John Mylroie
Mississippi State University, Geosciences, Faculty Member
espanolLa Isla de Mona, una pequena meseta carbonatada levantada tectonicamente que sobresale de las aguas del Canal de la Mona, es un ambiente muy fragil y densamente karstificado. El trabajo de exploracion se llevo a cabo por el... more
espanolLa Isla de Mona, una pequena meseta carbonatada levantada tectonicamente que sobresale de las aguas del Canal de la Mona, es un ambiente muy fragil y densamente karstificado. El trabajo de exploracion se llevo a cabo por el Proyecto Isla de Mona, en cooperacion con el Departamento de Recursos Naturales y Ambientales de Puerto Rico (DRNA), incluyendo las contribuciones de muchos investigadores y espeleo- logos voluntarios de EE.UU. y Puerto Rico en el curso de 12 expediciones, que han abarcado un periodo de 14 anos (desde 1998 hasta 2013). Mas de 200 cuevas se han documentado en la isla hasta la fecha, la mayor parte de este inventario se compone de cuevas del tipo “flank margin” aunque tambien se incluyen cuevas marinas, simas y cuevas de talud. El ejemplo con un desarrollo mas grande de cuevas en la isla es el Sistema Faro: un entramado laberintico de camaras en el extremo oriental de la isla, con mas de 40 entradas sobre el acantilado con vistas al Mar Caribe. La cartografi...
Research Interests: Geography and Humanities
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Definitions Karst is a landscape created by dissolution of soluble rock, made up of caves, springs, sinkholes, sinking streams, and unusual rock sculpture. Karren refers to the various etchings, carving, and sculpting of soluble rock by... more
Definitions Karst is a landscape created by dissolution of soluble rock, made up of caves, springs, sinkholes, sinking streams, and unusual rock sculpture. Karren refers to the various etchings, carving, and sculpting of soluble rock by dissolution; these features are in the decimeter to meter scale. Carbonates are sedimentary rocks consisting of calcium and/or magnesium combined with CO3 1⁄4. Flank margin caves are caves developed by mixing dissolution within the margin of the freshwater lens. Sea or littoral caves are caves produced by wave energy and bioerosion on rocky coasts. Syndepositional caves are caves produced within a soluble rock as that rock is being deposited. A hybrid cave is a cave developed by one process, overprinted by a second process, such as a flank margin cave overprinted by littoral processes.
Research Interests:
Research Interests:
Guam is the largest and southernmost of the Mariana Islands (Fig. 1). It is 550 km2 in area, 48 km long, and varies in width from 6-19 km (Fig. 2). The Mariana Islands are thought to have been first inhabited between 3000 and 2000 BC... more
Guam is the largest and southernmost of the Mariana Islands (Fig. 1). It is 550 km2 in area, 48 km long, and varies in width from 6-19 km (Fig. 2). The Mariana Islands are thought to have been first inhabited between 3000 and 2000 BC Spain colonized them subsequent to ...
Research Interests:
Research Interests:
Research Interests:
Fieldwork in the Bahamian Archipelago in the 1970s and 1980s identified a new cave type, the flank margin cave, as macroscopic dissolutional voids developed in the margin of a freshwater lens, under the flank of the enclosing landmass.... more
Fieldwork in the Bahamian Archipelago in the 1970s and 1980s identified a new cave type, the flank margin cave, as macroscopic dissolutional voids developed in the margin of a freshwater lens, under the flank of the enclosing landmass. These voids are produced by three conditions that exist at the lens margin: mixing dissolution, organic decay horizons, and the increase in freshwater flow rate. The water flow enters flank margin caves as diffuse flow and exits as diffuse flow, a flow regime that produces dissolutional sculpture lacking turbulent flow features, such as asymmetric scallops. The caves are tied to sea level, which controls the freshwater lens position, and as such are excellent indicators of past sea-level position. The caves form without entrances and become accessible only after subaerial erosion has breached their ceilings or walls. Flank margin caves initiate as individual globular dissolutional voids that then intersect as the voids enlarge, increasing cave size in...
Research Interests:
Rottnest Island and Kangaroo Island, eolianite-containing islands off Australia’s west and southern coasts, respectively, display extensive coastal caves and karst that contain valuable geologic information. On Rottnest Island, Late... more
Rottnest Island and Kangaroo Island, eolianite-containing islands off Australia’s west and southern coasts, respectively, display extensive coastal caves and karst that contain valuable geologic information. On Rottnest Island, Late Quaternary eolianites contain flank margin caves formed during MIS 5e, and may contain flank margin caves developed during the mid-Holocene sea-level highstand. Pit cave development, with subsequent cementation of infilling deposits, results in inversion of topography following surficial denudation. Pseudokarst forms such as sea caves and tafoni, and surficial polygonal structures, complicate karst interpretations. On Kangaroo Island, flank margin caves in Quaternary eolianites are preferentially preserved in protected embayments. Flank margin caves at ∼30 m elevation indicate much greater uplift rates and magnitudes than previously believed. As with Rottnest Island, sea caves and tafoni complicate karst interpretations and provide a cautionary note to those working on coastal caves and karst.
Research Interests:
Research Interests:
On the Island of San Salvador in the Bahama archipelago 30 breccia deposits can be found along the French Bay sea cliffs on the southeast-ern coast of the island. Breccia deposits of this type have not been observed on any other location... more
On the Island of San Salvador in the Bahama archipelago 30 breccia deposits can be found along the French Bay sea cliffs on the southeast-ern coast of the island. Breccia deposits of this type have not been observed on any other location on the island. These deposits have traditionally been interpreted as paleo-talus deposits from an eroding sea cliff formed on a transgressive eolianite deposited at the start of the oxygen isotope substage 5e sea-level highstand (ca. 125,000 years before present). New evidence supports a karst genesis. A survey of several deposits revealed a vertical restriction of +2 to +7 meters above sea level consistent with flank margin caves developed during the substage 5e still-stand. The morphologies of the features were found to be globular and contain distinct caliche boundaries, overhung lips, and smooth undulating bases. Petrographic results support a model in which voids are created and then infilled with a soil breccia. It can be concluded from these ...
ABSTRACT: The original definition of karst development in eogenetic rocks, as presented by H.L. Vacher and J.E. Mylroie in 2002, was “we use the term eogenetic karst for the land surface evolving on, and the pore system developing in,... more
ABSTRACT: The original definition of karst development in eogenetic rocks, as presented by H.L. Vacher and J.E. Mylroie in 2002, was “we use the term eogenetic karst for the land surface evolving on, and the pore system developing in, rocks undergoing eogenetic, meteoric diagenesis.” Since that time karst research has been extensively conducted on carbonate coasts and islands around the world. The majority of these locations are tropical to subtropical, as the carbonate rocks are still proximal to their environment of deposition. A decade later, our research has updated some facets of the original presentation. The top of the fresh-water lens was originally presented as a speleogenetic environment as a result of vadose/phreatic fresh-water mixing, primarily based on banana hole development in the Bahamas. The geochemical evidence for dissolutional aggressivity at the top of the lens was equivocal, and banana holes have been reinterpreted as flank margin caves sequentially developing...
Research Interests:
Abstract Barbados is a small island located on the crest of an accretionary prism at the eastern edge of the Caribbean Sea. Dolomite occurs in relatively small amounts in Pleistocene carbonates and in the underlying Oligocene–Miocene... more
Abstract Barbados is a small island located on the crest of an accretionary prism at the eastern edge of the Caribbean Sea. Dolomite occurs in relatively small amounts in Pleistocene carbonates and in the underlying Oligocene–Miocene chalk, which also contains a few small caves, distinctive authigenic calcites, and oil that ascended through a dense networks of fractures. The stable isotopes of calcites form a positive trend, while those of the dolomites form a negative trend. Dolomite δ18O values range from about +1 to +8‰ PDB, and δ13C values range from about +2 to −25‰ PDB. Sr-isotope ratios range from 0.7079 to 0.7094, which corresponds to a secular range from the Oligocene to the Holocene. The data presented in this study support the notion that the Barbados accretionary wedge has undergone a prolonged history of compression with concomitant expulsion of fluids that varied through time and space. At times these fluids were diluted relative to seawater and also undersaturated with respect to calcite, which resulted in limited dissolution along fractures and in their immediate vicinity. At other times the expelled pore fluids were prone to limited dolomitization, forming pods of dolomite. At yet other times the expelled fluids formed calcite as interstitial cements and around submarine points of exit in what appears to be “cold seeps” with calculated temperatures as low as +4 °C. The expelled fluids were chemically slightly modified seawater that contained thermogenic methane. Calculated temperatures of dolomitization range between +4 and +25 °C, which suggest fluid expulsion from sub-sea depths of zero to about –650 m. A temperature of +4 °C is the lowest ever determined for dolomite formation. The Sr-isotope data suggest that the hypogene fluids were expelled episodically between about 8 and 2 My ago. This study provides support for the hypothesis that dolomitization can result from fluid expulsion in an accretionary prism setting. However, the volumes of dolomite formed in Barbados are small and probably are similarly small in most other accretionary prism settings. Thus, regionally extensive, pervasive dolomitization is not to be expected from the dolomitizing process identified here. If elevated to the status of a model, dolomitization via fluid expulsion from an accretionary prism would be comparable in importance to the mixing zone model of dolomitization.
Research Interests:
Jama tipa »Flank margin«, nastala v pobočni breči v območju
The Bowen manuscript is an interesting and compelling review of a variety of data from world-wide locations to determine the actual elevation magnitude of the MIS 11 sea-level highstand. Given the significant debate in the literature... more
The Bowen manuscript is an interesting and compelling review of a variety of data from world-wide locations to determine the actual elevation magnitude of the MIS 11 sea-level highstand. Given the significant debate in the literature about the duration and elevation of the MIS 11 highstand, the manuscript provides “one stop shopping ” to view a variety of data sets relating to the question. The manuscript has a few minor technical errors that need correction (listed below). The primary concerns of this reviewer fall into two categories. First, the elevation of dissolutional caves that are tied to fresh-water lens position, and hence sea level, are not presented as sea-level indicators, although these caves are discussed in that sense in several of the papers quoted by the author C616 (e.g. Carew and Mylroie, 1995; 1999; Mylroie, 2008). Second, the author got a few of the facts incorrect when quoting from this reviewer’s own work, which casts possible doubts on the accuracy of the re...
Bell holes are vertical, cylindrical voids, higher than they are wide, with circular cross sections and smooth walls found in the ceilings of dissolutional caves primarily from tropical and subtropical settings. They range in size from... more
Bell holes are vertical, cylindrical voids, higher than they are wide, with circular cross sections and smooth walls found in the ceilings of dissolutional caves primarily from tropical and subtropical settings. They range in size from centimeter to meters in height and width. The origin of bell holes has been controversial, with two proposed categories: vadose mechanisms including bat activity, condensation corrosion, and vadose percolation; and phreatic mechanisms including degassing and density convection. Crooked Island, Bahamas has a number of caves with bell holes of unusual morphology (up to 7 m high and 1.5 m in diameter), commonly in tight clusters, requiring significant bedrock removal in a small area. In many cases, numerous bell holes are open to the surface, which requires that up to a meter or more of surface denudation has occurred since the bell hole first formed. Surface intersection has little impact on the phreatic mechanisms, which were time limited to cave genes...
Research Interests:
2 Abstract: Abaco Island, located on Little Bahama Bank, is the most northeastern island in the Bahamian archipelago. Abaco exhibits typical carbonate island karst features such as karren, blue holes, pit caves, banana holes and flank... more
2 Abstract: Abaco Island, located on Little Bahama Bank, is the most northeastern island in the Bahamian archipelago. Abaco exhibits typical carbonate island karst features such as karren, blue holes, pit caves, banana holes and flank margin caves. Landforms that resemble tropical cone karst and pseudokarst tafoni caves are also present. The three cave types of Abaco—flank margin caves, pit caves, and tafoni caves—are abundant, but each forms by very different mechanisms. Flank margin caves are hypogenic in origin, forming due to mixing dissolution at the margin of the freshwater lens. Since the lens margin is concordant with sea level, flank margin caves record the position of sea level during their formation. Flank margin caves exhibit phreatic dissolutional features such as bell holes, dissolutional cusps and spongework. Pit caves form as vadose fast-flow routes to the freshwater lens and are common on the Pleistocene eolianite ridges of the Bahamas. Pit caves are characterized b...
Research Interests:
The northwest coast of Curaçao is characterized by a series of Pleistocene-age reef terraces at four discrete elevations with dissolutional caves formed in the terraces at specific elevations (highest to lowest terraces, in meters above... more
The northwest coast of Curaçao is characterized by a series of Pleistocene-age reef terraces at four discrete elevations with dissolutional caves formed in the terraces at specific elevations (highest to lowest terraces, in meters above sea level: 90-175 m, 50-85 m, 10-45 m, and 5-10 m). Large scale rectilinear coastal reentrants called bokas occur in the lowest terrace, and are hundreds of meters long perpendicular to the coast, tens of meters wide, and have steep, vertical walls of up to more than ten meters height. Prominent coastline erosional features formed by a combination of cave collapse and wave erosion are also present in the lowest terrace. Reconnaissance field mapping in March of 2011 and 2012 documented 17 bokas and identified and surveyed numerous flank margin caves related to the reef terraces and the bokas. Quaternary uplift is evident by the position of the four elevated reef terraces adjacent to the coast. Eustatic sea-level changes, interacting with tectonic upli...
EDWARD F. FRANK Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455 USA JOHN MYLROIE Department of Geosciences, Mississippi State University,Mississippi State, MS 39762 USA JOSEPH TROESTER U.S. Geological... more
EDWARD F. FRANK Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455 USA JOHN MYLROIE Department of Geosciences, Mississippi State University,Mississippi State, MS 39762 USA JOSEPH TROESTER U.S. Geological Survey, GSA Center, 651 Federal Drive, Suite 400-15, Guaynabo, PR 00965-5703 E. CALVIN ALEXANDER, JR. Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455 USA JAMES L. CAREW Department of Geology, University of Charleston, Charleston, SC 29424 USA
Eogenetic karst has gained much attention over the past decade with research being done in young, diagenetically immature carbonates in Florida, Yucatan, and carbonate islands world-wide. These projects have focused on phreatic... more
Eogenetic karst has gained much attention over the past decade with research being done in young, diagenetically immature carbonates in Florida, Yucatan, and carbonate islands world-wide. These projects have focused on phreatic fresh-water flow, mixing effects, speleogenesis, aquifer response and storage, and contaminant transport. Less well studied are the outcomes of surface karstification and subsequent vadose flow. Exposed eogenetic carbonates develop an epikarst quite different from that found on telogenetic carbonates. Eogenetic properties (retention of primary porosity, maintenance of allochem heterogeneity, and differential cementation) are essential to the development the unique karren landforms found on young carbonate surfaces, especially in coastal areas, which are not solely caused by biological action as commonly believed and expressed by the term “phytokarst”. As eogenetic carbonates mature and approach telogenetic properties, their karren forms become more like class...
Research Interests:
San Salvador (Bahamas) is a carbonate island with dozens of flank margin caves formed in the phreatic zone by fresh seawater mixing within the freshwater lens. These caves have no direct connection with the sea, and form at or close to... more
San Salvador (Bahamas) is a carbonate island with dozens of flank margin caves formed in the phreatic zone by fresh seawater mixing within the freshwater lens. These caves have no direct connection with the sea, and form at or close to the tidally influenced fluctuating water table. After sea-level fall, in their subaerial parts caves are enlarged mainly by rock dissolution and by erosion close to the water level, condensation-corrosion and breakdown processes. For understanding the geomorphological features observed in these caves and how they are related to light attenuation, we investigated three sampling sites in the tidally influenced zone of Lighthouse Cave, which has been re-invaded by seawater during the Holocene sea-level highstand. A freshwater lens no longer exists within or adjacent to the cave. Rock samples were collected above and below the internal lake shores close to the entrance, and in the twilight and dark zones of this cave. Light and electron microscopy examinations were conducted for detecting microbial cells, as well as bioconstruction and bioweathering features. In addition, a high precision laser scanner was used for characterising sample microtopography. Our data showed that the microtopography and geomorphology of the lake shore samples (cave entrance) are dominated by bioweathering, whereas the samples of the twilight and dark zones are controlled by a combination of both bioweathering and bioconstructive processes depending on light availability. Bioconstructive structures, such as semi-planar lamination, at the fluctuating water level of the Lighthouse Cave show that dissolution due to water mixing of sea and freshwater in the Holocene is no longer the most important speleogenetic process. We propose that the geomorphological evolution is strongly influenced by the degree of rock diagenesis more than the initial mechanism of speleogenesis.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Banana holes are common karst features found within Pleistocene strandplains of San Salvador Island and throughout The Bahamas. Banana holes are typically meters to tens of meters wide, and one to six meters deep, ovoid in plan, and... more
Banana holes are common karst features found within Pleistocene strandplains of San Salvador Island and throughout The Bahamas. Banana holes are typically meters to tens of meters wide, and one to six meters deep, ovoid in plan, and usually contain phreatic dissolution features. A study of banana holes was conducted to see if their origin could be better explained, and to determine if their locations could be predicted using remote sensing. A detailed banana hole investigation of the Line Hole, Jake Jones Road, Hard Bargain, and South Victoria Hill areas of San Salvador was conducted during field visits in December 2010, May 2011, and December 2011, locating 390 banana holes, 70 of which were mapped. Plotting banana hole locations in ArcGIS shows they follow linear trends and are associated with low inland ridges. Facies in banana hole wall rock show an upward progression from shallow subtidal (herringbone cross beds) to intertidal (laminar beds and or back-beach breccia blocks) to ...
AbstractKarst on Guam is found in two distinct physiographic provinces. The northern half of the island is an uplifted karst plateau formed on Pliocene-Pleistocene reef-lagoon deposits. In the south, the karst is confined mostly to... more
AbstractKarst on Guam is found in two distinct physiographic provinces. The northern half of the island is an uplifted karst plateau formed on Pliocene-Pleistocene reef-lagoon deposits. In the south, the karst is confined mostly to Miocene remnants on uplifted weathered ...
Research Interests:
Research Interests: Geology and Field Trip
Abstract: The development of a comprehensive conceptual model for carbonate island karst began in the Bahamas in the 1970s. The use, initially, of cave and karst models created for the interior of continents, on rocks hundreds of millions... more
Abstract: The development of a comprehensive conceptual model for carbonate island karst began in the Bahamas in the 1970s. The use, initially, of cave and karst models created for the interior of continents, on rocks hundreds of millions of years old, was not successful. Models developed in the 1980s for the Bahamas, that recognized the youthfulness of the carbonate rock, the importance of fresh-water mixing with sea water, and the complications introduced by glacioeustatic sea-level change produced the first viable model, the flank margin cave model. This model explains the largest caves in carbonate islands as being the result of mixing zone dissolution in the distal margin of the fresh-water lens, under the flank of the enclosing land mass. The flank margin model, taken from the Bahamas to Isla de Mona, Puerto Rico, in the early 1990s, provided the first viable explanation for the very large caves there. Field work in the geologically-complex Mariana Islands in the late 1990s re...
Research Interests:
Research Interests:
The majority of limestone islands are made of eogenetic carbonate rock, with intrinsic high porosity and permeability. The freshwater lenses of small islands are dominated by diffuse flow regimes as the island perimeter is everywhere... more
The majority of limestone islands are made of eogenetic carbonate rock, with intrinsic high porosity and permeability. The freshwater lenses of small islands are dominated by diffuse flow regimes as the island perimeter is everywhere close to the meteoric catchment of the island interior. This flow regime produces flank margin caves at the lens margin, where dissolution is enhanced by mixing corrosion, superposition of organic decay horizons and higher flow velocities as the lens thins. The lens interior develops touching-vug flow systems that result in enhanced permeability and lens thinning over time. As islands become larger, the area (meteoric catchment) goes up by the square, but the island perimeter (discharge zone) goes up linearly; diffuse flow becomes inefficient; conduit flow develops to produce traditional epigenic cave systems that discharge the freshwater lens by specific turbulent flow routes, which in turn are fed by diffuse flow in the island interior. Locally, diffu...
Research Interests:
Research Interests:
Research Interests:
Page 1. Geology doi: 10.1130/0091-7613(1993)021<0475:ROTCRH>2.3.CO;2 1993;21;475-476 Geology John E. Mylroie, Bradley N. Opdyke and James CG Walker : Comment and Reply 2 effect on atmospheric CO and its 3 ...
Research Interests:
Research Interests:
ABSTRACT Models proposed by Ollier and Tratman (1969), Mylroie and Carew (1987) and Faulkner (2009a) variously hypothesize that a cave is post-glacial if it is controlled by glacially deranged drainage and contains no pre-Holocene... more
ABSTRACT Models proposed by Ollier and Tratman (1969), Mylroie and Carew (1987) and Faulkner (2009a) variously hypothesize that a cave is post-glacial if it is controlled by glacially deranged drainage and contains no pre-Holocene signatures. Results of tests on these models have rarely appeared in subsequent literature. Epigenetic maze caves are a type of cave that forms at applicable maximum rates, allowing them to form post-glacially; however maze caves that form in the shallow subsurface are prone to removal by glaciation. These two constraints indicate that many maze caves in glaciated regions might have formed since the last glaciation. Floodwater maze caves were used in this study to verify the post-glacial cave model of Mylroie and Carew (1987) by use of flow analysis in the karst of Joralemon Park, Albany County, New York. This study verifies the model with active caves being controlled by deranged drainage. Also tested was the hypothesis that many maze caves in other glaciated terrains are post-glacial; testing was by evaluation of criteria for post-glacial origin, and by calculating formation time for maze caves for selected sites in New York that provided a variety of geological settings (Barber Cave, Big Loop Cave, Glen Park Labyrinth). The criteria are: cave cross-sectional area; connection to deranged drainage; base level position; and presence of glacigenic sediment that was brought in only after glaciation. This study demonstrates that in typical continental glaciated terrains many maze caves are post-glacial.