ALBERT

Description: It is known that cyclic heating-cooling and wetting-drying can play a significant role in the long-term deterioration of building stone. These cycles can be modified by the deposition of atmospheric particulates, which darken surfaces, resulting in changes in the absorptivity and emissivity characteristics of the stone. The capacity of diesel and coal particulates to modify the moisture and temperature regime of Portland Limestone and Hollington Sandstone was investigated. Through a greater capacity to lower the albedo of the stone and enhance the absorption of radiant energy, diesel particulate was shown to significantly increase the rate of moisture loss, temperature, and rates of heating and cooling of Portland Limestone. With particulates from diesel combustion now becoming one of the dominant particulate types found in urban centres, potential implications for future stone conservation are discussed.

Description: Glacimarine dynamics and associated sedimentary processes are closely tied to glacial regime and reflect dominant climatic conditions. Quantitative measurements for subpolar glaciers, such as sediment yield, are limited especially near glacial termini where most sediment accumulates. Here we characterize the modern glacimarine environment, quantify sediment flux and yield, document landform genesis and hypothesize potential future behaviour of Kronebreen and Kongsvegen glaciers in inner Kongsfjorden, Svalbard. A minimum of 6.74x103 g m-2 d-1 (at least 300 mm a-1) of glacimarine sediment is building a grounding-line fan via submarine stream discharge from Kronebreen. Average daily sediment flux to the ice-contact basin is recorded to be 2.6x103 g m-2 d-1 or an average annual flux of 1.56x105 g m-2 a-1. We measure an average annual ice-contact sediment yield of 1.20x104 tonnes km-2 a-1 associated with the rapid genesis of grounding-line landforms. With forecasted warming we expect meltwater volumes and sediment flux to increase. Grounding-line deposits may aggrade above water, tending to stabilize the terminus at least initially if the sediment is sufficient to counteract total terminus ablation. This would hold until either the glaciers next surge or climatic warming ablates the glaciers through surface melting.

Description: For the past two decades geodetic measurements have quantified surface displacement fields for the continents, illustrating a general complexity. However, the linkage of geodetically defined displacements in the continents to mantle flow and plate tectonics demands understanding of ductile deformations in the middle and lower continental crust. Advances in seismic anisotropy studies are beginning to allow such work, especially in the Himalaya and Tibet, using passive seismological experiments (e.g. teleseismic receiver functions and records from local earthquakes). Although there is general agreement that measured seismic anisotropy in the middle and lower crust reflects bulk mineral alignment (i.e. crystallographic preferred orientation, CPO), there is a need to calibrate the seismic response to deformation structures and their kinematics. Here, we take on this challenge by deducing the seismic properties of typical mid- and lower-crustal rocks that have experienced ductile deformation through quantitative measures of CPO in samples from appropriate outcrops. The effective database of CPO and hence seismic properties can be expanded by a modelling approach that utilizes ‘rock recipes’ derived from the as-measured individual mineral CPOs combined in varying modal proportions. In addition, different deformation fabrics may be diagnostic of specific deformation kinematics that can serve to constrain interpretations of seismic anisotropy data from the continental crust. Thus, the use of ‘fabric recipes’ based on subsets of individual rock fabric CPO allows the effect of different fabrics (e.g. foliations) to be investigated and interpreted from their seismic response. A key issue is the possible discrimination between continental crustal deformation models with strongly localized simple-shear (ductile fault) fabrics from more distributed (‘pure-shear’) crustal flow. The results of our combined rock and fabric-recipe modelling suggest that the seismic properties of the middle and lower crust depend on deformation state and orientation as well as composition, while reliable interpretation of seismic survey data should incorporate as many seismic properties as possible.

Description: Fold and fabric patterns developed within a major Caledonian thrust nappe in NW Scotland reflect a progressive increase in regional D2 strain towards the basal ductile detachment. Within the upper greenschist to lower amphibolite facies thrust sheet, the main gently east-dipping foliations and SE-plunging transport-parallel lineations maintain a broadly similar orientation over c. 600 km2. Associated main phase, thrust-related folds (F2) are widely developed, and towards the base of the thrust sheet display progressive tightening and increasing curvilinearity of fold hinges ultimately resulting in sheath folds. Secondary folds (F3) are largely restricted to high-strain zones and are interpreted as flow perturbation folds formed during non-coaxial, top-to-the-NW ductile thrusting. These features are consistent with a structural model that incorporates plane strain pure-shear flattening with a superimposed and highly variable simple shear component focused into high-strain zones. The increase in strain over a distance of 30 km across strike is similar to the increasing deformation observed when structures are traced along strike to the north, and which are apparently related to proximity to basement-cover contacts. A U-Pb zircon age of 415{+/-}6 Ma obtained from a syn-D2 meta-granite confirms that regional deformation occurred during the Scandian phase of the Caledonian orogeny.

Description: Since the early descriptions published by Callaway in 1884, the gently dipping mylonites exposed along the Moine Thrust at the Stack of Glencoul have drawn generations of geologists to the northern part of the Assynt district. These mylonites, derived from Cambrian quartzites (footwall) and Moine pelites and psammites (hanging wall), have figured prominently in: a) early research into the influence of crystal plastic deformation and recrystallization on microstructural and crystal fabric evolution; b) debates on the kinematic interpretation of macro- and micro-structures and crystal fabrics; and c) debates on the tectonic significance of such kinematic data. In this paper first we briefly review the historical aspects of this research and then, using both previously published and unpublished data, document the finite strain and quartz fabric development at this classic mylonite locality. A tectonic interpretation of these data, together with quantitative estimates of flow vorticities associated with mylonite formation at the Stack of Glencoul, are presented in a companion paper by Law (2010).

Description: Our recent geological survey of the basement of central and northern Madagascar allowed us to re-evaluate the evolution of this part of the East Africa–Antarctica Orogen (EAAO). Five crustal domains are recognized, characterized by distinctive lithologies and histories of sedimentation, magmatism, deformation and metamorphism, and separated by tectonic and/or unconformable contacts. Four consist largely of Archaean metamorphic rocks (Antongil, Masora and Antananarivo Cratons, Tsaratanana Complex). The fifth (Bemarivo Belt) comprises Proterozoic meta-igneous rocks. The older rocks were intruded by plutonic suites at c. 1000 Ma, 820–760 Ma, 630–595 Ma and 560–520 Ma. The evolution of the four Archaean domains and their boundaries remains contentious, with two end-member interpretations evaluated: (1) all five crustal domains are separate tectonic elements, juxtaposed along Neoproterozoic sutures and (2) the four Archaean domains are segments of an older Archaean craton, which was sutured against the Bemarivo Belt in the Neoproterozoic. Rodinia fragmented during the early Neoproterozoic with intracratonic rifts that sometimes developed into oceanic basins. Subsequent Mid-Neoproterozoic collision of smaller cratonic blocks was followed by renewed extension and magmatism. The global ‘Terminal Pan-African’ event (560–490 Ma) finally stitched together the Mid-Neoproterozoic cratons to form Gondwana.

Description: The Early Palaeogene magmatic rocks of North and Silhouette Islands in the Seychelles contain clues to the Cenozoic geodynamic puzzle of the Indian Ocean, but have so far lacked precise geochronological data and palaeomagnetic constraints. New 40Ar/39Ar and U–Pb dates demonstrate that these rocks were emplaced during magnetochron C28n; however, 40Ar/39Ar and palaeomagnetic data from Silhouette indicate that this complex experienced a protracted period of cooling. The Seychelles palaeomagnetic pole (57.55°S and 114.22°E; A9512.3°, N=14) corresponds to poles of similar ages from the Deccan Traps after being corrected for a clockwise rotation of 29.4°±12.9°. This implies that Seychelles acted as an independent microplate between the Indian and African plates during and possibly after C27r time, confirming recent results based on kinematic studies. Our reconstruction confirms that the eruption of the Deccan Traps, which affected both India and the Seychelles and triggered continental break-up, can be linked to the present active Reunion hotspot, which is being sourced as a deep plume from the Plume Generation Zone.Supplementary material: Experimental data are available at http://www.geolsoc.org.uk/SUP18482.

Description: During the Mesozoic and Cenozoic Eras, regional tectonic processes, eustatic variations and the volume and distribution of non-carbonate sediment controlled the progressive expansion and rapid reduction of the accommodation space available for the deposition of carbonate sequences, in the area that is now the Mediterranean and Middle East. We present a simplified super-regional tectonostratigraphic history of this area from earliest Triassic time to the present day, to demonstrate the influence of these large-scale processes on the evolution of major Tethyan Mesozoic and Cenozoic carbonate sequences. The time period is divided into 11 tectonostratigraphic phases (TSP) two of which (1 and 11) are incomplete. Each TSP commenced with major changes in basin architecture in response to regional tectonic processes. Subsequent pulses of transgression and regression generated sequence stratigraphic hierarchies. These stratigraphic hierarchies reflect the interaction between regional and local tectonics, eustatic variations, carbonate growth processes, climate and non-carbonate sediment supply. A map is presented of a major second-order transgressive sequence (TST) within each TSP to illustrate the maximum extent of marine onlap. These maps also include the main plate configurations; active regional tectonic features and the resultant time averaged carbonate gross depositional systems that developed during the transgression. The sequence of maps illustrate that the volume of available accommodation space during the Mesozoic and Cenozoic Eras reached a maximum during the Late Cretaceous and has been progressively reduced during the Cenozoic Era to the present day minimum.

Description: The Barremian-Aptian upper Khami Group and Albian-Campanian Bangestan Group have been studied at outcrop in Lurestan, SW Iran. The upper Khami Group comprises a thin deltaic wedge (Gadvan Fm) transgressively overlain by shelfal carbonates (Dariyan Fm). The Dariyan Fm can be divided into lower and upper units separated by a major intra-Aptian fracture-controlled karst. The top of the Daryian Fm is capped by the Arabian plate-wide Aptian-Albian unconformity. The overlying Bangestan Group includes the Kazhdumi, Sarvak, Surgah and Ilam formations. The Kazhdumi Fm represents a mixed carbonate-clastic intrashelf basin succession, and passes laterally (towards the NE) into a low-angle Orbitolina-dominated muddy carbonate ramp/shoal (Mauddud Mbr). The Mauddud Mbr is capped by an angular unconformity and karst of latest Albian-earliest Cenomanian age. The overlying Sarvak Fm comprises both low-angle ramp and steeper dipping (5-10{degrees}) carbonate shelf/platform systems. Three regionally extensive karst surfaces are developed in the latest Cenomanian-Turonian interval of the Sarvak Fm, and are interpreted to be related to flexure of the Arabian plate margin due to the initiation of intra-oceanic deformation. The Surgah and Ilam Fm represent clastic and muddy carbonate ramp depositional systems respectively. Both The Khami and Bangestan groups have been affected by spectacularly exposed fracture-controlled dolomitization. Dolomite bodies are 100 m to several km in width, have plume-like geometry, with both fracture (fault/joint) and gradational diagenetic contacts with undolomitized country rock. Sheets of dolomite extend away from dolomite bodies along steeply dipping fault/joint zones, and as strata-bound bodies preferentially following specific depositional/diagenetic facies or stratal surfaces. There is a close link between primary depositional architecture/facies and secondary dolomitization. Vertical barriers to dolomitization are low permeability mudstones, below which dolomitizing fluids moved laterally. Where these barriers are cut by faults and fracture corridors, dolomitization can be observed to have advanced upwards, indicating that faults and joints were fluid migration conduits. Comparisons to Jurassic-Cenozoic dolomites elsewhere in Iran, Palaeozoic dolomites of North America and Neogene dolomites of the Gulf of Suez indicate striking textural, paragenetic and outcrop-scale similarities. These data imply a common fracture-controlled dolomitization process is applicable regardless of tectonic setting (compressional, transtensional and extensional).

Description: This paper describes the results of new stratigraphic correlations and petroleum systems analyses of the Triassic deposits in the Syrian Palmyrides. The correlations are based on well data and new palynological work which reconcile previous lithological and stratigraphic miscorrelations of Triassic sequences from this region. The sequences are subdivided into four Megacycles, which are directly related to the key elements of the petroleum systems of the Palmyrides. The hydrocarbon discoveries within these systems, the fluid contacts and hydrodynamics are explained with reference to the Megacycle subdivision. This subdivision is applied on a regional scale and is used to define the distribution of reservoir seal pairs for volumetric estimations.