bluuebunny/crossref_metadata_2025 huggingface dataset:
Calcrete morphology and karst development in the Upper Old Red Sandstone at Milton Ness, Scotland
Authors: Balin Donna F.
Published: April 2008

The Upper Old Red Sandstone at Milton Ness, Scotland, is notable for its excellent preservation of calcrete textures, which are comparable with some of the best Quaternary examples. It is also significant for the implications that can be drawn from the association between karst and calcrete, with this example interpreted to have formed entirely within a semi-arid environment. Karst cavities were developed in a mature hardpan calcrete, generated in sandy fluvial sediments with associated aeolian deposits. Subsequent to karst cavity generation, clasts derived from the subaerially exposed hardpan were locally transported and deposited as a laterally traceable bed connecting the tops of all the cavities. Both this bed and the karst infills were subsequently recalcretized in the final phase of the profile’s evolution. Although calcrete-karst associations often are interpreted as the alternation between semi-arid and humid climates, respectively, this example is interpreted to be a result of water accumulating on the nearly impervious hardpan surface under fairly constant semiarid conditions, evidenced by the recalcretization of both the karst infill and the calcrete-derived breccia (‘boulder calcrete’). Additional substrate modification also has taken place by plant roots; the remarkable development of rhizoliths in these Old Red Sandstone sediments should emphasize the need to consider plant influence on other non-marine rocks of post-Silurian age.
Early syndepositional tectonics of East Greenland’s Old Red Sandstone basin
Authors: Hartz Ebbe
Published: April 2008

East Greenland’s Old Red Sandstone basin formed in the interior of a megacontinent created by the Caledonian collision of Baltica and Laurentia. The basin has been regarded as a typical late- to post-orogenic extensional basin, formed in a collapsing orogen. Cross-cutting faults that have extended the basin substrata have been explained as Riedel and anti-Riedel shears that formed during basin initiation, but no detailed structural analysis has been presented. Analysis of geometrical relationships between faults and folds, and their relative timing with respect to the syn-tectonic deposits suggest a new model for basin evolution. In eastern Greenland, orogenic collapse was initiated at least as early asc.425 Ma. Thus, the preserved Devonian basins formed afterc.70 Ma of large-magnitude crustal extension. Thick successions of Mid-Devonian Old Red Sandstone were deposited in troughs controlled by orogen-parallel extension and east-west folding. Later north-south-trending extensional structures cut the basal deposits, as episodes of folding continued until Permian time. Folding continued forc.175 Ma after the Caledonian continent-continent collision and it is thus unrealistic to suggest that internal Caledonian forces caused these ‘late Caledonian spasms’. However, the collapsed orogen may have been thermally weakened, and the region was thus probably vulnerable to external forces resulting from the continuing orogenies along the rim of the megacontinent.
Deformation of the Old Red Sandstone of NW Spitsbergen; links to the Ellesmerian and Caledonian orogenies
Authors: McCann Andrew J.
Published: April 2008

The Late Silurian?-Devonian fluvial deposits of northern Spitsbergen were deposited on basement with Caledonian and earlier metamorphic ages in which two distinct terranes are recognized (Biskayerhalvøya and Krossfjorden). These form part of the central of three major terranes in Svalbard, assembled during the Caledonian Orogeny. The subsequent geological history of the Svalbard area has been strongly influenced by the north-trending structures which were active as transcurrent fault zones at this time. The unconformable base of the Siktefjellet Group, a Late Silurian?-earliest Devonian sequence of coarse conglomerates and breccias, overlain by fluvial sandstones, is preserved only on the Biskayerhalvøya terrane, and the final juxtaposition of the two terranes (during the Haakonian sinistral strike-slip phase) is interpreted to post-date the deposition of these sediments. The Lochkovian Red Bay Group, a sequence of conglomerates, fluvial sandstones and siltstones, was deposited on both terranes. This has been mapped and correlated throughout the basin exposure, allowing the reconstruction of the tectonic history. Sedimentation was influenced by active faulting during deposition of the oldest Wulffberget Formation, but subsequent deposits show little evidence of this. Deposition was interrupted in latest Lochkovian time by renewed sinistral strike-slip faulting, which broke up an area of the basin into rotating fault blocks, across which about 30 km of extension occurred. This was followed by east-west shortening, which uplifted the Red Bay basin and underlying basement, developing large folds, locally with related thrusting. The Monacobreen phase is defined to involve this deformation. The Andr0.000000e+00e Land Group reflects a subsequent renewal of subsidence, and re-establishment of an extensive fluvial basin, occupying an area east of the inverted Red Bay basin. Conglomeratic units that overlie the Red Bay Group are interpreted as the products of the reworking of the uplifted Red Bay basin and its basement. The Latest Devonian-Earliest Carboniferous Svalbardian phase again involved east-west shortening, with limited strike-slip faulting, but it is difficult to discriminate these effects from the Monacobreen phase in the Siktefjellet and Red Bay groups. A review of North Atlantic and Arctic Devonian basins shows that during deposition of the Red Bay and Andrée Land groups, the tectonics of Svalbard was more similar to that of the developing Ellesmerian orogen, than to that of the collapsing Caledonian orogen. A model is proposed that links the repeated extension and shortening seen from Early Devonian time in north Spitsbergen to anticlockwise rotation of the Chukotka-Alaska plate, about an axis near the position of Svalbard during Ellesmerian collision, coupled with minor Caledonian-related strike-slip movement along reactivated fault zones.
Lamination and primary production in fossil lakes: relationship to palaeoclimate in the Carboniferous-Permian transition
Authors: Clausing Andreas , Boy Jürgen A.
Published: April 2008

Comparative studies are made on the development of lamination in Recent, Paleogene and Permian lake sediments. The study concentrates on the relationship between primary production and lamina formation. The main phytoplankton development in lakes is correlated with environmental changes and it is often preserved in the lamination in chronological succession. Seasonal patterns may be especially represented. Morphological identification and classification of laminities is achieved by studies of Recent lake sediments. This leads to possible comparison, even in badly preserved ancient examples. Paleogene lamination can be clearly correlated with the Recent lamination by the relatively tenuous relationships of the phytoplankton. Permian lake sediments, however, are difficult to decipher, as the phytoplankton species are different or absent as a result of taphonomy. Nevertheless, morphological comparisons suggest periodic sedimentation and lamination development that is clearly similar to that in lakes today. As the same physical properties apply, this seasonal sedimentation can also be used as an additional tool for the reconstruction of environmental and climatic changes in the Carboniferous-Permain boundary strata.
Global terrestrial productivity in the Mesozoic era
Authors: Beerling D. J.
Published: April 2008

This paper describes a global-scale modelling approach for investigating the structure and productivity of terrestrial vegetation in the Mesozoic era. General circulation model (GCM) palaeoclimate simulations (by the University of Reading) for Kimmeridgian and Cenomanian time are described as driving datasets for the University of Sheffield Dynamic Global Vegetation Model (SDGVM). The validity of these GCM palaeoclimates is reviewed. Global patterns of terrestrial net primary productivity (NPP) and leaf area index (LAI) have been simulated with the SDGVM, which models plant physiological processes and the biogeochemical cycling of carbon and nitrogen in soils and vegetation. An important feature of this modelling approach is that it requires no underlying map of soils or vegetation type. Global NPP in Kimmeridgian and Cenomanian time was high (117.6 and 106.8 Gt Ca
−1
, respectively) compared with the present-day level (57.0 Gt Ca
−1
). The high concentrations of atmospheric CO
2
at each interval significantly influenced the NPP and LAI of Mesozoic vegetation, to an extent dependent on climate. CO
2
effects on the structure of vegetation in Kimmeridgian and Cenomanian time were sufficient to markedly influence key land surface variables required by GCMs for climate predictions, and point to the need to include direct CO
2
-vegetation interactions in climate models. Two approaches to testing the modelled NPP patterns were devised, one using palaeobotanical information on tree growth, and the other based on a comparison of measurements and predictions of the stable carbon isotope ratios of fossil plants. Both approaches provided some support for the global-scale simulations, indicating the feasibility of modelling vegetation activity in ancient climates from a knowledge of present-day processes.
The Maastrichtian (Late Cretaceous) climate in the Northern Hemisphere
Authors: Golovneva Lena B.
Published: April 2008

This investigation of the Maastrichtian climate in the Northern Hemisphere is based on taxonomic and ecological studies of fossil floras, leaf physiognomy and the distribution of dinosaurian faunas. Fossil plant evidence indicates that the climate during Maastrichtian time was warm temperate at high and middle latitudes, and subtropical south of 40°N. Precipitation was relatively high (about 700–800 mm) and evenly distributed over the year. The annual range of temperatures was similar to that of modern maritime climates, but the latitudinal gradient was lower than at present. At high latitudes cold-month mean temperatures were about 3–4°C and probably never dropped below 0°C for extended periods. It seems that these comparatively mild winter temperatures in polar regions were a result of the heating of these areas by warm oceanic upwelling.
An integrated micropalaeontological approach applied to Late Pleistocene-Holocene palaeoclimatic and palaeoenvironmental changes (Gaeta Bay, Tyrrhenian Sea)
Authors: Amore F. O. , Ciampo G. , Di Donato V. , Esposito P. , Russo Ermolli E. , Staiti D.
Published: April 2008

An integrated micropalaeontological approach has been used to characterize the last climatic cycle in the Tyrrhenian Sea. Three gravity cores, drilled in the Gaeta Bay continental shelf, have been analysed by means of quantitative methods applied to different taxonomic groups. In particular, calcareous nannofossils, planktonic Foraminifera, ostracods and palynomorphs have been studied to detect palaeoclimatic trends. The Last Glacial period has been identified in the lower part of two cores (C8 and C9), and an older cold period is represented in the lower part of the more proximal core (C5). The upper part of all the cores clearly records the Holocene period, whereas the Late Glacial period is not always easily detectable. Pollen seems to precede the Holocene climatic optimum. Climatic curves have been reconstructed for all the taxonomic groups and high-resolution palaeobathymetric reconstruction has been inferred on the basis of the ostracod assemblages.
Late Glacial and Post-Glacial pollen records and inferred climatic changes from Lake Balaton and the Great Hungarian Plain
Authors: Nagy-Bodor E. , Járai-Komlódi M. , Medve A.
Published: April 2008

In Hungary, the Great Plain and the western part of Transdanubia had different geomorphological and climatic characteristics during the Late Glacial, the Holocene and the present day. As a result, the vegetation in the two areas was also different, as indicated by palynological data. In Late Glacial times the Great Plain had an extremely continental climate whereas the western part of Transdanubia had a somewhat milder one. This clear distinction can be made on the basis of pollen spectra between the palaeo-vegetation of Transdanubia and that of the Great Plain.

A comparison of the pollen data, and the climatic changes indicated by the carbonate content, and δ
18
O
PDB
and δ
13
C
PDB
isotope ratios of the sediments of Lake Balaton, have shown that these data can be correlated beginning from the Bölling, the onset of permanent water coverage.
Pollen analysis of the Acerno palaeo-lacustrine succession (Middle Pleistocene, southern Italy)
Authors: Ermolli Elda Russo
Published: April 2008

Pollen analysis has been performed on a 98 m core recovered in the palaeo-lake of Acerno (Campania, Italy). This study identified four main vegetation zones that can be correlated with Quaternary climatic events. In particular, one interglacial-glacial cycle was recorded in the succession the duration of which was estimated at around 100 ka. The interglacial period (Zone 2) is characterized by large amounts of deciduous and altitudinal forest elements; Mediterranean xerophytes are rather rare because of the distance from the palaeo-sea coast. The interglacial-glacial transition (Zone 3) shows a very rapid decrease of the arboreal taxa and a contemporaneous increase in the frequency of the non-arboreal element. The genus
Pinus
, excluded from the pollen totals, shows its highest percentage and concentration values during the transition. The glacial period (Zone 4) is characterized by the dominance of herbaceous and steppe elements, and by rather large amounts of
Pinus
. The floral composition of the analysed succession allows a late mid-Pleistocene age to be proposed for the Acerno palaeo-lake.
Were climatic changes a driving force in hominid evolution?
Authors: Chaline J. , Durand A. , Dambricourt Malassé A. , David B. , Magniez-Jannin F. , Marchand D.
Published: April 2008

A comparison of externalist and internalist approaches in hominid evolution shows that the externalist approach, with its claim that climate was responsible for the appearance of bipedalism and hominization, now seems to be ruled out by the biological, palaeogeographical, palaeontological and palaeoclimatic data on which it was based. Biological data support the embryonic origin of cranio-facial contraction, which determined the increase in cranial capacity and the shift in the position of the
foramen magnum
implying bipedalism. In the internalist approach, developmental biology appears as the driving force of hominid evolution, although climate exerts a significant influence and was involved in the following ways: (1) in the prior establishment of ecological niches that allowed the common ancestor to become differentiated into three subspecies; (2) by dividing up the area of distribution of species, resulting in the present-day subspecies of gorillas and chimpanzees; (3) by facilitating relative fluctuations of the geographical areas of distribution of the various species, particularly the spread of australopithecines across the African savanna from north (Chad, Ethiopia) to south (South Africa); (4) by determining adaptive geographical differentiations among
Homo erectus
and
Homo sapiens
(pigmentation, haemoglobin, etc.).
Late Quaternary vertebrate taphocoenoses from cave deposits in southeastern Austria: responses in a periglacial setting
Authors: Fladerer Florian A.
Published: April 2008

Forty-seven species of birds and at least 78 mammalian taxa from caves in the extant submontane vegetational zone close to the periphery of the Middle and Late Pleistocene Alpine maximum glacial expansion are comprehensively summarized for the first time. The communities of the last glacial period show sympatries of today’s boreal-tundra species with those of East European to Central Asian steppe-communities and to a lesser extent with those of temperate woodlands. Shifts in the individual species’ ranges during the last glacial period (Würm Glacial) can be partly correlated with the climatic fluctuations in the Eastern Alps as they were observed sedimentologically and glaciologically. Analyses of high-resolution uppermost Pleniglacial/Late Glacial taphocoenoses (
c.
14–12 ka
bp
) in the Styrian foothills demonstrate a distinctly greater faunal diversity and reflect more diversified vegetational biota than in the Holocene. The evidence of Middle and Upper Palaeolithic human populations within the region is outlined. The presented results provide a foundation for subsequent and comparative studies in diversity and community changes in the adjacent regions.
Groundwater in headwaters: hydrological and ecological significance
Authors: Soulsby C. , Malcolm R. , Malcolm I.
Published: April 2008

The hydrological and ecological significance of groundwater has generally been under-estimated in headwater catchment studies within the Celtic regions. The paper presents data from headwater catchments in both upland and lowland settings in northern Scotland to address this gap in our understanding. Research in the 10 km
2
Allt a’ Mharcaidh catchment in the western Cairngorms has demonstrated that a range of groundwater sources in various drift deposits can account for
c.
50% of annual runoff, even in a high altitude headwater stream. Despite the traditional assumption that upland catchments have limited aquifer storage, oxygen isotope studies of groundwater imply mean water residence times of up to five years which indicate a range of groundwater sources in montane environments. Moreover, hydrogeochemical reactions in the saturated zone appear to regulate stream water chemistry at moderate and low flows. In such montane environments, groundwater discharges at springs create unique wetland habitats which often form the source of headwater streams and affect riparian areas. In lowland catchments the hydrological significance of groundwater is equally important. In addition, recent studies in a salmon spawning stream in the Newmills Burn, Aberdeenshire has shown that aquifer-stream interactions in hyporheic zones are crucial in maintaining habitat conditions conducive to the survival of salmonid eggs, and the subsequent population of salmon streams. It is concluded that interdisciplinary studies incorporating hydrogeological investigations are fundamental to a proper understanding of the hydrology and functional ecology of catchment systems in the Celtic regions.
Groundwater vulnerability mapping in Scotland: modifications to classification used in England and Wales
Authors: Lewis M. A. , Lilly A. , Bell J. S.
Published: April 2008

The recently published groundwater vulnerability map of Fife is the first in a series of maps for the Scottish Environment Protection Agency (SEPA), which includes the unpublished maps of the areas around Dumfries and Strathmore. Based on the methodology used on the Environment Agency maps of England and Wales, the lithology and permeability of the geological formations, and the physical and chemical properties of the soils are classified to produce 15 groundwater vulnerability classes. However, the Scottish maps incorporate several modifications that improve their accuracy and usefulness. These are:

(a)

the geological formations are classified solely on the basis of their permeability and do not also incorporate aquifer potential;

(b)

the occurrence of low permeability drift deposits at the surface are shown over the whole of the map area instead of only where they overlie aquifers;

(c)

areas where borehole data indicate that significant thicknesses of low permeability deposits are present in the drift sequence are shown. In these areas groundwater in the underlying solid rock formations may have a lower risk of contamination than indicated by the vulnerability zones. This is particularly useful information where the clay occurs beneath permeable drift deposits. The borehole distribution is shown to give an indication of the reliability of the boundaries;

(d)

nitrate vulnerable zones are shown;

(e)

the leaching potential classification of soils with organic surface layers has been improved.
Groundwater protection zone delineation at a large karst spring in western Ireland
Authors: Deakin J.
Published: April 2008

Pouladower Spring is a large karst spring in County Clare, Ireland which is being considered for use as a public supply. Groundwater protection zones have been delineated as a water quality management strategy for the spring. The Irish national groundwater protection scheme methodology is adapted to take account of the hydrological and hydrogeological complexities of the karst regime. The catchment area for the spring is large (approximately 380 km
2
) and comprises the zones of contribution for two major outlets of water, the spring and the River Fergus. The actual zone of contribution to the spring varies with different water level conditions and the risk to the source from any point within the catchment, at any given time, is less than that for a conventional groundwater source. The catchment area is highly vulnerable, but dilution and sedimentation occurring in the lakes up gradient of the source, the high throughput, and the contribution from fissures outside the main flow conduits have helped maintain good water quality at the spring. The source is considered to be a combination of both groundwater and surface water as they are intricately inter-linked throughout the catchment. An Inner Protection Area is delineated which does not provide the 100-days travel time to the source required by the national scheme, as this would be impractically large and over-protective. Rather, it delineates the area of highest hydrogeological risk to the source and should allow the local authority sufficient time to act in the event of an accidental spill. A certain degree of microbial contamination is inevitable in a karst regime and treatment is essential, as it would be for a surface water source. The remainder of the catchment is classed as an Outer Protection Area. These protection areas are then combined with the vulnerability in a GIS to give groundwater protection zones which will be used by the planners, in conjunction with groundwater protection responses, to control potentially contaminating activities.
Influent rivers: a pollution threat to Schwyll Spring, South Wales?
Authors: Hobbs Steven L.
Published: April 2008

A number of influent rivers cross the southern outcrop of the Carboniferous Limestone in South Wales. They lose a proportion of their flow to groundwater via both discrete sinks and leaky river beds. These influent rivers represent a pollution threat to local springs that is dependent upon many factors including antecedent conditions, pollutant type, the location of pollutant loss and the nature and volume of influent flow. An attempt is made to define the catchment area of Schwyll Spring public water supply, near Bridgend in South Wales, prior to considering the potential for pollution from influent rivers.
Groundwater resources in the Quaternary deposits and Lower Palaeozoic bedrock of the Rheidol catchment, west Wales
Authors: Hiscock K. , Paci A.
Published: April 2008

An assessment of the groundwater potential of the River Rheidol catchment in west Wales is presented, a region where groundwater is an important source of water to Aberystwyth. An alternative approach to a conventional well inventory was undertaken based on the manipulation of data within a geographic information system (GIS). The GIS application revealed that, in the lower reaches of the catchment, 25% of the total recorded abstractions fall on the boundaries between different geological units and, of these, two-thirds relate to the contact between Quaternary deposits and bedrock. These abstractions are typically correlated with spring sources and represent small domestic supplies from shallow, brick-lined pits dug into the valley sides. Simple catchment water balance calculations showed that groundwater abstractions are minor in comparison to total combined surface and groundwater runoff.

Compared with the weathered and fractured bedrock, the floodplain gravel aquifer is of greater significance and is further enhanced by an unquantified amount of induced recharge from the River Rheidol. However, the resource contained in the Quaternary gravels is vulnerable to mainly agricultural contaminants derived either from direct leaching through the thin unsaturated zone, especially on the floodplain, or from induced recharge from the River Rheidol.
Some case histories of geophysical downhole logging to examine borehole site and regional groundwater movement in Celtic regions
Authors: Buckley David K.
Published: April 2008

Many Celtic regions comprise hard fractured rock aquifers and hilly terrain. They are generally regions which have also been affected by repeated glaciation and deglaciation during the Pleistocene period. This has influenced their hydraulic properties and the groundwater flow systems which have developed. Geophysical borehole logging provides a useful method to examine the occurrence of groundwater, water inflows and the movement of water in local and regional groundwater flow systems. The downhole measurements show that wellbore flow, aquifer layering and separate groundwater circulations are common features of the hydrogeology.
Cretaceous-Palaeogene ocean and climate change in the subtropical North Atlantic
Authors: Norris Richard D. , Kroon Dick , Huber Brian T. , Erbacher Jochen
Published: April 2008

Ocean Drilling Program (ODP) Leg 171B recovered continuous sequences that yield evidence for a suite of ‘critical’ events in the Earth’s history. The main events include the late Eocene radiolarian extinction, the late Palaeocene benthic foraminiferal extinction associated with the Late Palaeocene Thermal Maximum (LPTM), the Cretaceous-Palaeogene (K-P) extinction, the mid-Maastrichtian event, and several episodes of sapropel deposition documenting the late Cenomanian, late Albian and early Albian warm periods. A compilation of stable isotope results for foraminifera from Leg 171B sites and previously published records shows a series of large-scale cycles in temperature and δ
13
C trends from Albian to late Eocene time. Evolution of δ
18
O gradients between planktic and benthic foraminifera suggests that the North Atlantic evolved from a circulation system similar to the modern Mediterranean during early Albian time to a more open ocean circulation by late Albian-early Cenomanian time. Sea surface temperatures peaked during the mid-Cretaceous climatic optimum from the Albian-Cenomanian boundary to Coniacian time and then show a tendency to fall off toward the cool climates of the mid-Maastrichtian. The Albian-Coniacian period is characterized by light benthic oxygen isotope values showing generally warm deep waters. Lightest benthic oxygen isotopes occurred around the Cenomanian-Turonian boundary, and suggest middle bathyal waters with temperatures up to 20 °C in the North Atlantic. The disappearance of widespread sapropel deposition in Turonian time suggests that sills separating the North Atlantic from the rest of the global ocean were finally breached to sufficient depth to permit ventilation by deep waters flowing in from elsewhere. The Maastrichtian and Palaeogene records show two intervals of large-scale carbon burial and exhumation in the late Maastrichtian-Danian and late Palaeocene-early Eocene. Carbon burial peaked in early Danian time, perhaps in response to the withdrawal of large epicontinental seas from Europe and North America. Much of the succeeding Danian period was spent unroofing previously deposited carbon and repairing the damage to carbon export systems in the deep ocean caused by the K-P mass extinction. The youngest episode of carbon exhumation coincided with the onset of the early Eocene Warm Period and the LPTM, and has been attributed to the tectonic closure of the eastern Tethys and initiation of the Himalayan Orogeny.
No extinctions during Oceanic Anoxic Event 1b: the Aptian-Albian benthic foraminiferal record of ODP Leg 171
Authors: Holbourn Ann , Kuhnt Wolfgang
Published: April 2008

Outstandingly well-preserved benthic foraminiferal successions from upper Aptian-lower Albian sediments at Site 1049 (Leg 171, Blake Nose escarpment, western North Atlantic) provide a detailed record of the faunal turnover across Oceanic Anoxic Event 1b (OAE 1b). Changes in abundance, diversity and species composition reflect strong fluctuations in carbon flux and bottom-water oxygenation. Before the onset of black shale sedimentation, the originally diverse assemblages are replaced by low-diversity associations, dominated by species inferred to be opportunistic phytodetritus feeders and thriving on an enhanced carbon flux to the sea floor. The 46 cm thick laminated black shale horizon corresponding to OAE 1b is virtually devoid of benthic formainifers or contains highly impoverished assemblages, suggesting that intense eutrophication and/or strong stratification triggered near anoxia at the sea floor during black shale deposition. Above the black shale, reoccurrence of the pre-black shale fauna points to relatively rapid bottom-water reoxygenation. The benthic formainiferal record of Leg 171 provides clear evidence that no major extinctions occurred across OAE 1b, as most of the species occurring below the black shale reappear above it. In contrast to other Cretaceous anoxic events, OAE 1b may have been more limited in duration or in geographical and water-depth extent, allowing recolonization from adjacent, more hospitable areas, once local conditions improved at the sea floor. Prolific radiation within the suborder Rotaliina and diversification of Textulariina with calcareous cement appear to have started in the Aptian time before OAE 1b, and continued into early Albian time to give rise to many of the modern lineages.
The Maastrichtian record at Blake Nose (western North Atlantic) and implications for global palaeoceanographic and biotic changes
Authors: MacLeod Kenneth G. , Huber Brian T.
Published: April 2008

Widespread biological, geochemical and sedimentological shifts within the Maastrichtian are well documented, but data are limited for the low-latitude Atlantic. New observations from Ocean Drilling Program (ODP) sites located on Blake Nose in the subtropical western North Atlantic increase information concerning the Maastrichtian history of this critical region. Planktonic δ
18
O results suggest up to 6 °C of local surface water warming (or 4‰ decrease in salinity) at the same time as most of the globe was cooling. Benthic δ
13
O and δ
13
C values of both planktonic and benthic taxa show little if any directional trend or excursions on long time scales; however, planktonic and benthic taxa exhibit strong δ
13
C and δ
18
O cycles (up to 0.8 and 0.6‰, respectively) across a short interval of high-resolution sampling. Other portions of the cores have not yet been studied at high resolution. The last occurrence of inoceramid shell fragments on Blake Nose matches previously documented global patterns, i.e. a mid-Maastrichtian extinction event that occurred later in low latitudes than in high southern latitudes. Models for Maastrichtian change seem to be converging on variation in intermediate to deep water ocean circulation as a unifying process. Blake Nose data are consistent with this conclusion, but demonstrate new regional patterns and emphasize the importance of precise and accurate chronostratigraphic correlation in understanding Maastrichtian change.
Geochemistry of the Cretaceous-Tertiary boundary at Blake Nose (ODP Leg 171B)
Authors: Martínez-Ruiz F. , Ortega-Huertas M. , Kroon D. , Smit J. , Palomo-Delgado I. , Rocchia R.
Published: April 2008

The Cretaceous-Tertiary (K-T) boundary at Blake Nose, in the NW Atlantic, is recorded by a coarse, poorly graded and poorly cemented layer mostly consisting of green spherules that are mainly composed of smectite. Geochemical patterns across the boundary are governed by the source material of the spherule bed and postdepositional processes. The chemical composition and the nature of this bed indicate that it derived from melted target rocks from the Chicxulub impact structure. Ir and other typical extraterrestrial elements do not present significant enrichments, which suggests that the spherule bed material derived from crustal rocks. Ir instead reaches its highest concentration in the burrow-mottled calcareous ooze above the spherule bed, suggesting that it is associated to the finest fraction deposited after the target-rock-derived material. Only the Ni and Co content show slight enrichments within the upper part of the spherule layer, although most of the trace element profiles resulted from diagenetic alteration. During the alteration of glass to smectite, the concentrations of certain trace elements, such as the rare earth elements, were severely changed. In addition, oxygen-poor conditions also led to the remobilization of redox-sensitive elements, which show enhanced concentration at the top or above the spherule bed. Diagenetic remobilization may have also affected the Ir concentration.
Astronomical calibration of the Danian time scale
Authors: Röhl Ursula , Ogg James G. , Geib Tricia L. , Wefer Gerold
Published: April 2008

Ocean Drilling Program Sites 1001A (Caribbean Sea) and 1050C (western North Atlantic) display obliquity and precession cycles throughout polarity zone C27 of the late Danian stage (earliest Cenozoic time). Sliding-window spectra analysis and direct cycle counting on downhole logs and high-resolution Fe variations at both sites yield the equivalent of 35–36 obliquity cycles. This cycle-tuned duration for polarity chron C27 of 1.45 Ma (applying a modern mean obliquity period of 40.4 ka) is consistent with trends from astronomical tuning of early Danian polarity chron C29 and
40
Ar/
39
Ar age calibration of the Campanian-Maastrichtian magnetic polarity time scale. The cycle-tuned Danian stage (
sensu
Berggren
et al.
1995, in SEPM Special Publications,
54
, 129–212) spans 3.65 Ma (65.5–61.85 Ma). Spreading rates on a reference South Atlantic synthetic profile display progressive slowing during the Maastrichtian to Danian stages, then remained relatively constant through late Palaeocene and early Eocene time.
Orbitally forced climate change in late mid-Eocene time at Blake Nose (Leg 171B): evidence from stable isotopes in foraminifera
Authors: Wade Bridget S. , Kroon Dick , Norris Richard D.
Published: April 2008

Previous stable oxygen isotopic data from surface-dwelling foraminifera indicate that Eocene tropical sea surface temperatures (SSTs) were significantly lower than at present. Here we show that stable isotopic analyses (δ
18
O, δ
13
C) of the late mid-Eocene mixed-layer dweller
Morozovella spinulosa
are consistent with mid-Eocene mid-latitude SSTs close to, or slightly lower than modern temperatures at Blake Nose, western North Atlantic. In contrast, isotopic analyses of the benthic foraminifer,
Nuttalides truempyi
reveal a gradual fall in mean bottom-water temperatures from 8 to 7 °C over
c
. 500 ka years. These deep intermediate-water temperatures are significantly higher than modern ones and are similar to intermediate- and bottom-water temperatures recorded from earlier in Palaeogene and late Cretaceous time.

Large shifts are seen in the δ
18
O and δ
13
C values of the planktonic foraminifers, of up to 1‰ and 2.6‰, respectively, that probably reflect temperature and nutrient fluctuations controlled by regional changes in upwelling intensity and runoff. The surface to benthos δ
18
O gradient decreases from 3‰ PDB to a minimum of
c.
0.5‰ PDB over 400 ka, which could relate to the intensity of upwelling. Spectral analysis reveals precessional forcing in the foraminiferal δ
18
O records, which shows the direct influence of low-latitude insolation on surface-water stratification. Monsoonal wind systems may have forced the upwelling cycles and/or freshwater input. The benthic foraminifer δ
18
O record also contains the obliquity cycle, in addition to the precessional cycles, indicating the inheritance of mid- and high-latitude forcing to subtropical deep waters.
Episodicity during orogenesis
Authors: Lister G. S. , Forster M. A. , Rawling T. J.
Published: April 2008

Deformation events and episodes of metamorphic mineral growth are usually regarded as relatively local phenomena. It is not expected that specific events and episodes within an orogenic sequence should exactly correlate over large distances. There is no obvious reason, for example, to assume that deformation and/or metamorphic events in the Western European Alps would directly correlate with events taking place in the Aegean continental crust,
c.
1000 km distant. Yet linked episodes of deformation and metamorphism appear to take place at the same time over large distances, even in these apparently unrelated segments of the same orogenic belt. This large-scale episodic behaviour appears to be associated with switches in tectonic mode, from compressional orogenesis to extensional tectonism, and may be the result of orgenic surges and/or periods of lithospheric extension following accretion events. The effect of these switches is greatest in back-arc environments, in the over-riding plate above major subduction zones. In these environments, roll-back of the subducting lithospheric slab after individual accretion events ensures that the amount of lithospheric extension after each accretion event is large. As a result this is where coherent high-pressure metamorphic terranes formed in the preceding accretion event are exhumed, and where remnants of newly emplaced ophiolite sheets are stranded by newly formed detachment faults.
The structure and rheological evolution of reactivated continental fault zones: a review and case study
Authors: Holdsworth R. E. , Stewart M. , Imber J. , Strachan R. A.
Published: April 2008

Repeated reactivation of structures and reworking of crustal volumes are characteristic, though not ubiquitous, features of continental deformation. Reactivated faults and shear zones exposed in the deeply exhumed parts of ancient orogenic belts present opportunities to study processes that influence the mechanical properties of long-lived fault zones at different palaeo-depths. Ancient basement fault systems typically comprise heterogeneous, superimposed assemblages of fault rocks formed at different times and depths for which down-temperature thermal histories are most common. Several lithological and environmental factors influence the evolution of fault rock fabrics and rheology, but most fault/shear zone arrays appear to develop as self-organized deformation systems. Once mature, the kinematic and mechanical evolution of the system is strongly influenced by the rheological behaviour of the interconnected fault/shear zone network.

A case study from the crustal-scale Great Glen Fault Zone (GGFZ), Scotland, reveals a complex evolution of mid- to upper-crustal deformation textures formed adjacent to the frictional-viscous transition. Fluid influx in the mid-crust has led to reaction softening of the rock aggregate as strong pre-existing phases such as feldspar are replaced by fine-grained, strongly aligned aggregates of weak phyllosilicates. In addition, a grainsize-controlled switch to fluid-assisted diffusional creep occurs in the highest strain regions of the fault zone. It is proposed that this led to a shallowing and narrowing of the frictional-viscous transition and to long-term overall weakening of the fault zone relative to the surrounding wall-rocks. Cataclasis is particularly important in the deeper part of the frictional regime as it helps to promote retrograde metamorphism and changes in deformation regime, by both reducing grainsize and promoting pervasive fluid influx along fault strands due to grain-scale dilatancy. Equivalent processes are likely to occur along many other long-lived, crustal-scale fault zones.
Tectonic feedback, intraplate orogeny and the geochemical structure of the crust: a central Australian perspective
Authors: Sandiford M. , Hand M. , McLaren S.
Published: April 2008

The geological record of intraplate deformation in central Australia implies that past tectonic activity (basin formation, deformation and erosion) has modulated the response of the lithosphere during subsequent tectonic activity. In particular, there is a correspondence between the localization of deformation during intraplate orogeny and the presence of thick sedimentary successions in the preserved remnants of a formerly widespread intracratonic basin. This behaviour can be understood as a kind of ‘tectonic feedback’, effected by the long-term thermal and mechanical consequences of changes in the distribution of heat producing elements induced by earlier tectonism. From a geochemical point of view, one of the most dramatic effects of intraplate orogeny in central Australia has been the exposure, in the cores of the orogens, of deep crustal rocks largely depleted in the heat producing elements. The geochemical structuring of the crust associated with the erosion of the heat-producing upper crust resulted in long-term cooling of the deep crust and upper mantle with associated lithospheric strengthening. This is illustrated here by mapping the consequences of deformation and associated tectonic responses onto the
h-q
c
plane, where
h
is the characteristic length-scale for heat production distribution, and
q
c
is the total crustal heat production. Because rates of intraplate deformation in central Australia appear to be much slower than that typical of plate margin orogens, it is possible that the ongoing geochemical structuring of the crust has played an important role in terminating intraplate orogeny in central Australia by providing a ‘thermal lock’. The diagnostic geophysical signature of this lock may be the extraordinary gravity anomalies of the central Australian intraplate orogens.
Tectonic evolution of the Reynolds-Anmatjira Ranges: a case study in terrain reworking from the Arunta Inlier, central Australia
Authors: Hand M. , Buick I. S.
Published: April 2008

The Reynolds-Anmatjira Range region forms part of the Arunta Inlier in central Australia and has undergone four tectonothermal cycles that span an interval of
c.
1450 Ma. The first two cycles were the Stafford Tectonic Event
c.
1820 Ma, and the Strangways Orogeny
c.
1770–1780 Ma, both of which were associated with regional low-pressure high-temperature metamorphism up to granulite grade that was coeval with the emplacement of voluminous sheet-like granites. The subsequent Chewings Orogeny occurred at around 1590–1570 Ma and was a long-lived event that produced regional low-pressure greenschist to granulite facies metamorphism without obvious associated magmatism. During the mid-Palaeozoic Alice Springs Orogeny (400–300 Ma), the terrain was dissected by a system of sub-greenschist to mid-amphibolite facies shear zones. In the Reynolds Range, the Proterozoic events produced a single regional foliation that is axial planar to simple large-scale folds. The composite regional Proterozoic foliation increases in grade smoothly from northwest to southeast, producing a pattern of isograds that is remarkably similar to those that formed during the mid-Palaeozoic Alice Springs Orogeny. Despite this simple pattern, the isograds reflect the superimposed metamorphic effects of four unrelated tectonothermal cycles. Without geochronological and stratigraphic information, the degree of terrain reworking in the Reynolds-Anmatjira Range region could have been largely obscured by the apparent simplicity of many of the structural and metamorphic relationships.
High-grade reworking of Proterozoic granulites during Ordovician intraplate transpression, eastern Arunta Inlier, central Australia
Authors: Scrimgeour Ian , Raith Johann G.
Published: April 2008

In the Huckitta region of the eastern Arunta Inlier, central Australia, two terrains with distinct metamorphic histories are separated by a zone of sinistral strike-slip mylonitic deformation and reworking, the Entire Point Shear Zone (EPSZ). To the south of the EPSZ, in the Harts Range Group, Ordovician (
c.
470 Ma) intraplate granulite facies metamorphism (
c.
800°C, 8–10 kbar) was followed by decompression to
c.
7 kbar. In contrast, the Kanandra Granulite, to the north of the EPSZ, is characterized by Palaeoproterozoic high-grade metamorphism at 770–850°C and 5–7 kbar, followed by inferred near-isobaric cooling. Juxta-position of these terrains along the EPSZ occurred at upper amphibolite facies conditions (700°C, 7 kbar), and resulted in extensive reworking of the Kanandra Granulite. Monazite growth within EPSZ mylonites is dated at 445 ± 5 Ma, whilst a garnet amphibolite gives a Sm-Nd isochron age of 434 ± 6. The timing of this deformation is broadly coincident with the inferred onset of south-vergent compressional deformation in the Harts Range region to the south. This suggests that juxtaposition of the Ordovician granulite terrain with the surrounding Proterozoic terrains occurred during intraplate sinistral transpression in the late Ordovician. Further reworking of the Kanandra Granulite occurred at mid-amphibolite to greenschist facies conditions, during north-vergent mylonitic deformation that exhumed the Ordovician high-grade terrain during the 400–300 Ma Alice Springs Orogeny. Although this zone of Palaeozoic reworking is <5 km wide, it forms the northern margin of Palaeozoic high-grade intraplate deformation and represents a major tectonic boundary in central Australia.
Fluid-rock interaction in the Reynolds Range, central Australia: superimposed, episodic, and channelled fluid flow systems
Authors: Cartwright Ian , Buick Ian S. , Vry Julie K.
Published: April 2008

The Reynolds Range, central Australia, is a polymetamorphic Proterozoic terrain within the Arunta Inlier. The terrain comprises a diverse sequence of metasedimentary rocks (including pelites, psammites, quartzites, marls and marbles) intruded by with two generations of granites. The Reynolds Range preserves evidence of undergoing several metamorphic events, including: phases of contact metamorphism at 1.82 Ga and 1.78 Ga; regional metamorphism at 1.6 Ga that varied in grade from greenschist facies (
c.
400°C) to granuite facies (750–800°C) at 400–500 GPa; and metamorphism at up to amphibolite facies (550–600°C at 500–600 MPa) in the Alice Springs Orogeny at
c.
334 Ma, the affects of which are recorded mainly within shear zones. Fluid flow occurred during both contact metamorphic events, cooling from the peak of regional metamorphism at 1.57–1.58 Ga, and additionally during Alice Springs shearing. By contrast, there is little fluid-rock interaction that can be attributed to the prograde stages of regional metamorphism, implying that fluids generated by metamorphic devolatilization at that time escaped relatively rapidly and did not interact with the rocks as a whole.

Fluid flow changed the mineralogy and stable isotope ratios of rocks, and locally caused extensive metasomatism. During cooling from the peak of regional metamorphism, the fluids were derived from crystallization of partial melts and reflect internal fluid recycling. However, at least some fluid flow during contact metamorphism and shearing involved external fluids. In both contact metamorphic episodes, igneous and locally surface-derived fluids interacted with the country rocks adjacent to the granite plutons. During Alice Springs shearing, large volumes of surface-derived fluids infiltrated the middle crust. Much of the fluid flow was channelled on scales ranging from hecto- to millimetres as a result of variations in intrinsic permeability caused by deformation or reaction enhancement.