and/or tidally influenced fluvial channel sediments; (2) lithofacies association II ( Glossifungites and Skolithos ichnofacies) is estuarine and/or proximal lagoonal in origin; (3) lithofacies association III ( Skolithos and Cruziana ichnofacies) is from the distal lagoon to shallow shelf; and (4) shoreface and foreshore sediments ( Skolithos ichnofacies) comprise lithofacies association IV. Five depositional sequences, one in the Upper Nsukka Formation (Paleocene), two in the Imo Formation (Paleocene), and one each in the Ameki Group and Ogwashi-Asaba Formation (Eocene), are identified. Each sequence is bounded by a type-1 sequence boundary, and contains a basal fluvio-marine portion representing the transgressive systems tract, which is succeeded by shoreface and foreshore deposits of the highstand systems tract. In the study area, the outcropping Ogwashi-Asaba Formation is composed of non-marine/coastal aggradational deposits representing the early transgressive systems tract. The occurrence of the estuarine cycles in the Palaeogene succession is interpreted as evidence of significant relative sea level fluctuations, and the presence of type-1 sequence boundaries may well be the stratigraphic signature of major drops in relative sea level during the Paleocene and Eocene. Sequence architecture appears to have been tectono-eustatically controlled.

Palynological and sequence stratigraphic analysis of the Napo Group in the Pungarayacu 30 well, Sub-Andean Zone, Ecuador

The study of palynomorphs and calcareous nannofossils from the Albian–Campanian Napo Group in the Pungarayacu 30 well in the Subandean Zone of Ecuador has led to a new biostratigraphic framework revealing the existence of several hiatuses for this area. The palynological and palynofacies data are used together with other fossils and lithological evidence to define a sequence stratigraphic framework. The distribution of palynomorphs and palynofacies indicates a strong terrestrial input for the lower part of the Napo Group (Napo Basal and Lower Napo formations). In the upper part (Middle and Upper Napo formations), terrestrial input is reduced and a restricted marine environment with several dysoxic–anoxic intervals can be inferred. The hydrocarbons present in the well studied have traditionally been regarded as locally sourced. However, several lines of evidence (TAS, Tmax and VR) prove the immature stage of the source rock in this borehole as well as in a larger area.

Sedimentary organic matter in distal clinoforms of Miocene slope sediments; Site 903 of ODP Leg 150, offshore New Jersey (U.S.A.)

ABSTRACT A study of sedimentary organic matter (palynofacies) was carried out for paleoenvironmental purposes in the siliciclastic, Miocene upper-slope sediments of Ocean Drilling Project (ODP) Site 903, Leg 150. Two groups of organic constituents were distinguished: a fraction derived from the continent, made of phytoclasts, pollen, and spores, and a marine fraction consisting of amorphous organic matter (AOM), dinoflagellate cysts, and foraminiferal linings. Palynofacies data reflect the overall trend of the Haq et al. (1987) eustatic curve. The rise in eustatic sea level during the early Miocene is associated with high levels of AOM and total organic carbon, indicative of low-energy, starved, deeper-water conditions. In contrast, during a fall in sea level from the early middle Miocene to the late Miocene, AOM became diluted by continental organic matter associated with prograding clinoforms. Site 903 penetrated the distal part of progradational, well-developed clinoforms of Miocene age. Most of the seismic reflections bounding these clinoforms are the pelagic correlatives to sequence boundaries observed beneath the adjacent shelf, and they correlate well with the sea-level records of Haq et al. (1987). Within packages of clinoforms, palynofacies show important percentage variations. In most cases, seismic reflectors (i.e., sequence boundary correlatives) seem to be associated with an increase in AOM indicative of a condensed section. Seismic stratigraphic interpretation landward of Site 903 indicates that these condensed sections may correspond to the downlap surface of prograding lowstand or highstand wedges. Above the condensed section, AOM becomes progressively diluted by the renewed progradation of terrigenous sediments. The concentration of marine AOM near sequence boundaries, the ages of which correlate with the Haq et al. (1987) eustatic curve, tends to demonstrate that the distribution of AOM in the middle and upper Miocene slope sediments at Site 903 may be to a large extent related to relative sea-level variations.

Palynofacies analysis of sediments from the Côte d'Ivoire-Ghana transform margin: Preliminary correlation with some regional events in the Equatorial Atlantic

Analyses of the palynofacies and sporomorph thermal alteration indices (TAI) of sediments from Ocean Drilling Program (ODP) Sites 959 to 962 in the Côte d'Ivoire-Ghana Transform Margin, West Africa were undertaken to (1) determine the source and depositional conditions of the organic matter in the sediments, (2) refine a paleobathymetric curve derived from other data for Site 959, which drilled the most continuous sedimentary sequence from Pleistocene to Albian and (3) interpret the paleothermal history of the area. Twelve types of dispersed organic matter were identified: amorphous organic matter (AOM), marine palynomorphs, algae, resins, black debris, yellow-brown fragments, black-brown fragments, cuticles, plant tissue, wood, sporomorphs and fungi. The relative abundances of these organic matter components at each site were analyzed using cluster analysis, resulting in the identification of seven palynofacies assemblages at Site 959, five each at sites 960 and 961, and four at Site 962. Amorphous organic matter (which is chiefly marine derived), black debris and wood have played the most significant role in defining palynofacies assemblages. The palynofacies assemblages show some correlation with lithologic units, sediment sources and depositional environments. Previous palynofacies studies in passive margins have demonstrated that changes in the ratio of AOM to terrestrial organic matter are related primarily to proximal-distal positions of depositional environments relative to the shoreline. However, this assumption does not always hold true for a transform margin where tectonic factors play an important role in the organic matter distribution, at least in the early stages of evolution. Lithofacies, CCD paleodepths for the North Atlantic, trace fossil association, benthic foraminifera and palynofacies data were the criteria used for reconstructing a paleobathymetric curve for Site 959. A cyclicity in the organic matter distribution of the Upper Miocene to Lower Pliocene pelagic sediments could be related to fluctuations in productivity of biosiliceous and calcareous organisms, and sedimentation rates. A drastic increase in the amount of AOM and a decrease in black debris and wood in the carbonate and clastic rocks (Lithologic Unit IV) overlying the tectonized Albian sediments (Lithologic Unit V) at Sites 959 and 960 coincide with the presence of an unconformity. Qualitative color analysis of palynomorphs was undertaken for all sites, although the main focus was on Site 959 where detailed organic geochemical data were available. At Site 959, TAI values indicate an immature stage of organic maturation (<2) down to the black claystones of Lithologic Unit III at about 918.47 mbsf. Below this, samples show an increase with depth to a moderately mature stage (>2 except for the claystone samples between 1012.52 and 1036.5 mbsf, and one limestone sample at 1043.4 mbsf), reaching peak levels of 2.58 to 3.0 in the tectonized Albian sediments below the unconformity. These TAI values show a positive correlation with the T max values derived from Rock-Eval pyrolysis data. The highest values recorded in the basal tectonized units at all the sites (Sites 960–962 have mean values between 2.25 and 3.13) may be related to high heat flow during the intracontinental to syntransform basin stage in the region.

High-resolution palynofacies investigation of Kimmeridgian sedimentary cycles

Abstract Palynofacies analysis is used as a tool to investigate in detail the palaeoenvironmental variations through several sedimentary cycles in the Kimmeridge Clay of Kimmeridge Bay, Dorset, UK. Evidence is given of palaeoenvironmental variations within cycles corresponding to those expected for obliquity orbital forcing. In addition, a second cyclical palaeoenvironmental variation, probably precessional forced, is seen in the palynofacies data. Further small-scale variations in palynofacies characteristics, which are not evident in the sedimentology, are also identified and allow cycles to be divided into a number of distinct palaeoenvironmental units. It is proposed that the obliquity cycle had its greatest effects on the marine environment, while the precessional cycle mainly affected the terrestrial environment. The abundance of useful palaeoenvironmental and palaeoclimatic information obtainable through high-resolution sampling in conjunction with a tool such as palynofacies analysis, provides evidence for and information about orbital forcing additional to that of most orbital forcing studies as it allows variations within cycles to be investigated.

Palynological review of the Brent Group, UK sector, north sea

Abstract A biostratigraphical zonation of the Brent Group, applicable within local oil field areas, has been established. It comprises 11 palynozones and subzones, eight of which are confined to the Ness Formation. Palynomorph associations and palynofacies types are shown to broadly correspond to specific palaeoenvironments. A regional ‘event’ scheme is outlined which establishes chronostratigraphical correlations and suggests temporal relationships between deltaic and delta front sediments. Integrated palynofacies data have allowed the development of deltaic sub-palaeoenvironments and lithofacies to be examined with respect to time and, in this way, to chart the possible progress of the delta as it prograded. Similarly, this approach enables possible areas of concentrated fluvial channel activity to be identified and the likely migration of these fluvial fairways with time. The implications of this depositional model for reservoir development and performance is discussed, showing the varying orientation of the delta front and barrier sands as it changed from a predominantly N-S trend during its early stages to WNW-ESE in its final stages.

Comparison of organic geochemical and palynofacies methods: Example from the Upper Triassic Gassum Formation in Denmark

Copenhagen, February 19th, 1991. Disseminated organic matter from the · Upper Triassic to Lower Jurassic Gassum Formation in the Gassum-1 deep well has been analyzed by palynological and organic geochemical methods. Tue paper compares the effects of the different preparation methods on the organic matter. The kerogen isolation process (demineralisation by HF) is found to cause major changes in the Rock-Eva! parameters, but not in carbon isotope composition of organic matter. Tm.,- and HI-values determined from kerogen concentrates are more consistent with the palynofacies data than those determined from whole rock samples. The differences are ascribed to analytical problems when dealing with low-TOC whole rock samples. Palynofa­cies data obtained from unfiltered and filtered kerogen concentrates demonstrate a variable loss of amorphous organic matter during filtration ( up to 1()()%). Other palynomorph distributions are not seriously affected by filtration. The loss in amorphous organic matter has no influence on the Rock-Eva! data and carbon isotope composition. Comparison of polynofacies and carbon isotope data identifies three organic matter sources with characteristic isotopic composition.

Palynostratigraphy and palynofacies reconstruction of the Upper Jurassic to Lowermost Cretaceous of the Draugen Field, offshore Mid Norway

In 1984 Norske Shell discovered the Draugen Field with well 6407/9-1 at the edge of the Trøndelag Platform, offshore Mid Norway. The discovery was made in the offshore marine bar sands of the Upper Jurassic Rogn Formation. Based on the palynological assemblages observed in the Rogn and the overlying Spekk Formation four zones and seven subzones can be recognized. They range in age from Mid Oxfordian to Late Ryazanian. Furthermore, four palynofacies have been recognized, characteristic of different offshore marine environments: from lower offshore with stagnant bottom conditions to upper bar washover deposits. Integration of palynofacies data with the stratigraphic framework shows that in the Mid Oxfordian to Early Kimmeridgian the highest energy and the source area lay to the south and the southwest. During the later part of the Kimmeridgian the highest energy sequences (upper bar with washover deposits) are found in the north-central and south of the area. During the Portlandian to Late Ryazanian waterdepth increased rapidly resulting in a lower offshore environment with stagnant bottom conditions. From the depositional history it may be concluded that the Rogn bar could develop in the Draugen area because the uplifted faulted margin of the Trøndelag Platform created the right energy conditions for development and preservation of the bar.

Source-area environments of late Jurassic and early Cretaceous sediments in Southeast England

Source-area environments of Late Jurassic and Early Cretaceous sediments in Southeast England. Proc. Geol. Ass. 95 (2), 149-163. Clay mineralogical and palynofacies data indicate that the Jurassic-Cretaceous transition in Southeast England was marked by a change in climate from semi-arid with less than 500 mm of rain per annum, to humid temperate with more than 1000 mm. Soils and weathering profiles on the Anglo-Brabant Massif, the main source of the sediments deposited in the Weald Basin, changed from alkaline and poorly-leached (pedocals) to acidic and well-leached (podzols), and the vegetation became significantly more diverse. Temperatures remained warm throughout, averaging 20-25°C and dropping to about 10°C in cool spells. The climatic change was essentially local due to uplift of various massifs in Northwest Europe and not linked to global shifts in climatic zones. During the Early Cretaceous, faulting caused fluctuations in the elevation of the Anglo-Brabant Massif that were sufficient to continue to affect the climate locally. When the Massif was relatively high, rainfall was also high, ferns and lycopods were widespread, chemical weathering and acid leaching in the soils and weathering profiles were intense, and there was considerable run-off into the basin leading to rapid dumping of sandy sediments. When it was low, there was less rain and hence not as much leaching of the soils, the ferns and lycopods were more restricted in their distribution, and run-off into the basin was reduced. This led to the deposition of mostly fine silt and clay. Evaporation during these periods often raised salinities within the basin.