Evolution of diagenetic conditions and burial history in Buntsandstein Gp. fractured sandstones (Upper Rhine Graben) from in-situ δ¹⁸O of quartz and ⁴⁰Ar/³⁹Ar geochronology of K-feldspar overgrowths

In-situ δ¹⁸O measured in the quartz overgrowths help identify temperature and fluid origin variations responsible for cementation of the pore network (matrix and fracture) in the Buntsandstein Gp. sandstone reservoirs within the Upper Rhine Graben. The overgrowths record two types of the evolution of δ¹⁸O: 1) a monotonous decrease of the δ¹⁸Oovergrowth interpreted as linked to an increasing burial temperature and 2) random fluctuations, interpreted as pointing out the injection of allochthonous fluids in faulted areas, on the cementation processes of the pore network (both intergranular and fracture planes). Fluids causing the quartz cementation are either autochthonous buffered in ¹⁸O from clay illitisation; or allochthonous fluids of meteoric origin with δ¹⁸O below − 5%. These allochthonous fluids are in thermal disequilibrium with the host sandstone. The measured signal of δ¹⁸Oovergrowth measured from samples and calculated curves testing hypothetic δ¹⁸Ofluid are compared to T–t evolution during burial. This modelling proposes the initiation of quartz cementation during the Jurassic and is validated by the in-situ ⁴⁰Ar/³⁹Ar dating results obtained on the feldspar overgrowths predating quartz overgrowths. A similar diagenetic history is recorded on the graben shoulders and in the buried parts of the basin. Here, the beginning of the pore network cementation predates the structuration in blocks of the basin before the Cenozoic graben opening

Late Pleistocene and Holocene environmental history of northeastern Geographical Society Ø, East Greenland, inferred from Loon Lakes sediment record

A sediment sequence from Loon Lake, Geographical Society Ø, East Greenland, was geophysically, sedimentologically, biogeochemically, and biologically investigated in order to reconstruct the entire history of the lake. The chronology of the 10.25 m long sequence is based on three AMS 14C dating performed on marine fossils. In the basal part of the sedimentary record a diamicton represents the deposition during the Last Glacial Maximum. Subsequent to deglaciation at c. 10,250 cal. yr BP Loon Lake area was inundated by the sea and marine sediments were deposited. A turbidite interspersed into the marine sediments at around 8300 cal. yr BP could be a result of the Storegga Tsunami or of increased meltwater supply after the 8.2 kyr BP cooling event. Marine sedimentation continued at least until c. 7500 cal. yr BP, when the isostatic rebound terminated this state. Full limnic conditions became established at c. 6000 cal. yr BP. Compared with other studies in this area such a late isolation is presumably a result of the delayed retreat of the fjord-filling outlet glacier in the Kejser Franz Josephs Fjord. The climate history documented in the Loon Lake sediments is widely masked by the sea-level history

Late Pleistocene to early Holocene environmental changes on Store Koldewey, coastal north-east Greenland

A lake sediment sequence from southern Store Koldewey, north-east Greenland, has been investigated using a multidisciplinary approach, including geophysical, geochemical, biogeochemical, biological and sedimentological methods. Chronological constraints are provided by accelerator mass spectrometry (AMS) C-14 dating of bulk sediment and complemented with published water moss ages. The record consists of three major sediment units. Their individual structural, textural, geophysical and geochemical characteristics indicate variable input of sediment and meltwater due to variable proximity of the ice margin and therefore reflect the growth and decay of a local glacier during the late Weichselian. Radiocarbon dating of bulk sediment samples from the lowermost unit gave ages of 42 to 34 calibrated thousand years (cal Ky B.P.) and indicates that this material is redeposited in the lake basin during or after the ice advance at the end of the Pleistocene. Increased meltwater and sediment input from a retreating ice margin following the Younger Dryas is indicated by the occurrence of a sandy to gravely section. Fine-grained and laminated sediments were deposited during the Pleistocene-Holocene transition and indicate calm sedimentation conditions with an ice margin outside of the lake catchment. The reoccurrence of coarse sediments during the early Holocene may indicate increased meltwater input in response to the cold spell at about 9.3 Kya with increased snow accumulation rather than fluctuations of local glaciers. The dating results furthermore show that AMS C-14 dating of bulk sediment samples deposited during glacier decay in High Arctic environments can give problematic ages