How Hannibal conquered geology

During his crossing of the Alps, Hannibal is said to have cleared a large rockfall with the aid of fire and ‘vinegar’. Would such a treatment have worked? Modern research suggests that it would.     

Geology and jungle fieldwork in eastern Indonesia

Collecting geological information from the jungles and islands of eastern Indonesia depends largely on traditional fieldwork methods involving much footwork and messing about in boats. Coupled with modern laboratory and computing techniques, information gained on the ground is being used to interpret the tectonic development of east Indonesia, the Philippine Sea and the western Pacific.     

The Late Quaternary sedimentary record in Scoresby Sund, East Greenland

Until recently, little was known about the Quaternary marine sedimentary record in East Greenland. Geophysical and geological investigations in Scoresby Sund were undertaken to characterize the nature and chronology of this record. Seismic records show that almost 70% of the outer fjord system is covered by about 10 m of unlithified sediments, making direct correlation with the Quaternary records on land and the adjacent continental margin difficult. These acoustically unstratified sediments are scoured by icebergs above 550 m water depth. Almost 90% of core material is massive diamicton of Holocene age, deposited mainly from iceberg rafting and turbid meltwater. Sedimentation rates are 0.1 -0.3 m 1000 yr-¹. Thicker accumulations of unlithified Quaternary sediments in Scoresby Sund occur as sediment ridges and in two other major depocentres. A low sediment ridge runs across the mouth of Scoresby Sund, and is interpreted as an end moraine of Late Weichselian Flakkerhuk stadial age. The very restricted sediment thickness suggests that grounded ice filled the fjord during the Flakkerhuk and an ice shelf was not present. High inputs of ice rafted debris to the continental margin at about 18 000 BP indicate this as a probable age for the moraine. During the Allerød Interstadial, ice probably retreated from the outer fjord system, since massive diamictons similar to those of Holocene age are present at the base of most cores. A major depocentre of acoustically stratified sediments at the head of Hall Bredning is interpreted to represent ice proximal deposits from a glacier margin extending across the fjord. It is adjacent to dated moraines on land and is inferred to be of Milne Land stadial age (about 10 000 BP). A similar age is interpreted for acoustically laminated sediments and a moraine at the entrance of Vikingebugt, on the south side of Scoresby Sund. Dated kame terraces in the inner fjord system indicate that ice retreated to its present position 6–7000 years ago.     

A climatological study of polar stratospheric clouds (1989–1997) from LIDAR measurements over Dumont d'Urville (Antarctica)

Backscatter lidar data from the French Antarctic base in Dumont d'Urville (66.40°S, 140.01°E), including aerosol background and observations of polar stratospheric clouds (PSCs), have been collected since 1989. In the present work we present a climatological study of PSCs, using a data base consisting of almost 90 observations. The seasonal evolution of PSCs, their optical classification, and their relationship with the observation temperature were studied. The first PSC was observed on day number 175 (15 June) and the last on day number 260 (7 September). The characteristic mid‐cloud altitude decreases through the season at a rate of 2.5 km/month. Type Ia, Ib, and II PSCs — identified by their optical properties — have been observed. External mixtures of these types have also been observed. These observations have been related to the local temperature measured by radiosondes. The relationship between PSC type and the period of the winter season was also investigated. Mixed (solid and liquid) type I clouds are mostly observed at the beginning of the winter. Type II clouds are observed only during the coldest period around midwinter, although temperatures below the frost point begin earlier and persist longer than this. Type Ia, solid‐particle, clouds are observed mostly at the end of the winter.     

Holocene stratigraphy and depositional history of the Narragansett Bay System, Rhode Island, U.S.A.

ABSTRACT An extensive seismic reflection survey has been used to gain further knowledge of Holocene stratigraphy and depositional history in the Narragansett Bay System (NBS). The early Holocene stream-dissected surface beneath the NBS is interpreted as having been flooded by the Holocene sea in a manner suggested by Oldale & O'Hara's (1980) sea-level-rise curve. The sea initially is believed to have penetrated the pre-NBS East Passage trunk valley about 9000 yr BP and subsequently spread landward via the trunk valley and its branches. The Holocene sediments display stratigraphic relationships that differ spatially. At passage mouths, the basal unconformity is inferred to be covered over with some 3 m of paralic and 5 m of marine sands and silts separated, by a transgressive unconformity. In contrast the interior sequences reveal (a) a valley section up to more than 15 m thick in which the regressional unconformity is overlain by probable lower fluvial and/or estuarine sand-silt facies that commonly grades upward to an estuarine silt-clay facies and (b) an interfluve section in which a basal transgressive unconformity is blanketed by an estuarine nearshore sand-silt facies that locally may change upward to a silt-clay facies. Primarily Holocene silt-clay accretion, produced by sedimentation processes associated with net non-tidal estuarine circulation, infilled the evolving NBS. Depositional bodies, lenticular in shape and comprised of 12 m or more of sediment, developed in lowlands near Gould Island (?9000 yr BP), in Upper Narragansett Bay (?7500 yr BP), around Hope Island (?7500 yr BP) and in Mt Hope Bay (?6250 yr BP) with an average minimal sedimentation rate of 1.6–2.2 mm yr^-1. Silt-clay deposition, commonly gas-bearing, has buried the basal relief in most of the NBS upper and middle portions except for middle East Passage. A comparison of NBS sedimentation with that of Chesapeake, Delaware and Hudson Estuaries shows that the estuaries to the south have accumulated more sediment over a slightly longer period yet, with the exception of the higher rate in the Hudson Estuary, the sedimentation rates appear to be similar.     

Burial dolomitization and porosity development in a mixed carbonate-clastic sequence: an example from the Bowland Basin, northern England

Widespread dolomitization and leaching occur in the Asbian to Brigantian (Dinantian) sequence of the Bowland Basin. Within this mudrock-dominated succession, dolomite is developed in calcarenites and limestone breccia/conglomerates deposited in a carbonate slope environment (Pendleside Limestone) and also within graded quartz wackes deposited by density currents in a generally ‘starved’ basin environment (Pendleside Sandstone). The dolomitized intervals range in thickness from less than one metre to several tens of metres and have a stratabound nature. All stages of calcite cement pre-date dolomitization and calcite veins are dolomitized. Dolomite crystals replace neomorphic spar and may also contain insoluble residues that were concentrated along stylolites. Thus dolomitization was a late stage process within the carbonate diagenetic sequence. A late-stage diagenetic origin is also indicated within the sandstones, with dolomite post-dating the development of quartz overgrowths. Six main textural styles of dolomite are observed: (1) scattered; (2) mosaic; (3) subhedral to euhedral rhombic; (4) microcrystalline; (5) single crystal and (6) saddle. The style of dolomite developed is dependent on the host rock mineralogy, on whether it is space-filling or replacive and also on temperature. Chemically the dolomite varies from near stoichiometric compositions to ankeritic varieties containing up to 20 mole % FeCO₃. Generally the dolomites have isotopic compositions depleted in δ¹⁸O compared to the host limestone, with similar or lighter δ¹³C values. Initial dolomite was of the scattered type, but with progressive replacement of the host a mosaic dolostone with a sucrosic texture was produced. There was a general increase in the Fe and Mn content and reduction in δ¹⁸O ratio of the crystals during dolomitization. Leaching is restricted to partly dolomitized horizons, where calcite, feldspars, micas, clays and, to some extent, dolomite have been leached. This has produced biomouldic and vuggy secondary porosity within the carbonates, whereas in the sandstones honeycombed, corroded and floating grains associated with oversized pores occur. Porosity within both carbonates and sandstones is reduced by ferroan dolomite/ankerite cements. Field, petrographic and chemical characteristics indicate that dolomitizing solutions were predominantly derived from the enclosing mudrocks (Bowland Shales) during intermediate/deep burial. Fluid migration out of the mudrocks would have been sided by dehydration reactions and overpressure, the fluids migrating along the most permeable horizons—the coarse grained carbonates and sandstones that are now dolomitized and contain secondary porosity.     

The Stability of Sodalite in a Synthetic Syenite plus Aqueous Chloride Fluid System

Natural feldspathoidal syenites may be approximated by assemblagescontaining some or all of the phases sodalite, nepheline, oneor two alkali feldspars, and aqueous chloride fluid in the systemNaAISi₃O₈-KAISi₃O₈-NaAISiO₄-KAISiO₄-NaCI-KCI-H₂O. The stabilityof sodalite in these assemblages was studied in the range 500–700°C and 600–2000 bars fluid pressure. Sodalite appears to be a stable phase on the vapor-saturatedliquidus in this system over a wide range of pressure. At or near the vapor-saturated liquidus minimum in this system,three distinct types of sodalite-bearing syenite can crystallize.Nepheline-sodalite-one alkali feldspar rocks, nepheline-sodalite-twoalkali feldspars rocks and sodalite-analcime-bearing rocks crystallizebelow 1600 bars, between 1600 and 2750 bars and above 2750 barsfluid pressure, respectively. The effects of closed-system cooling on the assemblage sodalite-nepheline-twoalkali feldspars-aqueous fluid are different and distinguishablefrom the effects of metasomatism. Closed-system cooling resultsin replacement of K-feldspar by albite, feldspathoids remainingnearly unchanged, while metasomatism generally results in sismultaneousenrichment or impoverishment in sodalite plus K-feldspar.     

SELECTION OF SEISMIC PICKING BASED UPON THE DIP,MOVE-OUT AND AMPLITUDE OF EACH EVENT*

The general use of continuous CDP seismic lines means that the neighbourhood of each depth point can be considered according to two sets of co-ordinates: — the co-ordinates of the abscissa on the seismic lines and the reflection time, which allow investigation of the local dip of coherent events; — the co-ordinates of the reflection time and the move out, which allow investigations of the average velocity for these same events. The combination of both investigations for each coherent event is a very convenient operation for the seismologist, and can provide some useful interpretation aids such as velocity profiles, or information on the interval velocities. The principles which we use consist in the examination of a large range of possibilities, of which only the most coherent are chosen. Some examples are shown.