bluuebunny/crossref_metadata_2025 huggingface dataset:
Authigenic potassium feldspar: a tracer for the timing of palaeofluid flow in carbonate rocks, Northern Calcareous Alps, Austria
Authors: Spötl Christoph , Kunk Michael J. , Ramseyer Karl , Longstaffe Fred J.
Published: April 2008

Feldspar is a common authigenic constituent in Permian carbonate rocks which occur as tectonically isolated blocks within the evaporitic Haselgebirge mélange in the Northern Calcareous Alps (NCA). Coexisting with pyrite, anhydrite, (saddle) dolomite, magnesite, fluorite and calcite, K-feldspar and minor albite record an event of regionally extensive interaction of hot brines with carbonate rocks. Detailed petrographic, crystallographic and geochemical studies reveal a variability in crystal size and shape, Al-Si ordering, elemental and stable isotopic compositions of the K-feldspar, which is only partially consistent with the traditional view of authigenic feldspar as a well-ordered, compositionally pure mineral.
40
Ar-
39
Ar step-heating measurements of authigenic potassium feldspar from several localities yield two age populations, an older one of 145–154 Ma, and a younger one of
c.
90–97 Ma. Most age spectra reflect cooling through the argon retention temperature interval, which was rapid in some localities (as indicated by plateau ages) and slower in others. Rb-Sr isotope data are more difficult to interpret, because in many K-feldspar samples they are controlled largely by Sr-bearing inclusions. The Jurassic
40
Ar-
39
Ar dates are interpreted as minimum ages of feldspar growth and hence imply that fluid-rock interaction is likely to be simultaneous with or to slightly predate mélange formation. Deformation associated with the closure and subduction of the Meliata-Hallstatt ocean south of the NCA during the Upper Jurassic is regarded as the principal geodynamic driving force for both enhanced fluid circulation and mélange formation. Some localities were reheated beyond the argon retention temperature for microcline during mid-Cretaceous nappe stacking of the NCA, thus obliterating the older signal.
Dating fluid flow in shear zones: Rb-Sr and U-Pb studies of syntectonic veins in the Néouvielle Massif, Pyrenees
Authors: Wayne D. M. , McCaig A. M.
Published: April 2008

Rb-Sr and Pb-Pb data are reported from separated minerals (amphibole, albite, calcite, epidote), altered wall rocks, and fluid inclusions trapped in quartz, from veins associated with retrogressive shear zones cutting the Néouvielle granodiorite massif in the central French Pyrenees. Alteration in the shear zones was caused by movement of hypersaline brines during deformation. Shear zones with similar kinematics occur in granodiorites and high grade gneisses throughout the northern Axial Zone of the Pyrenees, and have been attributed variously to both the Variscan and Alpine orogenies. Rb-Sr data on a syntectonic, polymineralic vein and its altered wall rock support an Alpine age for deformation and fluid flow, giving an isochron of 47 ± 8 Ma, or 48 ± 2 Ma if albite is excluded. Another vein gives a similar age for altered wall rock and albite, but chlorite and quartz-hosted fluid inclusions are out of equilibrium. Pb data plot as quasi-linear arrays on ratio plots, with no age significance. The usefulness of this latter technique is restricted by the slow rate of uranium decay in these young rocks, but in any case Pb isotopic ratios do not appear to have homogenized during vein formation.
Thermal history and timing of fluid flow at the Ardèche palaeomargin, France
Authors: Pagel Maurice , Clauer Norbert , Disnar Jean-Robert , Mossmann Jean-Rémi , Sureau Jean-François , Steinberg Michel , Vinchon Charlotte
Published: April 2008

The fluid evolution, the timing of fluid flow and the thermal history of the faulted Ardèche passive palaeomargin, France, were reconstructed using detailed mineralogical, petrological, geochemical and geophysical studies applied on core material from Triassic sandstone and Liassic carbonate units of the BA1 and MM1 boreholes. It could be shown that an early cementation significantly reduced the porosity of the rocks. Application of various geothermometers and chronothermometers showed that the outcropping Jurassic units underwent a degree of diagenetic evolution corresponding to the onset of the oil window. In the Triassic sandstone, temperatures reached 130–145°C as recorded by the dolomitic cements. Fluids in thermal disequilibrium with their host rock were found, implying supply of fluids from deeper levels. The decrease of temperature below 120 ± 10°C during the Eocene is explained by the erosion of 1900 m of mainly Cretaceous sediments. A fault system was active at different periods, especially at 190 Ma and during the post-Cretaceous uplift.
Unravelling complex filling histories by constraining the timing of events which modify oil fields after initial charge
Authors: Lisk M. , Eadington P. J. , O’Brien G. W.
Published: April 2008

Complex and multiphase charge histories are a feature of many hydrocarbon discoveries. Previous descriptions of charge history that have relied on the chemical properties of hydrocarbons do not define the geometry of hydrocarbon accumulations prior to the attainment of their present state. In this paper, examples of oil charge studies conducted on hydrocarbon discoveries from the Australian North West Shelf are presented to demonstrate the application of a new technique for the mapping of hydrocarbon charge called GOI™ (Grains containing Oil-bearing fluid Inclusions). In Australian oil fields GOI values in oil leg samples are an order of magnitude higher than in underlying water zones and record the maximum oil saturation experienced through time. An empirical threshold for oil saturation consistent with accumulation (GOI > 5%) rather than migration (GOI < 1%) of oil has been established from a database of 20 Australian oil fields. Oil inclusions are retained if oil is lost from the pore spaces of the rock, which allows GOI to be used to identify relict oil columns and locate the original oil-water contact. GOI measurements allow the original size and disposition of palaeo-oil columns to be determined and the physical events controlling the composition and size of hydrocarbon accumulations to be deduced in space and time. These data allow issues which cause changes to the original fluid contacts, such as trap integrity, tilting and gas displacement, to be confidently identified and characterized. When combined with conventional approaches to prospect evaluation, these new data allow a more sophisticated description of the filling history of hydrocarbon discoveries. They also allow the oil charge risk associated with new plays to be appropriately constrained before new drilling is commissioned.
Predicting the distribution of small faults in a hydrocarbon reservoir by combining outcrop, seismic and well data
Authors: Steen Ø. , Sverdrup E. , Hanssen T. H.
Published: April 2008

This paper investigates the possibility of identifying small faults in a hydrocarbon reservoir from spatial derivatives of seismic horizons (dip, azimuth, rate of change of dip), combined with well log structural data and analogue models. The analogue models include examples from the literature and a faulted surface constructed from Kilve beach, Bristol Channel, which represent typical surface attributes associated with small faults and artefacts produced by modelling. Well log structural data of good quality were integrated with the seismic data to study the 1D spatial distribution of subseismic faults and their expression on seismic horizons. The results suggest that dip and azimuth modelling can be useful, but the methods need to be combined to achieve reliable interpretations of the individual features. The rate of dip change has less potential to trace individual structures, unless the signal/noise ratio is very high. The ductile strain observed on seismic sections is, to a large degree, assumed to be produced by subseismic faults. The amount of ductile strain may be quantified by calculating the rate of dip change across curved seismic horizons. Exact predictions of fault densities are difficult because of the inaccuracies related to the modelling technique and the variability in fault and fold styles that occurs on a subseismic scale. Detailed dipmeter and core interpretation can be used to calibrate structural dip and spatial frequency of faults.
Fault sealing processes in siliciclastic sediments
Authors: Fisher Q. J. , Knipe R. J.
Published: April 2008

The microstructure and petrophysical properties of fault rocks from siliciclastic hydrocarbon reservoirs of the North Sea are closely related to the effective stress, temperature and sediment composition at the time of deformation, as well as their post-deformation stress and temperature history. Low permeability fault rocks may develop due to a combination of processes including: the deformation induced mixing of heterogeneously distributed fine-grained material (principally clays) with framework grains, pressure solution, cataclasis, clay smear, and cementation. Fault rocks can be classified into various types (disaggregation zones, phyllosilicate-framework fault rocks, cataclasites, clay smears, and cemented faults/fractures) based upon their clay and cement content as well as the amount of cataclasis experienced. In the absence of extensive cementation, the distribution of fault rock types along a fault plane can often be predicted from a detailed knowledge of the reservoir sedimentology. The permeability of fault rocks can vary by over six orders of magnitude, depending on the extent to which the porosity reduction processes have operated. Utilizing the strong link between the petrophysical properties of fault rocks and their geohistory allows the risks associated with fault seal evaluation to be reduced.
Thermal effects of fluid flow in steep fault zones
Authors: Fleming C. G. , Couples G. D. , Haszeldine R. S.
Published: April 2008

Two-dimensional, porous-medium, steady-state, coupled fluid- and heat-transport models are used to investigate some of the hydrogeological and thermal consequences of steeply dipping fault damage zones in a normally pressured basin setting. Simple geometries and conservative petrophysical properties can produce large-scale buoyancy-driven circulation, both outside and within the fault zone. An average (homogeneous) basin permeability of only 7 mD
k
h
(horizontal permeability) and 0.07 mD
k
v
(vertical permeability) results in a free convection cell of this type, with the upflow being localized by a 300 m wide fault zone (50 mD
k
h
, 0.5 mD
k
v
). Steady-state temperature anomalies as large as 15°C at the top of the fault zone can be produced by this arrangement. Smaller values of basin permeability still result in a similar circulation pattern, but at flow rates which produce temperature anomalies that are below detection levels. When the basin fill is more heterogeneous (layered), higher permeabilities can exist in some layers without large-scale convection occurring, because of the dampening effect of other, lower permeability units. In realistic geometrical configurations that are similar to the North Sea Central Graben, the fluid flow system is dominated by within-fault-zone convective circulation that produces local (<10 km half-wavelength), high amplitude (50°C) temperature anomalies which are comparable to the largest of those actually observed in the subsurface.
The impact of faults on fluid flow in the Heidrun Field
Authors: Knai T. A. , Knipe R. J.
Published: April 2008

A quantitative analysis of fault seal properties has been used in reservoir simulation modelling in the Heidrun Field. The inclusion of microstructural and petrophysical data from core analysis has resulted in a better prediction of reservoir communication and drainage patterns during production. Three main fault rock types were observed in the Heidrun cores, namely;
cataclasites
developed from clean sandstones,
phyllosilicate framework fault rocks
, created from impure sandstones and
clay smears
. The clay content of the host sediment is the controlling factor in determining which fault rock type dominates in the fault zones. Fault plane geometries were assessed from seismic-based juxtaposition analysis for input into the reservoir simulation model. The fault planes were divided into areas following the reservoir zonation, and transmissibility multipliers were assigned to each subarea of the fault planes in the model. The transmissibility multipliers are a function of fault rock permeability and fault rock width, as well as the matrix (host rock) permeability and the dimensions of the grid blocks used in the simulation model. Introducing a quantitative description of the faults has had a significant effect on the results of the reservoir simulation runs and has played an important role in the successful modelling and prediction of the observed gas breakthrough and pressure evolution. After actively using the transmissibilities during history matching of the simulation model, a remarkably good match to the observed well rates and pressures (flowing and shut-in) for the Jurassic Fangst and Upper Tilje reservoir units was achieved.
Facies and curvature controlled 3D fracture models in a Cretaceous carbonate reservoir, Arabian Gulf
Authors: Ericsson J. B. , McKean H. C. , Hooper R. J.
Published: April 2008

The Late Cretaceous Ilam Formation of the Arabian Gulf’s Fateh Field is a very heterogeneous, fractured carbonate reservoir. Porosity, matrix permeability and facies trends do not appear to be related, but fracture density exhibits a strong relationship to both facies distribution and structural curvature. Three-dimensional (3D) models of dip change, position with respect to the crest of the field, facies and porosity variation are combined to produce a qualitative 3D model of fracture density which matches empirical fracture density data from more than 16 750m of interpreted image log. The fracture model aids in transmissibility prediction for reservoir simulation, producing a better history match and decreasing uncertainty for future drilling programmes.
Is the oceanic Moho a serpentinization front?
Authors: Minshull T. A. , Muller M. R. , Robinson C. J. , White R. S. , Bickle M. J.
Published: April 2008

Our main constraint on the volume of melt coming out of the mantle at mid-ocean ridges is the thickness of oceanic crust determined by seismic methods. The recovery of serpentinized peridotites in the rift valleys of slow-spreading ridges has led recently to a revival of the suggestion that the seismically defined lower oceanic crust may include partially serpentinized peridotite. Both seismic and geochemical data from a recent experiment on the very slow-spreading Southwest Indian Ridge indicate that, away from the fracture zone valley, a total melt thickness of ∼4 km is being generated. However, in one region, around Ocean Drilling Program (ODP) hole 735B, where ∼2 km of the upper crust is estimated to have been removed, the seismic data indicate a crustal thickness of 5 km. Here, the seismically determined Moho is interpreted as a serpentinization front. Serpentinization is facilitated if there are readily available pathways for seawater to reach the upper mantle, and if the upper mantle is cool. These conditions frequently are met at fracture zones on slow-spreading ridges, in the ocean-continent transition zone at non-volcanic rifted margins, and at the axes of extinct rifts. In all these locations, serpentinization sufficient to lower mantle velocities to normal oceanic crustal velocities does not reach a depth of more than 5 km beneath the seabed, and commonly normal mantle velocities of ∼8 km s
−1
are also reached at shallow depths. Therefore, although in some anomalous locations the seismically defined crustal thickness can only be used as an upper limit on the melt supply, for normal oceanic crust, where the seismically defined crustal thickness is ∼7 km, the Moho is probably not a serpentinization front, but rather a petrological boundary between mafic rocks above and ultramafic rocks below.
Precipitation of hydrothermal sediments on the active TAG mound: implications for ochre formation
Authors: Goulding H. C. , Mills R. A. , Nesbitt R. W.
Published: April 2008

Submersible and drilling studies of the active TAG hydrothermal mound (26°N, Mid-Atlantic Ridge) have led to new models of fluid flow and evolution within an active mineral deposit which has implications for Fe-oxide and ochre precipitation. Metalliferous sediments from the top of the hydrothermal mound accumulate from a combination of processes including slumping and oxidation of chimney material and
in situ
precipitation of low-temperature phases from fluids that percolate through the mound. Geochemical proxies of hydrothermal processes allow identification of the mode of formation of one sediment core from the southeastern periphery of the TAG mound. The Fe rich sediment is capped with a ∼5 cm thick kaolinite, illite, chlorite, smectite layer which formed from alteration and replacement of basalt and diagenetic reactions within the hydrothermal sediment. Underlying this layer is a ∼10 cm thick zone of Mn, Cu, Zn and Pb enrichment which is controlled by the sharp redox gradients in the core. The base of the core is characterized by Mn-poor, Fe-rich oxide that is dominated by goethite, haematite and amorphous Fe oxides equivalent to ochreous and gossan material. Rare earth element (REE) patterns from the different layers within the core allow interpretation of the modes of formation of sediment in the light of existing fluid flow models for TAG. The basal layer is dominated by
in situ
precipitation of Fe oxide phases from evolved fluids that result from significant within-mound anhydrite precipitation. The REE data for the upper part of the core demonstrate mixing with sea water which provides the oxidizing conditions for Mn precipitation along with Cu, Zn and Pb enrichment from the evolved fluid. Sea water ingress results in higher V/Fe and P/Fe ratios in the upper part of the core but no enhanced U/Fe ratio. The uppermost clay-rich layer hosts the majority of the REE inventory for the core and the significant positive Eu anomaly indicates recrystallisation of the phyllosilicate phases from the ochreous material during diagenesis. REE data from land-based ochre and gossan sediments demonstrate that the TAG model may be applicable to a wide variety of sites throughout the geological record.
Oxygen-isotope correlation of marine terraces and uplift of the Mesa hills, Santa Barbara, California, USA
Authors: Trecker M. A. , Gurrola L. D. , Keller E. A.
Published: April 2008

Resolving the chronology of marine terrace sequences is critical for determining uplift rates along tectonically active coastlines. Unfortunately, lack of suitable dating materials often makes this difficult. We present here oxygen isotopic data from 21 shells of
Olivella biplicata
from four marine terraces in the Santa Barbara and Ventura area located in southern California, USA. Terraces U-series dated at 47 ± 0.5 ka
BP
at Isla Vista and 70 ± 2 ka
BP
at Santa Barbara City College (SBCC) provide age control for the isotopic data. Shells from the Isla Vista and SBCC terraces yield average values of 1.117‰ and 0.627‰. respectively, and shells from a non-U-series dated terrace at Punta Gorda and an undated terrace at Santa Barbara Point yield average values of 1.010‰ and 0.751‰, respectively. The data indicate that stable oxygen isotopic signatures preserved in marine terrace molluscs provide a useful tool for correlating undated terraces with those of known age. Furthermore, we are able to correlate samples collected from offset fragments of the Punta Gorda terrace on either side of the Red Mountain fault, demonstrating the utility of this method for correlating terraces across structural features. Using oxygen isotopic data coupled with the U-series dated wave-cut platform at SBCC we calculate a rate of uplift ranging from 0.62 ± 0.03 mm/year (where the elevation of the first emergent terrace is 41 m) to 0.54 ± 0.05 mm/year (where the elevation of the first emergent terrace is 36 m) for marine terrace flights preserved on the Mesa hills anticline located in the city of Santa Barbara, California.
Deformation of the 125 ka marine terrace in Italy: tectonic implications
Authors: Bordoni Paola , Valensise Gianluca
Published: April 2008

In peninsular Italy, marine terraces and shorelines created during oxygen-isotope substage 5e, known historically as the Tyrrhenian highstand, provide a reliable and homogeneous datum of vertical motions during the past 125 000 years. Published accounts of 121 locations on the Tyrrhenian inner edge were reinterpreted and used to calculate both local and regional uplift rates. The data show arching of southern Italy between the Tyrrhenian and the Adriatic coasts and of the Calabrian Arc between the Sangineto and the Longi-Taormina tectonic lineaments at rates of up to 1.2 mm/year for the past 125 000 years. They also suggest that the present configuration of the southern Apennines is the product of post-Early Pleistocene regional uplift superimposed on Tortonian to Early Pleistocene thrusting. Uplift patterns are characterized by different wavelengths in different geodynamic settings, suggesting a close link with the depth of the causative tectonic sources.
Archaeological evidence for vertical movement on the continental shelf during the Palaeolithic, Neolithic and Bronze Age periods
Authors: Flemming N. C.
Published: April 2008

Submarine archaeological sites of human occupation on the continental shelf provide evidence of palaeo-shorelines during the last 50 000 years, with possibly longer periods of accessible data. Sites are widely distributed globally, and provide a rich source of peripheral information on landscapes, climate, water supply, sediment transport, and soil types, which are relevant to coastal tectonics and processes, in addition to location, elevation, and date. More than 500 sites have been discovered world-wide where there are the remains of human occupation under the sea. Artefacts embedded in a few metres of sediments can survive multiple marine transgression, given local topography that creates suitable wave and current conditions. The raw data have been analysed to separate glacial eustatic fluctuations of global sea level and local or regional tectonic processes. The number of sites in the Mediterranean permits the detection of regional vertical tectonic displacement with a spatial resolution of a few tens of kilometres in many regions. In other parts of the world the density of sites is not yet sufficient to achieve this, but indicators of vertical movements, or lack of vertical movement, provide valuable point data. Continuing discovery of new sites indicates that the technique will provide data with improved spatial resolution, and outside the Americas, over a timescale extending to hundreds of millennia, and possibly one million years
Late Quaternary tectonism along the Pacific coast of the Californias: a contrast in style
Authors: Orme Antony R.
Published: April 2008

Marine terraces and associated features are examined along 1500 km of coast at the seaward margin of that part of the North American plate that has been captured by the Pacific plate. This coast embraces parts of three morphotectonic provinces, each with its own distinctive tectonic style, namely the southern Coast Ranges, western Transverse Ranges, and northern Peninsular Ranges. Based primarily on the 125 ka shoreline, four magnitudes of late Quaternary deformation are recognized: (1) high uplift rates exceeding 1.0 m per 1000 years; (2) moderate uplift rates between 1.0 and 0.1 m per 1000 years; (3) low uplift rates less than 0.1 m per 1000 years; and (4) variable net subsidence. The highest rates of uplift and subsidence are associated with the intense fold-thrust tectonics of the western Transverse Ranges nearest the Big Bend in the San Andreas fault, and diminish in magnitude to east and west. Moderate uplift rates occur in both the southern Coast Ranges and the northern Peninsular Ranges adjacent to the western Transverse Ranges, commonly associated with block uplift and subsidence between high-angle reverse faults within a broader strike-slip scenario. This suggests that compression and transpression are significant features of these areas and that the continued rotation and relative westward motion of the western Transverse Ranges, within the broader context of shear distributed across the San Andreas fault system, continue to have an impact on regions immediately to the north and south. Uplift diminishes with distance from the Transverse Ranges and is low for Baja California south of Punta Banda. The style of late Quaternary deformation is similar to that defined by earlier Quaternary marine limits, but intensity varies, most notably in the western Transverse Ranges.
Slip parameters for the Rann of Kachchh, India, 16 June 1819, earthquake, quantified from contemporary accounts
Authors: Bilham Roger
Published: April 2008

The 16 June 1819 Rann of Kachchh earthquake was felt throughout much of India. Although significant vertical movements of the ground caused flooding of regions near sea level, damming of a distributary of the Indus river, widespread liquefaction, and a local tsunami, the geometry of the fault plane has hitherto remained obscure. Dislocation models based on deformation data gathered 7 and 25 years after the earthquake suggest that a near-surface reverse fault slipped locally more than 11 m, and that rupture extended at least 80 km along strike. Estimates of maximum uplift and depression during the earthquake yield similar, but not identical, solutions to those based solely on a levelling profile across the zone of uplift, known as the Allah Bund. The inferred 50–70°N-dipping fault plane beneath the Allah Bund is unfavourably steep for reverse faulting, and its down-dip width (6–10 km) short for slip exceeding 10 m. Some forms of listric fault geometry are also consistent with the observed surface deformation fields, with increased fault width (15–25 km) and similar coseismic slip. A geometric moment magnitude of
M
= 7.7 ± 0.2 is obtained from the inferred slip parameters, assuming uniform along-strike slip, consistent with a magnitude estimated empirically from the intensity distribution. Although a recurrence of the Kachchh earthquake is unlikely soon because of low inferred contractional strain rates in the region, the westward continuation of the Kachchh rift zone could host future ruptures contiguous with the 1819 event, with important consequences for the city of Karachi.
Late Holocene coastal tectonics at Falasarna, western Crete: a sedimentary study
Authors: Dominey-Howes Dale , Dawson Alastair , Smith David
Published: April 2008

The late Holocene sedimentary record of Falasarna Harbour, western Crete, includes detailed evidence of tsunamis and serves as an independent dataset to evaluate the magnitude and timing of coastal tectonic movements in an area affected by contrasting tectonic regimes. Analysis of a foraminiferal assemblage makes it possible to identify suites of tsunami-deposited sediments within normal sedimentary sequences. The palaeo-environmental record is then complemented with a sequence of raised fossil marine notches. The transitional boundary between marine and terrestrial sedimentation indicates tectonic uplift at
c.
ad
63–75 ± 90 radiocarbon years
bp
, which is in conflict with previously published interpretations. No sedimentary evidence can be found for a tsunami believed to be associated with a large uplift event during
ad
365.
Possible tsunami deposits from the 1855 earthquake, North Island, New Zealand
Authors: Goff James R. , Crozier Michael , Sutherland Venus , Cochran Ursula , Shane Phil
Published: April 2008

A series of three fining-upward sequences from deposits in the Okourewa Stream bank on the south coast of the North Island, New Zealand, investigated by grain-size, diatom, radiocarbon, geochemical and macrofaunal analyses have been tentatively interpreted as the products of a tsunami. The proposed event consisted of three separate waves (the second being the largest) generated by a surface rupture of a local fault. Changes in diatom assemblages and the presence of marine shells, pumice, and beach pebbles may represent a tsunami advancing inshore over beach, freshwater channel, and coastal wetland environments. Deposition occurred between
ad
500 and 1890. The event in question may have currently the
ad
1855 rupture of the West Wairarapa fault.
A Quaternary proximal foreland ramp and its continental fringe, Arabian Gulf, UAE
Authors: Kirkham A.
Published: April 2008

During Quaternary time, the southern flank of the Arabian Gulf can be considered as a classic, foreland basin ramp setting in which the sedimentological processes operating changed drastically along strike. The combined effects of sea-level fluctuations and wind, which have dominated the Quaternary coastal morphology and coastal evolution, are observed at a resolution rarely achieved in the stratigraphic record of palaeoramp sequences. The facies distributions and diagenetic characteristics of the relatively thin Pleistocene-Holocene strata provide valuable insights into the complex stratigraphy that can develop within an inner ramp and its continental fringe.

In the UAE, Pleistocene sediments comprising mainly aeolian dunes overlie a deeply eroded topography of Upper Miocene strata. These sediments become increasingly carbonate rich and calcite cemented northwards towards the coast. Here they experienced severe aeolian deflation due to the later marine flooding of the aeolian sources on the formerly exposed areas lower down the ramp profile, and wind erosion along the coastal area because of a lack of sediment supply. The antecedent topography of Miocene and Pleistocene escarpments, mesas, islands, cemented seif dunes and coastal deflationary ‘Stokes surfaces’ provided a highly varied Holocene ramp margin undergoing coastal progradation (with offlap) during the 1–2 m relative sea-level fall of late Holocene time. Since then, marine carbonate deposition and evaporite diagenesis have dominated the Holocene sequence, but it is aeolian processes that largely control their ultimate distribution within the constraints of the contemporaneous sea-levels. Longshore currents, lateral and leeward accretion, infilling of stranded lagoons and deflation on a massive scale testify to the crucial role of wind in the development of this proximal ramp. The Holocene aeolian sediments, though extensive, are very different in character from the Pleistocene sediments.

Two generations of Holocene supratidal anhydrites are recognized. The earlier one was partly transgressive, but the later one is regressive. In addition to the present-day oolith factories on the ebb tidal deltas at the seaward ends of tidal channels between the barrier islands of central Abu Dhabi, oolith factories also exist on exposed beaches and tidal embayments of western Abu Dhabi. They also occurred within Pleistocene and Holocene embayments. Flat-topped and sometimes shingled hardgrounds representing isochronous events extend over very large areas. So also do commonly observed iron oxide bands formed beneath the sabkha surfaces.
Carbonate sedimentation during early foreland basin subsidence: the Eocene succession of the French Alps
Authors: Sinclair H. D. , Sayer Z. R. , Tucker M. E.
Published: April 2008

The Eocene Infranummulitic Formation and Nummulitic Limestones of the external chains of the French Alps in Haute Savoie and Alpes Maritimes unconformably overlie the Mesozoic passive margin succession, and were deposited during the onset of subsidence of the underfilled Alpine foreland basin. The Infranummulitic Formation represents detrital deposition in localized structural lows in braided fluvial, fan delta, coastal plain and lagoonal environments; the resultant facies record late lowstand and early transgressive sedimentation. A transgressive surface separates the fluvial-dominated conglomerates from lagoonal facies, and a ravinement surface separates lagoonal from ramp facies of the overlying Nummulitic Limestones. The combination of infilling of topographic lows by the Infranummulitic Formation, and the transgressive ravinement process, reduced local slope gradients inherited from the topography of the European foreland, thus encouraging the subsequent development of a low-angle carbonate ramp during continued transgression.

The Nummulitic Limestones represent highstand sedimentation on a low-energy, wave-dominated, carbonate ramp characterized by large benthic Foraminifera. The inner ramp accumulated bioclastic banks and shoals composed of peloids, calcareous red algae and
Nummulites
. The middle ramp is recorded by wackestones with a diverse assemblage of flat Foraminifera; occasional storm events generated winnowed packstones. The outer ramp is represented by mudstones and marls with a sparse biota. The Nummulitic Limestones pass upwards into hemipelagic marls.

The drowning of the Nummulitid-rich ramp is unlikely to have been caused by flexural subsidence of the foreland plate. Possible other contributing factors to the demise of the carbonate ramp were nutrient excess from the siliciclastic-rich orogenic margin to the basin, and/or glacio-eustatic sea-level rise.
Constructional dynamics for a Lower Cretaceous carbonate ramp (Gorbea Massif, north Iberia)
Authors: Gómez-Pérez Irene , Fernández-Mendiola Pedro A. , García-Mondéjar Joaquín
Published: April 2008

The lower Albian distally steepened Egalezaburu carbonate ramp is composed of four stacked cycles with homogeneous characteristics throughout the section. Relative sea-level changes accounted for cycle formation and changes in facies distribution. During transgression and highstands, fossiliferous boundstones were deposited on the inner ramp, and argillaceous mudstones formed on the mid- and outer ramp. Shallow marine benthic communities flourished in open, moderate-energy environments, controlled by the depth of the photic zone. During lowstands, shallow-water sedimentation shifted basinward, and skeletal grainstones dominated shallow-water environments on the mid-ramp, controlled by the depth of the wave-base. Meanwhile megabreccias accumulated locally in oversteepened sites, at the mid- to outer ramp transition. The resulting cycles differ from the inner to the mid-ramp: shallowing-upward muddy cycles formed in the inner ramp during transgressions and highstands, as deepening-upward cycles with a basal grainy unit formed on the mid-ramp during lowstand to early highstand. Photic zone and wave-base levels, controlled by relative sea-level fluctuations, were the main controls on facies types and distribution and cycle development for the Egalezaburu ramp.
Depositional facies and sequence stratigraphy of a Lower Carboniferous bryozoan-crinoidal carbonate ramp in the Illinois Basin, mid-continent USA
Authors: Lasemi Zakaria , Norby Rodney D. , Treworgy Janis D.
Published: April 2008

The Lower Carboniferous Fort Payne and Ullin Formations in the Illinois Basin form the transgressive and highstand systems tracts that were deposited in a carbonate ramp setting. During deposition of the Ullin Limestone, biotic communities dominated by fenestrate bryozoans and echinoderms (primarily crinoids) proliferated, possibly in response to global tectonic, biological, and oceanographic events that affected bathymetry and nutrient supply. The Fort Payne Formation consists of a dark grey-brown, siliceous and argillaceous lime mudstone in the lower part (transgressive systems tract) and a very fine-grained wackestone to packstone with rare mud mounds in the upper part (early highstand), and was deposited in an outer ramp to basinal environment. During deposition of the lower Ullin Limestone (mostly early highstand), bryozoan-crinoidal build-ups accreted both laterally and vertically into several relatively large carbonate banks, which were partly surrounded by siliceous Fort Payne sea. Bryozoans (primarily fenestrates) were especially prevalent during the late stage of bank development and formed mud-free bioherms up to 120 m thick. In places, carbonate mud mounds also formed during the early stage of bank deposition. Bioherm development declined during deposition of the upper Ullin Limestone (late highstand), and a broad, storm-dominated carbonate ramp was established that became the site for widespread deposition of bryozoan-crinoidal sandwaves. Gradual shallowing led to ooid formation at the end of Ullin deposition. This sequence was terminated by a relative rise in sea level that resulted in deposition of the transgressive facies of the lower part of the overlying Salem Limestone. The depositional style and the nature of skeletal material of the Fort Payne and Ullin Formations are similar to those of cool-water carbonates. A deep-water setting along with upwelling of cool, nutrient-rich oceanic waters may have been responsible for the proliferation of bryozoans and crinoids at this time. The deep-water setting and abundant nutrient supply also may have restricted the formation of ooids and proliferation of shallow-water calcareous organisms.
Mud buildups on a Middle Devonian carbonate ramp (Algerian Sahara)
Authors: Wendt Jobst , Kaufmann Bernd
Published: April 2008

During sea-level highstand in late Mid-Devonian time, a carbonate ramp was established on the vast shelf of the Northwest African Craton, in the Ahnet and Mouydir Basins of southern Algeria. The ramp was at least 400 km wide and 700 km long and sloped, in front of a local shoal of rugose-tabulate-stromatoporoid dominated biostromes, towards the west into the Reggane Basin and towards the north into the Béchar Basin. Mid- and inner ramp zones were presumably situated in the area of the present Hoggar Massif and have been removed by erosion. Subsidence rates during Mid-Devonian time were considerably lower than during the preceding and subsequent periods of clastic sedimentation in Early and Late Devonian time. Spectacular mud buildups formed in an outer ramp setting and developed from small, lens-shaped, to steep, conical mounds, which eventually amalgamated into mud ridges and mud ‘atolls’. Orientation of mound rows and ridges matches older NW-SE and N-S tectonic lineaments, which were probably rejuvenated during Mid-Devonian time. Stable isotope values of early marine cements, composition of the buildup fauna, and the emplacement and orientation of neptunian dykes do not indicate, however, that buildup growth was triggered by hydrothermal activity or cold seeps.
A theory of the Earth: Hutton and Humpty Dumpty and Holmes
Authors: Anderson Don L.
Published: April 2008

Paradoxes can be viewed as a bother or as a rich source of information. Paradoxes, fallacies and logical inconsistencies, along with the unstated assumptions behind old worldviews often form the foundation for a new worldview. This is where science differs from myth and just-so stories.

Mantle dynamicists and geochemists have developed a worldview that, in many respects, is incompatible with modern theories of planetary accretion, geodynamics and geophysics, and with the geological context of volcanoes. A primordial undegassed mantle, as both the furnace and the fuel of midplate volcanoes, occupies a central role in the geochemical models. Although modern data alone are sufficient to overturn this view, it is interesting to address it in terms of its own assumptions, fallacies and inconsistencies, and the history of ideas. This is a vast field, so, in honour of James Hutton, I focus on volcanoes, their products, their causes and their sources.

The following axioms are developed which point toward a different kind of world from the pristine primordial worldviews and the plume paradigm.

•

Linear volcanic chains delineate the stress field, not the displacement field, of the lithosphere.

•

Lithospheric architecture, not the core-mantle boundary, dictates the planform of convection in the mantle.

•

Incipient melting is the normal state of the upper mantle.

•

The lower mantle is depleted in the heat producing elements compared to the crust, upper mantle and the bulk silicate Earth.

•

The Earth is depleted in volatile elements.

•

High
3
He/
4
He ratios in mantle materials imply a deficit of
4
He.

•

Primordial heat contributes a significant part of the Earth’s heat flow.

These axioms [
A
] are the inverse of the assumptions of the plume and primordial mantle paradigms [not-
A
] and the new and the old views are to each other as looking-glass worlds. An ‘axiom’ is a self-evident truth or an established rule. It is also an undemonstrated proposition concerning an undefined set of elements and relationships. The above ‘axioms’ [
A
] are not true axioms but [not-
A
] provide the axiomatic framework of the current world model. These [not-
A
] propositions are treated as self-evident truths so [
A
] can also be called axioms, even though they are falsifiable. The prevailing worldview, the ‘standard model’, attributes both melting and volcanic chains to deep mantle upwellings controlled by the bottom of the system with most of the original radioactivity and volatile inventory of the Earth in the deep mantle. This is not only inconsistent with modern data but also with the previous worldview embedded in the axioms. These axioms have not been pushed out by better ideas, or falsified; they have simply been overlooked or forgotten. Mantle dynamics is controlled from the top, not the bottom.
Hot little crucibles are pressured to reveal and calibrate igneous processes
Authors: Wyllie Peter J.
Published: April 2008

The fires of Hutton’s (1726–1797) Plutonists could not be quenched by the oceans of Werner’s (1750–1817) Neptunists. Hall (1761–1832) was convinced that Hutton’s theory could be proved by experiments, but he deferred to the fears of his older colleague that failed experiments might discredit the theory (which needed no further proof), and completed the experiments only after Hutton’s death. Hutton censured those who ‘judge of the great operations of the mineral kingdom, from having kindled a fire, and looked into the bottom of a little crucible’. Hall believed that ‘the imitation of the natural process is an object which may be pursued with rational expectation of success’. Following many discussions between Hutton and Hall, three topics were pursued in Hall’s experiments: 1790, the magmatic origin of granites, younger than schists; 1798, whinstones/dolerites are as magmatic as known lavas; 1805, powdered calcite is transformed to marble and melted by the effects of compression (and water) in modifying the action of heat. The latter involved the first high-pressure, high-temperature apparatus and earned Hall the title ‘Father of Experimental Petrology’. Subsequent development of these topics is outlined, with reference to debates about primary basalts, granitization, and carbonatites.
Impacts from space: the implications for uniformitarian geology
Authors: Marvin Ursula B.
Published: April 2008

The geological implications of the Earth’s collisions with other bodies in space have become fully evident only since the opening of the Space Age. In the early eighteenth century, most western natural philosophers accepted the view, inherited from Aristotle and confirmed on mechanistic grounds by Isaac Newton, that interplanetary space is empty of solid matter. In the final decade of that century, two books, one by Ernst F. F. Chladni of Wittenberg and one by James Hutton of Edinburgh, contributed to the rise of meteorite studies and uniformitarian geology, respectively. Although they arose almost simultaneously, these two branches of science, one of which postulated the fall to Earth of solid bodies from space while the other endorsed only strictly endogenous processes acting upon the Earth, evolved separately over the next 200 years. This paper traces the long estrangement between mainstream geology and the science of meteorites. The two disciplines collided head-on in 1980 when a team of scientists headed by the physicist, Luis Alvarez, of the University of California, hypothesized that the massive extinctions at the end of the Cretaceous were triggered by the hypervelocity impact of a large body from space. Many geologists rejected outright such an exotic cause. More recently, as evidence has accumulated for the K-T impact as well as for many other crater-forming impacts, we are beginning to realize that unpredictable collisions have played a role of fundamental importance throughout the history of the solar system.
Vestiges of a beginning and the prospect of an end
Authors: Dalziel Ian W. D.
Published: April 2008

‘No vestige of a beginning, …’ In one sense the first half of James Hutton’s famous statement of 1788 holds true today — the oldest parts of Earth’s crust identified in two centuries of ‘modern’ study look not unlike those being formed at present. Yet the age of the planet can now be determined as close to 4.5 billion years, and radiometric ages of vestigial rocks and minerals approach 90 per cent of that value. The history of the planet is becoming clearer. We can now accurately reconstruct the geography of Pangea in early Mesozoic times. Remnants of older rifted continental margins suggest the existence of previous supercontinents for which hypothetical reconstructions have been proposed — a global-scale Huttonian process of tectonic renewal. Their mode of fragmentation and comparison with the other terrestrial planets suggest a functional connection between surficial plates and deep-seated mantle plumes, which may extend back to the Archaean. The fossil record, geochemistry, and molecular biology provide a timeline for life on Earth which does extend to the Archaean, almost as far as the oldest rocks and minerals. The history of endogenic tectonism, environmental change and biological evolution was punctuated, and to some extent at least influenced, by bolide impacts.

Like Hutton, in the rocks we can still read ‘no prospect of an end’, though astrophysical evidence indicates the demise of the Earth, or at least of its biosphere, will inevitably come 5000 million years into the future when our Sun will become a red giant, enveloping all its planets in a gaseous holocaust. Detection of complex organic molecules in the comas of comets that recently traversed the inner Solar System has shown, however, that the basic chemical building blocks of life are present in interstellar space. Evidence is steadily building up for the existence of planets around other stars of the Milky Way. Hence life need not be limited in either space or time by the existence of the Earth itself. Indeed, contemporary cosmology entertains possibilities that the entire universe that we recognize may be boundless, permanently expanding, or perhaps even part of a continuum of evolving universes. In this ultimate sense, therefore, the concluding sentence of the
Theory of the Earth
by the ‘founder of modern geology’ can be considered as valid today as it was 200 years ago.
The Dynamic Earth project and the next millennium
Authors: Monro S. K. , Crosbie A. J.
Published: April 2008

Two hundred and fifty years ago Edinburgh was a focus of intellectual ferment. The Enlightenment fired concern for an understanding of the science of the natural world. Hutton’s
Theory of the Earth
not only provided a comprehensive view of the planet and its processes but also altered the perception of time. The next millennium will see a new global Englightenment. The communications revolution is extending an awareness of science, but there is also an increased responsibility on scientists to make the results of their work understandable and accessible to the general public. Edinburgh’s ‘Dynamic Earth’ exhibition will play a major part in delivering a better public understanding of the planet, generating that same sense of excitement felt by Hutton and his colleagues when first they looked into ‘the abyss of time’. It will demonstrate that the Earth is a dynamic system, and show how landscapes are formed by a complex interaction between the geosphere, atmosphere, hydrosphere and biosphere and that these processes continue today. The challenge of Hutton’s concept that ‘the present is the key to the past’ lies in what it implies about the future. The presentation within the Dynamic Earth will help visitors make up their own mind about what the future may hold.