115-558: East Kirkton Quarry , or simply East Kirkton , is a former limestone quarry in West Lothian , Scotland, now a renowned fossil site. The quarry is known for terrestrial and freshwater fossils about 335 million years old, from the late Viséan stage of the Mississippian subperiod (Early Carboniferous Period ). The quarry is a 200-meter-long (~650 ft) depression located in the town of Bathgate . Geographically, it sits at
230-455: A Mohs hardness of 2 to 4, dense limestone can have a crushing strength of up to 180 MPa . For comparison, concrete typically has a crushing strength of about 40 MPa. Although limestones show little variability in mineral composition, they show great diversity in texture. However, most limestone consists of sand-sized grains in a carbonate mud matrix. Because limestones are often of biological origin and are usually composed of sediment that
345-463: A bloom of cyanobacteria or microalgae . However, stable isotope ratios in modern carbonate mud appear to be inconsistent with either of these mechanisms, and abrasion of carbonate grains in high-energy environments has been put forward as a third possibility. Formation of limestone has likely been dominated by biological processes throughout the Phanerozoic , the last 540 million years of
460-574: A Viséan-age volcanic ash deposit in East Lothian . It is uncertain whether this similarity betrays a preference for volcanic areas or simply broader biostratigraphy . Plant fossils have been fossilized through several different chemical pathways. In the East Kirkton Limestone, robust plant parts such as gymnosperm branches and Stigmaria roots are often preserved by permineralization ( petrification ). During permineralization,
575-557: A broader trend of decreasing reliance on an amphibious lifestyle during the Carboniferous Period. As early as the 1820s, East Kirkton was noted to be an enigmatic site, relevant to broad debates on the nature of geological processes. In the late 18th and early 19th centuries, petrologists (geologists who study the formation of rocks) were split into two camps. Neptunists argued that most rocks precipitated out of mineral-rich waters, while plutonists identified magma as
690-434: A carbonate rock outcrop can be estimated in the field by etching the surface with dilute hydrochloric acid. This etches away the calcite and aragonite, leaving behind any silica or dolomite grains. The latter can be identified by their rhombohedral shape. Crystals of calcite, quartz , dolomite or barite may line small cavities ( vugs ) in the rock. Vugs are a form of secondary porosity, formed in existing limestone by
805-616: A central quartz grain or carbonate mineral fragment. These likely form by direct precipitation of calcium carbonate onto the ooid. Pisoliths are similar to ooids, but they are larger than 2 mm in diameter and tend to be more irregular in shape. Limestone composed mostly of ooids is called an oolite or sometimes an oolitic limestone . Ooids form in high-energy environments, such as the Bahama platform, and oolites typically show crossbedding and other features associated with deposition in strong currents. Oncoliths resemble ooids but show
920-449: A change in environment that increases the solubility of calcite. Dense, massive limestone is sometimes described as "marble". For example, the famous Portoro "marble" of Italy is actually a dense black limestone. True marble is produced by recrystallization of limestone during regional metamorphism that accompanies the mountain building process ( orogeny ). It is distinguished from dense limestone by its coarse crystalline texture and
1035-949: A composition reflecting the organisms that produced them and the environment in which they were produced. Low-magnesium calcite skeletal grains are typical of articulate brachiopods , planktonic (free-floating) foraminifera, and coccoliths . High-magnesium calcite skeletal grains are typical of benthic (bottom-dwelling) foraminifera, echinoderms , and coralline algae . Aragonite skeletal grains are typical of molluscs , calcareous green algae , stromatoporoids , corals , and tube worms . The skeletal grains also reflect specific geological periods and environments. For example, coral grains are more common in high-energy environments (characterized by strong currents and turbulence) while bryozoan grains are more common in low-energy environments (characterized by quiet water). Ooids (sometimes called ooliths) are sand-sized grains (less than 2mm in diameter) consisting of one or more layers of calcite or aragonite around
1150-412: A considerable fraction of the limestone bed. At depths greater than 1 km (0.62 miles), burial cementation completes the lithification process. Burial cementation does not produce stylolites. When overlying beds are eroded, bringing limestone closer to the surface, the final stage of diagenesis takes place. This produces secondary porosity as some of the cement is dissolved by rainwater infiltrating
1265-483: A drop of dilute hydrochloric acid is dropped on it. Dolomite is also soft but reacts only feebly with dilute hydrochloric acid, and it usually weathers to a characteristic dull yellow-brown color due to the presence of ferrous iron. This is released and oxidized as the dolomite weathers. Impurities (such as clay , sand, organic remains, iron oxide , and other materials) will cause limestones to exhibit different colors, especially with weathered surfaces. The makeup of
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#17327905069281380-489: A few aquatic or semi-aquatic species certainly inhabited the area as well. Though few of East Kirkton's fish species have been formally described, available information suggests that the East Kirkton lake hosted a diverse freshwater ecosystem. Body types seen in East Kirkton fish include fusiform (tuna-shaped) generalist predators and deep-bodied durophages ( Eurynotus ). The fish fauna is comparable to other sites in
1495-426: A few layers, are limited in diversity and preservation. They mainly include fish scales, plant fragments, and shells of ostracods (tiny bivalved crustaceans ). Ironstone nodules are also present. The Geikie Tuff is more than 4 m (13 ft) thick at the main outcrop, though it can reach 8 m (26 ft) thick in exploratory boreholes . Stratigraphic sections acquired via boreholes have demonstrated that
1610-637: A few million years, as this is the most stable form of calcium carbonate. Ancient carbonate formations of the Precambrian and Paleozoic contain abundant dolomite, but limestone dominates the carbonate beds of the Mesozoic and Cenozoic . Modern dolomite is quite rare. There is evidence that, while the modern ocean favors precipitation of aragonite, the oceans of the Paleozoic and middle to late Cenozoic favored precipitation of calcite. This may indicate
1725-455: A few thousand years. As rainwater mixes with groundwater, aragonite and high-magnesium calcite are converted to low-calcium calcite. Cementing of thick carbonate deposits by rainwater may commence even before the retreat of the sea, as rainwater can infiltrate over 100 km (60 miles) into sediments beneath the continental shelf. As carbonate sediments are increasingly deeply buried under younger sediments, chemical and mechanical compaction of
1840-451: A few years later. Wood and his colleagues published on their initial finds in a 1985 Nature letter. Two notable taxa mentioned in the 1985 letter were the oldest known harvestman (a "daddy longleg", dubbed Brigantibunum in 2005) and the oldest known temnospondyl amphibian (described as Balanerpeton in 1993). East Kirkton is perhaps most famous for Westlothiana , a small tetrapod discovered in 1988 and initially reported to be
1955-495: A fragmentary tetrapod skull among the limestone slabs of the quarry's spoil heap. According to popular accounts, he became aware of the spoil heap while refereeing a football match in a nearby field. Wood purchased the abandoned quarry from the West Lothian District Council the following summer. Wood and University of Cambridge paleontologist Timothy R. Smithson began systematic fossil collection from
2070-523: A greater diversity of plant and fish remains. The East Kirkton Limestone (units 36–88) is by far the thickest, most fossiliferous, and most geologically diverse sequence in the quarry. Most layers are laminated (thinly layered) limestone , with a fine-grained texture of calcareous spherulites (bead-like grains). Black Shale , coarse tuffaceous limestone, silica ( chert and chalcedony ), pyrite , gypsum , and tuff beds may occur in some layers. Tetrapod, arthropod, and plant fossils are abundant throughout
2185-435: A limestone sample except in thin section and are less common in ancient limestones, possibly because compaction of carbonate sediments disrupts them. Limeclasts are fragments of existing limestone or partially lithified carbonate sediments. Intraclasts are limeclasts that originate close to where they are deposited in limestone, while extraclasts come from outside the depositional area. Intraclasts include grapestone , which
2300-471: A lower Mg/Ca ratio in the ocean water of those times. This magnesium depletion may be a consequence of more rapid sea floor spreading , which removes magnesium from ocean water. The modern ocean and the ocean of the Mesozoic have been described as "aragonite seas". Most limestone was formed in shallow marine environments, such as continental shelves or platforms . Such environments form only about 5% of
2415-525: A lower diversity of organisms and a greater fraction of silica and clay minerals characteristic of marls . The Green River Formation is an example of a prominent freshwater sedimentary formation containing numerous limestone beds. Freshwater limestone is typically micritic. Fossils of charophyte (stonewort), a form of freshwater green algae, are characteristic of these environments, where the charophytes produce and trap carbonates. Limestones may also form in evaporite depositional environments . Calcite
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#17327905069282530-523: A mechanism for dolomitization, with one 2004 review paper describing it bluntly as "a myth". Ordinary seawater is capable of converting calcite to dolomite, if the seawater is regularly flushed through the rock, as by the ebb and flow of tides (tidal pumping). Once dolomitization begins, it proceeds rapidly, so that there is very little carbonate rock containing mixed calcite and dolomite. Carbonate rock tends to be either almost all calcite/aragonite or almost all dolomite. About 20% to 25% of sedimentary rock
2645-657: A new geological map of Scotland in 1862. Geikie completed a larger map in 1892. In 1863 he published an important essay "On the Phenomena of the Glacial Drift of Scotland", in Transactions of the Geological Society of Glasgow , in which the effects of ice action in that country were for the first time clearly and connectedly delineated. In 1865 Geikie's Scenery of Scotland (3rd edition, 1901)
2760-406: A north-south tangent between Bathgate and Linlithgow. The nearby West Kirkton Quarry is a slightly younger marine limestone deposit. West Kirkton failed to produce any significant fossils, as it had been filled in and redeveloped by the time Stan Wood began his excavations in 1985. The rocks of East Kirkton dip (tilt) into the west wall of the quarry. Magnetometer and resistivity surveys reveal
2875-448: A plausible source of mud. Another possibility is direct precipitation from the water. A phenomenon known as whitings occurs in shallow waters, in which white streaks containing dispersed micrite appear on the surface of the water. It is uncertain whether this is freshly precipitated aragonite or simply material stirred up from the bottom, but there is some evidence that whitings are caused by biological precipitation of aragonite as part of
2990-555: A popular audience was The Story of a Boulder; or, Gleanings from the Note-Book of a Geologist (1858). His ability at once attracted the notice of his chief, Sir Roderick Murchison , with whom he formed a lifelong friendship, and whose biographer he subsequently became. Geikie completed some early geological mapping with Murchison on complicated regions of schists in the Scottish Highlands ; and they jointly published
3105-563: A predecessor to the tuff material. The Little Cliff Shale (units 21–36) is the thinnest interval exposed at the site. It reaches its greatest thickness (about 1.85 m or 6.07 ft) near the middle of the quarry's west wall. The sediments of the Little Cliff Shale include blue-gray shale interspersed with greenish tuff. Fossils and ironstone are more common than in the Geikie Tuff, with the addition of scorpion cuticle and
3220-449: A radial rather than layered internal structure, indicating that they were formed by algae in a normal marine environment. Peloids are structureless grains of microcrystalline carbonate likely produced by a variety of processes. Many are thought to be fecal pellets produced by marine organisms. Others may be produced by endolithic (boring) algae or other microorganisms or through breakdown of mollusc shells. They are difficult to see in
3335-668: A regurgitate. Elongated spiralling coprolites are rarer and would have been produced by elasmobranchs akin to modern sharks. Irregular or strand-like coprolites may have been produced by tetrapods, though fish cannot be excluded. Massive clusters of phosphatized grains were probably produced by large omnivorous eurypterids like Hibbertopterus , or less likely large rhizodont fish. Little Cliff Shale, Geikie Tuff Little Cliff Shale Geikie Tuff Little Cliff Shale Little Cliff Shale Apart from arthropods , other identified invertebrates include freshwater ostracods ( Carbonita ) and bivalves ( Curvirimula ?). Ostracods likely formed
3450-564: A robust scientific theory . The land south of the quarry was developed for housing while the quarry sat abandoned. The prevailing view was that, with the exception of rare freshwater eurypterids, East Kirkton's fossil content was comparatively unremarkable. One notable study in the century since Geikie's paper was by Muir and Walton (1957), who reviewed previous research and investigated the carbonate's microscopic texture and origin in more detail. East Kirkton's decades of obscurity ended in 1984, when Scottish fossil collector Stan Wood discovered
3565-695: A separate branch of the Geological Survey was established for Scotland, he was appointed director. On the foundation of the Murchison professorship of geology and mineralogy at the University of Edinburgh in 1871, he became the first occupant of the chair . He continued to hold these two appointments until 1881. In that year, he was awarded the Murchison Medal of the Geological Society of London and he succeeded Sir Andrew Ramsay in
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3680-538: A small north-south fault just west of the quarry. Vertical displacement of strata along the fault would have been responsible for bringing fine-grained sediments to the surface. The fault indicates that the localized nature of the site is a consequence of modern tectonic processes rather than ancient restricted deposition. Three distinctive geological intervals can be found at the quarry: the Geikie Tuff (youngest / highest), Little Cliff Shale (middle), and East Kirkton Limestone (oldest / lowest). The most well-exposed area
3795-962: Is Geikie Gorge in the Napier Range in the Kimberley region of Western Australia, Mount Geikie in the Canadian Rockies, Mount Geikie in Wyoming, Geikie Peak in the Grand Canyon, and the Geikie Slide in the Atlantic Ocean northwest of Scotland . He died at his home, "Shepherd's Down" in Haslemere , Surrey and is buried there in the village churchyard. In 1871, Geikie married Alice Gabrielle Anne Marie Pignatel, daughter of Eugene Pignatel of Lyons. They had
3910-589: Is The Teaching of Geography (1887). His other books include Scottish Reminiscences (1904) and Landscape in History and other Essays (1905). His Birds of Shakespeare was published in 1916. He was the editor of The Geological Structure of the North-West Highlands of Scotland (1907, His Majesty's Stationery Office), written by B. N. Peach , John Horne , William Gunn (1837–1902), C. T. Clough , L. W. Hinxman , and J. H. H. Teall . Geikie
4025-412: Is a 15 m (49 ft) thick outcrop at the northwest edge of the quarry. Here, the three intervals are subdivided further into a series of thin units, labelled 1 to 88 from the top of the outcrop (the youngest point) to the bottom of the outcrop (the oldest point). The Geikie Tuff (units 1–31), as the name implies, consists mainly of yellowish-green volcaniclastic tuff . Fossils, though abundant in
4140-560: Is also favored on the seaward margin of shelves and platforms, where there is upwelling deep ocean water rich in nutrients that increase organic productivity. Reefs are common here, but when lacking, ooid shoals are found instead. Finer sediments are deposited close to shore. The lack of deep sea limestones is due in part to rapid subduction of oceanic crust, but is more a result of dissolution of calcium carbonate at depth. The solubility of calcium carbonate increases with pressure and even more with higher concentrations of carbon dioxide, which
4255-482: Is an uncommon mineral in limestone, and siderite or other carbonate minerals are rare. However, the calcite in limestone often contains a few percent of magnesium . Calcite in limestone is divided into low-magnesium and high-magnesium calcite, with the dividing line placed at a composition of 4% magnesium. High-magnesium calcite retains the calcite mineral structure, which is distinct from dolomite. Aragonite does not usually contain significant magnesium. Most limestone
4370-402: Is carbonate rock, and most of this is limestone. Limestone is found in sedimentary sequences as old as 2.7 billion years. However, the compositions of carbonate rocks show an uneven distribution in time in the geologic record. About 95% of modern carbonates are composed of high-magnesium calcite and aragonite. The aragonite needles in carbonate mud are converted to low-magnesium calcite within
4485-474: Is clusters of peloids cemented together by organic material or mineral cement. Extraclasts are uncommon, are usually accompanied by other clastic sediments, and indicate deposition in a tectonically active area or as part of a turbidity current . The grains of most limestones are embedded in a matrix of carbonate mud. This is typically the largest fraction of an ancient carbonate rock. Mud consisting of individual crystals less than 5 μm (0.20 mils) in length
4600-416: Is commonly white to gray in color. Limestone that is unusually rich in organic matter can be almost black in color, while traces of iron or manganese can give limestone an off-white to yellow to red color. The density of limestone depends on its porosity, which varies from 0.1% for the densest limestone to 40% for chalk. The density correspondingly ranges from 1.5 to 2.7 g/cm . Although relatively soft, with
4715-420: Is controlled largely by the amount of dissolved carbon dioxide ( CO 2 ) in the water. This is summarized in the reaction: Increases in temperature or decreases in pressure tend to reduce the amount of dissolved CO 2 and precipitate CaCO 3 . Reduction in salinity also reduces the solubility of CaCO 3 , by several orders of magnitude for fresh water versus seawater. Near-surface water of
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4830-545: Is converted to low-magnesium calcite. Diagenesis is the likely origin of pisoliths , concentrically layered particles ranging from 1 to 10 mm (0.039 to 0.394 inches) in diameter found in some limestones. Pisoliths superficially resemble ooids but have no nucleus of foreign matter, fit together tightly, and show other signs that they formed after the original deposition of the sediments. Silicification occurs early in diagenesis, at low pH and temperature, and contributes to fossil preservation. Silicification takes place through
4945-503: Is deposited close to where it formed, classification of limestone is usually based on its grain type and mud content. Most grains in limestone are skeletal fragments of marine organisms such as coral or foraminifera . These organisms secrete structures made of aragonite or calcite, and leave these structures behind when they die. Other carbonate grains composing limestones are ooids , peloids , and limeclasts ( intraclasts and extraclasts [ ca ] ). Skeletal grains have
5060-460: Is described as coquinite . Chalk is a soft, earthy, fine-textured limestone composed of the tests of planktonic microorganisms such as foraminifera, while marl is an earthy mixture of carbonates and silicate sediments. Limestone forms when calcite or aragonite precipitate out of water containing dissolved calcium, which can take place through both biological and nonbiological processes. The solubility of calcium carbonate ( CaCO 3 )
5175-617: Is described as micrite . In fresh carbonate mud, micrite is mostly small aragonite needles, which may precipitate directly from seawater, be secreted by algae, or be produced by abrasion of carbonate grains in a high-energy environment. This is converted to calcite within a few million years of deposition. Further recrystallization of micrite produces microspar , with grains from 5 to 15 μm (0.20 to 0.59 mils) in diameter. Limestone often contains larger crystals of calcite, ranging in size from 0.02 to 0.1 mm (0.79 to 3.94 mils), that are described as sparry calcite or sparite . Sparite
5290-462: Is distinguished from micrite by a grain size of over 20 μm (0.79 mils) and because sparite stands out under a hand lens or in thin section as white or transparent crystals. Sparite is distinguished from carbonate grains by its lack of internal structure and its characteristic crystal shapes. Geologists are careful to distinguish between sparite deposited as cement and sparite formed by recrystallization of micrite or carbonate grains. Sparite cement
5405-629: Is estimated to belong to the Brigantian (uppermost Viséan global stage) of the Mississippian Subperiod (the lower part of the Carboniferous Period). This would place it near the end of the regional Dinantian stage. In numerical terms, the site may be 330 to 338 million years old, with 335 million years as a common estimate. East Kirkton is one of many geographically restricted limestone deposits cropping out on
5520-560: Is one of the first minerals to precipitate in marine evaporites. Most limestone is formed by the activities of living organisms near reefs, but the organisms responsible for reef formation have changed over geologic time. For example, stromatolites are mound-shaped structures in ancient limestones, interpreted as colonies of cyanobacteria that accumulated carbonate sediments, but stromatolites are rare in younger limestones. Organisms precipitate limestone both directly as part of their skeletons, and indirectly by removing carbon dioxide from
5635-473: Is otherwise chemically fairly pure, with clastic sediments (mainly fine-grained quartz and clay minerals ) making up less than 5% to 10% of the composition. Organic matter typically makes up around 0.2% of a limestone and rarely exceeds 1%. Limestone often contains variable amounts of silica in the form of chert or siliceous skeletal fragments (such as sponge spicules, diatoms , or radiolarians ). Fossils are also common in limestone. Limestone
5750-472: Is produced by decaying organic matter settling into the deep ocean that is not removed by photosynthesis in the dark depths. As a result, there is a fairly sharp transition from water saturated with calcium carbonate to water unsaturated with calcium carbonate, the lysocline , which occurs at the calcite compensation depth of 4,000 to 7,000 m (13,000 to 23,000 feet). Below this depth, foraminifera tests and other skeletal particles rapidly dissolve, and
5865-518: Is secondary dolomite, formed by chemical alteration of limestone. Limestone is exposed over large regions of the Earth's surface, and because limestone is slightly soluble in rainwater, these exposures often are eroded to become karst landscapes. Most cave systems are found in limestone bedrock. Limestone has numerous uses: as a chemical feedstock for the production of lime used for cement (an essential component of concrete ), as aggregate for
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#17327905069285980-623: Is still among the best paradigms of the amphibian-amniote transition. East Kirkton was the main subject of a conference hosted by the Royal Society of Edinburgh in 1992. The conference produced a series of over 20 papers published in 1993–94 as "Volcanism and early terrestrial biotas" (volume 84, issues 3–4 of Earth and Environmental Science Transactions of the Royal Society of Edinburgh). New species have continued to be described from Wood's collections and other expeditions up to
6095-400: Is that spherulite formation at East Kirkton follows a complex mineralization pathway. In the reconstructed sequence of spherulite formation, freshwater lakes are supplied with high concentrations of dissolved alkaline minerals and microbial acids. These conditions encourage the precipitation of fibrous calcite, which accumulates on strands of organic material such as algae or cyanobacteria In
6210-407: Is the main source of the material lime . It is composed mostly of the minerals calcite and aragonite , which are different crystal forms of CaCO 3 . Limestone forms when these minerals precipitate out of water containing dissolved calcium. This can take place through both biological and nonbiological processes, though biological processes, such as the accumulation of corals and shells in
6325-905: The Bathgate Hills near the center of the Midland Valley , a fossil-rich region of southeast Scotland. The site is dominated by volcanic tuff , limestone , and silica deposits of large freshwater lakes associated with hot springs and local basaltic (high-iron) volcanism . Three geological intervals are exposed: the East Kirkton Limestone (oldest), Little Cliff Shale (middle), and Geikie Tuff (youngest). The East Kirkton Limestone in particular has produced numerous well-preserved fossils of tetrapods (four-limbed vertebrates ) and arthropods (multi-legged chitinous invertebrates like millipedes and arachnids ). East Kirkton had been ignored by paleontologists since
6440-704: The Bathgate Hills Volcanic Formation . It is equivalent in time to rocks from the upper part (Hopetoun Member) of the West Lothian Oil-Shale Formation , exposed north of Linlithgow . Both formations are part of the broader Strathclyde Group (informally termed the Oil-Shale Group) found throughout the Midland Valley of Scotland. By comparison to equivalent oil shale strata, the East Kirkton
6555-690: The canyons of the Colorado River confirmed his long-standing views on erosion, the volcanic regions of Wyoming , Montana and Utah supplied him with valuable data in explanation of volcanic phenomena. The results of his further researches were given in an essay entitled "The History of Volcanic Action during the Tertiary Period in the British Isles," in Transactions of the Royal Society of Edinburgh (1888). His views on volcanic geology were delivered in his presidential addresses to
6670-436: The 1840s, but Scottish fossil collector Stan Wood managed to procure the land in 1985, sparking a rush of scientific interest. New species from East Kirkton have been named on a regular basis since 1990, and nearly all of these species have been found nowhere else. Notable discoveries include Westlothiana (one of the most reptile-like Mississippian tetrapods), Balanerpeton (a common early representative of amphibians in
6785-573: The Clyde Plateau , completely lacked any form of limestone deposition. The East Kirkton Limestone was deposited at a time and place at the intersection between these two environments, as the expanding dry plateau began to displace the brackish lake, enabling the development of a riparian ecosystem in the Bathgate area. East Kirkton was located close to the equator in the Viséan. The climate
6900-578: The Dinantian, the Midland Valley would have been a subtropical lowland rift zone. Faults and cooled lava flows would have contributed to the landscape by diverting rivers and damming lakes, as would the progradation of deltaic systems further east. Some of the lakes may have filled in volcanic craters, forming low crater lakes (also known as maars ). Most individual volcanoes were small but numerous, emphasizing basaltic and phreatic eruptions alongside hot springs. Modern equivalent environments include
7015-496: The Earth's history. Limestone may have been deposited by microorganisms in the Precambrian , prior to 540 million years ago, but inorganic processes were probably more important and likely took place in an ocean more highly oversaturated in calcium carbonate than the modern ocean. Diagenesis is the process in which sediments are compacted and turned into solid rock . During diagenesis of carbonate sediments, significant chemical and textural changes take place. For example, aragonite
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#17327905069287130-442: The East Kirkton Limestone. Bilignea B. solida East Kirkton Limestone Woody gymnosperm stems or branches up to 3.5 cm (1.4 inches) in diameter. Eristophyton E. fasciculare East Kirkton Limestone Common woody gymnosperm branches up to 6 cm (2.4 inches) in diameter. L. kingswoodense Limestone Limestone ( calcium carbonate CaCO 3 ) is a type of carbonate sedimentary rock which
7245-459: The Geikie Tuff. The surrounding woods were probably drier during the deposition of the Little Cliff Shale and East Kirkton Limestone. The East Kirkton flora is fairly typical among Viséan Scotland, most species found here have been reported previously from the Midland Valley. Gymnosperm wood and fern leaves (particularly Spathulopteris and Sphenopteridium ) are the most common plant fossils at East Kirkton. These plants are also abundant at Weaklaw,
7360-601: The Geological Society of London in 1891 and 1892 and afterward embodied in his book The Ancient Volcanoes of Great Britain (1897). Other results of his travels are collected in Geological Sketches at Home and Abroad (1882). Geikie wrote a biography of Edward Forbes (with G Wilson), and biographies of his predecessors Sir Roderick Impey Murchison (two volumes, 1875) and Sir Andrew Crombie Ramsay (1895). His book Founders of Geology consists of
7475-729: The Mississippian Oil Shales of Scotland. Only the Granton Shrimp Bed , a fully marine environment, lacks freshwater fish and tetrapods. Beside direct body fossils of fish, coprolites are also found in several layers near the Little Cliff Shale-East Kirkton Limestone transition. Small pellet- bullet- and cigar-shaped coprolites are common, often containing ostracod shells, and in one case, bone fragments. One irregular mass, containing ostracods and plant fragments, may be
7590-424: The age of East Kirkton, which is much older than the known aquatic members of the group. True amniotes are also absent, and only a single microsaur fossil has been discovered. The rarity of microsaurs may be due to geographic rather than environmental factors, since few fossils of the group are known from other British sites. Overall, East Kirkton has a more terrestrial character than other Scottish fossil sites, though
7705-434: The base of roads, as white pigment or filler in products such as toothpaste or paint, as a soil conditioner , and as a popular decorative addition to rock gardens . Limestone formations contain about 30% of the world's petroleum reservoirs . Limestone is composed mostly of the minerals calcite and aragonite , which are different crystal forms of calcium carbonate ( CaCO 3 ). Dolomite , CaMg(CO 3 ) 2 ,
7820-527: The base of the aquatic food chain, since they have been found as stomach contents in several fish and tetrapod fossils. Little Cliff Shale Little Cliff Shale The plant fossils of East Kirkton are fragmentary but diverse, and small fragments of fusain (fossilized charcoal) are common in the East Kirkton Limestone. The area was likely forest or open woodland frequented by wildfires . There are few aquatic plants apart from algal laminations, and lycopsid fragments (an indicator of swamp forests) are only common in
7935-657: The beds. This may include the formation of vugs , which are crystal-lined cavities within the limestone. Diagenesis may include conversion of limestone to dolomite by magnesium-rich fluids. There is considerable evidence of replacement of limestone by dolomite, including sharp replacement boundaries that cut across bedding. The process of dolomitization remains an area of active research, but possible mechanisms include exposure to concentrated brines in hot environments ( evaporative reflux ) or exposure to diluted seawater in delta or estuary environments ( Dorag dolomitization ). However, Dorag dolomitization has fallen into disfavor as
8050-578: The bottom with the concave face downwards. This traps a void space that can later be filled by sparite. Geologists use geopetal structures to determine which direction was up at the time of deposition, which is not always obvious with highly deformed limestone formations. The cyanobacterium Hyella balani can bore through limestone; as can the green alga Eugamantia sacculata and the fungus Ostracolaba implexa . Archibald Geikie Sir Archibald Geikie OM KCB FRS FRSE (28 December 1835 – 10 November 1924)
8165-432: The calcareous minerals of East Kirkton Limestone (mostly calcite ) are probably not directly hydrothermal in origin. Nevertheless, East Kirkton is a useful model for the formation of spherulite-rich freshwater limestone in volcanic settings. Most limestones with spherulites are dependent on a high proportion of clay particles, but clay makes up only a small portion of the East Kirkton Limestone. The prevailing interpretation
8280-545: The configuration of land surfaces, and particularly the erosion of valleys by the action of running water. Geikie's book, based on extensive personal knowledge of the country, was an able contribution to the doctrines of the Edinburgh school, of which he himself soon began to rank as one of the leaders. In 1880, he was elected as a member to the American Philosophical Society . In 1867, when
8395-401: The deposition of the East Kirkton Limestone. East Kirkton tetrapod fossils have all been preserved in aquatic sediments of the East Kirkton Limestone. A majority of the fossils come from laminated spherulitic limestone slabs (units 70 and below), though the best-preserved specimens come from a thin black shale layer (unit 82). Fish fossils do not occur alongside tetrapod fossils, suggesting that
8510-466: The depositional fabric of carbonate rocks. Dunham divides the rocks into four main groups based on relative proportions of coarser clastic particles, based on criteria such as whether the grains were originally in mutual contact, and 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
8625-469: The deposits are highly porous, so that they have a spongelike texture, they are typically described as tufa . Secondary calcite deposited by supersaturated meteoric waters ( groundwater ) in caves is also sometimes described as travertine. This produces speleothems , such as stalagmites and stalactites . Coquina is a poorly consolidated limestone composed of abraded pieces of coral , shells , or other fossil debris. When better consolidated, it
8740-406: The earth's oceans are oversaturated with CaCO 3 by a factor of more than six. The failure of CaCO 3 to rapidly precipitate out of these waters is likely due to interference by dissolved magnesium ions with nucleation of calcite crystals, the necessary first step in precipitation. Precipitation of aragonite may be suppressed by the presence of naturally occurring organic phosphates in
8855-399: The first refers to the grains and the second to the cement. For example, a limestone consisting mainly of ooids, with a crystalline matrix, would be termed an oosparite. 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. Robert J. Dunham published his system for limestone in 1962. It focuses on
8970-572: The formation of distinctive minerals from the silica and clay present in the original limestone. Two major classification schemes, the Folk and 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 (grains), matrix (mostly micrite), and cement (sparite). The Folk system uses two-part names;
9085-429: The geologic record are called bioherms . Many are rich in fossils, but most lack any connected organic framework like that seen in modern reefs. The fossil remains are present as separate fragments embedded in ample mud matrix. Much of the sedimentation shows indications of occurring in the intertidal or supratidal zones, suggesting sediments rapidly fill available accommodation space in the shelf or platform. Deposition
9200-465: The group Temnospondyli ), and Pulmonoscorpius (the largest known terrestrial scorpion ). The East Kirkton area represents an unconventional environment: dry woodlands and mineral-rich lakes nestled among volcanic cinder cones . Aquatic animals, though not uncommon, are less diverse than those found in the swampy coal forests and coastal sediments prevalent at other Scottish Carboniferous fossil sites. The prevalence of terrestrial organisms represents
9315-843: The honorary Doctor of Laws (LL.D) from the University of Glasgow in June 1901. He received a knighthood in 1891, the Knight Commander of the Most Honourable Order of the Bath in 1907 and the Order of Merit in 1914. In 1905 he received the RSGS Livingstone Medal . Dorsa Geikie , a wrinkle ridge system on the Moon , and the mineral geikielite , a magnesium-titanium oxide, are both named after him, as
9430-610: The inaugural course of lectures (founded by Mrs George Huntington Williams) at Johns Hopkins University , Baltimore, delivered in 1897. In 1897 he issued a Geological Map of England and Wales, with Descriptive Notes . In 1898 he delivered the Romanes Lectures , which was published under the title of Types of Scenery and their Influence on Literature . The study of physical geography in Great Britain improved largely due to his efforts. Among his works on this subject
9545-711: The joint offices of Director-General of the Geological Survey of the United Kingdom and Director of the Museum of Practical Geology , London, from which he retired in February 1901. A feature of his tenure of office was the impetus given to microscopic petrography , a branch of geology to which he had devoted special study, by a splendid collection of thin sections of British rocks . Later he wrote two Survey Memoirs, The Geology of Central and Western Fife and Kinross (1900), and The Geology of Eastern Fife (1902). From
9660-423: The lake. This periodic supply of spherulite grains is responsible for the laminated appearance of the limestone, alternating between microscopic bands of dark clay and organic material, and thicker (though still narrow) bands of calcite. Diagenesis (underground heat and pressure) fractures and warms the calcite after deposition, introducing voids and further reprecipitation within the molds of algal strands. During
9775-412: The limestone as freshwater due to the prevalence of plant fossils and the absence of marine fossils. He drew attention to the occurrence of volcanic tuff at the site, and attributed the silica and carbonate to hot spring mineralization. When the quarry ceased operations in 1844, the site was, for the most part, forgotten as a geological footnote. Scottish geologist Archibald Geikie (1861) determined that
9890-482: The limestone is unknown, but about 9 m (30 ft) are exposed on the main outcrop. Stable isotope data help to pin down the origin of minerals like silica and pyrite in the limestone. Hydrogen and oxygen isotope ratios indicate that the chert beds precipitated from meteoric water heated to around 60 °C (140 °F), with a minor amount of mineral recycling after deposition. Sulfur molecules in pyrite are rather lightweight, arguing that crystal formation
10005-505: The limestone of "Kirkton" was not a single unit, but instead two distinct sequences, one at the nearby West Kirkton quarry and the other at East Kirkton. He supported Hibbert's interpretation, considering the Kirkton quarries to represent large lakes influenced by hot springs on an ancient volcanic plain. East Kirkton saw little attention in the following decades, as neptunism diminished in most applications while plutonism established itself as
10120-539: The limestone. Conversely, fish are absent beyond unit 36 and ostracods are mostly restricted to black shale-bearing horizons. Many laminated beds are deformed or warped, and stromatolitic crusts and algal filaments are common. Small slumping features can be seen in some layers, likely corresponding to the slope between shallow and deep parts of a lake bed. The lake bed was probably oxygen-deprived, according to trace metal geochemical markers and an absence of bioturbation (animal-mediated disturbance). The true thickness of
10235-463: The medium from which most rocks originate. Experiments on carbonate -based rocks (such as limestone) supported neptunist interpretations of petrology, while evidence from silica-based rocks (such as granite ) favored plutonist views. East Kirkton presented a contradiction: thick layers of carbonate (limestone) intermingled alongside rarer siliceous ( chert ) beds, emphasizing how both rock types can occur in close succession. The first geologist to study
10350-469: The mineral dolomite , CaMg(CO 3 ) 2 . Magnesian limestone is an obsolete and poorly-defined term used variously for dolomite, for limestone containing significant dolomite ( dolomitic limestone ), or for any other limestone containing a significant percentage of magnesium . Most limestone was formed in shallow marine environments, such as continental shelves or platforms , though smaller amounts were formed in many other environments. Much dolomite
10465-410: The ocean basins, but limestone is rarely preserved in continental slope and deep sea environments. The best environments for deposition are warm waters, which have both a high organic productivity and increased saturation of calcium carbonate due to lower concentrations of dissolved carbon dioxide. Modern limestone deposits are almost always in areas with very little silica-rich sedimentation, reflected in
10580-555: The oldest known reptile in 1989. Wood's excavations at East Kirkton, and then-unnamed Westlothiana , were featured in the first episode of Lost Worlds, Vanished Lives , a 1989 BBC documentary hosted by Sir David Attenborough . Westlothiana has subsequently been reinterpreted as a stem - amniote reptiliomorph . In other words, it was an amphibian closely related to amniotes (the group containing dry-adapted tetrapods like reptiles and mammals , with reinforced eggs and thickened skin). Thanks to its degree of completeness, Westlothiana
10695-411: The original organic material is sequentially replaced with silica and/or carbonate carried by alkaline groundwater . More commonly, heat and pressure compresses organic matter into carbonaceous films . These coalified compressions of wood and foliage can be found in practically every layer of the site. Some fossils are both compressed and permineralized, particularly in the upper layers (units 44–48) of
10810-563: The outset of his career, when he started to investigate the geology of Skye and other of the Western Isles , he took a keen interest in volcanic geology, and in 1871 he brought before the Geological Society of London an outline of the Tertiary volcanic history of Britain. Many difficult problems, however, remained to be solved. Here he was greatly aided by his extensive travels not only throughout Europe, but in western America. While
10925-420: The present day. In 2011, Cambridge paleontologist Jennifer A. Clack named a new species of East Kirkton microsaur , Kirktonecta milnerae , in honour of the site. East Kirkton Quarry has been designated as both a Local Geodiversity Site (LGS) of West Lothian and a Site of Special Scientific Interest (SSSI). The East Kirkton Quarry preserves up to 19 m (62 ft) of strata from the mid-lower part of
11040-431: The quarry from 1985 to 1990. With news of the discovery, a team of National Museums of Scotland geologists (headed by W.D. Ian Rolfe ) initiated a stratigraphic investigation in 1987–1992. Fossils discovered by Wood include an expansive sample of both terrestrial and freshwater fossil arthropods and early amphibians from the East Kirkton Limestone. A smaller sample of fish and plant fossils were found in younger strata
11155-426: The reaction: Fossils are often preserved in exquisite detail as chert. Cementing takes place rapidly in carbonate sediments, typically within less than a million years of deposition. Some cementing occurs while the sediments are still under water, forming hardgrounds . Cementing accelerates after the retreat of the sea from the depositional environment, as rainwater infiltrates the sediment beds, often within just
11270-482: The relative purity of most limestones. Reef organisms are destroyed by muddy, brackish river water, and carbonate grains are ground down by much harder silicate grains. Unlike clastic sedimentary rock, limestone is produced almost entirely from sediments originating at or near the place of deposition. Limestone formations tend to show abrupt changes in thickness. Large moundlike features in a limestone formation are interpreted as ancient reefs , which when they appear in
11385-460: 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 (1992). It adds some diagenetic patterns to the classification scheme. Travertine is a term applied to calcium carbonate deposits formed in freshwater environments, particularly waterfalls , cascades and hot springs . Such deposits are typically massive, dense, and banded. When
11500-410: The sea, have likely been more important for the last 540 million years. Limestone often contains fossils which provide scientists with information on ancient environments and on the evolution of life. About 20% to 25% of sedimentary rock is carbonate rock, and most of this is limestone. The remaining carbonate rock is mostly dolomite , a closely related rock, which contains a high percentage of
11615-479: The sediments increases. Chemical compaction takes place by pressure solution of the sediments. This process dissolves minerals from points of contact between grains and redeposits it in pore space, reducing the porosity of the limestone from an initial high value of 40% to 80% to less than 10%. Pressure solution produces distinctive stylolites , irregular surfaces within the limestone at which silica-rich sediments accumulate. These may reflect dissolution and loss of
11730-662: The sediments of the ocean floor abruptly transition from carbonate ooze rich in foraminifera and coccolith remains ( Globigerina ooze) to silicic mud lacking carbonates. In rare cases, turbidites or other silica-rich sediments bury and preserve benthic (deep ocean) carbonate deposits. Ancient benthic limestones are microcrystalline and are identified by their tectonic setting. Fossils typically are foraminifera and coccoliths. No pre-Jurassic benthic limestones are known, probably because carbonate-shelled plankton had not yet evolved. Limestones also form in freshwater environments. These limestones are not unlike marine limestone, but have
11845-435: The shallow part of a lake. The fibrous calcite acts as a base for radiating balls of botryoidal (lumpy) calcite. Even once the algae die and settle, the calcite continues stacking up into crusts and domes on the lake bed. Fluctuating mineral concentrations lead to constant corrosion and reprecipitation of the calcite. Wave action breaks up the calcite crusts into smaller grains, which are periodically washed into deeper parts of
11960-446: The site was John Fleming (1825), a Scottish neptunist who considered both the carbonate and chert to be derived from heated groundwater. During the 1830s and 1840s, the quarry yielded some interesting fossils of Carboniferous plants and eurypterids ("sea scorpions", a type of extinct arthropod), though this was not uncommon for quarries in the area. English geologist Samuel Hibbert (1836) discussed Fleming's interpretation, identifying
12075-666: The system of volcanoes around the Mozambique Channel and the Chaîne des Puys in France. Towards the north and east was a large lake or estuary system known to geologists as Lake Cadell . It was responsible for the deposition of most sediments comprising the West Lothian Oil-Shale Formation. An expanse of dry volcanic uplands were located west of East Kirkton. These uplands, formally known as
12190-481: The tetrapods lived in or around shallower bodies of water than those supporting the local freshwater fish. The tetrapod species of East Kirkton are all endemic , though some broader groups ( dendrerpetontids , aistopods , " anthracosaurs ", etc.) can be found at other Carboniferous locales. Notably absent are adelogyrinids , Crassigyrinus , Doragnathus , and lysorophians , all of which are considered fully aquatic. The absence of lysorophians could be explained by
12305-614: The tuff is overlain by basalt . Pseudomorphs of olivine and plagioclase crystals indicate that the tuff is basaltic in nature. The volcanic grains are coarse and rounded, sorted into discontinuous lenticular layers with graded bedding . This suggests that the volcanic material was not directly supplied by a pyroclastic flow , base surge , or ash fall . Rather, it was washed down as debris from older ash deposits, settling underwater alongside wood and other non-volcanic fragments. The area most likely experienced small intermittent cinder cone eruptions, providing basaltic ash or lava as
12420-533: The water by photosynthesis and thereby decreasing the solubility of calcium carbonate. Limestone shows the same range of sedimentary structures found in other sedimentary rocks. However, finer structures, such as lamination , are often destroyed by the burrowing activities of organisms ( bioturbation ). Fine lamination is characteristic of limestone formed in playa lakes , which lack the burrowing organisms. Limestones also show distinctive features such as geopetal structures , which form when curved shells settle to
12535-553: The water. Although ooids likely form through purely inorganic processes, the bulk of CaCO 3 precipitation in the oceans is the result of biological activity. Much of this takes place on carbonate platforms . The origin of carbonate mud, and the processes by which it is converted to micrite, continue to be a subject of research. Modern carbonate mud is composed mostly of aragonite needles around 5 μm (0.20 mils) in length. Needles of this shape and composition are produced by calcareous algae such as Penicillus , making this
12650-483: Was a Scottish geologist and writer. Geikie was born in Edinburgh in 1835, the eldest son of Isabella Thom and her husband James Stuart Geikie , a musician and music critic. The elder brother of James Geikie , he was educated at Edinburgh High School and University of Edinburgh . In 1855 Geikie was appointed an assistant with the British Geological Survey . Among his early publications for
12765-471: Was elected Fellow of the Royal Society in 1865. Geikie was Foreign Secretary of the Royal Society from 1890 to 1894, Joint Secretary from 1903 to 1908 and elected president in 1909 and awarded their Royal Medal in 1896. He was President of the Geological Society of London in 1891 and 1892, and again in 1906 and 1907. He was also President of the British Association in 1892. He received
12880-416: Was likely deposited in pore space between grains, suggesting a high-energy depositional environment that removed carbonate mud. Recrystallized sparite is not diagnostic of depositional environment. Limestone outcrops are recognized in the field by their softness (calcite and aragonite both have a Mohs hardness of less than 4, well below common silicate minerals) and because limestone bubbles vigorously when
12995-567: Was mediated by bacterial activity. Yet the pyrite was also heavy enough to imply a constant supply of sulfur-34 , likely from older gypsum beds heated by magmatic activity. Both the silica and pyrite support historical interpretations of a hydrothermal influence on the East Kirkton Limestone. Another hypothesis, based on strontium isotope trends, is that heat and alkaline groundwater are byproducts of chemical reactions between tuff minerals and carbon dioxide molecules seeping in via meteoric water (such as rain). Contrary to earlier suggestions,
13110-406: Was published, which was, he claimed, the first attempt to elucidate in some detail the history of the topography of a country. In the same year he was elected a Fellow of the Royal Society . At this time the Edinburgh school of geologists, prominent among them Sir Andrew Ramsay , with his Physical Geology and Geography of Great Britain were maintaining the supreme importance of denudation in
13225-529: Was warm and semi-arid , gradually becoming wetter as the Carboniferous progressed. Rainfall was prevalent enough to support woodlands and lake ecosystems, but infrequent enough to dissuade coal forests and allow gypsum deposition. The more humid conditions of the Geikie Tuff may correspond to the expansion of a larger lake into the East Kirkton area. Chert and pyrite, alongside permineralized plant fossils, may indicate that hot springs were prevalent during
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