Burial Phase Research Articles

Timing is everything: radiocarbon dating multiple levels in the Mycenaean tholos tomb of Petroto, Achaia, Greece

ABSTRACTReuse in Mycenaean tholoi (bee-hive shaped tombs) has been studied for centuries. Initially, bodies are interred on tomb floors, but moved after decomposition to make space for later burials. Extensive reuse can produce burial levels that are poorly understood often due to a lack of absolute dating. The Petroto tholos is a prime case study for dating multiple burial levels because all eight levels were sequential as later burials did not disturb previous depositions. The initial burial phase has been dated by ceramic chronology to the Late Helladic IIB-IIIA (ca. 1440–1400 BC). Radiocarbon dating of human bone samples yield for Level 7 (middle burial level) 3105 +/− 35 BP (1420–1305 cal BC) and for Level 3 (final burial) 2965 +/− 35 BP (1255–1120 cal BC). The ceramic and radiocarbon dates show that the tomb was used over for approximately 300 years during the Mycenaean period and never used again.

Characteristics of phosphorus components in surface sediments from a Chinese shallow eutrophic lake (Lake Taihu): new insights from chemical extraction and 31P NMR spectroscopy.

As a primary factor responsible for lake eutrophication, a deeper understanding of the phosphorus (P) composition and its turnover in sediment is urgently needed. In this study, P species in surface sediments from a Chinese large eutrophic lake (Lake Taihu) were characterized by traditional fractionation and 31P nuclear magnetic resonance (NMR) spectroscopy, and their contributions to the overlying water were also discussed. Fractionation results show that NaOH-P predominated in the algal-dominated zone, accounting for 60.1% to total P in Zhushan Bay. Whereas, refractory fractions including HCl-P and residual-P were the main P burial phases in the macrophyte-dominated zone, the center and lakeshore. Recovery rates of the total P and organic P were greatly improved by using a modified single-step extraction of NaOH-EDTA, ranging from 22.6 to 66.1% and from 15.0 to 54.0%. Ortho-P, monoester-P, and pyro-P are identified as the major P components in the NaOH-EDTA extracts by 31P NMR analysis. Trace amount of DNA-P appeared only in sediments from algal- and macrophyte-dominated zones, ascribing to its biological origin. The relative content of ortho-P is the highest in the algal-dominated zone, while the biogenic P including ester-P and pyro-P is the highest in the macrophyte-dominated zone. Moreover, ortho-P and pyro-P correlated positively with TP and chlorophyll a in the overlying water, whereas only significant relationships were found between monoester-P, biogenic P, and chlorophyll a. These discrepancies imply that inorganic P, mainly ortho-P, plays a vital role in sustaining the trophic level of water body and algal bloom, while biogenic P makes a minor contribution to phytoplankton growth. This conclusion was supported by the results of high proportion of biogenic P in algae, aquatic macrophytes, and suspended particulate from the published literature. This study has significant implication for better understanding of the biogeochemical cycling of endogenous P and its role in affecting lake eutrophication.

A Late Cretaceous mixed (turbidite-contourite) system along the Uruguayan Margin: Sedimentary and palaeoceanographic implications

The Late Cretaceous is a critical period in the evolution of the South Atlantic. Significant changes in the tectonic configuration of continental landmasses and marine basins during this time lead to major shifts in the sedimentary and oceanographic regimes. Using a combination of 2D and 3D seismic data with well data from the Uruguayan Margin, this work provides a new, highly detailed description of the Late Cretaceous sedimentary evolution of the margin and its regional and global palaeoceanographic implications.The Polonio Drift System (PDS), occupies the middle to lower-slope of the Uruguayan Margin. The PDS is characterised by four channel-drifts, which propagate obliquely (120–170°) from the palaeoslope and exhibit over 800m of local relief relative to the surrounding seafloor. Seismic interpretation identified four seismic units (SU.1–SU.4), separated by five major discontinuities (R.1–R.5). These record the onset (Albian–upper Turonian, 113–89.8Ma), growth (Coniacian–upper Maastrichtian, 89.8–66Ma), and burial (Paleocene, 66–56Ma) phases for the PDS. During the onset stage, down-slope processes dominate but, three major shifts in the sedimentary stacking pattern occur. These coincide with palaeoceanographic changes in the South Atlantic during the Cenomanian–Turonian (100.5–89.9Ma), Campanian-Maastrichtian (83.6–66Ma) and Paleocene (66–56Ma), following the opening of the Falkland/Malvinas-Agulhas Seaway (FAS), the subsidence of the Walvis-Ridge and the opening of the Vema channel. Bottom current influence first occurs during the growth stage (Coniacian–Campanian) when mounded deposits shift from aggradational and slightly progradational towards the N (SU.2), to clear lateral migration towards the S (SU.3). This sedimentary pattern indicates a regional palaeoceanographic shift in bottom current flow from northerly, to a subsequent southerly direction. Bottom currents do not appear to have actively eroded sediment, although they apparently had the potential to pirate and entrain fine-grained material from turbidity plumes, which build on underlying bathymetric features such as basement horsts and channel-levees. These produce large mounded morphologies adjacent to channels. Drift growth ceases following the termination of shelf progradation (R.4), enabling sluggish bottom currents contributed to a homogeneous sedimentary drape. Bottom currents intensify in the beginning of the Paleocene, forming contourite depositional systems with well-developed contourite terrace along the middle slope. Further research can elucidate the nature and mechanics of turbidite–contourites interactions along continental margins. This work offers new insights for the implications and consequences of the interaction of turbidites and contourites, which can improve the characterisation of deep-water deposits and understanding palaeoceanographic interpretations.

Bone diagenesis variability among multiple burial phases at Al Khiday (Sudan) investigated by ATR-FTIR spectroscopy

In this study the diagenetic pathways of archaeological human bones are investigated through Fourier transform infrared spectroscopy in attenuated total reflection mode (ATR-FTIR). Archaeological excavations at Al Khiday (16-D-4 site, Khartoum, Sudan) revealed a multi-stratified cemetery with distinct burial phases, chronologically attributed to different periods spanning from the Early Holocene to the beginning of the 1st millennium CE. ATR-FTIR measurements are carried out on a set of 56 bone samples, representative of each burial phase. Parameters related to collagen content and to bioapatite crystallinity and structural carbonate are calculated from infrared spectra in order to monitor the types and extent of diagenetic alteration, to assess the preservation state of bones and to define the alteration processes occurring during burial. A new method is here developed to quantify the amount of secondary calcite and to remove its contribution to the infrared spectrum, when interfering with the signal of structural carbonate from bioapatite.Considering the wide span of time covered by the archaeological record, the variability of bones alteration among burial phases is related to the climatic changes occurring in central Sudan during the Holocene. The more humid environment occurring in the Early Holocene, characterised by higher precipitation rates, seasonal swamps and palaeo-lakes, progressively changed towards drier conditions until the current arid climate of the Sub-Saharan belt. The change of palaeoenvironmental and local burial conditions over time differently influenced the types and extent of diagenetic processes affecting bones during burial.In this research are also discussed advantages and disadvantages of ATR-FTIR spectroscopy with respect to the more established FTIR spectroscopy in transmission mode.

Phosphorus release from coastal sediments: Impacts of the oxidation-reduction potential and sulfide

The release of phosphorus (P) from benthic sediments can affect the P content, nutrient status and quality of overlying waters in coastal ecosystem. This study was carried out to investigate the influence of oxidation-reduction potential (ORP) and sulfide on P release from sediments in the coastal estuary of the Yuniao River, China. The results showed that ferric iron-bound P was the main P burial phase in the sediments. The P concentration in overlying water increased with ORP decrease and sulfide increase, displaying a significant linear correlation with the ORP and sulfide concentration. The results indicate that decreased ORP may elevate the zero equilibrium phosphorus concentration, enhancing the capability of P release. And increased sulfide may react or capture reactive iron in sediments, reducing the P adsorption capacity and accelerating P release. Therefore, the control of ORP and sulfide production is important in the sink/source conversion of P in coastal sediments.

End-of-life Care and Beyond

ABSTRACTOne of the challenges of palliative care is to honour the personal wishes of culturally diverse patients while meeting ‘universal medical relief standards’. Diverging perspectives on good care can result in intercultural negotiations, such as those analysed in this paper between Dutch care professionals and immigrant families with a Turkish and Moroccan background. Fewer tensions are apparent during the burial care phase. This paper outlines the experiences of immigrant families and their Dutch care professionals in the transition from palliative care to burial care. Their narratives highlight how undertakers offer burials that follow the funeral rituals practised in their customers’ (predominantly Muslim) home countries and therefore employ bilingual staff to fulfil the specific wishes of the families. Palliative care professionals, on the other hand, tend to follow their Dutch interpretation of ‘universal medical relief standards’. The contrast not only reveals cultural diversity, but also different logics of care; while undertakers follow the logic of the market and the logic of family life, health care professionals tend to follow the logics of professionalism and politics.

Vivianite is a major sink for phosphorus in methanogenic coastal surface sediments

Studies of authigenic phosphorus (P) minerals in marine sediments typically focus on authigenic carbonate fluorapatite, which is considered to be the major sink for P in marine sediments and can easily be semi-quantitatively extracted with the SEDEX sequential extraction method. The role of other potentially important authigenic P phases, such as the reduced iron (Fe) phosphate mineral vivianite (Fe(II)3(PO4)*8H2O) has so far largely been ignored in marine systems. This is, in part, likely due to the fact that the SEDEX method does not distinguish between vivianite and P associated with Fe-oxides. Here, we show that vivianite can be quantified in marine sediments by combining the SEDEX method with microscopic and spectroscopic techniques such as micro X-ray fluorescence (μXRF) elemental mapping of resin-embedded sediments, as well as scanning electron microscope–energy dispersive spectroscopy (SEM–EDS) and powder X-ray diffraction (XRD). We further demonstrate that resin embedding of vertically intact sediment sub-cores enables the use of synchrotron-based microanalysis (X-ray absorption near-edge structure (XANES) spectroscopy) to differentiate between different P burial phases in aquatic sediments. Our results reveal that vivianite represents a major burial sink for P below a shallow sulfate/methane transition zone in Bothnian Sea sediments, accounting for 40–50% of total P burial. We further show that anaerobic oxidation of methane (AOM) drives a sink-switching from Fe-oxide bound P to vivianite by driving the release of both phosphate (AOM with sulfate and Fe-oxides) and ferrous Fe (AOM with Fe-oxides) to the pore water allowing supersaturation with respect to vivianite to be reached. The vivianite in the sediment contains significant amounts of manganese (∼4–8wt.%), similar to vivianite obtained from freshwater sediments. Our results indicate that methane dynamics play a key role in providing conditions that allow for vivianite authigenesis in coastal surface sediments. We suggest that vivianite may act as an important burial sink for P in brackish coastal environments worldwide.

Geochemical Characteristics and Hydrocarbon Generation Processes of Cretaceous Source Rocks in the Songliao Basin

The Fulongquan Depression is a major production area for natural gas in the Songliao Basin. This study was based on geochemical analysis of source rocks. Our results indicate that the kerogen types are primarily type III. These rocks represent a source of gas in a highly mature stage. The basin was formed during two major events of tectonic subsidence and uplift between 144 and 95 Ma before present. These periods were followed by a stable sedimentary burial phase. In the Cretaceous fault period, processes of secondary hydrocarbon generation were present. Corresponding to the two major tectonic subsidence movements, there were two key hydrocarbon generation processes. Contingent on research on sedimentary facies, source rock thicknesses, and the distribution and intensity of hydrocarbon generation, the northern and southern parts of this depression represent favorable areas for the exploration and development of hydrocarbon extraction.

Synchroneity of cratonic burial phases and gaps in the kimberlite record: Episodic magmatism or preservational bias?

A variety of models are used to explain an apparent episodicity in kimberlite emplacement. Implicit in these models is the assumption that the preserved kimberlite record is largely complete. However, some cratons now mostly devoid of Phanerozoic cover underwent substantial Phanerozoic burial and erosion episodes that should be considered when evaluating models for global kimberlite distributions. Here we show a broad temporal coincidence between regional burial phases inferred from thermochronology and gaps in the kimberlite record in the Slave craton, Superior craton, and cratonic western Australia. A similar pattern exists in the Kaapvaal craton, although its magmatic, deposition, and erosion history differs in key ways from the other localities. One explanation for these observations is that there is a common cause of cratonic subsidence and suppression of kimberlite magmatism. Another possibility is that some apparent gaps in kimberlite magmatism are preservational artifacts. Even if kimberlites occurred during cratonic burial phases, the largest uppermost portions of the pipes would have been subsequently eroded along with the sedimentary rocks into which they were emplaced. In this model, kimberlite magmatism was more continuous than the preserved record suggests, implying that evidence for episodicity in kimberlite genesis should be carefully evaluated in light of potential preservational bias effects. Either way, the correlation between burial and kimberlite gaps suggests that cratonic surface histories are important for understanding global kimberlite patterns.

Sedimentary iron–phosphorus cycling under contrasting redox conditions in a eutrophic estuary

Phosphorus (P) is often a limiting nutrient within freshwater and estuarine systems, thus excess inputs of P from anthropogenic activities (dominantly agriculture) can induce eutrophication in receiving water bodies. The sequestration of P within estuarine sediments is controlled by sorption and precipitation processes, which are impacted by local redox conditions and burial environment. Despite the global spread of oxygen depletion in coastal marine systems, P burial under reducing conditions remains poorly understood. We investigated P cycling in relation to iron (Fe) redox chemistry in sediments from the eutrophic Peel-Harvey Estuary in Western Australia, using a combination of porewater analysis, sequential chemical P extractions, synchrotron-based micro-scale X-ray fluorescence mapping and Fe K-edge X-ray absorption spectroscopy, and PO43− sorption experiments. The sediments represented redox regimes varying from strongly reducing, organic-rich sediments with little or no reactive Fe(III) (oxyhydr)oxides to oxygenated sediments that were enriched in reactive Fe(III) phases. Organic P and Fe-associated P were the main P burial phases, and the latter was quantitatively important even in sediments with an overall strongly reducing character. We attribute this to adsorption of P onto micro-scale Fe(III) oxyhydroxide enrichments and/or Fe-bearing clay minerals. The organic-rich sediments showed a strong decline in P contents with depth; P was released from organic matter and Fe phases but apatite precipitation was apparently inhibited in these sediments. Despite greater and stronger PO43− sorption capacity, the oxic sediments contained relatively little P due to a lack of the primary P source in marine sediments: organic matter. Our results provide detailed insight into P burial in dynamic estuarine sediments and show that micro-scale spectroscopic analyses greatly advance our understanding of P sequestration processes.

Effect of Head and Face Insulation on Cooling Rate During Snow Burial

Avalanche victims are subjected to a number of physiological stressors during burial. We simulated avalanche burial to monitor physiological data and determine whether wearing head and face insulation slows cooling rate during snow burial. In addition, we sought to compare 3 different types of temperature measurement methods. Nine subjects underwent 2 burials each, 1 with head and face insulation and 1 without. Burials consisted of a 60-minute burial phase followed by a 60-minute rewarming phase. Temperature was measured via 3 methods: esophageal probe, ingestible capsule, and rectal probe. Cooling and rewarming rates were not statistically different between the 2 testing conditions when measured by the 3 measurement methods. All temperature measurement methods correlated significantly. Head and face insulation did not protect the simulated avalanche victim from faster cooling or rewarming. Because the 3 temperature measurement methods correlated, the ingestible capsule may provide an advantageous noninvasive method for snow burial and future hypothermia studies if interruptions in data transmission can be minimized.

On the isotope composition of reactive iron in marine sediments: Redox shuttle versus early diagenesis

The isotope composition of reactive iron (Fe) in marine sediments and sedimentary rocks is a promising tool for identifying Fe sources and sinks across ocean basins. In addition to cross-basinal Fe redistribution, which can modify Fe isotope signatures, Fe minerals also undergo diagenetic redistribution during burial. The isotope fractionation associated with this redistribution does not affect the bulk isotope composition, but complicates the identification of mineral-specific isotope signatures. Here, we present new Fe isotope data for Peru margin sediments and revisit previously published data for sediments from the California margin to unravel the impact of early diagenesis on Fe isotope compositions of individual Fe pools.Sediments from oxic California margin sites are dominated by terrigenous Fe supply with Fe release from sediments having a negligible influence on the solid phase Fe isotope composition. The highly reactive Fe pool (sum of Fe bound to (oxyhydr)oxide, carbonate, monosulfide and pyrite) of these sediments has a light isotope composition relative to the bulk crust, which is consistent with earlier studies showing that continental weathering shifts the isotope composition of Fe (oxyhydr)oxides to lighter values. Ferruginous sediments within the Peruvian oxygen minimum zone are depleted in Fe relative to the lithogenic background, which we attribute to extensive Fe release to the water column. The remaining highly reactive Fe pool has a heavier isotope composition compared to California margin sediments. This observation is in agreement with the general notion of an isotopically light benthic Fe efflux. Most of the reactive Fe delivered and retained in the sediment is transferred into authigenic mineral phases within the topmost 10 to 20cm of the sediments. We observe a first-order relationship between the extent of pyritization of Fe monosulfide and the isotope composition of authigenic pyrite. With increasing pyritization, the isotope composition of authigenic pyrite approaches the isotope composition of the highly reactive Fe pool. We argue that the isotope composition of authigenic pyrite or other Fe minerals that may undergo pyritization may only be used to trace water column sources or sinks if the extent of pyritization is separately evaluated and either close to 100% or 0%. Alternatively, one may calculate the isotope composition of the highly reactive Fe pool, thereby avoiding isotope effects due to internal diagenetic redistribution. In depositional settings with high Fe but low sulfide concentrations, source and sink signatures in the isotope composition of the highly reactive Fe pool may be compromised by sequestration of Fe within authigenic silicate minerals. Authigenic silicate minerals appear to be an important burial phase for reactive Fe below the Peruvian oxygen minimum zone.

Bone diagenesis at the micro-scale: Bone alteration patterns during multiple burial phases at Al Khiday (Khartoum, Sudan) between the Early Holocene and the II century AD

Histological analysis is widely applied to archaeological and fossil bones in order to identify diagenetic changes in bone microstructure. Diagenetic processes, affecting bones from the body deposition to the discovery, strongly depend on environmental conditions; therefore the study of diagenetic alterations provides valuable information on the taphonomic history of bones and on their burial environment. Histological analysis was performed on 58 samples of human compact bone found at Al Khiday (Khartoum, Sudan), a multi-stratified archaeological site that revealed a cemetery with distinct burial phases dating from the Early Holocene to the II century AD. The well-defined archaeological context provides a set of bone samples belonging to the same site but buried in different phases and under different environmental conditions: Central Sudan was characterised by a humid environment with seasonal swamps and palaeo-lakes in the Early Holocene, while in the II century AD the environmental conditions were more similar to the current arid climate of the Sub-Saharan belt.Scanning electron microscopy (SEM) and high-resolution X-ray computed micro-tomography (μ-CT) analysis revealed extensive bacterial and fungal attack, and secondary phases precipitation and dissolution in the samples. The analysis of textural relationships between each diagenetic feature enabled to establish a relative chronological sequence of events acting during burial. Moreover, different patterns of diagenetic alterations were observed for burial phases of different ages, proving a strong relationship between diagenesis and environmental conditions.

Are iron-phosphate minerals a sink for phosphorus in anoxic Black Sea sediments?

Phosphorus (P) is a key nutrient for marine organisms. The only long-term removal pathway for P in the marine realm is burial in sediments. Iron (Fe) bound P accounts for a significant proportion of this burial at the global scale. In sediments underlying anoxic bottom waters, burial of Fe-bound P is generally assumed to be negligible because of reductive dissolution of Fe(III) (oxyhydr)oxides and release of the associated P. However, recent work suggests that Fe-bound P is an important burial phase in euxinic (i.e. anoxic and sulfidic) basin sediments in the Baltic Sea. In this study, we investigate the role of Fe-bound P as a potential sink for P in Black Sea sediments overlain by oxic and euxinic bottom waters. Sequential P extractions performed on sediments from six multicores along two shelf-to-basin transects provide evidence for the burial of Fe-bound P at all sites, including those in the euxinic deep basin. In the latter sediments, Fe-bound P accounts for more than 20% of the total sedimentary P pool. We suggest that this P is present in the form of reduced Fe-P minerals. We hypothesize that these minerals may be formed as inclusions in sulfur-disproportionating Deltaproteobacteria. Further research is required to elucidate the exact mineral form and formation mechanism of this P burial phase, as well as its role as a sink for P in sulfide-rich marine sediments.

Paleozoic Exotic Blocks of the Crimean Mountains: Stratigraphy and Origin

Based on numerous geological data obtained by the authors for several decades, the stratification of Permian and Carboniferous ancient and exotic blocks of Crimean Mountains is performed. The sequence of geological events that cause their origin is revealed. Carnian-Norian, Rhaetian-Hettangian and Early-Pliensbachian phases of collapse, sliding and burial of Paleozoic blocks are specified. Final stage (block re-deposition) is confined to the Toarcian and Aalenian ages. The data obtained allow re-interpreting the origin of ancient exotic blocks of the Crimea.

Models for dynamic evaluation of mudstone/shale cap rocks and their applications in the Lower Paleozoic sequences, Sichuan Basin, SW China

The estimation of the sealing capability of cap rocks dynamically is one of the fundamental geological problems that must be resolved in petroleum exploration. In this paper, a porosity–capillary pressure (ϕ–Pc) method was used to estimate the sealing capacity during cap rock burial and a permeability–capillary pressure (K–Pc) plus over-consolidation ratio (OCR) method to estimate the sealing capacity during uplift. Based on 120 capillary pressure–porosity measurements, a ϕ–Pc mathematical model has been established for the burial phase. By analyzing the permeability data measured from 12 mudstone/shale samples from different stratigraphic intervals under step loading conditions, a permeability–confining pressure (K–P) mathematical model has been constructed. Moreover, capillary pressure–permeability data measured from 141 mudstone or shale cap rocks have been used to establish a K–Pc mathematical model for seal capacity evaluation during uplift. Additionally, the OCR of mudstone or shale was calculated from the results of reconstructed burial and uplift histories. These mathematical models were used in case studies in the Sichuan Basin, South China. The results indicate that capillary pressure (Pc) is inadequate in evaluating sealing capacity of cap rocks but the combination of parameters Pc and OCR works well. The agreement between calculated and measured values shows the effectiveness and reliability of the models for dynamic estimation of the sealing capacity of mudstone/shale cap rocks established in this study.

Iron and manganese shuttles control the formation of authigenic phosphorus minerals in the euxinic basins of the Baltic Sea

Microanalysis of epoxy resin-embedded sediments is used to demonstrate the presence of authigenic iron (Fe) (II) phosphates and manganese (Mn)-calcium (Ca)-carbonate-phosphates in the deep euxinic basins of the Baltic Sea. These minerals constitute major burial phases of phosphorus (P) in this area, elevating the total P burial rate above that expected for a euxinic depositional environment. Particle shuttles of Fe and Mn oxides into the deep euxinic basins act as drivers for P-bearing mineral authigenesis. While Fe(II) phosphates are formed continuously in the upper sediments following the sulfidization of Fe-oxyhydroxides and release of associated P, Mn-Ca-carbonate-phosphates are formed intermittently following inflow events of oxygenated North Sea water into the deep basins. The mechanism of Fe(II) phosphate formation differs from previously reported occurrences of vivianite formation in marine sediments, by occurring within, rather than below, the sulfate-methane transition zone. The spatial distribution of both authigenic phases in Baltic sediments varies in accordance with the periodic expansion of anoxia on centennial to millennial timescales. The results highlight the potential importance of authigenic P-bearing minerals other than carbonate fluorapatite for total P burial in euxinic basins.

The Baer Depression Tuffaceous Sandstone Reservoir Characteristics and Logging Response Research Status, Problems

In logging field, saturation evaluation in tuffaceous sandstone reservoirs has been a difficult issue to be solved urgently. It is mainly due to the effect of complex pore structures in tuffaceous sandstone reservoirs. Compared with the normal sandstones, the tuffaceous sands have the properties of diversity origination, complex mineral components, easily transformed mineral, complex digenesis and porosity evolution .The comprehensive analyses of cores, thin slices, SEM, mercury-injection data and former research outcome of Beier oilfield on the porous structure and reservoir physical property of sandstones. The tuffaceous alteration is different under different burial phase and diagenetic environment and has different effects on the porosity of coarse grain have a constructive affection to the secondary porosity.

Phosphorus diagenesis in deep-sea sediments: Sensitivity to water column conditions and global scale implications

The geological record bears evidence of various periods of wide-scale oceanic anoxia that are associated with perturbations of the marine carbon and phosphorus (P) cycles. In this study, we examine the impact of changes in bottom water oxygen and organic matter (OM) input on burial of P in deep-sea sediments using a reactive-transport model. Results show that the burial of key reactive P phases, namely authigenic calcium associated P minerals (Ca–P), organic P (org P) and iron-bound P (Fe–P), responds non-linearly to both water column forcings, namely water column oxygenation and OM loading. High organic matter (OM) flux with either very low or high oxygen (~180μM) favor the formation of authigenic Ca–P, while low oxygen and intermediate to high OM fluxes promote org P burial. Iron-bound P is only preserved in the sediment when oxygen levels are high and OM fluxes low. The conditions for maximum P recycling (or minimum P burial) are low bottom water oxygen concentrations and low OM fluxes to the sediment–water interface (hypoxic, oligotrophic deep-sea settings). The bivariate dependence of P burial on oxygen and OM flux was implemented in an existing box model of the global marine P, oxygen and organic carbon cycles, replacing simple empirical redox functions for P burial. The response of the original and new box model to decreased ocean mixing was then assessed, in the context of a long-term response. In the new model, org P instead of authigenic Ca–P is the dominant burial phase of P in deep-sea environments during periods of oceanic anoxia. Nevertheless, reduced ocean mixing leads to a similar response in total P burial and, as a consequence, to a similar increase in deep water anoxia and decrease in open ocean productivity whether an empirical or mechanistic description of phosphorus diagenesis is considered.

Facies controlled porosity evolution of the Neoproterozoic Upper Bhander Sandstone of Western India

Abstract The Upper Bhander Sandstone is dominantly composed of quartzarenites. The basal and top portions are sandstones, with the middle section comprising thinly bedded shales with interlayer silt and sandstone units. The sandstone units are composed of several varieties of quartz, feldspar, micas, rock fragments and heavy minerals. The Upper Bhander Sandstone was deposited in a transgressive phase and later modified by tidal processes and wave- and storm-dominated processes in a tide-influenced Barrier Beach Complex of the shallow marine environment. This study reveals that, during mechanical compaction, a rearrangement of grains took place and point and long contacts were formed. The early silica cementation and shallow burial resulted in high primary porosity. This phase was followed by chemical compaction and the replacement of silica cement by iron cement (Fe-cement) under the deep burial phase of these sandstones. Dissolution of Fe-cement and feldspars resulted in secondary porosity development. Quartz overgrowths are better developed on coarse- to medium-sized grains than on fine-sized grains. These observations suggest a progressive compaction, which initiated at the sediment–water interface and continued till deep burial diagenesis in a rapidly subsiding basin. The existing optical porosity of the Upper Bhander Sandstone is 4% and the minus cement porosity is 18%.