Abstract A transect of three holes drilled across the Blake Nose, western North Atlantic Ocean, retrieved cores of black shale facies related to the Albian Oceanic Anoxic Events (OAE) 1b and 1d. Sedimentary organic matter (SOM) recovered from Ocean Drilling Program Hole 1049A from the eastern end of the transect showed that before black shale facies deposition organic matter preservation was a Type III–IV SOM. Petrography reveals that this SOM is composed mostly of degraded algal debris, amorphous SOM and a minor component of Type III–IV terrestrial SOM, mostly detroinertinite. When black shale facies deposition commenced, the geochemical character of the SOM changed from a relatively oxygen-rich Type III–IV to relatively hydrogen-rich Type II. Petrography, biomarker and organic carbon isotopic data indicate marine and terrestrial SOM sources that do not appear to change during the transition from light-grey calcareous ooze to the black shale facies. Black shale subfacies layers alternate from laminated to homogeneous. Some of the laminated and the poorly laminated to homogeneous layers are organic carbon and hydrogen rich as well, suggesting that at least two SOM depositional processes are influencing the black shale facies. The laminated beds reflect deposition in a low sedimentation rate (6m Ma −1 ) environment with SOM derived mostly from gravity settling from the overlying water into sometimes dysoxic bottom water. The source of this high hydrogen content SOM is problematic because before black shale deposition, the marine SOM supplied to the site is geochemically a Type III–IV. A clue to the source of the H-rich SOM may be the interlayering of relatively homogeneous ooze layers that have a widely variable SOM content and quality. These relatively thick, sometimes subtly graded, sediment layers are thought to be deposited from a Type II SOM-enriched sediment suspension generated by turbidites or direct turbidite deposition.

Abstract The coal-bearing Early Permian succession of the Paraná Basin in southernmost Brazil is linked to a third-order depositional sequence, where the most important coals occur in the initial transgressive systems tract. In the Candiota area, the main coal zone consists of 17 seams, which were analyzed for petrographic properties (macerals, gelification index, tissue-preservation index, vitrinite reflectance). These results are compared to the high-resolution sequence-stratigraphic framework to enhance our understanding of the stratigraphic controls on coal formation, coal distribution, and coal quality, providing guidelines for optimal exploitation. The results show that local changes in accommodation trends and high sediment influx practically preclude coal formation in the lowstand and highstand systems tracts, whereas major coal development occurred in the transgressive systems tract. Seam distribution and thickness are controlled directly by flooding events, as depicted by the parasequences mapped in the study area. The main variations in thickness and extent occur at, or close to, the parasequence bounding surfaces. The most important coals, which are as much as 2.50 m in thickness, occur in the initial transgressive systems tract. Coal petrographic parameters suggest an overall drying-upward trend in the coal seams developed in the upper part of third-order sequence 2, with significant differences of coal properties relative to their stratigraphic position between and within the parasequences. Detailed petrographic analysis of seam subsections indicates a transgressive nature for the thick coal seams occurring in parasequence 4 (CCI and CCS seams). These are characterized by decreased vitrinite reflectance at the base and top of the coal seams. The high inertinite content of the overlying BL seam at the top of PS 4 suggests accumulation of the precursor peat in a regressive phase of the parasequence.

Abstract The organic-rich upper Lower Jurassic Da'anzhai Member (Ziliujing Formation) of the Sichuan Basin, China is the first stratigraphically well-constrained lacustrine succession associated with the Toarcian Oceanic Anoxic Event (T-OAE; c. 183 Ma). The expansion of the palaeo-Sichuan mega-lake, probably one of the most extensive freshwater systems to have existed on the planet, is marked by large-scale lacustrine organic productivity and carbon burial during the T-OAE, possibly owing to intensified hydrological cycling and nutrient supply. New molecular biomarker and organic petrographical analyses, combined with bulk organic and inorganic geochemical and palynological data, are presented here, providing insight into aquatic productivity, land-plant biodiversity and terrestrial ecosystem evolution in continental interiors during the T-OAE. We show that lacustrine algal growth during the T-OAE accounted for a significant organic-matter flux to the lakebed in the palaeo-Sichuan mega-lake. Lacustrine water-column stratification during the T-OAE facilitated the formation of dysoxic–anoxic conditions at the lake bottom, favouring organic-matter preservation and carbon sequestration into organic-rich black shales in the Sichuan Basin. We attribute the palaeo-Sichuan mega-lake expansion to enhanced hydrological cycling in a more vigorous monsoonal climate in the hinterland during the T-OAE greenhouse.

Abstract During the Late Permian (Zechstein), the Southern Permian Basin (SPB) of Europe was a shallow epicontinental and evaporitic sea surrounded by large continental masses. It has been assumed that both the cyclic Zechstein deposition and internal cyclicity of the lower Zechstein carbonate units resulted from glacio-eustatic fluxes of marine waters and evaporation in the stable arid climatic conditions. The Main Dolomite (Ca2) is the carbonate unit of the second Zechstein cycle. The Main Dolomite (MD) deposits formed the Kamień Pomorski carbonate platform, which was attached to land at the northern margin of the SPB (NW Poland). Study of stable carbon and oxygen isotopic composition and major and minor elements distribution reveal palaeoclimatic instability induced by a relative rise in precipitation during MD deposition. A tendency towards increased climatic humidity towards the end of the unit reflected by an increased fluvial contribution argues for either a local- and/or regional-scale of temporal flow of wet humid air masses. Chemical weathering and erosion on the nearby Fennoscandian High caused dilution of carbonate accumulation by very fine siliciclastics in the proximal part of the platform. A lack of internal cycles of a regional extent in the investigated platform implies that it was not global glacio-eustatic influxes but a combination of events, such as local relative sea-level fluctuations induced by climate impact and variation of the palaeoenvironmental parameters, that determined the development of the platform. Future research should investigate the effects of the climate and local tectonics to reveal the basinal dynamics and depositional history of the MD carbonate platforms.