Episodic fluid flow within continental rift basins: some insights from field data and mathematical models of the Rhinegraben

Vitrinite reflectance data from a petroleum exploration well in the northern Upper Rhinegraben show an unusual vertical maturity trend. Above and below a 500 m thick marl layer the vitrinite reflectance levels are consistent with modern, conductive, geothermal gradients. Between about 1000 and 1500 m depth, however, vitrinite reflectance levels are significantly elevated (about 0.6%Ro). This anomaly cannot be explained with one‐dimensional conductive or conductive–convective heat transfer models, and thermal effects of sedimentation or igneous intrusion seem implausible for this geological setting. The thermal anomaly that formed this maturation anomaly must have been hydrothermal in origin, two‐dimensional in nature, and persisted long enough to elevate the vitrinite reflectance values within this marl unit, yet it must have dissipated before the thermal perturbation would have altered the organic matter below and above the unit. In this study, we propose that the vitrinite reflectance anomalies were caused by a transient thermal inversion induced by episodic, lateral flow of hot (130–160°C) groundwater along conductive fractures and bedding planes. Heat flow constraints suggest that fluids must have moved rapidly up a vertical feeder fault from a depth of at least 3.6 km before migrating laterally. To test this hypothesis, we present a suite of simple, idealized mathematical models of groundwater flow, heat transfer, thermal degradation of kerogen and vitrinite systematics to explore the episodic flow that could have produced the observed thermal anomaly. In these simulations, a single, horizontal aquifer is sandwiched between two less permeable units: the total dimensions of the vertical section model are 4 km thick by 10 km long. The top of the aquifer coincides with the position of the observed thermal maturity anomaly in the Rhinegraben. Boundary conditions along the left edge of this aquifer were varied through time to allow for the migration of hot fluids out into the basin. Inflow temperature, horizontal velocity, duration and frequency of flow and thickness of the aquifer were varied. We found that a thermal maturity anomaly could only be produced by a rather restrictive set of hydrothermal conditions. It was possible to produce the observed vitrinite reflectance anomaly by a single hydrothermal flow event of 130°C fluid migrating laterally into the aquifer at a rate of 1 m a^?1 for about 10 000 years. The anomaly is spatially confined to near the left edge of the basin, near the feeder fault. If the flow event lasted longer than 100 000 years, then the maturation anomaly disappeared as the lower confining unit approached steady‐state thermal conditions. It is possible that such an event occurred about 5 million years ago in response to increases in fault permeability associated with far field Alpine tectonism.     

The crowsteps motif in Nabataean architecture: insights into its meaning and use

Nabataeans, in constructing their tombs, added many symbols and geometrical forms, plants and animals. Crowsteps, as a geometrical form, are the most common among these symbols. This study investigates the use of the crowsteps motif found frequently on the facades of Nabataean tombs. The primary focus is to replace models of typological explanation for the introduction of crowsteps into the Nabataean rock‐cut facades. The study begins with tracing the origin of the crowsteps motif and the way it was adopted by the Nabataeans to become one of the most significant features in the making of Nabataean architectural vocabularies. It then provides a theoretical framework for explaining the use and meaning of the crowsteps in Nabataean architecture. Thematic analysis of related literature and existing architectural remains allows us to suggest that crowsteps served both sacred and secular purposes. Sacredly, crowsteps were used to connect the deceased with the principal deities through metaphorical representation either as a ‘high place’ or as a ‘throne’. Secularly, crowsteps served basic human needs: representing identity, wealth and social structure. The study also considers that the Nabataean rock‐cut crowsteps activated the dialogue between different cultural traditions and helped in shaping the ideological cult and identity of the Nabataeans.     

Some medieval Yemenite numismatic problems – observations on some recently sold coins

The article addresses some of the problems arising from the publication of a recent numismatic catalogue including coins from all parts of the Islamic world. The problems concern in particular the coins of the medieval Yemen and the article comprises a critique of those coins listed under the Arabian peninsula and the Yemen.
Catalogue nos. 101 and 104 are dealt with in some detail since they are erroneously ascribed to mints in Mecca and Minā, respectively. The former is struck in the name of a Zaydī imam, the latter is Rasulid and labelled as having been struck "for a special occasion". The intriguing question of the mysterious Ayyubid prince, al-'Ādil Abū Bakr, arises too (nos. 125 etc.), although no definitive answer can yet be suggested. Much more information is now available on the striking of coins in Tha'bāt during Rasulid times. A number of other points bearing on the numismatics, the history, and the geography of the medieval Yemen are discussed in the article.     

The crystallinity of ancient bone and dentine: new insights by transmission electron microscopy

We studied various archaeological and palaeontological bones and dentines from different burial environments by Fourier transform infrared spectroscopy (FT–IR), X–ray diffraction (XRD) and transmission electron microscopy (TEM), in the framework of a general study of diagenesis. FT–IR and XRD were used to evaluate the global preservation state of the bone and dentine mineral phase by determining a splitting factor (SF) or a crystallinity index (CI), respectively. These data can be combined with studies on the nanometer scale made with TEM. This latter technique,coupled with electron microdiffraction, provides determination of dimensions and shapes of individual bone and dentine apatite nanocrystals as well as of secondary minerals formed during diagenesis. It enables us to distinguish between heat–induced recrystallization processes and crystal growth in solution occurring during diagenesis.     

The height distribution of radio meteors: observations at 6 MHz

As part of a program aimed at deriving the true influx to the Earth of small meteoroids we have measured the height distribution of radio meteors to limiting magnitude + 6 (mass ~ 1.0 mg) at a frequency of 6 MHz for the combined Daytime Arietid and Zeta Perseid showers, and also for the Eta Aquarids; these showers have widely different velocities but no substantial dependence upon velocity is apparent. The distributions peak at ~ 105 km, 10 km above the peak found using conventional VHP meteor radars and in line with observations previously made by us at 2 MHz. Instrumental limitations confine the span of heights to 84 <h <116 km, but it is notable that within this range the 6 MHz height distributions appear to be symmetric, with a swift drop-off above 105 km; this contrasts with the asymmetric 2 MHz distribution which showed a slow drop-off with many meteors to 140 km. The origin of this difference is probably due to diffusion and the finite-velocity effect, which will be considered in a subsequent paper.     

The height distribution of radio meteors: observations at 2 MHz

Conventional meteor radars, operating at wavelengths of around 5–15 m, are unable to detect high-altitude meteors due to the wavelength-dependent echo ceiling. It is suggested that the ‘missing mass’ in the 10⁻⁶–10⁻² g range of interplanetary material is in fact a high-velocity component which is normally undetected since it ablates at high altitude. This contention is supported by previous work. In this paper we describe measurements of the heights of radio meteors (limiting magnitude about +7) at a wavelength of 150 m (frequency 2 MHz), for which the echo ceiling is above 140 km. The resultant true height distribution is found to peak at ~ 104 km, about 10 km above the peak found by conventional meteor radars. The majority of meteors are detected at or above this peak, and substantial numbers are seen right up to 140 km. It is therefore concluded that the ‘missing mass’, comprising the vast majority of the meteoric input to the atmosphere, ablates well above 100 km.     

A sea of potential: The politics of global ocean observations

The Global Ocean Observing System (GOOS) is creating a new understanding of the world ocean. With a vast and heterogeneous network of sensors, it converts the ocean's properties into flows of information, creating a “data double” of a dynamic sea. This view of the ocean underlies not only international geopolitics but also more broadly emergent modes of government. This paper analyzes changing strategies for governing global ocean observations to better understand the shifting coconstitution of nature, technology, and politics. In particular, I inquire into the GOOS's recent developments, which indicate a new conception of the ocean as a space of potentiality. I argue that this emergent understanding poses problems for our conventional political analytics, particularly that of biopolitics. To account for this shift, I draw on and extend Elizabeth Povinelli's offering of geontopolitics, which identifies a departure from the fundamental distinctions between life and nonlife made by biopolitics, seeing instead the potential for unpredictable changes not only in human subjects but also in geophysical systems and the contemporary planetary environmental conditions they shape. Emphasizing how geontopolitics both names a new mode of government and signifes its limits, Povinelli suggests three figures, following Foucault's four figures of biopolitics. I conclude by suggesting the world ocean as a fourth figure of geonotopolitics, as that which is so imbricated with life as to be indistinct from it. Throughout, I maintain that like Foucault's figures of biopolitics, the world ocean must be understood as inseparable from the knowledge relations that make it legible.     

The changing biosphere: recent insights from paleoenvironmental science into drivers,mechanisms and impacts

Paleoenvironmental science has experienced a recent surge in interest and activity as concerns grow over global environmental change. Key research questions in the biotic realm of paleoenvironmental science focus on explaining climatic change at time scales of decades to centuries and understanding ecosystem responses to these changes. Biotic responses are increasingly being studied at smaller spatial scales to identify local factors that determine the sensitivity of a particular system to climatic change. These findings can then be applied to solving a variety of problems, such as setting conservation targets or testing mechanisms for observed climatic and biogeographic phenomena. Research approaches commonly used today include hypothesis testing, which has now become more sophisticated as paleoecologists and paleoclimatologists integrate with modellers. Other frameworks involve the quantitative integration of multiple proxy indicators and the use of extensive publicly available data networks to produce new datasets for paleoclimatic reconstructions and other applications.     

The future of geomagnetic storm predictions: implications from recent solar and interplanetary observations

Within the last 7–8 years, there has been a substantial growth in our knowledge of the solar and interplanetary causes of geomagnetic storms at Earth. This review article will not attempt to cover all of the work done during this period. This can be found elsewhere. Our emphasis here will be on recent efforts that expose important, presently unanswered questions that must be addressed and solved before true predictability of storms can be possible. Hopefully, this article will encourage some readers to join this effort and perhaps make major contributions to the field.     

The red-stained flint crescent from Gesher: new insights into PPNA hafting technology

A red-stained flint crescent found in the Pre-Pottery Neolithic A (ca. 9000 BC) site of Gesher, Israel, provides us with a unique opportunity to study the hafting technology of a particular tool type in the Levant. We present here a reconstruction, based on chemical and mineralogical analyses, of the hafting technologies and materials employed in the process. Use will also be made of relevant studies of the archaeological record. Local material was used for the production of an elastic adhesive paste, mud plaster, which was then hardened to hold the crescent securely in the haft. The study contributes insight into the hafting technology that was most probably implemented in the production and maintenance of composite tools during the Early Neolithic period.