Coupled stalagmite – Alluvial fan response to the 8.2 ka event and early Holocene palaeoclimate change in Greece

We explore the expression of early Holocene climatic change in the terrestrial Mediterranean of southern Greece. A regional palaeoclimate record from stable isotope and trace element geochemical proxies in an early Holocene (~12.4 ka to 6.7 ka) stalagmite is compared to the timing of palaeosol (entisol) development on an early Holocene alluvial fan located <100 km from the stalagmite site. Radiocarbon dated entisol development records fan abandonment surfaces, which can be coupled to the stalagmite climate signal. Variations in δ13C best record the main elements of palaeoclimatic change, more negative values indicating soil carbon input to karst groundwater under wetter conditions. The wettest conditions begin around 10.3 ka, coincident with the start of sapropel 1 deposition in the eastern Mediterranean. The widely documented northern hemisphere ‘8.2 ka event’ of cooler and drier conditions has a muted δ18O climatic signal in common with other stalagmite climate records from the wider Mediterranean. However, less negative δ13C values do record a period of episodic dryness between ~8.8 and ending at 8.2 ka. Wetter conditions re-established after 8.1 ka to the end of the record. The oldest alluvial fan entisols were developing by ~9.5 ka, and a prominent rubified entisol developed ~8.3 to 8.4 ka, indicating pedogenesis within dating error of the 8.2 ka event. The speleothem record of episodic dryness between ~8.8 and 8.2 ka, combined with other regional proxies, is consistent with the notion that precipitation patterns in Greece may have changed from predominantly winter frontal to summer convective during this period. Palaeosol formation on the alluvial fan may have been an allocyclic response to this change. It is plausible that fan-channel incision, driven by temporary development of a ‘flashier’ summer rainfall regime, isolated large areas of the fan surface allowing onset of prolonged pedogenesis there

Contourite depositional system after the exit of a strait: Case study from the late Miocene South Rifian Corridor, Morocco

Idealized facies of bottom current deposits (contourites) have been established for fine-grained contourite drifts in modern deep-marine sedimentary environments. Their equivalent facies in the ancient record however are only scarcely recognized due to the weathered nature of most fine-grained deposits in outcrop. Facies related to the erosional elements (i.e. contourite channels) of contourite depositional systems have not yet been properly established and related deposits in outcrop appear non-existent. To better understand the sedimentary facies and facies sequences of contourites, the upper Miocene contourite depositional systems of the South Rifian Corridor (Morocco) is investigated. This contourite depositional system formed by the dense palaeo-Mediterranean Outflow Water. Foraminifera assemblages were used for age-constraints (7.51 to 7.35 Ma) and to determine the continental slope depositional domains. Nine sedimentary facies have been recognized based on lithology, grain-size, sedimentary structures and biogenic structures. These facies were subsequently grouped into five facies associations related to the main interpreted depositional processes (hemipelagic settling, contour currents and gravity flows). The vertical sedimentary facies succession records the tectonically induced, southward migration of the contourite depositional systems and the intermittent behaviour of the palaeo-Mediterranean Outflow Water, which is mainly driven by precession and millennial-scale climate variations. Tides substantially modulated the palaeo-Mediterranean Outflow Water on a sub-annual scale. This work shows exceptional examples of muddy and sandy contourite deposits in outcrop by which a facies distribution model from the proximal continental slope, the contourite channel to its adjacent contourite drift, is proposed. This model serves as a reference for contourite recognition both in modern environments and the ancient record. Furthermore, by establishing the hydrodynamics of overflow behaviour a framework is provided that improves process-based interpretation of deep-water bottom current deposits

The Cholecystectomy As A Day Case (CAAD) Score: A Validated Score of Preoperative Predictors of Successful Day-Case Cholecystectomy Using the CholeS Data Set

Background Day-case surgery is associated with significant patient and cost benefits. However, only 43% of cholecystectomy patients are discharged home the same day. One hypothesis is day-case cholecystectomy rates, defined as patients discharged the same day as their operation, may be improved by better assessment of patients using standard preoperative variables. Methods Data were extracted from a prospectively collected data set of cholecystectomy patients from 166 UK and Irish hospitals (CholeS). Cholecystectomies performed as elective procedures were divided into main (75%) and validation (25%) data sets. Preoperative predictors were identified, and a risk score of failed day case was devised using multivariate logistic regression. Receiver operating curve analysis was used to validate the score in the validation data set. Results Of the 7426 elective cholecystectomies performed, 49% of these were discharged home the same day. Same-day discharge following cholecystectomy was less likely with older patients (OR 0.18, 95% CI 0.15–0.23), higher ASA scores (OR 0.19, 95% CI 0.15–0.23), complicated cholelithiasis (OR 0.38, 95% CI 0.31 to 0.48), male gender (OR 0.66, 95% CI 0.58–0.74), previous acute gallstone-related admissions (OR 0.54, 95% CI 0.48–0.60) and preoperative endoscopic intervention (OR 0.40, 95% CI 0.34–0.47). The CAAD score was developed using these variables. When applied to the validation subgroup, a CAAD score of ≤5 was associated with 80.8% successful day-case cholecystectomy compared with 19.2% associated with a CAAD score >5 (p < 0.001). Conclusions The CAAD score which utilises data readily available from clinic letters and electronic sources can predict same-day discharges following cholecystectomy

Testing rival tectonic uplift models for the Lechaion Gulf in the Gulf of Corinth rift

The Gulf of Corinth, central Greece, is a rapidly extending continental rift, the eastern part of which bifurcates into the active northern Alkyonides Gulf and the southern Lechaion Gulf. The Lechaion Gulf is considered an inactive relict of early rifting, yet the presence of late Quaternary shorelines is evidence of continuing uplift of the north, east and south margins of this basin. Models to explain uplift include uplift on the footwall of the southern Alkyonides Gulf fault system and the Xylocastro-Perachora faults or 'regional'isostatic uplift independent of fault slip. These models are tested by comparing predicted spatial uplift trends with those observed. Uplift rates since Marine Isotope Stage 7 of 0.31 ±0.04 mm a-1 on the Lechaion Gulf north coast are explained as displacement on the footwall of active faults. However, the south coast uplift cannot be explained by footwall uplift and is evidence for isostatic uplift that probably affects the whole of the southern Gulf of Corinth rift. Isostatic uplift rates of 0.22±0.01 mm a-1 at the Corinth canal increase westward towards the mouth of the Lechaion Gulf where it meets the modern rift, the Gulf of Corinth. © 2010 Geological Society of London

Fault architecture, basin structure and evolution of the Gulf of Corinth Rift, central Greece

The style of extension and strain distribution during the early stages of intra-continental rifting is important for understanding rift-margin development and can provide constraints for lithospheric deformation mechanisms. The Corinth rift in central Greece is one of the few rifts to have experienced a short extensional history without subsequent overprinting. We synthesise existing seismic reflection data throughout the active offshore Gulf of Corinth Basin to investigate fault activity history and the spatio-temporal evolution of the basin, producing for the first time basement depth and syn-rift sediment isopachs throughout the offshore rift. A major basin-wide unconformity surface with an age estimated from sea-level cycles at ca. 0.4Ma separates distinct seismic stratigraphic units. Assuming that sedimentation rates are on average consistent, the present rift formed at 1^2Ma, with no clear evidence for along-strike propagation of the rift axis. The rift has undergone major changes in relative fault activity and basin geometry during its short history. The basement depth is greatest in the central rift (maximum 3 km) and decreases to the east and west. In detail however, two separated depocentres 20^50 km long were created controlled by N- and S-dipping faults before 0.4Ma, while since ca. 0.4Ma a single depocentre (80 km long) has been controlled by several connected N-dipping faults, with maximum subsidence focused between the two older depocentres. Thus isolated but nearby faults can persist for timescales ca.1Ma and form major basins before becoming linked. There is a general evolution towards a dominance of N-dipping faults; however, in the western Gulf strain is distributed across several active N- and S-dipping faults throughout rift history, producing a more complex basin geometry

Uranium-thorium dating potential of the marine bivalve Lithophaga lithophaga

Poor chronological control hampers efforts to constrain uplift event frequency in the Eastern Mediterranean Basin and develop regional tectonic models. Borings of the colonial marine mollusc Lithophaga lithophaga are commonly associated with uplifted Mediterranean shorelines and the suitability of its fossil shell for uranium-series dating is investigated to assess its potential for refining uplift chronologies. Living specimens contain very little uranium but Holocene fossils suggest rapid post-mortem uptake from a marine source. However, in common with many other mollusc species, Pleistocene samples show clear evidence of subsequent exchange with uranium from groundwater and although two out of eight samples returned ages compatible with their stratigraphic locations, these may be chance results given the compelling evidence for general open system behaviour. Detrital contamination appears not to be a significant problem in pre-Holocene samples. Open system modelling, using techniques developed to correct for alpha recoil effects in reef corals, shows that the recoil mechanism is inadequate to explain the magnitude of the isotopic alterations observed. Our results show that whilst uranium-series dating of Holocene L. lithophaga shells may be possible, Pleistocene specimens suffer from significant geochemical alteration and cannot be used to refine crustal uplift chronologies over longer timescales

Corinth Rift margin uplift: new evidence from Late Quaternary marine shorelines

New evidence for uplift of the southern margin to the Corinth rift, one of the world's most rapidly extending continental regions, defines an area of uniform uplift separating a more rapidly uplifting western rift flank from a slowly backtilting eastern flank. This major tectonic boundary coincides with geophysical evidence for a junction between flat underlying subducted oceanic plate and steep subduction. We propose that trench rollback by the Anatolian plate over the subducting African plate has led to differential uplift and possible migration of active faulting at the southern rift margin in the last few million years