Paola Iacumin

OXYGEN ISOTOPE VARIATIONS OF PHOSPHATE IN MAMMALIAN BONE AND TOOTH ENAMEL

About eighty specimens from ten different species of mammals, collected from different areas under different climatic and environmental conditions, were measured for the oxygen isotopic composition of their bone and tooth phosphate. The equations relating these values to the mean oxygen isotopic composition of local meteoric water were also derived. The same equation can be used for goats, roe-bucks, and mouflons, despite the biological differences among these species. Measurements were made on about fourty different specimens of rabbit and hare from Europe, Africa, and Canada, but in this case the data obtained clearly show no direct relationship between the oxygen isotopic composition of local meteoric water and the isotopic composition of the skeletal phosphate. However, there seems to be an inverse relationship between the relative humidity of the studied areas and the δ 18O(PO43−) of the skeletal phosphate, thus suggesting the use of fossil bones of these mammal species as recorders of palaeoenvironmental relative humidity. Finally, a new equation was derived for the isotopic scale for horses, on the basis of all the previous data and of a few newly obtained results.

An isotopic palaeoenvironmental study of human skeletal remains from the Nile Valley

Stable isotope measurements were carried out on human skeletal remains from the Nile Valley, ranging in age from about 7000 to 1750 yr B.P. and on a set of other samples among which are archaeological food remains. Bone samples were analyzed for δ18O(PO3−4), δ18O(CO2−3) and δ13C(CO−3) of carbonate hydroxylapatite and δ13C and δ15N of collagen. Food remains and tissue samples were analyzed for their δ13C and δ15N values. The isotopic composition of bone collagen, apatite and food remains (partially representative of the diet in ancient Egypt) suggest a mixed diet including C3 plant food and, probably, animal resources (both fresh-water fish and C3 animals). A rather surprising observation is the lack of differences between isotopic composition of remains of different social classes spanning from the very poor village of Gebelein to the middle class of the rich town of Asyut to the distinguished people who underwent mummification processes after their death. From the palaeoclimatological point of view, the δ18O(PO3−4) values, ranging from 20.6 to 24.5‰, seem to reflect the isotopic composition of Nile river water (also related to relative humidity) rather than real climatic (temperature) variations through time. The oxygen isotope compositions of carbonate and phosphate of the same samples (from 30.2 to 32.5 and from 20.6 to 22.2, respectively) suggest isotopic equilibrium conditions, thus confirming the possibility of also using the carbonate measurements for palaeoclimatological studies, at least in the case of recent and well preserved samples.

Oxygen and carbon isotopic composition of fish otoliths

Oxygen and carbon isotopic composition of the aragonite of fish otoliths was measured on 175 specimens comprising 24 different species in 1989 and 1990. All specimens but two came from the northern Adriatic Sea or the northern Tyrrhenian Sea (two freshwater specimens were studied for comparison with the marine fish). The data obtained confirm the results of previous research suggesting the existence of equilibrium conditions between the otolith aragonite and ambient water with respect to ·18O(CO32-) values. Examination of one of the species indicated that the CaCO3 of otoliths probably accumulates continuously over time, seasonal isotopic changes being clearly visible (from a set of radial spot samples) for both oxygen and carbon isotopes. The apparent isotopic equilibrium with “ambient” water suggests that the δ18O(H2O) of the endolymph is equal to that of seawater and considerably different from that of fish body water. In the case of δ13C(CO32-), isotopic equilibrium with dissolved carbon species in seawater is never reached, even though the contribution of metabolic CO2 is variable among different species and even among different individuals of the same species. This rules out the possibility of using δ13C(CO32-) values obtained from fossil otoliths for paleoenvironmental and paleobiological conclusions.

Oxygen isotope measurements of mammoth and reindeer skeletal remains: an archive of Late Pleistocene environmental conditions in Eurasian Arctic

58 samples of fossil mammoth and reindeer teeth and bones of various ages and coming from different locations were studied for the oxygen isotopic composition of their phosphate. Samples from Siberia have interstadial (Marine Isotope Stage 3), stadial (MIS 2), late-glacial and post-glacial ages. Russian and Ukrainian samples refer to the late-glacial and transitional (between the interstadial and glacial stages) time. The δ18O of palaeoenvironmental waters were calculated from the δ18Op obtained from fossil samples by means of the isotope equations calibrated on modern specimens of elephants and deer respectively. The δ18Ow obtained are generally lighter than those measured nowadays in the same areas and not far from those measured on ice cores of Holocene age, the isotopic differences being not greater than a few δ units. The calculated values are also in fairly good agreement with some isotopic values obtained from Siberian permafrost samples. According to the results obtained it seems that the elephant and deer equations can be reasonably used respectively in the case of fossil mammoth and deer skeletons to evaluate environmental palaeowaters.

High-resolution δ18O analysis of tooth enamel phosphate by isotope ratio monitoring gas chromatography mass spectrometry and ultraviolet laser fluorination

Abstract The viability of oxygen isotope analysis of tooth enamel by UV laser ablation and fluorination has been demonstrated by comparison with the Ag3PO4 extraction method. In-situ analyses by UV laser fluorination using both isotope ratio mass spectrometry and isotope ratio monitoring gas chromatography mass spectrometry (irm-GCMS) microanalysis are comparable to those of the Ag3PO4 method with a mean precision of ±0.4‰ (1σ) for samples with δ 18 O values ranging from 10.8 to 20.8‰. UV laser ablation provides spatial resolution of 100 μm or less with no laser reaction rim. These data show that irm-GCMS offers a combination of spatial and analytical precision for in-situ sampling of biogenic apatites previously unobtainable by other means.

A stable isotope study of mammal skeletal remains of mid-Pleistocene age, Arago cave, eastern Pyrenees, France. Evidence of taphonomic and diagenetic effects

Abstract This study reports a set of 85 oxygen isotope measurements carried out on fossil bones of Cervus elaphus, Ovis sp. and Equus sp. from archaeological excavations in the Arago cave, eastern Pyrenees, south-eastern France, of ages ranging from about 650 to 450 ka. A large section of the thick sediment sequence filling the cave was flushed, for an unknown time, by meteoric water through a large opening in the limestone ceiling caused by karst erosion. Under these conditions, part of the biogenic material underwent partial solution and diagenesis; these processes may have caused considerable effects on the original isotopic composition of bone phosphate. The range of the isotopic values obtained from each stratigraphic level is quite wide, particularly in the case of horse remains whose δ18O(PO3−4) values cover a range of about 5‰ in the same stratigraphic level. However, a few isotopically heavy values were obtained from the three species which suggest the possibility of very warm climatic episods or, alternatively, of climatically dry periods. Altogether, the results clearly show that it is not possible to obtain quantitative palaeoclimatological and palaeoenvironmental information from fossils which underwent taphonomic and diagenetic effects, that these effects may take place readily and that time is one of the less important parameters affecting bone preservation. The uncertainties existing in the case of relatively old fossil bones (not always shared by isotope geochemists) are thus directly confirmed.

A stable isotope study of fossil mammal remains from the Paglicci cave, southern Italy, 13 to 33 ka BP: palaeoclimatological considerations

Abstract A set of 102 samples of fossil skeletal remains of mammals from a sediment sequence from the Paglicci cave in southern Italy, was studied for the oxygen isotopic composition of bone and tooth phosphate. The samples belong to Cervus elaphus, Bos primigenius and Equus caballus and come from various levels of a succession spanning about 33 to 13 ka BP (calibrated 14C ages). On the basis of X-ray diffraction studies on every sample, most of them show no evidence of recrystallisation and may thus be considered reliable for isotopic study. δ18Op values range from 16.8%o to 20.5%o (V-SMOW). Cervus and Bos samples show trends in their isotopic values that are similar to each other. The δ18Ow calculated from their δ18Op P values, using previously established equations, form sections of a climatic curve that agree quite well with the palaeoclimatological curve obtained from the GRIP ice core, despite minor differences in the timing and intensity of some climatic events. Despite the relatively low latitude of the area and its central position in the Mediterranean basin, we may conclude that major climatic changes left their signature on the isotopic composition of the samples studied.

An oxygen isotope study of silicates in the larderello geothermal field, Italy

Abstract Stable-isotope analyses were carried out on hydrothermal minerals sampled from the deep metamorphic units at Larderello, Italy. The ∂ 18 O values obtained for the most retentive minerals, quartz and tourmaline, are from + 12.0‰ to + 14.7‰ and 9.9‰ , respectively, and indicate deposition from an 18 O-rich fluid. Calculated ∂ 18 O values for these fluids range from + 5.3‰ to + 13.4‰ . These values, combined with available fluid inclusion and petrographic data, are consistent with the proposed existence of an early thermal fluid of probable magmatic origin and a late meteoric water. Mixing between these two fluids occurred locally.

Oxygen isotopic composition of lower cretaceous tholeiites and precambrian basement rocks from the paraná basin (Brazil) : The role of water-rock interaction

Abstract 107 rock samples from the Parana plateau, southern Brazil (86 tholeiites and 21 various rock-types from the Precambrian crystalline basement) were measured for their oxygen isotopic composition. Both the crustally uncontaminated tholeiites from the Northern Parana Province and the crustally contaminated basalts from the Southern Parana Province exhibit quite positive δ 18 O-values ranging from +6.0 to +11.5% and from +7.0 to +12.8%, respectively. These values are considerably higher than those expected for rocks deriving from mantle partial fusion (+5.7±0.3%). A simple process of crustal contamination and fractional crystallization cannot explain the results obtained as the oxygen isotopic composition of the samples from the crystalline basement ( +4.8 to +12.7%, mean value +8.8%) cannot explain a δ 18 O increase of the basalt magma higher than ∼ 2%o. According to various considerations, we conclude that the positive oxygen isotope values exhibited by the Parana basalts are the result of secondary post-eruptive hydrothermal exchange processes between rock and 18 O-enriched water. The 18 O-enriched water was substantially formed by isotopic exchange between normal (meteoric) groundwater and either the thick sedimentary sequence underlying the volcanic sequence in the Parana basin or the crystalline basement rocks.