Scratching the surface:Footprint of a late Carboniferous ice sheet

International audienceField observations in conjunction with aerial images from an unmanned aerial vehicle were used to create the first map of a glacial unconformity underlying the late Carboniferous Dwyka Group of South Africa. Crosscutting relationships reveal that the glacial unconformity at Oorlogskloof, in which flutes, grooves, and striae were ploughed into unconsolidated sand, formed in a three-phased process charting a periodic shift in the locus of subglacial erosion. The unconformity formed by a periodically decoupled ice sheet in a probable tidewater setting. This model contrasts with earlier views that the structures simply record progressive ice-margin liftoff during transgression, and they provide unique insight into the complex temporal development of a 300 Ma subglacial environment

New Perspectives on Glacial Geomorphology in Earth's Deep Time Record

International audienceThe deep time (pre-Quaternary) glacial record is an important means to understand the growth, development, and recession of the global cryosphere on very long timescales (10 6-10 8 Myr). Sedimentological description and interpretation of outcrops has traditionally played an important role. Whilst such data remain vital, new insights are now possible thanks to freely accessible aerial and satellite imagery, the widespread availability and affordability of Uncrewed Aerial Vehicles, and accessibility to 3D rendering software. In this paper, we showcase examples of glaciated landscapes from the Cryogenian, Ediacaran, Late Ordovician and Late Carboniferous where this approach is revolutionizing our understanding of deep time glaciation. Although some problems cannot be overcome (erosion or dissolution of the evidence), robust interpretations in terms of the evolving subglacial environment can be made. Citing examples from Australia (Cryogenian), China (Ediacaran), North and South Africa (Late Ordovician, Late Carboniferous), and Namibia (Late Carboniferous), we illustrate how the power of glacial geomorphology can be harnessed to interpret Earth's ancient glacial record

Ius Appulsus

... in florentissima Ienensi, Praeside Dn. Joachimo Kämpffer/ I.U.D. Publica Disputatione, eruditorum disquisitioni subiiciet, Auctor & Respondens Johannes Dietericus Kettler/ Norda Frisius Orientalis. Ad diem Augusti Anno 1680.Nicht identisch mit VD17 12:148535S (dort Respondent nicht als "Auctor & Respondens" bezeichnet; dort: Ausgabe ohne Widmung auf der Rückseite des Tbl.). - Nicht identisch mit VD17 27:721049C (dort Ausgabe ohne Widmung auf der Rückseite des Tbl.

Lex Rhodia De Iactu

Sub Praesidio ... Dn. Nicolai Christophori Lynckeri, ICti ... exposita & publico Examini subiecta A Johanne Dieterico Kettler, Norda-Ostfrisio Auctore & Respondente. Ad diem 19. Iulii. Anno M.DC.LXXIXNicht identisch mit VD17 12:156385H sowie 7:675652V (hier: Datum der Diss. gedruckt: "19. Iulii")Vorlageform des Erscheinungsvermerks: Jenae, Exprimebat Samuel Adolph. Müllerus

Complex development of a 300-million-year old subglacial unconformity in southern Namibia

International audienceThe expansion of ice masses across southern Africa during the Late Palaeozoic Ice Age (LPIA) at about300 Ma has been recognised in the literature for over a century, including the distribution of upland areas incontrolling the configuration of ice masses (Davis, 1908). In Namibia, increasing attention has focussed onlong and deep palaeovalley networks in the north, but comparatively little work has been attempted in thetopographically subdued plains of the south. The desert terrain of the Mariental area exposes diamictites ofthe Dwyka Formation discontinuously over about 300 km, extending further south to the Noordoewer areaat the Namibian-South African border along the Orange River. Whilst previously examined at a stratigraphiclevel, the nature of the contact between the Dwyka glacial rocks and underlying lithologies has not beensystematically investigated. This paper presents some preliminary results from fieldwork in austral winter2019, in which we describe a highly varying basal contact that records the processes of growth, flow andexpansion of ice masses across this part of Gondwana. Subglacially-produced unconformities may exhibitclassic glacially-striated pavements at basin margins, which substitute for soft-sediment striated surfacesin comparatively more “basinal” areas. Where these features are absent, additional criteria may be sought.In Mariental, spectacular soft-sediment shear zones exhibit a combination of brittle and ductile end productsare recognised, overprinted by shear bands. This type of subglacial unconformity developed over welldifferentiated, unconsolidated, siliciclastic materials. Where ice advanced over more poorly sorted materialor cannibalised pre-existing diamictites, “boulder-pavements” formed in which in single clast-thick boulderdominatedintervals were facetted and striated in situ by overriding ice. By integrating measurements ofstriation orientations, fold vergence and palaeocurrent information, former ice flow pathways can potentiallybe reconstructed over a wide area, which is suspected to have been dominated by Piedmont glaciers

Exhumed fjords of Namibia: A glimpse of the Late Paleozoic Ice Age in the Karoo Supergroup of the Kaokoland basin

International audienceThe Late Paleozoic Ice Age (LPIA) is the longest-lived and most extreme glacial period (from ca 360 to 260 Ma) of the Phanerozoic. Over this time span, ice masses are thought to have covered most of Gondwana, from South America to Australia. In southern Africa, the sedimentary, stratigraphic and geomorphic evidence of this glaciation is recorded in the Karoo Supergroup. The Kaokoland region of northern Namibia is characterized by a dense network of deep (200-700 m), large (5-15 km) and U-shaped incised valleys formed during the LPIA (Martin, 1981). A recent reappraisal of the morphology and sedimentary infill of these outstanding geomorphic features attests of their glacial origin. Valley flanks are spectacularly striated and scratched while valley floors are characterized by extensive whalebacks and roches moutonnées. Moreover, the sedimentary infill at the base of these valleys is mainly composed of coarse deposits (conglomerates, diamictites, erratics, striated clasts) interpreted as glaciogenic in origin. Of particular interest, however, is the presence of coarse (ranging from sand to boulders) glaciogenic sediments plastered on the sub-vertical and striated valley sides. Vitally, the elevation of these deposits in the valleys appears to correspond to a linear bench-like level, which may reflect a marginal moraine allowing for the maximum thickness of the LPIA glaciers to be derived, an unprecedented advance. For the first time in the characterization of a pre-Pleistocene glacial epoch, an ice thickness has been inferred. Collectively, these features prove that the valleys were carved and occupied by ice masses during the LPIA from which ice volume, and in turn their contribution to global eustasy, can directly be inferred. In addition, postglacial sedimentary succession abutting on valley flanks and showcasing marine, deltaic and estuarine affinities clearly indicate that these glacial valleys formed fjords in the immediate aftermath of the LPIA, after the retreat of the ice margins. Sealed by the Karoo Supergroup sediments through Carboniferous to early Cretaceous times, these major glaciogenic morphologic features have subsequently been exhumed during the Cenozoic. Thus, some desertic landscapes of northern Namibia correspond to a glacial relief inherited from the LPIA at ca ~ 300 Myr ago. Martin, H., 1981, The Late Paleozoic Dwyka Group of the South Kalahari Basin in Namibia and Botswana and the subglacial valleys of the Kaokoveld in Namibia, in Hambrey, M.J., and Harland, W.B. (eds.) Earth’s Pre-Pleistocene Glacial Record: New York, Cambridge University Press, 61–6

Decoding the late Palaeozoic glaciated landscape of Namibia: A photogrammetric journey

International audienceThe geometry of unconformities carved by deep time ice sheets is often obscured and restricted by discontinuous exposure, or outcrop conditions that do not readily permit the examination of glacial unconformities (for example, steeply dipping strata). Here, we present new uncrewed aerial vehicle (UAV) data from selected outcrops across northern, central and southern Namibia to shed further light on the nature of the basal Dwyka Group unconformity. This includes the onlap relationship of basal diamictites onto the Gomatum palaeo-fjord system in northern Namibia, highly complex mapped ice flow orientations elsewhere in the northern Kaokoveld, previously undiscovered grooves along the Fish River area, and a set of subglacial grooves along the border with South Africa along the Orange River. In the latter two cases, photogrammetric methods integrating orthophotos and digital elevation models reveal the presence of subglacial grooves. Furthermore, subglacial grooves often show different orientations to striations and fabrics measured in overlying diamictites, raising fresh questions about the nature of small-scale flow variations beneath Late Palaeozoic ice sheets

Aspects of the geomorphology of the Late Palaeozoic glaciated landscape of Namibia as revealed by photogrammetry

International audienceThe geometry of unconformities carved by deep time ice sheets is often obscured and restricted by discontinuous exposure, or outcrop conditions that do not readily permit the examination of glacial unconformities (for example, steeply dipping strata). Here, we present new uncrewed aerial vehicle (UAV) data from selected outcrops across northern, central and southern Namibia to shed new light on the nature of the basal Dwyka unconformity. This includes the onlap relationship of basal diamictites onto the Gomatum palaeo-fjord system in northern Namibia, highly complex mapped ice flow orientations elsewhere in the northern Kaokoveld, previously undiscovered grooves along the Fish River area, and a spectacular set of subglacial grooves along the border with South Africa along the Orange River. In the latter two cases, photogrammetric methods integrating orthophotos and digital elevation models reveal the presence of subglacial grooves for the first time, since the features are too subtle to observed using conventional approaches at outcrop. Furthermore, subglacial grooves often show different orientations to striations and fabrics measured in overlying diamictites, raising fresh questions about the nature of small-scale flow variations beneath Late Palaeozoic ice sheets