Abstract The late Varican intermontane Saar-Nahe Basin underwent an intensive episode of synsedimentary intra-basinal magmatism, with magmas ranging from tholeiitic basalts to rhyolites. Volcanism began late in the sedimentary history of the basin, after accumulation of about 5000–5500 m of continental sediments. Basic to silicic maar-diatremes formed mostly on hydraulically active faults or fault intersections. Basic to intermediate sills were emplaced at depths between about 2500 m and almost the original surface. Some sills inflated considerably in thickness. Silicic laccoliths intruded in the same depth range. Ongoing volume inflation of some laccoliths led to huge intrusive-extrusive domes, rock falls and probably block-and-ash flows and even to extensive thick lava extrusions. Some domes are composite or show evidence for magma mingling. In the Baumholder-Idar-Oberstein area, lava flows reach a cumulative thickness of 800–1000 m. Outside this thick lava pile, flows are concentrated in several thinner series. Basic to intermediate lava flows were frequently inflated to a thickness of up to 40 metres and were emplaced like thick flood basalts. Silicic tephra deposits are widespread and mostly phreatomagmatic in origin. The specific formation of maar-diatremes, sills, laccoliths and most tephra deposits is related to the uppermost 1500 to about 2500 m of the continental sediments of the basin fill. During volcanism and subvolcanism, these sediments were largely unconsolidated and water-saturated, and thus this soft sediment environment influenced very specifically the emplacement of the magmas in the basin. Inflation of laccoliths in this environment caused slumping and washing away of the updomed unconsolidated roof sediments. Consequently, the effective initial overburden decreased with time by this particular process of unroofing, and, upon further inflation, larger inflating intrusive domes became extrusive.

Abstract In the Saar-Nahe Basin, at the turn of Carboniferous to Permian, lacustrine organic matter-rich mudstone (paper shales), algal limestone (biostromes and bioherms), and deltaic sandstone accumulated in lakes, ponds, and flood basins under a tropical climate. Lakes were probably interconnected frequently by lowland meandering rivers to form more or less continuous waterways with rich plant and animal life. The paper shales provide key insights into paleoclimatic conditions and their relation to sediment supply in this fluvial-lacustrine system. Lamination was formed by varying input of suspended sediment to the lakes of equatorial Central Europe. During the wet season (summer), silt-rich suspensions were swept out into the lakes, driven by heavy rainfall after depositing coarser grained sediment at the lake margin. During the dry season (winter), floods were infrequent, and siliciclastic suspension input to the lakes was minimal. During the entire year, the biological production that formed organic matter-rich dark clay layers of the laminites was more or less constant. This seasonality of clastic input resulted in a variable thickness of intervals of delicate light/dark laminite couplets that are attributed to storm or flood events (weather-bedded). These strata demonstrate that hydrocarbon reservoir and source-prone lithofacies can accumulate in relatively close proximity. In this system, shales with significant amounts of organic matter are genetically related to profundal limestones as well as to algal bioherms and biostromes forming in the same lake or pond. Interbedded organic matter-lean siltstone resulted from the same floods that carried coarse clastics from rivers into flood-plain ponds and lakes, forming lacustrine deltas. The fine-grained strata can be quite useful for understanding the distribution of hydrocarbon play elements as they contain a relatively complete record of depositional conditions that is integrated across the entire alluvial landscape.