bluuebunny/crossref_metadata_2025 huggingface dataset:
Coagulation effects of in vitro serial haemodilution with a balanced electrolyte hetastarch solution compared with a saline‐based hetastarch solution and lactated Ringer's solution*
Authors: Roche A. M. , James M. F. M. , Grocott M. P. W. , Mythen M. G.
Published: March 2003

The hydroxyethyl starches are a group of compounds that has been associated with impairment of coagulation when large volumes are administered. The thrombelastograph® is commonly used to assess point‐of‐care whole blood coagulation. Little is known about the dose–response relationships of haemodilution, and it is reasonable to assume that a linear association exists. This may not be the case with altered electrolyte compositions of the fluids used for haemodilution. We have therefore conducted an in vitro study of haemodilution of human whole blood using lactated Ringer's solution and two high molecular weight hetastarches, one in a balanced salt solution, the other in a 0.9% saline solution. The thrombelastograph®, commonly used for the assessment of the coagulation effects of synthetic colloids, was used as the coagulation assessment device. Serial haemodilution with hetastarch in a balanced salt solution demonstrated a biphasic response (of r‐times and k‐times, as well as alpha angles), with haemodilution in the 20–40% range causing enhanced coagulation, and higher degrees of dilution causing a decrease in overall coagulation performance. A similar picture was observed with lactated Ringer's solution, but only significantly so in alpha angles. Hetastarch in saline did not display this initial increased coagulability at mild to moderate dilutions. This biphasic response of lactated Ringer's solution and hetastarch in a balanced salt solution reflects the complex interaction of fluids and the coagulation system, and that these effects cannot be attributed to simple haemodilution. On the other hand, there was a linear decrease in maximum amplitude with haemodilution. Maximum amplitude was particularly affected by both starches, which is an expected finding in view of the known interaction between the hydroxyethyl starches and von Willebrand's factor.
Calf compartment pressures in the Lloyd‐Davies position: a cause for concern?
Authors: Turnbull D. , Farid A. , Hutchinson S. , Shorthouse A. , Mills G. H.
Published: March 2003

Summary Lower limb compartment syndrome is a rare consequence of surgery where the lithotomy position is maintained for several hours. The aim of this study was to observe the effect of the lithotomy position on lower limb compartment pressure and blood flow to the lower limb in surgical patients having colorectal procedures. We prospectively studied 23 patients undergoing colorectal surgery requiring the lithotomy position and recorded lower limb compartment pressure, and the blood pressure in the upper and lower limbs. The lithotomy position led to a significant (p < 0.001) fall in blood pressure to the lower limb from 87 (SD 16) mmHg to 67.9 (SD 12) mmHg and a significant (p < 0.001) rise in lower limb compartment pressure from 13 (SD 7) mmHg to 31 (SD 12) mmHg. These two effects compromise blood flow to the lower limb in long surgical procedures where the lithotomy position is required. Intermittently lowering the legs and restoring blood flow may prevent compartment syndrome developing.
Estimating unmeasured anions in critically ill patients: Anion‐gap, base‐deficit, and strong‐ion‐gap
Authors: Story D. A. , Poustie S. , Bellomo R.
Published: March 2003

Summary We used 100 routine blood samples from critically ill patients to establish whether correcting the anion‐gap and base‐deficit for decreased plasma albumin improves agreement with the strong‐ion‐gap for estimating unmeasured anions and whether the modifications increase the proportion of samples with levels of anion‐gap or base‐deficit above the reference ranges. We used Bland− Altman analyses to compare the methods of estimating unmeasured ions. Compared with the strong‐ion‐gap, modification reduced the limits of agreement for both the anion‐gap and the base‐deficit. The bias for the base‐deficit was also reduced but the bias for the anion‐gap was increased. The proportion of samples with an anion‐gap > 22 meq.l−1 increased from 4 to 29% (p < 0.001), and the proportion with a base‐deficit > 5 meq.l−1 in creased from 8 to 42% (p < 0.001). Consequently, metabolic acidosis from unmeasured ions in critically ill patients maybe more frequent than often recognised.
A dedicated intravenous cannula for postoperative use Effect on incidence and severity of phlebitis
Authors: Panadero A. , Iohom G. , Taj J. , Mackay N. , Shorten G.
Published: March 2003

Summary A prospective, randomised, controlled clinical study was performed to compare the incidence and severity of postoperative peripheral venous thrombophlebitis associated with a single intravenous cannula used for both intra‐operative and postoperative purposes, and two cannulae, one used intra‐operatively and the other postoperatively. Sixty American Society of Anaesthesiologists (ASA) physical status I or II patients aged 18–65 years undergoing elective surgery were studied. The technique of cannula insertion was standardised. After surgery, the cannulation sites were examined daily by a blinded investigator for the presence and severity of thrombophlebitis using the Baxter Scale. The two groups were similar in terms of age, gender, weight, type and duration of surgical procedures, and drugs and fluids administered both intra‐operatively and postoperatively. The proportion of patients that developed phlebitis was significantly less in the two cannulae group (26.1%) than in the single cannula group (63.3%) (p < 0.0001). The severity of phlebitis was greater in the single cannula group than in the two cannulae group. These results indicate that the use of a dedicated cannula for postoperative use decreases the incidence and severity of postoperative, peripheral, cannula‐related phlebitis.
Traditional Chinese herbal medicine and anaesthesia
Authors: Kam P. C. A. , Liew S.
Published: March 2003

Summary An increasing number of people in the western world are using traditional Chinese herbal medicines. There are concerns that these Chinese medicines may contain potentially toxic ingredients and contaminants such as heavy metals. Undeclared conventional western drugs such as the non‐steroidal anti‐inflammatory and antihistamine drugs, steroids and oral hypoglycaemic agents are frequently added to Chinese herbal medicines. The constituents of the herbal products can cause adverse effects. The anaesthetist should be aware of the potential adverse effects of the herbal products, their contaminants and also of undeclared additives. The potential for drug interactions, coagulopathy and organ dysfunction caused by traditional Chinese herbal medicines has important anaesthetic implications.
Patient‐controlled epidural fentanyl following spinal fentanyl at Caesarean section
Authors: Cooper D. W. , Garcia E. , Mowbray P. , Millar M. A.
Published: March 2003

Spinal fentanyl can improve analgesia during Caesarean section. However, there is evidence that, following its relatively short‐lived analgesic effect, there is a more prolonged spinal opioid tolerance effect. The effectiveness of postoperative epidural fentanyl analgesia may therefore be reduced following the use of spinal fentanyl at operation. This randomised, double‐blind study was designed␣to assess whether patient‐controlled epidural fentanyl could produce effective analgesia following 25 µg of spinal fentanyl at operation. Patients undergoing elective Caesarean section received spinal bupivacaine combined with either fentanyl 25 µg (fentanyl group; n = 18) or␣normal saline (saline group; n = 18). Patient‐controlled epidural fentanyl was used for postoperative analgesia. The fentanyl group used a mean of 23.4 (SD 14.5) µg.h−1 of fentanyl, compared with 27.0 (10.8) µg.h−1 for the saline group (p = 0.41). Using a 0–100 mm visual analogue score for pain, the maximum pain score recorded at rest for the fentanyl group was median 24 [IQR 15–35] mm, compared with 15 [13–45] mm for the saline group (p = 0.41). The maximum pain score recorded on coughing for the fentanyl group was 29 [24–46] mm, compared with 27 [19–47] mm for the saline group (p = 0.44). Nine of the fentanyl group rated postoperative analgesia as excellent and nine as good, compared with 10 of the saline group who rated it as excellent and eight as good (p = 0.74). Epidural fentanyl can produce effective analgesia following the use of 25 µg spinal fentanyl at Caesarean section.
Alveolar recruitment strategy improves arterial oxygenation after cardiopulmonary bypass
Authors: Claxton B. A. , Morgan P. , Mckeague H. , Mulpur A. , Berridge J.
Published: March 2003

Summary Atelectasis occurs during general anaesthesia. This is partly responsible for the impairment of gas exchange that occurs peri‐operatively. During cardiopulmonary bypass, this atelectasis is exacerbated by the physical collapse of the lungs. As a result, poor arterial oxygenation is often seen postoperatively. We tested the effect of an ‘alveolar recruitment strategy’ on arterial oxygenation in a prospective randomised study of 78 patients undergoing cardiopulmonary bypass. Patients were divided equally into three groups of 26. Group ‘no PEEP’ received a standard post bypass manual lung inflation, and no positive end‐expiratory pressure was applied until arrival at intensive care unit. Group ‘5 PEEP’ received a standard post bypass manual inflation, and then 5 cmH2O of positive end‐expiratory pressure was applied and maintained until extubation on intensive care. The third group, ‘recruitment group’, received a pressure‐controlled stepwise increase in positive end‐expiratory pressure up to 15 cmH2O and tidal volumes of up to 18 ml.kg−1 until a peak inspiratory pressure of 40 cmH2O was reached. This was maintained for 10 cycles; the positive end‐expiratory pressure of 5 cmH2O was maintained until extubation on intensive care. There was a significantly better oxygenation in the recruitment group at 30 min and 1 h post bypass when compared with the no PEEP and 5 PEEP groups. There was no significant difference in any of the groups beyond 1 h. Application of 5 cmH2O positive end‐expiratory pressure alone had no significant effect on oxygenation. No complications due to the alveolar recruitment manoeuvre occurred. We conclude that the application of an alveolar recruitment strategy improves arterial oxygenation after cardiopulmonary bypass surgery.
The neuroanaesthesia workforce in Great Britain and Ireland
Authors: Farling P. A.
Published: March 2003

Summary A survey of the 36 units that provide a neuroanaesthesia service in Great Britain and Ireland was conducted. It shows the variation in the type of hospital, the number of whole‐time equivalent neuroanaesthetists, the number of operating sessions and the number of neurosurgical beds per million of the catchment population of each unit. On‐call commitment and arrangements for managing long cases are described. Current problems pertaining to neuroanaesthetic practice are mentioned. This survey will provide a basis for the planning of future neuroanaesthetic services, as the potential of expansion of neurosurgery and neuroradiology is realised. However, it is difficult to make accurate projections and hence advise on future workforce requirements in a climate of changing service delivery. Attention should be given to a number of workforce issues highlighted in this survey if recruitment into neuroanaesthesia is to be encouraged.
A comparison of target‐controlled with patient‐controlled administration of propofol combined with midazolam for sedation during dental surgery
Authors: Burns R. , McCrae A. F. , Tiplady B.
Published: March 2003

Summary Forty anxious day case patients undergoing extraction of third molar teeth under local anaesthesia with sedation, were studied in a randomised double‐blind controlled trial. A target‐controlled infusion of propofol was compared with patient‐controlled propofol for sedation, combined with a small dose of midazolam to improve amnesia. The objectives of the study were to measure the total dose of propofol used by the two groups and assess recovery and patient satisfaction. The mean dose of propofol used in the patient‐controlled sedation group was significantly less than the target‐controlled group (p < 0.00007). Five patients became over‐sedated in the target‐controlled group compared with none in the patient‐controlled group. Only one of the three tests of performance showed that the target‐controlled patients were more sedated. Patient satisfaction was high in both groups despite a greater recollection of events in the patient‐controlled group.
Changes in calcitonin gene‐related peptide, atrial natriuretic peptide and brain natriuretic peptide in patients undergoing coronary artery bypass grafting
Authors: Terazawa E. , Dohi S. , Akamastsu S. , Ohata H. , Shimonaka H.
Published: March 2003

Summary The initiation of cardiopulmonary bypass creates significant derangements in cardiovascular volume status and both endocrine and autonomic nervous system function. To examine whether such derangements might differ in patients with different pre‐operative physical status scores, we measured the plasma concentrations of calcitonin gene‐related peptide, atrial natriuretic peptide and brain natriuretic peptide, catecholamines and antidiuretic hormone, as well as haemodynamic variables, during and after cardiopulmonary bypass in 27 consecutive patients undergoing coronary artery bypass grafting. The pre‐operative levels of atrial natriuretic peptide and brain natriuretic peptide differed significantly between ASA II patients and III and IV patients [mean (SD) brain natriuretic peptide levels = 14 (8.2) vs. 129 (51) pg.ml−1]. Plasma calcitonin gene‐related peptide increased significantly in both groups after the initiation of cardiopulmonary bypass, and remained increased throughout cardiopulmonary bypass. The changes in plasma epinephrine, norepinephrine and antidiuretic hormone were similar to those reported previously. The changes in plasma calcitonin gene‐related peptide, atrial natriuretic peptide and brain natriuretic peptide did not correlate with any changes in haemodynamic variables before or after cardiopulmonary bypass. Measurement of plasma brain natriuretic peptide might usefully be included in the pre‐operative evaluation of patients with cardiac disease.
Generation of overpressure and compaction‐driven fluid flow in a Plio‐Pleistocene growth‐faulted basin, Eugene Island 330, offshore Louisiana
Authors: Gordon* David S. , Flemings Peter B.
Published: March 2003

The complex pressure and porosity fields observed in the Eugene Island (EI) 330 field (offshore Louisiana) are thought to result from sediment loading of low‐permeability strata. In this field, fluid pressures rise with depth from hydrostatic to nearly lithostatic, iso‐pressure surfaces closely follow stratigraphic surfaces which are sharply offset by growth‐faulting, and porosity declines with effective stress. A one‐dimensional hydrodynamic model simulates the evolution of pressure and porosity in this system. If reversible (elastic) compaction is assumed, sediment loading is the dominant source of overpressure (94%). If irreversible (inelastic) compaction and permeability reduction due to clay diagenesis are assumed, then thermal expansion of pore fluids and clay dehydration provide a significant component of overpressure (>20%). The model is applied to wells on the upthrown and downthrown sides of the major growth fault in the EI 330 field. Assuming that sediment loading is the only pressure source and that permeability is a function of lithology and porosity, the observed pressure and porosity profiles are reproduced. Observation and theory support a conceptual model where hydrodynamic evolution is intimately tied to the structural and stratigraphic evolution of this progradational deltaic system.
Exhumation of the Pyrenean orogen: implications for sediment discharge
Authors: Morris  , Sinclair  , Yell
Published: March 2003

Apatite fission track analyses of 21 samples from the central and eastern Pyrenees are modelled to generate time–temperature plots for the post 110±10 °C cooling history over the 40–10 Ma time interval. Modelled thermal histories have been converted into exhumation plots through the application of the present‐day geothermal gradient in the Pyrenees. The documented geology of the Pyrenees allows us to assume no significant extensional unroofing and subvertical exhumation trajectories, thus enabling exhumation to be translated into erosional denudation. Maps of denudation have been constructed for six, 5‐Myr time intervals. Denudation varied with a 20–50‐km length scale, and does not appear to have been related to the major structural zones of the mountain belt. Spatially averaged denudation rates for the six time intervals ranged from 34 to 61 mm kyr−1 assuming the present‐day geothermal gradient. Maximum rates of 240 mm kyr−1 occurred in the interval 35–30 Ma, in the region of the Querigut‐Millas massif.

Assuming the denudation resulted primarily from erosion, the denudation maps can be used to calculate sediment discharge through time to the neighbouring foreland basins. Using a series of rectangular drainage basins with a 2:1 aspect ratio (based on modern linear mountain belts) and a location of the main drainage divide based on the mean present‐day position, it is possible to evaluate the potential for spatial and temporal variations in sediment discharge as a function of denudation. The results show along‐strike variations in sediment discharge between drainage basins of 500%, and temporal variations from individual basins of >300%. A comparison of total sediment discharge per year to the Ebro and Aquitaine basins, assuming a fixed drainage divide, shows that the discharge to the south is likely to have been between 1.5 and 2.8 times greater than to the north.
Sediment supply and climate change: implications for basin stratigraphy
Authors: Leeder Mike R. , Harris Tracey , Kirkby Mike J.
Published: March 2003

The rate of sediment supply from erosional catchment to depositional basin depends primarily upon climate, relief, catchment slope and lithology. It varies in both time and space. Spatial changes in erosion rates due to variations in lithology are illustrated by contrasting rates of drainage divide migration away from faults of known ages. Time variations in relative sediment supply are extremely complex and vary widely according to the direction and magnitude of climate change. In many parts of the Great Basin and south‐western USA, glacial maximum climates were characterized by higher effective moisture and the altitudinal downward spread of woods and forests. Sparse data from alluvial fans indicate reduced sediment supply, despite the increased runoff evident from higher lake levels. The situation in Mediterranean areas is less clear, with rival climatic scenarios for vegetation ecotypes predicting contrasting runoff. In order to test these latter we run Cumulative Seasonal Erosion Potential [CSEP] experiments for present‐day and a variety of full‐glacial Mediterranean candidate climates. The results indicate the likelihood of enhanced sediment supply and runoff compared to the present day during full‐glacial times for a cool wet winter climate and a reduction in sediment supply and runoff for a full‐glacial cool dry winter climate. We then explore the consequences of such phase differences in sediment supply, and sea and lake levels for the stratigraphy of sedimentary basins. Highstands and lowstands of sea or lake may be accompanied by greater or lesser sediment and water supply, as determined by the regional climate and the direction of climatic change. Thus marine lowstands are not necessarily periods of great transfer of coarse clastic sediments to shelves and deep water basinal environments. Unsteady sediment supply has greatest implications for alluvial systems, in particular the effect that changing relative supplies of water and sediment have upon river and fan channel incision.
Numerical modelling of landscape evolution on geological time‐scales: a parameter analysis and comparison with the south‐eastern highlands of Australia
Authors: Van Der Beek* Peter , Braun Jean
Published: March 2003

Surface‐process models (SPMs) have the potential to become an important tool in predicting sediment flux to basins, but currently suffer from a lack of quantitative understanding of their controlling parameters, as well as difficulties in identifying landscape properties that can be used to test model predictions. We attempt to constrain the parameter values that enter a SPM by comparing predictions of landscape form (as expressed by hypsometric and fractal measures) and process rates obtained for different parameter sets with observations from the south‐eastern Australian highlands, a rifted margin mountain belt that has remained tectonically stable during Cenozoic times. We map the hypsometry and fractal characteristics of south‐eastern Australia and find that the roughness amplitude (G) correlates well with local relief, whereas the hypsometric integral (H ) correlates slightly better with elevation than with relief. The fractal dimension (D) does not correlate with any other morphometric measure and varies randomly throughout the region. Variograms generally show three kinds of scaling behaviour of topography with increasing wavelength, with topography only being truly self‐affine at wavelengths between ∼1 and 10 km. From a review of the available data on long‐term denudation rates in south‐eastern Australia, we infer that these have been 1–10 m Myr−1, and average escarpment retreat rates 0.2–1.0 km Myr−1, throughout the Cenozoic. Model predictions, using a SPM that includes hillslope diffusion and long‐range fluvial transport, suggest that landscape form evolves with time; after an initial phase where D, G and relief increase, all morphometric measures decrease with increasing denudation. The behaviour of GandH in the models is qualitatively compatible with the observations; D, however, varies predictably in the models, in contrast with its random behaviour in the real world. The observed present‐day morphology of SE Australia does not impose quantitative constraints on parameter values. The fractal analyses do impose general conditions of relative parameter values that have to be met in order to create ‘realistic’ topographies. They also suggest that there is no theoretical basis for including hillslope diffusion in SPMs with a spatial resolution coarser than 1 km. A comparison of the observed denudation and retreat rates with model predictions places order‐of‐magnitude constraints on parameter values. Thus, data pertaining to landscape evolution are much more valuable than static present‐day topography data for calibrating SPMs.
Sediment supply from landslide‐dominated catchments: implications for basin‐margin fans
Authors: Allen Philip A. , Hovius* Niels
Published: March 2003

The sediment flux from a mountainous catchment can be expressed as a function of a landslide rate constant κ which accounts for the vigour of hillslope erosion. Since the incising drainage network flushes all or a portion of the products of hillslope erosion to a range front where fan deposition takes place, a conservation of solid sediment volume allows the fan area and progradation distance to be calculated. These parameters are related primarily to the discharge of sediment from the catchment and to local tectonic subsidence.

A survey of modern alluvial fans in a wide range of climatic and tectonic settings shows that the effects of climate and bedrock lithology cannot be discriminated in the scatter of data of catchment area vs. fan area. However, by focusing on over 100 fans in the arid and semiarid zone of SW USA, the impact of tectonic subsidence rate is unambiguous. Although further quantitative data on local tectonic subsidence rates are urgently required, our preliminary analysis suggests considerable potential for reconstructing palaeocatchments where basin tectonic subsidence rates can be estimated. The progradation distances of fans from the northern and southern margins of the Middle Devonian Hornelen Basin of Norway, and the western and north‐eastern margins of the Mio‐Pliocene Ridge Basin, California, allow catchment sizes and denudation rates to be approximated. Although unique solution sets are not possible, an iteration of parameter values allows plausible parameter combinations to be calculated which shed light on the tectonic and sedimentary history of the proximal basin and upland source regions. Model results suggest significant asymmetry in basin subsidence rates, catchment slopes and transport mechanics between the two margins.
Erosion, deposition and basin‐wide variations in stream power and bed shear stress
Authors: Talling Peter J. , Sowter Matthew J.
Published: March 2003

Field data from four separate locations indicate that the rate at which river channel gradient decreases downstream is fundamentally different in areas of long‐term erosion and deposition. Gradient (S) and distance from the drainage divide (x) are related such that S is proportional to xφ. In areas of deposition φ<−3, whilst in areas of erosion φ>−1.1. These differences produce downstream increases and decreases in stream power and bed shear stress which also coincide with areas of erosion and deposition. This is the first time that such a basin‐wide coincidence has been demonstrated.

A strong positive correlation between stream power, bed shear stress and bedload transport rates has been clearly shown by previous empirical studies of loose‐bed channels. It is proposed that large‐scale patterns of erosion and deposition in alluvial basins result from downstream changes in bedload transport rates, produced by the observed trends in these two parameters. If this proposal is to be fully tested, further work is needed to assess the affects of downstream fining of bed material, short‐term fluctuations in discharge and downstream exchange of particles between the suspended load and bedload.
Partitioning of intermontane basins by thrust‐related folding, Tien Shan, Kyrgyzstan
Authors: Burbank  , McLean  , Bullen  , Abdrakhmatov  , Miller
Published: March 2003

Well‐preserved, actively deforming folds in the Tien Shan of Kyrgyzstan provide a natural laboratory for the study of the evolution of thrust‐related folds. The uplifted limbs of these folds comprise weakly indurated Cenozoic strata that mantle well‐lithified Palaeozoic bedrock. Their contact is a regionally extensive unconformity that provides a persistent and readily traceable marker horizon. Based on the deformation of this marker, preserved fold geometries support simple geometric models for along‐strike gradients in fold amplitude and displacement along the underlying faults, linkage among multiple structures, transfer of displacement among folds and evolution of the folds as geomorphic entities. Subsequent to initial uplift and warping of the unconformity surface, steeply dipping reverse faults cut the forelimbs of many of these folds. Wind gaps, water gaps, recent faulting and progressive stripping of the more readily eroded Cenozoic strata indicate the ongoing lateral propagation and vertical growth of fault‐related folds. The defeat of formerly antecedent rivers coincides in several places with marked increases in erosional resistance where their incising channels first encountered Palaeozoic bedrock. Persistent dip angles on the backlimbs of folds indicate strikingly uniform geometries of the underlying faults as they propagate both laterally and vertically through the crust. Deformation switches irregularly forward and backward in both time and space among multiple active faults and folds with no systematic pattern to the migration of deformation. This distributed deformation appears characteristic of the entire Kyrgyz Tien Shan.
Seismic stratigraphy of the Miocene–Pleistocene sedimentary basins of the Northern Tyrrhenian Sea and western Tuscany (Italy)
Authors: Pascucci  , Merlini  , Martini
Published: March 2003

Seismic and stratigraphic data of the inland Volterra Basin and of the Tuscan Shelf (Northern Tyrrhenian Sea) have been analysed to determine the tectono‐sedimentary evolution of this part of the Northern Apennines from the early Miocene (about 20 Ma) to the present. The area is a good example for better understanding the evolution of postcollisional related basins.

The study area is characterized by a series of sedimentary basins separated by tectonic ridges. Similar environmental conditions existed both onshore and offshore as indicated by the occurrence of similar seismic units. The units are separated by major unconformities. The cross‐sectional geometries of the deposits of these basins, as defined through seismic reflection profiles, change in a quasi‐regular manner through time and space.

Early stages (late Burdigalian to early Tortonian) of evolution of the basins are marked by either flat‐lying deposits, quasi‐uniform in thickness, probably remnants of originally wider and shallow settings, or, in places, by relatively small bowl‐shaped basins. The latter may have been strongly affected by the pre‐existing topography and tectonics, as they developed at or near the leading edges of pre‐Neogene substrate thrusts. These early deposits represent sedimentation during a transitional period from the end of compressional tectonics to the start of an extensional phase and represent a pre‐narrow rift stage of evolution of the region. The subsequent stage of tectonic evolution (late Tortonian to early Messinian), where preserved, is recorded by fault‐bounded triangular‐shaped basins interpreted as half‐grabens. This is one of the periods of major development of narrow rifts in the area. The following stage (late Messinian to Early Pliocene) is marked by variable types of basins, showing wide and deep bowl‐shaped geometries persistent in the offshore, whereas inshore (Volterra Basin) they alternate with half‐graben, synrift deposits. This period thus represents a transitional stage where part of the system is still affected by synrift sedimentation and part is developing into incipient post‐rift conditions. This stage was followed in early to middle Pliocene times by wide bowl‐shaped to blanket‐type deposits both in offshore and in inshore areas, indicating regional post‐rifting conditions. The pre‐, syn‐ and post‐rift stages have followed each other through time and space, starting first in the westernmost offshore area and shifting later toward the east, inshore.
Upper Triassic – Jurassic sequence stratigraphy and its structural controls in the western Ordos Basin, China
Authors: Liu S. , Yang S.
Published: March 2003

Upper Triassic, Lower–Middle Jurassic and Upper Jurassic strata in the western Ordos Basin of North China are interpreted as three unconformity‐bounded basin phases, BP‐4, BP‐5 and BP‐6, respectively. The three basin phases were deposited in three kinds of predominantly continental basin: (1) a Late Triassic composite basin with a south‐western foreland subbasin and a north‐western rift subbasin, (2) an Early–Middle Jurassic sag basin and (3) a Late Jurassic foreland molasse wedge. Within the Late Triassic composite basin BP‐4 includes three sequences, S4‐1, S4‐2 and S4‐3. In the south‐western foreland subbasin, the three sequences are the depositional response to three episodes of thrust load subsidence, and are mainly composed of alluvial fan, steep‐sloped lacustrine delta and fluvial systems in front of a thrust fault‐bounded basin flank. In the north‐western rift subbasin, the three sequences are the depositional response to three episodes of rift subsidence, and consist of alluvial fan – braid plain and fan delta systems basinward of a normal fault‐bounded basin margin. In the sag basin BP‐5 includes four sequences, S5‐1, S5‐2, S5‐3 and S5‐4, which reflect four episodes of intracratonic sagging events and mainly consist of fluvial, gentle‐gradient lacustrine delta and lacustrine systems sourced from peripheral uplifted flanks. BP‐6, deposited in the foreland‐type basin, includes one sequence, S6‐1, which is the depositional response to thrust load subsidence and is composed of alluvial fan systems. The formation and development of these three kinds of basins was controlled by Late Triassic and Jurassic multi‐episode tectonism of basin‐bounding orogenic belts, which were mainly driven by collision of the North China and South China blocks and subduction of the western Pacific plate.
Multiphase cooling and exhumation of the southern Adelaide Fold Belt: constraints from apatite fission track data
Authors: Gibson H. J. , Stüwe K.
Published: March 2003

Data from apatite fission track analysis are presented for 20 outcrop samples collected in the southern Adelaide Fold Belt, South Australia. Interpretation of these data, with the aid of numerical models which allow inference of multiphase cooling histories, indicate three discrete cooling events that are likely to correlate with sedimentation events in surrounding depositional settings. An event beginning some time after 85 Ma (Late Cretaceous) was characterized by cooling throughout the study area from temperatures of roughly 50 to 70 °C. An event beginning at 300–270 Ma (Late Palaeozoic) was characterized by cooling from temperatures >120 °C in all areas except for the Mount Lofty Ranges and Murray Bridge region, where peak temperatures were only 95–115 °C prior to Palaeozoic cooling. Some samples from these subregions of relatively cool Late Palaeozoic temperatures also retain evidence for even earlier cooling from temperatures >120 °C, beginning prior to 350 Ma. We interpret the post 85‐Ma event as the consequence of regional exhumation from a depth of 1.0–1.6 km. The Late Palaeozoic event (300–270 Ma) is interpreted as cooling associated with the termination of the Alice Springs Orogeny, while cooling prior to 350 Ma probably represents the final stages of Early Middle Palaeozoic unroofing of the southern Adelaide Fold Belt.

The results highlight the importance of regional, episodic postorogenic exhumation of Palaeozoic fold belts, where – in some cases – conventional methods have erroneously suggested relatively long‐term stability.
The Western Irish Namurian Basin reassessed
Authors: Wignall P. B. , Best J. L.
Published: March 2003

ABSTRACT Current basin models for the Western Irish Namurian Basin (WINB) envisage an elongate trough along the line of the present‐day Shannon Estuary that was infilled with clastic sediments derived from a hinterland that lay to the W or NW. This paper argues for an alternative basin configuration with source areas to the SW supplying sediment to a basin where deepest water conditions were in northern County Clare. Rapid subsidence along the present‐day Shannon Estuary ponded sediment in this area throughout the early Namurian and, only with the rapid increase of sedimentation rates within the mid‐Namurian (Kinderscoutian Stage), were substantial amounts of sediment able to prograde to the NE of the basin. This alternative model better explains the overwhelming predominance of NE‐directed palaeocurrents in the Namurian infill, but requires fundamental revisions to most aspects of current depositional models.

Deep‐water black shales (Clare Shale Formation) initially accumulated throughout the region and were progressively downlapped by an unconfined turbidite system (Ross Formation) prograding to the NE. This in turn was succeeded by an unstable, siltstone‐dominated slope system (Gull Island Formation) characterized by large‐scale soft‐sediment deformation, which also prograded to the NE. In the northern‐most basin outcrops, in northern County Clare, this early phase of basin infill was developed as a condensed succession of radiolarian‐rich black shales, minor turbiditic sandstones and undisturbed siltstones. The new basin model envisages the northern exposures of County Clare to be a distal, basin floor succession whereas the traditional model considers it a relatively shallow, winnowed, basin margin succession. Later stages of basin infill consist of a series of deltaic cycles that culminate in major, erosive‐based sandstone bodies (e.g. Tullig Sandstone) interpreted either as axial, deltaic feeder channels or incised valley fills genetically unrelated to the underlying deltaic facies. Within the context of the new basin model the former alternative is most likely and estimated channel depths within the Tullig Sandstone indicate that the basal erosive surface could have been generated by intrinsic fluvial scour without recourse to base‐level fall. The northerly flowing Tullig channels pass down‐dip into isolated channel sandbodies interbedded with wave‐dominated strata that suggest the deltas of the WINB were considerably more wave‐influenced than hitherto proposed. The retreat of the Tullig delta during sea‐level rise saw the rapid southerly retrogradation of parasequences, as may be expected if the basin margin lay to the SW of the present‐day outcrops.
Fluvial response to sea‐level changes: a quantitative analogue, experimental approach
Authors: Van Heijst M. W. I. M. , Postma G.
Published: March 2003

ABSTRACT Quantitative evaluation of fluvial response to allogenic controls is crucial for further progress in understanding the stratigraphic record in terms of processes that control landscape evolution. For instance, without quantitative insight into time lags that are known to exist between sea‐level change and fluvial response, there is no way to relate fluvial stratigraphy to the sea‐level curve. It is difficult to put firm constraints on these time‐lag relationships on the basis of empirical studies. Therefore, we have started to quantify time‐averaged erosion and deposition in the fluvial and offshore realms in response to sea‐level change by means of analogue modelling in a 4 × 8‐m flume tank. The rate of sea‐level change was chosen as an independent variable, with other factors such as sediment supply, discharge and initial geometry kept constant over the course of 18 experiments. Our experimental results support the common view that neither fall nor rise in sea level affects the upstream fluvial system instantaneously. An important cause for the delayed fluvial response is that a certain amount of time is required to connect initial incisions on the newly emergent shelf (canyons) with the fluvial valley. Lowering of the fluvial longitudinal profile starts only after the connection of an active shelf canyon with the fluvial valley; until that moment the profile remains steady. We quantified the process of connection and introduced the quantity ‘connection rate’. It controlled, in conjunction with the rate of sea‐level fall: (1) the amount of fluvial degradation during sea‐level fall; (2) the total sediment volume that bypasses the shelf edge; (3) the percentage of fluvial relative to shelf sediment in the lowstand delta; (4) the volume of the transgressive systems tract and (5) the amount of diachroneity along the sequence boundary. Our experiments demonstrate also that the sequence‐stratigraphic concept is difficult to apply to continental successions, even when these successions have been deposited within the influence of sea level.
The Miocene tectono‐sedimentary evolution of the southern Tyrrhenian Sea: stratigraphy, structural and palaeomagnetic data from the on‐shore Amantea basin (Calabrian Arc, Italy)
Authors: Mattei M. , Cipollari P. , Cosentino D. , Argentieri A. , Rossetti F. , Speranza F. ,   and, Di Bella L.
Published: March 2003

We report on new stratigraphic, palaeomagnetic and anisotropy of magnetic susceptibility (AMS) results from the Amantea basin, located on‐shore along the Tyrrhenian coast of the Calabrian Arc (Italy). The Miocene Amantea Basin formed on the top of a brittlely extended upper plate, separated from a blueschist lower plate by a low‐angle top‐to‐the‐west extensional detachment fault. The stratigraphic architecture of the basin is mainly controlled by the geometry of the detachment fault and is organized in several depositional sequences, separated by major unconformities. The first sequence (DS1) directly overlaps the basement units, and is constituted by Serravallian coarse‐grained conglomerates and sandstones. The upper boundary of this sequence is a major angular unconformity locally marked by a thick palaeosol (type 1 sequence boundary). The second depositional sequence DS2 (middle Tortonian‐early Messinian) is mainly formed by conglomerates, passing upwards to calcarenites, sandstones, claystones and diatomites. Finally, Messinian limestones and evaporites form the third depositional sequence (DS3). Our new biostratigraphic data on the Neogene deposits of the Amantea basin indicate a hiatus of 3 Ma separating sequences DS1 and DS2.

The structural architecture of the basin is characterized by faulted homoclines, generally westward dipping, dissected by eastward dipping normal faults. Strike‐slip faults are also present along the margins of the intrabasinal structural highs. Several episodes of syn‐depositional tectonic activity are marked by well‐exposed progressive unconformities, folds and capped normal faults. Three main stages of extensional tectonics affected the area during Neogene‐Quaternary times: (1) Serravallian low‐angle normal faulting; (2) middle Tortonian high‐angle syn‐sedimentary normal faulting; (3) Messinian‐Quaternary high‐angle normal faulting.

Extensional tectonics controlled the exhumation of high‐P/low‐T metamorphic rocks and later the foundering of the Amantea basin, with a constant WNW‐ESE stretching direction (present‐day coordinates), defined by means of structural analyses and by AMS data. Palaeomagnetic analyses performed mainly on the claystone deposits of DS1 show a post‐Serravallian clockwise rotation of the Amantea basin.

The data presented in this paper constrain better the overall timing, structure and kinematics of the early stages of extensional tectonics of the southern Tyrrhenian Sea. In particular, extensional basins in the southern Tyrrhenian Sea opened during Serravallian and evolved during late Miocene. These data confirm that, at that time, the Amantea basin represented the conjugate extensional margin of the Sardinian border, and that it later drifted south‐eastward and rotated clockwise as a part of the Calabria‐Peloritani terrane.
Interplay between lithospheric flexure and river transport in foreland basins
Authors: Garcia‐Castellanos Daniel
Published: March 2003

ABSTRACT Foreland basins form by lithospheric flexure under orogenic loading and are filled by surface transport of sediment. This work readdresses the interplay between these processes by integrating in a 3D numerical model: the mechanisms of thrust stacking, elastic flexural subsidence and sediment transport along the drainage network. The experiments show that both crustal tectonic deformation and vertical movements related to lithospheric flexure control and organise the basin‐scale drainage pattern, competing with the nonlinear, unpredictable intrinsic nature of river network evolution. Drainage pattern characteristics are predicted that match those observed in many foreland basins, such as the axial drainage, the distal location of the main river within the basin, and the formation of large, long‐lasting lacustrine systems. In areas where the river network is not well developed before the formation of the basin, these lithospheric flexural effects on drainage patterns may be enhanced by the role of the forebulge uplift as drainage divide. Inversely, fluvial transport modifies the flexural vertical movements differently than simpler transport models (e.g. diffusion): Rivers can drive erosion products far from a filled basin, amplifying the erosional rebound of both orogen and basin. The evolution of the sediment budget between orogen and basin is strongly dependent on this coupling between flexure and fluvial transport: Maximum sediment accumulations on the foreland are predicted for a narrow range of lithospheric elastic thickness between 15 and 40 km, coinciding with the Te values most commonly reported for foreland basins.
Digital rocks: linking forward modelling to carbonate facies
Authors: Boylan A. L. , Waltham D. A. , Bosence D. W. J. , Badenas B. , Aurell M.
Published: March 2003

Forward stratigraphic models usually display sediment types on simulated stratigraphic profiles as ‘facies’ defined only by their depth of deposition. More recently, ‘facies’ have been defined and displayed in terms of the dominant processes of deposition (e.g. in situ growth, pelagic production, turbidite deposition). Standard carbonate facies; that is, the Dunham classification, are defined by rock textures and grain composition that imply that a combination of processes acted together to generate a facies. For example, a bioclastic wackestone is a matrix‐supported rock containing up to 90% matrix and > 10% shelly grains. In terms of modelled processes, the muddy matrix could be generated by: (i) reworking of the shallow platform sediments, (ii) from pelagic deposition, or (iii) in situ production. A traditional depth of deposition process display would not be able to distinguish such a wackestone from any other facies deposited at this water depth and a majority process display would not combine reworked, pelagic muds and in situ contribution in one simulated ‘facies’. This paper introduces a new scheme that enables forward models to output simulated facies defined by a range of values for each of the controlling processes and thereby predicts rock textures within simulated stratigraphies. This approach has been applied to the Jurassic carbonate ramps of the Iberian Basin in northeastern Spain. It is shown to provide more accurate information about the processes that are being simulated, allowing more direct comparisons to be made with the facies observed in the field and providing potential for a more rigorous method for assessing the ‘goodness of fit’ of a simulated stratigraphy.