scholarly journals Stratigraphy, chronology and palaeontology of the Tertiary rocks of the Cheringoma Plateau, Mozambique

2021 ◽  
Vol 77 (1) ◽  
pp. 187-213
Author(s):  
Marion Bamford ◽  
Martin Pickford
Keyword(s):  
Water Table ◽  
High Water ◽  
Late Eocene ◽  
Rift System ◽  
Fossil Plants ◽  
Near Surface ◽  
Marine Molluscs ◽  
History Of Interpretation ◽  
History Of ◽  
African Rift

The discovery of fossil plants, marine molluscs and mammals in the Mazamba Formation, Cheringoma Plateau, Mozambique, opens a new chapter in the study of this part of the African Rift System. The evidence suggests that the Mazamba Formation is older than previously reported, probably late Eocene rather than Miocene. The fossil wood and stems indicate a frost-free tropical humid environment and a high water table soon after deposition, and the marine molluscs and mammals indicate proximity to the sea. There is also evidence for the occurrence of pans in the area during the late Eocene which also suggest a near-surface water table. This paper discusses the history of interpretation of the geology of the Cheringoma Plateau and describes and interprets the fossil plants, molluscs and mammals collected in 2012 and 2013. It is concluded that the Mazamba Formation, which overlies the fully marine Lutetian-Bartonian Cheringoma Limestone, is a coastal facies (fluvio-deltaic, lagoonal and onshore deposits) that accumulated on top of the marine limestones as sea level dropped late in the Bartonian. Mammalian bones from the White Patch sites represent a heavily built species about the dimensions of a pygmy hippopotamus, probably belonging to the order Embrithopoda. If so, then the Mazamba Formation is likely to correlate to the latest Bartonian or early Priabonian rather than to the Miocene as previously assumed.

The unexpected, recent history of horsetails in Australia

2019 ◽  
Author(s):  
Andrew C. Rozefelds ◽  
Mary E. Dettmann ◽  
Anita K. Milroy ◽  
Andrew Hammond ◽  
H. Trevor Clifford ◽  
...  
Keyword(s):  
Spatial Arrangement ◽  
Molecular Data ◽  
Leaf Sheath ◽  
Late Eocene ◽  
Fossil Flora ◽  
Fossil Plants ◽  
Outer Cortex ◽  
Early Oligocene ◽  
Extant Species ◽  
History Of

A new fossil flora from central Queensland, of late Eocene or early Oligocene age, has yielded a diverse assemblage of flowering plants and ferns, including the first evidence of horsetails (Equisetum L.) from the Cenozoic of Australia. The fossils assigned to Equisetum are based on a stem fragment, 2–3mm in diameter, and spreading leaf sheath and diaphragm. The leaf sheath is interpreted to consist of ~24–30 leaves. The spatial arrangement of regularly arranged depressions in a section of the outer cortex is interpreted as evidence of the leaf vascular traces, and indicates a similar number of vascular traces. This specimen provides the youngest evidence of the genus from Australia and indicates that Equisetum survived for at least another 50 million years after it was thought to be extinct in Australia. Whereas molecular data for extant species of Equisetum collectively suggest a comparatively recent origin and radiation, the fossil record of the genus indicates a significantly longer and more complex history. Fossils, such as the new specimen from Makowata, Queensland, will, therefore, play a key role in understanding the history and past distribution of Equisetum in Australia. A key challenge is to assemble and characterise the morphological traits of these living and fossil plants to better understand the origins, history and radiation of this remarkable group of euphyllophytes.

Wet in the Anthropocene – a report of exceptionally stable hydrological conditions in a small bog over the last 1500 years

2021 ◽  
Author(s):  
Katarzyna Marcisz ◽  
Piotr Kołaczek ◽  
Mariusz Gałka ◽  
Andrei-Cosmin Diaconu ◽  
Mariusz Lamentowicz
Keyword(s):  
High Resolution ◽  
Water Table ◽  
High Water ◽  
Fragmented Landscape ◽  
Target Number ◽  
Central Eastern Europe ◽  
Ne Poland ◽  
Water Tables ◽  
History Of ◽  
High Resolution Reconstruction

<p>Over the last few hundred years peatlands worldwide are experiencing substantial drying that is lowering their carbon storage potential. However, our high-resolution reconstruction of hydrological changes in a small <em>Sphagnum</em>-dominated peatland show that we can still observe healthy bogs in the fragmented landscape of Europe (Marcisz et al., 2020). We investigated last 1500 years history of a bog located in a young glacial landscape in Central Eastern Europe (NE Poland) using a multi-proxy approach and high-resolution dating. Our reconstruction showed a rare case of hydrological stability in the peatland that did not experience any dry shift over the last 1500 years, allowing for an undisturbed growth of <em>Sphagnum</em>, stable microbial communities, and high peat accumulation rates. High water tables (>12 cm depth to water table) influenced high resilience of the bog which was not affected by disturbances (deforestations, grazing or farming). Our palaeoecological data suggest that nature conservation practices which target high water tables are essential to maintain peatlands as a sink and not as a source of carbon in the future, supporting an earlier study that concluded a ca. 11-12 cm water table depth as a target number for peatland protection (Lamentowicz et al., 2019).</p><p>References:</p><p>Lamentowicz, M., Gałka, M., Marcisz, K., Słowiński, M., Kajukało-Drygalska, K., Druguet Dayras, M., Jassey, V.E.J., 2019. Unveiling tipping points in long-term ecological records from <em>Sphagnum</em>-dominated peatlands. Biology Letters 15, 20190043.</p><p>Marcisz, K., Kołaczek, P., Gałka, M., Diaconu, A.-C., Lamentowicz, M., 2020. Exceptional hydrological stability of a <em>Sphagnum</em>-dominated peatland over the late Holocene. Quaternary Science Reviews 231, 106180.</p>

X V III. Discussion

1965 ◽  
Vol 258 (1088) ◽  
pp. 205-213 ◽  
Keyword(s):  
Red Sea ◽  
Continental Drift ◽  
Rift System ◽  
Gulf Of Aden ◽  
Vertical Movements ◽  
Red Sea Rift ◽  
Geological Features ◽  
Carlsberg Ridge ◽  
History Of ◽  
African Rift

We have heard many excellent arguments in favour of continental drift, based on the most recent results of studies of the ocean floors, the fit of the continents, the palaeomagnetic picture, and several instances of the relation between geological features and the supposed movement of the continents. It has struck me that these geological features are very restricted in number; they are either the oceanic rifts or wrench faults. Let us have a look first at the oceanic rifts. They are directly connected, through the Carlsberg Ridge and the Gulf of Aden with the Red Sea Rift and then through the Ethiopian faults with the famous African rifts. The history of the African rift system is relatively well known, and we know for certain that they represent principally vertical movements of the Earth’s crust, which have lasted at least from the Tertiary and probably since the Jurassic.

Geochronology of the Nabwal Hills: a record of earliest magmatism in the northern Kenyan Rift Valley

2005 ◽  
Vol 143 (1) ◽  
pp. 25-39 ◽  
Author(s):  
IAN McDOUGALL ◽  
RONALD T. WATKINS
Keyword(s):  
Late Miocene ◽  
Alkali Feldspar ◽  
East African Rift ◽  
Late Eocene ◽  
Rift System ◽  
Crustal Extension ◽  
East African Rift System ◽  
East African ◽  
Metamorphic Basement ◽  
African Rift

The Nabwal Hills, northeast of Lake Turkana, contain a record of magmatism associated with the initiation and early development of the East African Rift System in northernmost Kenya. The predominantly volcanic Asille Group, 1400 m thick, directly overlies metamorphic basement and comprises a sequence of basaltic lava flows with significant intervals of rhyolitic pyroclastic units, and minor intercalations of fluviatile sediments. The basement gneisses yield K–Ar cooling ages on biotite of 510 and 522 Ma, typically Pan-African. The 40Ar–39Ar ages on alkali feldspar crystals from the rhyolitic units are concordant and show that the Asille Group spans an interval from at least 34.3 to 15.8 Ma, continuing to at least as young as 13 Ma based on previous measurements. Vertebrate fossil sites, containing primate remains, at Irile and Nabwal are shown to be 17 ± 2 Ma old, Early Miocene, based upon K–Ar age measurements on immediately overlying basalts. Variably reliable whole rock K–Ar ages, determined on basalt samples from low in the sequence, indicate that volcanism commenced as early as 34.8 Ma ago. The overall geochronological results show that magmatism in the Nabwal Hills began about 35 Ma ago in Late Eocene times, interpreted as the time of initiation of crustal extension that led to the development of this segment of the East African Rift System. The Asille Group is tilted about 6° to the SSW. This tilting occurred later than 13 Ma ago, and prior to the eruption of the flat-lying Gombe Group basalts. These basalts may have begun erupting about 6 Ma ago in Late Miocene times, although much of this volcanism occurred between about 3.9 and 4.2 Ma ago in Pliocene times. It is suggested that the main rifting, which continues today, commenced in Late Miocene times, less than 13 Ma ago, and is partly reflected in the tilting of the Asille Group.

scholarly journals Seasonally frozen soil modifies patterns of boreal peatland wildfire vulnerability

2018 ◽  
Author(s):  
Simon J. Dixon ◽  
Max C. Lukenbach ◽  
Nicholas Kettridge ◽  
Kevin J. Devito ◽  
Richard M. Petrone ◽  
...  
Keyword(s):  
Water Balance ◽  
Water Table ◽  
High Water ◽  
Vital Role ◽  
Frozen Soil ◽  
Near Surface ◽  
Smoldering Combustion ◽  
Global Carbon ◽  
Frost Layer ◽  
Water Contents

Abstract. Peatlands play a vital role in the global carbon cycle, acting as one of the most important global carbon sinks. However, an understanding of their environmental processes, particularly in relation to a changing climate, remains inchoate. In particular, the role seasonal ice or frost layers play in altering spring water balance, and thus vulnerability to deep smoldering combustion during wildfire is not fully understood. Continental boreal peatlands are characterized by periodic wildfire disturbance, which releases carbon, but can also inhibit short-term peat productivity and carbon sequestration as the peatland recovers, with recovery timescales linked to the severity or depth of burning. The presence of seasonal frost layers coincides with drier spring conditions and an enhanced risk of wildfire. Two-dimensional numerical modelling was conducted using HYDRUS-2D, a variably saturated flow model, to simulate water balance in the vadose zone and assess vulnerability to fire during prolonged rain free periods in the presence of continuous and discontinuous frost. Our results show there is a lack of horizontal water transfer which increases spatial variability in water balance and leads to pronounced heterogeneity in the risk of smoldering combustion and the potential for deep combustion at hummock-hollow interfaces. Peatlands are broadly divided into areas which are characterized by a dry near-surface and high water contents at depth (water conserving), and those with a wetter near-surface, but comparatively lower water contents at depth (productive). Those areas with dry near-surfaces will be more vulnerable to wildfire and characterize around 50 % of hummocks and 25 % of hollows. In the presence of a seasonal frost layer productive peat layers in hollows will show substantial drying out due to the frost layer disconnecting the surface from the water table; this approximately doubles the proportion of hollows vulnerable to wildfire. Breaks in the frost layer allows areas to maintain hydrological connectivity to a falling water table, but this connectivity is limited in lateral extent and can drive further spatial heterogeneity in vulnerability to wildfire ignition in the weeks when the frost layer begins to thaw.

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