Quartz cementation and related sedimentary architecture of the Triassic Solling Formation, Reinhardswald Basin, Germany

The Olenekian Solling Formation of the Reinhardswald Basin was studied with the aim to examine the dependency of the degree of silica diagenesis on the sedimentary architecture. The Solling Formation is composed of stacked sandstone/clay-siltstone cycles deposited by braided (i.e., subarkoses) and meandering (i.e., subarkosic wackes) river systems. The sand-dominated braided rivers of the Lower Solling Formation are characterized by channels and downstream accretion, whereas mixed load meandering rivers of the Upper Solling Formation are represented by lateral accretion and laminated sands. Diagenetic processes which modified the sandstone-siltstone successions include compaction, feldspar alteration, and cementation. Sandy, clay-poor successions are highly quartz cemented (i.e., silica importers), whereas clay- and mica-rich successions are more compacted (i.e., silica balanced or silica exporters). Three quartz cement generations with a total volume of up to 18% indicate that silica from several different sources cemented the sandy fluvial architectural elements of the Lower Solling Formation. Cementation includes silica supply from internal and external to the sandstone layers, which are silica from grain margin dissolution, from feldspar alteration, silica released from clay-siltstones and silica precipitated from basinal brines. This cementation history is supported by cathodoluminescence observations and fluid inclusion studies, and a consistent burial history was successfully modeled by simulation of the thermal subsidence. In contrast to the Lower Solling Formation, the fluvial architectural elements of the mixed load systems of the Upper Solling Formation contain only one quartz cementation phase with a total volume up to 8%. The Reinhardswald Basin shows a dependency of the fluvial architecture and the diagenetic features. For that we define the term “diagenetic architecture”.