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

Abstract

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.

Fracture evaluation of the plutonic basement in the Upper Magdalena Basin: Implications for the development of naturally fractured reservoirs in the Northern Andes

“…This property can be closely linked to the high fracture intensity and high number of fracture sets with different orientations, formed during their polyphasic deformation history, increasing the possibility of forming Y and X nodes, as well as C‐C branches and a C B values over 1.5 (Sanderson & Nixon, 2015, 2018). These results are comparable with those of previous studies on another crystalline basement (e.g., Bossennec et al, 2021; Le Garzic et al, 2011; McCaffrey et al, 2020).…”

“…Four shade maps were produced using four illumination directions (0°, 45°, 90° and 315°) in the study area, which included the La Plata Granite and Páez Massif. Valleys and crests were extracted from each of the four shade maps (e.g., Bossennec et al, 2021; Celestino et al, 2020; Cianfarra & Salvini, 2015; Wise et al, 1985; Figure 3a).…”

“…another crystalline basement (e.g., Bossennec et al, 2021;Le Garzic et al, 2011;McCaffrey et al, 2020).…”

Pre- to early-rift thermal conditions of the Upper Rhine Graben using geological and organic geochemical controls

“…The sedimentwater interface temperature (SWIT, in °C) and the paleo-water depth (PWD, in m) were used to estimate the temperature at the top of the sedimentary column through time. Finally, the evolution of the basal heat flow over time is based on Bossennec et al (2021;see below).…”

“…The SWIT was determined according to Bruss (2000), who compiled temperature data based on palynological and palynofacies studies of the URG from Stahmer (1980), Schuler (1990) and Sittler and Ollivier-Pierre (1994). Finally heat flow from Bossennec et al, (2021) were used. These authors estimated its value by calibrating the temperature derived from δ 18 O measured in quartz overgrowths of URG Buntsandstein samples with burial temperature profiles modelled under OpenFlow © and based on Böcker (2015).…”