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A series of maps placing the study in context. (A–C) Study areas of the Dwyka Group in southern Namibia, compiled from Martin (1981), Visser (1983), Bangert et al. (1999) and Geiger (1999). (D) Simplified regional‐scale geological map emphasising the connections between Namibia and South America during the LPIA. Slightly modified from Griffis et al. (in press)
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The expansion of ice masses across southern Africa during the Late Palaeozoic Ice Age has been known for 150 years, including the distribution of upland areas in controlling the configuration of glaciation. In Namibia, increasing attention has focussed on long and deep palaeovalley networks in the Kaokoland region in the north, but comparatively li...
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The extremely variable and widespread cetoniine species Mausoleopsis amabilis (Schaum, 1844) is reviewed here using analyses of over 1500 specimens and observations across its entire distribution range. As a result, M. a. heterospila (Gerstaecker, 1867) is reinstated as a valid subspecies and a new subspecies, M. a. interrupta ssp. nov., is also er...
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... Recent research at Namibian basins displays areas below diamictites where the basal unconformity may be undulating, highly irregular and heterogeneous, with areas of heavy sediment injections into fractured bedrock that are interpreted to be subglacial (Le Heron et al., 2021b) and not only clastic dykes; the latter may be common subglacially (e.g., Sokołowski & Wysota, 2020). Sediment injections are regular features of SGFs, and together with the general appearance of the area, this may indicate an origin by SGFs and not glaciation (Dufresne et al., 2021;Molén, 2021Molén, , 2023aMolén & Smit, 2022). ...
Models (paradigms) and former interpretations have often been presupposed when conducting field research. In the 19th century diamictites were for the first time interpreted to have originated from ancient glaciations. These interpretations have to a large part prevailed in the geological community, although there has been much progress in the areas of sedimentology, glaciology and physical geography. The present work is an effort to find criteria which most clearly discriminate between geological features produced by different processes, mainly glaciation and mass flow, the latter predominantly sediment gravity flows. Geological features which have been interpreted to have formed by glaciation throughout pre-Pleistocene Earth history are compared to similar-appearing geological features formed by mass flow and tectonics, so as to uncover variations in the appearance between features resulting from these different processes. The starting point for this comparison is documentation of the appearance of Quaternary products of erosion and deposition, in order to discern the origin of older formations. It is shown that the appearance and origin of pavements, dropstones, valleys, small-scale landforms, surface microtextures and most other geological features may in some cases be equivocal, but in others the details are indicative of the process which generated the feature. Detailed geological field data which have been compiled by geologists from outcrops of pre-Pleistocene strata, more often than is considered in most papers, commonly point to a mass flow origin, mainly a sediment gravity flow origin, rather than a glaciogenic origin. A process of multiple working hypotheses or interpretations is therefore advocated, based mainly on a comparison of the appearance of features formed by different geological processes documented from different research disciplines. Instead of starting with current interpretations or models, this multiple working hypothesis or methodology helps to avoid confirmation bias and jumping to conclusions.
... Recent research at Namibian basins displays areas below diamictites where the basal unconformity may be undulating, highly irregular and heterogeneous, with areas of heavy sediment injections into fractured bedrock that are interpreted to be subglacial (Le Heron et al., 2021b) and not only clastic dykes; the latter may be common subglacially (e.g., Sokołowski & Wysota, 2020). Sediment injections are regular features of SGFs, and together with the general appearance of the area, this may indicate an origin by SGFs and not glaciation (Dufresne et al., 2021;Molén, 2021Molén, , 2023aMolén & Smit, 2022). ...
Models (paradigms) and former interpretations have often been presupposed when conducting field research. In the 19th century diamictites were for the first time interpreted to have originated from ancient glaciations. These interpretations
have to a large part prevailed in the geological community, although there has been much progress in the areas of sedimentology, glaciology and physical geography.
... A rich sedimentary archive of the Late Palaeozoic Ice Age (LPIA; 360 to 254.5 Ma; Fielding et al., 2023) is recorded over large parts of Gondwana (e.g. Montañez and Poulsen, 2013;Le Heron et al., 2021;Limarino and López-Gamundí, 2021;Rosa and Isbell, 2021;Montañez, 2022). In northern Africa the record is far less well known. ...
... In particular, the mid-to high-latitude Paraná and Kalahari basins of Brazil and Namibia, respectively, hosts arguably the world's highest fidelity record of this transition given the abundance of core and outcrop data across these passive intracratonic basins, the well-preserved nature of glacial record, and the large area over which glaciogenic deposits can be traced. Sedimentologic studies and detrital zircon geochronology have documented one of the richest Phanerozoic archives of the dynamic nature of late Paleozoic glaciation in this region, documenting a glaciogenic record characterized by multiple advance-retreat cycles before transitioning into post glacial marine or littoral depositional systems (Vesely et al., 2015;Mottin et al., 2018;Vesely et al., 2018;Fedorchuk et al., 2019a;Griffis et al., 2019b;Zieger et al., 2019Le Heron et al., 2021Dietrich et al., 2021). Furthermore, high-resolution U-Pb zircon chemical abrasion -thermal ionizing mass spectrometry (CA-TIMS) calibrated ages for these successions allows for the establishment of a multi-basin stratigraphic framework across this ...
... Here we briefly review some of the subglacial and the immediate postglacial record in the Kalahari Basin as well as the current temporal constraints on the deposits. Namibia hosts one of the highest fidelity records of the late Paleozoic glaciation, preserving ancient fjord networks, a complex basal unconformity that extends for 100's of kms in outcrop and large linear erosional features including drumlins, which attest to the subglacial history of this region (Figs 2 and 3B;Martin 1981;Dietrich et al., 2019;Andrews et al., 2019;le Heron et al., 2021). During the acme of the LPIA a large, at least 1.7 km thick, ice sheet covered northern Namibia . ...
... Ultimately, these valleys were filled with marine rocks and given the scale and well-preserved nature of the deposits are regarded as one of the world's best-preserved examples of a pre-Cenozoic fjord network Le Heron et al., 2022). In southern Namibia, equally impressive outcrops within the Aranos and Karasburg subbasins of the greater Kalahari, record a complex system of fluvial incision, subglacial erosion, and ice proximal deposits, which overlie unconformably Precambrian-Cambrian basement attesting to the growth and progradation of ice across this region Le Heron et al., 2021). Boulder beds striated and polished surfaces, and subglacial shearing of unconsolidated sediments are documented across these regions and confirm subglacial and proglacial conditions (Figs. 2, 3B and 3E;Visser, 1983;Le Heron et al., 2021). ...
Icehouse climate systems occur across an abbreviated portion of Earth history, comprising ∼25% of the Phanerozoic record. The Late Paleozoic Ice Age (LPIA) was the most extreme and longest lasting glaciation of the Phanerozoic and is characterized by periods of acute continental scale glaciation, separated by periods of ice minima or ice-free conditions on the order of <10 ⁶ years. The late Paleozoic glaciogenic record of the Paraná and Kalahari basins of southern Gondwana form one of the largest, best preserved, and well calibrated records of this glaciation. In the Carboniferous, the eastern and southern margins of the Paraná Basin and the Kalahari Basin were characterized by subglacial conditions, with evidence for continental and upland glaciers. In the latest Carboniferous, these basins transitioned from subglacial reservoirs to ice-free conditions evidenced by the widespread deposition of marine deposits juxtaposed on subglacial bedforms. High-precision U-Pb zircon CA-TIMS geochronologic constraints from volcanic ash deposits in the deglacial marine black shales of the Kalahari Basin and from fluvial and coal successions, which overlie marine deposits in the Paraná, indicate subglacial evidence in these regions is constrained to the Carboniferous. The loss of ice in these regions is congruent with a late Carboniferous peak in p CO 2 and widespread marine anoxia in the late Carboniferous. The permeant retreat of glaciers in basinal settings, despite an early Permian p CO 2 nadir, highlight the influence of short-term perturbations on the longer-term CO 2 record and suggests an ice-threshold had been crossed in the latest Carboniferous. A definitive driver for greenhouse gases in the LPIA, such as abundant and sustained volcanic activity or an increased biologic pump driven by ocean fertilization, is unresolved for this period. Lastly, the proposed Carboniferous apex for the high-latitude LPIA record is incongruent with observations from the low-latitude tropics where an early Permian peak is proposed.
... In particular, the mid-to high-latitude Paraná and Kalahari basins of Brazil and Namibia, respectively, hosts arguably the world's highest fidelity record of this transition given the abundance of core and outcrop data across these passive intracratonic basins, the well-preserved nature of glacial record, and the large area over which glaciogenic deposits can be traced. Sedimentologic studies and detrital zircon geochronology have documented one of the richest Phanerozoic archives of the dynamic nature of late Paleozoic glaciation in this region, documenting a glaciogenic record characterized by multiple advance-retreat cycles before transitioning into post glacial marine or littoral depositional systems (Vesely et al., 2015;Mottin et al., 2018;Vesely et al., 2018;Fedorchuk et al., 2019a;Griffis et al., 2019b;Zieger et al., 2019Le Heron et al., 2021Dietrich et al., 2021). Furthermore, high-resolution U-Pb zircon chemical abrasion -thermal ionizing mass spectrometry (CA-TIMS) calibrated ages for these successions allows for the establishment of a multi-basin stratigraphic framework across this ...
... Here we briefly review some of the subglacial and the immediate postglacial record in the Kalahari Basin as well as the current temporal constraints on the deposits. Namibia hosts one of the highest fidelity records of the late Paleozoic glaciation, preserving ancient fjord networks, a complex basal unconformity that extends for 100's of kms in outcrop and large linear erosional features including drumlins, which attest to the subglacial history of this region (Figs 2 and 3B;Martin 1981;Dietrich et al., 2019;Andrews et al., 2019;le Heron et al., 2021). During the acme of the LPIA a large, at least 1.7 km thick, ice sheet covered northern Namibia . ...
... Ultimately, these valleys were filled with marine rocks and given the scale and well-preserved nature of the deposits are regarded as one of the world's best-preserved examples of a pre-Cenozoic fjord network Le Heron et al., 2022). In southern Namibia, equally impressive outcrops within the Aranos and Karasburg subbasins of the greater Kalahari, record a complex system of fluvial incision, subglacial erosion, and ice proximal deposits, which overlie unconformably Precambrian-Cambrian basement attesting to the growth and progradation of ice across this region Le Heron et al., 2021). Boulder beds striated and polished surfaces, and subglacial shearing of unconsolidated sediments are documented across these regions and confirm subglacial and proglacial conditions (Figs. 2, 3B and 3E;Visser, 1983;Le Heron et al., 2021). ...
... In Western Gondwana, glacial stages or advances and retreats were frequent in the Carboniferous (Ezpeleta et al. 2020, Le Heron et al. 2021, López Gamundí et al. 2021. ...
The ichnogenus Psammichnites herein restricted to Psammichnites gigas is based on comparison of morphology, feeding behaviour, contrast between the burrows and the host rock, and possible producers. The record of siphonal activity as a “snorkel device” is discussed. The diagnosis of the ichnogenus Olivellites now is amended and includes all the records of Psammichnites in the post-Cambrian. Olivellites is now documented in successions other than the classical tidal flat deposits facies of the Carboniferous of the USA. We propose that the producer of Olivellites was an animal with capacity for displacement to different shallow infaunal levels for different feeding strategies. An interpretation of detritus feeding behavior with sediment displacement (pasichnia) is favoured here. The producer of Olivellites was likely to have been a bivalved mollusc that evolved after the Late Ordovician mass extinction. It was euryhaline and lived in a broad bathymetric range, and is recorded in temperate to glacially related successions. The material of Olivellites implexus from western Argentina is the youngest record of the ichnogenus from Western Gondwana.
Namibia is remarkable in terms of its network of approximately 300-million-year-old fjords, cut by Gondwanan glaciers at high palaeolatitudes during the Late Palaeozoic Ice Age (LPIA). A classic suite of structures is preserved on Proterozoic bedrock, including striations, roches moutonnées and other subglacial features within many of these palaeovalleys. Some palaeovalleys are plastered with comparatively thin diamictites (a few metres) of presumed subglacial origin, in turn capped by ice marginal delta successions (tens of metres). Close examination of deposits in the outer Orutanda Fjord palaeovalley reveals an architecture that shows departure from this trend. There, boulder-bearing diamictites pass laterally into highly contorted heterolithic successions comprising folded and faulted sandstones, siltstones and shales. Aerial imagery from UAVs in tandem with traditional field observations permits mapping of assemblages of soft-sediment deformation structures (tight to recumbent folds, deformation bands, faults, sheath folds) together with spatial mapping of the long-axis of boulders in diamictite. Collectively, this assemblage of structures points towards subglacial deformation, and hence an origin as a “deforming bed” beneath a glacier. Whilst several open questions remain regarding the precise deformation mechanisms, the concept of glacial re-advances into a deeply incised palaeovalley is proposed, by direct analogy to similar stratigraphic architectures in the LPIA record of South America.
The Garub fluorite deposit in south Namibia is hosted by a Neoproterozoic tuffisite diatreme which is cut by a hydrothermal
vein with base metal mineralization. Petrographic observations indicate a single hydrothermal event producing a paragenesis of fluorite-baryte with base metal sulfides, quartz and carbonates. Microthermometry data from fluid inclusions show that hydrothermal fluorite and baryte were precipitated from a high-salinity (16.9–22.7 wt% NaCl + CaCl2), moderate-temperature brine (180–210 °C). This brine formed by mixing between a warmer, Ba- and F-rich endmember likely representing a deep-seated basement brine (chemically equilibrated with Namaqua-Natal-Metamorphic Complex basement rocks) and a cooler, SO4- and Ca-rich endmember
that likely equilibrated with Nama Group limestone. Chlorine/Br mass ratios between 152 and 612 indicate the mixing of a fluid with a halite dissolution brine signature (endmember 1) and an equally saline brine derived
from Nama Group limestone (endmember 2). Rubidium/Cesium (Rb/Cs) ratios between 2.2 and 20.5 provide evidence for significant fluid interaction with clay minerals. Since clay minerals are abundant in the tuffisite of the Garub diatreme, these Rb/Cs ratios indicate that fluids migrated along the diatreme-gneiss contact along a zone
of weakness. Late-stage quartz and calcite likely reflect cooling and induced a shutdown of the hydrothermal system. The sulfide phases in this hydrothermal vein are strongly depleted in trace elements compared to other hydrothermal vein districts, which is interpreted as an inherited signature of the fluid source. There is no record of evaporites in the sedimentary rocks of the Nama Group. Based on the fluid chemistry of the mixed fluid, which clearly indicates halite dissolution and water-rock interaction with basement rocks, it is
concluded that the basement brine fluid endmember is likely generated through cryogenic brine formation during the large scale Dwyka glaciation event. As a farfield consequence of Pangea breakup fluid pathways were established that acted as host structures for the Garub fluorite deposit. This could be the first evidence for unconformity-related hydrothermal fluorite deposit formation in the context of Dwyka cryogenic brine formation in
southern Africa.
For more than 150 years, geologic characteristics claimed to be evidence for pre-Pleistocene glaciations have been debated. Advancements in recent decades, in understanding features generated by mainly glacial and mass flow processes, are here reviewed. Detailed studies of data offered in support of pre-
Pleistocene glaciations have led to revisions that involve environments of mass movements. Similarities and differences between Quaternary glaciogenic and mass movement features are examined, to provide a more systematic methodology for analysing the origins of more ancient deposits. Analyses and evaluation of data are from a) Quaternary glaciogenic sediments, b) formations which have been assigned to pre-Pleistocene glaciations, and c) formations with comparable features associated with mass movements (and occasionally tectonics). Multiple proxies are assembled to develop correct interpretations of ancient strata. The aim is not per se to reinterpret specific formations and past climate changes, but to enable data to be evaluated using a broader and more inclusive conceptual framework.
Regularly occurring pre-Pleistocene features interpreted to be glaciogenic, have often been shown to have few or no Quaternary glaciogenic equivalents. These same features commonly form by sediment gravity flows or other non-glacial processes, which may have led to misinterpretations of ancient deposits. These features
include, for example, environmental affinity of fossils, grading, bedding, fabrics, size and appearance of erratics, polished and striated clasts and surfaces (“pavements”), dropstones, and surface microtextures. Recent decades of progress in research relating to glacial and sediment gravity flow processes have resulted in proposals by geologists, based on more detailed field data, more often of an origin by mass movements and tectonism than glaciation.
The most coherent data of this review, i.e., appearances of features produced by glaciation, sediment gravity flows and a few other geological processes, are summarized in a Diamict Origin Table.
Keywords Diamictite, Tillite, Sediment gravity flow (SGF), Striation, Groove, Dropstone, Paleoclimate, Fossil vegetation, Glaciogenic proxies, Surface microtexture, Late Paleozoic ice age
