The Early–Middle Ordovician graptolite genus Azygograptus in South China: New material and paleogeographic implications Publication date: 1 November 2019 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 533 Author(s): Wenhui Wang, Linna Zhang, Hao Liu, Xin Deng, Jingqiang Tan Abstract This study presents a new analysis of three species of the Ordovician graptolite genus Azygograptus Nicholson & Lapworth from the Wenxiakou section in the Zhongxiang area of Hubei Province. The paleogeographic occurrences of the genus within South China were plotted on an up-to-date paleogeographic map based on a revised data set of graptolite occurrences from 68 localities compiled by the online Geobiodiversity Database (GBDB). The paleogeographic distribution of Azygograptus follows a nearshore-offshore trend, and the taxonomic diversity of Azygograptus is higher in nearshore high-energy environments than in offshore low-energy environments. However, graptolites also gathered in deeper-water environments surrounding oldlands partly due to the high-nutrient inputs and rapid deposition. Azygograptus is found not only in high-latitude cold-water regions as endemic taxa but also in low-latitude regions. Oceanic circulation may account for the rapid dispersal of Azygograptus from high-latitude regions, such as Britain and Scandinavia, to low-latitude regions, such as South China, eventually resulting in their observed paleogeographic distribution.

Seismic imaging of the Olduvai Basin, Tanzania Publication date: 1 November 2019 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 533 Author(s): Kai Lu, Sherif Hanafy, Ian Stanistreet, Jackson Njau, Kathy Schick, Nicholas Toth, Harald Stollhofen, Gerard Schuster Abstract A 5.6-km-long line of refraction and reflection seismic data spanning the Pliocene-Pleistocene fill of the Olduvai Basin, Tanzania is presented. The line is oriented along a northwest-southeast profile through the position of Olduvai Gorge Coring Project (OGCP) Borehole 2A. Our aims are to (1) delineate the geometry of the basin floor by tracing bedrock topography of the metaquartzitic and gneissic basement, (2) map synsedimentary normal faults and trace individual strata at depth, and (3) provide context for the sequence observed in OGCP cores. Results with refraction tomography and poststack migration show that the maximum basin depth is around 405 m (±25 m) in the deepest portion, which quadruples the thickness of the basin-fill previously known from outcrops. Variations in seismic velocities show the positions of lower density lake claystones and higher density well-cemented sedimentary sequences. The Bed I Basalt lava is a prominent marker in the refraction seismic results. Bottom-most sediments are dated to >2.2 Ma near where Borehole 2A bottoms out at the depth of 245 m. However, the seismic line shows that the basin-fill reaches a maximum stratigraphic thickness of around 380 m deep at Borehole 2A, in the western basin where the subsidence was greatest. This further suggests that potential hominin palaeoenvironments were available and preserved within the basin-fill possibly as far back as around 4 Ma, applying a temporal extrapolation using the average sediment accretion rate.

Reef shallowing is a critical control on benthic foraminiferal assemblage composition on nearshore turbid coral reefs Publication date: 1 November 2019 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 533 Author(s): J.A. Johnson, C.T. Perry, S.G. Smithers, K.M. Morgan, S.A. Woodroffe Abstract Declining water quality represents a major threat to the coral reefs of Australia's Great Barrier Reef (GBR). Due to their close proximity to river point sources, reefs situated on the inner-shelf of the GBR are widely perceived to be most susceptible to the increased discharge of nutrients and sediments from coastal catchments, many of which have been modified since European settlement. However, the impact and magnitude of water quality change on the GBR's inner-shelf reefs remains unclear. Much of the uncertainty can be attributed to a paucity of long-term records with which to assess ecological and environmental change over appropriate reef-building timescales. Here, we present benthic foraminiferal palaeo-records from three proximal nearshore turbid-zone reefs located within the central region of the GBR. Bayesian age-depth modelling was used to identify the core intervals corresponding to the timing of European settlement in the region (c. 1850 CE), enabling the investigation of: (1) the composition and variability of benthic foraminiferal assemblages during reef shallowing towards sea level; and (2) whether any signal of increased nutrient and sediment inputs, as the result of historical land-use change, can be discerned on the most nearshore reefs of the central GBR. Multivariate analyses identified two assemblage groups, delineated by a significant increase in the relative abundance of Pararotalia spp. up-core. Our results suggest that post-European settlement associated increases in nutrient and sediment inputs are unlikely to have driven the observed shifts in benthic foraminiferal assemblage composition. Rather, we interpret changes in the composition of benthic foraminiferal assemblages as being linked to changes in hydrodynamic energy, light availability and the carbonate content of reef-matrix sediments during reef shallowing towards sea level. Our findings support the hypothesis that nearshore turbid-zone reefs have a higher resistance to increased nutrient and sediment inputs than those located further offshore, towards the inner/mid-shelf boundary of the GBR. Graphical abstract Conceptual model of the influence of key abiotic factors (i.e., carbonate sediment, light availability and wave energy) on the structure and vertical distribution of benthic foraminiferal assemblages on nearshore turbid coral reefs (a1 = Group 1; a2 = Group 2). Scanning electron micrographs of key genera contributing to overall assemblage composition are presented, with subsidiary taxa listed in rank order of importance. The model also considers the spatial variation in prevailing sedimentary regimes between windward and leeward reef locations, primarily controlled by wave energy and water depth (presented relative to lowest astronomical tide; LAT).

Depositional systems and paleogeography of Upper Cretaceous-Paleogene deep-sea flysch deposits of the Magura Basin (Western Carpathians) Publication date: 1 November 2019 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 533 Author(s): František Tet'ák, Daniel Pivko, Martin Kováčik Abstract The Outer Western Carpathians are part of the Alpine-Himalayan orogenic belt, and they are formed mostly by the Upper Cretaceous and Paleogene deep-sea “flysch” sequences. Orava region (northern Slovakia), situated in the central part of the Magura Nappe, has an important position for the solution of the geological structure and development of the Magura Nappe. At the beginning of the research, determination of the sedimentary sequences of the Magura Nappe and the fundamental lithotypes and lithofacies was required. A total of 1164 paleocurrent measurements were measured and assigned to lithotypes and lithostratigraphic units obtained during the detailed sedimentological study. The main purpose of the research was the interpretation of the filling history and tectonic activity of the Magura Basin. The results of the detailed sedimentological study were integrated with published data from surrounding regions. Presented palinspastic maps propose a reconstruction of the filling history and tectonic activity in chronological order during the Upper Cretaceous to Oligocene. Maps focus in detail on the western part of the Magura Basin, but they display its surroundings as well. The sedimentary record reflects the activity and gradual shifting of the Western Carpathian accretionary wedge to the north, the uplift of source areas, and the changes in the sea level of the Magura Basin. The paleocurrent analyses joined with the sedimentological and petrographic research allowed to reconstruct the paleogeographic properties of the northern sources of detritic material (Hostýn, Fore-Magura and Silesian Ridges), of the southern source of the material (Western Carpathians accretionary wedge) and of intrabasinal sources as well (Szczawina and Southern-Magura Ridges). We propose a discussion about the character of filling history, defining and position of the source areas and about Hostýn Ridge defined here.

New insights into the provenance of Cenozoic strata in the Qaidam Basin, northern Tibet: Constraints from combined U-Pb dating of detrital zircons in recent and ancient fluvial sediments Publication date: 1 November 2019 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 533 Author(s): Bowen Song, Kexin Zhang, Yafei Hou, Junliang Ji, Jiaxuan Wang, Yibo Yang, Tinglu Yang, Chaowen Wang, Tianyi Shen Abstract Determining the provenance of Cenozoic strata in the Qaidam Basin is key to understanding the basin-mountain coupling history in the northern Tibetan Plateau (TP). However, the specific source areas of Cenozoic strata in the northern Qaidam Basin remain highly debated. Here, we combine analyses of detrital zircons UPb geochronology for recent and ancient fluvial sediments from the northern Qaidam Basin to trace source areas of Cenozoic strata and reconstruct related mountain-building processes. The results indicate that the diagnostic 270–240 Ma zircon UPb peak, which was previously recognized as the unique input of a southern source area, is widespread in the recent fluvial sediments of the northern Qaidam Basin. Given our new zircon UPb data, the source-to-sink transport processes of Cenozoic sediments in the northern Qaidam Basin can be summarized as follows. (1) The northern Qaidam Basin has received the eroded detrital material from a dominantly northern source throughout the Cenozoic. (2) The Qaidam BeiShan was uplifted already at least by the early Eocene and served as the single contributor of detritus to the Dahonggou (DHG) region, suggesting that far-field stress due to the India-Asia collision had been propagated to this region as early as the early Eocene. (3) An abrupt change in provenance is observed in the DHG region during 46.5–43.7 Ma. We interpret this middle Eocene source change as reflecting the onset of growth of the North Altyn Tagh Range, implying that the North Altyn Tagh Range was already serving as an important source area for the DHG region by the middle Eocene. (4) The South Qilian Range served again as the dominant source area for the DHG region after 24.6 Ma. The shift in provenance from the North Altyn Tagh Range to the South Qilian Range can be attributed to the uplift of the Saishiteng Shan.

The antiquity of the Sahara Desert: New evidence from the mineralogy and geochemistry of Pliocene paleosols on the Canary Islands, Spain Publication date: 1 November 2019 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 533 Author(s): Daniel R. Muhs, Joaquín Meco, James R. Budahn, Gary L. Skipp, Juan F. Betancort, Alejandro Lomoschitz Abstract The Sahara is the largest warm desert in the world, but its age has been controversial, with estimates ranging from Miocene to Holocene. Mineralogical and geochemical data show that paleosols of Pliocene to mid-Pleistocene age on Fuerteventura and Gran Canaria in the Canary Islands have developed in part from inputs of dust from Africa. These paleosols contain quartz and mica, minerals that are abundant in African dust but are rare in the basaltic rocks that dominate the Canary Islands. Trace elements with minimal mobility, Sc, Cr, Hf, Th, and Ta as well as the rare earth elements, show that paleosols have compositions that are intermediate between those of local rocks and African-derived dust. Thus, results reported here and in a recently published study by others indicate that 9 paleosols record delivery of African dust to the Canary Islands between ~4.8–2.8 Ma, ~3.0–2.9 Ma, ~2.3–1.46 Ma, and ~0.4 Ma. A long-term paleosol record of African dust input agrees with deep-sea records off the coast of western Africa that imply increased dust fluxes to the eastern Atlantic Ocean at ~4.6 Ma. It is concluded that the Sahara Desert has been in existence as an arid-region dust source, at least intermittently, for much of the Pliocene and continuing into the Pleistocene.

European charophyte evolution across the Cretaceous–Paleogene boundary Publication date: 1 November 2019 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 533 Author(s): Alba Vicente, Zoltán Csiki-Sava, Carles Martín-Closas Abstract The Cretaceous–Paleogene (K/Pg) boundary has traditionally been considered a key moment in charophyte evolution, marked by the extinction of two important Mesozoic families, the Porocharaceae and the Clavatoraceae, and a major turnover within the Characeae. However, new data presented here suggest that one species of the European Porocharaceae (based on gyrogonites) and one species of the Clavatoraceae (based on thalli), persisted into the basal Danian. In addition, a taxonomic revision of the Characeae, coupled with an updated biostratigraphy, shows that this family underwent a step-wise extinction during the latest Cretaceous with only a small number of species becoming extinct at the K/Pg boundary. As a result, changes in charophyte floras around the K/Pg boundary in Europe cannot be considered to represent a major turnover in charophyte evolution. Its effects were more comparable to a normal stage boundary event rather than to a major erathem boundary one. Similar disappearance patterns at the K/Pg boundary have also been recorded in other taxa, including fish and amphibians, showing that aquatic freshwater biotas may somehow be resilient to catastrophic events such as those that occurred during the K/Pg crisis.

Sedimentology and U-Pb dating of Carboniferous to Permian continental series of the northern Massif Central (France): Local palaeogeographic evolution and larger scale correlations Publication date: 1 November 2019 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 533 Author(s): C. Ducassou, M. Mercuzot, S. Bourquin, C. Rossignol, P. Pellenard, L. Beccaletto, M. Poujol, E. Hallot, A.C. Pierson-Wickmann, C. Hue, E. Ravier Abstract The Carboniferous to Permian volcanic-sedimentary succession shown by the LY-F core from the Lucenay-lès-Aix area, in the northern part of the Massif Central, has been studied in order to obtain both landscape reconstructions (sedimentological analyses) and geochronological constraints (U-Pb dating on zircon and apatite). The lowermost part of the core consists mainly of lacustrine deposits with Gilbert-type delta and volcaniclastic-rich fan delta deposits including several altered volcanic ash layers (tonstein). In contrast, in the uppermost part of the core, playa-lake deposits dominate. LA-ICP-MS U-Pb analyses were performed on both zircon and apatite grains from interbedded tonsteins. This coupled U-Pb dating approach allows to assess potential reworking of volcanic material or the occurrence of non-volcanic grains, such as xenocrysts, in order to provide better evaluations for the depositional ages of the tonsteins. These investigations reveal that sedimentation took place between the late Gzhelian and the late Sakmarian (i.e., between c. 301 and 290 Ma). This sedimentary succession can therefore be compared to those from adjacent basins for which geochronological constraints are available (i.e., Autun and Lodève basins, resp. located north and south of the Massif Central). This study provides a reference section for future comparisons with similar sections from other Carboniferous to Permian basins, in France as well as elsewhere in Europe.

Interplay between biotic and environmental conditions in pre-salt Messinian microbialites of the western Mediterranean (Upper Miocene, Mallorca, Spain) Publication date: 1 November 2019 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 533 Author(s): Pablo Suarez-Gonzalez, Concha Arenas, M. Isabel Benito, Luis Pomar Abstract Microbial buildups that predate the Messinian salinity crisis, including one of the few Phanerozoic examples of ‘giant’ microbialites, crop out upon the island of Mallorca (W Mediterranean). Sedimentological and geochemical data from microbialites and associated deposits, both essentially dolomitic, indicate that they grew in shallow marine conditions but relatively restricted from the open marine realm. Two microbialite-bearing sequences occur, both consisting of subtidal to supratidal deposits. Periods of restriction led to evaporative and hypersaline conditions that favored the development of microbialites and local precipitation of sulfates. By contrast, ephemeral periods marked by more open conditions were devoid of microbialites and allowed production of bioclastic deposits. Microbialites range from decameter- to decimeter-scale, reflecting differences in accommodation space. Despite contrasting sizes, all microbialite bodies record similar mesostructure evolution through time, from thrombolites to stromatolites, with a sharp transition between these endmembers. The change from subtidal to shallower, more restricted and saline intertidal environments triggered biotic substitution of thrombolite-generating microbial communities to stromatolite-generating ones. Furthermore, a wide variety of microstructures, from agglutinated to micritic with fossilized microbes, indicates that two main accretion processes occurred: microbially-influenced primary dolomite precipitation and grain trapping and binding, which were controlled by the interaction between microbes and changes in environmental conditions (e.g. grain supply, hydrodynamics and hydrochemistry). Therefore, the diversity of macro-, meso- and microstructures of these microbialites was caused by a complex interplay between depositional, biotic and hydrological parameters, which offers useful insights for the palaeoecological interpretation of other examples, at any scale and throughout geological time.

Detrital zircon provenance comparison between the Paleocene-Eocene Nangqian-Xialaxiu and Gongjue basins: New insights for Cenozoic paleogeographic evolution of the eastern Tibetan Plateau Publication date: 1 November 2019 Source: Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 533 Author(s): Yang Zhang, Wentao Huang, Yuanyuan Zhang, Marc Poujol, Stéphane Guillot, Pierrick Roperch, Guillaume Dupont-Nivet, Zhaojie Guo Abstract Paleogeographic reconstructions of terranes can greatly benefit from the provenance analysis of sediments. A series of Cenozoic basins provide key sedimentary archives for investigating the growth of the Tibetan Plateau, yet the provenance of the sediments in these basins has never been constrained robustly. Here we report sedimentary petrological and detrital zircon geochronological data from the Paleocene-Eocene Nangqian-Xialaxiu and Gongjue basins. Sandstone detrital modes and zircon morphology suggest that the samples collected in these two basins were sourced from recycled orogen. Detrital zircon geochronology indicates that sediments in the Nangqian-Xialaxiu Basin are characterized by two distinct age populations at 220–280 Ma and 405–445 Ma. In contrast, three predominant age populations of 207–256 Ma, 423–445 Ma, and 1851–1868 Ma, and two subordinate age populations of ~50 Ma and ~2500 Ma, are recognized in the Gongjue Basin. Comparison with detrital zircon ages from the surrounding terranes suggests that sediments in the Nangqian-Xialaxiu Basin come from the neighboring thrust belts, whereas sediments from the Gongjue Basin are predominantly derived from the distant Songpan-Ganzi Terrane with minor contribution from the surrounding areas. A three-stage Cenozoic evolution of the eastern Tibetan Plateau is proposed. During the Paleocene, the Nangqian-Xialaxiu Basin appeared as a set of small intermontane sub-basins and received plentiful sediments from the neighboring mountain belts; during the Eocene, the Gongjue Basin kept a relatively low altitude and was a depression at the edge of a proto-Plateau; since the Oligocene, the Tibetan Plateau further uplifted and the marginal Gongjue Basin was involved in the Tibetan interior orogeny, indicating the eastward propagation of the Tibetan Plateau.