Wetlands in the Triassic Basin
Tracy San Filipo
Triassic Basin Soils
December 5, 2008
The Triassic Period is the first of three periods that comprise the Mesozoic era (Stuckey
1965). It extends from about 180 million years ago (mya) to about 150 mya, and is followed by the Jurassic Period, which covers from about 150 mya to about 125 mya (Stuckey 1965). The final period of the Mesozoic era is the Cretaceous Period, the end of which is placed at about 70 mya (Stuckey 1965). During the Triassic period, rifting occurred, which, in addition to separating the North American and African plates, produced a series of basins in eastern North
America (Hoffman and Gallagher 1989). These basins subsequently filled with sediment, and formed a series of belts oriented northeastward stretching from South Carolina to as far north as
Nova Scotia (Hoffman and Gallagher 1989; Parker 1979). In 1892, the soils of these belts- and
Triassic rocks in general-were classified as the Newark group (or Newark Supergroup) based on the presence of such rocks and soils in Newark, New Jersey (Stuckey 1965; Parker 1979;
Hoffman and Gallagher 1989). The rift system underlying these basins has also been called the
Newark rift system (Hoffman and Gallagher 1989).
Variation exists in how the individual basins of this system are referred to. In North
Carolina, the Triassic Basin includes four physically detached areas within the Piedmont region
(Daniels et al . 1999). Hoffman and Gallagher (1989) use the standard term “Deep River basin” to describe the part of the Triassic basin within North Carolina that includes two of the four physically separate nonadjacent areas, but note that the term “Durham Triassic basin” had been used for the same location by some authors earlier in the 1980s. They include the subdivision of the Deep River basin into the Durham basin, Wadesboro basin, and Sanford basin, and seem to consider the cross structures that are the basis for these subdivisions equally substantial
(Hoffman and Gallagher 1989). However, Daniels et al . (1999) only divided this area into two
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December 5, 2008 basins, with one labeled as the Durham-Sanford basin and the other as the Wadesboro Basin.
Stuckey (1965) states that there are two belts in North Carolina- the Dan River basin and the
Deep River basin- but that other authors have used the Sanford Basin, the Wadesboro basin, the
Deep River basin, and the Durham basin to describe parts of the Deep River basin. He mentions that the Dan River basin lies in both North Carolina and Virginia, but does not mention that it is alternatively called the Danville basin (Stuckey 1965; Woods et al . 1999). Hoffman and
Gallagher (1989) provide a figure indicating that both the Dan River and Danville are used for the basin that overlaps North Carolina and Virginia, but the small area of Triassic basin soil in
NC that Stuckey (1965) claims is generally included in the Dan River basin is labeled Davie
County. The figure also names the other basins as follows: Wadesboro in NC and SC, Sanford in
NC, Durham in NC, Scottsburg in VA, Basins north of Scottsburg in VA, Farmville in VA,
Richmond in VA, Taylorsville in VA, Scottsville in VA, Barboursville in VA, Culpeper in VA and MD, Gettysburg in MD and PA, Newark in NJ, PA, and NY, Pomperaug in CT, Hartford in
CT and MA, Deerfield in MA, Fundy or Minas in Nova Scotia and Canada, and Chedabucto in
Nova Scotia and Canada (Hoffman and Gallagher 1989). A similar degree of variation should be expected when considering the names given for the basins outside of North Carolina; the
Culpeper basin in Maryland and Virginia has also been called the Triassic Culpeper Basin, and the Newark basin has been partitioned into a multitude of hydrogeologic units (Elless et al . 1996;
Herman 2001). Another potential point of confusion related to this is that “Triassic Basins” is used by some to refer exclusively to areas in Virginia, North Carolina, and South Carolina
(Griffith et al . 2002).
Because the Triassic Basin classification can be used to refer to all of the basins created during a time period, differences can be expected in the Triassic Basin soils between disparate
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December 5, 2008 locations. It would also be an oversimplification to assume that the soils in a given Triassic Basin are exclusively Triassic sediments. While as recently as 1965 it was reported by Stuckey that there were no Jurassic outcrops in North Carolina, others have since then documented early
Jurassic diabase in the Triassic basin of North Carolina (Stuckey 1965; Hoffman and Gallagher
1989). These dikes and sheets of Jurassic diabase may have an ecological value as they add another potential complexity for habitat variation (Hoffman and Gallagher 1989; North Carolina
Natural Heritage Program 1992). The Carbonton Diabase Sill, located in Chatham County The presence of Jurassic diabase is not unique to the Triassic Basins of North Carolina. Rather, soils and rocks associated with the Jurassic time period have been grouped with those associated with the Triassic time period on geologic maps and databases, and in the literature. Even when separated in part of a discussion, Triassic-Jurassic has been used to refer to both (Herman 2001).
The Triassic sediments included sandstones, shales, conglomerates, siltstones, and mudstones (Daniels et al . 1999). Hoffman and Gallagher (1989) were able to distinguish between three belts within the Durham basin based on lithofacies (macro-scale classification of sedimentary unit) associations. The lithofacies associations involved seven lithofacies, four of which consisted of combinations of siltstone, sandstone, and conglomerate (Hoffman and
Gallagher 1989). Pebbly sandstone, sandstone, and conglomerate made up the remaining three
(Hoffman and Gallagher 1989). Through a thorough assessment of these belts, Hoffman and
Gallagher (1989) determined that one of the belts had most likely been formed by the sediments of a braided stream, one by the sediments of a meandering stream, and one by sediments forming an alluvial fan. Despite these variations, the Triassic Basin uplands in North Carolina are dominated by three soil series-Mayodan, Creedmoor and White Store (Daniels et al . 1999). In regards to drainage classes, Mayodan is well drained, Creedmoor is moderately well drained and
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December 5, 2008 somewhat poorly drained, and White Store is moderately well drained (Soil Survey Staff). White
Store is an Oxyaquic, so it will not develop redoximorphic features even if periodically saturated
(Soil Survey Staff). Another potential issue with redoximorphic features in Triassic soils is that some have red parent materials. However, wetlands may occur in the vicinity of these soils but on less extensive soils that are not Triassic sediments.
Floodplains in the Triassic Basins of the Southeast
Because the headwaters for larger streams are often located in another soil type, the soils and sediments of the floodplains of North Carolina’s Triassic Basin are often not the same type as those located in the immediate vicinity (Daniels et al . 1999). A combination of the Wehadkee and Chewacla soil series are an example of the dominant soil types around streams in the
Durham Triassic Basin (Becky L. Ward Consulting 2006). These are the major types of alluvial soils in the Piedmont in general, but they do not cover extensive areas (Lee 1955). Their drainage classes are poorly drained and somewhat poorly drained respectively (Lee 1955). The Wehadkee soil series specifically occurs around streams and on floodplains, being deposited there as sediment after being eroded from soils that had been formed from metamorphic or igneous rocks
(Soil Survey Staff). The rocks that developed into this soil type include schist, gneiss, phyllite and granite, among others (Soil Survey Staff). The Carolina Slate Belt, another subset of the
Piedmont region in North Carolina, borders the Triassic basins and includes volcanic igneous rocks, gneiss, schist, and phyllite in its composition (Daniels et al . 1999). It is conceivable that some of the Wehadkee and Chewacla soils in the Triassic Basin were eroded from areas in the
Carolina Slate Belt based on this. Although the Wehadkee and Chewacla soils are fairly general
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December 5, 2008 to the Piedmont region, streams in Triassic Basins remain distinctive. One example of this is their baseflows, which are considered to be the lowest in North Carolina (DWQ 2003).
Another trend related to the streams of the Triassic Basin in North Carolina involves the size of their floodplains relative to other floodplains in the Piedmont region. In 1979, Parker
(1979) reported that the floodplain of Crabtree Creek reached a width of half a mile along the portion of the stream that was located in the Triassic Basin, and the Neuse River had a floodplain a mile wide in the Triassic Basin, but that both of these floodplains narrowed abruptly upon transitioning onto areas dominated by metamorphic rock. This is part of a general pattern of floodplains broadening when moving from the Carolina slate belt or felsic crystalline areas of the
Piedmont into the Triassic Basin (Daniels et al . 1999). Although the Triassic Basin floodplains are considered broad, floodplains widened even further with the transition into the coastal plain soils. However, because the floodplains of the Triassic Basin are closer in width to that of the coastal plain, in counties that consist of mountainous soils, Triassic basin soils, and other
Piedmont soils, wetlands might occur in the Triassic basin portion that are otherwise rare in the county. One example of this in North Carolina is the swamp forest in Orange County, which has a very small area of Triassic Basin soils (North Carolina Natural Heritage Program, 2005). The
Triassic basin floodplains have a larger percentage of their area in Swamp forest in areas with the relevant environmental characteristics, and it has been suggested that floods may last longer in
Triassic Basins (NatureServe 2005). The swamp forests and species found there are common in the coastal plain area of North Carolina, but become rare as they extend further westward into the Piedmont (North Carolina Natural Heritage Program, 2005).
The floodplains in the Triassic Basin generally having more in common with the floodplains of the Coastal Plain (NatureServe 2005). The explanation for this pattern seems to be
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December 5, 2008 that the Triassic Basin soils erode more easily and have more developed floodplains (Griffith et al . 2002; NatureServe 2005). Southern Piedmont Large Floodplain Forests- a woody wetland type in NatureServe’s Terrestrial Ecological Classification under the section devoted to the
Southeastern Region of the United States- systems are one of the classifications used to denote the fact that the floodplains of the Triassic Basin are broader (NatureServe 2005). While in the rest of the Piedmont only larger streams and rivers are classified as having Southern Piedmont
Large Floodplain forests, the Triassic basins have floodplains that fall into this category for the smaller streams (NatureServe 2005). Both the duration of flooding and wind can have an important impact on this system (NatureServe 2005). Tree species common to these forests range from American Sycamore to Swamp Chestnut Oak in the canopy, and from Eastern Bottlebrush
Grass to Indian Woodoats lower down (NatureServe 2005). Although sandy substrates are normal for the streams in the Triassic Basin, gravel bars, clayey areas, and bedrock areas may be integrated in with the sandy alluvium (DWQ 2003; NatureServe 2005). These gravel bars may be utilized by trees such as Black Willow or herbs, while the drier sections of the wetland may include species such as American beech (NatureServe 2005).
Historical anthropogenic changes to the river basins of the Triassic Basin in North
Carolina have, however, affected these trends on a local scale. In Durham County, the difference in the extent of the floodplains and wetlands surrounding both streams and rivers between the areas underlain by Carolina slate belt soils and the Triassic Basin soils is less pronounced now than it was before the construction of the current number of reservoirs. According to Griffith et al . (2002), extensive areas of bottomland hardwoods covered the larger floodplains of the
Triassic Basin in North Carolina. When Jordan Lake, Falls Lake, Harris Reservoir, and other reservoirs were created, much of this land covered in bottomland hardwood forest was flooded,
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December 5, 2008 converting it into these water bodies (Griffith et al . 2002). The changes in hydrology caused by the reservoirs also impacted some of the areas that were not directly destroyed.
The NC Wetlands Restoration Program publication put forth by the Division of Water
Quality (DWQ) also noted that the creation of Falls Lake caused a loss of these wetlands, although they referred the wetlands as Piedmont/Mountain Swamp Forest (NCWRP 1998). The terms Piedmont/Mountain Swamp Forest and bottomland hardwood are not synonymous, but seem to overlap in the relevant area in this case, with the Piedmont/Mountain Swamp Forest seeming to refer to the floodplain forests specifically in the Piedmont (DRC 2006). In addition to the destruction of these habitats by reservoirs in Durham County, large areas of
Piedmont/Mountain Swamp Forest have been removed or disrupted in Virginia with the construction of reservoirs (DRC 2006).
Other Noteworthy Wetlands in the Triassic Basins
While the floodplain forests seem to be some of the most important wetlands of the
Triassic Basin in the Southeast, there are other wetlands of note. Leaksville Loam Forests is one specific site in the Triassic Basin of North Carolina that contains an Upland Depression Swamp
Forest with a significant amount of swamp white oak ( Quercus bicolor ) (North Carolina Natural
Heritage Program 1999). Roundhouse Road Forest is another site, and in addition to swamp white oak, the Upland Depression Swamp contains willow oak (North Carolina Natural Heritage
Program 1999). Assuming that these are similar to the classification of Southern Piedmont
/Ridge and Valley Upland Depression Swamp or other such ecosystems, these wetlands are isolated wetlands based on depressions with limited drainage (NatureServe 2005). Pee Dee River
Skunk Cabbage Seep is another wetland in the Triassic Basin of North Carolina, and it is
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December 5, 2008 considered important by the North Carolina Natural Heritage Program (2001). Its importance is based on the presence of skunk cabbage, a species usually found further north (North Carolina
Natural Heritage Program 2001).
In Virginia, vernal pools are reported to be associated with the Triassic Basin area
(Crawford 2001). These vernal pools are significant because they serve as breeding grounds for amphibians (Crawford 2001). More specifically, in 2003, it was reported that most of the known range of the Mole salamander in Virginia was in or near the Danville Triassic basin, and it is one of the species that uses vernal pools and similar wetlands for breeding (Hayslett 2003).
Moving up into the Northeast, other important wetlands occur on the Triassic Basins.
One example of this is the Great Swamp Wildlife Refuge in New Jersey. It is located on Triassic
Basin soils and contains swamp forest with pin oak, sweet gum, red maple, swamp white oak, and shagbark hickory trees (Collins and Anderson 1994). Skunk cabbage is also present (Collins and Anderson 1994).
Woods et al . (1999) described two ecoregions in relation to the Triassic Basin – the
Triassic Lowlands and the Triassic Uplands. In the Triassic Lowlands ecoregion of
Pennsylvania, after the historical destruction of wetlands, the remaining wetlands are providing important support for a number of endangered species, including the New Jersey chorus frog and the bog turtle (Woods et al. 1999).
Redoximorphic features in soils with red parent materials
Because the Triassic basin soils include red shales, being able to reliably identify hydric field indicators may be more of a challenge for some of the wetlands in the basins. In general, the redoximorphic features that are used to identify soils as hydric can be more difficult to detect in
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December 5, soils with red parent materials (USDA, NRCS. 2006). This is widely acknowledged, as is
2008 evidenced by the specific indicator listed in Field Indicators of Hydric Soils in the United States to address some of the problematic soils (USDA, NRCS. 2006). The field indicator is TF2. Red
Parent Material, and in a note next to the description of this indicator, it is stated that redox depletions and black or dark reddish black soft manganese masses are conspicuous relative to alternative redox features in some of the problem soils (USDA, NRCS. 2006). In this note, a number of examples are listed to convey the types of soils that this indicator is appropriate for
(USDA, NRCS. 2006). Triassic-Jurassic sediments are included on this list, although the list is specifically referring to the Connecticut River Valley (USDA, NRCS. 2006).
Rabenhorst and Parikh (2000) have argued that soils should be tested more thoroughly to determine whether or not they are problematic, and limit the use of the TF2. Red Parent Material to soils that are demonstrated to be significantly less conductive to developing redoximorphic features. In response to variations in reports on the expression of redoximorphic features in
Triassic Basin soils with red parent materials, Elless et al . conducted a study in 1996 (1996).
This study involved examining several sites in Maryland, measuring the water table depths during the wet season biweekly for two consecutive years and using this as a basis for comparison of redoximorphic features (Elless et al . 1996). The conclusions of this study were that the differences in redox features could not be explained by any of the factors considered apart from that caused by red parent material (Elless et al . 1996). Another study indicated that the Triassic Basin soils derived from red parent material in Maryland may have horizons and saturation conditions to develop reducing conditions to affect manganese, but that fall short of reducing iron (Elless and Rabenhorst 1994).
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December 5, 2008
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