Palaeoenvironments of the late Triassic Rhaetian Sea: Implications from oxygen and strontium isotopes of hybodont shark teeth (original) (raw)
Related papers
2013
Fossil shark remains occur in both marine and nonmarine Late Palaeozoic deposits, therefore their palaeoecology is controversial. The oxygen and strontium isotopic composition of biogenic fluorapatite in 179 teeth, scales and spines predominantly of hybodontid (Lissodus) and xenacanthiform (Orthacanthus, Xenacanthus, Bohemiacanthus, Triodus) sharks from various Late Carboniferous (Moscovian) to Early Permian (Artinskian) basins of Europe are used as ecological tracers to decipher diadromous or obligate freshwater lifestyle of the investigated taxa. The δ 18 O P values of the different shark teeth range from 11.7 to 20.2‰ within the different basins with mean values of 16.9 ± 0.5‰ for the Bohemian Massif, 16.2 ± 0.8‰ for eastern Germany, 18.2 ± 1.0‰ for southwestern Germany, 18.5 ± 0.7‰ for southern-central Spain, 17.6 ± 0.4‰ for Sardinia, and 16.6 ± 0.5‰ VSMOW for the French Massif Central. The tooth δ 18 O P values from the basins are mostly depleted by 1-5‰ relative to those of shark teeth from contemporaneous marine settings. Oxygen isotope signatures of co-occurring taxa do not show systematic differences excluding habitat effects for different shark groups. However, distinctly higher δ 18 O P values from Puertollano and Saar-Nahe can be attributed to significant evaporative enrichment in 18 O of the ambient water in the ancient lacustrine environments due to a warm and dry climate and sufficient residence time in the basins. The strontium isotopic composition of the teeth varies between 0.70824 and 0.71216 with a mean value of 0.71031. These 87 Sr/ 86 Sr ratios are always more radiogenic in comparison to the 87 Sr/ 86 Sr record of seawater of their stratigraphic age. Overall, the investigated tooth samples yield low δ 18 O P and high 87 Sr/ 86 Sr values deviating from bioapatite values expected for contemporaneous marine vertebrates and typical for freshwater settings. This indicates a fully freshwater adapted lifestyle for a variety of fossil shark taxa in Late Palaeozoic European basins.
Palaeogeography Palaeoclimatology Palaeoecology, 1998
The Upper Marine Molasse sediments of southern Germany were deposited during the Early to Middle Miocene, a period of significant change for the global Miocene palaeoceanography, palaeoclimate, and the regional palaeogeography because of the ongoing Alpine–Himalayan orogeny. To address the influence of the Alpine uplift on climate and oceanography of the northern Alpine molasse basin, a combined O-, Sr-, and Nd-isotope study was undertaken on fossil teeth from sharks (Synodontaspis sp., Galeocerdo cf. aduncus, Chaenogaleus sp.), and button-like teeth from the bony fish of the Upper Marine Molasse (Chrysophrys molassica). Average δ18O values for hydroxyapatite of teeth from two sites are 20.3‰ (1σ=0.6) and 21.2‰ (1σ=0.5), while their average 87Sr/86Sr and 143Nd/144Nd ratios are 0.70850 (±0.00001, 2σ) and 0.70882 (±0.00003, 2σ), and 0.51220, and 0.51223 (both at ±0.00001, 2σ), respectively. By comparison to the Sr-evolution curve for the global ocean, the Sr-isotope compositions suggest ages of about 22 and 17 Ma for the teeth. These ages are in good agreement with the depositional ages, which suggests open marine conditions. Open marine conditions are also compatible with (1) lower average δ18O values and 87Sr/86Sr ratios for the one site compared to higher δ18O values and higher 87Sr/86Sr ratios for the other site, (2) estimates for seawater temperatures which are similar to other estimates from deposits of similar latitude and age, (3) a comparison of seawater temperatures with average ambient air temperature estimates deduced from continental palaeoclimate indicators. Nd-isotope compositions are compatible with an influence of the North Atlantic on the Paratethys. Assuming constant salinity and seawater oxygen isotope composition, a 4°C cooling can be inferred from average δ18O values of the teeth between 22 and 17 Ma. This is similar to trends observed for foraminiferal records from the Mediterranean Tethys, but different from foraminiferal and molluscan records of the North Atlantic and the North Sea during this period, and allows for the possibility that the Alpine orogeny had an influence on the regional, circum-Alpine climate.
d18OP values and 87Sr/86Sr ratios were determined on disarticulated xenacanthiform, hybodontid and ctenacanthid shark tooth material from several Early Permian (Sakmarian–Kungurian) continental bone beds of northern Texas and southern Oklahoma as well as from the marine Middle Permian (Roadian) of northern Arizona. The d18OP values derived from the teeth of bone beds are in the range of 17.6–23.5‰ VSMOW, and are mostly depleted in 18O by 0.5–5‰relative to proposed coeval marine d18OP values. This indicates an adaptation to freshwater habitats on the Early Permian coastal plain by several sharks. Distinctly higher d18OP values from two bone beds are attributed to significant evaporative enrichment in 18O in flood plain ponds. 87Sr/86Sr ratios of around 0.71077 are notably more radiogenic than 87Sr/86Sr of contemporaneous seawater. In contrast, the isotopic composition of teeth from the marine Kaibab Formation is characterised by low d18OP values in the range of 13.4–15.6‰ VSMOW while 87Sr/86Sr ratios of around 0.70821 are closer to the Roadian seawater value. The distinctly depleted d18OP values cannot be readily explained by fluvially affected freshening in a nearshore marine environment, so a diagenetic alteration of the Kaibab material seems to be more likely, excluding it from further interpretation.
Permian sedimentary rocks exposed in the southwestern USA record a highly diverse shark fauna from marine and continental environments. Especially mixed marine and “typically freshwater-considered” shark faunas in Early Permian (Sakmarian–Kungurian) continental bone beds complicate palaeoecological evaluation of the available taxa. These bone beds were originally formed on a coastal plain along the northeastern margin of the Midland Basin in western equatorial Pangaea that was dominated by meandering rivers and associated floodplain environments with repeatedly intercalated marine limestones. The oxygen and strontium isotope composition of biogenic apatite in fossil shark teeth has demonstrated its worth to widen the knowledge regarding palaeoenvironmental conditions as well as habitat preferences of the investigated fishes. δ18OP values and 87Sr/86Sr ratios were determined on 36 disarticulated teeth from four bone beds of northern Texas (Conner Ranch, Coprolite Site, Spring Creek B...
Isotopic composition of recent shark teeth as a proxy for environmental conditions
Geochimica Et Cosmochimica Acta, 2001
The O, C, and Sr isotope compositions of teeth from ten species, belonging to five families, and three orders of sharks were measured to determine the influence of habitat, diet, and possible species-specific fractionation effects on the isotopic composition of biogenic phosphate from fish. The sharks were recently caught in subtropical waters off the KwaZulu-Natal (KZN) coast of South Africa, as well as from cold waters in Prince William Sound (PWS), Alaska, and Victor Bay (VB), Nunavut, Canada.δ18O values of tooth phosphate (δ18OP) range from 20.9 to 23.5‰ for the KZN sharks. For most species the range in measured δ18OP values is about 0.6‰, but it may be as high as 1.1‰ for different teeth from a single shark. Dentine and enameloid within individual teeth have no apparent differences in δ18OP values. The δ18OP values of the KZN shark teeth reflect the typical habitat of the studied species, primarily the thermal structure of the water column off KZN at depths between 20 and 280 m. The δ18OP values of teeth from different Greenland sharks from VB and Pacific sleeper sharks from PWS are very homogeneous, averaging 25.8 and 24.7‰, respectively. These values appear to be in equilibrium with deep (>500 m) ocean waters in each case at temperatures of about −0.3°C or less. There is little discernable evidence for species-specific fractionation effects for the oxygen isotope composition of phosphate in the studied marine fish.The oxygen isotope composition of carbonate in apatite averages about 9.1‰ higher than corresponding δ18OP values, in agreement with equilibrium fractionation between carbonate and phosphate, but with a large variance (1σ = ±1.5‰). δ18OC values also vary by up to 1‰ between enameloid and dentine within single teeth, but in a non-systematic way. Differences in δ13C values between carbonate in enameloid and dentine is also large (up to 8‰) but the δ13C values vary systematically. Enameloid is always enriched in 13C compared to dentine and the 13C content increases with developmental stage of the teeth. δ13C values measured for enameloid (1.6 to 4.8‰) appear to approach equilibrium with dissolved inorganic carbon in seawater. In contrast, δ13C values for dentine range from −6.4 to −2.3‰ for KZN sharks, and −9.0 to −10.8‰ for the cold-water sleeper sharks, and are compatible with a predominantly dietary carbon source. The 87Sr/86Sr ratios of teeth from KZN sharks as well as those from PWS and VB are uniform, averaging 0.709167. Sr content varies from 1270 to 2100 ppm, a range that is similar to that in well preserved fossilized teeth. Seawater Sr is thus clearly incorporated in vivo. Concentrations of Sm and Nd are in the ppb range and contrast the ppm range in fossilized teeth, indicating a postmortem incorporation of rare earth elements in apatite of the teeth.
Mineralogia, 2011
We report the results of high-precision (±0.05‰) oxygen isotope analysis of phosphates in 6 teeth of fossil sharks from the Mangyshlak peninsula. This precision was achieved by the offline preparation of CO2 which was then analyzed on a dual-inlet and triple-collector IRMS. The teeth samples were separated from Middle-and Late Bartonian sediments cropping out in two locations, Usak and Kuilus. Seawater temperatures calculated from the 18 O data vary from 23-41 o C. However, these temperatures are probably overestimated due to freshwater inflow. The data point at higher temperature in the Late Bartonian than in the Middle Bartonian and suggest differences in the depth habitats of the shark species studied.
Palaeogeography, Palaeoclimatology, Palaeoecology, 2008
The 87 Sr/ 86 Sr isotopic composition of the enameloid tips of teeth of Scapanorhynchus texanus, a common and widespread upper Cretaceous shark, differs from that found in the dentine inner portions of the same teeth. Using a marine 87 Sr/ 86 Sr isotopic evolution curve, we converted the 87 Sr/ 86 Sr isotopic composition of different sections of the teeth to numerical ages. Portions of fossil teeth dominated by enameloid (but that include some dentine) yield numerical ages (74.2 ± 0.8 Ma, 2 standard error [S.E.]) that fall within the upper Cretaceous, and are consistent with the known geologic age range of these fossils. As the proportion of dentine present in samples of the teeth increases, the 87 Sr/ 86 Sr-derived numerical ages trend from biostratigraphically reasonable upper Cretaceous ages to those that are far younger and biostratigraphically impossible (about 32 Ma, i.e., Oligocene). This deviation in isotopic composition (and numerical age) is likely the result of post-burial diagenetic alteration of dentine, which is generally more susceptible to such alteration than enameloid. To avoid the contaminating effects of dentine, we sampled only the enameloid portion of twelve S. texanus teeth by scratching their surfaces. The enameloid scratch samples yield numerical ages (78.8 ± 0.4 Ma, 2 S.E.) older than those obtained for any of the sectioned samples. This suggests that sampling only the surface enameloid of shark teeth is useful in reducing spurious isotopic results arising from post-burial alteration of teeth. The numerical age for the enameloid scratch samples is consistent with the known early Campanian-early Maastrichtian occurrence of S. texanus in North America and with the radiometric age of the deposit from which these samples were recovered.