Radioisotopic dating of volcanic minerals is a powerful method for establishing absolute time constraints in sedimentary basins, which improves our understanding of the chronostratigraphy and evolution of basin processes. The relative plate motions of Greenland, North America, and Eurasia changed several times during the Palaeogene. However, the timing of a key part of this sequence, namely the initiation of compression between Greenland and Svalbard, is currently poorly constrained. The formation of the Central Basin in Spitsbergen is inherently linked to changes in regional plate motions, so an improved chronostratigraphy of the sedimentary sequence is warranted. Here we present U-Pb zircon dates from tephra layers close to the basal unconformity, which yield a weighted-mean 206Pb/238U age of 61.596 ± 0.028 Ma (2σ). We calculate that sustained sedimentation began at ~61.8 Ma in the eastern Central Basin based on a sediment accumulation rate of 71.6 ± 7.6 m/Myr. The timing of basin formation is broadly coeval with depositional changes at the Danian-Selandian boundary around the other margins of Greenland, including the North Sea, implying a common tectonic driving force. Furthermore, these stratigraphic tie points place age constraints on regional plate reorganization events, such as the onset of seafloor spreading in the Labrador Sea.

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The timing and character of coarse siliciclastic sediment delivered to deep-water environments in active rift basins is governed by the complicated interactions of tectonics, climate, eustasy, hinterland geology, and shelf process regime. The stratigraphic archives of deep-water syn-rift basin-fills provide records of palaeoenvironmental changes (e.g. climate and vegetation) in onshore catchments, particularly where they are connected by narrow shelves. However, a chronostratigraphically constrained record of climatic fluctuations and process responses in the hinterland source area recorded in deep-water deposits is rare. Here, we integrate a fully cored research borehole with outcrop exposures of deep-water syn-rift stratigraphy to reconstruct palaeoenvironmental change within the stratigraphy of the West Xylokastro Fault Block in the Corinth Rift, Greece. We used palaeomagnetic and palynological analyses from borehole core samples to develop a chronostratigraphic and palaeoenvironmental model, which we compare to global records of Early-Mid Pleistocene climate and eustatic change. This framework allows establishment of a chronostratigraphic and palaeoenvironmental context to stratigraphic variability encountered in outcrop and in the borehole. Our results show that the ∼240 m thick studied succession was deposited from ∼1.1 to 0.6 Ma across the Early-to Mid-Pleistocene transition. During the Early Pleistocene, obliquity-paced climatic variability is largely coherent with vegetation changes of forest coverage within catchments on the southern margin of the Corinth Rift. Large magnitude, eccentricity-paced cyclicity dominant after the Mid-Pleistocene Transition can alter sediment supply from onshore catchments during the warming stages of severe interglacials where expansion of forest cover may trap sediment within catchments. Conglomeratic grade sediment delivery to the deep-water is enhanced during glacial periods, interpreted to reflect sparse forest cover and large winter storms, and during semi-arid, grassland-dominated interglacial highstands during severe interglacials. Base-level rise during minor interglacials is easily outpaced by high sediment supply and is seldom represented stratigraphically. The study demonstrates the value of integrated palynological and sedimentological studies, whilst applying a conservative approach to interpretation when dealing with sparse palynological records from proximal deep-water stratigraphy. The case study provides conceptual models where climatic and vegetation changes can begin to be incorporated as a key control on sediment flux from onshore drainage basins to deep-water syn-rift successions.

<p>The sedimentary record of deep-water lakes is often used to investigate past climate and environmental change. Correct identification however, of the main controls driving the production and transport of sediment to the deepest parts of tectonically active basins is often challenging, especially when trying to differentiate autogenic from allogenic factors. This study focuses on the changes observed in a deep-water sedimentary system that evolved from mudstone-dominated to the development of a lacustrine sand-dominated channel-lobe distributary fan and back to mudstone deposition during the Pliocene climatic optimum in the Corinth Rift, Greece. This is a multidisciplinary study that involves the integration of sedimentology and structural geology with digital outcrop modelling, palynology, palaeomagnetology and geochronology.</p> <p>The studied sedimentary system consisted of a coarse-grained delta (Mavro delta) that fed the deep-water Rethi Dendro Formation (RDF) in the Amphithea fault block during the Pliocene and Early Pleistocene. These syn-rift deposits were sourced from a major hinterland catchment, the Olvios catchment, draining the southern, fault-controlled margin of the rift. The depocentre was located at the exit of a structurally controlled sediment fairway, ~15 km from the source of sediment and ~12 km basinwards from the basin margin coastline. The stratigraphy of the RDF in the study area is well constrained due to the combination of detailed surface mapping and logging with LiDAR, photogrammetry and UAV surveys of large-scale exposures in the Sythas river valley. These were integrated with the information obtained from the analysis of rock cores obtained through wells drilled immediately behind the cliffs where the RDF is exposed. The Amphithea fault block has a half-graben configuration and tilting of the hangingwall was one of the main tectonic controls on the evolution of the depocenter fill. The stratigraphic interval considered in this study is ~130 m thick. It was deposited above a ~6° angular unconformity and it is composed predominantly of fine-grained hemipelagic dominated units, interrupted by the development of an ~30 m thick sandstone-dominated channelized lobe unit. Detailed palynological analysis of this interval shows significant changes in pollen and spore assemblages that are used to interpret the palaeoflora developed in the drainage catchments. The palynoflora in fine-grained hemipelagic intervals is dominated by temperate forests mixed with subtropical elements, whereas the channelized lobe unit is dominated by palynofloras typical of open herbaceous vegetation including steppic taxa, suggesting a dryer and cooler climate. The shift from forest- to herbaceous-dominated palynological assemblages is gradual, recorded from 5 m below the facies change marking the base of the channelized lobe unit.  In contrast, the top of the channelized lobe unit coincides with the abrupt change back to the forest-dominated pollen assemblage. The correlation between the establishment of a sand-dominated channel-lobe distributary fan in the basin floor with the predominance of open herbaceous vegetation is interpreted to reflect the highly erodible condition of land covered in this type of vegetation. In contrast, during periods when forests are dominant, erodibility decreases.</p>