Decadal-centennial-scale solar-linked climate variations and millennial-scale internal oscillations during the Early Cretaceous.

Understanding climate variability and stability under extremely warm 'greenhouse' conditions in the past is essential for future climate predictions. However, information on millennial-scale (and shorter) climate variability during such periods is scarce, owing to a lack of suitable high-resolution, deep-time archives. Here we present a continuous record of decadal- to orbital-scale continental climate variability from annually laminated lacustrine deposits formed during the late Early Cretaceous (123-120 Ma: late Barremian-early Aptian) in southeastern Mongolia. Inter-annual changes in lake algal productivity for a 1091-year interval reveal a pronounced solar influence on decadal- to centennial-scale climatic variations (including the ~ 11-year Schwabe cycle). Decadally-resolved Ca/Ti ratios (proxy for evaporation/precipitation changes) for a ~ 355-kyr long interval further indicate millennial-scale (~ 1000-2000-yr) extreme drought events in inner-continental areas of mid-latitude palaeo-Asia during the Cretaceous. Millennial-scale oscillations in Ca/Ti ratio show distinct amplitude modulation (AM) induced by the precession, obliquity and short eccentricity cycles. Similar millennial-scale AM by Milankovitch cycle band was also previously observed in the abrupt climatic oscillations (known as Dansgaard-Oeschger events) in the 'intermediate glacial' state of the late Pleistocene, and in their potential analogues in the Jurassic 'greenhouse'. Our findings indicate that external solar activity forcing was effective on decadal-centennial timescales, whilst the millennial-scale variations were likely amplified by internal process such as changes in deep-water formation strength, even during the Cretaceous 'greenhouse' period.

Syngenetic rapid growth of ellipsoidal silica concretions with bitumen cores.

Isolated silica concretions in calcareous sediments have unique shapes and distinct sharp boundaries and are considered to form by diagenesis of biogenic siliceous grains. However, the details and rates of syngenetic formation of these spherical concretions are still not fully clear. Here we present a model for concretion growth by diffusion, with chemical buffering involving decomposition of organic matter leading to a pH change in the pore-water and preservation of residual bitumen cores in the concretions. The model is compatible with some pervasive silica precipitation. Based on the observed elemental distributions, C, N, S, bulk carbon isotope and carbon preference index (CPI) measurements of the silica-enriched concretions, bitumen cores and surrounding calcareous rocks, the rate of diffusive concretion growth during early diagenesis is shown using a diffusion-growth diagram. This approach reveals that ellipsoidal SiO2 concretions with a diameter of a few cm formed rapidly and the precipitated silica preserved the bitumen cores. Our work provides a generalized chemical buffering model involving organic matter that can explain the rapid syngenetic growth of other types of silica accumulation in calcareous sediments.

Early post-mortem formation of carbonate concretions around tusk-shells over week-month timescales.

Carbonate concretions occur in sedimentary rocks of widely varying geological ages throughout the world. Many of these concretions are isolated spheres, centered on fossils. The formation of such concretions has been variously explained by diffusion of inorganic carbon and organic matter in buried marine sediments. However, details of the syn-depositional chemical processes by which the isolated spherical shape developed and the associated carbon sources are little known. Here we present evidence that spherical carbonate concretions (diameters φ : 14 ~ 37 mm) around tusk-shells (Fissidentalium spp.) were formed within weeks or months following death of the organism by the seepage of fatty acid from decaying soft body tissues. Characteristic concentrations of carbonate around the mouth of a tusk-shell reveal very rapid formation during the decay of organic matter from the tusk-shell. Available observations and geochemical evidence have enabled us to construct a 'Diffusion-growth rate cross-plot' that can be used to estimate the growth rate of all kinds of isolated spherical carbonate concretions identified in marine formations. Results shown here suggest that isolated spherical concretions that are not associated with fossils might also be formed from carbon sourced in the decaying soft body tissues of non-skeletal organisms with otherwise low preservation potential.

Primary prevention of cardiovascular disease with pravastatin in Japan (MEGA Study): a prospective randomised controlled trial.

BACKGROUND: Evidence-based treatment for hypercholesterolaemia in Japan has been hindered by the lack of direct evidence in this population. Our aim was to assess whether evidence for treatment with statins derived from western populations can be extrapolated to the Japanese population. METHODS: In this prospective, randomised, open-labelled, blinded study, patients with hypercholesterolaemia (total cholesterol 5.69-6.98 mmol/L) and no history of coronary heart disease or stroke were randomly assigned diet or diet plus 10-20 mg pravastatin daily. The primary endpoint was the first occurrence of coronary heart disease. Statistical analyses were done by intention to treat. This trial is registered at ClinicalTrials.gov, number NCT00211705. FINDINGS: 3966 patients were randomly assigned to the diet group and 3866 to the diet plus pravastatin group. Mean follow-up was 5.3 years. At the end of study, 471 and 522 patients had withdrawn, died, or been lost to follow-up in the diet and diet plus pravastatin groups, respectively. Mean total cholesterol was reduced by 2.1% (from 6.27 mmol/L to 6.13 mmol/L) and 11.5% (from 6.27 mmol/L to 5.55 mmol/L) and mean LDL cholesterol by 3.2% (from 4.05 mmol/L to 3.90 mmol/L) and 18.0% (from 4.05 mmol/L to 3.31 mmol/L) in the diet and the diet plus pravastatin groups, respectively. Coronary heart disease was significantly lower in the diet plus pravastatin group than in the diet alone group (66 events vs 101 events; HR 0.67, 95% CI 0.49-0.91; p=0.01). There was no difference in the incidence of malignant neoplasms or other serious adverse events between the two groups. INTERPRETATION: Treatment with a low dose of pravastatin reduces the risk of coronary heart disease in Japan by much the same amount as higher doses have shown in Europe and the USA.