Geochemical and stable isotope patterns of calcite cementation in the Upper Cretaceous Chalk, Uk: Direct evidence from calcite-filled vugs in brachiopods

2012 ◽  
Vol 62 (2) ◽  
pp. 143-172 ◽  
Author(s):  
Xiufang Hu ◽  
Christopher Jeans ◽  
Tony Dickson
Keyword(s):  
Organic Matter ◽  
Stable Isotope ◽  
Trace Element ◽  
Upper Cretaceous ◽  
Direct Evidence ◽  
Isotope Analysis ◽  
History Of Research ◽  
History Of ◽  
Calcite Cementation ◽  
The Uk

ABSTRACT Hu, X-F, Jeans, C.V. and Dickson, J.A.D. 2012. Geochemical and stable isotope patterns of calcite cementation in the Upper Cretaceous Chalk, UK: Direct evidence from calcite-filled vugs in brachiopods. Acta GeologicaPolonica, 62 (2), 143-172. Warszawa. The history of research into the cementation of the Upper Cretaceous Chalk of the UK is reviewed. Calcitefilled vugs within the shell cavities of terebratulid brachiopods from the Cenomanian Chalk of eastern England have been investigated by cathodoluminesence imaging, staining, electron microprobe and stable isotope analysis. This has provided the first detailed analysis of the geochemistry of the Chalk’s cement. Two cement series, suboxic and anoxic, are recognized. Both start with a Mg-rich calcite with positive δ 13 C values considered to have been precipitated under oxic conditions influenced by aerobic ammonification. The suboxic series is characterized by positive δ 13 C values that became increasingly so as cementation progressed, reaching values of 3.5‰. Manganese is the dominant trace element in the earlier cement, iron in the later cement. Mnand Fe-reducing microbes influenced cement precipitation and the trace element and δ 13 C patterns. The anoxic series is characterized by δ 13 C values that became increasingly negative as cementation progressed, reaching values of -6.5‰. Trace elements are dominated by iron and manganese. Sulphate-reducing microbes influenced cement precipitation and the trace element and δ 13 C patterns. Both cement series are related closely to lithofacies and early lithification pre-dating the regional hardening of the Chalk. The suboxic series occurs in chalk which was continuously deposited and contained hematite pigment and limited organic matter. The anoxic series was associated with slow to nil deposition and hardground development in chalks that originally contained hematite pigment but no longer do so, and an enhanced supply of organic matter.

scholarly journals Barium stable isotopes as a fingerprint of biological cycling in the Amazon River basin

2020 ◽  
Vol 17 (23) ◽  
pp. 5989-6015
Author(s):  
Quentin Charbonnier ◽  
Julien Bouchez ◽  
Jérôme Gaillardet ◽  
Éric Gayer
Keyword(s):  
Organic Matter ◽  
Stable Isotope ◽  
Trace Element ◽  
Isotope Composition ◽  
Silicate Weathering ◽  
Biological Cycling ◽  
Biological Uptake ◽  
Dissolved Load ◽  
Silicate Rocks

Abstract. The biological cycle of rock-derived nutrients on the continents is a major component of element transfer between the Earth's surface compartments, but its magnitude currently remains elusive. The use of the stable isotope composition of rock-derived nutrients, which can be fractionated during biological uptake, provides a promising path forward with respect to quantifying biological cycling and its overall contribution to global element cycling. In this paper, we rely on the nutrient-like behaviour of the trace element barium (Ba) and use its elemental and stable isotope compositions in dissolved and sediment load river samples to investigate biological cycling in the Amazon Basin. From these measurements, we show that dissolved Ba mainly derives from silicate rocks, and a correlation between dissolved Ba and K abundances suggests that biological cycling plays a role in the Ba river budget. Furthermore, the isotope composition of Ba (δ138Ba) in the dissolved load was found to be significantly different from that of the parent silicate rocks, implying that dissolved Ba isotopic signatures are affected by (i) the precipitation of soil-forming secondary phases as well as (ii) biological uptake and release from dead organic matter. Results from an isotope mass balance method applied to the river dissolved load data indicate that, after its release to solution by rock weathering, Ba is partitioned between the river dissolved load, secondary weathering products (such as those found in soils and river sediments), and the biota. In most sub-catchments of the Amazon, river Ba abundances and isotope compositions are significantly affected by biological cycling. Relationships between estimates of Ba cycled through biota and independent metrics of ecosystem dynamics (such as gross primary production and terrestrial ecosystem respiration) allow us to discuss the role of environmental parameters such as climate or erosion rates on the biological cycling of Ba and, by extension, the role of major rock-derived nutrients. In addition, catchment-scale mass and isotope budgets of Ba show that the measured riverine export of Ba is lower than the estimated delivery of Ba to the Earth surface through rock alteration. This indicates the existence of a missing Ba component, which we attribute to the formation of Ba-bearing particulate organics (possibly accumulating as soil organic matter or currently growing biomass within the catchments) and to organic-bound Ba exported as “unsampled” river particulate organic matter. Given our findings on the trace element Ba, we explore whether the river fluxes of most major rock-derived nutrients (K, Mg, Ca) might also be significantly affected by biological uptake or release. A first-order correction of river-derived silicate weathering fluxes from biological cycling shows that the carbon dioxide (CO2) consumption by silicate weathering at the mouth of the Amazon could be several times higher than the previously reported value of 13 × 109 mol CO2 yr−1 (Gaillardet et al., 1997). Overall, our study clearly shows that the chemical and isotope compositions of rivers in the Amazon – and most likely in other large river basins – bear a biological imprint, thereby challenging common assumptions made in weathering studies.

Multi-chemical fingerprinting of contrasted waters flowing within the unconventional Okavango Delta: evidence of an original ‘island reactor’

2020 ◽  
Author(s):  
Aline Dia ◽  
Olivier Dauteuil ◽  
Marc Jolivet ◽  
Mélanie Davranche ◽  
Martine Bouhnic-le-Coz ◽  
...  
Keyword(s):  
Organic Matter ◽  
Trace Element ◽  
Water Samples ◽  
Isotope Analysis ◽  
Water System ◽  
Strong Relationship ◽  
Speciation Analysis ◽  
Critical Metals ◽  
Hydrological System ◽  
Circumneutral Ph

<p>The 20.000 km<sup>2</sup> swamp of the Delta is organized into islands, flood plains and permanent and seasonal channels. Most of these islands display a surprising vegetation distribution composed of tree rings surrounding the islands and limiting an inner domain with scarce vegetation. Whereas the hydrology of the Okanvango wetlands is governed by a series of drivers such as, sedimentation, climate, tectonic and biological processes, the potential of the use of multi-chemical tracing has not been so far much investigated. The conducted study as part of a multidisciplinary project dedicated to the understanding of the functioning of the Delta, involved water samples collected both upstream and downsream the river, close to one of these islands and also recovered within the island as well. The main objective of this geochemical investigation was to better constrain the interactions prevailing in between these islands and the water chemical record. pH, conductivity (C), dissolved organic and inorganic carbon (DOC & DIC) concentrations were measured as well as those of major anion and cation and trace cation concentrations as well. Whichever the tracers are considered, two contrasted groups of samples were evidenced depending on their sampling positioning regarding the island. The samples recovered only within the island displayed pH around and over 9 and higher conductivities, whereas the other showed lower circumneutral pH values and conductivities as well. The high conductivities of the water samples fom the island also correspond to the highest DOC and DIC concentrations. The strong relationship linking the high DIC values and the high pH in the island samples records probably alkaline CO<sub>3</sub><sup>2-</sup> et HCO<sub>3</sub><sup>- </sup>-rich waters resulting from water-rock interactions with carbonates. The marked DOC enrichment has mostly to be related to microbial or photo-degradation of plant-derived organic matter and/or hydrological condition variations promoting DOC release. Significant, Cl<sup>-</sup>, SO<sub>4</sub><sup>2-</sup>, NO<sub>2</sub><sup>-</sup>enrichments as well as major cation ones were also evidenced in the same group of samples within the island. However, the most surprising results are sourced in the trace element fingerprinting. This latter includes huge enrichment in heavy, critical metals and metalloids as well (e.g. Cr, Pb, V, REE, U, Th or As). Beyond the only marked REE-spike, Upper Continental Crust-normalized REE patterns displayed markedly contrasted shapes exhibiting two types of waters with circumneutral pH ones with MREE-enrichment, whereas the alkaline waters evidenced a classical continuous enrichment throughout the whole series from LREE to HREE and a positive Ce anomaly. The use of such multi-tracing allowed an efficient fingerprinting of two distint types of waters to get clues to further constrain both the dynamics of such islands and the functioning of the water system. Still in progress, the study will be completed by (i) the stable isotope analysis, (ii) the modeling of the minerals possibly at equilibrium with the waters and of the organic matter-trace element interactions, (iii) the speciation analysis of some enriched elements, (iv) the comparison between water and solid samples analyses and (v) the understanding of the relations in between the concentrations and locations in the hydrological system.</p>

The Coarse-Pounded Corn People

2016 ◽  
Author(s):  
Martin D. Gallivan ◽  
Victor D. Thompson
Keyword(s):  
Stable Isotope ◽  
Isotope Analysis ◽  
Late Woodland ◽  
Skeletal Remains ◽  
Spatial Practices ◽  
Native Communities ◽  
Late Woodland Period ◽  
History Of ◽  
Burial Grounds ◽  
Chickahominy River

Chapter 5 focuses on archaeological investigations along the Chickahominy River and a history of residential settlements, subsistence practices, and burial grounds during the Middle to Late Woodland transition. In the sixth century A.D., Native communities living along the Chickahominy River began to bury the deceased in communal burial grounds (ossuaries) located in the drainage’s swampy interior. During the Late Woodland period, new places were established along the Chickahominy with the construction of dispersed farmsteads, burial grounds, and a palisaded compound. In this history of placemaking we see evidence of the spatial practices whereby forager-fishers became the Chickahominy. As is apparent from colonial accounts of the Chickahominy, the “coarse-pounded corn people,” a horticultural economy was a part of this ethnogenetic process. Bioarchaeological study of skeletal remains from the Chickahominy, including stable isotope analysis, provides a basis for considering the history of maize-based horticulture in the region.

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