Some Effects of Partial Recrystallisation on 14C dating Late Pleistocene Corals and Molluscs

1972 ◽  
Vol 2 (02) ◽  
pp. 244-252 ◽  
Author(s):  
John Chappell ◽  
Henry A. Polach
Keyword(s):  
Sea Level ◽  
Carbon Isotope ◽  
Thin Section ◽  
Late Pleistocene ◽  
Closed System ◽  
X Ray Diffraction ◽  
14C Dating ◽  
Shallow Marine ◽  
X Ray ◽  
Shell Carbonate

The issue of sea level during the last interstadial revolves largely around the problem of achieving reliable 14C dates for shell carbonate from Late Pleistocene shallow marine and littoral deposits. A set of 27 samples were collected from Late Pleistocene reefs in New Guinea, and measurements made of 13C, 14C, plus the degree of recrystallisation (determined by X-ray diffraction). The original fibrous aragonite structure of the samples (corals and clams) is seen in thin section to recrystallise in two quite different modes. The carbon isotope results strongly suggest that one mode, the sparry calcite recrystallisation, represents an open geochemical system which allows contamination by more recent 14C, while the subtle coarsening mode of recrystallisation represents a closed system, often yielding reliable results. The reliability of the latter can be validated if a similarly recrystallised sample, known to be outside the range of 14C dating, shows a background 14C count.

scholarly journals Improved AMS 14C Dating of Shell Carbonates Using High-Precision X-Ray Diffraction and a Novel Density Separation Protocol (Cards)

Radiocarbon ◽  
2010 ◽  
Vol 52 (2) ◽  
pp. 735-751 ◽  
Author(s):  
Katerina Douka ◽  
Robert E M Hedges ◽  
Thomas F G Higham
Keyword(s):  
Secondary Phase ◽  
X Ray Diffraction ◽  
14C Dating ◽  
X Ray ◽  
Density Separation ◽  
Low Magnesium ◽  
Effective Removal ◽  
Magnesium Calcite ◽  
Shell Carbonate ◽  
Initial Results

One critical variable in the successful application of radiocarbon dating is the effective removal of carbonaceous contaminants. In the case of marine carbonates, contamination appears usually in the form of secondary low-magnesium calcite, the stable polymorph of calcium carbonate and byproduct of the post-mortem recrystallization or replacement of the autochthonous phase, originally in the form of high-magnesium calcite or aragonite. Depending on the nature of the depositional environment, the secondary phase may be contemporary in age with the original shell carbonate and may have even been derived from it by dissolution-recrystallization processes, or can be an exogenous contaminant of younger or older age. The limited ability of current pretreatment protocols to detect and remove the secondary mineralogical phases prior to dating carbonates has been one of the reasons marine shell and coral 14C determinations are often difficult to validate in terms of their reliability. We have developed a new pretreatment protocol designed to achieve greater reliability and accuracy in the dating of this material. The method entails 2 steps. The first one involves the improved detection and quantification of secondary calcite in aragonite using X-ray diffraction, at a precision of ∼0.1% and ∼0.8%, respectively. Next, where this is required, a novel density separation step using non-toxic heavy liquids (CarDS) is applied to the diagenetic sample. This enables the clear separation of calcite and aragonite, with only the latter kept for dating. We have applied the new steps, screening and separation, on standard and archaeological examples and our initial results suggest that it is successful and reproducible. In this paper, we describe the method and initial results.

Re-evaluating the origins of late Pleistocene fire areas on Santa Rosa Island, California, USA

2012 ◽  
Vol 78 (2) ◽  
pp. 353-362 ◽  
Author(s):  
Torben C. Rick ◽  
John S. Wah ◽  
Jon M. Erlandson
Keyword(s):  
Late Pleistocene ◽  
Younger Dryas ◽  
Fire Regimes ◽  
Fire Frequency ◽  
X Ray Diffraction ◽  
X Ray ◽  
Sedimentary Deposits ◽  
Natural Fires ◽  
Human Colonization ◽  
Santa Rosa Island

AbstractAt the close of the Pleistocene, fire regimes in North America changed significantly in response to climate change, megafaunal extinctions, anthropogenic burning and possibly, even an extraterrestrial impact. On California's Channel Islands, researchers have long debated the nature of late Pleistocene “fire areas,” discrete red zones in sedimentary deposits, interpreted by some as prehistoric mammoth-roasting pits created by humans. Further research found no evidence that these red zones were cultural in origin, and two hypotheses were advanced to explain their origin: natural fires and groundwater processes. Radiocarbon dating, X-ray diffraction analysis, and identification of charcoal from six red zones on Santa Rosa Island suggest that the studied features date between ~ 27,500 and 11,400 cal yr BP and resulted from burning or heating, not from groundwater processes. Our results show that fire was a component of late Pleistocene Channel Island ecology prior to and after human colonization of the islands, with no clear evidence for increased fire frequency coincident with Paleoindian settlement, extinction of pygmy mammoths, or a proposed Younger Dryas impact event.

Mechanochemical Reaction Between Sulfur and Ilmenite

1998 ◽  
Vol 51 (10) ◽  
pp. 947 ◽  
Author(s):  
Nicholas J. Welham
Keyword(s):  
Closed System ◽  
Thermal Processing ◽  
Ball Mill ◽  
Inert Gas ◽  
Iron Sulfate ◽  
Mechanochemical Reaction ◽  
X Ray Diffraction ◽  
Rutile Tio2 ◽  
X Ray ◽  
Closed Tube

An ilmenite (FeTiO3) concentrate has been milled with sulfur in a laboratory-scale ball mill for 100 h under a variety of conditions. X-Ray diffraction and thermal processing have shown that reaction occurs within the mill forming pyrite (FeS2) and rutile (TiO2). The reaction was of greatest extent in a mill run under 400 kPa of inert gas; some reaction occurred in a mill under 10-2 Pa, whereas little reaction was observed when either water or air was present. Annealing of the product powders showed that reaction to TiO2 and FeS2 could be achieved in a closed system after 1 h at 400C but with the evolution of SO2, whereas annealing at 800C also gave TiO2 and FeS2, but without formation of SO2 which was thought to have disproportionated to form iron sulfate(VI). Closed-tube annealing of unmilled sulfur and milled ilmenite showed the same reactions as milled powders but of much greater extent.

Variations of fluvial patterns and infilling history of a paleoincised valley system during Late Pleistocene to Holocene, Offshore Pahang River, Peninsular Malaysia

2018 ◽  
Vol 6 (1) ◽  
pp. T39-T50
Author(s):  
Md Mostafizur Rahman ◽  
Edlic Sathiamurthy ◽  
Guangfa Zhong ◽  
Jianghua Geng ◽  
Zhifei Liu
Keyword(s):  
Sea Level ◽  
Late Pleistocene ◽  
Peninsular Malaysia ◽  
Glacial Cycle ◽  
Shallow Marine ◽  
3D Data ◽  
Data Volume ◽  
History Of ◽  
Late Pleistocene To Holocene ◽  
Cover Thickness

High-resolution 2D acoustic profiles, combined with time slices from a 3D data volume, were used to investigate the paleoincised valleys offshore of the present-day Pahang River, South China Sea. Paleovalleys were formed during the regressive phase of the last glacial cycle. They were submerged and possibly filled during valley formation and postglacial marine transgression. Interpretation of acoustic profiles illustrates that the valleys were incised and infilled during the regression and low stand followed by subsequent deglacial sea-level rise. They were overlain by a transgressive ravinement surface suggesting transitional deposits between fluvial-dominated filling and shallow-marine deposition. This ravinement surface is overlain by Holocene shallow marine deposits. A low-sinuosity low-stand valley system changed to a high-sinuosity meander belt and eventually evolved into a deltaic distributary channel system before the complete submergence of the area. The average Late Pleistocene surface lies between 53 and 64 m below present-day mean sea level in the study area with approximately 16–50 m of valley incision. The Holocene shallow marine cover thickness varies from 5 to 10 m.

scholarly journals 14C Dating and Material Analysis of the Lime Burial of Cova de Na Dent (Mallorca, Spain)

Radiocarbon ◽  
2014 ◽  
Vol 56 (2) ◽  
pp. 387-398 ◽  
Author(s):  
Guy De Mulder ◽  
Roald Hayen ◽  
Mathieu Boudin ◽  
Tess Van den Brande ◽  
Louise Decq ◽  
...  
Keyword(s):  
Bronze Age ◽  
Simultaneous Thermal Analysis ◽  
Balearic Islands ◽  
Crushed Rock ◽  
Petrographic Analysis ◽  
X Ray Diffraction ◽  
14C Dating ◽  
X Ray ◽  
Bone Fragments ◽  
The Bronze Age

Lime burials are a characteristic phenomenon of the protohistoric funerary tradition on the Balearic Islands. At Cova de Na Dent, a lime burial has been sampled for analysis. The lime burial was made up of lime and fragmented bones. Six layers were sampled and described in the laboratory according to their color, the consistency of the deposition, and the aspect and quantity of the bone fragments. Bone samples and lime were dated. The lime was analyzed by using petrographic analysis, X-ray diffraction, FTIR spectroscopy, and simultaneous thermal analysis. The results show that the bones were cremated in the presence of crushed rock carbonate. The14C dates on the lime suggest an earlier chronology for this ritual, starting in the Bronze Age, as generally is accepted.

scholarly journals Comparative Study on Thermodynamic and Geochemical Characteristics between Cemented and Clotted Parts of Thrombolite

Crystals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1017
Author(s):  
Dingxiang Zhuang ◽  
Yan Guo ◽  
Song Chen
Keyword(s):  
Thermal Stability ◽  
Thermal Analysis ◽  
Carbon Isotope ◽  
Carbonate Rocks ◽  
Oil And Gas ◽  
Stable Carbon Isotope ◽  
Geochemical Characteristics ◽  
Stable Carbon ◽  
X Ray Diffraction ◽  
X Ray

Carbonate rocks are widely distributed in nature and are one of the main reservoir rocks for oil and gas. Microbes play an important role in the formation of carbonate rocks. Compared with the cemented part with fewer microorganisms (abiotic minerals), the nucleation and growth of the clotted part with more microorganisms (biotic minerals) are affected by the metabolic activities of microorganisms, so it has a unique morphology and crystal structure. However, there are still some confusing questions such as ones regarding the unique thermal decomposition characteristics and geochemical characteristics, which have rarely been studied. Here, X-ray diffraction (XRD) was used to determine the mineral composition of the cemented and clotted part in the same thrombolite. Then, thermal analysis and stable isotope geochemistry were used to explore the thermal stability and stable carbon isotope. The results of X-ray diffraction (XRD) show that the mineral components of the cemented and clotted part in the thrombolite are calcites, but their crystallinity is different. The crystallinity of the clotted part in the thrombolite is higher than that of the cemented part. Thermal analysis results show that the activation energy and the thermal stability of the clotted part in the thrombolite are relatively higher. In addition, the stable carbon isotope results show that, compared with the chemical precipitated calcite in the cemented part, the microorganisms in the clotted part absorb more 12C through photosynthesis, which results in more 13C in the clotted part, and the carbon isotope δ13C value is higher. This study helps to distinguish the crystallographic, thermodynamic and geochemical characteristics of cemented and clotted parts in thrombolite, and may be helpful to deepen our understanding of abiotic and biotic minerals.

A thin-section holder for selected area X-ray diffraction.

1986 ◽  
Vol 13 (4) ◽  
pp. 187-194
Author(s):  
Yasuo KANAZAWA ◽  
Hiromoto NAKAZAWA
Keyword(s):  
Thin Section ◽  
X Ray Diffraction ◽  
X Ray ◽  
Area X

Clay mineral transformations in podzolized tills in central Finland

Clay Minerals ◽  
1997 ◽  
Vol 32 (4) ◽  
pp. 531-544 ◽  
Author(s):  
D. Righi ◽  
M. L. Räisänen ◽  
F. Gillot
Keyword(s):  
Ethylene Glycol ◽  
Sea Level ◽  
Clay Minerals ◽  
X Ray Diffraction ◽  
Fine Silt ◽  
Land Uplift ◽  
X Ray ◽  
Mixed Layers ◽  
Low Charge ◽  
Mineral Transformations

AbstractTransformations of clay minerals were studied in a sequence of podzols (Entic Cryorthods) of increasing age (5500-10000 years BP) developed from till materials in central Finland. The age of the soils was estimated according to altitude above the present sea level, with reference to the age of ancient shorelines and the rate of land uplift. Clay minerals in fine (<0.1 µm), coarse (0.1-2 µm) clay and fine silt (2-5 µm) fractions were studied by X-ray diffraction. The layer charge of expandable minerals was estimated on the basis of their re-expansion with ethylene glycol following K-saturation and heating to 110°C Pedogenic transformations of clay minerals occur essentially in the E horizons of the podzols. Smectites and illite-smectite mixed-layers are the dominant clay minerals in the E horizons of soils older than 6500 years. The number of mixed-layers decreases with evolution of the soil, leaving a nearly pure smectite phase in the oldest soil (10000 years). The smectites are dioctahedral with a tetrahedral charge. Groups of low-charge and highcharge interlayers are both present in the samples, but low-charge smectite layers were found only in the two older soils (9500-10000 years). This suggests alteration with time of the high-charge smectites.

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