bluuebunny/crossref_metadata_2025 huggingface dataset:
A geographical information system for the archaeological area of Pompeii
Authors: Pareschi M. T. , Stefani G. , Varone A. , Cavarra L. , Giannini F. , Meriggi A.
Published: April 2008

The increasing degradation of archaeological evidence in the circumvesuvian area requires a suitable and exhaustive census of all the archaeological features of the area that are accessible now or that have come to light at some time in the past. The high population density of the area demands a conservation policy based on appropriately planned prevention, rather than on occasional intervention with the criterion of ‘saving what can be saved’. Here we present a geographical information system (GIS) of the archaeological data in their territorial environment for the circumvesuvian area, with the aim of providing a useful tool for archaeological feature management. The database includes the following:

(1)

Current information on the circumvesuvian area (18 council districts with a total area coverage of about 250 km
2
). The database consists mainly of vector data at the original scale of 1:5000 (although raster images are also included), and it is updated to the period 1988–1995, depending on the zone. The digital information includes natural and man-made features: roads, buildings, railways, spot heights, etc.

(2)

Archaeological sites. The ‘objects’ are organized in three main ‘layers’: areas with building constraints, buried elements (of uncertain and certain location), visible constructions (e.g. aqueduct, amphitheatre, honorary arch, forum, harbour structures, theatre, temple, roads, villas, etc.). The census is at present under development. To date, about 300 structures have been included in the GIS in the area of interest.
Apulian Bronze Age pottery as a long-distance indicator of the Avellino Pumice eruption (Vesuvius, Italy)
Authors: Cioni Raffaello , Levi Sara , Sulpizio Roberto
Published: April 2008

During the Bronze Age, Vesuvius had a Plinian eruption whose deposits are known as the Avellino Pumice. The eruption spread a blanket of white and grey pumice across southern Italy, and there was a severe impact on proximal areas. Assessment of volcanological factors for the Plinian phase gives intensities of 5.7 × 10
7
kg s
−1
for the white pumice phase and 1.7 × 10
8
kg s
−1
for the grey pumice phase, corresponding to column heights of 23 and 31 km, respectively. Volume (magnitude) calculations using the crystal concentration method (CCM) give respectively 0.32 and 1.25 km
3
of deposit, in a total minimum period of about 3 h. Archaeometric studies on Bronze Age domestic pottery from several settlements in Apulia (SE Italy) reveal the presence of pumice fragments mixed with the clay, and petrological and chemical criteria suggest that these pumices are from the Avellino eruption. This relationship allows us to fix precise correlations between different archaeological facies of the Italian Bronze Age. To explore the possibility of an extensive use of pumices in these distal regions (about 140 km from Vesuvius), we calculated the possible thickness of the tephra blanket. We propose a method to extrapolate proximal data on the deposit to calculate its minimum distal thickness. Such a method could also be used in volcanic hazard studies to assess the distal impact of large past eruptions.
The archaeology of a Plinian eruption of the Popocatépetl volcano
Authors: Plunket Patricia , Uruñuela Gabriela
Published: April 2008

The northeastern flank of the Popocatépetl volcano in western Puebla, Mexico, has been subject to intense and destructive volcanic activity since the Terminal Preclassic period (100
BC-AD
100), and it is still one of the highest-risk sectors in the region. Between
AD
50 and 100 the communities that dotted this slope, an area known locally as Tetimpa, were abruptly buried by a pumice-fall deposit that preserved the buildings, activity areas and agricultural fields but devastated the settlements and made the region uninhabitable for generations to come. It is probable that this violent eruption had an important social and ideological impact on the emerging urban centre at Cholula 15 km to the east. The Preclassic occupation of the region can be divided into the Early (700–200
BC
) and Late (50
BC-AD
100) Tetimpa phases. These appear to be separated by a short period of abandonment that might reflect an intensification of volcanic activity. This paper deals primarily with the Late Tetimpa phase, the occupation that was destroyed by a Plinian eruption in the second half of the first century. Excavations by the Universidad de las Américas-Puebla have uncovered agricultural fields with hand-made furrows interspersed with households consisting of two or three rooms on low stone platforms around an open patio. At the centre of the patio is a small shrine or altar; the themes of these shrines vary but they include volcano effigies. Architecture is simple but household patterning reflects strict adherence to rules for generating the domestic environment. Houses show little or no modification or renovation, suggesting a very short occupation. This is further supported by the fact that no burials have been located in the nine domestic areas explored to date. The evacuation of the settlement appears to have been abrupt, as many household goods, particularly large or heavy items, were left behind. We have not found any human remains under the collapsed roofs of the houses, and it would seem that the majority of the population took refuge at nearby towns and villages on the valley floor.
Volcanic disasters and cultural discontinuities in Holocene time, in West New Britain, Papua New Guinea
Authors: Torrence Robin , Pavlides Christina , Jackson Peter , Webb John
Published: April 2008

An evaluation of the relationship between culture change and the history of volcanic activity from the Witori and Dakataua volcanoes in West New Britain province, Papua New Guinea, demonstrates the importance of studies focusing on long time spans to an understanding of cultural adaptation to volcanic disasters. Using a chronostratigraphy based on several techniques for matching tephras, the cultural responses to five volcanic events are compared and contrasted between the Willaumez Peninsula and Yombon, areas whose environment and proximity to the volcanoes vary significantly. Archaeological analyses of material show that human groups did not immediately adjust to the effects of the most severe volcanic events but abandoned both regions. In contrast, adaptation on a long-term basis may be indicated by the occurrence of a punctuated trend in lithic technology inferred to reflect a decrease in mobility and an increase in the intensification of subsistence practices. This pattern, combined with limited radiocarbon dating, suggests that the length of abandonment decreased after each eruption, probably because of changes in social organization and subsistence practices. The paper demonstrates the value of collaboration between archaeology and geology in the study of long-term human responses to natural hazards.
Forward stratigraphic modelling of forced regressions: evidence for the genesis of attached and detached lowstand systems
Authors: Ainsworth R. B. , Bosscher H. , Newall M. J.
Published: April 2008

A complex series of interactions between subsidence, eustasy and sediment supply determine whether a forced regressive shoreface will be physicallyattachedto underlying sandy deposits, ordetachedand encased in marine mudstone. Using a Shell-developed and proprietary forward stratigraphic modelling system, these interactions of controls on clastic depositional geometries can be simulated. Upper Cretaceous subsurface and outcrop data from the Western Interior Basin of Canada form the basis of this study. The outcrop data suggest that high frequency (200 000 years), relatively low amplitude (8 m) relative sea-level changes occurred during deposition of the studied succession. When these parameters are convolved with the Haq third-order eustatic sea-level curve and a constant rate of subsidence and sediment supply, a series of attached lowstand, forced regressive shorefaces are generated by the forward stratigraphic modelling system. In order to generate a detached lowstand shoreface a relatively large magnitude, high frequency eustatic fall or a high frequency tectonic uplift is required. The modelling studies also suggest that (i) forced regressive deposits preferentially develop as attached lowstand systems, (ii) detached lowstand systems in most cases initially develop as attached lostand systems which are subsequently detached by transgressive-regressive wave erosion, (iii) if the sequence boundary is picked below the sharp-based, forced regressive shoreface (attached and detached lowstand systems tract interpretation) or above it (falling-stage systems tract interpretation) it must remain in that position relative to the correlative down-dip, sharp-based shoreface sandbodies regardless of whether those bodies are attached or detached and (iv) the role of sediment supply as a controlling parameter in the generation of forced regressions appears to be a secondary one.
Recognition and distinction of normal and forced regression in cyclothemic strata: a Plio-Pleistocene case study from eastern North Island, New Zealand
Authors: Haywick Douglas W.
Published: April 2008

The Tangoio block of eastern North Island, New Zealand contains an exceptionally well exposed, 550 m thick sequence of Plio-Pleistocene cyclothemic sedimentary rocks, the Petane Group, that were deposited along the western margin of a shallow (<200 m) pericontinental seaway. The cyclicity that characterizes the Petane Group in this area was generated through recurring 40 ka (sixth-order) sea-level changes of c. 75–150 m. Data from more than 100 sections indicates that the strata consist of five distinct cyclothems, each consisting of a lower formation of mudstone deposited in midshelf environments (highstand system tract, HST), and an upper formation dominated by coarse-grained facies deposited in shallow marine and occasionally non-marine environments. Western exposures of HST mudstones in the lower portion of the Petane Group shoal up into shallow marine siliciclastic sandstones, fluvial gravels and siltstones. The transition is gradational and is consistent with progradation of a siliciclastic shoreline during late sea-level highstand. The shoaling upward siliciclastic sandstone interval represents a regressive system tract (RST) whereas the fluvial beds represent a lowstand system tract (LST). LST gravel beds are sharply overlain by a transgressive surface of erosion and fining-upward siliciclastic sandstone facies of a transgressive systems tract (TST).

Carbonate sediments replaced siliciclastic sandstones as the dominant coarse-grained lithology in the upper Petane Group, probably due to bypass of siliciclastic sediment during sea-level fall. Transitions from HST mudstone into carbonate sand and bioclastic limestone (coquina) are generally sharp everywhere except the downdip eastern portions of the Tangoio block. The contacts represent regressive surfaces of erosion produced during falling stages of sea-level and/or ravinement surfaces formed during rising phases of sealevel (transgressive surfaces of erosion). Carbonate facies atop these erosional surfaces are generally interpreted as TST deposits, except for the uppermost limestones in the Petane Group that occur below a sequence boundary and therefore represent a forced regression systems tract (FRST). Stratal position is the only distinguishing characteristic of FRST limestones in the Petane Group, otherwise they are identical to TST deposits. In eastern portions of the Tangoio block, HST mudstones pass gradationally into RST calcareous sandstones and LST limestones. Systems tracts here are bounded by correlative conformities rather than erosive surfaces indicating continuous sedimentation during sea-level fall and lowstand. Differences in sedimentation and subsidence rates between carbonate and siliciclastic sedimentary systems, are responsible for the different stratal architecture of systems tracts in the Petane Group.
Late Permian Foraminiferal Biofacies Belts in Turkey: Palaeogeographic and Tectonic Implications
Authors: Altiner Demir , Özkan-Altiner Sevinç , Koçyiğit Ali
Published: April 2008

Upper Permian marine carbonates are distinguished in two contrasting biofacies belts in Turkey. The Southern Biofacies Belt, represented by low-energy inner platform deposits of the Tauride Belt and the Arabian Platform, is rich in algae and smaller foraminifera but poor in fusulines. The Kubergandian and Murgabian stages are missing, although the rest of the Upper Permian consists of monotonous, shallow-marine carbonate deposits. The extremely tectonised and fragmented Northern Biofacies Belt includes the Upper Permian of the Karakaya Orogen and outer platform or platform margin deposits of the Tauride Belt. These deposits are rich in parachomata-bearing fusulines comprising
Cancellina, Verbeekina, Afghanella, Sumatrina, Neoschwagerina
and
Yabeina
. The reconstructed biostratigraphic scheme indicates that all Upper Permian stages (Kubergandian-Dorashamian) are present.

The lateral continuity of the two biofacies belts is detected by the presence of tongues of he Northern Biofacies Belt pinching out in the Southern Biofacies Belt. Upper Permian blocks in the Karakaya Orogen display similar palaeontologic and biofacies characteristics, with the outer platform or platform margin deposits of the Taurides constituting the northernmost extension of the carbonate platform. This platform was probably facing a basin or a trough to the north. The lack of any transgressive Upper Permian deposits resting unconformably on the pre-Permian basement of the Sakarya Continent strongly suggests that such a basin was located between the Late Permian carbonate platform in the south and the basement rocks of the future Sakarya Continent in the north.
A Geotraverse Across Northwestern Turkey: Tectonic Units of the Central Sakarya Region and their Tectonic Evolution
Authors: Göncüoğlu M. Cemal , Turhan Necati , Şentürk Kamil , Özcan Ahmet , Uysal Şükrü , Yaliniz M. Kenan
Published: April 2008

In the Central Sakarya area of Turkey there are two main Alpine continental units, separated by a south verging ophiolitic complex which represents the root zone of the İzmir-Ankara Suture Belt.

The Central Sakarya Terrane in the north includes two ‘Variscan’ tectonic units in its basement. The Söğüt Metamorphic rocks represent a Variscan ensimatic arc complex and the Tepeköy Metamorphic rocks are characteristically a forearc-trench complex. The unconformably overlying Triassic Soğukkuyu Metamorphic rocks correspond to a part of the Karakaya Formation and are interpreted as a Triassic rift basin assemblage. These units are unconformably overlain by a transgressive sequence of Liassic-Late Cretaceous age that represents the northeastward deepening carbonate platform of the Sakarya Composite Terrane.

The middle tectonic unit (the Central Sakarya Ophiolitic Complex) comprises blocks and slices of dismembered ophiolites, blueschists and basic volcanic rocks with uppermost Jurassic-Lower Cretaceous radiolarite-limestone interlayers. Geochemical data from basalt blocks suggest mid-ocean ridge basalt (MORB)- and suprasubduction-type tectonic settings within the Neotethyan İzmir-Ankara Ocean.

The southern tectonic unit includes basal polyphase metamorphosed clastic rocks (Sömdiken Metamorphics), intruded by felsic and basic dykes and overlain by thick-bedded marbles. This assemblage is unconformably overlain by continental clastic rocks gradually giving way to thick-bedded recrystallized limestones, cherty limestones and pelagic limestones intercalated with radiolarites, and finally by a thick high pressure-low temperature (HP-LT) metamorphic synorogenic flysch sequence. This succession is identical to the passive continental margin sequences of the Tauride Platform. It is suggested that this passive margin was subducted during the Late Cretaceous in an intraoceanic subduction zone and affected by HP-LT metamorphism. The emplacement of the allochthonous oceanic assemblages and the collision with the Central Sakarya Terrane was complete by the end of the Cretaceous.
Structural Correlation of the Southern Transcaucasus (Georgia)-Eastern Pontides (Turkey)
Authors: Yilmaz Alİ , Adamia Shota , Chabukiani Alexander , Chkhotua Tamara , ErdoĞan Kemal , Tuzcu SevİM , KarabiyikoĞlu Mustafa
Published: April 2008

The eastern Pontides (northeastern Turkey) and Transcaucasus (Georgia) belong to the same geological belt representing an active margin of the Eurasian continent. According to palaeotectonic-palaeogeographic reconstructions, based on regional geological, palaeomagnetic, palaeobiogeographical and petrological data, the eastern Pontides and the major part of the Transcaucasus, situated to the north of the North Anatolian-Lesser Caucasian ophiolitic suture, comprise island arc, forearc, back and interarc basins. The eastern Pontide segment of the belt consists of three structural units which, from north to south, are the northern, central and southern units. The northern unit, the southeastern Black Sea coast-Adjara-Trialeti Unit, represents a juvenile back arc basin formed during the Late Cretaceous (pre-Maastrichtian). This unit separates the southern and northern Transcaucasus zones. The central Artvin-Bolnisi Unit is also known as the northern part of the southern Transcaucasus and is characterized by Hercynian basement, unconformably overlying the Upper Carboniferous-Lower Permian molasse and Upper Jurassic-Cretaceous arc association. The southern unit is the imbricated Bayburt-Karabakh Unit and is known as the southern part of the southern Transcaucasus. This unit has a similar basement to the Artvin-Bolnisi Unit and also includes a chaotic assemblage; it unconformably overlies the Upper Jurassic-Cretaceous forearc association. The eastern Pontide system is interpreted as the product of interference between a spreading ridge and subduction zone during Late Jurassic-Cretaceous times. The North Anatolian-Lesser Caucasus Suture, comprising ophiolites, mélanges and an ensimatic arc association, separates the overlying system from the Anatolian-Iranian Platform in the south. Maastrichtian-Lower Eocene cover rocks in the region unconformably overlie all the other units. Middle Eocene rifting resulted in the formation of new basins, some of which closed during an Oligocene-Early Miocene regression. Others, such as the Black Sea and Caspian Basins, have survived to the present day as relict basins.
Neogene Paratethyan Succession in Turkey and Its Implications for the Palaeogeography of the Eastern Paratethys
Authors: Görür Naci , Çağatay Namik , Sakinç Mehmet , Akkök Remzi , Tchapalyga Andrey , Natalin Boris
Published: April 2008

The Neogene marginal succession of the Eastern Paratethys (EP) crops out along the southern Black Sea coast and in the Marmara region of Turkey, and provides important clues to the tectono-sedimentary and palaeoceanographic conditions.

In the Tarkhanian stage, the southern margin of the EP basin was largely a carbonate platform covered by warm, marine waters. From the end of the Tarkhanian to the Early Chokrakian there was an overall emergence throughout the basin, which is indicated by an influx of siliciclastic sediments. The fossil assemblage indicates that normal marine conditions persisted during most of this period, except for a salinity reduction towards the end due to an eustatic isolation of the basin, which in turn led to anoxic bottom water conditions. The Late Chokrakian isolation became even more severe during the Karaganian as indicated by the endemic fossil assemblage indicating brackish-marine conditions. Carbonate platform conditions prevailed in the northern Pontides during this time. In the Early Konkian, the basin was reconnected briefly with the world ocean by a transgression from the Indo-Pacific Ocean. In the Late Konkian there was a return to brackish-marine conditions.

Lower Sarmatian sediments are absent in the southern margin of the EP, but elsewhere in the basin this stage is characterized by a widespread marine transgression. In the Middle-Late Sarmatian, the EP basin was partially isolated with freshening and anoxic bottom-water conditions. During this time there was a brief marine transgression from the Mediterranean into the Marmara region, but it did not reach the Paratethyan basin. The Pontian is characterized by an extensive transgression from the EP that inundated the Marmara and northeastern Aegean regions. The connection with the Marmara Basin was cut off during the Kimmerian and re-established during the Late Akchagylian, when the EP basin was inundated by the Mediterranean waters via the Sea of Marmara as a result of increased North Anatolian Fault activity and a short-term global sea level rise.
Episodic Graben Formation and Extensional Neotectonic Regime in West Central Anatolia and the Isparta Angle: A Case Study in the Akşehir-Afyon Graben, Turkey
Authors: Koçyİğİt Alİ , ünay Engİn , Saraç Gerçek
Published: April 2008

Central and Western Anatolia form a continental back-arc region related to the Hellenic-Cyprus convergent plate boundary of the Anatolian and African Plates. The Akşehir-Afyon Graben (AAG), the easternmost extension of the west Anatolian horstgraben system, is located at the junction of Central Anatolia and eastern limb of the Isparta Angle. The AAG is 4–20 km wide and 90 km long. It trends west-northwest-east-southeast and is an actively growing rift containing two sedimentary infills of continental fluviolacustrine origin bounded on both sides by oblique-slip normal faults. The older infill is folded, thrust faulted and early Late Miocene in age. The younger infill, which is nearly horizontally bedded, is Plio-Quaternary in age and rests on the older infill with angular unconformity. The deformation of the older infill and the angular unconformity indicate a Late Miocene phase of compression, which separates two extensional periods. The second phase of extension has lasted since the Pliocene and is part of the current extensional neotectonic regime of both west Central Anatolia and the Isparta Angle, despite being previously reported as a compressional neotectonic regime.

The graben-bounding Akşehir Fault Zone (AFZ) and the Karagöztepe Fault Zone display well-preserved fault surfaces and slickenlines. Although stereographic plots of the fault slip data show that the graben-bounding structures are oblique-slip normal faults, the AFZ has also been described as a single reverse fault. Both the field and seismic data, particularly the 1921 Argıthanı-Akşehir and 1946 Ilgın-Argıthanı earthquakes, indicate that the AAG is an active neotectonic structure. However, it can also be interpreted to lie in a seismic gap when its rate of seismicity is compared with that of the Gediz-Simav Graben forming its west-northwestern extension.
Palaeomagnetic Study of the Erciyes Sector of the Ecemiş Fault Zone: Neotectonic Deformation in the Southeastern Part of the Anatolian Block
Authors: Tatar Orhan , Piper John D. A. , Gürsoy Halil
Published: April 2008

In the Turkish sector of the Afro-Eurasian collision zone, continuing northward motion of the Arabian promontory is extruding the Anatolian region to the west. Although the East Anatolian Fault Zone (EAFZ) is recognized as the southern boundary of this tectonic escape, distributed deformation is occurring across a broad zone extending for at least 300 km to the northwest, which includes a number of major dextral and sinistral fault lineaments. The longest of these lineaments is the Ecemiş Fault Zone, although the long-term significance of deformation, and specifically strike-slip, across this zone is disputed. This zone is also the locus of major volcanic activity in the Kayseri region. The present paper reports a palaeomagnetic study of young (1–2 Ma) lava flows which has aimed to identify recent block rotations resulting from regional deformation in this region. Rock magnetism shows the lavas to be dominated by low-Ti magnetite assemblages of primary cooling related origin. Although grain properties are predominantly multidomain, significant fractions of single domains are always present and responsible for a stable thermoremanence of normal and reversed polarity. Whilst group mean directions show that the blocks in this sector of Anatolia show the typical counterclockwise rotation resulting from tectonic escape, in this case by
c
. 10° during the last 1 Ma, larger differential rotations in both senses are identified across the Sultansazhği Depression. Comparable differential rotations recorded by the 2.8 ± 0.2 Ma Incesu Ignimbrite have resulted from the pull-apart in this sector of the Ecemiş Zone which has accommodated emplacement of the Erciyes volcanic centre since the termination of ignimbrite activity. Within the wedge-shaped terrane confined between the EAFZ in the south and the North Anatolian Fault Zone in the north, the degree of counterclockwise rotation during tectonic escape within the last 2–3 Ma has diminished from
c
. 25° in the east to
c
. 10° towards the southwest. This corresponds to a transition from highly strained to a less-strained lithosphere as the width of the semi-plastic Anatolian terranes confined between the Arabian-Eurasian pincer broadens out to the west.
S-I-A-type Intrusive Associations: Geodynamic Significance of Synchronism Between Metamorphism and Magmatism in Central Anatolia, Turkey
Authors: Boztuğ Durmuş
Published: April 2008

The Central Anatolian crystalline region, comprising metasediments, ophiolitic slabs and numerous intrusives, has been called the Kırşehir Massif, the Kırşehir Block or Central Anatolian Crystalline Complex. Intrusive associations in Central Anatolia are summarized as: (1) a syncollisional, S (or C
ST
)-type, peraluminous and two-mica leuco-granitic association; (2) a post-collisional, I (or H
LO
)-type, metaluminous, high-K calcalkaline, typically K-feldspar megacrystic monzonitic association; and (3) an A-type, post-collisional and within-plate alkaline association comprising a high-K and silica-oversaturated alkaline, K-feldspar megacrystic monzonitic and synoptic subgroup, and a silica-undersaturated alkaline feldspathoid-sodalite syenite porphyry subgroup.

Radiometric data suggest that metamorphism and magmatism in Central Anatolia were synchronous during the Late Cretaceous. This implies that metamorphism may have been generated by inverted metamorphism induced by the Anatolide-Pontide collision and was linked to a decreasing metamorphic grade from the north (i.e. from the main suture zone) towards the south (i.e. Taurides). Collision-related intrusive rocks within this crystalline body reflect differences in geological setting, mineralogical-chemical composition and associated ore deposition. Published data considering the distribution and timing of metamorphism and magmatism in the Central Anatolia suggest that both are related to the Anatolide-Pontide collision along the İzmir-Ankara-Erzincan Suture Zone in the Late Cretaceous. Various magmatic episodes affected along the passive margin of the Anatolides, including a syncollisional peraluminous episode, a post-collisional calc-alkaline hybrid and a post-collisional within-plate alkaline episode.
Sedimentation associated with estuarine frontal systems
Authors: McManus John
Published: April 2008

Estuarine fronts may develop in several locations, across the water body as transverse, halocline-related features, as overbank spills, or where tidal flats release waters into principal tidal channels. In many estuaries longitudinal fronts originate at headlands or are associated with major sandbanks (Bowman 1988). Commonly a front separates a nearshore water mass from that of the main flow of tidal waters. In the marginal waters flows are slower than in the main channels, and suspended sediments and pollutants released to these marginal zones do not mix freely with the principal tidal waters entering and leaving the estuary. These nearshore waters also often differ in temperature from the channel waters (Anderson
et al.
1992). It is suggested that the linear convergent frontal systems provide the ideal sites for the accumulation of sediment, and exert some control on the distribution of longitudinal estuarine sand banks. Some, but not all of these are associated with headlands. The geomorphological evolution of the sand bank systems within the upper and middle reaches of the Tay Estuary, Scotland, are discussed in relation to present and past locations of longitudinal fronts. The Middle Bank, off Dundee, is seen to occur between the lines of longitudinal fronts formed during the flood and ebb phases of the tide. The Naughton Bank, off Balmerino is related to an ebb phase headlnad-induced flow separation. In the seaward reaches longitudinal fronts locate the outer margins of the tidal flats and become axially convergent in the Tayport-Broughty Ferry narrows.
Processes controlling import of fine-grained sediment to tidal areas: a simulation model
Authors: Bartholdy Jesper
Published: April 2008

Salt marsh and mud flat sedimentation in the Wadden Sea and in similar depositional regions is usually dependent on the net import of fine-grained sediments from adjacent marine environments. This net import takes place as a result of several processes such as settling lag and scour lag. This paper utilizes a database comprising time series of tidal velocity and turbidity in the Grådyb tidal area of western Denmark as the basis of a simple conceptual model which describes the transport, deposition and resuspension of finegrained material in the area. The results demonstrate that: (a) grain sizes close to the sand/silt boundary are most sensitive to lag effects; (b) scour lag is much more important than settling lag; (c) raised temperatures enhance the net-lag effect for silt with increasing importance for finer grain sizes; (d) with increased suspended concentrations, the time it takes to resuspended the material deposited at slack water (the resuspension lag) is of increasing importance for the net-lag effect.
Shoreline change and fine-grained sediment input: Isle of Sheppey Coast, Thames Estuary, UK
Authors: Nicholls Robert J. , Dredge Andrew , Wilson Theresa
Published: April 2008

The northern coast of the Isle of Sheppey comprises actively-eroding cliffs up to 50 m high cut into the London Clay. From 1867 to 1998 the average cliff-top recession was about 1 m a
−1
, while the maximum recession was 1.9 ± 0.08 m a
−1
. From 1897 to 1998, this provided at least 4.5 × 10
5
t a
−1
of fine-grained sediment to the Thames Estuary system and southern North Sea. This sediment input due to erosion is comparable in magnitude with fluvial sediment input from the Thames. The sinks for this material are unclear, but it is likely that the Essex and Kent estuaries and marshes have historically been important in this regard. Given climate change and accelerated sea-level rise, estuaries will again act as sinks, and it is prudent to maintain these supplies of sediment so that these estuarine systems can adjust to this forcing. To maintain sediment supply, shoreline management and estuary management needs to recognize more explicitly the importance and scale of fine-grained sediment supply and transport, including any implications for statutory land use planning.
Physical modelling of the rheology of clean and sediment-rich polycrystalline ice using a geotechnical centrifuge: potential applications
Authors: Irving Duncan H. B. , Rea Brice R. , Harris Charles
Published: April 2008

A self-weight stress gradient is developed through the body of a glacier such that strain rates are highest in the lowest few metres as described by Glen’s flow law and other stress- and temperature-dependent relationships. Conventional laboratory technology limits the size and complexity of physical models of glacier ice, particularly in the complicated basal ice layers. A geotechnical centrifuge can be used to replicate such stress regimes in a controlled environment using a scaled model of the field ‘prototype’ that is subjected to an accelerational field that is a factor
N
greater than that of the Earth,
g
. The development of a technique employing a geotechnical centrifuge as a testbed for such physical models is described. Strain rates of 10
−6
–10
−7
s
−1
are calculated for models of low and moderate stress, high temperature ice. Relationships between the physical models and glacial systems suggest a scaling of the effects of transient creep by 1:
N
, diffusion creep by 1:
N
2
–1:
N
3
and power law creep by 1:1. Preliminary results demonstrate the potential applications of the technique in the fields of glaciology and glacial geomorphology, in particular where low stresses and high temperatures are key characteristics of a glacial system and in systems containing several stratigraphic units.
Deformation histories and structural assemblages of glacier ice in a non-steady flow regime
Authors: Lawson Wendy J. , Sharp Martin J. , Hambrey Michael J.
Published: April 2008

Deformation histories of ice exposed at various locations on the centreline in the ablation area of surge-type Variegated Glacier were estimated using a technique based on evaluation of strain-rate fields derived from velocity gradients. The analysis indicates that ice exposed in the upper part of the ablation area a few years after the 1982–83 surge had experienced a relatively simple deformation history that included one surge-related high magnitude deformation event. Ice exposed in the terminal lobe at the same time had experienced six surge phases during its approximately 100 year-long residence time. The histories of accumulation of cumulative strain are complex, and indicate that measures of cumulative strain can mask the effects of large but transient strain events. They also demonstrate that substantial cumulative strain can be ‘undone’ during subsequent deformation to leave a cumulative strain signal that is unrepresentative of earlier cumulative strain states.

Structural relationships in general do not reflect the complexity of the deformation histories experienced by the ice. A preliminary analysis of the relationships between the deformation histories and structural assemblages suggests, in particular, that brittle structures are reactivated several times during the history of the ice.
The stress distribution related to the boudinage of a visco-elastic material: examples from a polar outlet glacier
Authors: Marmo Brett A. , Wilson Christopher J. L.
Published: April 2008

Quantitative stress measurements related to the development of mesoscale structures in rock are difficult, if not impossible. A method for determining the stress distribution and history during the development of mesoscale boudinage structures in ice is introduced here. Boudinage structures in fracture trace ice have been observed in the outlets glaciers of the Framnes Mountains, east Antarctica. Fracture traces are preserved when creasses fill with surface melt water, which freezes to form coarse-grained columnar ice. A 4.0 km flow-parallel traverse across the Central Ice Stream of the Framnes Mountains is presented to illustrate the boudinage of fracture traces with a mean width of 0.30 m. Field-based measurement of the geometric evolution of boudinage structures has been combined with surface flow rate measurements to quantitatively determine the strain rate at which the boudinage structures formed. The strain rate measurements provide boundary constraints on several two-dimensional finite difference models that have been used to analyse the stress distribution related to the formation of boudinage structures in a visco-elastic solid. The results reveal the development of pressure-shadows during the boundinage of layered rocks, and demonstrate the degree of refraction of stress across rheological boundaries, which have important ramifications for the analysis of planar and linear fabrics in rocks.
The potential contribution of high-resolution glacier flow modelling to structural glaciology
Authors: Hubbard Alun , Hubbard Bryn
Published: April 2008

The three-dimensional stress and strain fields derived through high-resolution flow modelling of Haut Glacier d’Arolla, Switzerland are used to predict the generation, passage and surface expression of a variety of structural forms at the glacier. Flow vectors and strain ellipses are computed and illustrated in plan-form and long section. The model is used to predict the formation and orientation of surface crevasses, and, once healed, the downglacier evolution of their traces. Similarly, the evolution of primary stratification where it crops out at the glacier surface is predicted. The resulting stratification pattern compares well with that revealed in aerial photographs of the glacier. Finally, the three-dimensional strain field is used to track the (accumulation area) burial, (englacial) transport and (ablation area) exposure of ice deposited within a pre-defined elevation range. This
deposition-transport-exposure
tracking allows the location of ice that was initially deposited at any defined location on the glacier to be identified. Such information is of significance in interpreting, for example, the distribution of ash and isotopic horizons within a glacier. We conclude that high-resolution three-dimensional flow modelling has the potential to provide a powerful tool for investigating the genesis and evolution of valley glacier structures.
Continuity comes first: recent progress in understanding subglacial deformation
Authors: Alley R. B.
Published: April 2008

Subglacial till deformation is glaciologically and geologically important, but is difficult to model owing to numerous uncertainties related to till generation and the flow law for till deformation. I review recent results with the hope of at least focusing the uncertainties. Fine-grained subglacial tills often are sufficiently soft that continuity issues are more important than the ‘flow law’ of the till in affecting glacier behavior. Non-steady forcing, coarse clasts and an irregular ice-till contact favour till deformation to significant depths and thus rapid subglacial transport of till. Over long times, site history is important in till continuity and thus in glacier behaviour.
Evidence against pervasive bed deformation during the surge of an Icelandic glacier
Authors: Fuller Sarah , Murray Tavi
Published: April 2008

Hagafellsjökull Vestari, Iceland, surged in 1980 and advanced about 700 m. Subsequent retreat of the ice front has exposed a suite of streamlined bedforms and former subglacial sediments. Investigations were undertaken on the recently deglaciated forefield to explore the degree of ice-bed coupling during the surge. The morphometry of flutes at this site suggest that the ice was relatively well coupled to its bed. Widespread till wedges show that ploughing was a dominant process. These observations suggest that pervasive deformation of the sedimentary bed at high water pressures in surge was a strong possibility. However, evidence from the micromorphology of drumlin sediments shows laterally continuous clay bands preserved between till layers within a drumlin. Thus pervasive deformation of the whole sediment thickness did not occur. There is evidence only of a thin layer of deformation (<16 cm). We propose that at low effective pressures there was a reduction in the strength of the ice-bed interface rather than a reduction in sediment strength. Motion was concentrated at the sole with localized and shallow deformation where clasts ploughed through the substrate.
Laboratory investigations of the strength, static hydraulic conductivity and dynamic hydraulic conductivity of glacial sediments
Authors: Hubbard Bryn , Maltman Alex
Published: April 2008

We report the first data on how effective pressure and deformation influence the hydraulic conductivity of glacial sediments. Fifty eight static hydraulic conductivity tests, 28 triaxial deformation tests and 25 dynamic hydraulic conductivity tests (in which hydraulic conductivity is measured simultaneously with deformation) have been undertaken on seven samples of glacial sediments recovered from the margins of Haut Glacier d’Arolla, Switzerland, and from Traeth y Mwnt, mid Wales. Testing reveals that hydraulic conductivity is inversely related to effective pressure, particularly at effective pressures below
c.
100 kPa. Over the full range of effective pressures used (50–900 kPa), this relationship is best described by a negative power law above a base hydraulic conductivity value, termed
K
0
. The value of
K
0
varies between samples by over three orders of magnitude, from 10
−8
m s
−1
to 10
−11
m s
−1
. These values vary directly, but weakly, with the square of the effective grain-size of the samples tested.

Dynamic testing revealed a commonly repeated pattern of sample failure: axial stress approached a maximum value after which the sample deformed in a ductile manner from its initially cylindrical shape to a barrel shape. Most commonly, sample deformation and failure were accompanied by a decrease in hydraulic conductivity, although increases were also recorded. Dynamic testing also resulted in strongly linear relationships between effective pressure and the yield stress at failure. Such relationships are broadly consistent with a Mohr-Coulomb type model, revealing significant inter-sample variability in frictional resistance, and a cohesive term that is statistically indistinguishable from zero.
Moraine-mound formation by englacial thrusting: the Younger Dryas moraines of Cwm Idwal, North Wales
Authors: Graham David J. , Midgley Nicholas G.
Published: April 2008

The Younger Dryas (
c.
11-10 ka
bp
) moraine-mound complex (‘hummocky moraine’) in the historically important site of Cwm Idwal, North Wales, has previously been interpreted using periglacial, subglacial, ice-marginal and englacial models. In this paper the morphology and sedimentology of these landforms is described and the competing hypotheses tested against this evidence. It is demonstrated that an englacial thrusting model, developed for polythermal glaciers in Svalbard, best fits the available evidence. Thrusting probably resulted from longitudinal compression against a reverse bedrock slope, although a frozen snout, downglacier of sliding ice, may also have been a trigger. It is suggested that the role of ice-deformation, especially thrusting, in landform development has been underestimated, and that the englacial thrusting model may find application in the interpretation of other sites in the palaeo-landform record.
Molecular evidence on the evolution of the Bivalvia
Authors: Campbell D. C.
Published: April 2008

Despite widespread agreement on the monophyly of several major taxa of bivalves, others remain uncertain and the relationships among them are debated. The present study compares new and published morphological phylogenies with new analyses based on 18S gene sequences.

All but one family and all superfamilies in the Bivalvia were monophyletic in all the analyses. Several higher taxa, including most subclasses and orders, were also resolved as monophyletic. Only Myoida shows strong evidence for polyphyly, with at least two origins from Veneroida. Autobranchia was supported as monophyletic in the parsimony analyses. Within Pteriomorphia, Ostreoida is the sister taxon of Pterioida, if not derived from within it, rather than closest to Pectinoida. The numerous points of agreement with morphology based analyses suggests that both types of evidence are converging on a common phylogeny; however, differences remain to be resolved by further study.
A new look at early bivalve phylogeny
Authors: Cope John C. W.
Published: April 2008

In the 30 years since publication of the bivalve
Treatise
, (Moore, R. C. (ed.) 1969.
Treatise on Invertebrate Paleontology. Part N. Mollusca 6, Bivalvia
, Geological Society of America and University of Kansas) important new faunas have been described from the early and mid Cambrian and from the early and mid Ordovician. These contain significant new forms, including some long-ranging intermediate groups, that indicate the relationships between the principal bivalve clades, but lack of fossils from the late Cambrian and earliest Ordovician is a major hindrance. The principal phase of bivalve diversification followed on from the evolution of the filibranch gill in the latest Cambrian or earliest Ordovician. The fundamental division of the class is into two subclasses, Protobranchia and Autolamelli branchiata; links between the two can be demonstrated in the early Ordovician. Major divisions of each subclass are recognized as superorders.

Within the Protobranchia, the Nuculoida developed specialist food-gathering palps and an enlarged foot. Diverging early from the protobranch stock were other bivalves that lived symbiotically with sulphur-oxidizing chemoautotrophic bacteria; this allowed colonization of anaerobic substrates and produced two distinct stocks: the deeply infaunal anteriorly elongate Solemyoida and the shallower infaunal Nucinelloida.

The Autolamellibranchiata, initially identified by strongly asymmetrical hinges, diversified in three directions, each characterized by distinctive hinges. The Trigonioida were characterized by ligamental nymphs and frequently denticulate teeth, and rapidly regained greater symmetry; the Anomalodesmata also developed a strong ligamental insertion within nymphs and largely lost their dentition, whilst the Heteroconchia, principally with a shell including a complex crossed-lamellar structure, had various combinations of cardinal and lateral teeth. Heteroconch diversifications were mainly in the Mesozoic and Cenozoic, but one Ordovician group, the Glyptarcoidea, is a good ancestor for the Pteriomorphia.

The following new taxa are proposed: Cardiolarioidea superfam. nov., Eritropidae fam. nov. and Catamarcaidae fam. nov.
A preliminary phylogeny for rudist bivalves: sifting clades from grades
Authors: Skelton Peter W. , Smith Andrew B.
Published: April 2008

The taxonomic history of the late Jurassic-Cretaceous rudist bivalves (Superfamily Hippuritoidea) is reviewed and a new phylogeny based on cladistic analysis of 32 skeletal characters is proposed. Informative characters include: relative thickness and structures of the outer (calcitic) shell layer; valve asymmetry and attachment to the substrate by either the left or right valve; form of the ligament; and, in the aragonitic inner shell, the dentition and shelly supports (myophores) for the adductor muscles, as well as accessory cavities and blind-ending (pallial) canals. The myocardinal complex (teeth and myophores) is especially important for discriminating clades previously lumped in paraphyletic or even polyphyletic taxa (e.g. Caprinidae,
sensu lato
, in the bivalve
Treatise
(Moore, R. C. (ed.) 1969.
Treatise on Invertebrate Paleontology, Part N. Mollusca 6, Bivalvia
, Geological Society of America and University of Kansas).

As outgroup, a megalodontid bivalve was used, as this shares three derived traits (massive dentition, modified parivincular ligament and posterior myophores) in common with rudists. The clade of all rudists is united by possession of an outer shell layer of fibrillar prismatic calcite (albeit greatly reduced in a few taxa). Two subclades are distinguished according to the attachment of the shell — either by the left valve (all ‘diceratids’, except
Diceras
and
Valletia
, plus the monophyletic requieniids), or by the right valve (
Diceras, Valletia
and all other rudists). Monophyly of some previously established families is substantiated. These include Caprinidae,
sensu stricto
(Skelton, P. W. 1978.
Philosophical Transactions of the Royal Society of London, Series B
,
284
, 305–318), Radiolitidae (with
Agriopleura
as sister taxon) and Hippuritidae (with
Tepeyacia
emerging as a possible sister taxon), while others are resolved into distinct clades. There is some evidence for the Polyconitidae Mac Gillavry (1937), though with negligible bootstrap support.