Limnic Sediments Research Articles

Resistivity investigation of an infilled kettle hole

An electrical resistivity survey of a lacustrine infilled basin in drift (Abbot Moss, N. England) clearly revealed the morphometry and internal structure of the basin. The technique also delimited extensions to the basin, which are buried beneath colluvium outside the present area of peat accumulation. Resistivity drilling has definite advantages over hand boring particularly for deposits formed between deglaciation and the onset of limnic sedimentation, or for sequences containing inpenetrable sand horizons. Geophysical techniques can provide an overall framework and gross stratigraphy of limnic deposits within which more detailed conventional Quaternary studies can be assessed.

Late-devensian and flandrian vegetational history of Bodmin Moor, Cornwall

A largely palynological study of new exposures of lake and mire sediments from Bodmin Moor, Cornwall, together with radiocarbon dating of the polliniferous deposits has allowed, for the first time in southwest England, description of dated local and regional pollen assemblage zones which can be correlated with the pollen zones of Godwin and the chronozones of West. Reconstruction of the vegetational history of the Late-Devensian, early and later Flandrian periods is attempted by using, wherever possible, values for the pollen content of sediments to illuminate real pollen taxon percentage fluctuations. Deposition of limnic sediments in the Late-Devensian started shortly before 13000 b.p. when the dominant vegetation, open grass heaths, snow-beds and flushes, reflects the cold climate. Soils at this time were subject to erosion by snow melt-water. Ensuing climatic amelioration permitted invasion by juniper scrub and about 12000 b.p. expansion of tree birches took pace. Climatic recession occurring under strongly oceanic conditions (marked by considerable amorphous solifluction of the upland soils and the development of grass/sedge mires) was initiated about 11000 b.p., but its duration here cannot be accurately estimated. Within this threefold pattern of Late-Devensian deposition 12 distinct pollen assemblages are described from four profiles. Pollen of Artemisia norvegica, Astragalus alpinus and Saxifraga stellaris is confined to the earlier and later colder periods. In the intervening warmer period, but not the colder periods, there is slight pollen and macroscopic fossil evidence of Betula nana. An unexplained unconformity exists at the base of the Flandrian deposits. Early Flandrian vegetation is characterized by the spread of tree birches and Salix in the valleys, with Empetrum and juniper on the hillsides. The two latter genera are replaced before 9000 b.p. by Corylus followed almost immediately by the spread of Quercus. Throughout the Flandrian Quercus , Betula and Corylus , although the dominant woodland genera, probably colonized only the more sheltered sites on the upland. Archaeological and palynological records have been correlated as far as possible, the only substantial pollen record of human activity being that of Plantago , which spread encouraged by Bronze Age pastoralism. There is also pollen evidence of scanty cereal cultivation. Areas on the Atlantic fringes of Europe show a marked similarity in their early Flandrian forest history, particularly with regard to the slight role played by Pirns in relation to Quercus compared with stations further east. This similarity must derive from the proximity of the tempering influences of the North Atlantic Drift.

A coring method for lake surface sediments

A technique for coring flocculent limnic sediments, involving the use of a Livingstone piston sampler and dry ice is described. The technique is most useful when detailed stratigraphic analysis of surface sediments is important.

The pollen stratigraphy of a dated section of Late Pleistocene lake sediment from central Alberta

A 5.5 m section of limnic sediment from Lofty Lake in the Mixedwood Section of the Boreal Forest in central Alberta has yielded the first complete Late Pleistocene pollen stratigraphy for the province. The basal organic sediment was radiocarbon dated at 11 400 ± 190 y (GSC-1049) and a layer of Mount Mazama type ash was recognized at the 398 cm level. This represents the furthest extension into Canada of Mazama ash records. Five pollen assemblage zones have been identified—at the base, a Populus – Salix – Shepherdia – Artemisia assemblage, which is unique in the Late Pleistocene of N. America, and is interpreted as a pioneer forest and shrub community which occupied the area immediately following deglaciation. This is succeeded by a spruce dominated assemblage which conforms in general to many early Late Pleistocene Picea assemblages from western Canada and adjacent United States, interpreted as a pioneering version of the boreal forest. There follows a tree birch-dominated assemblage with poplar and hazel, suggesting a slight amelioration of climate, and this trend appears to have continued to about 6000 B.P. when a birch – alder – herb assemblage reaches its maximum; this is followed by a spruce – birch – alder assemblage, which continued to the present and is interpreted as an expression of a deterioration in climate about 3500 B.P. The apparent absence at the site of grassland, although the birch – alder – herb assemblage suggests that the grassland might have advanced closer to the site than at present (240 km (150 miles)), supports the hypothesis that there was never a Late Pleistocene connection between the Peace River and the main southern grasslands.

Angiospermous leaves from the Lower Cretaceous Kome Formation of northern West Greenland

The Korne Formation occurs on the north side of Nûgssuaq peninsula (70°5'N) in northern West Greenland. It extends from Ikorfat (53°5'W) eastwards to Kûk. The limnic sediments of the Korne Formation, comprising shales, coal seams and sandstones, lie on weathered Precambrian gneisses and are overlain by a younger limnic formation with more sandy sediments. The two formations are separated by a low-angle unconformity at a height of 400-500 m. The upper limnic formation has been shown by means of plant microfossils to belong to the lower part of the Upper Cretaceous. In the western part of the area the two limnic formations are overlain by marine sediments of Senonian age (Rosenkrantz, 1951).

CONTRIBUTIONS TO THE HOLOCENE PALEOECOLOGY OF WESTCENTRAL CANADA: A LATE-GLACIAL DEPOSIT FROM THE MISSOURI COTEAU

A buried deposit of limnic sediment was excavated from a site on the Missouri Coteau of Saskatchewan, within the Mixed Prairie section of the Great Plains. Carbon-14 determinations indicate that the section is late-glacial, possibly deposited during an interstadial terminated by the Condie (= Valders?) re-advance. On the basis of the records of about 60 taxa of Tracheophyta and a pollen diagram, the section is characterized by lower, middle, and upper plant assemblages. It is suggested that the lower and upper assemblages, distinguished mainly by a Picea – Shepherdia canadensis – Salix – Artemisia pollen spectrum, indicate the prevalence on mesic sites of a spruce forest. The middle assemblage, having an array of macrofossils and a few microfossils of temperate geographical affinity and a pollen spectrum suggesting relatively less spruce and (or) more herbaceous vegetation, is interpreted in terms of a mixed spruce–poplar forest on mesic sites with shrub and grassland communities on the more xeric habitats. This tripartite division of the section in terms of ecologically concordant plant assemblages suggests an amelioration of environment followed by a deterioration which was probably correlative with the Condie re-advance.

De miocæne Formationer i Danmark

The Miocene Formations of Denmark.The Miocene sediments of Denmark are restricted to the central and western part of the peninsula of Jutland. The Danish Miocene basin forms the northern part of the Miocene North Sea Basin which also covered parts of Northern Germany, Holland and Belgium. More than 200 metres of mainly micaceous clays and sands, often richly fossiliferous, were deposited. The distribution and thickness of the Miocene in Denmark is shown on the map, fig. 1, page 10.Since long the Danish Miocene has been subdivided time-stratigraphically in a Lower, Middle, and Upper division on the basis of paleontological studies by J.P.J. Ravn (1907) and Nørregaard (1916). Works by Sorgenfrei (1940, 1958) and Rasmussen (1956) recently increased our knowledge of the Danish Miocene molluscan faunas and formations.The following 6 formations are now recognized in the Miocene of Denmark (cf. fig. 7, page 41):6. Gram formation (marine). Rasmussen 1956, p. 16 (Age: Upper Miocene).5. Hodde formation (marine). This paper, p. 32 (Age: Middle Miocene).4. Odderup formation (limnic). This paper, p. 30 (Age: Middle Miocene).3. Arnum formation (marine). Sorgenfrei, 1958, p. 28 (Age: Middle Miocene).2. Ribe formation (limnic). Sorgenfrei, 1958, p. 28 (Age: Middle or Lower Miocene).1. Klintinghoved formation (marine). Klintinghoved clay, Sorgenfrei, 1940, p. 68 (Age: Lower Miocene).The type section of the Odderup formation is defined as the interval from 28,2 to 40,3 m below surface in DGU well file no. 103.50 (at Odderup Brickworks). The form ation consists of limnic sediments of quartz sands with lignite.The type section of the Hodde formation is from 13,8 to 23,4 m below surface in the well DGU well file no. 113.33 a, Hoddemark (NE of Varde). The formation consists of marine sediments of micaceous clays and sands with beds of quartz sand.The distribution of the Marine Middle Miocene of Denmark is shown on map, fig. 2, page 30 and the distribution of the Marine Upper Miocene is shown on map fig. 4, page 34.

Moodys Branch-Cockfield Contact in Sabine Parish, Louisiana, and Adjacent Areas

Brackish or marginal-marine upper Cockfield sediments are exposed between the Red and Sabine rivers in western Louisiana. These clays, silts, and sands are complexly lenticular and interfinger with many deltaic fresh-water beds of similar composition. The Jacksonian Moodys Branch formation, overlying the Cockfield, consists of rather uniform, glauconitic, marine sands throughout its known outcrop in this area. Two sedimentary facies comprise the Cockfield directly below the Moodys Branch. In southwest Sabine Parish marginal-marine deposits (Creola member) predominate; elsewhere, fresh-water deltaic sediments underlie the marine beds of the Moodys Branch. Brackish deposits occur in places stratigraphically below these fresh-water deposits. In both occurrences the contact is sharp. However, borings, extending from the Moodys Branch several feet into the Cockfield, are commonly encountered. At one locality deltaic fresh-water Cockfield grades through several feet into the Moodys Branch. Analysis of the microfauna found in the Creola and Moodys Branch sediments shows that more than half of the species collected do not cross the Moodys Branch-Cockfield boundary. Furthermore, the Creola fauna is much less abundant. This change, although indicative of some break in deposition, is considered primarily ecologic. In this area there is small, but apparent, stratigraphic discontinuity between the Moodys Branch and Cockfield formations. The term diastem most nearly expresses this relationship when viewed locally. These strata and their contact relationships are favorably comparable with conditions in parts of the Louisiana coast where marine sands are encroaching on contemporaneous and slightly older brackish and limnic sediments.