Episodic burial and exhumation in North-East Greenland before and after opening of the North-East Atlantic

The geology of North-East Greenland (70–78°N) exposes unique evidence of the basin development between the Devonian collapse of the Caledonian Orogen and the extrusion of volcanics at the Paleocene–Eocene transition during break-up of the North-East Atlantic. Here we pay special attention to unconformities in the stratigraphic record – do they represent periods of stability and non-deposition or periods of subsidence and accumulation of rocks followed by episodes of uplift and erosion? To answer that and other questions, we used apatite fission-track analysis and vitrinite reflectance data together with stratigraphic landscape analysis and observations from the stratigraphic record to study the thermo-tectonic history of North-East Greenland. Our analysis reveals eight regional stages of post-Caledonian development: (1) Late Carboniferous uplift and erosion led to formation of a sub-Permian peneplain covered by coarse siliciclastic deposits. (2) Middle Triassic exhumation led to removal of a thick cover including a considerable thickness of upper Carboniferous – Middle Triassic rocks and produced thick siliciclastic deposits in the rift system. (3) Denudation at the transition between the Early and Middle Jurassic affected most of the study area outside the Jameson Land Basin and produced a weathered surface above which Middle–Upper Jurassic sediments accumulated. (4) Earliest Cretaceous uplift and erosion along the rifted margin and further inland accompanied the Mesozoic rift climax and produced coarse-grained sedimentary infill of the rift basins. (5) Mid-Cretaceous uplift and erosion initiated removal of Cretaceous post-rift sediments that had accumulated above the Mesozoic rifts and their hinterland, leading to cooling of Mesozoic sediments from maximum palaeotemperatures. (6) End-Eocene uplift was accompanied by faulting and intrusion of magmatic bodies and resulted in extensive mass wasting on the East Greenland shelf. This event initiated the removal of a thick post-rift succession that had accumulated after break-up and produced a peneplain near sea level, the Upper Planation Surface. (7) Late Miocene uplift and erosion, evidenced by massive progradation on the shelf, resulted in the formation of the Lower Planation Surface by incision below the uplifted Upper Planation Surface. (8) Early Pliocene uplift raised the Upper and the Lower Planation Surfaces to their present elevations of about 2 and 1 km above sea level, respectively, and initiated the formation of the present-day landscape through fluvial and glacial erosion. Additional cooling episodes of more local extent, related to igneous activity in the early Eocene and in the early Miocene, primarily affected parts of northern Jameson Land. The three earliest episodes had a profound impact beyond Greenland and accompanied the fragmentation of Pangaea. Younger episodes were controlled by plate-tectonic processes, possibly including dynamic support from the Iceland Plume. Our results emphasise that gaps in the stratigraphic record often reflect episodes of kilometre-scale vertical movements that may result from both lithospheric and sub-lithospheric processes.

Peneplains and tectonics in North-East Greenland after opening of the North-East Atlantic

Elevated plateaus with deeply incised valleys characterise elevated, passive continental margins (EPCMs) in all climate zones. These features are, however, a topic of debate regarding when and how the large-scale landscapes formed. We have investigated and mapped the partly glaciated landscape of North-East Greenland (70–78°N). The area consists of crystalline basement and Palaeozoic–Mesozoic rift basins, capped by Palaeogene basalts that erupted during the northeast Atlantic break-up. Our stratigraphic landscape analysis reveals a typical EPCM dominated by two elevated erosion surfaces, extending 200 km east–west and 900 km north–south. The low-relief Upper Planation Surface (UPS; c. 2 km above sea level) cuts across basement and Palaeogene basalts, indicating that it was graded to base level defined by the Atlantic Ocean in post-basalt times and subsequently uplifted. The UPS formed prior to the deposition of mid-Miocene lavas that rest on it, south of the study area. In the interior basement terrains, the Lower Planation Surface (LPS) forms fluvial valley benches at c. 1 km above sea level, incised below the UPS. The LPS is thus younger than the UPS, which implies that it formed post mid-Miocene. Towards the coast, the valley benches merge to form a coherent surface that defines flat-topped mountains. This shows that the LPS was graded to near sea level and was subsequently uplifted. Hence, both the UPS and the LPS formed as peneplains – erosion surfaces graded to base level. The fluvial valley benches associated with the LPS further indicates that full glacial conditions were only established after the uplift of the LPS in the early Pliocene (c. 5 Ma). The uplift of the LPS led to re-exposure of a Mesozoic etch surface. We conclude that episodes of late Neogene tectonic uplift shaped the stepped landscape and elevated topography in North-East Greenland.

Terrestrial kaolin deposits trapped in Miocene karstic sinkholes on planation surface remnants, Transdanubian Range, Pannonian Basin (Hungary)

In the Transdanubian Range, Pannonian Basin, Hungary, karstic sinkholes on a planation surface of Triassic carbonates are filled by grey clayey–silty kaolin deposits. The provenance and accumulation age of these strongly altered terrestrial karst-filling sediments are constrained by X-ray powder diffraction, heavy mineral analysis and zircon U–Pb dating. The heavy minerals of the Southern Bakony Mountains samples are dominated by the ultra-stable zircon–rutile–tourmaline association. Zircon U–Pb data indicate accumulation between 20 and 16 Ma. Furthermore, Archaean to Palaeogene grains were also determined, reflecting the principally fluvial recycling of Eocene bauxites and their cover sequences. In contrast, the sample from the Keszthely Hills consists almost exclusively of airborne material including zircons of 18–14 Ma, reflecting a dominant contribution from the Carpathian–Pannonian Neogene volcanism. The shift in the Miocene age components is inferred to have been caused by the landscape evolution and burial history of the planation surface remnants controlled by local block tectonics.

Denudation history of the French Massif Central: new insights from thermochronology, basement-basin cross-sections and semi-automated planation surfaces mapping

<p>Documenting surface uplift of basement areas is challenging, usually due to large gaps in the sedimentary record. In order to address this issue for the French Massif Central, we here investigate its denudation history through an integrated study that involves planation surface mapping, Apatite Fission-Track (AFT) Analysis and basement to basin cross-sections.</p><p>First, Planation surfaces were identified using a semi-automated fuzzy classification of pixels based on relationships between DEM derivatives (slope, curvature, ruggedness and incision) and field-recognized training samples.  Then, their different generations and age ranges were discriminated from hypsometry, fault partitioning and relationships with dated sedimentary and/or volcanic remnants, providing constraints on basement exhumation. Afterwards, integrating the previous planation surface analysis, geological cross-sections were produced from the Massif Central basement to the surrounding basins (Aquitaine Basin and Paris Basin). These sections provide local thicknesses estimates of the missing sedimentary cover over basement domains. Theses local thicknesses and exhumation phases were finally used as constraints to produce a thermal history modelling and a denudation map of different areas of the French Massif Central estimated from AFT inversion.</p><p>Our results show different burial and exhumation patterns with i) a main burial of its western parts (Limousin, Rouergue) during Jurassic times followed by an important regional denudation (1 to 2 km of missing cover and crystallized basement) during the early Cretaceous and ii) an Upper Cretaceous burial of its northeastern parts (Morvan, Forez) followed by an uppermost Cretaceous to Paleogene exhumation (<1 km of missing cover and crystallized basement). This further illustrates the different behavior of each units of the Massif Central during the Mesozoic to Cenozoic times. These results will ultimately be discussed and placed back into the western European deformation framework.</p><p> </p><p>(This work is founded and carried out in the framework of the BRGM-TOTAL project Source-to-Sink)</p>

Late Miocene–Pliocene climate evolution recorded by the red clay cover on the Xiaoshuizi planation surface, NE Tibetan Plateau

The Pliocene climate and its driving mechanisms have attracted substantial scientific interest because of their potential as an analog for near-future climates. The late Miocene–Pliocene red clay sequence of the main Chinese Loess Plateau (CLP) has been widely used to reconstruct the history of interior Asian aridification and the Asian monsoon. However, red clay sequences deposited on the planation surface of the Tibetan Plateau (TP) are rare. A continuous red clay sequence was recently discovered on the uplifted Xiaoshuizi (XSZ) planation surface in the Maxian Mountains, northeastern (NE) TP. In this study, we analyzed multiple climatic proxies from the XSZ red clay sequence with the aim of reconstructing the late Miocene–early Pliocene climate history of the NE TP and to assess regional climatic differences between the central and western CLP. Our results demonstrate the occurrence of minimal weathering and pedogenesis during the late Miocene, which indicates that the climate was arid. We speculate that precipitation delivered by the paleo East Asian summer monsoon (EASM) was limited during this period and that the intensification of the circulation of the westerlies resulted in arid conditions in the study region. Subsequently, enhanced weathering and pedogenesis occurred intermittently during 4.7–3.9 Ma, which attests to an increase in effective moisture. We ascribe the arid–humid climatic transition near ∼4.7 Ma to the expansion of the paleo-EASM. The warming of the high northern latitudes in response to the closure of the Panama Seaway may have been responsible for the thermodynamical enhancement of the paleo-EASM system, which permitted more moisture to be transported to the NE TP.

Late Miocene-Pliocene climate evolution recorded by the red clay covered on the Xiaoshuizi planation surface, NE Tibetan Plateau

As an analogue for predicting the future climate, Pliocene climate and its driving mechanism attract much attention for a long time. Late Miocene-Pliocene red clay sequence on the main Chinese Loess Plateau (CLP) has been widely applied to reconstruct the history of interior aridification and Asian monsoon climate. However, the typical red clay sequences deposited on the planation surface of Tibetan Plateau are rare. Recently, continuous red clay has been found on the uplifted Xiaoshuizi peneplain in the Maxian Mountains, northeastern (NE) Tibetan Plateau (TP). To reconstruct the late Miocene-early Pliocene climate history of NE Tibetan Plateau and to assess the regional differences between the central and western CLP, multiple climatic proxies were analyzed from the Xiaoshuizi red clay sequence. Our results demonstrate the minimal weathering and pedogenesis from 6.7 to 4.8 Ma, which implicates that the climate was sustained arid. We speculate that precipitation delivered by the paleo-Asian Summer Monsoon (ASM) was limited during this period, and instead the intensification of the westerlies circulation resulted in arid condition in the study region. Subsequently, enhanced weathering and pedogenesis occurred during the interval of 4.8–3.6 Ma, which attests to increasing effective moisture. Thus, we ascribe the obvious arid-humid climate transition near 4.8 Ma to the palaeo-ASM expansion. Increasing Arctic temperatures, the vast poleward expansion of the tropical warm pool into the subtropical regions and water freshening in the subtropical Pacific in response to the closure of the Panamanian Seaway may have been responsible for the thermodynamical enhancement of the paleo-ASM system, which permitted more moisture to be carried to the NE Tibetan Plateau.

Geological evolution of the southwestern part of the Veporic Unit (Western Carpathians): based on fission track and morphotectonic data

Zircon and apatite fission track (FT) and morphotectonic analyses were applied in order to infer quantitative constraints on the Alpine morphotectonic evolution of the western part of the Southern Veporic Unit which is related to: (1) Eo-Alpine Cretaceous nappe stacking and metamorphism of the crystalline basement in the greenschist facies. (2) Exhumation phase due to underthrusting of the northerly located Tatric-Fatric basement (~ 90–80 Ma), followed by a passive en-block exhumation with cooling through ~ 320–200 °C during the Palaeocene (ZFT ages of ~ 61–55 Ma). (3) Slow Eocene cooling through ~ 245–90 °C, which most likely reflected erosion of the overlying cover nappes and the Gosau Group sediments. Cooling reached up to 60 °C till the Oligocene (AFT ages of ~ 37–22 Ma) in association with erosion of cover nappes. The efficient Eocene erosion led to the formation of the first Cenozoic planation surface with supergene kaolinization in many places. (4) The early Miocene erosion coincided with surface lowering and resulted in the second planation surface favourable for kaolinization. (5) In the middle Miocene, the study area was covered by the Poľana, Javorie, and Vepor stratovolcanoes. (6) The late Miocene stage was related to the erosion and formation of the third Cenozoic planation surface and the final shaping of the mountains was linked to a new accelerated uplift from the Pliocene.