Diagenetic replacement of Micas by Carbonates

In the Ordovician sandstones of the Cantabrian Mountains a replacement of the micas by carbonate minerals could be observed. The absence of metamorphic minerals suggests a diagenetic replacement. This is supported by the finding of the same type of replacement in some undisturbed Pliocene sediments of an intramontane basin in the French Pyrenees. It seems that replacement can occur at any stage during diagenesis

Sedimentological aspects of four Lower-Paleozoic formations in the northern part of the province of León (Spain)

This paper deals with the sedimentary structures and sedimentary petrography of the four lowermost formations of the Paleozoic as developed in the Northern part of the Province of León (Cantabrian Mountains, Spain). Three of the four formations have a detrital character, and one consists of dolomites and limestones. Mineralogically, the detrital formations are mature. Consequently the differences are small, but diagnostic. The source rocks will have been non-sedimentary. The Herreria Sandstone Formation is the oldest formation. Only its upper 200 metres are described here. This part consists of medium-grained quartzites with intercalations of shales, coarse quartzites, and conglomeratic beds. The detrital quartzes contain various kinds of inclusions and are often composite. Microcline, the common feldspar, is often kaolinized. Both minerals are secondarily enlarged. The source of the secondary quartz is duscussed; this quartz is held to have been supplied partially, and precipitated, form formational waters. The latter have the tendency to increase salinity, which lowers the silica solubility. The layers show predominantly a parallel lamination, but cross-lamination occurs as well. In two parts of the sequence the layers are wedge-shaped. The depositional environment is assumed to have been shallow, near the shore, with fluviatile influences. The Laucara Dolomite Formation can be subdivided into Dolomite s.l. and Griotte. The Lancara Dolomite s.l. contains dolomites, limestones, oolitic limestones, and breccias. The diagenetic process of grain growth transformed the original detrital texture of the limestones and dolomites. Dolomitization is assumed to have been postdepositional. Recrystallization due to mechanical stresses occurs as well. The oolitic limestones too are built up of various types of calcite in a textural sense. The time-relations between these types is discussed. These limestones contain authigenic quartzes, indicating high salinity of the environment. The Lancara Griotte consists of nodular limestones and shale layers with limestone nodules. The limestones are detrital in origin. The origin of the griotte is discussed: it is attributed to solutional processes. The depositional environment of the Lancara Dolomites s.l. is thought to be comparable to the recent Bahama Bank deposits. That of the Griotte is less distinct, but must have been shallow neritic. The red colour of the griotte may point to a warm, humid climate. The Oville Sandstone Formation is characterized by its clayey nature, high lime content, and the authigenic mineral glauconite. The micas show replacement by carbonates, a relatively unknown process. The origin and source of the glauconite is dealt with: cryptocrystalline aggregates are thought to have initially been clay, while the crystalline glauconites are altered micas. Of special interest are the slump structures. Since they are the result of a thixotropic behaviour of the sediments some rheological principles are briefly reviewed. It is also stated that internal slumping and convolute laminations are related in the sense that both are expressions of a false-body thixotropic state of the sediment. Such a state is to be expected within a certain range of moisture content: internal slumping occurs at the lowest values, convolute lamination at the highest values of the range. However, convolute lamination is observed more commonly in turbidity deposits because such deposits settle at higher rates than other sediments, consequently their moisture contents must have been higher. In this thin-bedded complex, parallel lamination dominates but small-scale cross-lamination is also present. Other sedimentary structures observed are load casts, pseudo-nodules and “Linsen” structures. The depositional environment is held to have been deltaic i.e. the formation represents a chain of deltas. The Barrios Quartzite Formation consists of quartzites with few shale beds and locally a conglomerate. The quartzes are limpid and do not contain inclusions. Composite grains are scarce. Feldspars are not kaolinized, only sericitized. The occurrence of the mica phengite is diagnostic. Most of the beds are wedge-shaped, which gives the formation a special appearance. Most beds have an slightly inclined lamination. Like the Oville deposits the Barrios sands are held to be deposits of a deltaic environment

Epidemiological investigation of a Rift Valley fever outbreak in humans and livestock in Kenya, 2018

On the last week of May of 2018, a community-based syndromic surveillance system detected mass abortions and deaths of young livestock in northeastern Kenya. Two weeks later, Rift Valley fever (RVF) was confirmed in humans presenting with febrile illness and hemorrhagic syndrome in the same region. A joint animal and human response team carried out an investigation to characterize the outbreak and identify drivers of disease transmission. Here, we describe the outbreak investigation and findings. A total of 106 human cases were identified in the months of May and June 2018: 92% (98) and 8% (8) of these cases occurring in the northern and western regions of Kenya, respectively. Seventy-six (72%) were probable cases, and 30 (28%) were laboratory confirmed by ELISA and/or PCR. Among the confirmed cases, the median age was 27.5 years (interquartile range = 20), and 60% (18) were males. Overall, the case fatality rate was 7% (n = 8). The majority of the confirmed cases, 19 (63%), reported contact with livestock during slaughter and consumption of meat from sick animals. All confirmed cases had fever, 40% (12) presented with hemorrhagic syndrome, and 23% (7) presented with jaundice. Forty-three livestock herds with at least one suspect and/or confirmed animal case were identified. Death of young animals was reported in 93% (40) and abortions in 84% (36) of livestock herds. The outbreak is indicative of the emergence potential of RVF in traditionally high- and low-risk areas and the risk posed by zoonosis to livestock keepers

High-resolution optical dating of Late Holocene storm surge deposits – a showcase from Schokland (Noordoostpolder, the Netherlands)

Storm surges have a major impact on land use and human habitation in coastal regions. Our knowledge of this impact can be improved by correlating long-term historical storm records with sedimentary evidence of storm surges, but so far few studies have applied such an approach. Here we apply, for the first time, state-of-the-art optically stimulating luminescence (OSL) methods to obtain high-resolution age information on a sequence of Late Holocene storm surge deposits. By combining this chronological framework of storm surges with other reconstruction methods, we investigate the storm surge impact on the former island Schokland, located in a former inlet of the North Sea (central Netherlands). During the Late Holocene, Schokland transformed from a peat area that gradually inundated (~800 CE) via an island in a marginal marine environment (~1600 CE) to a land-locked island in the reclaimed Province of Flevoland (1942 CE). These transitions are recorded in the sediment archive of the island, consisting of silty clay with sandy intervals deposited during storm surges. A series of ten quartz OSL ages, obtained using best-practice methods to deal with incomplete resetting of the OSL signal and dose rate heterogeneity, reveal two periods of storm surge deposition, around 1600 CE and between 1742 and 1822 CE. Historical sources indicate that major storm surges hit Schokland during these periods. Laboratory analyses (thermogravimetry, grain-size, foraminifera, bivalves and ostracods) corroborates the existence of the two sets of storm surge deposits within the clay sequence. Our study sets a benchmark for obtaining robust depositional age constraints from storm surge sediments, and demonstrates the great potential of modern OSL methods to contribute to improved assessment of storm surge risk. © 2018 John Wiley & Sons, Ltd