LA-ICP-MS U-Pb dating and REE patterns of apatite from the Tatra Mountains,Poland as a monitor of the regional tectonomagmatic activity

This study presents apatite LA-ICP-MS U-Pb age and trace elements concentrations data from different granite types from the Tatra Mountains, Poland. Apatite from monazite and xenotime-bearing High Tatra granite was dated at 339 ± 5 Ma. The apatite LREE patterns reflect two types of magmas that contributed to this layered magma series. Apatite from a hybrid allanite-bearing diorite from the Goryczkowa Unit was dated at 340 ± 4 Ma with apatite LREE depletion reflecting the role of allanite and titanite during apatite crystallization. Apatite crystals from a hybrid cumulative rock from the Western Tatra Mountains were dated at 344 ± 3 Ma. Apatite is one of the main REE carriers in this sample and exhibit flat REE patterns. Taking into account the relatively low closure temperature of the U-Pb system in apatite (350–550°C), the c. 340 Ma apatite ages mark the end of high temperature tectonometamorphic activity in the Tatra Mountains.     

Geochronology of plutonic rocks from the Sanandaj-Sirjan zone,Iran and new zircon and titanite U-Th-Pb ages for granitoids from the Marivan pluton

The Sanandaj-Sirjan zone of Iran is a metamorphic belt consisting of rocks which were metamorphosed under different pressure and temperature conditions and intruded by various plutons ranging in composition from gabbro to granite. The majority of these granitoids formed along the ancient active continental margin of the Neo-Tethyan ocean at the southeastern edge of the central Iranian microplate. Geochronological data published in recent years indicate periodic plutonism lasting from Carboniferous through Mesozoic to late-Paleogene times (from ca. 300 to ca. 35 Ma) with climax activity during the mid- and late-Jurassic. The age constraints for plutonic complexes, such as Siah-Kouh, Kolah-Ghazi, Golpayegan (Muteh), Azna, Aligoodarz, Astaneh, Borujerd, Malayer (Samen), Alvand, Almogholagh, Ghorveh, Saqqez, Marivan, Naqadeh and Urumieh, clearly indicate the periodic nature of magmatism. Therefore, the Sanandaj-Sirjan zone preserves the record of magmatic activity of a complete orogenic cycle related to (1) Permocarboniferous(?) rifting of Gondwana and opening of the Neo-Tethyan ocean, (2) subduction of the oceanic crust, (3) continental collision and (4) post-collision/post-orogenic activities. The formation of the Marivan granitoids, northwestern Sanandaj-Sirjan zone, for which we present U-Pb zircon and titanite ages of ca. 38 Ma, can be related to the collisional and post-collisional stages of this orogenic cycle.     

Upper Cretaceous volcanoclastic deposits from the Haţeg basin,south Carpathians (Romania): K-Ar ages and intrabasinal correlation

In order to constrain the age of the Upper Cretaceous continental Densuş-Ciula Formation from the Haţeg basin, South Carpathians, and correlate it with the other continental unit that occurs in the region, the Sanpetru Formation, we separated and dated by the K-Ar method biotites and amphiboles from volcanoclastic deposits. The mineral phases analysed are from two tuff layers and volcanic bombs cropping out near Rachitova village. Two tuff layers from the Densuş-Ciula Formation give early Maastrichtian ages of 69.8±1.3 and 71.3±1.6 Ma, respectively. The ages determined for the tuff layers constrain the age of deposition for the Densuş-Ciula Formation and enable further correlations with the available palaeomagnetic data from the deposits occurring along the Sibişel Valley that belong to the Sanpetru Formation. The volcanic bombs collected near to Răchitova village are andesites and dacites. The age determined by K-Ar method on hornblende separated from a volcanic bomb is 82.7±1.5 Ma, which is older than the underlying Campanian marine deposits in turbidite facies. This suggests that the volcanic bombs were re-deposited during the early Maastrichtian. Thus, the volcanics found at Răchitova have at least two origins: one type is related to an explosive synsedimentary volcanic activity, and the other type is represented by older andesitic/dacitic bombs, which most probably originate from a volcanic centre situated in the Haţeg region.     

Chemical U-Th-Pb geochronology: A precise explicit approximation of the age equation and associated errors

In a single decaying system, the age determined from the exponential decay law is directly related to its linear Maclaurin approximation. This relationship can be additively extended to several decaying systems resulting in the same daughter element, by using proportionality functions, thus allowing an explicit formulation of the age as a function of element concentrations. The values of the binary proportionality function for the ²³⁸U-²³⁵U-Pb system and the ternary proportionality function for the ²³²Th-²³⁸U-²³⁵U-Pb system were determined by iterations of the exponential decay formula up to 4 Ga, with a step of 10 Ma, for a set of 24 different U/Th ratios. From the iteration data, the expressions of the two functions and the associated coefficients were determined by polynomial regression and mathematical programing on conveniently separated time and compositional intervals. Additional time- and composition-dependent age corrections optimized by mathematical programming of the residuals lead to an accuracy of 0.005 Ma of the resulting age. The error propagation can be traced through all the operations defined by explicit formulas according to simple error propagation rules, finally allowing the calculation of the standard error of the result. The formulas and parameters derived can be used in a calculation spreadsheet.     

U-Pb dating of zircon: A sourcing method for pottery from La Morena archaeological site,north-west Colombia*

U-Pb zircon radiometric dating and petrographic thin-section analysis were used for provenance identification of Ferrería and Marrón Inciso pottery styles from La Morena archaeological site in northwestern Colombia. U-Pb dating was applied to zircons recovered from pottery and rock samples from nearby geological units. The results suggest at least three distinct sources: the metamorphic rock unit on which the archaeological site is located, a granodiorite unit that outcrops further away from the site, and a mafic rock that cannot be attributed with certainty. U-Pb in zircons proved to be effective as a provenance method, where ages of the possible source rocks are well constrained, and can be applied to areas where traditional sourcing methods may be problematic.     

A possible early age for a diprotodon (Marsupialia: Diprotodontidae) fossil from the Papua New Guinea highlands

MENZIES, J., DAVIES, H.L., DUNLAP, W.J. & GOLDING, S.D., June, 2008. A possible early age for a diprotodon (Marsupialia: Diprotodontidae) fossil from the Papua New Guinea highlands. Alcheringa 32, 129–147. ISSN 0311-5518.

A fossil diprotodon jawbone coated and impregnated with a well-cemented fine breccia or tuff was recovered from weakly consolidated Pleistocene lacustrine sediments near Yonki in the Papua New Guinea highlands. The fine breccia includes angular rock and mineral fragments derived from country rock, accretionary lapilli and clay minerals. It does not include any identifiable primary volcanic material. The presence of accretionary lapilli and lack of volcanic clasts suggests an origin by phreatic eruption—an explosive eruption driven by the violent escape of gas. Minerals in the fine breccia have an age of 13.2 ± 0.2 Ma, middle Miocene, as indicated by ⁴⁰Ar/³⁹Ar analysis. This is the age of the country rock that was blasted by the phreatic eruption. Igneous activity in the Yonki area is thought to have ceased at 7.4 Ma (younger age limit of Elandora Porphyry; late Miocene), and so it is likely, but not certain, that the phreatic eruption occurred not later than 7.4 Ma. The jawbone, as far as can be told from its poor condition, is dentally similar to the late Pliocene and possibly Pleistocene ‘Kolopsis’ watutense recovered from other sites in New Guinea. Probably, the jawbone, or the living marsupial, was buried in the fine breccia at the time of the phreatic eruption, and its remains were subsequently reworked by river erosion and redeposited in the lacustrine sediments. Recrystallization and loss of primary texture in some of the bone may be a result of heating at the time of, or preceding, the eruption.     

ESR dating of the Donggutuo Palaeolithic site in the Nihewan Basin, northern China

The fluvio-lacustrine sequences in the Nihewan Basin, northern China, provide important terrestrial archives about Palaeolithic settlements and, therefore, about early human occupation in high northern latitude in East Asia. Here we present detailed ESR dating of the Donggutuo Palaeolithic site, located in this basin. Four levels A, B, C and E of the Donggutuo archaeological layer yield ESR ages ranging from 1060±129 ka to 1171±132 ka with a mean of 1119±132 ka. The ages are consistent with the paleomagnetic data, which show that the Donggutuo Palaeolithic site lies just below the onset of the Jaramillo normal subchron (0.99–1.07 Ma). Furthermore, our results indicate that the reliable ESR dating range of bleached quartz using Ti-Li centre can be effectively extended to 1100 ka and the Ti-Li centre was zeroed before the last deposition, which requires improvement of the understanding of the bleaching mechanism conditions.     

Multi-method luminescence investigations on quartz grains of different sizes extracted from a loess section in Southeast Romania interbedding the Campanian Ignimbrite ash layer

In this study we present luminescence investigations of four samples of loess bracketing the Campanian Ignimbrite/Y5 tephra at the Rasova-Valea cu Pietre site, on the eastern bank of the Danube River, southeastern Romania. Investigations involved SAR-OSL dating on aliquots of fine (4–11 μm) and medium-grained (63–90 μm) quartz, as well as single grain analyses on 125–180 μm quartz. Luminescence dating results coupled with glass-shard chemical fingerprinting assign the depositional age and origin of the ash layer to that of the Campanian Ignimbrite/Y5 tephra, dated elsewhere using ⁴⁰Ar/³⁹Ar to 39.28 ± 0.11 ka. Fine-grained (4–11 μm) quartz SAR-OSL analyses yielded ages of 44.4 ± 4.5 ka below the ash, and 41.4 ± 4.2 ka above the ash layer. Single grain analysis on coarse-grained quartz, however, demonstrates that coarse material from these samples exhibits low sensitivity and responds poorly to internal checks of the SAR protocol in comparison with the finer sediment. This observation highlights the need for more extensive investigations into the luminescence properties of quartz as well as into the origin of quartz contributions from different primary sources in the Lower Danube loess steppe.     

Rapid denudation of Higher Himalaya during late Pliestocence, evidence from OSL thermochronology

Optically Stimulated Luminescence (OSL) of quartz, with closure temperatures of 30–35°C in conjunction with Apatite Fission Track (AFT; closure temp. ～120°C) and ⁴⁰Ar-³⁹Ar (biotite closure temperature ～350°C), were used to obtain cooling ages from Higher Himalayan crystalline rocks of Western Arunachal Himalaya (WAH). Cooling age data based on OSL, AFT and Ar-Ar thermochronology provide inference on the exhumation — erosion history for three different time intervals over million to thousand year scale. Steady-state exhumation of ～0.5 mm/yr was observed during Miocene (>7.2 Ma) till Early Pleistocene (1.8 Ma). Onset of Pleistocene glacial/interglacial conditions from ～1.8 Ma formed glaciated valleys and rapid erosion with rivers incising deep valleys along their course. Erosion enables midcrustal partial melts to move beneath the weak zone in the valley and causes an erosion-induced tectonic uplift. This resulted in a rapid increase in exhumation rate. The OSL thermochronology results suggest increased erosion over ～21 ka period from Late Pleistocene (2.5 mm/yr) to Early Holocene (5.5 mm/yr) and these are to be contrasted with pre 1.8 Ma erosion rate of 0.5 mm/yr. Enhanced erosion in the later stage coincides with the periods of deglaciation during Marine Isotope Stages (MIS) 1 and 2. The results of the present study suggest that in the present setting OSL thermochronology informed on the short-term climatic effect on landscape evolution and techniques like the AFT and ⁴⁰Ar-³⁹Ar provided longer-term exhumation histories.     

Optical dating of alluvial deposits at the orogenic front of the andean precordillera (Mendoza,Argentina)

Well constrained numerical ages of alluvial fan sediments are key to understanding the chronology of alluvial episodes and tectonic activity at the front of the Andean Precordillera. We tested the application of radiocarbon and optically stimulated luminescence (OSL) dating in the distal part of an alluvial fan five kilometers north of Mendoza. For OSL dating a large number of aliquots (n > 70) — each composed of ∼50 quartz grains — were measured in order to obtain reliable burial ages despite scattered dose distributions. Owing to a feldspar contamination in all samples, an infrared stimulation was inserted before each OSL measurement, which reduced the feldspar OSL signal successfully. By using the minimum age model we obtained stratigraphically consistent burial ages of alluvial deposits in a depth profile. The uppermost ∼1 m of sediment is composed of debris flow deposits buried 770±76 years ago. Three plant remnants used for radiocarbon dating from the same layer, however, yielded ages younger than 350 years, which are interpreted to underestimate the depositional age. Underneath the debris flow, a major unconformity cuts a series of distal alluvial fan sediments with interstratified floodplain deposits, which are composed of sandy and calciterich silt layers, respectively. Three samples from this unit which were distributed over one meter of sediment thickness yielded statistically concordant OSL ages of 12.3±1.2 ka, 12.3±1.2 ka, and 11.7±1.1 ka. The deposition of these sediments during the latest Pleistocene coincides with a phase of cool and humid climate, which occurred before the alluvial fan propagated farther into the foreland. The overlying debris flow sediments are associated with alluvial fan incision during the arid Late Holocene.     

Luminescence dating of prehistoric hearths in Northeast Qinghai Lake and its paleoclimatic implication

Archeological research has been trying to provide evidence relevant to understanding both the timing of and processes responsible for human colonization of the Qinghai-Tibetan Plateau (QTP). Hearth is one of the most extensive, important, and typical prehistoric humanity activity evidence on the QTP. However, there are a number of hearths lacking charcoal material because of the wind and water erosion. Fortunately, most of these hearths can be dated by luminescence dating on the remnant sediments around the hearth. In this study, 18 optically stimulated luminescence (OSL) samples from 14 hearths in Yandongtai site (YDT) and Bronze Wire site (BW) in the northeast of Qinghai Lake area were systematically dated. The OSL ages range from 6.8 ± 0.7 to 14.4 ± 1.2 ka. There is a good agreement between OSL dating results and charcoal ages during the last deglaciation period, which indicates that OSL method has great potential in dating hearth on QTP. Combined with the previous dating results from other hearths, the age of hearths concentrates in 11–13 ka BP, i.e., the Younger Dryas (YD) chronozone. The increased number of hearths indicates reinforced colonization in the Qinghai Lake area during YD cold event, implying that the cold climate during YD event was not severe enough to hinder the inhabitation of prehistoric humanity at an elevation of 3.2 km.     

The origin of deep subsurface microbial communities in the Witwatersrand Basin, South Africa as deduced from apatite fission track analyses

The first fission track analyses of detrital apatite grains from the subsurface of the Kaapvaal Craton were utilized to delineate the thermal history for the northern margin of the Witwatersrand Basin, South Africa, where evidence for subsurface thermophilic and hyperthermophilic microorganisms have been discovered. Fission track apatite ages for core samples ranged from 21 to 422 Ma. The trend of decreasing age with increasing depth parallels a trend previously reported for fission track data from surface samples collected from the higher altitude centre and lower altitude margins of the Kaapvaal Craton, South Africa. These new fission track ages are older than the surface samples of equivalent elevation, indicating that the uplift history and/or the geothermal gradient of the centre of the Kaapvaal Craton is distinct from that of its margins. Modelling of one sample collected from a depth of 3.7 km records cooling from 120°C at 75 Ma at a rate of approximately 1.4°C m.y.^?1 and reaching present day temperatures at 30 Ma. This modelling result when compared to other apatite fission track dates indicate that this cooling trend followed a 90‐Ma thermotectonic event. The fission track data also indicate that heated fluid migration, which is observed today in this region of the Witwatersrand Basin, was also active in the past in order to explain the greater palaeogeothermal gradient (18 versus 8°C km^?1). The fission track results suggest that at approximately 70 Ma only hyperthermophilic microorganisms could have existed at palaeodepths >3.2 km depth in the Witwatersrand Basin, and that the current meso/thermophilic microbial communities living at or beneath the present depth of 1.7 km in the Witwatersrand Basin must have migrated to their current location since 70 Ma. Any hyperthermophilic microorganisms found at the present depths 1.2–3.7 km could be descendents of subsurface hyperthermophiles that colonized the crust since the early Mesozoic to Palaeozoic eras.     

The chronology of the Neolithic sequence at Dikili Tash,Macedonia, Greece: TL dating of domestic ovens*

The chronological sequence of a major reference site for Neolithic periods in southeastern Europe and the Aegean, Dikili Tash (Macedonia, Greece), has been reassessed by TL. Baked adobe material samples extracted from domestic ovens, directly associated with specific occupational levels, have been studied. The fine‐grain technique has been used for equivalent dose determination. K, U and Th contents and the equilibrium state of U‐series have been measured by low‐background gamma spectroscopy. Since the archaeological levels were already partly excavated, the environmental dose‐rate was evaluated by a reconstruction technique combining laboratory analysis and on‐site measurements. The TL results (weighted average of multiple age determination, oven 400, middle of the Dikili Tash I (DT‐I) phase, 5500 ± 320 bc ; oven 600, end of DT‐I, 4920 ± 310 bc ; house 3, DT‐II, 4260 ± 280 bc ; house 4, DT‐II, 4510 ± 410 bc ) are in general agreement with the timeframe deduced from previous radiocarbon dates. This convergence strengthens the settlement's chronology, established now by independent dating methods.     

An Archaeomagnetic Study of a Roman Bath in Southern France

Absolute Thellier–Thellier archaeointensity determinations were conducted on 137 tiles and sedimentary blocks from five different structures from the ‘Site de la Molère’, southern France, to constrain the archaeological interpretation of a relative age difference between structures and add new data to the French secular variation database. We present 89 new archaeointensity and 20 new directional results, with averages of 57 (±8) μT in the second century ad and 68 (±7) μT in the third century ad . The overall data trend is consistent with the limited available data, indicating rapidly increasing field intensity from the second to the third century ad .     

Examining quartz OSL age underestimation for loess samples from Luochuan in the Chinese Loess Plateau

When using quartz OSL to date loess samples from the Chinese Loess Plateau, it has been reported that the agreement between OSL ages and the independent ages is limited to the samples younger than ～70 ka with a corresponding D_e of ～230 Gy, and a sample with an expected age of 780 ka was dated to 107 ka, corresponding to 403 Gy. The growth curves of these samples do not saturate at doses of 700 Gy, and a linear growth part was observed for doses higher than 200 Gy. However, the maximum measured age of ～100 ka imply that the D_e determined using this linear part of a growth curve could be problematic, or that the quartz OSL signal is not as stable as previously thought and has a barrier age of ～100 ka. In the current study, we examine the reasons for the age underestimation. We examined the shape of growth curves, anomalous fading, thermal stability, etc. The results show that, for the loess samples examined, quartz OSL does not fade anomalously, and the barrier age of ～100 ka is due to the fact that the OSL signals are less thermally stable, the lifetime of 0.311 Ma at 20°C obtained is much smaller than those for quartz samples from other regions such as Australia (～100 Ma).     

Rodent-based age appraisal of the Lower Siwalik Subgroup of Kalaunta,Ramnagar, Jammu,India

Parmar, V., Magotra, R., Norboo, R. & Prasad, G.V.R., July 2016. Rodent-based age appraisal of the Lower Siwalik Subgroup of Kalaunta, Ramnagar, Jammu, India. Alcheringa 41, xx-xx. ISSN 0311-5518.

Rocks of the Lower Siwalik Subgroup exposed around Ramnagar town in Jammu, India, have been known for more than 90 years to yield Chinji-equivalent (14.2–11.2 Ma) hominoid fossils. In 1997, the fossil ape Sivapithecus reported near Kalaunta village in the vicinity of Ramnagar was argued to be about 18 Ma old by its discoverers. This had implications for hominoid evolutionary studies, as molecular clock calibrations are commonly based on Sivapithecus first appearance datum (FAD). In a paper published in 2010, the identification of this hominoid tooth was questioned and reassigned to a suid. Recently, based upon the discovery of an indeterminate fossil bovid from the supposedly hominoid-yielding site near Kalaunta, an age estimate between ca 13.9 and 10.8 Ma was provided. As rodent biochronology has proven to be useful in age assignment of upper Cenozoic terrestrial sequences, the age of the fossil-bearing Lower Siwalik Subgroup of Kalaunta is re-assessed based upon newly recovered cricetid taxa. The cricetid rodents from this site comprise Punjabemys downsi and P. mikros. These two species are known to exist in the well-dated Potwar Siwalik Group succession between 14.3 and 12.6 Ma and between 16.3 and 13.0 Ma, respectively. Based on the overlapping temporal ranges of the cricetid taxa and an indeterminate Bovidae (ca 13.9–10.8 Ma) reported previously from this area, an age of 13.9–13.0 Ma is inferred for rocks occurring in the vicinity of Kalaunta. The new finds refute earlier claims of rocks in the area extending back to ca 18 Ma or as young as 10.8 Ma.

Varun Parmar [varunparmarvp@gmail.com], Rahul Magotra [rahulmagotra01@gmail.com] and Rigzin Norboo [norboo04@gmail.com], Post Graduate Department of Geology, University of Jammu, Jammu, 180 006, India; Guntupalli Veera Raghavendra Prasad [guntupalli.vrprasad@gmail.com], Department of Geology, Centre for Advanced Studies, University of Delhi, Delhi, 110 007, India.     

Infrared radiofluorescence (IR-RF) dating of middle pleistocene fluvial archives of the Heidelberg Basin (Southwest Germany)

The infrared radiofluorescence (IR-RF) dating technique was applied to eight fluvial samples that were collected from two sediment cores at the Heidelberg Basin located near Viernheim and Ludwigshafen in southwest Germany. Based on the IR-RF derived ages of the samples it was possible to establish a chronological framework for the Mid-Pleistocene fluvial deposits of the Heidelberg Basin. The results allow us to distinguish between four main periods of aggradation. The lowermost sample taken from 100 m core depth lead to an IR-RF age of 643 ± 28 ka pointing to a Cromerian period of aggradation (OIS 17–16). For the Elsterian it is now possible to distinguish between two aggradation periods, one occurring during the Lower Elsterian period (OIS 15) and a second during the Upper Elsterian period (OIS 12–11). For the so called Upper interlayer (or “Oberer Zwischenhorizont” — a layer of organic-rich and finer-grained deposits), the IR-RF results point to a deposition age of around 300 ka, with samples taken directly on top and out of this layer yielding IR-RF ages of 288 ± 19 ka and 302 ± 19 ka, respectively. Hence, the measured IR-RF ages clearly point to a deposition during the Lower Saalian period (OIS 9–8) whereas earlier studies assumed a Cromerian age for the sediments of the Upper Interlayer based on pollen records and also mollusc fauna. The new IR-RF dataset indicates that significant hiatuses are present within the fluvial sediment successions. In particular the Eemian and Upper Saalian deposits are missing in this part of the northern Upper Rhine Graben, as the 300 ka deposits are directly overlain by Weichselian fluvial sediments. It is obvious that time periods of increased fluvial aggradation were interrupted by time periods of almost no aggradation or erosion which should have been mainly triggered by phases of increased and decreased subsidence of the Heidelberg Basin.     

Single-grain OSL dating at La Grotte des Contrebandiers (‘Smugglers’ Cave’), Morocco: improved age constraints for the Middle Paleolithic levels

Optically stimulated luminescence (OSL) measurements of individual quartz grains are reported for Middle Paleolithic (MP) or Middle Stone Age (MSA) deposits in La Grotte des Contrebandiers, Morocco. Single-grain measurements enable rejection of grains that may lead to under- or over-estimation of age due to malign luminescence properties or remobilisation of grains after burial. We identified the former using a range of experimental procedures and objective rejection criteria. Three post-depositional factors influenced the distribution pattern of equivalent dose (D_e) values for the remaining single grains: the disintegration of roof spall liberating unbleached, older grains into otherwise well-bleached sediments; the intrusion of a small number of younger grains from the overlying Upper Paleolithic deposits; and small-scale differences in the beta dose received by individual grains. Roof spall contamination was a significant problem, so we characterised the OSL signals and obtained D_e values for the calcareous sandstone in which the cave is formed, which allowed bedrock-derived grains in the MP/MSA deposits to be identified and rejected prior to age determination. We collected 31 samples from the MP/MSA deposits, and were able to calculate ages for 30 of them. These ages suggest that MP/MSA occupation of Contrebandiers was restricted to the interval between about 120 and 90 ka ago (Marine Isotope Stages 5d to 5b). Weighted mean OSL ages were obtained for samples associated with archaeologically sterile deposits at the base of the excavations (126 ± 9 ka), followed by two phases of the Moroccan Mousterian (122 ± 5 and 115 ± 3 ka), interspersed with archaeologically sterile deposits (112 ± 4 ka). The base and top of the Aterian were dated to 107 ± 4 and 96 ± 4 ka, respectively. Based on the grand weighted mean ages of 116 ± 3 and 103 ± 3 ka for the Moroccan Mousterian and Aterian at Contrebandiers, we suggest that these two industries may be separated by an occupation hiatus of up to 13 ± 3 ka at this site. Our single-grain OSL chronology confirms previous age estimates obtained for Contrebandiers and other sites in the vicinity, but are generally more precise and stratigraphically more coherent, due to the inherent advantages of measuring individual quartz grains and rejecting contaminant and other unsuitable grains before age determination.     

Reconstruction of palaeo-burial history and pore fluid pressure in foothill areas: a sensitivity test in the Hammam Zriba (Tunisia) and Koh-i-Maran (Pakistan) ore deposits

The burial and pore fluid pressure history of fluorite ore deposits is reconstructed: (i) at Hammam Zriba–Djebel Guebli along the eastern margin of the Tunisian Atlas; and (ii) at Koh‐i‐Maran within the northern part of the Kirthar Range in Pakistan. Both the deposits are hosted by Late Jurassic carbonate reservoirs, unconformably overlain by Late Cretaceous seals. Microthermometric analyses on aqueous and petroleum fluid inclusions with pressure–volume–temperature–composition (PVTX) modeling of hydrocarbon fluid isochores are integrated with kinematics and thermal 2D basin modeling in order to determine the age of mineralization. The results suggest a Cenozoic age for the fluorite mineralization and a dual fluid migration model for both ore deposits. The PVTX modeling indicates that the initial stage of fluorite cementation at Hammam Zriba occurred under fluid pressures of 115 ± 5 bars and at a temperature close to 130°C. At Koh‐i‐Maran, the F3 geodic fluorite mineralization developed under hydrostatic pressures of 200 ± 10 bars, and at temperatures of 125–130°C. The late increase in temperature recorded in the F3 fluorites can be accounted for by rapid rise of hotter fluids (up to 190°C) along open fractures, resulting from hydraulic fracturing of overpressured sedimentary layers.     

RESEARCH REPORT: MAGNETIC INVESTIGATIONS AND THE AGE OF A MEDIEVAL KILN AT KUNGAHÄLLA (SOUTH‐WEST SWEDEN)*

The results from a magnetic survey and archaeomagnetic investigation of a medieval brick kiln at Kungahälla in Bohuslän (south‐west Sweden) are reported. Detailed magnetic total field and magnetic gradient measurements over known traces of the kiln showed marked local magnetic anomalies of up to 200 nT, revealing the rectangular shape of the kiln remains. Palaeomagnetic investigations of the remanent magnetization of 12 bricks from the kiln floor gave precise definitions of both the direction of the archaeomagnetic field [(D_m, I_m) = (66.7°, 8.8°), k = 655, α₉₅= 1.7°] and the palaeointensity [B_m= 69.0 ± 3.6 µT]. An archaeomagnetic date is obtained by comparing the direction of the archaeomagnetic field found in the kiln with a geocentral dipole‐transformation of the British master‐curve for secular variation. Of two possible archaeomagnetic dates (ad 1280 ± 50 or ad 1480 ± 50), the ad 1280 ± 50 age is in good accordance with the C‐14 ages and archaeological dates as well as with direct historical evidence, whereas a c. 100 years younger TL date appears to be too young.