Controls on tidal sedimentation and preservation : Insights from numerical tidal modelling in the Late Oligocene–Miocene South China Sea, Southeast Asia

Numerical tidal modelling, when integrated with other geological datasets, can significantly inform the analysis of physical sedimentation processes and the depositional and preservational record of ancient tide-influenced shoreline–shelf systems. This is illustrated in the Oligo–Miocene of the South China Sea (SCS), which experienced significant changes in basin physiography and where tide-influenced, shoreline–shelf deposition is preserved in ca 10 sub-basins. Palaeogeographic reconstructions, palaeotidal modelling and regional sedimentary facies analysis have been integrated in order to evaluate the spatial–temporal evolution and physiographic controls on tidal sedimentation and preservation during the ca 25 Myr Oligo–Miocene record in the SCS. Palaeotidal modelling, using an astronomically forced and global tidal model (Fluidity) at a maximum 10 km resolution, indicates that spring tides along Late Oligocene–Middle Miocene coastlines were predominantly mesotidal– macrotidal and capable of transporting sand, which reflects two main conditions: (1) increased tidal inflow through wider ocean connections to the Pacific Ocean; and (2) tidal amplification resulting from constriction of the tidal wave in a ‘blind gulf’ type of basin morphology. Since the Middle–Late Miocene, a reduction in the amplitude and strength of tides in the SCS was mainly due to diminishing tidal inflow from the Pacific Ocean caused by the northward movement of the Philippines and Izu-Bonin-Mariana arc. Sensitivity tests to palaeogeographic and palaeobathymetric uncertainty indicate that regional–scale (100–1000s 29 km) palaeogeographic changes influencing tidal inflow versus outflow can override local30 scale (1–100s km) changes to tidal resonance and convergence effects (funnelling and shoaling), such as shelf width and shoreline geometry. Palaeotidal model results compare favourably to the distribution and sedimentary fabric of Oligo–Miocene, tide-influenced, shoreline–shelf successions in peripheral SCS basins. However, the preservation potential of tidal deposits is lower in open coastline environments, probably due to enhanced reworking during storms and river floods

Tectonic evolution of the Malay and Penyu Basins, offshore Peninsular Malaysia

The Malay and Penya Basins, offshore Peninsular Malaysia, were formed during the early Oligocene as a result of regional dextral shear deformation caused by the indentation of India into Eurasia in the early Tertiary. Pre-existing basement inhomogeneities exerted a strong control on basin development. The Penyu Basin developed, initially, as isolated grabens and half-grabens at basement fault intersections, in response to roughly N-S extension. The major structures which include low-angle listric normal faults, pull-apart rhomb grabens and flower structures, suggest that "thin-skinned" crustal extension and strike-slip tectonics have played an important role in basin evolution.Basement faults in the Malay Basin are oblique (E-W trending) to the basin trend (NW-trending). The Basin developed by transtension of NW-trending sinistral shear zone, in which fault-bounded blocks rotate in response to the shear deformation, producing a series of E-trending half-graben depocentres. The Basins were subjected to transpressive inversion during the middle-late Miocene, as a result of rotation of the regional stress field, caused by progressive indentation of India into Eurasia.Subsidence analysis suggests that lithospheric stretching was the dominant process of basin formation. The high heat flows (85-100 mW m⁻²) are consistent with stretching factors, β, of 1.2 to 4.3. In the Malay Basin, uplift of the basin flanks preceeded subsidence during the rifting phase as a result of non-uniform stretching and lateral heat flow from the centre of the Basin. Both basins are undercompensated isostatically and characterised by low negative free-air gravity anomaly in the order of -20 mGal. Undercompensation suggests that the basins were formed, partly, by "thin-skinned" crustal extension which did not involve stretching of the subcrustal lithosphere

Tectonic evolution of the Malay and Penyu Basins, offshore Peninsular Malaysia

The Malay and Penya Basins, offshore Peninsular Malaysia, were formed during the early Oligocene as a result of regional dextral shear deformation caused by the indentation of India into Eurasia in the early Tertiary. Pre-existing basement inhomogeneities exerted a strong control on basin development. The Penyu Basin developed, initially, as isolated grabens and half-grabens at basement fault intersections, in response to roughly N-S extension. The major structures which include low-angle listric normal faults, pull-apart rhomb grabens and flower structures, suggest that "thin-skinned" crustal extension and strike-slip tectonics have played an important role in basin evolution.Basement faults in the Malay Basin are oblique (E-W trending) to the basin trend (NW-trending). The Basin developed by transtension of NW-trending sinistral shear zone, in which fault-bounded blocks rotate in response to the shear deformation, producing a series of E-trending half-graben depocentres. The Basins were subjected to transpressive inversion during the middle-late Miocene, as a result of rotation of the regional stress field, caused by progressive indentation of India into Eurasia.Subsidence analysis suggests that lithospheric stretching was the dominant process of basin formation. The high heat flows (85-100 mW m⁻²) are consistent with stretching factors, β, of 1.2 to 4.3. In the Malay Basin, uplift of the basin flanks preceeded subsidence during the rifting phase as a result of non-uniform stretching and lateral heat flow from the centre of the Basin. Both basins are undercompensated isostatically and characterised by low negative free-air gravity anomaly in the order of -20 mGal. Undercompensation suggests that the basins were formed, partly, by "thin-skinned" crustal extension which did not involve stretching of the subcrustal lithosphere.</p

Quality-assurance of heat-flow data: The new structure and evaluation scheme of the IHFC Global Heat Flow Database

Since 1963, the International Heat Flow Commission has been fostering the compilation of the Global Heat Flow Database to provide reliable heat-flow data. Over time, techniques and methodologies evolved, calling for a reorganization of the database structure and for a reassessment of stored heat-flow data. Here, we provide the results of a collaborative, community-driven approach to set-up a new, quality-approved global heat-flow database. We present background information on how heat-flow is determined and how this important thermal parameter could be systematically evaluated. The latter requires appropriate documentation of metadata to allow the application of a consistent evaluation scheme. The knowledge of basic data (name and coordinates of the site, depth range of temperature measurements, etc.), details on temperature and thermal-conductivity data and possible perturbing effects need to be given. The proposed heat-flow quality evaluation scheme can discriminate between different quality aspects affecting heat flow: numerical uncertainties, methodological uncertainties, and environmental effects. The resulting quality codes allow the evaluation of every stored heat-flow data entry. If mandatory basic data are missing, the entry is marked accordingly. In cases where more than one heat-flow determination is presented for one specific site, and all of them are considered for the site, the poorest evaluation score is inherited to the site level. The required data and the proposed scheme are presented in this paper. Due to the requirements of the newly developed evaluation scheme, the database structure as presented in 2021 has been updated and is available in the appendix of this paper. The new quality scheme will allow a comprehensible evaluation of the stored heat-flow data for the first time

Evaluation of a quality improvement intervention to reduce anastomotic leak following right colectomy (EAGLE): pragmatic, batched stepped-wedge, cluster-randomized trial in 64 countries

Background Anastomotic leak affects 8 per cent of patients after right colectomy with a 10-fold increased risk of postoperative death. The EAGLE study aimed to develop and test whether an international, standardized quality improvement intervention could reduce anastomotic leaks. Methods The internationally intended protocol, iteratively co-developed by a multistage Delphi process, comprised an online educational module introducing risk stratification, an intraoperative checklist, and harmonized surgical techniques. Clusters (hospital teams) were randomized to one of three arms with varied sequences of intervention/data collection by a derived stepped-wedge batch design (at least 18 hospital teams per batch). Patients were blinded to the study allocation. Low- and middle-income country enrolment was encouraged. The primary outcome (assessed by intention to treat) was anastomotic leak rate, and subgroup analyses by module completion (at least 80 per cent of surgeons, high engagement; less than 50 per cent, low engagement) were preplanned. Results A total 355 hospital teams registered, with 332 from 64 countries (39.2 per cent low and middle income) included in the final analysis. The online modules were completed by half of the surgeons (2143 of 4411). The primary analysis included 3039 of the 3268 patients recruited (206 patients had no anastomosis and 23 were lost to follow-up), with anastomotic leaks arising before and after the intervention in 10.1 and 9.6 per cent respectively (adjusted OR 0.87, 95 per cent c.i. 0.59 to 1.30; P = 0.498). The proportion of surgeons completing the educational modules was an influence: the leak rate decreased from 12.2 per cent (61 of 500) before intervention to 5.1 per cent (24 of 473) after intervention in high-engagement centres (adjusted OR 0.36, 0.20 to 0.64; P &lt; 0.001), but this was not observed in low-engagement hospitals (8.3 per cent (59 of 714) and 13.8 per cent (61 of 443) respectively; adjusted OR 2.09, 1.31 to 3.31). Conclusion Completion of globally available digital training by engaged teams can alter anastomotic leak rates. Registration number: NCT04270721 (http://www.clinicaltrials.gov)