24The evolution of deltas and submarine fans is often envisioned as largely controlled by 25 relative sea-level (RSL) variations. However, in some cases, RSL can have less effect on 26 delta and submarine fan activity than sediment supply and shelf geomorphology. In order 27to document the relative importance of these three factors on deltaic and submarine fan 28 evolution in a former glaciated environment, this paper documents the delivery of coarse 29 sediment to the Laurentian Channel (eastern Canada). The well-constrained stratigraphic 30 and geomorphological framework of both the glacio-isostatically uplifted deltas and the 31 modern Laurentian Channel fans allow us to document and contrast the evolution of 32 river-fed deltas, river-fed canyon/fan systems and longshore drift-fed fans during 33 deglacial and postglacial times. The evolution of these different types of fans can be 34 divided into three phases. The first phase is characterized by delta progradation on the 35 shelf while RSL was at its maximum, although already falling, and the ice-margin 36 gradually retreated inland. The second phase is characterized by the delivery of deltaic 37 sediment in the deep realm of the Laurentian Channel, permitted by the supply of large 38 amounts of glaciogenic sediments derived from the retreating ice margin and the 39 lowering of the RSL. At the same time, sediment instability along the steep Laurentian 40 3 Channel formed small incisions that evolved into submarine canyons where the narrow 41 shelf allowed the trapping of longshore sediment. The third phase is characterized by the 42 withdrawal of the ice-margin from the watershed of the main rivers and the drastic 43 decrease in sediment supply to the deltas. Consequently, the delta fronts experienced 44 strong coastal erosion, even though RSL was still lowering in some cases, and the eroded 45 sediments were transferred onto the shelf and to adjacent bays. This transfer of coastal 46 sediments allowed the continued activity of longshore drift-fed canyons. The retreat of 47 the ice margin from the watersheds thus controlled the supply of sediment and induced a 48 change in delta type, passing from river-dominated to wave-dominated. This paper 49 highlights the role of the type of sediment supply (ice-contact, glaciofluvial and 50 longshore drift) in the timing and activity of submarine fans in high-latitude 51 environments. It proposes a conceptual model for high-latitude shelves where sediment 52 delivery to submarine fans is mostly controlled by structural inheritance (watershed area 53 and shelf geomorphology) rather than RSL fluctuations. Therefore, although RSL fell 54 during delta progradation, this study demonstrates that it was not the main contributor to 55 delta and submarine fan growth. This has wider implications for the extraction of sea-56 level information from stratigraphic successions. 57

Although much is known about the Ordovician tectonics of the South European Variscides, aspects of their geodynamic evolution and palaeogeographic reconstruction remain uncertain. In Sardinia, Variscan tectonic units include significant vestiges of Ordovician evolution, such as a fold system that affected only the Cambrian–Lower Ordovician successions, and are cut by a regional angular unconformity. A comparison of the stratigraphy and tectonic structures of the successions below and above the Lower Ordovician unconformity and a reinterpretation of biostratigraphic data allow us to identify significant differences between the stacked tectonic units. The unconformity is sealed as follows: (i) in the Sulcis–Iglesiente Unit (Variscan External Zone, SW Sardinia) by Middle–Upper Ordovician continental and tidal deposits; and (ii) in the Sarrabus and Gerrei units (part of the Variscan Nappe Zone, SE Sardinia) by Middle–Upper Ordovician calc–alkaline volcanic rocks. Therefore, at the same time, one tectonic unit was situated close to a rifting setting and the others were involved in a convergent margin. Of note are the different durations associated with the unconformities in the tectonic units (17 Myr in the Sulcis–Iglesiente Unit, 6 Myr in the Sarrabus and Gerrei units) and the occurrence (or absence) of glacio-marine deposits indicating that the units were located at different palaeo-latitudes during the Ordovician. These results suggest that the SW and SE Sardinia blocks did not share the same geodynamic setting during the Ordovician, implying that they were situated in different palaeogeographic positions at this time and subsequently amalgamated during the Variscan Orogeny. Furthermore, stratigraphic and tectonic correlations with neighbouring areas, such as the eastern Pyrenees, imply alternative palaeogeographic reconstructions to those proposed previously for some peri-Mediterranean Variscan terranes.

This review illustrates the most important features of Ordovician succession of the Sardinian basement. We focus on stratigraphy and tectonic structures in the tectonic units of External and Nappe zones of the Variscan basement. The Ordovician successions are characterized by unconformities related to tectonics events ascribed to the Sardic and Sarrabese phases. The different time gap of the unconformity-related gaps in the External (17 Ma) and Nappe (6 Ma) zones, the recent work on trilobite fossil content, and the occurrence of a volcanic arc only in the Nappe Zone (Sarrabus and Gerrei units) highlight significant discrepancies suggesting that these domains did not share the same geodynamic setting and palaeogeographic position during the Ordovician. This implies they were amalgamated only in Variscan times. Whereas for the external and nappe zones the Ordovician features are clear, on the contrary the high-grade metamorphic Inner Zone, where numerous Ordovician ortho- and para-gneiss, needs more detailed studies to define a complete framework of the Ordovician evolution of Sardinia. The present revision of data on the best-preserved succession of the Sardinian tectonic units suggests that at least two distinct terranes, that did not share the same Ordovician evolution, were amalgamated only during the Variscan Orogeny.

 Glacial erosion is necessary to provide the sediment supply required for turbidity 23 currents to be generated on delta fronts 24  Lakes formed during glacial retreat significantly alter sediment delivery, stopping 25 turbidity currents 26  Pattern of retreating glaciers dictates the non-linear nearshore hydrodynamics of fjords 27 This article is a non-reviewed preprint published at EarthArXiv Abstract 28 Glacier and ice sheet mass loss as a result of climate change is driving important coastal changes 29 in Arctic fjords. Yet, limited information exists for Arctic coasts regarding the influence of 30 glacial erosion and ice mass loss on the occurrence and character of turbidity currents in fjords 31 which themselves affect delta dynamics. Here, we show how glacial erosion and the production 32 of meltwaters and sediments associated with the melting of retreating glaciers control the 33 generation of turbidity currents in fjords of eastern Baffin Island (Canada). The subaqueous 34 parts of 31 river mouths were mapped by high-resolution swath bathymetry along eastern Baffin 35 Island in order to assess the presence or absence of sediment waves formed by turbidity currents 36 on delta fronts. By extracting glaciological and hydrological watershed characteristics of these 37 river mouths, we demonstrate that the presence and areal extent of glaciers is a key control for 38 generating turbidity currents in fjords. However, lakes formed upstream during glacial retreat 39 significantly alter the course of sediment routing to the deltas by forming temporary sinks, 40 leading to the cessation of turbidity currents in the fjords. Due to the different deglaciation 41 stages of watersheds in eastern Baffin Island, we put these results into a temporal framework 42 of watershed deglaciation to demonstrate how the retreat pattern of glaciers, through the 43 formation and filling of proglacial lakes, affects the activity of deltas.44

The Ordovician successions of France and neighbouring areas of Belgium and Germany are reviewed and correlated based on international chronostratigraphic and regional biostratigraphic charts. The same three megasequences related to the rift, drift, and docking of Avalonia with Baltica can be tracked in Belgium and neighbouring areas (Brabant Massif and Ardenne inliers), western (Rhenish Massif) and northeastern Germany (Rügen). The remaining investigated areas were part of Gondwana in the Ordovician. The Armorican Massif shares with the Iberian Peninsula a Furongian-Early Ordovician gap (Toledanian or Norman gap), and a continuous Mid-Late Ordovician shelf sedimentation. The Occitan Domain (Montagne Noire and Mouthoumet massifs), eastern Pyrenees and northwestern Corsica share with southwestern Sardinia continuous shelf sedimentation in the Early Ordovician, and a Mid Ordovician “Sardic gap”. In the Ordovician, the Maures Massif probably belonged to the same Sardo-Occitan domain. The Vosges and Schwarzwald massifs display comparable, poorly preserved Ordovician successions, suggesting affinities with the Teplá-Barrandian and/or Moldanubian zones of Central Europe.