Introduction

Appreciation, knowledge, and understanding of cave and karst systems have changed dramatically since the creation of the Geological Society of America in 1888. Caves are now widely recognized as important geological features and karst as a distinctive and significant geologic terrain that covers ~20% of the planet's land surface. Karst aquifers are the world's most productive yet vulnerable groundwater systems, serving as the sole or primary water supply for hundreds of millions of people worldwide. Karst systems have evolved dynamically across time, reflecting changes in climate and regional tectonism, and the subsequent crustal scale hydrologic responses invoked by these processes. We are only now becoming aware of the complexity of groundwater flow within karst and epikarst systems, and are striving to link our understanding of such heterogeneous flow processes to contamination studies and hazard assessment. Cave crystalline and sedimentary deposits are becoming recognized as some of the richest and most diverse sources of sedimentological, paleoclimatic, archaeological, and even geophysical data. Cave fauna and microorganisms are offering startling insights into geological processes while pointing the way in finding extraterrestrial life.

The following papers are the more expanded scholarly versions of nineteen presentations made at the 2013 GSA Annual Meeting in Denver, Colorado. This Special Paper highlights the changes in the study and application of cave and karst systems since the origin of the Geological Society of America, and uses that accumulated knowledge as a platform to look ahead toward advancements on the horizon.

Chapters 1 and 2 are coordinated, overlapping chapters by two of the founding fathers and guiding lights of North American cave and karst research, Derek Ford and William B. White, respectively. They have published two major karst textbooks (White, 1988; Ford and Williams 1989, 2007) and they, their students, and students of their students have played major roles in the modern development of cave and karst research around the globe.

In Chapter 1, “The science of caves and karst: From the beginning of the Geological Society of America to ca. 1960,” Derek Ford traces the roots of cave and karst science back to the recognition of the “uniformitarian principle (1800s), basic understanding of processes of carbonate and sulfate rock dissolution and precipitation (1820s), and the equations of Hagen, Poiseuille, and Darcy for groundwater flow in porous, fractured, and soluble media (1840–1856)” (p. 1). In the 1850s, the word “karst” (meaning “stony ground”) from the “classical” karst region of western Slovenia came into general use as a geographic term. Ford writes, “The first U.S. Geological Survey (USGS) report on hydrogeology by Chamberlin in 1885 was one of many early texts that stressed the importance of conduit flow in limestone areas” (p. 1).

Between ~1890 and 1930, karst research focused on the spectacular western Slovenian karst region. Ford states that during this time period, “Definition of the principal types of surface landforms and” theories “for their development within cycles of erosion [were proposed]. [T]wo sharply contrasted models for storage and flow in limestone aquifers, and promotion of a theory that accessible caves formed chiefly in the vadose zone” were actively contested in the karst literature (p. 1). Throughout the nineteenth and early twentieth centuries, cave and karst science were considered to be primarily in the domain of geography and geomorphology, and in Europe, “speleology,” the study of caves, gained scientific respectability.

According to Ford, following Meinzer's (1927) publication on major springs in the United States, “American scientists entered the debates in force, proposing that caves should develop primarily below the water table, along it, or create [the water table]; they also emphasized the importance of soil CO₂ in boosting rates of dissolution in carbonate rocks” (p. 1). Laptev (1939) recognized the principle of mixing corrosion—but his Russian publication was not read widely by western karst workers. Bögli's (1964) independent work introduced the important concept of mixing corrosion to English-speaking karst researchers.

Ford further argues,

In the later 1940s and 1950s, the formative studies of solution kinetics began, while improvements in methods of measuring solute concentrations set the stage for global rate models to be developed in succeeding decades. Spatial quantitative analysis came to dominate study of surface landforms, particularly sinkhole distribution patterns. The confusion that had arisen regarding the development of meteoric water (epigene) caves was resolved with a general model emphasizing the controlling roles of lithology and geologic structure: Increasingly, it was recognized that these two variables also explained many of the differences observed between karst aquifers and landform assemblages in different geographical areas. (p. 1)

In Chapter 2, “Science of caves and karst: A half century of progress,” William B. White emphasizes a fundamental paradigm shift in the study of caves and karst around 1960. The focus shifted from geographic-based studies of caves, speleogenesis, and karst landscapes to using caves and their contents to provide information on issues of much wider geologic interest. Anthropologists studying the origin and evolution of humans had long known caves contained important accumulations of hominid fossils, and they and scientists with other backgrounds began to develop and apply new instrumentation and techniques to the study of archaeologically relevant cave contents. The discovery, exploration, and mapping of caves and, thereby, access to the caves and their contents for scientific study dramatically expanded.

In the 1960s, geochemical descriptions of carbonate waters were restructured in terms of the saturation index, CO₂ partial pressure, pH, and other parameters based on work by Donald Langmuir and his students (see Langmuir, 1997). Advances in equilibrium chemistry were paced by advances in the chemical kinetics of carbonate dissolution and the latter proved to be the key to understanding the development of conduit systems specifically and carbonate karst phenomena generally. The essential insight was the discovery that the dissolution rate of calcite is a complex “function of the undersaturation of the solution” and that the rate decreases “by several orders of magnitude when the saturation index reaches about −0.3 or ~83% saturation (Berner and Morse, 1974)” (p. 22). This fundamental process allows dissolution to proceed deep inside a porous carbonate rock (see Dreybrodt and Buhmann, 1991; Palmer, 1991).

Karst hydrology is bringing a growing recognition of the importance of conduit and fracture flow hydrodynamics and intimate, rapid interconnection of surface-groundwater systems to the science of groundwater hydrogeology. Greatly improved tracer techniques helped to define karst drainage basins that often bear little resemblance to the overlying surface watersheds (Jones, 1973; Quinlan and Ewers, 1989a). White explains that karst hydrology has moved from qualitative descriptions to complex computer models, owing to efforts by “Wolfgang Dreybrodt and his students in Germany, by Franci Gabrovšek in Slovenia, and by Georg Kaufmann and his associates in Germany among others” (p. 28) that take account of matrix, fracture, and conduit permeability (see Dreybrodt et al., 2005).

Karst springs and aquifers have been used as human water supplies since the dawn of history and rising populations have significantly increased both the water consumption and the pollution impacts on these resources. White notes, “Sediment and contaminant transport as well as new understanding of sinkhole collapses and other land-use hazards have become part of the hydrogeologic framework of karst” (p. 19) and the environmental management of karst water resources.

He concludes, “All aspects of cave and karst science have been revolutionized by the development of accurate dating methods for speleothems and for clastic sediments in caves” (p. 19). The use of speleothems as paleoclimate archives is one of the most important, visible results of cave and karst science. Pioneering U/Th geochronologic studies on speleothems by Derek Ford, Henry Schwarcz, and their students in the 1970s (Harmon et al., 1975) proved the utility of dating speleothems. Their technique used α-spectroscopy and required 20–100 g of sample, which limited the method's accuracy and resolution. Edwards et al. (1987) used ultra clean chemistry techniques and thermal ionization mass spectrometry to reduce the sample size requirements for U/Th dating on calcite to milligrams, while significantly increasing the precision of the isotope ratios, and thereby improved the isotopically derived dates by more than two orders of magnitude. When applied to speleothems (e.g., Richards and Dorale, 2003; Dorale et al., 2004) and combined with millimeter resolution stable isotopic and chemical data, these techniques produce the highest resolution, most accurately dated paleoclimate records available to science (Fairchild and Baker, 2012). Such records extend back to 500,000 yr B.P. and represent the “gold standard” for paleoclimate research.

In Chapter 3, “Karst mapping in the United States: Past, present, and future,” David J. Weary and D.H. Doctor discuss the concepts behind the 2014 publication by the USGS of new “digital maps and databases in 2014 depicting the extent of known karst, potential karst, and pseudokarst areas of the United States, including Puerto Rico and the U.S. Virgin Islands” (p. 35). Comprehensive karst maps of the United States date back to the 1969 map published by the USGS based on compilations by William E. Davies. Veni (2002) published a widely used, detailed colored version of a U.S. karst map.

According to Weary and Doctor (p. 35), their (2014) maps and database “are based primarily on the extent of potentially karstic soluble rock types, and rocks with physical properties conducive to the formation of pseudokarst features. These data were compiled and refined from multiple sources at various spatial resolutions, mostly as digital data supplied by state geological surveys. The database includes polygons delineating areas with potential for karst tagged with attributes intended to facilitate classification of karst regions.” The maps show that “approximately 18% of the surface of the 50 United States is underlain by significantly soluble bedrock. In the eastern United States, the extent of outcrop of soluble rocks provides a good first approximation of the distribution of karst and potential karst areas. In the arid western states, the extent of soluble rock outcrop tends to overestimate the extent of regions that might be considered as karst under current climatic conditions, but the new data set encompasses those regions nonetheless” (p. 35).

Publishing the karst information as a database has the major advantage that it can and will be revised as needed. The 2014 karst map will be updated as new information becomes available.

In Chapter 4, “Historical review and forward view of cave and karst research in Texas,” George Veni and Nico Hauwert divide the history of Texas scientific cave and karst research into two periods, from 1849 to 1982 and from 1983 to the present. They find evidence that cave and karst research in Texas is currently transitioning into a third period.

While Weary and Doctor's (2014) U.S. karst map shows that 24.7% of Texas is underlain by karstic rocks (19.1% carbonates, 5.6% evaporites), and 10.2% by unconsolidated pseudokarst terrain, Texas karst does not “look” much like the sinkhole plains of the eastern United States, the classic karst areas of Europe or the spectacular tropical karsts. The Edwards (Balcones fault zone) Aquifer and the adjacent Edwards-Trinity Aquifer of Texas' Edwards Plateau comprise one of the largest and most significant karst areas and karst aquifer systems in the United States. While this fact has been internationally recognized for many years, it has not been fully appreciated by geologists in Texas. From 1849 to 1982, the word “karst” was essentially unknown to most geologists and hydrologists working in Texas. Veni and Hauwert write, “Caves were occasionally mentioned in geological reports until 1948, but they were rarely studied. In the 1960s, cave explorers-turned-scientists began investigating Texas caves, but their work was often seen as lightweight science because caves were usually considered geologic curiosities of little importance” (p. 49).

Veni and Hauwert conclude that the second phase of Texas karst research began in 1983 with the work of two karst scientists, Ernest Kastning and Albert Ogden. Veni and Hauwert explain that Kastning's (1983a) dissertation and papers (Kastning, 1983b, 1986) “applied state-of-the-art karst theory to explain cave and karst development” of the Edwards Plateau and the Balcones fault zone (p. 57). His research was published in recognized, peer-reviewed journals and brought a new level of scientific credibility to Texas karst research.

Also in 1983, Veni and Hauwert explain (p. 57), Albert Ogden began work at San Marcos' Southwest Texas State University's Edwards Aquifer Research and Data Center. He and his students focused on collecting hydrologic and geochemical data in ways that quantified conduit flow conditions within the aquifer. Ogden's team was the first to conduct successful tracer tests in the Edwards Aquifer and documented flow paths to Hueco and San Marcos Springs, and identified “at least two hydrologically and geochemically distinct sources within the aquifer” (Ogden et al., 1985; Ogden, 1986; Ogden and Collar, 1989).

At the same time, national karst scientists' expertise gained scientific respect and caves and karst began to appear with greater frequency in technical reports. A major driver in Texas karst science was the listing of several karst endangered species in the Edwards Aquifer region, which required detailed hydrogeologic cave and karst characterization in support of the biological research.

Veni and Hauwert also explain that major population growth and increased water usage for agricultural irrigation threatened water shortages and led to the establishment of various water management authorities across the Edwards Aquifer region, and that these organizations began to conduct increasingly sophisticated karst research on the aquifers. Along with university researchers and state and federal governmental agencies, these organizations are bringing modern karst hydrogeological concepts, tools, and models to the environmental management of Texas karst resources.

In Chapter 5, “Morphometric analysis of cave patterns using fractal indices,” Patricia N. Kambesis, Erik B. Larson, and John E. Mylroie use fractal mathematics (Curl, 1986) to determine if cave patterns, such as some of those described by Palmer (2011), could be differentiated based on analysis of their fractal geometry, and to ascertain if distinct cave morphologies displayed characteristic ranges of fractal indices. The relevant parameters include “fractal dimension, which quantifies the complexity of a pattern, and lacunarity, which quantifies the texture of a pattern. Three-dimensional cave survey data were used to generate cave models that were converted to cave pattern image files and analyzed with image-processing software” (p. 67). Fractal indices were calculated for digital patterns on 150 caves of known types—30 each of tafoni, littoral caves, stream caves, flank margin caves, and continental hypogene caves. The quantitative morphological distinctions in cave patterns as identified by fractal dimension and lacunarity proved to be statistically significant within the subset of cave types analyzed for this study.

As Kambesis et al. explain, similarities in shapes produced by different geological or hydrogeological processes and/or multi-generational overprinting by sequential processes can skew fractal indices so geological and hydrogeological context is critical when interpreting fractal indices. Current limitations on the application of this morphological technique include the fundamental 2D nature of most cave mapping and the bias toward human-sized passages in the cave maps. The ongoing development of LiDAR techniques to produce highly detailed 3D maps of caves with a wide dynamic scale range is a promising source of new input data for this type of morphometric analysis.

In Chapter 6, “Geologic history of the Black Hills caves, South Dakota,” Arthur N. Palmer, Margaret V. Palmer, and James B. Paces describe the deep time evolution of karst within the Black Hills region. This area is home to classic sites including Wind and Jewel Caves, each of which formed within the Madison Limestone over several stages in response to more than 300 Ma of regional geologic events. The earliest stage involved eogenetic (early diagenetic) reactions within the (then) recently deposited Mississippian carbonates that resulted in the formation of breccias and solution voids. (Evans and Soreghan, this volume, Chapter 18, describe analogous paleocave deposits in Colorado.) Although subsequent subaerial exposure of the carbonates allowed for the development of small caves and karst, the entire carbonate surface was later buried by ~2 km of Pennsylvanian–Cretaceous sediments. Hydrologic activity and speleogenesis were enhanced during Laramide uplift, and paleokarst voids that had initially formed in the Paleozoic were enlarged during post-Laramide times to the present day.

Although earlier studies have invoked rising thermal waters to explain the development of cave systems within the Madison Limestone, Palmer et al. argue that the depth and morphology of the cave passageways instead indicate a nearly closed system in which carbonate is dissolved by water infiltrating through a thin veneer of interbedded quartz arenite (the Minnelusa Formation), producing low pCO₂, while recharging waters with higher pCO₂ directly into Madison Limestone outcrops. This episodic development of the Black Hills cave and karst system has resulted in four distinct styles of calcite deposition: Mississippian-age ferroic calcite associated with sulfate replacement; white scalenohedra in paleovoids deposited while the Madison Limestone was buried under younger sediment; palisade crusts that formed as springs were blocked by sediments accumulated during the Oligocene–Miocene; and laminated crusts that formed during late Pleistocene water-table fluctuations (Palmer et al., p. 87). The combination of careful field observations, mineralogy, and radioisotopic dating continues to be a powerful means for unraveling the >100 Ma geologic history that can be preserved in many karst environments.

In Chapter 7, “Depth and timing of calcite spar and ‘spar cave’ genesis: Implications for landscape evolution studies,” David D. Decker, Victor J. Polyak, and Yemane Asmerom propose a new speleogenesis model for the formation of scalenohedral calcite spar in 1–10 m geode-like caves.

They write:

During the formation of the Basin and Range landscape, decompression melting formed copious amounts of CO₂, which, at the temperature and depth at which it was released from the magma body, was in the supercritical regime. Supercritical CO₂ [scCO₂] is highly mobile, and so it made its way upward, where it interacted with the Capitan aquifer at the depth where it transforms to subcritical CO₂, creating a low-pH carbonic acid that formed geode-like caves in the limestone/dolostone ~400–800 m below the water table and/or surface. As the scCO₂ diminished at the end of each igneous episode, the acidic waters became more alkaline and began depositing scalenohedral calcite spar in the same vugs that had “recently” been dissolved. This is a novel model in that it invokes a different phase of CO₂ that has a narrow pressure and temperature range in which it can both dissolve and precipitate calcite. (p. 110)

This paper adds a new speleogenic significant fluid, super-critical CO₂, to karst science and demonstrates the value of both radiogenic and stable Sr isotope measurements to cave and karst science. Polyak et al. (1998) had previously used Ar/Ar dating of authigenic cave alunite to extend the range of datable cave deposits into the millions of years range. Polyak et al. (2008) had demonstrated that U/Pb dating of speleothem calcite extended the range of datable cave deposits into the 10s to 100s of millions of years range. Cave deposits often include materials datable by radiometric techniques from the present back through the Paleozoic.

In Chapter 8, “The importance of advection for CO₂ dynamics in the karst critical zone: An approach from dimensional analysis,” Matthew D. Covington introduces simple models for CO₂ transport within fractures and conduits of the vadose zone. These simple models consider the relative importance of different processes in karst systems and possible interactions among them. Covington notes, “In the past, vadose zone gas dynamics have typically been treated as diffusive, where advective transport, within both the gas and liquid phases, is neglected (Penman, 1940a, 1940b; Marshall, 1959; Wood and Petraitis, 1984). Buoyancy-driven flows have received recent consideration within fracture systems (Weisbrod and Dragila, 2006; Weisbrod et al., 2009; Nachshon et al., 2008)” (p. 122). Advective processes could play more significant roles in dissolutionally enlarged fractures in karst systems.

Covington examines the possibility of advective air flows that are driven by chimney-effect pressure gradients. Previous studies demonstrated that advection would be a dominant process for CO₂ transport in human-enterable caves (Frisia et al., 2011; Fairchild and Baker, 2012). The dimensional analysis conducted by Covington suggests that chimney effect airflows also play important CO₂ transport roles in fractures or relatively small pathways enlarge by dissolution. Covington's model “also provides a mathematical starting point for quantifying advective effects and understanding the influence they may have on CO₂ distributions in time and space” (p. 126).

In Chapter 9, “Initial pipe development within epikarst microfractures,” Maria Inés Dragila, Katrina M. Hay, and Stephen W. Wheatcraft investigate the role played by wavy free-surface fluid films on the geochemical erosion of microfractures and the development of initial channelization within microfractures. The natural evolution of a free-surface film is divided into three liquid pools with potentially distinct chemical signatures. In addition, Dragila et al. “introduce a liquid mode, i.e., film-embedded capillary droplets, not previously reported that may provide the highest solute transfer rate and therefore play an important role in the initial development of pipe conduits within epikarst microfractures” (p. 130). Experiments presented by Dragila et al. address whether capillary droplets would form naturally from solitary waves in an evolving film. These droplets would persist and grow by collecting liquid from the film. “While dissolution kinetics will affect the erosion or depositional role of the laminar film, the capillary droplets will always act to erode the matrix because pore-water extraction into the droplet is driven by advective rather than diffusion or chemical kinetics” (p. 135). This experimental study indicates that the dissolve-and-sweep phenomenon of films and the formation of capillary droplets could contribute to the evolution of micropipe formation within epikarst microfractures.

In Chapter 10, “On the efficacy of monitoring wells in karstic carbonate aquifers,” Ralph O. Ewers reviews case studies performed at contaminated sites to evaluate how to adequately monitor groundwater contamination in karst aquifers. He finds that conventional monitoring wells and piezometers often yield misleading information concerning aquifer properties, groundwater flow, and contaminant movement (p. 137). These findings are in accord with the highly anisotropic and heterogeneous nature of the aquifers (Quinlan, 1989; Quinlan and Ewers, 1989b).

Ewers lists the following warnings on the use of monitoring wells in karst aquifers:

(1) Monitoring wells may be unreliable in detecting contaminant releases. (2) A monitoring well that detects a contaminant is unlikely to provide valid data regarding the quantity of the release or the velocity and direction of the contaminant movement. (3) Water levels measured in wells often give erroneous indications of groundwater flow direction. (4) Well water levels and chemical parameters taken at random or traditional quarterly calendar intervals give little insight into the fluctuations that may actually occur in the well. (5) Head fluctuations in wells in response to nearby pumping or injection do not necessarily indicate flow connections. (6) Traditional well tests in carbonate aquifers typically do not sense the most important elements of the permeability structure. (7) Virtually every well in a carbonate aquifer is influenced by a unique suite of permeability and recharge elements. (p. 137)

Despite the many, documented failures of monitoring wells in karst aquifers, monitoring wells are specified by regulation and law in virtually every groundwater contamination site investigation. Alternative and more appropriate means of aquifer assessment and monitoring in these aquifers are available, including wells augmented with tracer investigations and the use of springs and other access points to the conduit elements of the porosity system—but are rarely used.

In Chapter 11, “Assessing structural control on groundwater flow in the Morrell Cave springshed, Sullivan County, Tennessee,” Taylor Burnham, Ingrid Luffman, Michael Whitelaw, and Yongli Gao explore the role of geologic structures that influence the location of recharge points, flow paths, velocities, and discharge locations within Morrell Cave and at the resurgence of Morrell Spring, in the Morrell springshed, Sullivan County, Tennessee.

The map of Morrell Cave (Adams et al., 1973) was georeferenced using the surface coordinates of three cave locations that were acquired by innovative, if unconventional, techniques due to local power line interference. Quantitative dye tracer studies established groundwater flow paths and velocities from the swallets of allogenic recharge to the cave streams in Morrell Cave and Morrell Spring. Detailed geologic mapping along with the dye trace results indicate that the Morrell Cave fault (within the cave), the dominant NW-SE–trending joint set and the NE-SW joint set control the groundwater flow systems into and out of the Morrell Cave system (Burnham et al., p. 161).

Allogenic recharge from the northern slopes of Holston Mountain enters the karst system through numerous swallets. Upon entering the subterranean system, groundwater flows to the NW following dominant joint trends that transect local folding. Once the groundwater reaches Morrell Cave, the flow turns to the NE and parallels a shallow thrust fault, along which Morrell Cave has developed, before resurging at Morrell Spring.

In Chapter 12, “Geochemistry of cave pools connected to an alpine epikarst—Timpanogos Cave National Monument, Utah,” Lee J. Florea, Chelsie R. Dugan, and Camille McKinney investigate the dynamic geochemistry within the epikarst of an alpine karst aquifer in Timpanogos Cave National Monument in the Wasatch Mountains near Salt Lake City, Utah, USA. The primary goal of this study was to identify potential sources of recharge to the cave pools in this alpine karst setting. Analysis of water samples collected weekly in the spring and summer of 2012 demonstrated “three modes of recharge: (1) diffuse recharge through the permeable matrix of the carbonate rock, (2) rapid recharge through open fractures in the epikarst, and (3) rapid recharge via piston flow through fractures occluded with colluvium” (p. 165). Major “ions in the cave pools and river water were HCO₃ ⁻, Ca²⁺, and Mg²⁺, which resulted from reactions between groundwater” and karst bedrock such as limestone and dolomite (p. 170). Other significant ions included SO₄ ²⁻, Cl⁻, K⁺, and Na⁺, which may have originated from other sources such as aerosols, noncarbonate rocks, and sediments surrounding the study area. During the spring and summer of 2012, cave pools recharged by diffuse flow maintained relatively stable water levels. On the contrary, water levels in cave pools characterized by rapid recharge were highly variable. The geochemistry of those cave pools was strongly influenced by the timing and rate of recharge. Isotopic ratios of sulfur and carbon and cation-anion ratios imply that sulfide oxidation may cause the dissolution of the carbonate bedrock.

In Chapter 13, “Analysis of hydrologic and geochemical time-series data at James Cave, Virginia: Implications for epikarst influence on recharge in Appalachian karst aquifers,” Sarah Eagle, William Orndorff, Benjamin Schwartz, Daniel H. Doctor, Jonathan Gerst, and Madeline Schreiber conducted “time series (2007–2014) of hydrologic and geochemical data of drip water collected within James Cave, Virginia” (p. 181). The primary goal was to investigate how the epikarst zone affects the quantity and quality of recharge in a doline-dominated Appalachian karst terrain. Study of the epikarst has been highly challenging due to intrinsic complexity and instrumentation limitations (Williams, 2008). However, improvements in instrumentation and data logging in recent years made it possible to automatically collect high-resolution hydrologic and geochemical time-series data in caves. This study combined high-resolution hydrologic and geochemical data sets from a cave in southwestern Virginia to examine seasonal and annual variability in hydrology and geochemistry of epikarst discharge. A combined hydrogeochemical data set was used to build a conceptual model of physical and chemical interactions in the epikarst. Methods developed for this study can be extended to study other doline-dominated karst systems with similar geologic conditions and temperate climates (p. 182).

In Chapter 14, “Caves, hills, and caches: The importance of karst landscapes for the Prehispanic and contemporary Maya,” Brent K.S. Woodfill, Jon Spenard, and Megan Parker review the interactions between humankind and the karst region of Mexico and northern Central America. Archaeologists have long known that caves hold deep and multifaceted meaning for Prehispanic and contemporary Maya. The locations and layouts of caves often defined the precise locations of Maya communities, and were thought to be “homes of gods, spirits, and ancestors as well as living beings themselves” (p. 197). However, modern cave surveys were only recently incorporated into large-scale archaeological projects. Such surveys have deepened our collective understanding of how caves were utilized by prehistoric people of the region, and the material remains found with caves have provided detailed information about the economy of the Maya, “changing political systems, land tenure, and responses to drought and other environmental changes” (p. 197). The Maya held an incredibly active relationship with the caves near their communities, often significantly modifying their entrances and mining clay sediments for use in pottery. These caves “continue to be important places for the contemporary inhabitants of the region, and therefore,” individuals conducting speleological research in the region are strongly encouraged “to collaborate with neighboring groups” (p. 197).

In Chapter 15, “Microclimate and niche constructionism in tropical bat caves: A case study from Mount Elgon, Kenya,” Joyce Lundberg and Donald A. McFarlane describe and discuss the role of bat communities on microenvironmental conditions in caves. Large populations of the bat Rousettus aegyptiacus were studied in three simple caves hosted within pyroclastic rock of Mount Elgon National Park, Kenya. One of these, Kitum Cave, has so few bats, that it essentially acts as a control, providing microclimatic data for caves without any significant biological activity. Lundberg and McFarlane overcame significant environmental challenges to collect seven days of temperature logger records, and to complete “on-site mapping of rock and air temperature, humidity, and air flow” to provide the “basis for modeling of heat, water, and CO₂ production and dispersion” (p. 211).

Surprisingly, Lundberg and McFarlane found that the bat communities generated elevated temperatures in Mackingeny Cave and Ngwarisha Cave on the order of ~18 °C above ambient (from ~12 °C to ~30 °C), while the control site only experienced a ~2 °C difference. Ultimately, this bat-generated energy is dissipated by ongoing air circulation, the strongest of which accompanies bat entry and exit flights, and by conduction directly into the host rock. These results have important implications for the long-term health of smaller, more fragmented bat communities. Modeling by Lundberg and McFarlane suggests that a population of at least 100,000 bats is needed to sustain a vital colony. These elevated temperatures may also play a potentially important role in the localized dissolution rate in a cave. The output energy of the bats was modeled to estimate corrosional potential in limestone, and rates of surface denudation would be ~1 m in ~80,000 yr. Thus, tropical bats serve as an important example of how cave macrobiology can be an effective agent of geomorphologic change within a karst system.

In Chapter 16, “High-resolution rainfall records for middle and late Holocene based on speleothem annual UV fluorescent layers integrated with stable isotopes and U/Th dating, Raccoon Mountain Cave, Tennessee, USA,” Steven G. Driese, Zheng-Hua Li, Hai Cheng, Jane L. Harvill, and Justin Sims demonstrate the power of modern speleothem micro-analytical tools to reconstruct paleoclimate records with time resolutions unattainable in other terrestrial climate proxies. The stalagmite studied was found to have experienced a complex history including depositional and erosional periods, hiatuses, and perhaps sediment burial intervals. However, the analytical techniques allowed the identification of intervals of annual UV fluorescent (UVf) layers from which the authors were able to extract a high-resolution rainfall record from segments of the speleothem.

The authors find that

the middle Holocene is typified by 100–400 yr intervals of higher rainfall characterized by thin UVf layers (0.003–0.010 mm) and more-negative δ¹³C values (−3‰ to −6‰ Peedee belemnite [PDB]), punctuated by shorter periods (5–20 yr, rarely 50–100 yr) of lower rainfall with thicker UVf layers (0.030–0.080 mm) and less-negative δ¹³C values (−1‰ to −3‰ PDB); “extreme drought” events are characterized by both the thickest UVf layers (0.150–0.170 mm) and the least-negative δ¹³C values (+0.05‰ to −1‰ PDB). The late Holocene, in comparison, is characterized by overall wetter conditions and more regular (sinusoidal curve) behavior, suggesting 50–100 yr cycles of higher and lower rainfall with [thin] UVf layers. (p. 231–232)

The ‘thin, more-negative δ¹³C UVf layers in wet periods’ versus ‘thicker, less-negative δ¹³C UVf layers in dry periods’ finding was opposite of the authors' initial working hypothesis and counterintuitive (p. 243).

The authors conclude that the “thickness of annual layers in speleothems can be used to resolve detailed paleorainfall records, provided there is preservation of organic matter sufficient to excite UVf response; however, relationships among changes in rainfall amounts, stable isotope values of speleothem calcite, and thicknesses of UVf annual layers (≈growth rates) are not straightforward” (p. 232).

In Chapter 17, “Middle Pleistocene glacial outwash in poljes of the Dinaric karst,” K.R. Adamson, J.C. Woodward, and P.D. Hughes examine the Pleistocene alluvial records in karst poljes surrounding Mount Orjen in western Montenegro and explore the records' wider significance. The poljes around Mount Orjen contain some of the best-preserved records of Middle Pleistocene glacial outwash in the Mediterranean. These thick deposits of permeable coarse-grained alluvium are an important element of regional hydrogeology. Detailed sedimentological analysis and uranium-series dating indicate that the Orjen poljes “were filled with thick deposits of coarse- and fine-grained alluvium prior to 350 ka, during the major glacial phase of MIS [marine isotope stage] 12” (p. 247). In fact, “a record of at least four glaciations [is] preserved on Mount Orjen—two from the Middle Pleistocene (MIS 12 and 6) and two from the last cold stage (MIS 5d-2), including the Younger Dryas” (p. 247).

This paper highlights the dominant control of the glaciokarst system on the formation and preservation of the region's polje sedimentary records. The thick outwash deposits in the poljes of Montenegro represent an important legacy of an extensive Middle Pleistocene glaciation whose wider impacts have not been fully appreciated. The authors argue that many of the poljes in the classic karst landscapes of the wider Dinaric Alps were also filled with glacial outwash during the Middle Pleistocene.

In Chapter 18, “Long-distance sediment transport and episodic resedimentation of Pennsylvanian dust (eolian silt) in cave passages of the Mississippian Leadville Limestone, southwestern Colorado, USA,” James E. Evans and Michael Soreghan describe and discuss the implications of

Early Pennsylvanian (309–318 Ma) paleocave sediments hosted in the Mississippian (345–359 Ma) Leadville Limestone [that] were partly derived from long-distance (>2000 km) source areas. In addition to showing the importance of long-distant dust transport in cave sediments, because these paleocave deposits are derived from loess, their presence may document the earliest terrestrial signature of the late Paleozoic ice age in North America.

The Leadville Limestone was subject to karst processes following late Mississippian eustatic sea-level fall. (p. 263)

Preserved paleokarst features include phreatic tubes, breakout domes, tower karst, poljes, sinkholes, solution-enhanced joints, surficial flutes, and solution pans. The sediment fills and karst breccias in the paleokarst features contain interbedded paleo-speleothems. (Palmer et al., this volume, Chapter 6, describe similar paleocave fills in the caves of Black Hills, South Dakota.)

Evans and Soreghan contend, “The overlying Pennsylvanian Molas Formation is a loessite (eolian siltstone) composed of angular quartz silt with ferruginous kaolinite rims” (p. 263). The depositional properties of the loess facilitated its remobilization and piping into the underlying karst features. Indeed, “The U-Pb ages of accessory zircons indicate that the source areas for the eolian silt are from the peri-Gondwanan terranes and Grenville Province of eastern and southern North America, which are ~2000 km to the east. There is also a provenance signature from the rising Ancestral Rocky Mountains” (p. 263).

The paleocave sediments in the Leadville Limestone are compositional and textural matches to the overlying loess in the Molas Formation. The paleocave sediments contain sequences of inundites and debrites separated by mud drapes with mud cracks, which are interbedded with flowstones and dripstones.

Evans and Soreghan write, “Cave sediments are increasingly utilized as archives of geologic change. Recognition that dust is a significant component of cave sediments highlights the inherited properties from distant source areas, land-atmosphere transfer processes, [and] land-surface deposition processes” (p. 264) in karst systems.

In Chapter 19, “Paleomagnetic constraints on the Atapuerca karst development (N Spain),” J.M. Parés, A.I. Ortega, A. Benito-Calvo, A. Aranburu, J.L. Arsuaga, J.M. Bermúdez de Castro, and E. Carbonell provide a case study on how chemical and clastic deposits within caves can act as valuable archives of geophysical information. Both carbonates and clastic sediments record the orientation of Earth's magnetic field as they are deposited, and in cave studies where the age of the sediments are often difficult to assess, paleomagnetic methods can provide an independent means for determining the age of cave fill. These magnetically derived sediment ages can be used to constrain the formational history of a cave.

Parés et al. examine the Atapuerca karst system in northern Spain, which displays a multilevel karst developed during incision of the Arlanzón River (a tributary of the Duero River). By measuring the geomagnetic polarity of oriented chemical and clastic sediments collected from dispersed cavities throughout the Atapuerca karst, the authors were able to provide minimum ages for the multilevel karst development. Furthermore, these ages have implications for the incision history and water-table evolution in the Atapuerca karst during the Pleistocene. The paleomagnetic results from this study show that most of the levels developed while the Earth's magnetic field was in a reversed state during the Matuyama chron (0.78–2.58 Ma), but before the middle Pleistocene. Cosmogenic burial ages of sediments infilling the karstic passages are consistent with this interpretation. Such paleomagnetic studies are still in their infancy, and with recent improvements in instrument sensitivity and spatial resolution, geophysical studies of chemical and clastic sediments in caves are on the cusp of a series of exciting discoveries.