bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tectonic quiescence punctuated by strike-slip movement: influences on Late Jurassic sedimentation in the Moray Firth and the North Sea region
Authors: Frost R. E. , Rose J. F. 
Published: April 2008

Abstract
Present geological models do not explain all of the observed Upper Jurassic structural and depositional relationships, not only within the Moray Firth but also the entire North Sea region. Observations based on modern 2D seismic reflection sections, well and onshore outcrop data, have led to a significant reappraisal of the Upper Jurassic which may have far-reaching consequences for presently accepted models. Analysis of the Upper Jurassic sediments in the Moray Firth almost invariably indicates an onlapping, non-rotated parallel-bedded sequence. The onlapped topography resulted from a rapid tectonic pulse of probable Callovian age, the loosely-termed ‘mid Cimmerian’ event, which will be redefined. This likely synchronous event terminated the broadly paralic deposition of the Brent Group and equivalents. Extensive seismic reflection data, well and outcrop evidence from the region strongly suggests that the resulting relief was ‘frozen’, i.e. not driven by, nor creating, vertical earth movements. During this generally tectonically quiescent Late Jurassic period, the lows were passively filled with little apparent subsidence. This relatively low-energy environment may explain the deposition of sands proximal to eroded margins, and also the occurrence of parallel-bedded source rocks where tectonic quiescence would have been beneficial to the maintenance and preservation of anoxic conditions. Evidence of earthquake activity based on grain-size distributions suggests that fault movements were local, of probable strike-slip origin and may have been the result of post ‘mid Cimmerian’ strain energy release along contemporaneously eroding margins. These movements resulted in different localised tectono-stratigraphic sand pulses. The recognition of passive infill during what appears to be a regionally tectonically quiescent period, from intra-Callovian to the major Late Ryazanian sea-level rise, suggests that the intra-Callovian (‘mid Cimmerian’) event, which signalled the beginning of the period, was probably synchronous across the North Sea region. It would be unreasonable to expect contemporaneous passive infill and subsidence-generated sedimentation in adjacent basins if this were not the case. The virtual absence of any evidence of syn-depositional rotation of the Upper Jurassic sediments also suggests that the intra-Callovian event was geologically rapid. It should be noted that these observations, involving a generally tectonically quiescent period which was both rapidly formed and ended, are incompatible with the application of the necessarily gradual processes of thermal subsidence models and classical rifting, which are considered inappropriate for the region during the Late Jurassic period.
The Puffin Field: the appraisal of a complex HP-HT gas-condensate accumulation
Authors: Dickinson B. 
Published: April 2008

Abstract

The Puffin Field was discovered by well 29/5a-1, drilled in 1981 to test a Base Cretaceous closure. The well encountered over-pressured gas-condensate-bearing Upper Jurassic shallow marine sandstones below 14,000 ft. The well flowed over 20 × 10
6
SCFGD with 2650 barrels per day of condensate. Appraisal of the discovery, which fell into five phases, involved the acquisition of two 3D seismic surveys and drilling of eight wells. This paper describes the appraisal of Puffin from an historical perspective.

The initial geological model involved an intra-graben horst draped by a relatively uniform blanket of Fulmar Formation sandstones. The first two apprisal wells were disappointing and hinted at previously unsuspected complexities. The second pair of appraisal wells, although proving up further hydrocarbons, penetrated thick Triassic sequences, with the Pentland and Fulmar Formations being absent. These results were incompatible with the existing geological model and a new model was developed. This envisaged the presence of several large Triassic-cored pods, formed in response to salt withdrawal and local tectonism, separated by narrow elongate zones (inter-pods) in which Middle and Upper Jurassic sections were present. Four further appraisal wells were drilled and proved the model to be robust with respect to stratigraphy and structure, although it did not always accurately predict hydrocarbon distribution.
The reservoir geology of the shallow marine Fulmar Formation and fluvial Skagerrak Formation reservoirs will be outlined. The wells indicated considerable differences in hydrocarbon contacts between wells and differences in fluid gradients and pressures between the pods. The geological evolution of the field will be described.
Laminated diatomaceous sediments: controls on formation and strategies for analysis
Authors: Sancetta Constance 
Published: April 2008

Abstract
This paper summarizes observations and ideas developed over a decade studying a variety of laminated sediments. Laminations of alternating lithic (dark) and biogenic (light) particles occur near land masses, where the lithic laminae may be interpreted as a record of precipitation, and the biogenic laminae as a record of primary production resulting from wind stress. The seasons corresponding to each type can be predicted from regional climatology. Biogenic laminae frequently consist of sublaminae representing a sequence of production events, so that several seasons of information may be included. Laminations of two types of biogenic particles are unusual, but have been reported from deep-sea settings. The physical control on these laminations is very indirect, and their occurrence is more probably a result of complex ecologic interactions. Although many laminar couplets are true varves, problems can occur when the normal cycle of alternating conditions is disturbed. Examples include the occurrence of a heavy rainstorm producing a dark lamination within the light lamina of a productive season, juxtaposition of two dark laminae from separate rainy seasons if the intervening productive events did not occur, and continuous rainfall throughout a productive season such that the light biogenic material is masked by the dark lithic material. Such cases, while complicating the use of laminae for time control, may provide useful information on interannual variability if they can be accurately identified. As an alternative to generating very long time series, it is suggested that selected clusters of samples combined with the use of analyses of variance may provide such information. Another strategy is the use of factor analysis to define seasonal proxies from the top part of a section; the proxies may then be projected downcore to derive information on seasonal trends of the past.
Preparation and analysis techniques for studies of laminated sediments
Authors: Pike Jennifer , Kemp Alan E. S. 
Published: April 2008

Abstract
Laminated sediments commonly represent the highest resolution continuous records available of marine and lacustrine variability. To exploit this information effectively careful sampling and preparation procedures must be followed, thus the method of analysis chosen must have sufficient resolution to recover the data. The scanning electron microscope, because of its good spatial resolution, is an ideal tool for analyzing laminated sediment fabric. Backscattered electron imagery produces preserved flux data on intra-annual time-scales, which enables high-resolution fabric studies, palaeoenvironmental reconstructions and compilation of data for time-series analysis. This contribution summarizes the techniques used for laminated sediment fabric investigation and discusses the use of the scanning electron microscope, including the best preparation method for thin sections and the procedure for backscattered electron imagery analysis.
The potential for palaeoclimate records from varved Arctic lake sediments: Baffin Island, Eastern Canadian Arctic
Authors: Hughen Konrad A. , Overpeck Jonathan T. , Anderson Robert F. , Williams Kerstin M. 
Published: April 2008

Abstract

Tidewater lakes on Baffin Island in the eastern Canadian Arctic offer an excellent opportunity to study interannual to century-scale Arctic climatic change. Freeze-cores were analysed from three lakes in southeastern Baffin Island: Upper Soper Lake, Ogac Lake and Winton Bay Lake. The sediment record in each lake consists of massive sediments overlain by an organic-rich, finely laminated section which continues to the surface. The laminae in Ogac Lake were studied in detail and consist of two types. The light layers are composed almost entirely of intact diatom frustules, primarily
Chaetoceros
spp. The darker layers are dominated by clay and silt-sized terrigenous mineral grains, including abundant quartz and feldspars. These couplets are probably deposited as the result of diatom blooms in the late spring/summer growing season followed by settling of grains introduced by summer runoff. Sedimentation rates based on
210
Pb dates agree well with rates based on laminae counts in both Ogac and Winton Bay Lakes, indicating that the laminae couplets are annually deposited varves. Our experience suggests that shallow-silled tidewater lakes with varved sediments may be relatively common along the coast of Baffin Island. It should thus be possible to create a network of sites with annually dated palaeoclimate records.
Varved sediments in Sweden: a brief review
Authors: Petterson Gunilla 
Published: April 2008

Abstract
This paper gives an introduction to studies made on varved (annually laminated) sediments in Sweden. Varve studies began in the late 19th century when Gerard de Geer correlated glacial clay-varves in order to establish a geochronology over the latest deglaciation. Both the chronology and its connection to present sediment deposition has continuously been revised during this century. As well as for glacial clay-varve deposits, annual formation of sediment laminae has also been found in estuarine, marine and lacustrine environments. Varved sediments, of different origins, first mainly used for dating purposes, have today also become an important tool for detailed reconstructions of past environmental changes.
Conflicting indicators of palaeodepth during deposition of the Upper Permian Castile Formation, Texas and New Mexico
Authors: Leslie A. B. , Kendall A. C. , Harwood G. M. , Powers D. W. 
Published: April 2008

Abstract
The Upper Permian Castile Formation of the Delaware Basin, Texas and New Mexico has commonly been interpreted as a deep-basin, deep-water evaporite deposit, based on the lateral continuity of mm-thick, anhydrite-calcite laminations. The identification of pseudomorphs after bottom-growth gypsum crystals throughout the Castile Formation implies that during much of the time, deposition occurred within a partially desiccated basin from supersaturated brines at most 40 m deep. The pseudomorphs are commonly poorly preserved within nodular horizons which were previously interpreted as mesogenetic alterations of former laminae. The nodular horizons themselves contain pseudomorphs after displacive lenticular gypsum crystals that suggest a synsedimentary, shallow-water origin for both bottom-growth and nodular textures. In contrast, structureless beds of sulphate up to 0.5 m, thick which are most common in the eastern part of the basin, appear to have been deposited from density currents as turbidites, implying relatively deep water. The evidence provided by pseudomorphs after gypsum within the Castile Formation suggests that average water depths across the basin were at times less than 40 m and could not have exceeded 200 m. Synsedimentary fault control may have partly accommodated the turbiditic sedimentation in the eastern part of the basin, although the depositional environment would require a remarkable coincidence between deposition and subsidence. The evidence as a whole suggests a delicate balance between subsidence, sedimentation and water depth during deposition of the Castile Formation.
A survey of occurrences of Holocene laminated sediments in California Borderland Basins: products of a variety of depositional processes
Authors: Gorsline D. S. , Nava-Sanchez Enrique , de Nava Janette Murillo 
Published: April 2008

Abstract
Laminated sediments are found in several contemporary depositional settings in basins of the California Continental Borderland. These primary structures are preserved either as a result of anoxia (or near anoxia) in the bottom water when oxygen demand is greater than the oxygenation rate, or as a result of sedimentation rates in excess of bioturbation rates. The controlling processes in the anoxic settings include cyclic seasonal variation in the composition of hemipelagic deposition (hemipelagic laminae), and/or formation and destruction of bacterial mats as a result of periodic bottom water flushing of normally low-oxygen bottom waters (cyclic organic-rich laminae). Non-bioturbated hemipelagic laminations occur in San Pedro, Santa Monica and Santa Barbara Basins. Low-oxygen bottom waters and exclusion of macrobenthos have been characteristic of San Pedro Basin for a few decades. These conditions have existed in Santa Monica Basin for a few centuries and in Santa Barbara Basin for most of the Holocene. Physical sedimentation processes include rapid deposition from turbidity currents. Fine grained contemporary distal turbidites occur in Santa Monica, San Pedro, San Diego, Santa Cruz and San Nicolas Basins. Turbidity current flows into the deep basin floor occur at century scale in Santa Monica Basin and at somewhat longer frequencies in San Pedro Basin. Frequency of such flows is at the kilo-year level in San Diego Trough, Santa Cruz Basin and San Nicolas Basin. Such events are of interest because they show that submarine canyons will remain active through a high sea-level period. In narrow-shelf, active margins, canyons may not be shut off as generally occurs on passive margins when sea level rises rapidly, as is typical of climatically driven sea level fluctuations.
Laminated sediments of Santa Monica Basin, California continental borderland
Authors: Hagadorn James W. 
Published: April 2008

Abstract

Laminated sediments from Santa Monica Basin differ from other laminated sediments of the California Continental Borderland (such as varved sediments of Santa Barbara Basin) because lamina couplets represent a 3–6 year time interval and are affected by distinct local oceanographic and climatic processes. Unfortunately, mechanisms which control the temporal pattern of laminations in this basin are poorly understood. In addition, this laminated sediment record has been underutilized in paleoceanographic and paleoclimatic studies. In an attempt to identify mechanisms which control lamination formation and in order to obtain paleoclimatic and paleoceanographic records from this region, a sediment core from this basin was analysed using a suite of geochemical, sedimentary, and micropaleontologic techniques. This box-core (core DOE 26) was collected from the centre of the basin and was vertically sub-sampled at one millimetre increments, providing a temporal resolution of 1–3 years per sample. A variety of paleoceanographic and paleoclimatic records were constructed via analysis of these samples and include proxy records of: (a) regional rainfall — as expressed by gross variations in downcore density profiles; (b) relative contribution of terrestrial and marine organic carbon to the basin — as expressed by downcore variations in the isotopic composition of total organic carbon (TOC); (c) Primary productivity — as expressed in downcore variations in the carbon isotopic composition of planktonic foraminifera; (d) changes in sea surface temperatures —reflected in downcore variations in the oxygen isotopic composition of
N. pachyderma
(dextral); (e) large-scale changes in bottom-water oxygen conditions — as expressed by downcore changes in abundance of oxygen- sensitive benthic foraminifera. To extract additional information from these proxy records, spectral analysis was also employed in this study. Although ENSO-length signals are present in several records, decadal-length signals appear to dominate records from this basin. This dominance suggests the presence of a longer-term forcing function (other than the ENSO phenomena) which strongly influences this region. Considered together, preliminary results suggest that the flux of organic carbon is a dominant factor affecting lamination variability in Santa Monica Basin. Organic carbon fluxes in this basin are mainly affected by primary productivity, and to a lesser extent, by terrestrial input. Variations in bottom oxygen conditions may not control lamination variability; rather, long-term depression of oxygen levels appears to allow preservation of this organic matter as laminated sediments.
The nature of varved sedimentation in the Cariaco Basin, Venezuela, and its palaeoclimatic significance
Authors: Hughen Konrad A. , Overpeck Jonathan T. , Peterson Larry C. , Anderson Robert F. 
Published: April 2008

Abstract

A laminated sediment record of the last 12 600 radiocarbon years from the anoxic Cariaco Basin provides a rare opportunity to study interannual to millenial-scale climatic change in a marine setting. Sedimentological and radiometric analyses of laminae couplets in the basin sediments indicate that they are annually deposited varves. The varves consist of light and dark laminae which are deposited as the result of the Intertropical Convergence Zone’s annual north-south migration over the tropical North Atlantic, and the impact of this migration on regional upwelling and rainfall patterns. Light laminae contain planktonic fossils (predominantly diatoms) and are an indicator of productivity over the basin during the winter-spring upwelling season. Dark laminae contain terrigenous mineral grains and are an indicator of runoff from northern South America during the late summer-fall rainy season. Varve measurements developed using X-ray images and thin sections indicate that a continuous 14 000 calendar year long varve chronology may be generated. Preliminary measurements of thickness of individual light and dark laminae for the period 12.6 to 9 ka
BP
show similar palaeoclimate signals. Thickness of dark laminae, interpreted as measuring changes in regional runoff, increased rapidly at 10.8 ka
BP
and decreased rapidly at 9.8 ka
BP
, an interval coincident with the Younger Dryas cold period. Thickness of light (diatom-rich) laminae, indicative of productivity and possibly upwelling intensity, also show an increase at 10.8 ka
BP
, and a rapid decrease at 9.8 ka
BP
, simultaneous with the changes in the dark laminae. Current work is focusing on building long multiple-core varve chronologies and using these for palaeoclimatic reconstructions and geochronological research.
Laminated sediments from the oxygen-minimum zone of the northeastern Arabian Sea
Authors: Schulz H. , Von Rad U. , Von Stackelberg U. 
Published: April 2008

Abstract

Holocene and late Pleistocene hemipelagic muds with fine, mm-scale laminations were discovered during the International Indian Ocean Expedition (IIOE) 30 years ago in the northeastern Arabian Sea, where an expanded mid-water oxygen-minimum zone (OMZ) impinges on the continental slope and prevents bioturbation. In 1993, R.V.
Sonne
revisited Pakistani waters in order to study in more detail the complex interactions between surface and deep water hydrography, productivity and terrigenous input which form and preserve organic-rich sediments. Laminated sediments frequently occur along the Indian-Pakistani continental margin between 300 and 900 m water depth. The zone of high organic carbon contents roughly coincides with the depth of the present OMZ (200–1200 m water depth). However, resedimentation processes influence the character of sediment laminae and the distribution of organic carbon in the slope sediments. Microscopic and SEM studies suggest that the lamination may be due to the seasonal changes of surface productivity and to the lateral supply of fine-grained sediment. We infer that the OMZ must have varied considerably in space and time. This is documented by the distinct, possibly cyclic alternations of dark-coloured, organic-carbon-rich, laminated intervals with light-coloured, carbonate-rich, bioturbated sedimentary sequences, reflecting variations between anoxic to suboxic and oxic bottom water conditions.
Detailed volcanic geology of the MARNOK area, Mid-Atlantic Ridge north of Kane transform
Authors: Lawson Kate , Searle Roger C. , Pearce Julian A. , Browning Paul , Kempton Pamela 
Published: April 2008

AbstractWe present the results of a detailed study of the volcanic geology of the median valley floor of the Mid-Atlantic Ridge in two adjacent but contrasting spreading segments immediately north of the Kane transform fault, based on a high-resolution deep-towed sidescan sonar (TOBI) survey, near-bottom photographic traverses, and geochemical analyses from 28 precisely sited sets of dredge samples. This has allowed us to assess the relative importance of small (intersegment) and large (transform) boundaries on magmatic processes at slow spreading ridges.We find that the petrological effect of the transform (so-called ‘transform fault effect’) is minor compared to the manifestation of the second-order segmentation. The southern, ‘narrowgate’-type segment has a poorly developed neovolcanic zone, which tapers towards its bathymetric centre where continuous faulting causes rapid dismemberment. Flat-topped seamounts are preferentially located at the ends of the segment, particularly near the non-transform offset. There is a striking variation in the degree of fractionation along the length of this segment: primitive lavas were sampled at the centre, while more fractionated basalts, showing a greater range of parental compositions, form discrete volcanic edifices at the ends. In contrast, the northern segment has a wider inner valley, and syn-magmatic faults extend up to 15 km along the crest of its robust axial volcanic ridge. The along-segment trend of increasing MgO towards the bathymetric crest of the axial volcanic ridge is similar to, but less well-defined than, that for the southern segment.There is no variation in the bulk degree of melting along the segments as determined from the major element geochemistry; hence, melt migration is favoured over focused mantle upwelling as the main cause of the crustal thickness variations which define second-order segmentation. Radigenic isotopes show only very small variations with no systematic pattern emerging within or between the ridge segments. The isotopic irregularities are not related to the variations in incompatible elements, implying that the latter result from dynamic melting processes rather than from long-lived source heterogeneity. A model is developed which relates the volcanology, tectonic style and the geochemical trends to the episodicity of magma supply and eruption.