In crystallography, the terms crystal system, crystal family, lattice system each refer to one of several classes of space groups, point groups, or crystals. Informally, two crystals are in the same crystal system if they have similar symmetries, although there are many exceptions to this. Crystal systems, crystal families and lattice systems are similar but different, there is widespread confusion between them: in particular the trigonal crystal system is confused with the rhombohedral lattice system, the term "crystal system" is sometimes used to mean "lattice system" or "crystal family". Space groups and crystals are divided into seven crystal systems according to their point groups, into seven lattice systems according to their Bravais lattices. Five of the crystal systems are the same as five of the lattice systems, but the hexagonal and trigonal crystal systems differ from the hexagonal and rhombohedral lattice systems; the six crystal families are formed by combining the hexagonal and trigonal crystal systems into one hexagonal family, in order to eliminate this confusion.
A lattice system is a class of lattices with the same set of lattice point groups, which are subgroups of the arithmetic crystal classes. The 14 Bravais lattices are grouped into seven lattice systems: triclinic, orthorhombic, rhombohedral and cubic. In a crystal system, a set of point groups and their corresponding space groups are assigned to a lattice system. Of the 32 point groups that exist in three dimensions, most are assigned to only one lattice system, in which case both the crystal and lattice systems have the same name. However, five point groups are assigned to two lattice systems and hexagonal, because both exhibit threefold rotational symmetry; these point groups are assigned to the trigonal crystal system. In total there are seven crystal systems: triclinic, orthorhombic, trigonal and cubic. A crystal family is determined by lattices and point groups, it is formed by combining crystal systems which have space groups assigned to a common lattice system. In three dimensions, the crystal families and systems are identical, except the hexagonal and trigonal crystal systems, which are combined into one hexagonal crystal family.
In total there are six crystal families: triclinic, orthorhombic, tetragonal and cubic. Spaces with less than three dimensions have the same number of crystal systems, crystal families and lattice systems. In one-dimensional space, there is one crystal system. In 2D space, there are four crystal systems: oblique, rectangular and hexagonal; the relation between three-dimensional crystal families, crystal systems and lattice systems is shown in the following table: Note: there is no "trigonal" lattice system. To avoid confusion of terminology, the term "trigonal lattice" is not used; the 7 crystal systems consist of 32 crystal classes as shown in the following table: The point symmetry of a structure can be further described as follows. Consider the points that make up the structure, reflect them all through a single point, so that becomes; this is the'inverted structure'. If the original structure and inverted structure are identical the structure is centrosymmetric. Otherwise it is non-centrosymmetric.
Still in the non-centrosymmetric case, the inverted structure can in some cases be rotated to align with the original structure. This is a non-centrosymmetric achiral structure. If the inverted structure cannot be rotated to align with the original structure the structure is chiral or enantiomorphic and its symmetry group is enantiomorphic. A direction is called polar if its two directional senses are physically different. A symmetry direction of a crystal, polar is called a polar axis. Groups containing a polar axis are called polar. A polar crystal possesses a unique polar axis; some geometrical or physical property is different at the two ends of this axis: for example, there might develop a dielectric polarization as in pyroelectric crystals. A polar axis can occur only in non-centrosymmetric structures. There cannot be a mirror plane or twofold axis perpendicular to the polar axis, because they would make the two directions of the axis equivalent; the crystal structures of chiral biological molecules can only occur in the 65 enantiomorphic space groups.
The distribution of the 14 Bravais lattices into lattice systems and crystal families is given in the following table. In geometry and crystallography, a Bravais lattice is a category of translative symmetry groups in three directions; such symmetry groups consist of translations by vectors of the form R = n1a1 + n2a2 + n3a3,where n1, n2, n3 are integers and a1, a2, a3 are three non-coplanar vectors, called primitive vectors. These lattices are classified by the space group of the lattice itself, viewed as a collection of points, they represent the maximum symmetry. All crystalline materials must, by definition, fit into one of these arrangements. For convenience a Bravais lattice is depicted by a unit cell, a factor 1, 2, 3 or 4 larger than the primitive cell. Depending on the symmetry of a crystal or other pattern, the fundamental domain is again smaller, up to a factor 48; the Bravais lattices were studied by Moritz Ludwig Frankenheim in 1842, who found that there we
Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite crystallographic structural planes. These planes of relative weakness are a result of the regular locations of atoms and ions in the crystal, which create smooth repeating surfaces that are visible both in the microscope and to the naked eye. Cleavage forms parallel to crystallographic planes: Basal or pinacoidal cleavage occurs when there is only one cleavage plane. Graphite has basal cleavage. Mica has basal cleavage. Cubic cleavage occurs on. Halite has cubic cleavage, therefore, when halite crystals are broken, they will form more cubes. Octahedral cleavage occurs. Fluorite exhibits perfect octahedral cleavage. Octahedral cleavage is common for semiconductors. Diamond has octahedral cleavage. Rhombohedral cleavage occurs when there are three cleavage planes intersecting at angles that are not 90 degrees. Calcite has rhombohedral cleavage. Prismatic cleavage occurs. Spodumene exhibits prismatic cleavage. Dodecahedral cleavage occurs.
Sphalerite has dodecahedral cleavage. Crystal parting occurs when minerals break along planes of structural weakness due to external stress or along twin composition planes. Parting breaks are similar in appearance to cleavage, but only occur due to stress. Examples include magnetite which shows octahedral parting, the rhombohedral parting of corundum and basal parting in pyroxenes. Cleavage is a physical property traditionally used in mineral identification, both in hand specimen and microscopic examination of rock and mineral studies; as an example, the angles between the prismatic cleavage planes for the pyroxenes and the amphiboles are diagnostic. Crystal cleavage is of technical importance in the electronics industry and in the cutting of gemstones. Precious stones are cleaved by impact, as in diamond cutting. Synthetic single crystals of semiconductor materials are sold as thin wafers which are much easier to cleave. Pressing a silicon wafer against a soft surface and scratching its edge with a diamond scribe is enough to cause cleavage.
Elemental semiconductors are a space group for which octahedral cleavage is observed. This means. Most other commercial semiconductors can be made in the related zinc blende structure, with similar cleavage planes. Cleavage Mineral galleries: Mineral properties – Cleavage
The chlorites are a group of phyllosilicate minerals. Chlorites can be described by the following four endmembers based on their chemistry via substitution of the following four elements in the silicate lattice. In addition, zinc and calcium species are known; the great range in composition results in considerable variation in physical, X-ray properties. The range of chemical composition allows chlorite group minerals to exist over a wide range of temperature and pressure conditions. For this reason chlorite minerals are ubiquitous minerals within low and medium temperature metamorphic rocks, some igneous rocks, hydrothermal rocks and buried sediments; the name chlorite is in reference to its color. They do not contain the element chlorine named from the same Greek root; the typical general formula is: 34O102 · 36. This formula emphasizes the structure of the group. Chlorites have a 2:1 sandwich structure, this is referred to as a talc layer. Unlike other 2:1 clay minerals, a chlorite's interlayer space is composed of 6.
This 6 unit is more referred to as the brucite-like layer, due to its closer resemblance to the mineral brucite. Therefore, chlorite's structure appears as follows: -t-o-t-brucite-t-o-t-brucite... That's why they are called 2:1:1 minerals. An older classification divided the chlorites into two subgroups: the orthochlorites and leptochlorites; the terms are used and the ortho prefix is somewhat misleading as the chlorite crystal system is monoclinic and not orthorhombic. Chlorite is found in igneous rocks as an alteration product of mafic minerals such as pyroxene and biotite. In this environment chlorite may be a retrograde metamorphic alteration mineral of existing ferromagnesian minerals, or it may be present as a metasomatism product via addition of Fe, Mg, or other compounds into the rock mass. Chlorite is a common mineral associated with hydrothermal ore deposits and occurs with epidote, sericite and sulfide minerals. Chlorite is a common metamorphic mineral indicative of low-grade metamorphism.
It is the diagnostic species of the zeolite facies and of lower greenschist facies. It occurs in the quartz, sericite, garnet assemblage of pelitic schist. Within ultramafic rocks, metamorphism can produce predominantly clinochlore chlorite in association with talc. Experiments indicate that chlorite can be stable in peridotite of the Earth's mantle above the ocean lithosphere carried down by subduction, chlorite may be present in the mantle volume from which island arc magmas are generated. Chlorite occurs in a variety of locations and forms. For example, chlorite is found in certain parts of Wales in mineral schists. Chlorite is found in large boulders scattered on the ground surface on Ring Mountain in Marin County, California. Clinoclore and chamosite are the most common varieties. Several other sub-varieties have been described. A massive compact variety of clinochlore used as a decorative carving stone is referred to by the trade name seraphinite, it occurs in the Korshunovskoye iron skarn deposit in the Irkutsk Oblast of Eastern Siberia.
Chlorite is so soft. The powder generated by scratching is green, it feels oily. The plates are not elastic like mica. Talc feels soapy between fingers; the powder generated by scratching is white. Mica plates are elastic. Various types of chlorite stone have been used as raw material for carving into sculptures and vessels since prehistoric times. List of minerals Thuringite Hurlbut CS, Klein C. Manual of Mineralogy. New York: Wiley & Sons. ISBN 0471805807. Grove TL, Chatterjee N, Parman SW, et al.. "The influence of H2O on mantle wedge melting". Earth Planet. Sci. Lett. 249: 74–89. Bibcode:2006E&PSL.249...74G. Doi:10.1016/j.epsl.2006.06.043. "The Mineral Chlorite". Amethyst Galleries. 1996. Archived from the original on 25 Nov 2004. Retrieved 22 Mar 2019. "Chlorite Group: Mineral information and localities". Mindat.org. Retrieved 22 Mar 2019. "Chlorite". Maricopa.edu. Archived from the original on 12 Nov 2014. Retrieved 22 Mar 2019.]
Western Canada referred to as the Western provinces and more known as the West, is a region of Canada that includes the four provinces of Alberta, British Columbia and Saskatchewan. British Columbia is culturally, economically and politically distinct from the other parts of Western Canada and is referred to as the "west coast" or "Pacific Canada", while Alberta and Manitoba are grouped together as the Prairie Provinces and most known as "The Prairies"; the capital cities of the four western provinces, from west to east, are. With the exception of Winnipeg, the largest city in Manitoba, all other provincial capitals of the Western Provinces are located in the second-largest metropolitan areas of their respective province. Western Canada is the traditional territory of numerous First Nations predating the arrival of Europeans; as Britain colonized the west, it established treaties with various First Nations, took control of other areas without opposition and fought with other First Nations to take control of Western Canada.
Not all lands were ceded by the First Nations to British control and land claims are still ongoing. In 1858, the British government established the Colony of British Columbia, governing that part of Canada still known as British Columbia; the British government established the Hudson's Bay Company which controlled most of the current area of Western Canada, northern Ontario and northern Quebec, the area known as Rupert's Land and the North-Western Territory. In 1870, the British government transferred the lands of the company to Canada; the area of Western Canada not within British Columbia was established as the Northwest Territories under Canadian control. The Western Canadian provinces other than British Columbia were established from areas of the Northwest Territories: Manitoba established as a province of Canada in 1870, following the enacting of the Manitoba Act. British Columbia: Under terms that Canada would absorb the colony's debt, would begin to subsidize public work, would begin to construct a railway allowing travel from British Columbia to Ontario, British Columbia agreed to join Canadian confederation in 1871.
Saskatchewan: Established as province in 1905, with the implementation of the Saskatchewan Act. Alberta: In 1905, the same year as Saskatchewan, Alberta was established as province. Just like Saskatchewan had the Saskatchewan Act, Alberta had the Alberta Act; as of the 2016 Census, the total population of Western Canada was nearly 11.1 million, including 4.65 million in British Columbia, 4.07 million in Alberta, 1.1 million in Saskatchewan, 1.28 million in Manitoba. This represents 31.5% of Canada's population. While Vancouver serves as the largest metropolitan area in Western Canada at nearly 2.5 million people, Calgary serves as the largest municipality at over 1.2 million people. As of the 2016 Census, Statistics Canada recognized ten census metropolitan areas within Western Canada, including four in British Columbia, three in Alberta, two in Saskatchewan, one in Manitoba; the following is a list of these areas and their populations as of 2016. From 2011 to 2016, the fastest growing CMAs in the country were the five located in Alberta and Saskatchewan: Calgary, Saskatoon and Lethbridge.
These were the only CMAs in the country to register growth over 10%. The three fastest growing CMAs - Calgary and Saskatoon - were unchanged from the previous intercensal period. Western Canada consists of the country's four westernmost provinces: British Columbia, Alberta and Manitoba, it covers 2.9 million square kilometres – 29% of Canada's land area. British Columbia adjoins the Pacific Ocean to the west, while Manitoba has a coastline on Hudson Bay in its northeast of the province. Both Alberta and Saskatchewan are landlocked between British Manitoba; the Canadian Prairies are part of a vast sedimentary plain covering much of Alberta, southern Saskatchewan, southwestern Manitoba. The prairies form a significant portion of the land area of Western Canada; the plains describes the expanses of flat, arable agricultural land which sustain extensive grain farming operations in the southern part of the provinces. Despite this, some areas such as the Cypress Hills and Alberta Badlands are quite hilly and the prairie provinces contain large areas of forest such as the Mid-Continental Canadian forests.
In Alberta and British Columbia, the Canadian Cordillera is bounded by the Rocky Mountains to the east and the Pacific Ocean to the west. The Canadian Rockies are part of a major continental divide that extends north and south through western North America and western South America; the continental divide defines much of the border between Alberta and British Columbia. The Columbia and the Fraser Rivers have their headwaters in the Canadian Rockies and are the second- and third-largest rivers to drain to the west coast of North America. To the west of their headwaters, across the Rocky Mountain Trench, is a second belt of mountains, the Columbia Mountains, comprising the Selkirk, Purcell and Cariboo Mountains sub-ranges; the coast of British Columbia enjoys a moderate oceanic climate because of the influence of the Pacific Ocean, with temperatures similar to those of the British Isles. Winters are wet and summers dry; these areas enjoy the mildest winter weather in all of Canada, as temperatures fall much below the freezing mark.
The mountainous Interior of the province is drier
Limestone is a carbonate sedimentary rock, composed of the skeletal fragments of marine organisms such as coral and molluscs. Its major materials are the minerals calcite and aragonite, which are different crystal forms of calcium carbonate. A related rock is dolostone, which contains a high percentage of the mineral dolomite, CaMg2. In fact, in old USGS publications, dolostone was referred to as magnesian limestone, a term now reserved for magnesium-deficient dolostones or magnesium-rich limestones. About 10% of sedimentary rocks are limestones; the solubility of limestone in water and weak acid solutions leads to karst landscapes, in which water erodes the limestone over thousands to millions of years. Most cave systems are through limestone bedrock. Limestone has numerous uses: as a building material, an essential component of concrete, as aggregate for the base of roads, as white pigment or filler in products such as toothpaste or paints, as a chemical feedstock for the production of lime, as a soil conditioner, or as a popular decorative addition to rock gardens.
Like most other sedimentary rocks, most limestone is composed of grains. Most grains in limestone are skeletal fragments of marine organisms such as foraminifera; these organisms secrete shells made of aragonite or calcite, leave these shells behind when they die. Other carbonate grains composing limestones are ooids, peloids and extraclasts. Limestone contains variable amounts of silica in the form of chert or siliceous skeletal fragment, varying amounts of clay and sand carried in by rivers; some limestones do not consist of grains, are formed by the chemical precipitation of calcite or aragonite, i.e. travertine. Secondary calcite may be deposited by supersaturated meteoric waters; this produces speleothems, such as stalactites. Another form taken by calcite is oolitic limestone, which can be recognized by its granular appearance; the primary source of the calcite in limestone is most marine organisms. Some of these organisms can construct mounds of rock building upon past generations. Below about 3,000 meters, water pressure and temperature conditions cause the dissolution of calcite to increase nonlinearly, so limestone does not form in deeper waters.
Limestones may form in lacustrine and evaporite depositional environments. Calcite can be dissolved or precipitated by groundwater, depending on several factors, including the water temperature, pH, dissolved ion concentrations. Calcite exhibits an unusual characteristic called retrograde solubility, in which it becomes less soluble in water as the temperature increases. Impurities will cause limestones to exhibit different colors with weathered surfaces. Limestone may be crystalline, granular, or massive, depending on the method of formation. Crystals of calcite, dolomite or barite may line small cavities in the rock; when conditions are right for precipitation, calcite forms mineral coatings that cement the existing rock grains together, or it can fill fractures. Travertine is a banded, compact variety of limestone formed along streams where there are waterfalls and around hot or cold springs. Calcium carbonate is deposited where evaporation of the water leaves a solution supersaturated with the chemical constituents of calcite.
Tufa, a porous or cellular variety of travertine, is found near waterfalls. Coquina is a poorly consolidated limestone composed of pieces of coral or shells. During regional metamorphism that occurs during the mountain building process, limestone recrystallizes into marble. Limestone is a parent material of Mollisol soil group. Two major classification schemes, the Folk and the Dunham, are used for identifying the types of carbonate rocks collectively known as limestone. Robert L. Folk developed a classification system that places primary emphasis on the detailed composition of grains and interstitial material in carbonate rocks. Based on composition, there are three main components: allochems and cement; the Folk system uses two-part names. It is helpful to have a petrographic microscope when using the Folk scheme, because it is easier to determine the components present in each sample; the Dunham scheme focuses on depositional textures. Each name is based upon the texture of the grains. Robert J. Dunham published his system for limestone in 1962.
Dunham divides the rocks into four main groups based on relative proportions of coarser clastic particles. Dunham names are for rock families, his efforts deal with the question of whether or not the grains were in mutual contact, therefore self-supporting, or whether the rock is characterized by the presence of frame builders and algal mats. Unlike the Folk scheme, Dunham deals with the original porosity of the rock; the Dunham scheme is more useful for hand samples because it is based on texture, not the grains in the sample. A revised classification was proposed by Wright, it adds some diagenetic patterns and can be summarized as follows: See: Carbonate platform About 10% of all sedimentary rocks are limestones. Limestone is soluble in acid, therefore forms many erosional landforms; these include limestone pavements, pot holes, cenotes and gorges. Such erosion landscapes are known
Potassium is a chemical element with symbol K and atomic number 19. It was first isolated from the ashes of plants, from which its name derives. In the periodic table, potassium is one of the alkali metals. All of the alkali metals have a single valence electron in the outer electron shell, removed to create an ion with a positive charge – a cation, which combines with anions to form salts. Potassium in nature occurs only in ionic salts. Elemental potassium is a soft silvery-white alkali metal that oxidizes in air and reacts vigorously with water, generating sufficient heat to ignite hydrogen emitted in the reaction, burning with a lilac-colored flame, it is found dissolved in sea water, is part of many minerals. Potassium is chemically similar to sodium, the previous element in group 1 of the periodic table, they have a similar first ionization energy, which allows for each atom to give up its sole outer electron. That they are different elements that combine with the same anions to make similar salts was suspected in 1702, was proven in 1807 using electrolysis.
Occurring potassium is composed of three isotopes, of which 40K is radioactive. Traces of 40K are found in all potassium, it is the most common radioisotope in the human body. Potassium ions are vital for the functioning of all living cells; the transfer of potassium ions across nerve cell membranes is necessary for normal nerve transmission. Fresh fruits and vegetables are good dietary sources of potassium; the body responds to the influx of dietary potassium, which raises serum potassium levels, with a shift of potassium from outside to inside cells and an increase in potassium excretion by the kidneys. Most industrial applications of potassium exploit the high solubility in water of potassium compounds, such as potassium soaps. Heavy crop production depletes the soil of potassium, this can be remedied with agricultural fertilizers containing potassium, accounting for 95% of global potassium chemical production; the English name for the element potassium comes from the word "potash", which refers to an early method of extracting various potassium salts: placing in a pot the ash of burnt wood or tree leaves, adding water and evaporating the solution.
When Humphry Davy first isolated the pure element using electrolysis in 1807, he named it potassium, which he derived from the word potash. The symbol "K" stems from kali, itself from the root word alkali, which in turn comes from Arabic: القَلْيَه al-qalyah "plant ashes". In 1797, the German chemist Martin Klaproth discovered "potash" in the minerals leucite and lepidolite, realized that "potash" was not a product of plant growth but contained a new element, which he proposed to call kali. In 1807, Humphry Davy produced the element via electrolysis: in 1809, Ludwig Wilhelm Gilbert proposed the name Kalium for Davy's "potassium". In 1814, the Swedish chemist Berzelius advocated the name kalium for potassium, with the chemical symbol "K"; the English and French speaking countries adopted Davy and Gay-Lussac/Thénard's name Potassium, while the Germanic countries adopted Gilbert/Klaproth's name Kalium. The "Gold Book" of the International Union of Physical and Applied Chemistry has designated the official chemical symbol as K.
Potassium is the second least dense metal after lithium. It is a soft solid with a low melting point, can be cut with a knife. Freshly cut potassium is silvery in appearance, but it begins to tarnish toward gray on exposure to air. In a flame test and its compounds emit a lilac color with a peak emission wavelength of 766.5 nanometers. Neutral potassium atoms have 19 electrons, one more than the stable configuration of the noble gas argon; because of this and its low first ionization energy of 418.8 kJ/mol, the potassium atom is much more to lose the last electron and acquire a positive charge than to gain one and acquire a negative charge. This process requires so little energy that potassium is oxidized by atmospheric oxygen. In contrast, the second ionization energy is high, because removal of two electrons breaks the stable noble gas electronic configuration. Potassium therefore does not form compounds with the oxidation state of higher. Potassium is an active metal that reacts violently with oxygen in water and air.
With oxygen it forms potassium peroxide, with water potassium forms potassium hydroxide. The reaction of potassium with water is dangerous because of its violent exothermic character and the production of hydrogen gas. Hydrogen reacts again with atmospheric oxygen, producing water, which reacts with the remaining potassium; this reaction requires only traces of water. Because of the sensitivity of potassium to water and air, reactions with other elements are possible only in an inert atmosphere such as argon gas using air-free techniques. Potassium does not react with most hydrocarbons such as mineral kerosene, it dissolves in liquid ammonia, up to 480 g per 1000 g of ammonia at 0 °C. Depending on the concentration, the ammonia solutions are blue to yellow, their electrical conductivity is similar to that of liquid metals. In a pure solution, potassium reacts with ammonia to form KNH2, but this reaction is accelerated by minute amounts of transition metal s
Marl or marlstone is a calcium carbonate or lime-rich mud or mudstone which contains variable amounts of clays and silt. The dominant carbonate mineral in most marls is calcite, but other carbonate minerals such as aragonite and siderite may be present. Marl was an old term loosely applied to a variety of materials, most of which occur as loose, earthy deposits consisting chiefly of an intimate mixture of clay and calcium carbonate, formed under freshwater conditions, it describes a habit of coralline red alga. The term is today used to describe indurated marine deposits and lacustrine sediments which more should be named'marlstone'. Marlstone is an indurated rock of about the same composition as marl, more called an earthy or impure argillaceous limestone, it has a blocky subconchoidal fracture, is less fissile than shale. The term'marl' is used in English-language geology, while the terms Mergel and Seekreide are used in European references; the lower stratigraphic units of the chalk cliffs of Dover consist of a sequence of glauconitic marls followed by rhythmically banded limestone and marl layers.
Upper Cretaceous cyclic sequences in Germany and marl–opal-rich Tortonian-Messinian strata in the Sorbas basin related to multiple sea drawdown have been correlated with Milankovitch orbital forcing. Marl as lacustrine sediment is common in post-glacial lake-bed sediments found underlying peat bogs, it has been used as acid soil neutralizing agent. Marl was extensively mined in Central New Jersey as a soil conditioner in the 1800s. In 1863, the most common marl was blue marl. While the specific composition and properties of the marl varied depending on what layer it was found in, blue marl was composed of 38.70% silicic acid and sand, 30.67% oxide of iron, 13.91% carbonate of lime, 11.22% water, 4.47% potash, 1.21% magnesia, 1.14% phosphoric acid, 0.31% sulphuric acid. Marl was in high demand for farms. An example of the amount of marl mined comes from a report from 1880, from Marlboro, Monmouth County, New Jersey, which reported the following tons of marl sold during the year: OC Herbert Marl Pit – 9961 tons Uriah Smock Marl Pit – 4750 tons CM Conover Marl Pit – 760 tonsIn the Centennial Exhibition report in 1877, marl is described in many different forms and came from 69 marl pits in and around New Jersey.
The report identified a number of agricultural marls types, including clay marl, blue marl, red marl, high bank marl, shell layer marl, under shell layer marl, sand marl, green marl, gray marl, clayey marl. Agricultural lime D. Russell, J. and Kerry Kelts. 2003. Classification of lacustrine sediments based on sedimentary components. Journal of Paleolimnology 29: 141–154. Chalk of Kent by C. S. Harris Geochemistry and time-series analyses of orbitally forced Upper Cretaceous marl–limestone rhythmites, abstract Palaeoenvironmental Interpretation of the Early Postglacial Sedimentary Record of a Marl Lake