development in East Texas is controlled primarily by a
combination of suffosion and preferential flow paths, often
creating small ephemeral sinkholes but occasionally persistent
features develop in more indurated facies. Pseudokarst occurs
in Claiborne (Eocene) strata in Angelina, Cherokee,
Nacogdoches, Panola, Rusk, San Augustine and Shelby counties.
Strata consist of interbedded fine- and coarse-grained clastics
with variable cementation and associated permeabilities.
Preferential fluid migration along fractures and bedding planes
create local voids through suffosion that stope upward to
create sinkholes and incised collapse valleys often associated
with persistent and ephemeral springs. GIS-based delineation of
pseudokarst sinkholes is complicated in the region by low
gradient fluvial systems and extensive anthropogenic
overprinting regionally, which create numerous constructional
closed depressions. Sinkhole densities coupled with slope
analyses indicate clustered regions of pseudokarst development
within Carrizo, Queen City and Sparta sandstones. Known
pseudokarst caves within the region include features developed
along low permeability boundaries where discharge interface
features occur. Gunnels Cave is an end member product of
natural suffosion processes in East Texas with more than 160
meters of surveyed passage and a collapse sinkhole covering
approximately a hectare. Smaller suffosion sinkholes occur
along steep gradients but generally remain associated with
fracture-controlled flow paths, either forming bypass features
or enlarged regions associated with spring discharge.
Anthropogenic pseudokarst sinkholes are generally associated
with leaky pipelines and focused groundwater recharge from
impermeable surfaces and produce local geohazards.
Traditionally East Texas is not known for extensive pseudokarst
development; however, isolated caves and sinkholes can be
locally significant and potential geohazards. --
13TH SINKHOLE CONFERENCE NCKRI SYMPOSIUM 2 CLASTIC SINKHOLE AND PSEUDOKARST DEVELOPMENT IN EAST TEXAS Kevin W. Stafford, Melinda G. Shaw-Faulkner, Wesley A. Brown Department of Geology, Stephen F. Austin State University, P.O. Box 13011, SFA Station, Nacogdoches, Texas, 75962-3011, firstname.lastname@example.org Introduction Traditionally, East Texas has never been considered a dominant karst region because of the lack of soluble dominated by Cenozoic clastic sediments associated and evaporite strata in the region are deeply buried units that are heavily exploited for hydrocarbon resources (Nichols et al., 1968). These deeper strata inevitably host hypogene karst associated with hydrocarbon maturation strata are limited to pseudokarst development, where paths creates void space. Pseudokarst includes any geomorphic features that exhibit morphologies similar to true karst features but have not been formed from solutional processes (Palmer, 2007). Pseudokarst traditionally includes caves, sinkholes and springs but generally lacks karren development. In East Texas, these traditional characteristics have been documented as widespread occurrences, but never in small, ephemeral suffusion features commonly occur recharge of shallow groundwater systems. Springs systems discharge along low permeability horizons discharge vertically to the land surface along preferential While pseudokarst development is relatively rare in East Texas compared to true karst development in other regions of the state (Elliot and Veni, 1994), these features do provide unique ecological and culture resources for reports that thirty seven pseudokarst caves and karst features exist in sixty one counties that cover the greater Abstract Pseudokarst development in East Texas is controlled primarily by a combination of suffosion and preferential but occasionally persistent features develop in more indurated facies. Pseudokarst occurs in Claiborne (Eocene) strata in Angelina, Cherokee, Nacogdoches, Panola, Rusk, San Augustine and Shelby counties. clastics with variable cementation and associated fractures and bedding planes create local voids through suffosion that stope upward to create sinkholes and incised collapse valleys often associated with persistent and ephemeral springs. systems and extensive anthropogenic overprinting regionally, which create numerous constructional closed depressions. Sinkhole densities coupled with slope analyses indicate clustered regions of pseudokarst development within Carrizo, Queen City and Sparta sandstones. Known pseudokarst caves within the region include features developed along low permeability boundaries where discharge member product of natural suffosion processes in East Texas with more than 160 meters of surveyed passage and a collapse sinkhole covering approximately a hectare. Smaller suffosion sinkholes occur along steep gradients but generally remain associated with features or enlarged regions associated with spring discharge. Anthropogenic pseudokarst sinkholes are generally associated with leaky pipelines and focused groundwater recharge from impermeable surfaces and produce local geohazards. Traditionally East Texas is not known for extensive pseudokarst development; however, isolated caves and sinkholes can be locally 311
NCKRI SYMPOSIUM 2 13TH SINKHOLE CONFERENCE 2010), which consist of the Carrizo, Reklaw, Queen City, Weches, Sparta, Cook Mountain and Yegua formations, in ascending order (Shelby et al., 1968). Carrizo Sand ferruginous. The Reklaw Formation is composed of lignitic. The Weches Formation is primarily glauconitic sand with clay interbeds that is often lenticular with local grained massive sandstone that is locally carbonaceous and commonly contains interbeds of silty or sandy clay. The Cook Mountain Formation is primarily clay or marly sand, but locally grades into sheet clays and glauconitic sands. The Yegua Formation is dominated by clay with minor sandstone beds and local concretionary limestone (Shelby et al., 1968). on seven counties (Angelina, Cherokee, Nacogdoches, Panola, Rusk, San Augustine and Shelby) (Figure 1), where pseudokarst cave development is primarily limited to coarser grained, sandstone facies of the Claiborne and Sparta formations, while springs and seeps can be found throughout all facies of the Wilcox, Claiborne and Jackson groups where permeability horizons intersect the land surface. lentils and deltaic silts, with sand abundance increasing series of marine and continental sediment deposits as the Eocene strandline migrated in response to sea level seven formations (Figure 2) detailed below. Jackson forming thin beds mixed with argillaceous clays and lentils of coarse sands. Tuffaceous material derived from Eocene pyroclastic eruptions is common throughout the Pseudokarst development in East Texas has only been 312 Figure 2. Simplified stratigraphic section of East Texas Eocene units. Yellow indicates relative abundance of sandstone dominate facies, while grey represents relative abundance of mudstone facies. Claiborne Group divided into formations. Figure 1. Digital elevation model of seven East Texas counties encompassing study area. Note the extensive drainage development associated with low gradient fluvial systems in East Texas clastic strata (data from Texas Natural Resources Information System).
13TH SINKHOLE CONFERENCE NCKRI SYMPOSIUM 2 313 to early Cenozoic through buckling induced by the large, low amplitude, anticlinal feature in East Texas Fault Zone borders the eastern and northern portions Zone dissecting the study area (Figure 4), associated Lawrence shear system respectively (Adams, 1990). These fault systems have produced abundant near vertical fractures throughout the study area primarily planes for fluid migration. Stratigraphically the region is dominated by Eocene clastics (Figure 2). Wilcox strata are largely undifferentiated in the region because of heterogeneous and lignite lenses, with total thicknesses exceeding 500 Angelina, Cherokee, Nacogdoches, Panola, Rusk, San Augustine and Shelby counties cover 15,146 km 2 within the Interior Coastal Plains (Wermund, 1996), Climate in the region is subtropical humid with annual mm, respectively (Estaville and Earl, 2008). Average precipitation increases slightly in late fall and spring with slight decreases in late summer. Temperature averages Earl, 2008). The region is dominated by mixed pine and hardwood forests with numerous low gradient streams. East Texas Geology East Texas is dominated by the deposition of Cenozoic clastic sediments associated with the transgression and regression of coastal strandlines that deposited extensive fluvial, deltaic, lagoonal including strata of the Wilcox, Claiborne and Jackson groups as well as overlying quaternary alluvium region is dominated by the Sabine Arch (Figure 4), a basement uplift formed during the late Mesozoic Figure 3. Simplified geologic map of East Texas study area, with Jackson and Wilcox Groups undivided. Cook Mountain, Reklaw, Yequa and Weches formations of the Claborne Group are undivided. Carizzo, Queen City and Sparta sandstones are presented in contrast because these formations are known to host pseudokarst development (data from Texas Natural Resources Information System). Figure 4. Simplified structural map of East Texas, including the Sabine Arch, Mexia-Talco Fault System and the Elkhart-Mt. Enterprise Fault Zone (adapted from Martin, 1978). Enlarged area shown on inset map by dashed box outline.
NCKRI SYMPOSIUM 2 13TH SINKHOLE CONFERENCE 314 East Texas Pseudokarst Pseudokarst development in East Texas occurs as sinkholes, springs and isolated caves in competent facies, while loose, unconsolidated sediments host numerous small suffosion features (Stafford et al., 2010). As with any environment where competent bedrock is overlain by loose unconsolidated material, suffosion features occur as both natural and anthropogenically enhanced structures. Many of these suffosion features act as macropores and systems. True pseudokarst development does occur in the Carrizo, Queen City and Sparta sandstones; some of these features are directly associated with sinkholes, are associated with spring discharge along permeability horizons. Cave development is limited to competent facies and occurs most commonly in variably cemented zones, where heterogeneous cementation promotes both stable cave development and mechanical disaggregation of clastic grains. Boatman Cave Complex (Figure 5B) in northern Nacogdoches County represents typical pseudokarst development in East Texas, where a series of springs discharge from the Carrizo Sandstone at a low permeability contact. While only one of the three these small caves are each developed along a vertical fracture plane where laterally migrating groundwater has physically disaggregated sandstone grains near the land surface interface, resulting in three distinct springs converging and discharging into an incised valley. Each with the largest feature actively developing an upward stoping chimney. Most pseudokarst features in the East Texas region exhibit this typical morphology and are not associated with sinkhole development. At a slightly larger scale, Tonkawa Springs in northern Nacogdoches County is associated with Camp Tonkawa Cave (Figure 5C) which consists of cave development along an enlarged vertical fracture in the Carrizo sandstone. The cave is primarily developed along an through; a secondary spring inlet converges in the western portion of the cave before discharging to the not known for pseudokarst development in the region, the units in the region with recharge occurring proximal to Claiborne strata in the East Texas unconformably overlie Wilcox strata and consist of alternating and complexly and claystones of lagoonal, shallow marine and deltaic facies are more common towards the northern portion abundantly to the south. Claiborne strata consist of a typical rhythmic series of continental and shallow marine facies and ranges up to 450 m thick. Conformably deposits with zones of argillaceous and tuffaceous clays and tuff, which can reach total thicknesses of 90 m Within East Texas, previous pseudokarst development Recklaw, Queen City, Weches, Sparta, Cook Mountain and Yegua formations from oldest to youngest (Figure sand and 10% sandy clay with the lower portions more heterogeneously cemented by ferruginous sandy silty clay, 7% bentonite and glauconite clay and Sparta sandstones were all deposited in continental to littoral environments and are known to host pseudokarst features; however, the more indurated and heterogeneously cemented Carrizo strata appear to be the most favorable for zones for pseudokarst development. Other formations within the Claiborne promote pseudokarst development in the region.
13TH SINKHOLE CONFERENCE NCKRI SYMPOSIUM 2 315 meters long with over 160 m of surveyed passage and a depth of 12 meters. The cave consists of a linear dominant spring and two secondary springs. This suite of springs has formed a lower, northern passage and a higher, southern passage that converge into a single large chamber in the western portion of the cave. The chamber is approximately eight meters tall, almost ten meters wide and encompasses the central quarter of the cave. Throughout the cave, numerous small alcoves and ceiling structures occur suggesting a similar speleogenetic origin as Tonkawa Cave but on a much grander scale. The cave opens to the west, where spring discharge forms an incised valley with additional small alcove caves along its margins, while the eastern portion approximately 15 m wide and 50 m long that gently slopes into a watershed covering almost one hectare. the spring was previously exploited for natural spring water bottling and once powered a grist mill (Brune, 1981); however, much of the original morphology can still be discerned. While some of the four meter tall cave chamber appears to be the result of upward stoping processes, much of it appears smooth and indicative of that most of the cave was originally formed as pressurized morphology, suggesting that the spring associated with cave formation may have an artesian component to it. in the Carrizo Sandstone in Shelby County with the most extensive pseudokarst cave currently documented Figure 5. Simplified cave maps of representative pseudokarst caves in the study area, including (A) Bridges Cave, (B) Boatman Cave Complex, (C) Camp Tonkawa Cave and (D) Gunnels Cave.
NCKRI SYMPOSIUM 2 13TH SINKHOLE CONFERENCE 316 closed depressions within the 15,146 square kilometer not being actual pseudokarst features, based on similar by karst processes (Bryant, 2012). Closed depressions that overlapped or that occurred within ten meters of streams and rivers were removed as these features may collapse or suffusion pseudokarst features; however, it is probable that this process also removed some true Closed depressions that intersected or occurred within ten meters of ponds, lakes and surface impoundments were removed because they represent anthropogenic closed water resources. Closed depressions within ten meters of roads and highways were removed because it is probable that most of these features are the result of anthropogenic activity associated with infrastructure construction, based removed because pseudokarst development has not been documented in these strata within the study area. After City and Sparta sandstones; however, these features are limited to those closed depressions that cover at least one delineation of closed depressions is consistent with studies Density analyses of delineated closed depressions and probable pseudokarst sinkholes indicate clustered trends of development. The highest concentrations of closed depressions occur in Wilcox strata and Quaternary are primarily associated with abundant meandering, from the late 19 th century. In contrast to the pseudokarst caves described above, small bypass caves do develop in variably cemented and in the western portion of the study area is developed in the Sparta Sandstone where heavily hematite cemented horizons provide both permeability and structural breached a heavily indurated zone approximately one Flow continues to traverse laterally on top of a second indurated layer, where the cave formed over a distance of approximately ten meters. Small alcoves exist within the during intense storm events that rapidly increased the GIS Analysis of East Texas Pseudokarst Analyses of karst terrains have been greatly aided in the past decade by improved digital resources that enable the precision of the results are directly proportional to the quality of available data and is no replacement for high precision data, extensive vegetation and abundant state, LiDAR (Light Detection and Ranging) data does not occur for most of East Texas, with the exception of limited data recently collected through TNRIS (Texas Natural Resource and Information System) in the proximity of the are limited to low resolution (10 meter) digital elevation models derived from digitized 1:24,000 quadrangle maps densely forested regions has very limited application in A sinkhole analysis was conducted on the seven counties of interest in East Texas as an assessment of the feasibility for pseudokarst delineation across the region. Closed depressions were delineated across the study area through
13TH SINKHOLE CONFERENCE NCKRI SYMPOSIUM 2 317 cave in East Texas, is truly a unique anomaly occurring in an extremely low sinkhole density region. While density analyses does provide indications of regions of more probable pseudokarst development, the nature of the original data creates a distinct bias that eliminates the level of complexity in evaluating whether features are the result of pseudokarst development or are constructional In addition to density analyses, slope analyses can be used development; however, the same limitations of data are beyond the angle of repose for loose, unconsolidated sediments. Therefore, these regions are likely areas where collapse structures or incised valleys occur in more competent facies. By comparing regions where slopes greater than thirty degree occur with regions of of probable pseudokarst development can be delineated (Figure 8). While these high gradient regions continue to indicate the western portion of the study area likely has low gradient streams and oxbow lake environs in the northeastern portion of the study area (see DEM on Figure 1), with secondary abundant densities occurring in area. Density analyses of probable pseudokarst sinkholes (Figure 7) indicate that the greatest concentrations occur within the western portion of the study area in Sparta and Queen City sandstones and in the northern portion of Figure 6. Closed depression density identified through DEM analyses (data from Texas Natural Resources Information System). Figure 7. Probable pseudokarst sinkhole density identified through DEM analyses after filtering (data from Texas Natural Resources Information System). Figure 8. Comparison of steep scarps (slopes >30 degrees) with probably pseudokarst sinkhole density identified through DEM analyses after filtering (data from Texas Natural Resources Information System).
NCKRI SYMPOSIUM 2 13TH SINKHOLE CONFERENCE 318 through unconsolidated sediments throughout the economic loss, attesting to the need for greater public education within the region. In spring 2012, several small earthquakes, up to 4.8 in magnitude, occurred near Timpson, Texas in the study area, which were reported to have induced collapse and sinkhole formation. shallow suffusion features and were likely the result of water from leaky pipelines affected by the ground movement and are not associated with true pseudokarst development in the region. References Speleological Society. Estaville LE, Earl RA. 2008. Texas water atlas. College continental margin stratigraphic and structural characteristics of the upper continental margin. Tulsa (OK): American Association of Petroleum Summary of subsurface geology of northeast Texas. In: Beebe BW, Curtis BF, editors. Natural gases of North America. Tulsa (OK): American Association Cave Books. geology of Texas, Volume I stratigraphy, The the greatest pseudokarst development and warrants more should be investigated in more detail. Numerous high angle slopes occur within this region which are likely associated with entrenched valleys and potential spring discharge points that may have formed pseudokarst features in the Carrizo Sandstone. Conclusion Pseudokarst development is limited in East Texas and City and Sparta sandstones. Pseudokarst features include sinkholes, springs and caves, which are largely associated with the lateral and vertical migration of as variable ferruginous cementation primarily control the lateral development of pseudokarst caves. Most caves appear to be largely the result of lateral migration of shallow groundwater; however, speleogens in some caves suggest that an artesian component of groundwater pseudokarst features. Density analyses of digital elevation models of the region indicate that pseudokarst development is most extensive in Cherokee and Rusk counties (Figure 7); however, when coupled with slope analyses to identify entrenched valleys, other trends are discernible suggesting that northern Nacogdoches, southern Shelby and northwestern San Augustine counties are also probable sites of more intense pseudokarst development (Figure 8). Although these data are promising, the limitations of quadrangle maps presents a large sampling bias based on data quality, but these data do provide preliminary East Texas region. Most sinkholes and collapse structures in East Texas are the result of suffusion processes; however, true pseudokarst features are common within the region. Because suffusion features are more common, they provide greater infrastructure and economic concern in the region. Leaky pipelines, poor placement of storm runoff and building construction often focus water
13TH SINKHOLE CONFERENCE NCKRI SYMPOSIUM 2 319 Shelby CA, Pieper MK, Wright AC. 1968. Palestine Plain, Eddy County, New Mexico and Culberson of East Texas: geomorphic features and evolution. Programs 42 (2): 99.
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