bluuebunny/crossref_metadata_2025 huggingface dataset:
The geometries and deep structure of the northern North Sea rift system
Authors: Odinsen Tore , Christiansson Peter , Gabrielsen Roy H. , Faleide Jan Inge , Berge Anker M.
Published: April 2008

The enormous quantity of commercial reflection seismic lines across the North Sea Basin have made the area one of the most thoroughly studied continental settings in the world. Further insight in the deep architecture of the crust is provided by
c.
10 000 km deep reflection seismic data. Unfortunately, these unique databases have rarely been combined systematically to constrain possible tectonic models for the area. This paper is built on a full integration of high-quality commercial lines (7 s twt) and the deep (15 s twt) NSDP84-1 and -2 lines. The deep lines have been post-stack reprocessed and depth-converted. A number of deep wells have provided stratigraphic control along the lines. The overall reflective pattern in the lines divides the crust in three, with a reflective upper and lower crust separated by a less reflective middle crust. The lateral changes in reflectivity matches the observed variation in crustal thickness, where the thinnest crust coincides with the Viking Graben area with a total crustal thickness of 21–24 km, increasing to 30–36 km in the platform areas. The lower crust is seen as an undulating 4–10 km thick band with shallow dipping reflections, with a Moho that consists of reflections with variable lateral thickness and amplitude, rather than one single strong reflection. The structural analysis shows that the crust is cut by a number of large normal faults with varying geometries. It is assumed that some of these major faults are long-lived features rooted in old basement grains. The most spectacular normal faults developed during the Permo-early Triassic extensional phase, but were often reactivated during the Jurassic extensional phase, and with continued minor fault movement into the Cretaceous thermal cooling period. Integration of commercial and deep reflection seismic sections shows that three detachment levels are present within the crust. These levels, which control changes in fault geometries, are believed to represent lateral rheological interfaces combined with or intersected by long-lived zones of weaknesses. The uppermost level is represented by supra-basement low-angle normal faults controlled by gravity and/or lithological changes during extension. An intra-basement (middle crust) level between 5 and 7 s (twt) coincides with decreasing dip of the larger basin bounding faults. The lower crust is the deepest detachment level, which probably exerts control on the geometric changes of the upper-mantle shear zones and the largest crustal normal faults.
Crustal stress in and around Norway: a compliation of
in situ
stress observations
Authors: Fejerskov Morten , Lindholm Conrad , Myrvang Arne , Bungum Hilmar
Published: April 2008

In-situ
rock stresses yield information about geodynamic processes in the crust, and are important input data for almost all kinds of geomechanics work. Compilations of rock stress measurements, such as the World Stress Map, have been used to characterize the regional stress field. On the basis of new data from the Norwegian region, a map of the maximum horizontal stress (
σ
H
) direction, for both on- and offshore Norway, has been established. Four main stress provinces with different regional stress trends are identified. The Barents Sea and northern Norway province exhibits a very consistent N-S
σ
H
direction, with high horizontal stresses. In the Norwegian Sea and mid-Norway province the
σ
H
direction has rotated towards NW-SE. Also here, high horizontal stresses are measured and a compressional regime appears. In the northern North Sea and western Norway province the
σ
H
direction is more scattered. A WNW-ESE direction dominates, but a NNE-SSW trend, parallel to the major structures in the area, also appears. The stress regime is primarily compressional, but in the Stord area normal faulting earthquakes are observed. The southern North Sea province yields a very scattered
σ
H
direction. However, a NW-SE trend, which aligns with the stress system in western Europe, is identified. The high variation, both laterally and with depth, indicates near-isotropic horizontal stresses and influence by local features. The different stress determination techniques applied (overcoring, borehole breakouts and earthquake focal mechanisms) yield approximately the same stress orientation, and regional and internal variation, although they cover different depth intervals. They further manifest high horizontal stresses in the Norwegian area, generally exceeding the vertical stress. This indicates the presence of compressional tectonic stresses penetrating deep into the crust. The first-order stress pattern in Norway and adjacent offshore regions show a rotation in
σ
H
direction from N-S in the Barents Sea to WNW-ESE in the North Sea. This rotation can be explained by the ridge push effect alone, but other effects may also be contributing factors. The increased scatter in
σ
H
direction in the south is believed to be due to changes in the tectonic stress magnitudes, or related to relative changes in angle between the continental margin and the ridge push force.
Crustal stress in and around Norway: an evaluation of stress-generating mechanisms
Authors: Fejerskov Morten , Lindholm Conrad
Published: April 2008

Recent stress observations from
in situ
measurements and earthquake focal mechanisms in the Norwegian onshore and offshore areas are evaluated with the aim of characterizing the most important mechanisms for the present stress field in and around Norway. The evaluation is based on a set of stress indicators that include both shallow measurements (overcoring and borehole breakouts) and deep data (earthquake focal mechanisms). Computer simulations of simple stress-generation models were used to constrain the relative importance of different stress-generating mechanisms. The ridge push force associated with sea-floor spreading in the North Atlantic is considered to be the primary source of the compressional stress field observed in Norway. Regional influences from the continental margin density contrast, topography and flexure induced by sediment loading are of limited lateral extent, but are important in reorienting the stress field in certain areas. The observed tectonics and stresses are generally also in accord with tectonics expected from Fennoscandian uplift.
Displacement transfer and forced folding in the Maritimes basin of Nova Scotia, eastern Canada
Authors: Keller J. V. A. , Lynch G.
Published: April 2008

Field and seismic data in northern Nova Scotia, eastern Canada, demonstrate that displacement transfer from steep basement faulting to bedding-parallel detachment is necessary in the development of forced folds. Lateral translation of the strata above horsted and down-dropped blocks generates a monoclinal structure which, as the faults are kinematically linked, evolves in a manner similar to fault-bend folds in thrust-and-fold belts. In the case of partial transfer of displacement a breached drape syncline is developed. The breached syncline is characterized by steep upturned beds against the fault that truncates them. In the Nova Scotia example the detachment horizon is located at the base of a Visean evaporitic sequence, and is exposed in the study area showing shearing structures within the evaporites. Brittle fault rock types (gouge and cataclasite) and meso- to microstructures were formed, including stretching lineation, principal schistosity plane and secondary shear planes, as well as intrafolial to upright asymmetrical folds. The regionally extensive weak evaporitic layer was remarkably effective in transferring displacement between the two faults, with mechanical decoupling of the strata above the evaporitic detachment being observed in the horsted block 70 km away from the steep basement fault. Moreover, displacement was also transferred as much as 40 km onto the down-dropped block at the frontal part of the system.
Primary and ‘forced folds’ of the Columbia River basalt province, eastern Washington, USA
Authors: Watkinson A. J. , Hooper P. R.
Published: April 2008

The Yakima fold belt is a series of asymmetric, east-west anticlines separated by much broader synclines in the thick and otherwise horizontal sequence of Columbia River basalt flows. The folds have grown progressively over the last 17 Ma in response to regional north-south compression and east-west extension. This stress and strain pattern is reflected on a regional scale by the highly oriented north-northwest-south-southeast basalt feeder dykes, by the WNW- (right-lateral) and NNE- (left-lateral) trending conjugate fault system, and by the presence of a similar strain field measurable in the basalt flows today.

Peripheral to the Yakima fold belt, pre-basalt structures of different orientations project under the basalt pile. Some of these structures have continued to develop during and after basalt extrusion and have influenced structures in the basalt flows which are, therefore, ‘forced’.
Mantle exhumation along the Tirich Mir Fault Zone, NW Pakistan: pre-mid-Cretaceous accretion of the Karakoram terrane to the Asian margin
Authors: Zanchi A. , Poli S. , Fumagalli P. , Gaetani M.
Published: April 2008

The left-lateral strike-slip Tirich Mir Fault, Chitral, NW Pakistan, is associated with a belt of periodotites, metagabbros and gneisses named the Tirich Boundary Zone (TBZ), separating the Late Palaeozoic-Mesozoic units of the East Hindu Kush from the Palaeozoic successions of the Karakoram block. These rocks were metamorphosed up to upper amphibolite facies conditions, followed by a greenschist facies overprinting, and then thrust on to very low grade metasediments; they were finally intruded at shallow levels by the mid-Cretaceous Tirich Mir pluton. Ultramafic rocks along the fault zone include well-preserved spinel lherzolites and harzburgites (Tirich Gol, Barum valley, Arkari Gol), whereas schistose serpentinites occur in the Rich Gol. Whole-rock analyses and mineral chemistry of olivine, clinopyroxene, orthopyroxene and spinel from these peridotites show a depleted signature. Microstructural and petrological features suggest a mantle origin for these ultramafic bodies, which equilibrated at temperatures ranging from 1000–1100°C. Periodotites are faulted against partially metamorphosed igneous bodies including hornblende-gabbros, hornblende cumulates and quartz-diorites. Metamorphic rocks of the TBZ, which lay south of the ultramafic-mafic complex, include quartzites, amphibolites, garnet-sillimanite (± kyanite ± K-feldspar)-biotite gneisses and mica schists, locally displaying migmatitic textures.

A sub-continental character of the peridotites indicated by low temperatures of equilibration and by the presence of a deep crustal sequence. These characters along with the absence of an ophiolitic sequence may suggest that the TBZ represents a fragmented crust-mantle boundary developed along a zone of attenuated continental crust. The TBZ is interpreted as a sheared lithospheric section of a Jurassic-Early Cretaceous orogenic complex, formed as a consequence of the accretion of the Karakoram terrane to the southern side of the Pamir belts, which were progressively accreted to the Asian margin.
Metamorphic evolution,
40
Ar-
39
Ar chronology and tectonic model for the Neelum valley, Azad Kashmir, NE Pakistan
Authors: Fontan D. , Schouppe M. , Hunziker C. J. , Martinotti G. , Verkaeren J.
Published: April 2008

This paper describes the geology, tectonometamorphic history and geochronology of part of the northern flank of the Neelum valley in Azad Kashmir, NE Pakistan. Metamorphic crystalline rocks in this area belong to the Lesser and Higher Himalayan Crystalline complexes. Geological mapping of about 1500 km
2
confirms the presence of three main tectonic units characterized by similar lithostratigraphic sequences but with different tectonometamorphic histories. Whether these tectonic units belong to the Lesser or Higher Himalayan Crystallines depends on the, still controversial, position of the Main Central Thrust. A tectonic model, involving syn-convergent exhumation, is suggested that is consistent with new petrographic and geochronological data, and with a revised interpretation of the Main Central Thrust.
Stratigraphic and tectonic evolution of the northwestern Indian plate and Kabul Block
Authors: Badshah M. S. , Gnos E. , Jan M. Q. , Afridi M. I.
Published: April 2008

A 1: 500 000 scale geological map covering large parts of the northwest Pakistan-southeast Afghanistan border region between 31–34° N and 69–71° E has been compiled. The map covers the tribal areas of Kurram and of North and South Waziristan in Pakistan, where the map is based on unpublished data of the Federally Administered Tribal Areas Development Corporation. The map area comprises Precambrian crystalline rocks of the Indian and Kabul blocks, Permian to Quaternary sedimentary rocks, and the Late Cretaceous-Palaeocene Kabul-Altimur and Zhob-Waziristan-Khost ophiolite complexes. The Himalayan collision resulted in extrusion of the Kabul Block along the Chaman Fault system and formation of the Katawaz Basin which was filled with clastic deposits of the ‘Early-Indus’ fan. Ongoing contractional tectonics led to southward thrusting of the Spinghar Indian crystalline basement over the Miocene Murree Formation. New names and type sections are proposed for six units in the Spinghar and South Waziristan. These units are the Daradar Dolomite, Spinghar Quartzite, Sikaram Series, Makai Limestone, Wana Schist and Kaniguram Slates.
Aims and methods in territorial archaeology: possible clues to a strong fourth-century
AD
earthquake in the Straits of Messina (southern Italy)
Authors: Guidoboni Emanuela , Muggia Anna , Valensise Gianluca
Published: April 2008

This research was stimulated by the need to extend in time the record of Italy’s largest earthquakes, which commonly have repeat times of the same order as the length of the available historical record. As a test case we used the 1908 Straits of Messina earthquake, a large event that geologists assume to recur at intervals of roughly a millennium but whose predecessors are as yet unknown. The 1908 earthquake caused enormous territorial upheaval and left signs in the settlements that are still largely recognizable today. We hypothesized that the Straits of Messina, which were densely populated even in ancient times, may similarly retain evidence of one or more much older ‘upheavals’ of the settlement network, and that this evidence may be recognized through a careful analysis of archaeological observations. We found evidence that the settled area around the Straits of Messina contracted substantially around the middle of the fourth century
AD
, when many sites were abandoned or relocated. This contraction can hardly be justified by the then current economic and military setting. Specific archaeological findings within the cities of Messina and Reggio Calabria also suggest a serious decline of the region during the same period. The archaeological hypothesis is in good agreement with the available historical and palaeoseismological evidence and suggests that a large earthquake, perhaps similar to the 1908 event, took place in the area surrounding the Straits of Messina around the middle of the fourth century
AD
.
Ground-penetrating radar mapping of Minoan volcanic deposits and the Late Bronze Age palaeotopography, Thera, Greece
Authors: Russell James K. , Stasiuk Mark V.
Published: April 2008

The Late Bronze Age (LBA) eruption of Santorini volcano deposited ash over most of the eastern Mediterranean, distributed thick deposits of pyroclastic material over the local landscape, and instantly buried the Minoan-aged living surface of these islands. Ground-penetrating radar (GPR) studies of the LBA volcanic deposits on Thera have allowed us to establish the thickness of individual pyroclastic units, to trace units laterally, and to establish facies variations in areas where the deposits are unexposed. GPR data are presented for two sites: Site A is a survey over LBA volcanic deposits exposed in the Phira quarry, immediately south of the town of Phira, and Site B is a 550 m survey of the LBA deposits underlying the Akrotiri peninsula immediately north and south of the Akrotiri archaeological excavation. These traverses show that GPR can define structures as deep as 18–20 m (velocity 0.1 m ns
−1
) and can accurately map the thicknesses of the LBA volcanic deposits from the caldera wall to Thera’s southern coast. Furthermore, our best datasets suggest that the Phase 1 fall deposits can be differentiated from the Phase 2–4 deposits, and that GPR can clearly image the interface between the volcanic deposits and the underlying LBA living surface. Future GPR surveys could be used to delineate palaeotopographic lows and valleys associated with LBA streams or drainages or, used in combination with geological mapping, could refine the position and nature of LBA shorelines.
Tephrochronology of the Brooks River Archaeological District, Katmai National Park and Preserve, Alaska: what can and cannot be done with tephra deposits
Authors: Riehle James R. , Dumond Don. E. , Meyer Charles E. , Schaaf Jeanne M.
Published: April 2008

The Brooks River Archaeological District (BRAD) in Katmai National Park and Preserve is a classical site for the study of early humans in Alaska. Because of proximity to the active Aleutian volcanic arc, there are numerous tephra deposits in the BRAD, which are potentially useful for correlating among sites of archaeological investigations. Microprobe analyses of glass separates show, however, that most of these tephra deposits are heterogeneous mixtures of multiple glass populations. Some glasses are highly similar to pyroclasts of Aniakchak Crater (160 km to the south), others are similar to pyroclasts in the nearby Valley of Ten Thousand Smokes, and some are similar to no other tephra samples from the Alaska Peninsula. Moreover, tephra deposits in any one archaeological study site are not always similar to those from nearby sites, indicating inconsistent preservation of these mainly thin, fine-grained deposits. At least 15, late Holocene tephra deposits are inferred at the BRAD. Their heterogeneity is the result of either eruptions of mixed or heterogeneous magmas, like the 1912 Katmai eruption, or secondary mixing of closely succeeding tephra deposits. Because most cannot be reliably distinguished from one another on the basis of megascopic properties, their utility for correlations is limited. At least one deposit can be reliably identified because of its thickness (10 cm) and colour stratification. Early humans seem not to have been significantly affected by these tephra falls, which is not surprising in view of the resilience exhibited by both plants and animals following the 1912 Katmai eruption.
Comparison and cross-checking of historical, archaeological and geological evidence for the location and type of historical and sub-historical eruptions of multiple-vent oceanic island volcanoes
Authors: Day S. J. , Carracedo J. C. , Guillou H. , Pais Pais F. J. , Badiola E. Rodriguez , Fonseca J. F. B. D. , Heleno S. I. N.
Published: April 2008

Oceanic island volcanoes, like many others, have many small vents scattered over their flanks in addition to, or in place of, large summit vents. These small vents are commonly monogenetic and many eruptions of this type of volcano involve activity at more than one such vent: lines of volcanic cones are often produced by eruptions fed by dykes, and if more than one dyke is emplaced during an eruption these vents can be along different alignments, and many kilometres apart. Identifying which vents were produced in which eruptions is an important problem in reconstructing the development of multiplevent volcanoes. Reconstruction of historical and sub-historical eruptions of two oceanic island volcanoes, the Cumbre Vieja volcano on La Palma in the Canary Islands and Cha das Caldeiras volcano on Fogo, Cape Verde Islands, has indicated that historical eyewitness accounts and archaeological evidence can be extremely valuable adjuncts to detailed geological studies. In contrast, secondary accounts including folk memories and earlier accounts in the scientific literature are commonly inconsistent both with the eyewitness accounts and with the results of detailed geological mapping, archaeological evidence or other historical documents. A common source of error is confusion of the vents of historical eruptions with older but larger or more prominent volcanic vents that lie along the same line of sight as viewed from adjacent settlements or from convenient viewpoints. Examples of this are provided by mis-locations of the vents of the
AD
1677 eruption on La Palma and of some of the vents of the
AD
1951 eruption on Fogo. Another problem arises when the location or style of eruption on a volcano has changed in early historical time, as has occurred on Fogo. The differences between early historical accounts of eruptions on this volcano and the more detailed accounts of more recent eruptions has led to the discrediting of the former by some researchers, whereas geological studies have supported the early historical accounts.
Olmec stone sculpture: selection criteria for basalt
Authors: Hunt Patrick
Published: April 2008

The fact that Olmec monumental sculpture exclusively uses basaltic stone requires explanation. Although many possible stone selection criteria are potentially involved in Olmec culture for the deliberate choice of stone, it is unlikely that all or even many were considered when but one stone type (basalt) was chosen for such objects as colossal heads and monumental sculpture. It is suggested here that the consistent correlation between Olmec monumental sculpture and basalt is explicable, based on the deliberate criterion of stone selection for metaphysical reasons and by physical characterization: this mostly dark, vesicular stone was the most compelling reminder of underworld power expressed in volcanism and volcanic mountains, and was thereby appropriated for power in rulership of the Olmec culture.
Seismic stratigraphy of the Gulf of Cádiz continental shelf: a model for Late Quaternary very high-resolution sequence stratigraphy and response to sea-level fall
Authors: Hernández-Molina F. J. , Somoza L. , Lobo F.
Published: April 2008

Single-channel, very high-resolution seismic profiles allow detailed study of the Late Quaternary stratigraphic architecture of the Gulf of Cádiz continental margin, Southern Spain. The Late Quaternary stratigraphy of this area comprises fourth-order Type 1 composite depositional sequences, generated by asymmetric relative sea-level changes of 100–110 ka duration. The composite fourth-order sequences consist of forced regressive, lowstand, transgressive and highstand systems tracts. Volumetrically, the forced regressive and lowstand systems tracts are the most important components. The fourth-order composite sequences are themselves comprised of composite fifth-order sequences formed in response to asymmetric relative sea-level changes with a duration of 22–23 ka. Sediments within the forced regressive and lowstand systems tracts dominate the 5th-order sequences; their transgressive and highstand deposits are either (i) perched above present-day sea-level and so not recorded in marine seismic data, (ii) restricted to outer-mid-shelf positions, or (iii) may be absent from the shelf altogether at the resolution of this study (e.g.<0.5 m thick). The fifth-order sea-level falls were themselves modulated by minor cycles, generating very high-frequency (sixth-order) sequences. These very high-order sequences are recognized for the last 80 ka
bp
, and their development is attributed to asymmetric relative sea-level cycles operating on time scales of: 10–15 ka (Heinrich events), 4–4.5 ka. (P cycles), 2.3–0.97 ka. (Dansgaard-Oeschger oscillations h cycles) and 500–50 a. (c cycles). We have developed a depositional model that accounts for the very high-frequency hierarchy of Late Quaternary depositional sequences observed in the Gulf of Cadiz marine seismic record and incorporates the age of well-constrained highstand coastal deposits that are exposed along the southern Iberian coastline. The model developed serves to illustrate the evolution and importance of depositional systems during falling relative sea-level and forced regression. Development of the forced regressive systems tract appears to be particularly significant within Quaternary strata. This is because the Quaternary was strongly influenced by a high-amplitude, high-frequency glacioeustatic signal characterized by rapid sea-level rises, very short highstands, and gradual relatively long-term sea-level falls suggesting that forced regressive deposits are likely to predominate in continental margin successions subject to low rates of subsidence.
Palaeostress Inversion in a Multiphase Deformed Area: Kinematic and Structural Evolution of the Çankırı Basin (Central Turkey), Part 1 – Northern Area
Authors: Kaymakçi Nuretdin , White Stanley H. , Van Dijk Paul M.
Published: April 2008

The kinematic and structural evolution of the major structures affecting the Çankırı Basin, central Turkey, has been deduced from a palaeostress inversion study. Four palaeostress tensor configurations indicative of four-phase structural evolution have been constructed from the fault slip data collected from the Çankırı Basin. The first two phases indicate the dominant role of thrusting and folding, and are attributed to the collision between the Pontides and the Taurides, the proposed interface of which is straddled by the Çankırı Basin. Phase 1 occurred in the pre-Late Palaeocene and Phase 2 in the Late Palaeocene-pre-Burdigalian. The third phase is dominated by extensional deformation in the Middle Miocene. The latest phase has been active since then and is characterized by regional transcurrent tectonics.
Controls on suspended sediment deposition over single tidal cycles in a macrotidal saltmarsh, Bay of Fundy, Canada
Authors: Proosdij Danika Van , Ollerhead Jeff , Davidson-Arnott Robin G. D.
Published: April 2008

A field study was conducted on a section of Allen Creek marsh in the Bay of Fundy to examine changes in suspended sediment circulation and deposition over single tidal cycles. Net flow velocity, suspended sediment concentration and sediment deposition were measured over 13 individual tidal cycles during the summer of 1998. A vertical array was deployed in the low marsh region, consisting of three pairs of electromagnetic current meters, OBS
tm
probes and one pressure transducer. Sediment deposition was measured using full-cycle sediment traps. The temporal distribution of sediment deposition was monitored using sequential sediment traps exposed at different tidal stages. The data suggest that sediment deposition on the marsh surface is primarily controlled by the interaction of water flow, marsh morphology and vegetation. The highest amounts of sediment are deposited during conditions of high suspended sediment concentration and low wave activity, particularly when the relative roughness of the vegetation is the highest. Loss of suspended sediment from the water column was shown to be correlated with the sediment trap data; however, predictions of sediment deposition based on the variation in suspended sediment concentration were found to be valid only for conditions with less than 0.15 m high waves. For higher wave conditions, the use of suspended sediment loss calculations should be used primarily for estimating the relative rather than absolute values of deposition on the marsh surface.
A diagnostic tool to study long-term changes in estuary morphology
Authors: Townend Ian , Dun Richard
Published: April 2008

One method of studying the functional morphology of estuaries and the potential implications of developments is presented. The approach makes use of a hybrid modelling approach to predict the state of the estuary relative to its present day target steady state. The technique has now been applied to a number of UK estuaries, which allows the variability between systems to be illustrated. For one of the estuaries a range of modifications has been examined to try and identify how the functional behaviour of the system might be affected (e.g. remove flood banks) and these are discussed. Experience to-date has shown that this approach helps to develop an understanding of gross system behaviour and how this might change in the future. It does not provide detailed predictions for specific locations within the estuary, although the role of particular components in the system is highlighted.
Applications of ground-penetrating radar (GPR) to sedimentological, geomorphological and geoarchaeological studies in coastal environments
Authors: Neal Adrian , Roberts Clive L.
Published: April 2008

Acquisition of high resolution data regarding the stratigraphy and internal structure of coastal sedimentary sequences is becoming increasingly important in many sedimentological, geomorphological and geoarchaeological studies. Such information is usually obtained from the logging of field exposures, shallow trenches and cores. However, ground-penetrating radar (GPR), a relatively new and rapidly developing non-invasive geophysical technique, may also aid such investigations in certain coastal settings, providing additional, complimentary and often unique data sets. The technique is based on the transmission, reflection and reception of high frequency electromagnetic (radar) waves, with reflections occurring in the subsurface due to the varying electrical properties of the sediments. Such reflections can occur due the presence of primary sedimentary structures, lithological/material changes or water content changes. Examples presented from the UK indicate that the technique can accurately delineate the stratigraphy and internal sedimentary structure of coastal barriers, spits and strandplains, both above and below a fresh groundwater table. Sand and/or gravel-dominated beach-dune systems on moderate to high wave energy, macrotidal coasts appear to provide optimum settings for GPR deployment. In addition, the technique also has the potential to locate, map and provide stratigraphic context for a wide range of archaeological features that are commonly found in such coastal environments.
Vertical accretion versus elevational adjustment in UK saltmarshes: an evaluation of alternative methodologies
Authors: Cahoon Donald R. , French Jonathan R. , Spencer Thomas , Reed Denise , Möller Iris
Published: April 2008

Simultaneous measurements of vertical accretion from marker horizons and marsh-elevation change from sedimentation-erosion tables (SET) were made in selected marshes along the East Anglian coast of the UK in order to address the following objectives:

(1)

to ascertain the validity of treating accretion measurements obtained within tidally dominated, minerogenic saltmarshes as equivalent to surface elevation changes;

(2)

to explore the implications, in terms of physical and biological processes, of discrepancies between separately measured vertical accretion and elevation change within contrasting marsh types.

Data were collected from several marsh environments at Scolt Head Island and Stiffkey on the North Norfolk coast and at an experimental managed realignment project near Tollesbury, Essex. Scolt Head Island was selected for its long-term datasets of marsh accretion, Stiffkey for its contrasting open coast-back barrier settings, and Tollesbury for its experimental management, in order to illustrate the potential application of the SET method and evaluate the relationship between vertical accretion and elevation change in a variety of marsh settings.

The relationship between vertical accretion and elevation change varied widely among marsh settings of different age and height (within the tidal frame) at Scolt Head Island and Stiffkey. Rates of vertical accretion and elevation change were similar in the older and midheight settings on Scolt Head Island, indicating control of elevation change by surface accretionary processes (e.g. sediment deposition). However, subsurface processes controlled elevation at three of the marsh sites. Spartina Marsh, the youngest and lowest of the back barrier settings at Scolt Head Island, exhibited continuous shallow subsidence (vertical accretion greater than elevation change) over a 4-year period, implying that compaction controls elevation change. In the upper part of Hut Marsh and the interior of the Stiffkey marshes, elevation change exceeded vertical accretion suggesting that subsurface processes (e.g. organic accumulation) controlled elevation in these settings. Surface accretionary processes control elevation change in both the highly dynamic, outer marsh at Stiffkey and the low, restored marsh at Tollesbury. Despite the occurrence of shallow subsidence, all sites gained elevation at an annual rate comparable to that of sea-level rise. In summary, the SET provides the means to critically evaluate the influence of vertical accretion measures on elevation and represents an improved method by which to evaluate the vulnerability of a marsh to sea-level rise.
Holocene coastal lowlands in NW Europe: autocompaction and the uncertain ground
Authors: Allen J. R. L.
Published: April 2008

The continuous, progressive, irreversible and asympototic processes of sediment autocompaction play a significant but so far largely neglected role in determining the coevolving character of Holocene landscapes and sedimentary sequences formed in coastal marshlands. Autocompaction ensures that actual total sediment deposition rates are always greater than the rate at which sea-level rise creates accommodation space. High rates of autocompaction help to foster resource-rich, mineralogenic tidal marshes that can be readily exploited by humans from neighbouring higher ground, for example, dryland areas, or locations within the marshland where peat formation had persisted sufficiently late that domal, raised bogs had not yet completely collapsed. Subsequent autocompaction may bring about a significant inversion of relief. The general effects of autocompaction are a high degree of vertical stratigraphic distortion and displacement amounting to as much as a few metres, depending on the depth to ‘basement’, the lithologies present, and their order of deposition. Autocompaction results in inaccurate sea-level curves when based on intercalated peats, inaccurate rates of sea-level change when calculated on a bed-averaged basis, and inconsistent age-altitude relationships among archaeological sites preserved in coastal deposits. The challenge is to predict/retrodict autocompaction in Holocene coastal lowlands, in order to better understand sequence development, the evolution of surface environments, topography and landscape, and the constraints placed upon (and opportunities presented to) human communities living in these contexts.
The Humber estuary: managing the archaeological resource in a dynamic environment
Authors: van de Noort Robert , Ellis Stephen
Published: April 2008

The archaeology of the intertidal wetlands of the Humber estuary is of international importance, and includes prehistoric boats, trackways, fishtraps and platforms, Roman settlements and ports and Post-Medieval fishweirs. This resource is threatened by coastal erosion and flood defence improvement work. This paper outlines a strategic approach to the threatened archaeological resource in the Humber estuary.
Radar evidence of water-saturated sediments beneath the East Antarctic Ice Sheet
Authors: Siegert Martin J.
Published: April 2008

Ice-penetrating airborne radar data from East Antarctica were examined in order to identify regions of the ice-sheet base where water-saturated sediments are thought to occur. Distinctive radar returns are identified from three subglacial environments as follows. (1) A frozen ice-bedrock interface, which shows scattering of a weak radar signal. (2) An ice-water contact above a subglacial lake where the radar reflections are bright, and horizontally flat. (3) The surfaces of two regions of water-saturated basal sediment, one at the centre of the ice sheet and one near the ice margin, where the radar returns are almost as bright as those from the subglacial lake, but not as flat. Characterization of radar signals from these regions is valuable since the results can be compared with data from other areas of the ice-sheet base to establish the nature of the sub-ice contact at a continental scale. The subglacial geomorphology of sediments near the ice margin displays large-scale (
c.
10 km long,
c.
200 m high) features with slopes that are relatively steep up-glacier, and shallow down-glacier, plus small-scale (<1 km long, <50 m high) regularly spaced undulations. Such sub-ice physiography indicates that the radar data may display
in-situ
sedimentary structures.
An instability mechanism for drumlin formation
Authors: Fowler A. C.
Published: April 2008

Drumlins are subglacial bedforms that are formed by the interaction of ice flow with an erodible basal topography. The mechanism of their formation bears resemblance to similar processes that cause the formation of dunes and anti-dunes in rivers, and sand dunes in deserts. In 1998 Hindmarsh showed that the interaction of a shearing ice flow with a deformable basal till layer could cause an instability which promotes the growth of basal topography, though he was unable to give analytic criteria for the instability. Here we analyse Hindmarsh’s model, and by using certain approximations, we are able to give concise analytical parametric criteria for this instability. The resultant instability occurs if the basal shear stress is larger than a critical value which increases with increasing basal effective pressure, and which also depends on the basal till thickness. It is hypothesized that this instability is the basic mechanism involved in the formation of Rogen moraine and drumlins.
Evolutionary significance of fossil larval shell characters: a case study from the Ostreoidea (Bivalvia: Pteriomorphia)
Authors: Malchus Nikolaus
Published: April 2008

Prodissoconchs of Middle Jurassic oysters possess key characters for a new understanding of the hinge evolution within the Ostreoidea. The ancestral larval hinge most likely evolved from a mytilid-like provinculum through accelerated growth in an antero-ventral direction along a flat, helico-spiral trajectory. The posterior denticles moved into the centre of the hinge axis while the central and anterior denticles were reduced in size and eventually disappeared. The remaining, now central, posterior denticles evolved further into a secondary symmetrical hinge. In most oysters, except for example
Tiostrea
, the larval ligament maintained its relative position between posterior and anterior denticles, even though this is not obvious in the Ostreidae because of the loss of the anterior denticles. Larval and adult ligaments are continuous. The examined specimens provide further evidence for the plesiomorphic state of planktotrophy within the superfamily. Although additional direct evidence is lacking, consideration of all new available data favour the hypothesis that the postero-dorsal notch is uniquely derived by oysters. The ideas on character evolution put forward in this study are consistent with phylogeny hypotheses based on palaeontological-biological data and recent genetical studies.
Phenotypic plasticity of burrowing depth in the bivalve
Macoma balthica
: experimental evidence and general implications
Authors: Edelaar Pim
Published: April 2008

Depth of burrowing in bivalves presents the individual with a trade-off: burrowing more deeply increases safety against predators but shallow burrowing increases food intake. Large variation in burrowing depth exists both between and within species. This study investigated whether part of this variation in depth in the tellinid
Macoma balthica
can be attributed to phenotypic plasticity. A predatory crab and food availability were either offered or withheld in separate aquaria and the response in burrowing depth measured. Individuals burrowed more deeply in the presence of a crab but only to shallow depths in the presence of food. This suggests that individuals can assess their environment and subsequently make decisions on their burrowing depth.

Phenotypic plasticity like this flexible anti-predation behaviour in
M. balthica
can have farranging effects. In the presence of predators burrowing depth increases, reducing energy uptake and subsequent growth and reproduction, whereas increased burrowing depths reduces mortality by predation, further affecting prey and predator population dynamics.
Microfacies development in Late Archaean stromatolites and oolites of the Ghaap Group of South Africa
Authors: Wright David T. , Altermann Wladyslaw
Published: April 2008

Organism-environment feedbacks in Precambrian platformal carbonates and reefs were strongly influenced by the activities of diverse microbial ecosystems. Microfacies studies of representative platformal microbial carbonates, comprising cyanobacterial mat, stromatolites and giant ooids, from the Late Archaean Ghaap Group of South Africa have provided compelling evidence for an intimate relationship between taphonomic evolution, fabric development and mineralogy in rocks of the Gamohaan and Boomplaas formations. Cements, both in fold hinges and between the limbs of slump-folded and contorted, partially-degraded, pyritiferous stromatolitic laminae, were precipitated after deformation of organic fabrics, but before or during their compaction, indicating that cementation took place at the same time as anoxic organic degradation involving bacterial sulphate reduction. Bundles and strands of the organic remains of filamentous cyanobacteria, in varying states of degradation in both stromatolites and ooids, have been preserved by mineralization. Structural detail is usually best preserved in calcite, where cyanobacterial sheaths, 10 µm to 25 µm in diameter and hundreds of micrometres in length, can be clearly seen. Petrographic analysis of the microfabrics using cathodoluminescence reveals dolomicrite nucleated along the outer margin of some sheaths. Dolomicrospar and dolospar fabrics developed progressively in association with increasing sheath degradation, as evidenced by the sequential loss of structural detail, culminating in a xenotopic fabric comprising brown, inclusion-rich, anhedral crystals with irregular boundaries. Biogeochemical modelling supports a genetic link between bacterial sulphate reduction and (1) calcite precipitation in the contorted laminae, and (2) replacive dolomitization of the calcitic matrix in the stromatolites and ooids. The evidence indicates that anoxic organic diagenesis was an essential and major process in controlling carbonate precipitation and mineralogy in widespread microbialitic sediments of the Ghaap Group, a depositional environment analogous to many other Archaean, Proterozoic and, during periods of biotic stress, some Phanerozoic carbonate platforms.
Reefs and coral carpets in the northern Red Sea as models for organism-environment feedback in coral communities and its reflection in growth fabrics
Authors: Riegl Bernhard , Piller Werner E.
Published: April 2008

Coral framework construction and resultant growth fabrics in response to environmental factors were studied in the northern Red Sea, and the Gulfs of Suez and Aqaba. The dependence of growth fabric types on sea-floor topography, oceanography and the ecology of constituent coral species was investigated. Five types of coral frameworks and their growth fabrics were differentiated:
Acropora
reef framework (platestone to mixstone facies);
Porites
reef framework (domestone facies);
Porites
carpet (columnar pillarstone facies); faviid carpet (mixstone facies);
Stylophora
carpet (thin pillarstone facies). Two non-framework community types were found:
Stylophora-Acropora
community and soft coral communities. Reef frameworks and resultant growth fabrics show a clear ecological zonation along depth and hydrodynamic exposure gradients. Coral carpets build a framework lacking a distinct internal zonation since they only grow in areas without pronounced gradients. In the northern Red Sea they show a gradual change with depth from
Porites
(pillarstone) to faviid (mixstone) dominance.

The initiation of frameworks was governed by bottom topography (reefs on steep slopes and highs, coral carpets in flat areas). According to environmental conditions, different coral communities produce different framework and growth fabric types. In step with framework growth the environment is modified. The modified environment in turn modifies the coral communities. Thus an environment-organism-environment feedback loop exists.
Rudist lithosome development on the Maiella Carbonate Platform margin
Authors: Stössel Iwan , Bernoulli Daniel
Published: April 2008

Cenomanian to mid-Campanian rudist lithosomes, exposed along a transect across the Maiella carbonate platform margin (central Apennines, Italy), are described in terms of faunal and matrix composition, geometry, and facies association. On the external platform, the lithosomes reveal a complex geometry and a comparatively high faunal diversity, whereas lithosomes of the inner platform are generally thinner and show a simple, sheet-like geometry. Based on the abundance of lithosomes and of the associated rudist-derived calcarenites, we propose that lithosome formation and, hence, sediment production preferentially occurred on the outermost platform, although the preservation potential of bioconstructions was low in these high-energy environments. Reworking of rudists led to sediment export both towards more internal areas as well as towards the adjacent basin. In contrast, on the inner platform, rudist lithosome formation was restricted by the lack of an adequate substrate and by higher sedimentation rates.
A mid-Frasnian marine incursion into the southern part of the Munster Basin: evidence from the Foilcoagh Bay Beds, Sherkin Formation, SW County Cork, Ireland
Authors: Higgs K. T. , MacCarthy I. A. J. , O’Brien M. M.
Published: April 2008

The Munster Basin of southern Ireland contains a thick (7 km +) succession of Old Red Sandstone sediments interpreted as the product of various alluvial processes. The present study presents a preliminary sedimentological and palynological analysis of a grey succession informally known as the Foilcoagh Bay Beds, which is the lowest unit of the Sherkin Formation exposed in the southern part of the basin. Sedimentological analysis of the succession suggests that it is the product of sinuous distributary channels, flanked by permanently flooded overbank areas that endured occasional crevasse splay floods. These conditions evolved into a protected lagoon or lake that received periodic high energy floodings from an adjacent marine environment. Palynological study has refined the age of the Foilcoagh Bay Beds as mid-Frasnian time. Palynofacies analysis has provided direct evidence of marine influence as revealed by the presence of marine microfossils and abundant amorphous organic matter at some dark grey mudrock levels. This suggests deposition in a well-established lacustrine or lagoonal environment in which anoxic conditions prevailed at intervals and which was subjected to a period of marine incursion. The recognition of a marine influence in the Munster Basin at an early stage in its history has several important implications, including the following (1) previous models for the basin that suggested an enclosed centripetally draining entirely non-marine system have to be re-evaluated; (2) the drainage pattern and direction of the marine incursion were probably controlled by localized subsidence along an east-east direction; initiation of subsidence associated with the development of the east-west-trending South Munster Basin may have commenced much earlier than previously considered; (3) the occurrence of marine conditions has been tentatively correlated with the Rhinestreet mid-Frasnian sea-level highstand; (4) the recognition of marine conditions early in the known history of the basin provides a pathway for fish to have entered the basin; (5) the basin may have had a marine connection throughout much of Late Devonian time, opening the possibility for base-level control of the alluvial systems within the basin by external eustatic factors.