Petroleum Geology and Geochemistry of Oils and Possible Source Rocks of the Southern East Coast Basin, New Zealand

<p>The East Coast Basin of New Zealand contains up to 10,000 m of predominantly fine-grained marine sediments of Early Cretaceous to Pleistocene age, and widespread oil and gas seepages testify to its status as a petroleum province. A suite of oils and possible source rocks from the southern East Coast Basin have been analysed by a variety of geochemical techniques to determine the hydrocarbon potential and establish oil-oil and oil-source rock correlations. Results of TOC and Rock-Eval pyrolysis indicate that the latest Cretaceous Whangai Formation and Paleocene Waipawa Black Shale represent the only good potential source rock sequences within the basin. The middle to Late Cretaceous Glenburn and Te Mai formations, previously considered good potential source rocks, are organic-rich (TOC contents up to 1.30% and 1.52% respectively), but comprise predominantly Types III and IV (structured terrestrial and semi-opaque) kerogen and, therefore, have little hydrocarbon generative potential (HI values < 50). Early Cretaceous and Neogene formations are shown to have low TOC contents and have little source rock potential. The Waipawa Black Shale is a widespread, thin (< 50 m), dark brown, non-calcareous siltstone. It contains up to 1.9% sulphur and elevated quantities of trace metals. Although immature to marginally mature for hydrocarbon generation in outcrop, it is organic-rich (TOC content up to 5.69%) and contains oil and gas-prone Types II and III kerogen. The extracted bitumen comprises predominantly marine algal and terrestrial higher plant material and indicates that deposition occurred under conditions of reduced oxygen with significant anoxic episodes. The Whangai Formation is a thick (300-500 m), non-calcareous to calcareous siliceous mudstone. Although immature to marginally mature in outcrop, the Upper Calcareous and Rakauroa members have a TOC content up to 1.37% and comprise oil and gas-prone Types II and III (structured aqueous and structured terrestrial) kerogen. Bitumen extracts comprise predominantly marine organic matter with a moderate terrestrial higher plant component and indicate that deposition occurred under mildly reducing conditions, with periodic anoxic episodes indicated for the Upper Calcareous Member. Two families of oils are recognised in the southern East Coast Basin. The Kerosene Rock, Westcott, Tiraumea and Okau Stream oils comprise both algal marine and terrestrial higher plant material and were deposited under periodically anoxic conditions. They are characterised by high relative abundances of unusual C30 steranes (C30 indices of 0.24-0.40) and 28,30-bisnorhopane, low proportions of C28 steranes and isotopically heavy [delta] 13C values (-20.9 to -23.0 [per mil]). The Waipatiki and Tunakore oils from southern Hawke's Bay and the Kora-1 oil from the northern Taranaki Basin have similar geochemical characteristics and are also included in this family of oils. These same characteristics are also diagnostic of the Waipawa Black Shale and an oil-source rock correlation is made on this basis. The Knights Stream and Isolation Creek oils are derived from predominantly marine organic matter with a moderate terrestrial angiosperm contribution, and characterised by low relative abundances of C30 steranes (C30 indices of 0.06-0.12) and 28,30-bisnorhopane, high proportions of C28 steranes and isotopically light [delta] 13C values (-26.8 to -28.9 [per mil]). Also included in this family of oils, with a slightly greater marine influence, are the major seep oils of the northern East Coast Basin (Waitangi, Totangi and Rotokautuku). A tentative oil-source rock correlation with the Upper Calcareous and Rakauroa members of the Whangai Formation is based on their similar geochemical characteristics.</p>

Petroleum Geology and Geochemistry of Oils and Possible Source Rocks of the Southern East Coast Basin, New Zealand

<p>The East Coast Basin of New Zealand contains up to 10,000 m of predominantly fine-grained marine sediments of Early Cretaceous to Pleistocene age, and widespread oil and gas seepages testify to its status as a petroleum province. A suite of oils and possible source rocks from the southern East Coast Basin have been analysed by a variety of geochemical techniques to determine the hydrocarbon potential and establish oil-oil and oil-source rock correlations. Results of TOC and Rock-Eval pyrolysis indicate that the latest Cretaceous Whangai Formation and Paleocene Waipawa Black Shale represent the only good potential source rock sequences within the basin. The middle to Late Cretaceous Glenburn and Te Mai formations, previously considered good potential source rocks, are organic-rich (TOC contents up to 1.30% and 1.52% respectively), but comprise predominantly Types III and IV (structured terrestrial and semi-opaque) kerogen and, therefore, have little hydrocarbon generative potential (HI values < 50). Early Cretaceous and Neogene formations are shown to have low TOC contents and have little source rock potential. The Waipawa Black Shale is a widespread, thin (< 50 m), dark brown, non-calcareous siltstone. It contains up to 1.9% sulphur and elevated quantities of trace metals. Although immature to marginally mature for hydrocarbon generation in outcrop, it is organic-rich (TOC content up to 5.69%) and contains oil and gas-prone Types II and III kerogen. The extracted bitumen comprises predominantly marine algal and terrestrial higher plant material and indicates that deposition occurred under conditions of reduced oxygen with significant anoxic episodes. The Whangai Formation is a thick (300-500 m), non-calcareous to calcareous siliceous mudstone. Although immature to marginally mature in outcrop, the Upper Calcareous and Rakauroa members have a TOC content up to 1.37% and comprise oil and gas-prone Types II and III (structured aqueous and structured terrestrial) kerogen. Bitumen extracts comprise predominantly marine organic matter with a moderate terrestrial higher plant component and indicate that deposition occurred under mildly reducing conditions, with periodic anoxic episodes indicated for the Upper Calcareous Member. Two families of oils are recognised in the southern East Coast Basin. The Kerosene Rock, Westcott, Tiraumea and Okau Stream oils comprise both algal marine and terrestrial higher plant material and were deposited under periodically anoxic conditions. They are characterised by high relative abundances of unusual C30 steranes (C30 indices of 0.24-0.40) and 28,30-bisnorhopane, low proportions of C28 steranes and isotopically heavy [delta] 13C values (-20.9 to -23.0 [per mil]). The Waipatiki and Tunakore oils from southern Hawke's Bay and the Kora-1 oil from the northern Taranaki Basin have similar geochemical characteristics and are also included in this family of oils. These same characteristics are also diagnostic of the Waipawa Black Shale and an oil-source rock correlation is made on this basis. The Knights Stream and Isolation Creek oils are derived from predominantly marine organic matter with a moderate terrestrial angiosperm contribution, and characterised by low relative abundances of C30 steranes (C30 indices of 0.06-0.12) and 28,30-bisnorhopane, high proportions of C28 steranes and isotopically light [delta] 13C values (-26.8 to -28.9 [per mil]). Also included in this family of oils, with a slightly greater marine influence, are the major seep oils of the northern East Coast Basin (Waitangi, Totangi and Rotokautuku). A tentative oil-source rock correlation with the Upper Calcareous and Rakauroa members of the Whangai Formation is based on their similar geochemical characteristics.</p>

Ocean Aerobiology

Ocean aerobiology is defined here as the study of biological particles of marine origin, including living organisms, present in the atmosphere and their role in ecological, biogeochemical, and climate processes. Hundreds of trillions of microorganisms are exchanged between ocean and atmosphere daily. Within a few days, tropospheric transport potentially disperses microorganisms over continents and between oceans. There is a need to better identify and quantify marine aerobiota, characterize the time spans and distances of marine microorganisms’ atmospheric transport, and determine whether microorganisms acclimate to atmospheric conditions and remain viable, or even grow. Exploring the atmosphere as a microbial habitat is fundamental for understanding the consequences of dispersal and will expand our knowledge of biodiversity, biogeography, and ecosystem connectivity across different marine environments. Marine organic matter is chemically transformed in the atmosphere, including remineralization back to CO2. The magnitude of these transformations is insignificant in the context of the annual marine carbon cycle, but may be a significant sink for marine recalcitrant organic matter over long (∼104 years) timescales. In addition, organic matter in sea spray aerosol plays a significant role in the Earth’s radiative budget by scattering solar radiation, and indirectly by affecting cloud properties. Marine organic matter is generally a poor source of cloud condensation nuclei (CCN), but a significant source of ice nucleating particles (INPs), affecting the formation of mixed-phase and ice clouds. This review will show that marine biogenic aerosol plays an impactful, but poorly constrained, role in marine ecosystems, biogeochemical processes, and the Earth’s climate system. Further work is needed to characterize the connectivity and feedbacks between the atmosphere and ocean ecosystems in order to integrate this complexity into Earth System models, facilitating future climate and biogeochemical predictions.

Geologic controls on phytoplankton elemental composition

Although the nutrient content of planktonic organic matter (C:N:Porg) plays a crucial role in marine metazoan evolution and global biogeochemistry (1–3), its geologic history is poorly constrained, and it is often regarded as a constant “Redfield” ratio of C:N:Porg~106:16:1. We calculate C:N:Porg through the Phanerozoic by including nutrient- and temperature-dependent C:N:Porg parameterizations (4–6) in a model of long-term biogeochemical cycles (7). We infer a decrease from high Paleozoic C:Porg and N:Porg to present-day Redfield ratios. This gradual nutrient enrichment of marine organic matter stems from a decrease in the global average temperature and an increase in seawater phosphate availability, which are driven by various Phanerozoic events, mainly the middle to late Paleozoic emergence and expansion of land plants and the Triassic breakup of the supercontinent Pangaea. The nutrient enrichment of planktonic organic matter likely impacted the evolution of marine fauna and global biogeochemistry.

Flotsam and jetsam: a global review of the role of inputs of marine organic matter in sandy beach ecosystems

Sandy beaches are iconic interfaces that functionally link the ocean with the land by the flow of marine organic matter. These cross-ecosystem fluxes often comprise uprooted seagrass and dislodged macroalgae that can form substantial accumulations of detritus, termed ‘wrack’, on sandy beaches. In addition, the tissue of the carcasses of marine animals that regularly wash up on beaches form a rich food source (‘carrion’) for a diversity of scavenging animals. Here, we provide a global review of how wrack and carrion provide spatial subsidies that shape the structure and functioning of sandy beach ecosystems (sandy beaches and adjacent surf zones), which typically have little in situ primary production. We also examime the spatial scaling of the influence of these processes across the broader seascape and landscape, and identify key gaps in our knowledge to guide future research directions and priorities. Globally, large quantities of detrital kelp and seagrass can flow into sandy beach ecosystems, where microbial decomposers and animals remineralise and consume the imported organic matter. The supply and retention of wrack are influenced by the oceanographic processes that transport it, the geomorphology and landscape context of the recipient beaches, and the condition, life history and morphological characteristics of the taxa that are the ultimate source of wrack. When retained in beach ecosystems, wrack often creates hotspots of microbial metabolism, secondary productivity, biodiversity, and nutrient remineralization. Nutrients are produced during wrack break-down, and these can return to coastal waters in surface flows (swash) and the aquifier discharging into the subtidal surf. Beach-cast kelp often plays a key trophic role, being an abundant and preferred food source for mobile, semi-aquatic invertebrates that channel imported algal matter to predatory invertebrates, fish, and birds. The role of beach-cast marine carrion is likely to be underestimated, as it can be consumed rapidly by highly mobile scavengers (e.g. foxes, coyotes, raptors, vultures). These consumers become important vectors in transferring marine productivity inland, thereby linking marine and terrestrial ecosystems. Whilst deposits of organic matter on sandy beach ecosystems underpin a range of ecosystem functions and services, these can be at variance with aesthetic perceptions resulting in widespread activities, such ‘beach cleaning and grooming’. This practice diminishes the energetic base of food webs, intertidal fauna, and biodiversity. Global declines in seagrass beds and kelp forests (linked to global warming) are predicted to cause substantial reductions in the amounts of marine organic matter reaching many beach ecosystems, likely causing flow-on effects on food webs and biodiversity. Similarly, future sea-level rise and stormier seas are likely to profoundly alter the physical attributes of beaches, which in turn can change the rates at which beaches retain and process the influxes of wrack and animal carcasses. Conservation of the multi-faceted ecosystem services that sandy beaches provide will increasingly need to encompass a greater societal appreciation and the safeguarding of ecological functions reliant on beach-cast organic matter on innumerable ocean shores worldwide.

Generation potential, distribution area and maturity of the Barents-Kara Sea source rocks

Identification of the source rock potential and distribution area is the most important stage of the basin analysis and oil, and gas reserves assessment. Based on analysis of the large geochemical and geological data base of the Petroleum geology department of the Lomonosov Moscow State University and integration of different-scale information (pyrolysis results and regional palaeogeographic maps), generation potential, distribution area and maturity of the main source rock intervals of the Barents-Kara Sea shelf are reconstructed. These source rocks wide distribute on the Barents-Kara Sea shelf and are characterized by lateral variability of generation potential and type of organic matter depending on paleogeography. During regional transgressions in Late Devonian, Early Permian, Middle Triassic and Late Jurassic, deposited source rocks with marine organic matter and excellent generation potential. However in the regression periods, during the short-term transgressions, formed Lower Carboniferous, Upper Permian, Induan, Olenekian and Late Triassic source rocks with mixed and terrestrial organic matter and good potential. Upper Devonian shales contain up to 20.6% (average – 3%) of marine organic matter, have an excellent potential and is predicted on the Eastern-Barents megabasin. Upper Devonian source rocks are in the oil window on the steps, platforms and monoclines, while are overmature in the basins. Lower Permian shale-carbonate source rock is enriched with marine organic matter (up to 4%, average – 1.4%) and has a good end excellent potential. Lower Permian source rocks distribute over the entire Barents shelf and also in the North-Kara basin (Akhmatov Fm). These rocks enter the gas window in the Barents Sea shelf, the oil window on the highs and platforms and are immature in the North-Kara basin. Middle Triassic shales contain up to 11.2% of organic matter, there is a significant lateral variability of the features: an excellent generation potential and marine organic matter on the western Barents Sea and poor potential and terrestrial organic matter in the eastern Barents Sea. Middle Triassic source rocks are in the oil window; in the depocenters it generates gas. Upper Jurassic black shales are enriched with marine and mixed organic matter (up to 27,9%, average – 7.3%) and have an excellent potential. On the most Barents-Kara Sea shelf, Upper Jurassic source rock are immature, but are in the oil window in the South-Kara basin and in the deepest parts of the Barents Sea shelf.

Origin of the Particulate Organic Matter in a Monsoon-Controlled Bay in Southern China

In this study, the isotopic composition (δ13C and δ15N), total organic carbon content, total nitrogen content, and C/N ratios of suspended particulate organic matter (POM) in Zhanjiang Bay, which is a semi-enclosed bay with concentrated artificial activities in Southern China, were analyzed in order to investigate the seasonal variations in the principal POM sources in the monsoon region. In summer, the δ13C and δ15N values showed a weak correlation with the chlorophyll a (Chl a), suggesting that terrigenous sources were dominant. However, in winter, the particulate organic carbon and particulate nitrogen values were correlated with the Chl a in the middle bay and bay mouth. Moreover, the δ13C values showed a significant correlation with Chl a during the winter, indicating that the contribution of the in situ phytoplankton was relatively important and was affected by the monsoon in winter. Compared with the corresponding δ13C values, the δ15N values exhibited a complex spatial distribution. By using a Bayesian mixing model, in the upper bay, the source of POM was mainly from marine organic matter (49%) in summer, and almost an equilibrated contribution of all sources in winter. In the middle bay and bay mouth, the POM contribution mainly originated from marine organic matter (53%) during the winter. In contrast, the POM source was mainly soil organic matter (63%) in summer, suggesting that the POM was sourced from the runoff from the upstream basin. Our results suggest that the seasonal shifts of the source of POM should be taken into account when estimating C or N mass balance in the monsoon-controlled bay.

Microplastics Contamination versus Inorganic Particles: Effects on the Dynamics of Marine Dissolved Organic Matter

Microplastic contamination has been linked to a range of impacts on aquatic environments. One important area that is only beginning to be addressed is the effect of microplastics on marine carbon cycling and how these compare to the effects related to inorganic particles typically present in ocean waters. The present study explores these impacts on dissolved organic matter dynamics by comparing three scenarios: a particle-free environment, a particle-enriched system with polystyrene microplastics, and a particle-enriched system with inorganic particles (water insoluble SiO2). Natural marine organic matter was obtained by culturing a non-axenic strain of Chaetoceros socialis in 2 L flasks under each of three scenarios. Following the diatom growth phase, filtered samples from the three flasks containing dissolved organic matter and bacteria were incubated separately in the dark for 5 days to monitor changes in dissolved organic matter. Chromophoric dissolved organic matter (CDOM), a bulk optical property, was monitored daily to examine changes in its quality and quantity and to compare degradation dynamics in the three systems. CDOM absorbance (quantity) remained higher in the control with respect to particle-enriched systems, suggesting that the presence of particles led to different rates of CDOM production and degradation. Using indicators for CDOM that could be related to microbial activity, results showed a higher CDOM alteration in the particle-enriched systems. These results indicate that microplastics have a potential role in modifying marine organic matter dynamics, on a similar magnitude to that of biogenic inorganic particles. Given their increasing concentrations of marine ecosystems, their role in marine microbial processing of organic matter needs to be better understood.

Geochemical approaches in tsunami research: current knowledge and challenges

Over the past decade or so, geochemical techniques have been applied to the study of modern and past tsunamis. Seawater incursions and the introduction of marine organic matter can be detected through geochemical analysis, providing strong evidence that an event deposit was formed by saltwater inundation. Furthermore, the marine geochemical signature of an event may reveal the full extent of tsunami inundation far more precisely than can be obtained from sediment alone. Based mainly on literature published during the last 4 years, this paper summarizes the latest advances in and some problems with tsunami geochemical research, and specifically addresses organic and inorganic proxies with high preservation potential, geochemical characteristics of invisible tsunami deposits, handling of data from core scanners, and offshore environmental impacts. Recent studies have proposed that some organic and inorganic geochemical proxies have high preservation potential, and sometimes such evidence can be recognized from invisible tsunami deposits. Quantitative assessments of biomarkers are also effective for detecting allochthonous materials. Organic and inorganic proxies can be applied both to identify tsunami deposits and to accurately reconstruct tsunami inundation areas; however, there are as yet no universal criteria for accurate reconstruction of tsunami inundation areas by detecting invisible tsunami deposits using geochemical approaches. For deeper understanding of the behavior of geochemical characteristics derived from tsunami events, additional knowledge of the geochemical substances associated with modern and paleo-tsunami events is required. Specifically, further work is required on assessment of the environmental selectivity of geochemical proxies and refinement of core-scanner analysis for both organic and inorganic substances.