Caymanite, a cavity-filling deposit in the Oligocene–Miocene Bluff Formation of the Cayman Islands

1992 ◽  
Vol 29 (4) ◽  
pp. 720-736 ◽  
Author(s):  
Brian Jones
Keyword(s):  
Middle Miocene ◽  
Sediment Load ◽  
Second Phase ◽  
Sediment Source ◽  
Cayman Islands ◽  
Terra Rossa ◽  
Karst Terrain ◽  
Cavity System ◽  
Cavity Filling ◽  
Intercrystalline Pores

Caymanite is a laminated, multicoloured (white, red, black) dolostone that fills or partly fills cavities in the Bluff Formation of the Cayman Islands. The first phase of caymanite formation occurred after deposition, lithification, and karsting of the Oligocene Cayman Member. The second phase of caymanite formation occurred after joints had developed in the Middle Miocene Pedro Castle Member. Caymanite deposition predated dolomitization of the Bluff Formation 2–5 Ma ago.Caymanite is formed of mudstones, wackestone, packstones, and grainstones. Allochems include foraminifera, red algae, gastropods, bivalves, and grains of microcrystalline dolostone. Sedimentary structures include planar laminations, graded bedding, mound-shaped laminations, desiccation cracks, and geopetal fabrics. Original depositional dips ranged from 0 to 60°. Although caymanite originated as a limestone, dolomitization did not destroy the original sedimentary fabrics or structures.The sediments that formed caymanite were derived from shallow offshore lagoons, swamps, and possibly brackish-water ponds. Pigmentation of the red and black laminae can be related to precipitates formed of Mn, Fe, Al, Ni, Ti, P, K, Si, and Ca, which occur in the intercrystalline pores. These elements may have been derived from terra rossa, which occurs on the weathered surface of the Bluff Formation. Caymanite colours were inherited from the original limestone. Stratigraphic and sedimentologic evidence shows that sedimentation was episodic and that the sediment source changed with time. Available evidence suggests that caymanite originated from sediments transported by storms onto a highly permeable karst terrain. The water with its sediment load then drained into the subsurface through joints and fissures. The depth to which these waters penetrated was controlled by the length of the interconnected cavity system. Upon entering cavities, sedimentation was controlled by a complex set of variables.

The Characteristic of Algal Reef Carbonate Sedimentary and Pore Structure in the Xisha Islands: Evidence from Halimeda

2014 ◽  
Vol 1065-1069 ◽  
pp. 3291-3294
Author(s):  
Xin Wei Zhao ◽  
Hui Zhi Hao
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Energy Spectrum ◽  
Middle Miocene ◽  
Carbonate Sediments ◽  
Network Systems ◽  
Xisha Islands ◽  
Intercrystalline Pores ◽  
Algal Reef ◽  
Scanning Electron

Halimeda is an important reef-building green alga. Scanning electron microscopy (SEM) and energy spectrum tests on green and white Halimeda collected from Shidao Island in the Xisha Islands show that carbonate is predominantly deposited in the cortexes and medullas, especially in the aragonite raphides of them, as the case of calcium carbonate. These modern carbonate sediments are then compared with their ancient counterparts that are collected from Xichen-1 well in the Yongle Atoll, where a large number of Halimeda segments have been recognized in about 100-m-long late Miocene-middle Miocene whole-coring succession. In addition, there are developed great numbers of algal-frame holes, including secondary dissolved pores and intercrystalline pores in the medullas and in aragonites between cysts, which have formed particular network systems and pore throats.

scholarly journals Using SWAT to Evaluate Streamflow and Lake Sediment Loading in the Xinjiang River Basin with Limited Data

Water ◽  
2019 ◽  
Vol 12 (1) ◽  
pp. 39 ◽  
Author(s):  
Lifeng Yuan ◽  
Kenneth J. Forshay
Keyword(s):  
Soil Erosion ◽  
River Basin ◽  
Lake Sediment ◽  
Sediment Yield ◽  
Sediment Load ◽  
Poyang Lake ◽  
Sediment Source ◽  
Sediment Loading ◽  
Source Areas ◽  
Annual Sediment

Soil erosion and lake sediment loading are primary concerns of watershed managers around the world. In the Xinjiang River Basin of China, severe soil erosion occurs primarily during monsoon periods, resulting in sediment flow into Poyang Lake and subsequently causing lake water quality deterioration. Here, we identified high-risk soil erosion areas and conditions that drive sediment yield in a watershed system with limited available data to guide localized soil erosion control measures intended to support reduced sediment load into Poyang Lake. We used the Soil and Water Assessment Tool (SWAT) model to simulate monthly and annual sediment yield based on a calibrated SWAT streamflow model, identified where sediment originated, and determined what geographic factors drove the loading within the watershed. We applied monthly and daily streamflow discharge (1985–2009) and monthly suspended sediment load data (1985–2001) to Meigang station to conduct parameter sensitivity analysis, calibration, validation, and uncertainty analysis of the model. The coefficient of determination (R2), Nash–Sutcliffe efficiency (NSE), percent bias (PBIAS), and RMSE -observation’s standard deviation ratio (RSR) values of the monthly sediment load were 0.63, 0.62, 3.8%, and 0.61 during calibration, respectively. Spatially, the annual sediment yield rate ranged from 3 ton ha−1year−1 on riparian lowlands of the Xinjiang main channel to 33 ton ha−1year−1 on mountain highlands, with a basin-wide mean of 19 ton ha−1year−1. The study showed that 99.9% of the total land area suffered soil loss (greater than 5 ton ha−1year−1). More sediment originated from the southern mountain highlands than from the northern mountain highlands of the Xinjiang river channel. These results suggest that specific land use types and geographic conditions can be identified as hotspots of sediment source with relatively scarce data; in this case, orchards, barren lands, and mountain highlands with slopes greater than 25° were the primary sediment source areas. This study developed a reliable, physically-based streamflow model and illustrates critical source areas and conditions that influence sediment yield.

Dolomitization of the Oligocene–Miocene Bluff Formation on Grand Cayman, British West Indies

1990 ◽  
Vol 27 (8) ◽  
pp. 1098-1110 ◽  
Author(s):  
Suzanne M. Pleydell ◽  
Brian Jones ◽  
F. J. Longstaffe ◽  
H. Baadsgaard
Keyword(s):  
West Indies ◽  
Middle Miocene ◽  
Geochemical Data ◽  
High Porosity ◽  
British West Indies ◽  
Terra Rossa ◽  
Grand Cayman ◽  
Skeletal Material

The Oligocene–Miocene Bluff Formation on Grand Cayman is formed of hard, white, finely crystalline dolostone in which the precursor textures and fossil microstructures are commonly preserved. The dolostones have a high porosity (up to 25%) because of leaching of skeletal material, which was originally aragonite, and dissolution of the bedrock during the various phases of exposure and karst development.A major disconformity divides the Bluff Formation into the Cayman Member (Oligocene) and Pedro Castle Member (Middle Miocene). Cavities in the Cayman Member are commonly filled or partly filled with caymanite, dolomitized skeletal grainstone, terra rossa, and flowstone. Available evidence suggests that the caymanite and skeletal grainstone were emplaced prior to deposition of the Pedro Castle Member in Middle Miocene times, whereas the emplacement of the terra rossa and flowstone postdates dolomitization of the Bluff Formation.Petrographic and geochemical data suggest that there was only one phase of dolomitization that was mediated by normal seawater. There is no signifiant difference among 87Sr/86Sr ratios of the dolostones of the Cayman and the Pedro Castle members. The average 87Sr/86Sr ratio of 0.70905 for these dolostones is significantly lower than the average 87Sr/86Sr ratio of 0.70917 obtained from modern seawater around Grand Cayman. The 87Sr/86Sr ratios for the dolostones of the Bluff Formation, ranging from 0.70900 to 0.70914, suggest the dolomitization occurred 2–5 Ma ago. The underlying cause of the pervasive dolomitization is uncertain. Although it appears that "normal" seawater was responsible for that dolomitization, there is little evidence pointing to why it occurred 2–5 Ma ago.

Open and filled karst features on the Cayman Islands: implications for the recognition of paleokarst

1988 ◽  
Vol 25 (8) ◽  
pp. 1277-1291 ◽  
Author(s):  
Brian Jones ◽  
Duncan S. Smith
Keyword(s):  
Vadose Zone ◽  
Cayman Islands ◽  
Rock Body ◽  
Terra Rossa ◽  
Local Conditions ◽  
Preservation Potential ◽  
Show Evidence ◽  
Karst Feature ◽  
Two Stages ◽  
Overlying Strata

The dolostones of the Oligocene–Miocene Bluff Formation on the Cayman Islands are characterized by well-developed surficial, interface, and subsurface karst features that are open or filled with speleothems and sediment.Some of the open caves show evidence of a minimum of two stages of development related to dissolution in the phreatic zone and the vadose zone. The development of speleothemic formations (e.g., stalactites, stalagmites, columns) is limited in some caves but extensive in others. Some of the caves have limited amounts of sediment on their floors. In these caves, the speleothems and sediments are still formed of CaCO3 and thus contrast sharply with the dolostone of the Bluff Formation in which they occur. Some of the joints, sinkholes, and caves are filled with breccia, caymanite, terra rossa, terra rossa breccia, pisolitic limestone, and speleothems. Although filled, such karst features are analogous to the open karst features that occur elsewhere on the islands. The filling of joints, sinkholes, or caves is not directly related to the age of the karst development, since caves of the same age may be open or filled. This suggests that local conditions, such as the availability of sediment or the nature of the waters flowing through the caves, played an important role in determining whether a karst feature is filled.Surficial karst features have a low preservation potential, whereas interface and subsurface karst features have a high preservation potential in some circumstances. In the case of sinkholes this assumes that later transgressions did not remove the upper part of the rock body that contained the filled sinkholes. For caves this assumes that they were filled with speleothems and sediment prior to their reaching such a size that collapse of the overlying strata occurred because of the lack of support. If collapse occurs, the presence of caves can only be inferred from the resultant collapse breccias. A potentially valuable criterion for the recognition of paleokarst may lie in the fact that the rocks filling open karst features (e.g., joints, sinkholes, caves) may contrast sharply with the host strata in terms of both lithology and age.

Manganese precipitates in the karst terrain of Grand Cayman, British West Indies

1992 ◽  
Vol 29 (6) ◽  
pp. 1125-1139 ◽  
Author(s):  
Brian Jones
Keyword(s):  
West Indies ◽  
Climatic Conditions ◽  
British West Indies ◽  
Time And Space ◽  
Terra Rossa ◽  
Karst Terrain ◽  
Grand Cayman ◽  
Ongoing Process ◽  
Variable Morphology

Ten morphologically distinct forms of Mn precipitates (probably birnessite) occur in a wide variety of paleokarst features that characterize dolostones of the Bluff Formation on Grand Cayman. These Mn-rich precipitates, which commonly contain variable amounts and selections of Al, Si, Fe, K, Ti, Ni, Na. Mg, and Ca, are not evenly distributed throughout the Bluff Formation of Grand Cayman. Thus, some areas have abundant Mn precipitates, whereas other areas are devoid of such precipitates. Mn precipitates, of variable morphology, have teen found in stalactites, karst breccia, caymanite, terrestrial oncoids, and root calcretes and along fractures and cavities in the dolostone. There does not appear to be any correlation between the morphology and composition of the Mn precipitate and its host substrate.The Mn and its associated elements may have been derived from the terra rossa and (or) swamps that formed on the surface of the Bluff Formation at various times. The scattered distribution of the soils and swamps, with respect to time and space, accounts for the patchy occurrence of the Mn precipitates presently found in the Bluff Formation. Although some of the Mn precipitates are abiogenic in origin, others appear to have formed through the direct or indirect intervention of various microbes.Paragenetic analysis of the Mn precipitates and their associated cements shows that Mn precipitation has not been a constant, ongoing process. Indeed, Mn precipitation does not appear to be occurring at the present day. Available evidence suggests that Mn precipitation occurred at various times when climatic conditions were suitable for Mn mobilization.

Dolomitization of the Lower Ordovician Watts Bight Formation of the St. George Group, western Newfoundland: evidence of hydrothermal fluid alterationGeological Survey of Canada Contribution 20080544.

2009 ◽  
Vol 46 (4) ◽  
pp. 247-261 ◽  
Author(s):  
James Conliffe ◽  
Karem Azmy ◽  
Ian Knight ◽  
Denis Lavoie
Keyword(s):  
Hydrocarbon Exploration ◽  
Source Rocks ◽  
Second Phase ◽  
High Porosity ◽  
Mixing Zone ◽  
Ocean Water ◽  
Lower Ordovician ◽  
Saddle Dolomite ◽  
Porosity And Permeability ◽  
Intercrystalline Pores

The Watts Bight Formation in western Newfoundland consists of a Lower Ordovician succession of shallow-water carbonates and has been extensively dolomitized. These dolomites occur as both replacements and cements and are associated with complex changes in the rock porosity and permeability. Early replacement micritic dolomites (D1) are finely crystalline and indicate that dolomitization began during early stages of diagenesis. The calculated δ18O values of the earliest (D1) dolomitizing fluids (–6.4‰ to –9.5‰ VSMOW, Vienna Standard Mean Ocean Water) fall between the estimated δ18O values of Tremadocian seawater and meteoric waters and suggest mixing-zone dolomitization. A second phase of coarsely crystalline (up to 400 μm) dolomite (D2) replaces D1 dolomite and early calcite and is associated with enhancement in porosity and permeability through the development of intercrystalline pores. A late-stage saddle dolomite (D3) and late burial calcite cements significantly occluded the pores in some horizons. Petrography, fluid inclusions, and geochemistry show that D2 and D3 dolomites formed from warm (65–125 °C) saline (10 to 25 eq. wt.% NaCl + CaCl2) hydrothermal fluids. The calculated δ18Ofluid of D2 ranges from –4.5‰ to 3.6‰ VSMOW, and for D3 dolomites, calculated δ18Ofluid ranges from 1.4‰ to 8.4‰ VSMOW, suggesting an influx of basinal brines. The occurrence of high porosity associated with D2, combined with the laterally sealing tight limestone beds, presence of favourable source rocks, and thermal maturation, may suggest that the Watts Bight carbonates are possible potential hydrocarbon reservoirs and suitable targets for future hydrocarbon exploration in western Newfoundland.

scholarly journals 2D Sequential Restoration and Basin Evolution of the Wichianburi Sub-basin, Phetchabun Basin, Central Thailand

2020 ◽  
Vol 8 ◽  
Author(s):  
Sukonmeth Jitmahantakul ◽  
Jirapat Phetheet ◽  
Pitsanupong Kanjanapayont
Keyword(s):  
Middle Miocene ◽  
Normal Faults ◽  
Second Phase ◽  
Late Oligocene ◽  
Restoration Techniques ◽  
Before And After ◽  
Half Graben ◽  
Productive Area ◽  
Seismic Sections ◽  
Central Thailand

The Wichianburi Sub-basin is currently the only productive area in the southern part of the Phetchabun Basin, central Thailand. It is structurally dominated by NNW-SSE to NNE-SSW trending normal faults as a result of multistage rifting since the Late Oligocene. Half-graben and full-graben basin geometries can be observed from 2D regional seismic sections. In this study, structural restoration techniques were applied to validate the structural interpretation of the original hardcopy of the 2D seismic sections. Stratigraphic information is compiled from published papers and well reports. Our results revealed that most of the deformation was concentrated during the Late Oligocene. Main depocenters for the syn-rift sediments focused in the basin center along the west-dipping normal faults. These faults cut the prerift section and their orientations were possibly controlled by the Permo-Triassic fabrics that underlie the Phetchabun Basin. By measuring the length of the profiles before and after faulting, the restorations show that the extensions of the Wichianburi Subbasin decrease from 12.30% during the main rift phase (Late Oligocene to Early Miocene) to 2.53% during the second phase of rifting. Rifting only focused in the basin center with the development of NNW-SSE to N-S trending intrarift faults. Since the Middle Miocene, the Wichianburi Subbasin has developed under the tectonic phase of post-rift subsidence with interruption by intrusive activities.

scholarly journals Soil properties of agricultural area in karst terrain of Parakan, Pangandaran, West Java, Indonesia

2021 ◽  
Vol 8 (3) ◽  
pp. 2809-2814
Author(s):  
Reginawanti Hindersah ◽  
Yusi Firmansyah ◽  
Nia Kurniati
Keyword(s):  
Organic Carbon ◽  
Exchange Capacity ◽  
Karst Area ◽  
Phosphate Solubilizing Bacteria ◽  
Agricultural Field ◽  
Terra Rossa ◽  
Karst Terrain ◽  
Phosphate Solubilizing ◽  
Increase Plant Productivity ◽  
Microbiological Properties

a clayed soil characterized by reddish in colour, thick solum and neutral acidity. Farmers in Parakan area, Parigi District of Pangandaran, usually cultivate cash crops in terra rossa. Nowadays, farmers have no information about the properties of the soil, which is an important factor to maintain and increase plant productivity. The objective of this descriptive quantitative study was to verify the soil characteristic included physicochemical and microbiological properties in a selected agricultural field of Parakan. The soil samples were taken from three different areas covered with different vegetation. The study showed that terra rossa in the karst area is a non-saline soil with neutral acidity and low electrical conductivity. The texture of all soils were clay contained >50% clay particle. The soils were low in organic carbon, total nitrogen and available phosphor; but high in total phosphor and potassium, as well as cation exchange capacity. The population of soil microbes include total and fungal bacteria, as well as nitrogen-fixing Azotobacter and phosphate solubilizing bacteria, were average. In order to increase the organic carbon level; and the availability of phosphor and nitrogen, organic matter amendment is needed.

scholarly journals Miocene Rocks Around the Marádah Oasis, Central Sirt Basin, Libya: Facies Development and Implication on Stratigraphy

2021 ◽  
Vol 10 (1) ◽  
pp. 8
Author(s):  
Esam O. Abdulsamad ◽  
Saleh A. Emhanna ◽  
Ramzi S. Fergani ◽  
Hamad N. Hamad ◽  
Moataz A. Makhlouf ◽  
...  
Keyword(s):  
Middle Miocene ◽  
Sedimentary Facies ◽  
Second Phase ◽  
Depositional Sequence ◽  
Larger Benthic Foraminifera ◽  
Field Investigations ◽  
Gradual Development ◽  
Two Phases ◽  
Marly Limestone ◽  
Sirt Basin

The Miocene rocks of the Marádah Formation have been stratigraphically investigated from four stratigraphical sections around the Marádah Oasis in the Central Sirt Basin of Libya. The field investigations led to the identification of two members, the lower Qarat Jahannam Member and the upper Ar Ráhlah Member. Fourteen sedimentary facies at the outcrop-scale representing a gradual development of sedimentation from a continental clastic witness in the southwestern outcrops to transitional estuarine, lagoonal, and beaches to the proximal offshore in the northern outcrops, were recognized. The results indicates that the accumulation of the Marádah Formation is transgressive in nature and corresponding to two phases of deposition which have been mentioned in the earlier studies. The first phase is continental-dominated facies in which cross-bedded sandstones and calcareous sands comprise most of the depositional sequence of the lower Qarat Jahannam Member at the southwestern outcrops. This phase, however, is characterized by extremely bioturbated laminated-shale conquered by Skolithos ichnofacies in the lower part of the upper Ar Ráhlah Member at the northern outcrops. This phase is providing further evidence that the contact between the two members is diachronous everywhere in the study area. The clastic-phase has thought to be deposited in the Lower Miocene (Aquitanian-Burdigalian) since the lower Qarat Jahannam Member rests on an erosional surface of submarine origin in the southwestern outcrops above a 0.5 m. thick of a nummulitic unit of the Oligocene Bu Hashish Formation. The second phase is marine-dominated facies in which a bioclastic limestone unit rich in thick and disarticulated oysters, including Crassostrea gryphoides (Schlottheim), characterizes the sediments of the Ar Ráhlah Member at the southwestern outcrops. This phase also includes the upper part of the latter member at the northern outcrops in which a detrital limestone unit rich in turritelline gastropods is overlying by thick-bedded calcarenites rich in disarticulated oysters, gastropods, irregular echinoids (notably, Clypeaster and Echinolampas), bryozoans, and celestite corals. The upper part of the Ar Ráhlah Member at the northern outcrops, nevertheless, is terminated by a quite hard dolomitic limestone and by a pretty soft dolomitic marly limestone. Both lithologies, however, are combined with medium-sized oysters, including Ostrea digitalina Fuchs, and pectinid bivalves. The second phase, however, is interpreted to be deposited in the Middle Miocene (Langhian and Serravallian) based on the total-stratigraphic range of the larger benthic foraminifera Borelis melo melo (Fichtel & Moll), which recovered from the studied washed residues, and the associated microfacies.

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