Depositional environments in the Telychian Stage (Silurian) of the central Oslo region, Norway

Abstract

The Telychian succession in the central Oslo region was previously interpreted as deposited in a relatively deep, calm environment showing a continuous transgressive development. A new analysis of fossil assemblages shows that sediments in the central districts were deposited at varying water depths in an environment marked by intense infaunal activity in soft substrates. Two small-scale fluctuations in sea level are attributed to eustasy. The maximum deepening events occurred during the Monograptus turriculatus and Monoclimacis crenulata graptolite zones.Previous depositional models include development of a trough to the north of the Oslo region in early Telychian time, which formed due to isostatic loading caused by an advancing thrust front of the Caledonian Orogeny. Bathymetric analysis shows a deepening in the Ringerike district in the latest Aeronian, which here is interpreted as a distal effect of the loading to the north. The local deepening led to reversal of the epicontinental slope between the northern and western districts and the central districts and the development of an east-west elongate positive area further south. The thrust front acted as a source of siliciclastic material; and when the front halted in mid-Telychian time the trough was filled in gradually by a prograding coast or delta. The diachronous Vik Formation is viewed as a distal development of this progradation. When the east-west oriented positive area subsided the Vik Formation was deposited in Skien to the south.

Microstructural Characterization of As-Quenched and Heat Treated Al-Si-Mg Melt-Spun Ribbons

“…The intermetallic compounds were identified as Mg 2 Si phase with Chinese-script morphology; the Al 8 Si 6 Mg 3 Fe phase with both Chinese-script morphology and with indefiniteshaped; the Al 5 FeSi phase with needle-like morphology. The main reactions expected to occur during solidification are [2,3] Fig. 2 presents the XRD patterns of the conventionally cast, 22m/s and 56m/s melt-spun ribbons.…”

Rapidly Solidified Al-6Si-3Cu Alloy

“…The secondary dendrite arm spacing, DAS, was measured at regions along centre-line of the rapidly solidified samples, and the cooling rates (R) in the wedge castings were estimated from α-Al dendrite arm spacing measurements. [4]. However, depending on the amount of iron, manganese and magnesium the Al 5 Mg 8 Cu 2 Si 6 and Al 15 (Mn,Fe) 3 Si 2 phases cannot be observed.…”

“…The wedge-shape sample with varying cross-section dimensions provide different cooling rates along the length of the sample allowing the evaluation of the microstructure evolution as a function of the cooling rate (R) [5]. From literature data for the A319 alloy [4,[6][7], the relationship between secondary dendrite arms spacing, λ 2 , and local solidification time, t SL , for conventional casting was found to be 342 . 0 2 6 , 8 SL t = λ for the A319 alloy, where t SL is in seconds and λ 2 is in µm.…”

Paradox lost: wide gape in the Ordovician brachiopod Rafinesquina explains how unattached filter‐feeding strophomenoids thrived on muddy substrates

“…Instead, it must have rested on the sediment convex (ventral) valve up or convex (ventral) valve down. Large flat strophomenoids are widely cited as examples of 'snowshoe morphology', animals that adapt to soft sediments by being broad and flat to avoid sinking in, as in the eponymous snow gear (Rhoads 1970;Bowen et al 1974;F€ ursich & Hurst 1974;Alexander 1975;Thayer 1975;Walker & Alberstadt 1975;McGhee 1976;Grant 1981;Kammer 1985;Hiller & Theron 1988;Baarli 1990;Holland & Patzkowsky 2007;Layou 2009;Ernst & Bohaty 2010;Smrecak & Brandt 2017;Brett et al 2020).…”