Provenance of lower Cambrian quartz arenite on southwestern Baltica: Weathering versus recycling

Abstract

Lower Cambrian quartz arenite deposits have a world-wide occurrence and are also present on Baltica. However, the processes influencing the deposits from source to sink have not been accordingly investigated. The provenance of these deposits is crucial for the understanding of the extent of chemical weathering in the cratonic drainage area and reworking at the broad shallow shelves of Baltica during early Cambrian time. Provenance analysis and study of weathering effects was done for lower Cambrian sandstone from southern Scandinavia, including southern Norway, southern Sweden, and Bornholm (Denmark). For the quartz-arenite sandstone of the Ringsaker Member and the Hardeberga Formation, predominantly moderately weathered felsic–intermediate plutonic and meta-igneous source terranes are suggested from negative Eu anomalies, high LaN/YbN, and low to moderate Ti/Nb ratios, as well as trace amounts of plutonic lithoclasts. Similarly, a felsic–intermediate igneous and metamorphic signature is indicated in the heavy-mineral assemblage and a dominance of dark cathodoluminescence of quartz in a special study of samples from Bornholm, thus suggesting a mixed provenance of local granitoid–orthogneissic Mesoproterozoic basement and distant sources from the Transscandinavian Igneous Belt for the Hardeberga Formation on Bornholm. High percentages of mostly rounded ultra-stable heavy-mineral grains, quartz, and extremely high SiO2/Al2O3 ratios indicate a compositionally and texturally mature sand that was subjected to extensive to moderate weathering following removal of detritus from the source area. The main controls on the alteration of framework composition and the heavy-mineral assemblage are interpreted as surface weathering, based on moderate Chemical Index of Alteration values and meteoric flushing, and reworking by waves, based on an estimated low amount of feldspar before burial. Thus, the maturation of lower Cambrian quartz arenite on southwestern Baltica can be ascribed to a combination of processes including weathering in the source-rock area, extensive reworking, and early diagenesis. This study also highlights the importance of understanding alteration processes affecting the deposits from source to sink, and to be careful to describe quartz-rich rocks as simply recycled deposits.

Influencing Factors on Petrography Interpretations in Provenance Research—A Case-Study Review

“…The data include a sequence from the Permian to Palaeogene of Northern Europe (from Germany in the south to the Barents Sea in the north) with a transition from Permo-Triassic tectonically passive to rift-dominated continental and Jurassic to Cretaceous marine rift basins, to Palaeogene passive-margin marine environments [20,32,33,[36][37][38][39][40]. They also include coastal Cambrian passive-margin sandstone from Scandinavian Baltica [41][42][43], Silurian-Devonian intracratonic basin sandstone from the Paraná Basin in Brazil [35], Cretaceous [1] (solid black lines), and the modified versions of Dickinson et al [2] (dashed black lines) and Weltje [3] (grey lines). For the use of the discrimination fields, the Gazzi-Dickinson point-counting method should be used with a grain-matrix limit of 63 µm.…”

“…The data include a sequence from the Permian to Palaeogene of Northern Europe (from Germany in the south to the Barents Sea in the north) with a transition from Permo-Triassic tectonically passive to rift-dominated continental and Jurassic to Cretaceous marine rift basins, to Palaeogene passive-margin marine environments [20,32,33,[36][37][38][39][40]. They also include coastal Cambrian passive-margin sandstone from Scandinavian Baltica [41][42][43], Silurian-Devonian intracratonic basin sandstone from the Paraná Basin in Brazil [35], Cretaceous Alpine deposits [34,44], rift-related Iberian Cretaceous to Pyrenean Palaeogene continental to marine deposits [45,46], and recent intracontinental sand from central Spain [47]. The material represents fluvial, aeolian, lacustrine, deltaic, coastal, shallow-marine, slope, and deep-marine depositional environments.…”

“…In the data set, Arribas et al [47] and Caja et al [46] used the Gazzi-Dickinson method with separate classes for carbonate clasts and sand-sized quartz, feldspar, and mica crystals in rock fragments. Lorentzen et al [42,43] and Ärlebrand [40] used the Gazzi-Dickinson method but applied a 30 µm and 20 µm matrix cut-off, respectively. von Eynatten and Gaupp [34] and Augustsson et al [20] used a modified Gazzi-Dickinson method with all rock fragments counted as such.…”

“…As McBride [56] applied a smaller matrix cut-off (20 µm) than Garzanti [23] (63 µm), the scheme of McBride [56] possibly is most appropriate for the studies reviewed here that used grain-matrix-size limits of 20 µm or 30 µm [40,42,43]. This is because different grain sizes will produce sediment of different mineralogical compositions.…”

“…Others focus more on diagenetic processes than on provenance, thus presenting detailed information on the intergranular volume and mineralogical alterations and dissolutions, giving only fragmentary information on the framework composition (cf. the range of petrographic details, e.g., in Lorentzen et al [42,43]). A different focus alone may lead to the use of different compositional and textural categories for the petrographic results and thus different classification of the same components.…”