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Articoli di riviste sul tema "Thrombolites"

Autore: Grafiati

Pubblicato: 10 dicembre 2022

Ultima modifica: 28 gennaio 2023

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1

Siqueiros-Beltrones, D. A., U. Argumedo-Hernandez e O. U. Hernández-Almeida. "TROMBOLITOS LITIFICADOS DENTRO DE LA ENSENADA DE LA PAZ, B.C.S., MÉXICO". CICIMAR Oceánides 21, n. 1-2 (31 dicembre 2006): 155. http://dx.doi.org/10.37543/oceanides.v21i1-2.32.

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Lithified thrombolites in the Ensenada de La Paz, B.C.S., Mexico The beaches of the Ensenada de La Paz, B.C.S., México are bordered by sediment for mations of cyanophytic origin identified as recent thrombolites that represented the first record of live thrombolites for the region and México. In a later exploration, lithified thrombolites were discovered at Estero Zacatecas on the angle formed by El Mogote and the coastline, behind the mangrove fringe. It is feasible that the process of thrombolitic formation may have triggered the birth of the El Mogote sand bar.

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2

Siqueiros-Beltrones, D. A., U. Argumedo-Hernandez e O. U. Hernández-Almeida. "TROMBOLITOS LITIFICADOS DENTRO DE LA ENSENADA DE LA PAZ, B.C.S., MÉXICO". CICIMAR Oceánides 21, n. 1-2 (31 dicembre 2006): 155. http://dx.doi.org/10.37543/oceanides.v21i1-2.32.

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Lithified thrombolites in the Ensenada de La Paz, B.C.S., Mexico The beaches of the Ensenada de La Paz, B.C.S., México are bordered by sediment for mations of cyanophytic origin identified as recent thrombolites that represented the first record of live thrombolites for the region and México. In a later exploration, lithified thrombolites were discovered at Estero Zacatecas on the angle formed by El Mogote and the coastline, behind the mangrove fringe. It is feasible that the process of thrombolitic formation may have triggered the birth of the El Mogote sand bar.

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3

Layeb, Mohsen, Moez Ben Fadhel e Mohamed Ben Youssef. "Thrombolitic and coral buildups in the Upper Albian of the Fahdene basin (North Tunisia): stratigraphy, sedimentology and genesis". Bulletin de la Société Géologique de France 183, n. 3 (1 maggio 2012): 217–31. http://dx.doi.org/10.2113/gssgfbull.183.3.217.

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Abstract Within the Upper Albian marl/limestone pelagic to hemi-pelagic successions of Fahdene basin (northern Tunisia), small-scale thrombolitic and coral buildups were recognized for the first time. The exceptionally well-exposed and well-preserved buildups (i.e. Oued Siliana and Jebel Srassif buildups) were investigated for their biostratigraphic, petrographic, and genesis character. The vertical succession is characterized as shallowing upward and comprise four to nine conical and/or lenticular bioherms/biostromes (up to 4 m in diameter). Basal buildups consist of four to six deep water microbial thrombolites and are generally associated with the uppermost organic-rich black shale of the Mouelha member which corresponds to the Oceanic Anoxic Event OAE1d. These buildups change stratigraphic upward into three hermatypic hexacorallian thrombolites with abundant fossils and bioturbation traces. The geometry and the observed internal structures of the thrombolites suggest that microbial activity thrived carbonate precipitation and subsequent lithification, which in turn favoured preservation of the original structure of the buildups. The microbial thrombolites formed within or near the anoxic zone (related to the Oceanic Anoxic Event OAE1d) whereas the coral thrombolites grew in the photic zone. We suggest that the onset of the microbial thrombolites was induced by the presence of an eutrophic, hypersaline, and anoxic environment which is enhanced by the Late Albian sea level rise. Nevertheless, flourishing of metazoans that lead to the coral thrombolites was associated with an oxygenated and oligotrophic environment. Halokinetic dynamics and tilted-block fault systems provided conduits for nutrient-rich fluids and hydrocarbons which fueled chemosynthetic-based communities.

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4

GROTZINGER, J., E. W. ADAMS e S. SCHRÖDER. "Microbial–metazoan reefs of the terminal Proterozoic Nama Group (c. 550–543 Ma), Namibia". Geological Magazine 142, n. 5 (settembre 2005): 499–517. http://dx.doi.org/10.1017/s0016756805000907.

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Thrombolite and stromatolite reefs occur at several stratigraphic levels within the terminal Proterozoic Nama Group (c. 550–543 Ma) of central and southern Namibia. The reefs form integral parts of several carbonate platforms within the Nama Group, including the Kuibis platform of the northern Nama Basin (Zaris subbasin), and Huns platform (Witputs subbasin) of the southern Nama Basin. The reefs are composed of both thrombolites and stromatolites that form laterally continuous biostromes, isolated patch reefs, and isolated pinnacle reefs ranging in scale from a metre to several kilometres in width. In the majority of cases, the reefs occur stratigraphically as an integral facies within the transgressive systems tracts of sequences making up the Kuibis and Huns platforms. This suggests that a regime of increasing accommodation was required to form well-developed reefs, though reefs also occur sporadically in highstand systems tract settings. Within a given transgressive systems tract, a regime of increasing accommodation through time favours the transition from sheet-like biostromal geometries to more isolated patch and pinnacle biohermal geometries. Similarly, increasing accommodation in space, such as a transect down depositional dip, shows a similar transition from more sheet-like geometries in updip positions to more isolated geometries in downdip positions. Reefal facies consist of thrombolitic domes, columns and mounds with well-developed internal clotted textures, in addition to stromatolitic domes, columns and mounds, with crudely to moderately well-developed internal lamination. Stromatolites are better developed in conditions of relatively low accommodation, and updip locations, under conditions of higher current velocities and greater sediment influx. Thrombolites are better developed in conditions of relatively high accommodation and low sediment influx. Both types of microbialites are intimately associated with the first calcifying metazoan organisms, which may have attached themselves to the sediment surface or otherwise lived within sheltered depressions within the rough topography created by ecologically complex mats. The appearance of thrombolitic textures during terminal Proterozoic time is consistent with colonization of cyanobacterial mats by higher algae and metazoans, which would have been an important process in generating clotted textures. Fabrics in the Nama thrombolites are well preserved and show evidence of thrombolitic mesoclots being overgrown by fibrous marine carbonate, interpreted as former aragonite. This was followed by emplacement of geopetal micrite fills, and precipitation of dolomite as an isopachous rim cement, followed by occlusion of remaining porosity by blocky calcite spar.

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5

You, Xue Lian, Jing Quan Zhu, Qing Li, Ling Liu, Kai He e Shi Qiang Wu. "Microbialites from the Upper Cambrian in the Tarim Basin, Northwest China: Implication for Depositional Environments". Advanced Materials Research 734-737 (agosto 2013): 388–92. http://dx.doi.org/10.4028/www.scientific.net/amr.734-737.388.

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Microbialites from Penglaiba section, a well-exposed stratigraphic section in the northwestern area of the Tarim Basin are widely distributed throughout the Lower Qiulitage Formation of the Upper Cambrian. Stromatolites and thrombolites are recognized as the two major components. Thrombolites have two kinds of fabrics under the microscopy based on varying arrangements macroscopically, which are microbial reefs and clotted laminations. The microbial reefs are kind of round and irregular buildups with branched shapes and interconnection as frame, which played the major roles in protecting the other microbial structures against the tides and waves. Based on petrology, stratigraphy and micro-facies combination, depositional environments are indicated for varying water depths and energy. In addition, a model of peleaoenvironments is established in the Lower Qiulitage Formation. Both of thrombolites and stromatolites are associated in the subtidal zone, but in this sedimentary model, thrombolites deposited in the deeper water, in which this facies association is similar to what has happened in Bahamas.

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6

Siqueiros-Beltrones, D. A. "DIATOMEAS BENTÓNICAS ASOCIADAS A TROMBOLITOS VIVOS". CICIMAR Oceánides 21, n. 1-2 (31 dicembre 2006): 113. http://dx.doi.org/10.37543/oceanides.v21i1-2.30.

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Se determinó el primer elenco florístico de diatomeas asocia das a trombolitos vivos (protrombolitos). Estos sustratos que exhiben condiciones particulares de estabilidad, fueron descubiertos en playas de la Ensena da de La Paz, B.C.S. y representan un nuevo sustrato para el desarrollo de diatomeas bentónicas marinas. Se examinaron fragmentos de protrombolitos recolectados mensualmente, de agosto a noviembre de 2005, en cuatro sitios de la Ensenada. La envoltura de los protrombolitos consiste en un complejo de cianofitas: Microcoleus chthonoplastes, Oscillatoria limosa/Lyngbia aestuarii y otras formas filamentosas. Se identificaron 150 taxa de diatomeas, principalmente formas pennadas. La presencia de ciertos taxa evidencia la influencia de los manglares y ambientes hipersalinos aledaños. Aunque la composición de especies no difiere de otras asociaciones de la región, los taxa dominantes son distintos; los más frecuentes son: Mastogloia pumila (Grun.) Cleve, Mastogloia obliqua Hagelstein, Navicula formenterae Cleve, Nitzschia frustulum var. perminuta Grunow, Nitzschia scalpelliformis (Grun.) Grunow, Nitzschia sigma (Kütz.) W. Smith, Psammodyction constricta (Kütz.) Ralfs, Rhopalodia gibberula (Ehr.) O. Müller, Seminavis sp. 1. La riqueza de especies es considerada alta, dada la estabilidad y homogeneidad del sistema protrombolítico. Benthic diatoms associated to living thrombolites The first floristic account of benthic diatoms associated to recent (living) thrombolites or protrombolites was determined. These sedimentary formations generated by cyanophytes that exhibit particular conditions of stability were discovered in beaches of Ensenada de La Paz. These represent new substrata for the growth of marine benthic diatoms. Fragments of pro-thrombolites collected monthly from August to November in four sites of the Ensenada were examined. The pro-thrombolite cover consisted of a cyanophyte complex where Microcoleus chthonoplastes, Oscillatoria limosa/Lyngbia aestuarii, and other filamentous forms are the main components. A total of 150 diatom taxa were identified, mainly pennate forms. The presence of certain taxa shows the influence of nearby mangroves and hypersaline environments. Although the species composition does not seem to differ from other assemblages in the region, dominant taxa are different. The most frequent taxa were: Mastogloia pumila (Grun.) Cleve, Mastogloia obliqua Hagelstein, Navicula formenterae Cleve, Nitzschia frustulum var. perminuta Grunow, Nitzschia scalpelliformis (Grun.) Grunow, Nitzschia sigma (Küt z.) W. Smith, Psammodyction constricta (Kütz.) Ralfs, Rhopalodia gibberula (Ehren berg) O. Müller, Seminavis sp. 1. The species richness is high considering the stability and homogeneity of the pro-thrombolithic system.

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7

Siqueiros-Beltrones, D. A. "DIATOMEAS BENTÓNICAS ASOCIADAS A TROMBOLITOS VIVOS". CICIMAR Oceánides 21, n. 1-2 (31 dicembre 2006): 113. http://dx.doi.org/10.37543/oceanides.v21i1-2.30.

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Abstract (sommario):

Se determinó el primer elenco florístico de diatomeas asocia das a trombolitos vivos (protrombolitos). Estos sustratos que exhiben condiciones particulares de estabilidad, fueron descubiertos en playas de la Ensena da de La Paz, B.C.S. y representan un nuevo sustrato para el desarrollo de diatomeas bentónicas marinas. Se examinaron fragmentos de protrombolitos recolectados mensualmente, de agosto a noviembre de 2005, en cuatro sitios de la Ensenada. La envoltura de los protrombolitos consiste en un complejo de cianofitas: Microcoleus chthonoplastes, Oscillatoria limosa/Lyngbia aestuarii y otras formas filamentosas. Se identificaron 150 taxa de diatomeas, principalmente formas pennadas. La presencia de ciertos taxa evidencia la influencia de los manglares y ambientes hipersalinos aledaños. Aunque la composición de especies no difiere de otras asociaciones de la región, los taxa dominantes son distintos; los más frecuentes son: Mastogloia pumila (Grun.) Cleve, Mastogloia obliqua Hagelstein, Navicula formenterae Cleve, Nitzschia frustulum var. perminuta Grunow, Nitzschia scalpelliformis (Grun.) Grunow, Nitzschia sigma (Kütz.) W. Smith, Psammodyction constricta (Kütz.) Ralfs, Rhopalodia gibberula (Ehr.) O. Müller, Seminavis sp. 1. La riqueza de especies es considerada alta, dada la estabilidad y homogeneidad del sistema protrombolítico. Benthic diatoms associated to living thrombolites The first floristic account of benthic diatoms associated to recent (living) thrombolites or protrombolites was determined. These sedimentary formations generated by cyanophytes that exhibit particular conditions of stability were discovered in beaches of Ensenada de La Paz. These represent new substrata for the growth of marine benthic diatoms. Fragments of pro-thrombolites collected monthly from August to November in four sites of the Ensenada were examined. The pro-thrombolite cover consisted of a cyanophyte complex where Microcoleus chthonoplastes, Oscillatoria limosa/Lyngbia aestuarii, and other filamentous forms are the main components. A total of 150 diatom taxa were identified, mainly pennate forms. The presence of certain taxa shows the influence of nearby mangroves and hypersaline environments. Although the species composition does not seem to differ from other assemblages in the region, dominant taxa are different. The most frequent taxa were: Mastogloia pumila (Grun.) Cleve, Mastogloia obliqua Hagelstein, Navicula formenterae Cleve, Nitzschia frustulum var. perminuta Grunow, Nitzschia scalpelliformis (Grun.) Grunow, Nitzschia sigma (Küt z.) W. Smith, Psammodyction constricta (Kütz.) Ralfs, Rhopalodia gibberula (Ehren berg) O. Müller, Seminavis sp. 1. The species richness is high considering the stability and homogeneity of the pro-thrombolithic system.

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8

Siqueiros-Beltrones, D. A., O. U. Hernández-Almeida, S. González-Carrillo e U. Argumedo-Hernández. "PRO-THROMBOLITES FROM LAGUNA SAN IGNACIO, B.C.S., MEXICO". CICIMAR Oceánides 23, n. 1-2 (31 dicembre 2008): 83. http://dx.doi.org/10.37543/oceanides.v23i1-2.48.

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PROTROMBOLITOS EN LAGUNA SAN IGNACIO, B.C.S., MÉXICO Se presenta nueva información sobre la presencia de protrombolitos en lagunas costeras de la Península de Baja California. Los registros fotográficos de estructuras protrombolíticas en Laguna San Ignacio, B.C.S. apoyan la hipótesis de que éstas promovieron la formación de las lagunas costeras a lo largo del noroeste mexicano y que las especies de cianofitas involucradas son las mismas.

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9

SHAPIRO, R. S. "A Comment on the Systematic Confusion of Thrombolites". PALAIOS 15, n. 2 (1 aprile 2000): 166–69. http://dx.doi.org/10.1669/0883-1351(2000)015<0166:acotsc>2.0.co;2.

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10

Tang, Dongjie, Xiaoying Shi e Ganqing Jiang. "Mesoproterozoic biogenic thrombolites from the North China platform". International Journal of Earth Sciences 102, n. 2 (23 settembre 2012): 401–13. http://dx.doi.org/10.1007/s00531-012-0817-9.

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11

Siqueiros-Beltrones, D. A., O. U. Hernández-Almeida, S. González-Carrillo e U. Argumedo-Hernández. "PRO-THROMBOLITES FROM LAGUNA SAN IGNACIO, B.C.S., MEXICO". CICIMAR Oceánides 23, n. 1-2 (31 dicembre 2008): 83. http://dx.doi.org/10.37543/oceanides.v23i1-2.48.

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PROTROMBOLITOS EN LAGUNA SAN IGNACIO, B.C.S., MÉXICO Se presenta nueva información sobre la presencia de protrombolitos en lagunas costeras de la Península de Baja California. Los registros fotográficos de estructuras protrombolíticas en Laguna San Ignacio, B.C.S. apoyan la hipótesis de que éstas promovieron la formación de las lagunas costeras a lo largo del noroeste mexicano y que las especies de cianofitas involucradas son las mismas.

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12

Kennard, John M., e Noel P. James. "Thrombolites and Stromatolites: Two Distinct Types of Microbial Structures". PALAIOS 1, n. 5 (ottobre 1986): 492. http://dx.doi.org/10.2307/3514631.

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13

Desnues, Christelle, Beltran Rodriguez-Brito, Steve Rayhawk, Scott Kelley, Tuong Tran, Matthew Haynes, Hong Liu et al. "Biodiversity and biogeography of phages in modern stromatolites and thrombolites". Nature 452, n. 7185 (marzo 2008): 340–43. http://dx.doi.org/10.1038/nature06735.

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14

Grotzinger, John P., Wesley A. Watters e Andrew H. Knoll. "Calcified metazoans in thrombolite-stromatolite reefs of the terminal Proterozoic Nama Group, Namibia". Paleobiology 26, n. 3 (2000): 334–59. http://dx.doi.org/10.1666/0094-8373(2000)026<0334:cmitsr>2.0.co;2.

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Reefs containing abundant calcified metazoans occur at several stratigraphic levels within carbonate platforms of the terminal Proterozoic Nama Group, central and southern Namibia. The reef-bearing strata span an interval ranging from approximately 550 Ma to 543 Ma. The reefs are composed of thrombolites (clotted internal texture) and stromatolites (laminated internal texture) that form laterally continuous biostromes, isolated patch reefs, and isolated pinnacle reefs ranging in scale from a meter to several kilometers in width. Stromatolite-dominated reefs occur in depositionally updip positions within carbonate ramps, whereas thrombolite-dominated reefs occur broadly across the ramp profile and are well developed as pinnacle reefs in downdip positions.The three-dimensional morphology of reef-associated fossils was reconstructed by computer, based on digitized images of sections taken at 25-micron intervals through 15 fossil specimens and additionally supported by observations of over 90 sets of serial sections. Most variation observed in outcrop can be accounted for by a single species of cm-scale, lightly calcified goblet-shaped fossils herein described as Namacalathus hermanastes gen. et sp. nov. These fossils are characterized by a hollow stem open at both ends attached to a broadly spheroidal cup marked by a circular opening with a downturned lip and six (or seven) side holes interpreted as diagenetic features of underlying biological structure. The goblets lived atop the rough topography created by ecologically complex microbial-algal carpets; they appear to have been sessile benthos attached either to the biohermal substrate or to soft-bodied macrobenthos such as seaweeds that grew on the reef surface. The phylogenetic affinities of Namacalathus are uncertain, although preserved morphology is consistent with a cnidarian-like bodyplan. In general aspect, these fossils resemble some of the unmineralized, radially symmetric taxa found in contemporaneous sandstones and shales, but do not appear to be closely related to the well-skeletonized bilaterian animals that radiated in younger oceans. Nama reefs demonstrate that biohermal associations of invertebrates and thrombolite-forming microorganisms antedate the Cambrian Period.

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15

TURNER, E. C., N. P. JAMES e G. M. NARBONNE. "Taphonomic Control on Microstructure in Early Neoproterozoic Reefal Stromatolites and Thrombolites". PALAIOS 15, n. 2 (1 aprile 2000): 87–111. http://dx.doi.org/10.1669/0883-1351(2000)015<0087:tcomie>2.0.co;2.

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16

Siqueiros-Beltrones, D. A. "Role of Pro-Thrombolites in the Geomorphology of a Coastal Lagoon1". Pacific Science 62, n. 2 (aprile 2008): 257–69. http://dx.doi.org/10.2984/1534-6188(2008)62[257:ropitg]2.0.co;2.

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17

Aitken, J. D., e G. M. Narbonne. "Two Occurrences of Precambrian Thrombolites from the Mackenzie Mountains, Northwestern Canada". PALAIOS 4, n. 4 (agosto 1989): 384. http://dx.doi.org/10.2307/3514563.

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18

Gleeson, Deirdre B., David Wacey, Ian Waite, Anthony G. O'Donnell e Matt R. Kilburn. "Biodiversity of Living, Non-marine, Thrombolites of Lake Clifton, Western Australia". Geomicrobiology Journal 33, n. 10 (16 giugno 2016): 850–59. http://dx.doi.org/10.1080/01490451.2015.1118168.

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Browne, Kathleen M., e Robert V. Demicco. "Thrombolites of the lower devonian Manlius Formation of central New York". Carbonates and Evaporites 2, n. 2 (settembre 1988): 149–55. http://dx.doi.org/10.1007/bf03174314.

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20

Kah, Linda C., e John P. Grotzinger. "Early Proterozoic (1.9 Ga) Thrombolites of the Rocknest Formation, Northwest Territories, Canada". PALAIOS 7, n. 3 (giugno 1992): 305. http://dx.doi.org/10.2307/3514975.

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21

Kirkham, Anthony, e Maurice E. Tucker. "Thrombolites, spherulites and fibrous crusts (Holkerian, Purbeckian, Aptian): Context, fabrics and origins". Sedimentary Geology 374 (ottobre 2018): 69–84. http://dx.doi.org/10.1016/j.sedgeo.2018.07.002.

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22

Chacón B., Elizabeth, José Jorge Aranda-Gómez, Marcela Charles-Polo, Marco A. Sánchez-Ramos, Eric M. Rivera-Muñoz, Gilles Levresse e Beatriz Millán-Malo. "Biohermal thrombolites of the crater lake Rincón de Parangeo in Central México". Journal of South American Earth Sciences 85 (agosto 2018): 236–49. http://dx.doi.org/10.1016/j.jsames.2018.04.013.

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23

Nomchong, Brendan J., e Martin J. Van Kranendonk. "Diverse thrombolites from the c. 2.4 Ga Turee Creek Group, Western Australia". Precambrian Research 338 (marzo 2020): 105593. http://dx.doi.org/10.1016/j.precamres.2019.105593.

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24

Han, Zuozhen, Dingxiang Zhuang, Hui Zhao, Huaxiao Yan, Guangzhou Mao, Changhong Yao, Jiajia Wang et al. "Comparative study on thermal behaviors between micrites and thrombolites using thermogravimetric analysis". Journal of Thermal Analysis and Calorimetry 139, n. 2 (17 luglio 2019): 1229–42. http://dx.doi.org/10.1007/s10973-019-08559-0.

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Riding, R., J. C. Braga e J. M. Martin. "Oolite stromatolites and thrombolites, Miocene, Spain: analogues of Recent giant Bahamian examples". Sedimentary Geology 71, n. 3-4 (maggio 1991): 121–27. http://dx.doi.org/10.1016/0037-0738(91)90096-v.

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26

Barili, Rosalia, Joyce Elaine Neilson, Alexander Thomas Brasier, Karin Goldberg, Tatiana Pastro Bardola, Luiz Fernando De Ros e Melanie Leng. "Carbon isotopes, stratigraphy, and environmental change: the Middle–Upper Cambrian Positive Excursion (SPICE) in Port au Port Group, western Newfoundland, Canada". Canadian Journal of Earth Sciences 55, n. 11 (novembre 2018): 1209–22. http://dx.doi.org/10.1139/cjes-2018-0025.

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In many basins, Upper Cambrian carbonate successions display intervals with a positive carbon isotope excursion (CIE) of up to +5‰. In North America, this marks the boundary between the Sauk II–III super-sequences. A Steptoean positive carbon isotope excursion (SPICE) locality previously identified in the Port au Port peninsula, western Newfoundland, has been revisited and an additional potential SPICE locality found. In both locations, a CIE is found to be associated with a prominent bioherm and sandstone layer within a sequence of carbonate rocks. At March Point columnar stromatolites occur, whereas at Felix Cove thrombolites can be seen. In the latter, the sandstone immediately overlies the thrombolites coincident with the CIE, whereas at March Point a dolomitized grainstone occurs above the stromatolites. The sandstone at this locality post-dates the CIE. Although lower than the SPICE in some localities, a positive CIE is present in both sections: March Point (+1.1‰) and Felix Cove (+1.8‰). Additionally, δ13Corg rises from −30.0‰ to −22.0‰ at March Point and from −27‰ to −24.0‰ at Felix Cove and, in accordance with previously published work, we suggest that this could be the SPICE. Comparison of the stratigraphy and petrography between the two localities suggest that both depositional and diagenetic factors could have influenced the nature of the interpreted SPICE in Newfoundland. It is also possible that the local carbon isotopic signature may have been influenced by a semi-restricted depositional and early diagenetic environment related to the paleogeographic configuration rather than the global marine excursion.

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Hersi, O. Salad, D. Lavoie e G. S. Nowlan. "Reappraisal of the Beekmantown Group sedimentology and stratigraphy, Montréal area, southwestern Quebec: implications for understanding the depositional evolution of the Lower-Middle Ordovician Laurentian passive margin of eastern Canada". Canadian Journal of Earth Sciences 40, n. 2 (1 febbraio 2003): 149–76. http://dx.doi.org/10.1139/e02-077.

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Detailed lithostratigraphic mapping of the Beekmantown Group of southwestern Quebec has refined the field application of the previously proposed tripartite division of the group (i.e., Theresa, Beauharnois, and Carillon formations). The group is a peritidal-dominated succession that accumulated on the epicontinental Laurentian passive margin. Biostratigraphic data based on conodonts from this group indicate an Early to early Middle Ordovician age and are partially time-correlative with the Wallace Creek to Naylor Ledge strata of the Philipsburg Group, southern Quebec. This conodont biostratigraphy sheds new light on the temporal evolution and depositional framework of the Beekmantown platform. The platform evolved as a distally steepened ramp during deposition of the Theresa Formation and the Ogdensburg Member of the Beauharnois Formation (early to middle Ibexian). Correlative strata of the Philipsburg Group include the Wallace Creek and Morgan Corner formations, which represent outer platform sediments. The coarse-grained sandstone of the Theresa Formation accumulated in the innermost platform, whereas coarse-grained carbonates of the Ogdensburg Member indicate open-marine, subtidal to intertidal carbonate sand shoals. By late Ibexian, the platform developed a pronounced margin where thrombolites flourished under high-energy conditions. These are represented by the thrombolite-rich Hasting Creek and Naylor Ledge formations of the Philipsburg Group. Consequently, a broad lagoon formed on the lee side of the platform margin, where low-energy conditions prevailed and accumulation of burrow-mottled dolostones of the Huntingdon Member of the upper Beauharnois Formation took place. The lagoon became more restricted during the latest stages of the basin fill (Whiterockian), and high intertidal to supratidal sediments of the Carillon Formation were deposited.

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28

Lencina, Agustina I., Mariana N. Soria, Fernando J. Gomez, Emmanuelle Gérard e M. Eugenia Farias. "Composite microbialites: Thrombolite, dendrolite, and stromatolite associations in a modern environment, Pozo Bravo lake, Salar de Antofalla, Catamarca Puna, Argentina". Journal of Sedimentary Research 91, n. 12 (31 dicembre 2021): 1305–30. http://dx.doi.org/10.2110/jsr.2020.166.

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ABSTRACT Pozo Bravo is a high-altitude Andean lake that harbors modern microbialites thriving in hypersaline conditions in the Salar de Antofalla, one of the driest sites on Earth and located in the Puna region of Catamarca, northwest Argentine. Due to the lake physiography, microbialites are restricted to a narrow belt following Pozo Bravo lake variations. Microbialites exhibit a wide range of external morphologies including domal, discoidal, tabular, and horseshoe-like bioherms which vary considerably in size, as well as large biostromal terraces. As documented by other studies on modern microbialites, external morphology appears to be mainly the product of the environmental setting. In Pozo Bravo lake, high evaporation rates and hypersalinity (driven by high temperature and strong winds), water-level fluctuations, and lake-bottom topography are major controlling factors. The distinctive feature of Pozo Bravo microbialites is their internal structure, showing a gradual transition from a thrombolitic core to dendrolitic structures and to a sharply overlying stromatolitic layer within a single microbialite. We suggest that these various microbialite textures represent a gradual change within an environmental gradient based on lake-level variations, and the influence of these environmental factors on biological activity, mainly by cyanobacteria and diatoms. The study of this site is particularly relevant given that it represents an active system where progressive changes in microbialite type (from thrombolites to dendrolites and stromatolites) are recorded, providing an excellent natural laboratory to study these textural changes from a mechanistic perspective, and it may provide insights for better understanding of the microbialite geological record. In addition, given that these systems are threatened by human activities (mining of lithium-rich brines), its study and preservation are necessary.

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29

Mettraux, Monique, Peter Homewood, Said Al Balushi, Marcelle Marques Erthal e Nilo Siguehiko Matsuda. "Neoproterozoic microbialites in outcrops of the Qarn Alam salt dome, central Oman". GeoArabia 19, n. 3 (1 luglio 2014): 17–79. http://dx.doi.org/10.2113/geoarabia190317.

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ABSTRACT Limestones and mixed limestone and dolomite facies from the Neoproterozoic to early Cambrian Ara Group are exposed as blocks and rafts by the surface-piercing Qarn Alam salt dome in central Oman. These limestones and dolomites compose laminite-stromatolite-thrombolite-evaporite shallowing-up successions, and are remarkable in that they contain well-preserved microbial textures and fossils (both calcite and dolomite with very small but significant silicates and other mineral species) as well as pristine syn-depositional to very early diagenetic cements from the first stages of sediment lithification. The facies are described at scales ranging from outcrop (1–100 m) to the SEM (μm-scale). Outcrop-scale sedimentology and high-resolution stratigraphy are described in detail, and petrographic and geochemical analyses are recorded. The depositional environment is interpreted to have been shallow marine subtidal to intertidal and hypersaline supratidal, with low-energy tidal flats and channels, lagoons or salinas, and continental sabkhas. Both calcitic and dolomitic phases show microbial fossils and structures with fabrics of mineralised extra-cellular polymeric substances (EPS). The occurrence of syn-sedimentary primary dolomitic matrix in thrombolites is interpreted to result from the degradation of a thicker microbial mat, during or after growth, which provided the right micro-environmental conditions for the precipitation of dolomite. A caliche crust and sabkha evaporites (the white band) cap the laminite-thrombolite succession and together with karst breccias, fracture fills and neptunian dykes, record an emersion at the top of each of the depositional units. Stable isotopes of carbon and oxygen of the microbialite to evaporite facies show close values for δ13C (+2‰ to +4‰) but a broader range of δ18O (+0.5‰ to -5‰). These values, and their spread recorded within sets of laminae, indicate little to no diagenetic resetting and therefore should be close to original equilibrium values for seawater and early diagenetic fluids. Later diagenetic cements in fractures show entirely different values with δ13C in the range of -2‰ to -6‰, and δ18O from -7.5‰ to -11‰. Whereas dolomite shows no post-depositional diagenetic modification and records preservation of finely detailed EPS mineralisation, the calcite of clumps of clots and mesoclots shows neomorphism with reorganisation into crudely fascicular-optic crystals that cut across primary sediment and early diagenetic cement fabrics. Preservation of both sedimentary facies and the fossil record is remarkable for these ca. 540 million year old rocks and indicates that diagenesis had little effect on the microbialites at Qarn Alam.

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30

Mazzoleni, A. G., Y. Bone e V. A. Gostin. "Cathodoluminescence of aragonitic gastropods and cement in Old Man Lake thrombolites, southeastern South Australia". Australian Journal of Earth Sciences 42, n. 5 (ottobre 1995): 497–500. http://dx.doi.org/10.1080/08120099508728219.

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31

Petrash, Daniel A., Murray K. Gingras, Stefan V. Lalonde, François Orange, Ernesto Pecoits e Kurt O. Konhauser. "Dynamic controls on accretion and lithification of modern gypsum-dominated thrombolites, Los Roques, Venezuela". Sedimentary Geology 245-246 (marzo 2012): 29–47. http://dx.doi.org/10.1016/j.sedgeo.2011.12.006.

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32

LANDING, ED, JONATHAN M. ADRAIN, STEPHEN R. WESTROP e BJÖRN KRÖGER. "Tribes Hill–Rochdale formations in east Laurentia: proxies for Early Ordovician (Tremadocian) eustasy on a tropical passive margin (New York and west Vermont)". Geological Magazine 149, n. 1 (9 agosto 2011): 93–123. http://dx.doi.org/10.1017/s0016756811000598.

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AbstractSlow subsidence and tectonic quiescence along the New York Promontory margin of Laurentia mean that the carbonate-dominated Tribes Hill and overlying Rochdale formations serve as proxies for the magnitude and timing of Tremadocian eustatic changes. Both formations are unconformity-bound, deepening–shoaling, depositional sequences that double in thickness from the craton into the parautochthonous, western Appalachian Mountains. A consistent, ‘layer cake’ succession of member-level units of the formations persists through this region. The Tribes Hill Formation (late early Tremadocian, late Skullrockian, late Fauna B–Rossodus manitouensis Chron) unconformably overlies the terminal Cambrian Little Falls Formation as the lowest Ordovician unit on the New York Promontory. It was deposited during the strong early Tremadocian, or Stonehenge, transgression that inundated Laurentia, brought dysoxic/anoxic (d/a) slope water onto the shelf and led to deposition of the Schaghticoke d/a interval (black mudstone and ‘ribbon limestone’) on the Laurentian continental slope. The uniform lithofacies succession of the Tribes Hill includes a lower sand-rich member; a middle, dark grey to black mudstone that records d/a in eastern exposures; and an upper, shoaling-up carbonate highstand facies. A widespread (12000+ km2) thrombolitic interval in the highstand carbonate suggests the New York Promontory was rimmed by thrombolites during deposition of the Tribes Hill. Offlap and erosion of the Tribes Hill was followed by the relatively feeble sea-level rise of the Rochdale transgression (new) in Laurentia, and deposition of the Rochdale Formation. The Rochdale transgression, correlated with the Kierograptus Drowning Interval in Baltica, marks a eustatic rise. The Rochdale Formation represents a short Early Ordovician interval (early late Tremadocian, middle–late Stairsian, Macerodus dianae Chron). It correlates with a depositional sequence that forms the middle Boat Harbour Formation in west Newfoundland and with the Rte 299 d/a interval on the east Laurentian slope. The Rochdale has a lower carbonate with abundant quartz silt (Comstock Member, new) and an upper, thrombolitic (Hawk Member, new) high-stand facies. Tribes Hill and Rochdale faunas are mollusc-rich, generally trilobite-poor, and have low diversity, Laurentian faunal province conodonts. Ulrichodina rutnika Landing n. sp. is rare in Rochdale conodont assemblages. Trilobites are also low in diversity, but locally form coquinas in the middle Tribes Hill. The poorly preserved Rochdale trilobites include the bathyurid Randaynia, at least two hystricurid species and Leiostegium.

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33

Warren, Lucas V., Thomas R. Fairchild, Claudio Gaucher, Paulo C. Boggiani, Daniel G. Poiré, Luís E. Anelli e Julio C. G. Inchausti. "Corumbella and in situ Cloudina in association with thrombolites in the Ediacaran Itapucumi Group, Paraguay". Terra Nova 23, n. 6 (15 settembre 2011): 382–89. http://dx.doi.org/10.1111/j.1365-3121.2011.01023.x.

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34

Abu Samah, Mohamad Ezanie, Che Aziz Ali, Kamal Roslan Mohamed e Nurul Afifah Mohd Radzir. "Characterisation and interpretation of stromatolites and thrombolites Paleo-environment in Setul Limestone succession, Langkawi and Perlis". Bulletin of the Geological Society of Malaysia 66, n. 1 (1 dicembre 2018): 129–40. http://dx.doi.org/10.7186/bgsm66201816.

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35

Burne, Robert V., Linda S. Moore, Andrew G. Christy, Ulrike Troitzsch, Penelope L. King, Anna M. Carnerup e P. Joseph Hamilton. "Stevensite in the modern thrombolites of Lake Clifton, Western Australia: A missing link in microbialite mineralization?" Geology 42, n. 7 (luglio 2014): 575–78. http://dx.doi.org/10.1130/g35484.1.

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36

Osman, Jorge R., Pabla Viedma, Jorge Mendoza e Davor Cotoras. "Bacterial and Geochemical Composition of Thrombolites from Lake Sarmiento, Torres del Paine National Park of Chilean Patagonia". Geomicrobiology Journal 37, n. 4 (3 gennaio 2020): 376–88. http://dx.doi.org/10.1080/01490451.2019.1709107.

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37

Louyakis, Artemis S., Jennifer M. Mobberley, Brooke E. Vitek, Pieter T. Visscher, Paul D. Hagan, R. Pamela Reid, Reinhard Kozdon et al. "A Study of the Microbial Spatial Heterogeneity of Bahamian Thrombolites Using Molecular, Biochemical, and Stable Isotope Analyses". Astrobiology 17, n. 5 (maggio 2017): 413–30. http://dx.doi.org/10.1089/ast.2016.1563.

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38

Soudry, David, e Tuvia Weissbrod. "Morphogenesis and facies relationships of thrombolites and siliciclastic stromatolites in a Cambrian tidal sequence (Elat area, southern Israel)". Palaeogeography, Palaeoclimatology, Palaeoecology 114, n. 2-4 (aprile 1995): 339–55. http://dx.doi.org/10.1016/0031-0182(94)00087-o.

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39

Shapiro, Russell S. "Neoproterozoic-Cambrian microbialite record". Paleontological Society Papers 10 (novembre 2004): 5–16. http://dx.doi.org/10.1017/s1089332600002308.

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Abstract (sommario):

Microbes and the sedimentary record of their activity, microbialites, have existed since the Archaean. During the Neoproterozoic-Cambrian interval, there is a marked shift in the fossil record of microbialites with the widespread proliferation of thrombolites (clotted microbialites) and the appearance and proliferation of dendrolites (microbialites composed of dendritic clusters) alongside stromatolites (laminated microbialites). Calcimicrobes also diversified during this interval. The end of this resurgence coincided with the increase in invertebrate taxa at the end of the Early Ordovician. The ìMicrobialite Resurgenceî has long been recognized but the importance of the Neoporoterozoic microbialite record for deciphering trends of this interval has not been so widely realized. It is critical to note that some of the oldest skeletal invertebrates and calcimicrobes are found in Neoproterozoic microbial reefs. Also, microbe-invertebrate synecology and invertebrate abundance trends during this interval suggests that a simple model that keys the resurgence tied in to a lack of competition from reef-building sponges and corals may not be valid. Current re-evaluation of the environmental conditions, principally the fluctuations in the geochemical conditions of the global oceans and atmosphere, will likely shed new light on understanding the Neoproterozoic-Cambrian microbialite record.

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40

Riding, Robert. "Abiogenic, microbial and hybrid authigenic crusts: components of Precambrian stromatolites". Geologia Croatica 61, n. 2-3 (25 dicembre 2008): 73–103. http://dx.doi.org/10.4154/gc.2008.10.

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Authigenic seafloor carbonate crusts include fenestrate microbialite, thrombolite, and four types here designated Fine-grained Crust, Sparry Crust, Hybrid Sparry Fine-grained Crust, and Sparry Crust plus Coarse Grains. Each of the latter four types includes at least some layered examples that have generally been regarded as stromatolites. Recognition and interpretation of these various deposits assists understanding of stromatolite development. Sparry Crust is common in the Late Archaean-Mesoproterozoic. It includes botryoidal fans and other crystal pseudomorphs, microdigitate stromatolite, dendrite, isopachous laminite, and herringbone calcite. Although differing in primary mineralogy and bedform, these are all characterized by coarse sparry, commonly radial fibrous, fabric and appear light coloured in thin-section. They have commonly been referred to as seafloor cement, although they formed at the open sediment-water interface rather than as void-fills. Two of them in particular, isopachous laminite and microdigitate ‘tufa’, typically form isopachous layers with good vertical inheritance and have been regarded as stromatolites. In contrast to Sparry Crust, Fine-grained Crust has fine-grained (micritic, clotted, peloidal, filamentous) microfabric that appears dark in thin-section, and irregular uneven layering with relatively poor inheritance. Mixed crusts, composed of millimetric alternations of Sparry and Fine-grained crust, are here termed Hybrid Sparry Fine-grained Crust. Sparry Crust with coarse allochthonous grains - here termed Sparry Crust plus Coarse Grains – includes some examples that have been given formal stromatolite names, e.g., Gongylina and Omachtenia. Sparry, Hybrid, and Fine-grained crusts are common components of Precambrian stromatolites. Their relative abundances change through time. Archaean stromatolite fabrics are commonly obscured by recrystallization, but their preserved lamina arrangements suggest that many of them could be composed mainly of Sparry or Hybrid crust. During the Palaeoproterozoic-Mesoproterozoic, Sparry Crust fabrics were common in peritidal stromatolites, whereas Hybrid Crust appears to have dominated large subtidal domes and columns. Fine-grained Crust may not have become generally abundant until the Neoproterozoic, when it commonly formed both stromatolites and thrombolites. Phanerozoic normal marine stromatolites are also typically composed of Fine-grained Crust. Present-day analogues of Sparry Crust fabrics occur in some speleothem, hot spring, and splash-zone marine crusts, and of Fine-grained Crust in lithified microbial mats. Light-dark millimetric alternations of sparry and fine-grained crust that characterize Hybrid Crust have analogues in freshwater stromatolites. Taken together, these comparisons suggest that some Precambrian stromatolites are abiogenic, some microbial, and others are intimate hybrid mixtures of the two, and that - preservation permitting - these varieties can be distinguished using microfabric and lamina criteria.

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41

Yan, Zhen, Jianbo Liu, Yoichi Ezaki, Natsuko Adachi e Shengxian Du. "Stacking patterns and growth models of multiscopic structures within Cambrian Series 3 thrombolites at the Jiulongshan section, Shandong Province, northern China". Palaeogeography, Palaeoclimatology, Palaeoecology 474 (maggio 2017): 45–57. http://dx.doi.org/10.1016/j.palaeo.2016.07.009.

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42

Li, Rong. "Deciphering the diagenetic alteration degree in thrombolites across the Permian-Triassic boundary and the evaluation of REY as a proxy of palaeoseawater". Journal of Asian Earth Sciences 147 (ottobre 2017): 37–49. http://dx.doi.org/10.1016/j.jseaes.2017.07.022.

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43

Smith, Michael D., Sarah E. Goater, Elke S. Reichwaldt, Brenton Knott e Anas Ghadouani. "Effects of recent increases in salinity and nutrient concentrations on the microbialite community of Lake Clifton (Western Australia): are the thrombolites at risk?" Hydrobiologia 649, n. 1 (3 aprile 2010): 207–16. http://dx.doi.org/10.1007/s10750-010-0246-3.

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44

Abu Samah, Mohamad Ezanie, Che Aziz Ali e Kamal Roslan Mohamed. "Sedimentological And Stratigraphical Analysis Of Kaki Bukit Formation (Lower Setul Member) At Teluk Ewa, Pulau Langkawi". Bulletin Of The Geological Society Of Malaysia 72 (15 novembre 2021): 25–35. http://dx.doi.org/10.7186/bgsm72202103.

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Abstract (sommario):

The identification of new units on the carbonate sequence of Teluk Ewa (from Tg. Mendidih to Teluk Ewa) has given an idea for the review of stratigraphic succession of Kaki Bukit Formation (Lower Setul Member). The analysis is related to a sedimentology study, where the sedimentary sequences formed as a mixed siliciclastic–carbonate shallow marine system that combines the carbonate and silisiclastic deposits. Eight facies have been recognised such as (1) argillite facies, (2) interlayer of mudstone and limestone facies, (3) wavy stromatolites limestone facies, (4) linear stromatolites limestone facies, (5) heterolithic of mudstone-limestone facies, (6) shale facies, (7) massive limestone facies and (8) thrombolites limestone facies. Each facies are divided into four litostratigraphic units based on the evaluation from Malaysian Stratigraphic Nomenclature Committee (1997) and North American Stratigraphic Code 2005. (1) The clastic unit referring to the uppertmost part of Machinchang Formation maintains it's name. Meanwhile, the suggested nomenclature for the new units such as (2) The Sabung Member is referring to the basal carbonate unit comprising microbial facies and mixed silisiclastic-carbonate sediment. (3) The Pesak Seluar Member in the middle is a silisiclastic unit that consists of shale facies and (4) The Ewa Member at the top representing the upper limestone unit. All units show a similar litostratigraphic characteristics that are found in Tarutao Group, Pante Malaka Formation, Rung Nok Formation and Lae Tong Formation in Thailand as described by Wongwanich et al. (1990; 2002) and Imsamut & Abdul Rahman (2017).

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45

Lavoie, Denis, Pierre-André Bourque e Yvon Héroux. "Early Silurian carbonate platforms in the Appalachian orogenic belt: the Sayabec – La Vieille formations of the Gaspé–Matapédia basin, Quebec". Canadian Journal of Earth Sciences 29, n. 4 (1 aprile 1992): 704–19. http://dx.doi.org/10.1139/e92-061.

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The coeval Early Silurian (late Llandoverian to late Wenlockian) Sayabec and La Vieille formations represent the first occurrence of shallow-water platformal limestones and reefs in the Paleozoic sequence of the Gaspé Belt of the northern Appalachians. Both units display very similar fades, representing laterally well-zoned, south-dipping carbonate platforms with four parallel depositional belts. These, from nearshore to offshore, are (i) a peritidal mud flat dominated by microbial communities (laminites, stromatolites, thrombolites, oncolites); (ii) a low knob reef rim built by skeletal metazoans (corals, bryozoans, stromatoporoids), skeletal calcareous algae, and microbial communities; (iii) a well-sorted lime sand belt; and (iv) a deeper water nodular lime mud belt supporting a tabulate and rugose coral, stromatoporoid, skeletal algae, and large-shelled brachiopod biota. The two platforms developed at the margin of the Quebec Reentrant and St. Lawrence Promontory in the Gaspé Belt of the northern Appalachian Orogen. It is not clear whether they were parts of a single continuous platform stretching along the northern margin of the Gaspé Belt or two separate platforms occupying distinct tectonic blocks. The development of the Sayabec and La Vieille platforms corresponds to the peak of the first shallowing phase in the Gaspé Belt after the Taconian orogeny. The platforms, with their reefs, grew during a period of sea-level stability from the earliest to late Wenlockian. The reefs were killed by an influx of deeper water siliciclastic sediments during a late Wenlockian transgression.

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46

Wood, Rachel, e Amelia Penny. "Substrate growth dynamics and biomineralization of an Ediacaran encrusting poriferan". Proceedings of the Royal Society B: Biological Sciences 285, n. 1870 (10 gennaio 2018): 20171938. http://dx.doi.org/10.1098/rspb.2017.1938.

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The ability to encrust in order to secure and maintain growth on a substrate is a key competitive innovation in benthic metazoans. Here we describe the substrate growth dynamics, mode of biomineralization and possible affinity of Namapoikia rietoogensis , a large (up to 1 m), robustly skeletal, and modular Ediacaran metazoan which encrusted the walls of synsedimentary fissures within microbial–metazoan reefs. Namapoikia formed laminar or domal morphologies with an internal structure of open tubules and transverse elements, and had a very plastic, non-deterministic growth form which could encrust both fully lithified surfaces as well as living microbial substrates, the latter via modified skeletal holdfasts. Namapoikia shows complex growth interactions and substrate competition with contemporary living microbialites and thrombolites, including the production of plate-like dissepiments in response to microbial overgrowth which served to elevate soft tissue above the microbial surface. Namapoikia could also recover from partial mortality due to microbial fouling. We infer initial skeletal growth to have propagated via the rapid formation of an organic scaffold via a basal pinacoderm prior to calcification. This is likely an ancient mode of biomineralization with similarities to the living calcified demosponge Vaceletia. Namapoikia also shows inferred skeletal growth banding which, combined with its large size, implies notable individual longevity. In sum, Namapoikia was a large, relatively long-lived Ediacaran clonal skeletal metazoan that propagated via an organic scaffold prior to calcification, enabling rapid, effective and dynamic substrate occupation and competition in cryptic reef settings. The open tubular internal structure, highly flexible, non-deterministic skeletal organization, and inferred style of biomineralization of Namapoikia places probable affinity within total-group poriferans.

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47

Wang, Yuanchong, Weimin Jiang, Hangyu Liu, Bo Liu, Haofu Zheng, Xiaobo Song, Qiongxian Wang, Wenkai Wang e Yong Li. "Sedimentary and Diagenetic Features and Their Impacts on Microbial Carbonate Reservoirs in the Fourth Member of the Middle Triassic Leikoupo Formation, Western Sichuan Basin, China". Energies 13, n. 9 (6 maggio 2020): 2293. http://dx.doi.org/10.3390/en13092293.

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Abstract (sommario):

In recent years, the discovery of two gas fields in the fourth member of the Leikoupo Formation in the Western Sichuan Basin of SW China confirmed the exploration potential of microbial carbonates. The aim of the present study is to clarify the formation mechanism of the microbial reservoirs in the Leikoupo Formation. For this purpose, lithofacies, depositional environments, and diagenesis analyses were performed in samples collected from cores of 12 wells. The climate of study area was arid during Anisian time, and the water body was restricted. In such a climate, an evaporitic environment was developed, where ten types of lithofacies, dominated by microbial carbonates and gypsum rocks, were recognized. Thrombolites and stromatolites are the main high-quality reservoirs rock types in the fourth member of the Leikoupo Formation in the Western Sichuan Basin of SW China, which developed as microbial mounds, with reservoir space of microbial inter-clot pores, intra-clot pores, fenestral pores, inter-crystalline pores, and cracks. The microbial inter-clot pores are the main reservoir space, formed by trapping and binding of marls by benthic microbial communities. These pores were partially filled with evaporites because of the arid climate, which were subsequently dissolved (mainly gypsum) in the syn-depositional period, thus greatly improving the quality of reservoirs. Although some pores were occluded by multi-stage cements during the burial stage, major pores were well preserved own to the early dolomitization, rapid burial of the Leikoupo Formation, and early charging of hydrocarbon. The early dolomitization enhanced the anti-compaction ability of microbial carbonates during the burial stage. Rapid burial of the Leikoupo succession slowed down early cementation, and it also accelerated the maturation and expulsion process source rock to promote early charging of hydrocarbon in pores, which created a closed system, inhibiting strong burial cementation.

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48

Vrazo, Matthew B., Carlton E. Brett e Samuel J. Ciurca. "Paleoecological and stratigraphic controls on eurypterid Lagerstätten: a model for preservation in the mid-Paleozoic". Paleobiology 43, n. 3 (4 maggio 2017): 383–406. http://dx.doi.org/10.1017/pab.2016.52.

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AbstractRecent studies of eurypterid paleoecology suggest that formation of eurypterid Lagerstätten in the mid-Paleozoic of Laurentia was controlled by the presence of an ecological–taphonomic window that recurred predictably in nearshore, marginal environments during transgressions. We tested this hypothesis by performing a high-resolution taxonomic, environmental, and stratigraphic survey and quantitative analysis of all Silurian–Lower Devonian eurypterid-bearing intervals in the Appalachian basin, the most prolific region for eurypterid remains in the world. Canonical correspondence analysis of sedimentological and faunal associations revealed a strong lithologic gradient between groupings of eurypterid genera and associated taxa across the basin, and a significant association of eurypterids with microbialites (thrombolites, stromatolites) and evaporitic structures. Field observations confirmed that, stratigraphically, eurypterids in the basin frequently occur above the microbialite structures and beneath evaporites and other indicators of increased salinity or subaerial exposure. Following interpretation of these features within a sequence stratigraphic framework, we present a preservational model in which (1) eurypterids inhabited nearshore settings following freshening conditions concomitant with minor transgressions, (2) their remains were subsequently buried by storms or microbialite sediment baffling, and (3) subsequent long-term preservation of tissues was facilitated by regression and cyclical shallowing-up successions that promoted hypersalinity and anoxia. In the central and southern region of the basin, where microbial structures and evidence for hypersalinity are less common, a similar pattern of cyclical shallowing-upward deposition within eurypterid-bearing units holds. Thus, eurypterid preservation appears to reflect a combination of ecological preferences and abiotic conditions that promoted inhabitation and eventual preservation within the same setting. This study provides the first quantitative support for a sea level–based control on preservation of eurypterids and adds to the growing body of evidence that suggests that analysis of exceptional preservation in the fossil record benefits from interpretation within a sequence stratigraphic framework.

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49

Kuznetsov, V. G., e L. M. Zhuravleva. "Microbial carbonate rocks: composition, structures, textures, mechanisms and environments of formation. Emergence of the doctrine of microbial formations and their forms. Article 1". Proceedings of higher educational establishments. Geology and Exploration, n. 3 (21 novembre 2022): 8–18. http://dx.doi.org/10.32454/0016-7762-2022-64-3-8-18.

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Introduction. Concepts describing bacterial effects on mineral formation and, first of all, on the formation of carbonate deposits, started to appear late in the 19th century both in Russia and globally. The precipitation of materials was demonstrated to take place directly at the sedimentation stage and continue in the formed precipitate during diagenetic processes. Research in this direction has recently intensified. Rocks and their constituent parts formed as a result of bacterial activity have been referred to as “biosedimentary structures” or “microbiolites”.Aim. The paper presents the results of generalization and systematization of accumulated research data on the abovementioned forms.Materials and methods. In addition to literature materials, carbonate rocks of various ages – from the Vendian and Lower Cambrian of the Siberian platform to the Crimea Neogene and sediments of contemporary oceans – were examined using macro- and microscopic (mainly) methods of studying and describing specific objects. Article 1 considers the main morphological types of such carbonate formations, both in the form of individual structural components of sedimentary rocks and rocks themselves with peculiar structural characteristics.Results. Two main morphological groups of carbonate microbiolites were identified and characterized. The first group represents individual and independent forms of carbonate material, both of calcite, highly magnesian-dolomite and even pure magnesite composition. This type includes mineralized precipitates of bacterial forms represented by coccolites, tubules, filaments, as well as by plate and sheet structures – mineralized glycocalyx traces. In addition, this group features isolated carbonate objects, familiar to lithologists, including oolites, oncolites, microclusters of pelitomorphic carbonate materials, thrombolites and, apparently, such specific formations as tubiphytes, etc. The second group includes laminated forms of stromatolites with their specific internal structure, as well as mineralized microbial films and mats with a complex structure, etc.Conclusions. In the overwhelming majority of cases, microbiolites are formed at the sedimentation stage, and their morphology and type are determined by specific paleogeographic and paleoclimatic conditions.

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Zhuang, Dingxiang, Yan Guo e Song Chen. "Comparative Study on Thermodynamic and Geochemical Characteristics between Cemented and Clotted Parts of Thrombolite". Crystals 10, n. 11 (9 novembre 2020): 1017. http://dx.doi.org/10.3390/cryst10111017.

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Abstract (sommario):

Carbonate rocks are widely distributed in nature and are one of the main reservoir rocks for oil and gas. Microbes play an important role in the formation of carbonate rocks. Compared with the cemented part with fewer microorganisms (abiotic minerals), the nucleation and growth of the clotted part with more microorganisms (biotic minerals) are affected by the metabolic activities of microorganisms, so it has a unique morphology and crystal structure. However, there are still some confusing questions such as ones regarding the unique thermal decomposition characteristics and geochemical characteristics, which have rarely been studied. Here, X-ray diffraction (XRD) was used to determine the mineral composition of the cemented and clotted part in the same thrombolite. Then, thermal analysis and stable isotope geochemistry were used to explore the thermal stability and stable carbon isotope. The results of X-ray diffraction (XRD) show that the mineral components of the cemented and clotted part in the thrombolite are calcites, but their crystallinity is different. The crystallinity of the clotted part in the thrombolite is higher than that of the cemented part. Thermal analysis results show that the activation energy and the thermal stability of the clotted part in the thrombolite are relatively higher. In addition, the stable carbon isotope results show that, compared with the chemical precipitated calcite in the cemented part, the microorganisms in the clotted part absorb more 12C through photosynthesis, which results in more 13C in the clotted part, and the carbon isotope δ13C value is higher. This study helps to distinguish the crystallographic, thermodynamic and geochemical characteristics of cemented and clotted parts in thrombolite, and may be helpful to deepen our understanding of abiotic and biotic minerals.

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