Reelfoot Rift and Its Impact on Quaternary Deformation in the Central Mississippi River Valley

Home , Mississippi embayment, Reelfoot Lake, Sikeston Ridge

Reelfoot rift and its impact on Quaternary deformation in the central Mississippi River valley

Ryan Csontos University of Memphis, Ground Water Institute, 300 Engineering, Memphis, Tennessee 38152, USA Roy Van Arsdale Randel Cox University of Memphis, Earth Sciences, 1 Johnson Hall, Memphis, Tennessee 38152-3430, USA Brian Waldron University of Memphis, Civil Engineering, 110D Engineering Science Building, Memphis, Tennessee 38152, USA

ABSTRACT ridge, and the southern half of Crowley’s depth (Pujol et al., 1997) and has been attributed Ridge as compressional stepover zones that to reactivation of Reelfoot rift basement faults Geophysical and drill-hole data within the appear to have originated above basement (Kane et al., 1981; Braile et al., 1986; Dart and Reelfoot rift of Arkansas, Tennessee, Mis- fault intersections. The Lake County uplift Swolfs, 1998; Csontos, 2007). Specifi cally, the souri, and Kentucky, USA, were integrated has been tectonically active over the past earthquakes are occurring on a compressional to create a structure contour map and three- ~2400 yr and corresponds with a major seg- left stepover within a right-lateral strike-slip dimensional computer model of the top of the ment of the New Madrid seismic zone. The fault system (Russ, 1982; Schweig and Ellis, Precambrian crystalline basement. The base- aseismic Joiner ridge and the southern por- 1994). ment map and model clearly defi ne the north- tion of Crowley’s Ridge may refl ect earlier The general geometry of the Reelfoot rift was east-trending Cambrian Reelfoot rift, which uplift, thus indicating Quaternary strain mapped by Dart and Swolfs (1998) (Fig. 2); is crosscut by southeast-trending basement migration within the Reelfoot rift. however, here we integrate a more recent and faults. The Reelfoot rift consists of two major extensive data set (Csontos, 2007) to better map basins, separated by an intrarift uplift, that Keywords: Reelfoot rift, Mississippi embay- the rift. In addition, the base of the Mississippi are further subdivided into eight subbasins ment, New Madrid seismic zone, Mississippi Valley alluvium (Pliocene–Pleistocene uncon- bound by northeast- and southeast-striking River alluvium, geomorphology. formity) is mapped using 5077 shallow borings. rift faults. The rift is bound to the south by Comparison of the Pliocene–Pleistocene uncon- the White River fault zone and to the north INTRODUCTION formity with the Reelfoot rift structures indi- by the Reelfoot normal fault. The modern cates Quaternary fault reactivation far beyond Reelfoot thrust fault, responsible for most of The Reelfoot rift (Mississippi Valley graben), the footprint of the New Madrid seismic zone. the New Madrid seismic zone earthquakes, is beneath the northern Mississippi embayment, interpreted as an inverted basement normal has been interpreted as a Cambrian aulacogen GEOLOGY OF THE REELFOOT RIFT fault. (Ervin and McGinnis, 1975; Thomas, 1991) REGION Geologic interpretation of 5077 shallow (Fig. 1). Buried under as much as 8 km of Pha- borings in the central Mississippi River val- nerozoic sediments, the crystalline basement The geologic history of the Reelfoot rift ley enabled the construction of a structure rocks defi ning the rift have been mapped from region is poorly understood because the base- contour map of the Pliocene–Pleistocene gravity, aeromagnetic, seismic refraction, seis- ment rocks are largely buried beneath Phanero- unconformity (top of the Eocene–base of mic refl ection, and a few deep petroleum explo- zoic sediments, including Mississippi River Mississippi River alluvium) that overlies ration wells (Hildenbrand et al., 1977; Howe alluvium. However, regional mapping indicates most of the Reelfoot rift. This map reveals and Thompson, 1984; Howe, 1985; Hildenbrand that the central United States is underlain by both river erosion and tectonic deformation. and Hendricks, 1995; Langenheim and Hilden- several Precambrian terranes (Fig. 3). These Deformation of the Pliocene–Pleistocene brand, 1997; Dart and Swolfs, 1998; Parrish and terranes include the Superior Province (2700 unconformity appears to be controlled by the Van Arsdale, 2004; Csontos, 2007). The north- Ma), Penokean orogen (1880–1830 Ma), North- northeast- and southeast-trending basement ern end of the rift near the town of New Madrid, ern Central Plains orogen (1800–1700 Ma), faults. The northeast-trending rift faults have Missouri, was the site of the great 1811–1812 Southern Central Plains orogen (1700–1600 undergone and continue to undergo Quater- New Madrid earthquakes and it remains the Ma), Eastern Granite-Rhyolite Province (1470 nary dextral transpression. This has resulted most seismically active area east of the Rocky ± 30 Ma), Southern Granite-Rhyolite Prov- in displacement of two major rift blocks and Mountains (Johnston and Schweig, 1996) (Fig. ince (1370 ± 30 Ma), Midcontinent Rift Sys- formation of the Lake County uplift, Joiner 1). This seismicity ranges from 4 to 14 km in tem (1100–1000 Ma), and Grenville Province

Geosphere; February 2008; v. 4; no. 1; p. 145–158; doi: 10.1130/GES00107.1; 10 ﬁ gures; 2 animations.

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/4/1/145/3339867/i1553-040X-4-1-145.pdf by guest on 27 September 2021 Csontos et al. R—Arkansas; Figure 1. Reelfoot rift and New Madrid seismic zone earthquakes. CR—Crowley’s Ridge. DEM—digital elevation model. AL—Alabama; A AL—Alabama; Ridge. DEM—digital elevation model. 1. Reelfoot rift and New Madrid seismic zone earthquakes. CR—Crowley’s Figure TN—Tennessee. IL—Illinois; KY—Kentucky; MS—Mississippi;

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(Hildenbrand, 1985). During rifting the Reel- foot graben accumulated a maximum of 7 km of sediment, while outside the rift only 1.5 km of contemporary sediments accumulated (Howe and Thompson, 1984; Howe, 1985). Local erosion of nearby granite-rhyolite rocks provided Early Cambrian basal arkosic sediments (Crone et al., 1985; Dart and Swolfs, 1998). Howe and Thompson (1984) suggested that faulting occurred syndepositionally within and along the Rift margins up to Middle Cambrian time. After this, deposition within the rift shifted from subaerial to marine and as much as 6 km of marine Upper Cambrian Lamotte Sandstone, Bonterre Formation limestones, Elvins Group shales, and the Potsdam Supergroup were deposited (Thomas, 1985; Howe, 1985). Depo- sition kept pace with regional subsidence during Late Cambrian–Middle Ordovician time (Howe and Thompson, 1984; Howe, 1985; Dart and Swolfs, 1998), resulting in the thick, shallow- marine Knox (Arbuckle) carbonate Supergroup that overlies the rift (Thomas, 1985; Howe, 1985). From Middle Ordovician to Pennsylva- nian time, subsidence and uplift alternated due to distal effects of the Taconic, Acadian, and Alleghanian orogenies (Howe, 1985). Struc- tural reactivation within the Reelfoot rift began during the late Paleozoic with the assembly of Pangaea (Thomas, 1985; Howe, 1985). Middle Ordovician to mid-Cretaceous rocks are largely missing above the rift, partly due to nondeposi- tion (Permian–Late Cretaceous) and partly due to late Paleozoic and/or mid-Cretaceous uplift and erosion, which produced a major unconformity at the top of the Paleozoic section. Many Figure 2. Precambrian basement map of the Reelfoot rift (from Dart and Swolfs,1998). Cir- normal faults within the central United States cles—drill holes; thick solid lines—Vibroseis lines. Contour interval = 500 m. were inverted during the Paleozoic collisional processes (Howe and Thompson, 1984; Howe, 1985; Marshak and Paulsen, 1996). (1100–800 Ma) (Atekwana, 1996; Van Schmus Initiation of Reelfoot rifting may have been Cox and Van Arsdale (1997, 2002) pro- et al., 1996). Proterozoic rocks of the Reelfoot due to mantle plume upwelling that occurred posed that regional mid-Cretaceous uplift and rift region consist primarily of granite, granite along terrane boundaries (Dart and Swolfs, subsequent Late Cretaceous subsidence of the porphyry, and dioritic gneiss as determined from 1998). Alternatively, the Reelfoot rift may be a Mississippi embayment occurred because the drill cores (Thomas, 1985; Dart, 1992; Dart and consequence of right-lateral strike-slip motion North American plate drifted over the Bermuda Swolfs, 1998). Rocks of similar age in the East- along a northwest-oriented transform fault that hotspot. The thermally uplifted area formed a ern Granite-Rhyolite Province are exposed in formed the Paleozoic continental margin of north-trending arch from which ~2 km of Paleo- the St. Francois Mountains in southeastern Mis- southeastern Laurentia (Thomas, 1985, 1991). zoic strata were eroded during the mid-Creta- souri (Thomas, 1985; Dart and Swolfs, 1998). Whatever the mechanics, intracratonic extension ceous (Cox and Van Arsdale, 1997). Following The Reelfoot rift is part of the Reelfoot rift– ultimately succeeded in creating the Reelfoot the North American plate’s migration off the Rough Creek graben–Rome trough intracra- rift with an estimated extension between 17% hotspot during the Late Cretaceous, the eroded tonic rift zone that formed during the disas- (Nelson and Zhang, 1991) and 33% (Hilden- mid-Cretaceous arch subsided as it cooled, sembly of Rhodinia and opening of the Iapetus brand, 1985). forming the Mississippi embayment trough. Ocean (Thomas, 1976, 1983, 2006). Several Cambrian Reelfoot rifting occurred primar- Late Cretaceous and Cenozoic sediments record authors have proposed that the Reelfoot rift may ily along large normal faults that appear to transgressive-regressive sequences within the have formed along the boundary between adja- become listric with depth (Howe and Thomp- trough that include the McNairy, Clayton, Por- cent Precambrian terranes beneath the Eastern son, 1984; Howe, 1985; Nelson and Zhang, ters Creek, Fort Pillow, Flour Island, Claiborne Granite Rhyolite Province (Kane et al., 1981; 1991). However, the exceptionally straight mar- Group, Upland Complex, and the Mississippi Hildenbrand, 1985; Hendricks, 1988; Nelson gin faults suggest that these northeast-trending River alluvium (Howe and Thompson, 1984; and Zhang, 1991; Dart and Swolfs, 1998). rift structures originated as strike-slip faults Thomas, 1985).

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are dominated by glacio-fl uvial processes and sediments that produced Pliocene and Pleisto- cene landforms consisting mostly of terraces and valley trains (Saucier, 1974; Autin et al., 1991). Repeated changes in late Pliocene and Pleistocene base level have controlled much of the Mississippi Valley’s landforms and deposits through repeated degradation and aggradation. Four processes especially infl uenced base level through the Quaternary: glacio-eustatic sea- level changes, variations in rates and patterns of sediment yield, climatic changes, and tectonic activity. Pleistocene rivers carrying coarse- grained sediment were dominantly braided, in contrast to the high silt and clay sediment load of the Holocene rivers that now occupy mean- dering channels. Structural features affecting regional Qua- ternary stratigraphy within the Mississippi River valley include the Jackson Dome, Lake County uplift, Monroe uplift, Ouachita fold and thrust belt, Wiggins arch, and several fault zones (Autin et al., 1991; Schweig and Van Ars- dale, 1996; Cox et al., 2000). Based on shallow alluvial cores, Mihills and Van Arsdale (1999) recognized modern topographic relief mirroring the Pliocene–Pleistocene unconformity (base of Mississippi River alluvium), refl ecting deformation of the Lake County uplift, Reelfoot Lake basin, and the northeast Arkansas sunklands. Some of these structures have modifi ed local stream gradients and sedimentary processes during the Quaternary (Holbrook et al., 2006).

FAULTING WITHIN THE REELFOOT RIFT Figure 3. Precambrian geology of the south-central United States (from Van Schmus et al., 1996). G—Grenville Front, GIPB—Green Island plutonic belt, MCR—Midcontinent Rift, Bounding faults of the Reelfoot rift (Fig. 1) MGL—Missouri gravity low, RR—Reelfoot rift, SFM—St. Francois Mountains. Dashed have large normal displacements (Howe 1985; line extending from Texas to Ontario represents inferred eastern limit of pre–1600 Ma con- Nelson and Zhang, 1991; Parrish and Van Ars- tinental crust. Solid circles are drill-hole and outcrop samples for which depleted mantle dale, 2004). The northwestern margin of the rift age (T ) ≥ 1.55 Ga; open circles are drill-hole and outcrop samples for which T ≤ 1.55 DM DM is delineated by a steeply southeastward-dip- Ga. Black cross in northwestern Ohio is drill-hole OHSN-001; solid square in southeastern ping normal fault, displacing the Precambrian Michigan is drill-hole MIHI-001. erosional surface as much as 3 km (Howe, 1985; Nelson and Zhang, 1991). The southeastern rift margin consists of a pair of down-to-the-north- The Mississippi River Valley within the Mis- River, erosion of the Eastern Lowlands by the west steep normal faults with as much as 3 km sissippi embayment is a broad alluvial lowland ancestral Ohio River, and by Quaternary reac- of normal displacement on the more western (Fig. 1). Notable in eastern Arkansas is the 320- tivation of ridge-bounding faults (Van Arsdale fault, and 0.5 km on the more eastern fault in km-long Crowley’s Ridge, a northerly trending et al., 1995). Depositional environments within western Tennessee (Howe, 1985; Parrish and topographic high that divides the valley into the valley were ﬂ uvial during the Pliocene. This Van Arsdale, 2004). the Western and Eastern Lowlands. The ridge resulted in deposition of the Upland Complex, a Several faults have been identiﬁ ed within the ranges in width from 1.6 to 19 km and averages terrace of the ancestral Mississippi–Ohio river Reelfoot rift (Fig. 1). The Reelfoot reverse fault, 60 m above the surrounding lowlands. It is com- system (Van Arsdale et al., 2007). Repeated coincident with the northwest-trending seismic posed in ascending order of Eocene Wilcox and periods of glacial melt-water escape, sea-level zone in Figure 1, produces most of the current Claiborne Groups (Meissner, 1984), Pliocene change, loess deposition, and structural defor- seismicity. Surface deformation occurred along Upland Complex (Van Arsdale et al., 2007), and mation have produced various river terraces, this fault during the February 1812 earthquake. Pleistocene loess (Guccione et al., 1990). river courses, lakes, and areas of warping dur- The White River fault zone is an up-to-the-south Crowley’s Ridge formed due to erosion of the ing the Quaternary (Autin et al., 1991; Sch- fault, based upon gravity, magnetic (Hilden- Western Lowlands by the ancestral Mississippi weig and Van Arsdale, 1996). These landforms brand and Hendricks, 1995; Langenheim and

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Hildenbrand, 1997), and seismic refl ection data lated surface to yield a meaningful result. Both Both ArcGIS™ and Landmark™ provide 3-D (Howe, 1985), that may form a southern termi- Landmark™ and ArcGIS™ have this capabil- stereoscopy through the extensional packages nus to the Reelfoot rift. The Axial fault, a vertical ity, yet only ArcGIS™ offers a visual inspec- ArcScene™ and Geoprobe™, respectively, and fault (Howe, 1985) that trends down the center tion of the semi-variogram and an interactive using Sharper Technology Incorporated Crystal- of the rift, is the locus of the northeast-trending means of minimizing error through adjustment eyes stereo goggles, an emitter, and a DepthQ seismicity in Figure 1. of the semi-variogram parameters, while only Stereo3D projector. A number of southeast-trending strike-slip Landmark offers the capability to incorporate faults in southeastern Missouri and north- fault and break-line information into the inter- RESULTS eastern Arkansas may cross the Reelfoot rift polation. The semi-variogram model parameters (McCracken, 1971; Guinness et al., 1982; Zietz, determined in ArcGIS™ were entered into Land- Top of Precambrian Crystalline Basement 1982; Hildenbrand, 1985; Howe, 1985; Simpson mark’s Zmap™ package. Unfaulted interpolation Structure Contour Maps et al., 1986; Sims et al., 1987; Cox, 1988; Dart schemes were built in tandem within ArcGIS™ and Swolfs, 1998). Stark (1997) suggested that and Landmark Zmap™ for comparison. The top of the Precambrian crystalline base- major thrusting and transpressive deformation Faults were subsequently inserted into the ment unconformity, including the Reelfoot rift during the Late Proterozoic Grenville orogeny Zmap™ model as break lines and polygons to and Rough Creek graben, is illustrated in Figure modifi ed the rift region, resulting in orthogonal the interpolated Precambrian surface. These 4. In this map, no faults have been incorporated basement faults with southeast and northeast faults were obtained from published seismic into the model to displace the surface. The obvi- strikes. Many of these southeast-trending faults refl ection lines (Howe and Thompson, 1984; ous features are the Reelfoot rift, Rough Creek displace Paleozoic strata and thus have been Howe, 1985; Nelson and Zhang, 1991; Parrish graben, the high between these down-dropped active during the Phanerozoic (Stark, 1997). and Van Arsdale, 2004), gravity and magnetic areas, southern and northern closure of the Reel- lineaments (Hildenbrand, 1985; Hildenbrand foot rift, and a structural high in the center of the METHODS and Hendricks, 1995; Langenheim and Hilden- Reelfoot rift. brand, 1997), mapped faults (McCracken, 1971; Figure 5 focuses on the Reelfoot rift and adds A number of data types and mapping tech- Zietz, 1982; Kisvarsanyi, 1984; Simpson et al., into the model faults with their correct dips and niques were applied in this research. Picks for 1986; Sims et al., 1987; Haley et al., 1993), and displacements. These faults include the down- the unconformity on the top of the Precam- hypocenter alignments (J. Pujol, 2006, personal to-the-northwest Eastern Rift Margin normal brian crystalline basement were obtained from commun.; Csontos, 2007). Hypocenters were faults (Parrish and Van Arsdale, 2004), down- depth-converted seismic refl ection lines (Howe viewed within a Landmark Geoprobe™ three- to-the-southeast Western Rift Margin normal and Thompson, 1984; Howe, 1985; Nelson and dimensional (3-D) model to identify fault planes. fault (Nelson and Zhang, 1991), vertical Axial Zhang, 1991; Parrish and Van Arsdale, 2004) Hypocenter clusters appearing to follow planar fault with no displacement (Howe, 1985), and and petroleum exploration wells (Dart and surfaces were grouped into subsets and planar a down-to-the-southwest Reelfoot fault. In this Swolfs, 1998; Van Arsdale and ten Brink, 2000). trend surfaces were created using ArcGIS™ and model, the Reelfoot fault bounds the Reel- Earthquake hypocenter data were provided by Landmark Zmap™. The Eastern Rift margin, foot rift on the north and is interpreted to be a J. Pujol (2006, personal commun.). Pliocene– Western Rift margin, and Reelfoot faults were down-to-the-southwest normal fault. Seismic- Pleistocene unconformity (base of Mississippi assigned dip angle, dip azimuth, heave, and ity reveals that the Reelfoot fault is currently a River alluvium) data were obtained by geologi- throw values where available with Zmap™. thrust fault at depth and seismic refl ection pro- cally interpreting 3546 North American Coal The southeast-striking Ozark Plateau faults and fi les indicate that it steepens to a reverse fault in Company lignite exploration geologic shallow Axial fault were assigned vertical dips with no the upper 4 km (Purser and Van Arsdale, 1998; well logs and combining these with 1531 picks throw. Surface interpolation then utilized faults Csontos, 2007). However, the top of the Pre- that were previously made by the U.S. Army with dip, throw, and heave data to produce fault cambrian surface suggests that the southwestern Corps of Engineers (Mihills and Van Arsdale, plane polygons, while faults without these data side is down-dropped and thus the Reelfoot fault 1999). These data were imported into a database, were treated as vertical break lines. These fault probably has normal separation at this level. We mapped, and projected to a transverse mercator polygons and break lines were used to interrupt therefore have modeled the Reelfoot fault as an projection. The projection was centered at long the contouring algorithm at the fault planes and inverted Cambrian rift-bounding normal fault. 90°W and lat 35°N to minimize distortion of the continue interpolation on the opposite side of As is apparent in Figure 5, there are also sub- map area (Csontos, 2007). the fault using a new trend surface created for basins within the Reelfoot rift. The Precambrian database was maintained the fault-bound data subset. These faults were In the fi nal Reelfoot rift basement model and interpreted in the ArcGIS™ and Landmark then incorporated into the Zmap™ interpola- (Fig. 6; Animation 1), we extend one of the Graphics™ software packages. These packages tion algorithm to produce a Precambrian surface Eastern Margin faults north to include a Qua- each offer unique advantages for interpolation structure contour map displaced by faults. ternary fault scarp near Union City, Tennessee and interpretation of the data. The top of the The Pliocene–Pleistocene unconformity sur- (Cox et al., 2006), extend the Western Margin crystalline Precambrian was interpolated using face was mapped using ArcGIS™. Universal fault north to include the current seismicity ordinary kriging. Ordinary kriging is an inter- kriging was used to interpolate the surface, and trend north of New Madrid, Missouri (Baldwin polation algorithm typically used with geologic then the surface was clipped along the periphery et al., 2002), and extend the southeast-trending data. This algorithm calculates any overriding data points. vertical Grand River tectonic zone, Central Mis- trend to the data, and models these data as a Owing to the regional extent of these surfaces souri tectonic zone, Osceola fault zone, Bolivar- polynomial. The measured data are interpolated and their three-dimensionality, visual compari- Mansfi eld tectonic zone, and White River fault following removal of the trend. After interpo- son of these surfaces to control data (drill hole, zone through the Reelfoot rift. These southeast- lation, the random errors are assessed and the seismic refl ection data) was made easier through striking faults were projected across the Reel- trend polynomial is added back into the interpo- viewing them stereoscopically in Geoprobe™. foot rift by connecting mapped faults exposed

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Figure 4. (A) Precambrian unconformity data points (red dots and lines) from Howe (1985), Wheeler et al. (1997), Dart and Swolfs (1998), and Parrish and Van Arsdale (2004). AL—Alabama, AR—Arkansas, IL—Illinois, KY—Kentucky, MO—Missouri, MS—Mississippi, TN—Tennessee. (B) Precambrian unconformity structure contour map from A including the Reelfoot rift (RR) and the Rough Creek graben (RCG). NM—New Madrid. Yellow box denotes location of Figures 5 and 6. Elevation datum is sea level.

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Figure 5. Precambrian unconformity structure contour map with the addition of the two Eastern Rift Margin faults (EM), Axial fault (AF), Western Rift Margin fault (WM), and the Reelfoot fault (RF). NM—New Madrid. Elevation datum is sea level.

Figure 6. Precambrian unconformity structure contour map with the addition of southeast oriented faults. GRTZ—Grand River tectonic zone; CMTZ—Central Missouri tectonic zone; OFZ—Osceola fault zone; BMTZ—Bolivar-Mansﬁ eld tectonic zone; WRFZ—White River fault zone. EM—Eastern Rift Margin faults, AF—Axial fault, WM—Western Rift Margin fault, RF—Reelfoot fault, NM—New Madrid. Elevation datum is sea level.

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high trends southeast close to New Madrid, that these southeast-trending faults infl uenced Missouri, that coincides with the Lake County the geometry of the Reelfoot rift. uplift structure (Russ, 1982; Purser and Van Although we do not have well or seismic data Arsdale, 1998) and Reelfoot fault seismicity between the Reelfoot rift and the Rough Creek (Mueller and Pujol, 2005). Immediately east graben, regional depth to magnetic basement of this high is a low that corresponds with maps (Hildenbrand, 1985; Langenheim and the tectonically down-dropped Reelfoot Lake Hildenbrand, 1997) suggest that the basement basin (Russ, 1982). A second high extends rises between these two down-dropped struc- southwest from the Lake County uplift to near tures (Fig. 4). Thus, we have chosen to close the Marked Tree, Arkansas, that is coincident with Reelfoot rift at its northern end with a down-to- the Blytheville arch in the underlying Paleo- the-southwest normal fault (Fig. 6). This fault zoic strata (Johnston and Schweig, 1996) and coincides in location with the Reelfoot thrust Animation 1. If you are viewing the PDF of the southern arm of New Madrid seismic zone and reverse fault. However, the only displace- this paper or reading it offl ine, please visit seismicity (Fig. 1). This same high appears ment information we have on the Reelfoot fault http://dx.doi.org/10.1130/GES00107.S1 or to bound the southern ends of Big Lake and shows that there is 70 m of reverse displace- the full-text article on www.gsajournals.org Lake St. Francis sunklands. A third high on ment on the top of the Paleozoic section that to view Animation 1. the unconformity surface that we have named diminishes up section (Van Arsdale, 2000). We Joiner ridge, after Joiner, Arkansas, can be thus propose that the Reelfoot fault was a nor- traced northwest from the corner of Shelby mal fault during Reelfoot rifting, but was sub- in the Ozark Plateau with similar on-strike faults County, Tennessee (Fig. 8). sequently inverted and is a reverse fault in the and geophysical lineaments mapped in western In the Western Lowlands there are large post-Paleozoic section. The southern end of the Tennessee (Howe, 1985; Hildenbrand, 1985). elevation changes on the Pliocene–Pleistocene Reelfoot rift appears to be closed by the up-to- The southeast-trending faults are along the sub- unconformity surface. A 10-m-deep northeast- the-southwest White River fault zone. Our data basin margins of Figure 5 and break the Pre- trending closed depression is in the central are also limited in this area and it is possible that cambrian surface into nearly orthogonal fault- portion of the Western Lowlands that does not the Reelfoot rift continues south beneath the bound blocks, as described by Stark (1997). appear to be related to Quaternary river erosion. Appalachian-Ouachita thrust belt. For example, the relatively high central area of Bounding this low on the southeast is a high Extending down the center of the Reelfoot rift the Reelfoot rift is bound on the north by the region, and still farther southeast there is a sec- is the Axial fault. Although we have modeled Osceola fault zone and on the south by the Boli- ond low that may be related to river erosion. the Axial fault as terminating against the Reel- var-Mansfi eld tectonic zone. There are also very foot fault, this is speculative. The Axial fault close correlations between the northern closure DISCUSSION appears to have undergone both dip-slip and of the Reelfoot rift and the Grand River tectonic strike-slip movement. The northwestern side of zone and between the southern closure and the Precambrian Unconformity Surface the fault is generally downthrown relative to the White River fault zone. southeastern side (Howe and Thompson, 1984). The Precambrian unconformity surface Left-lateral strike-slip offset is also suggested by Pliocene–Pleistocene Unconformity beneath the central Mississippi River valley a series of offset ridges and depressions on the probably caps eroded 1.47 Ga Eastern Granite Precambrian surface (Fig. 6). In this study, 5077 geologic bore holes located Rhyolite Province rocks (Fig. 3). Rifting of this within the central Mississippi River valley were landscape formed the northeast-trending Reel- Reelfoot Rift Faults Projected to the interpreted to record the elevation of the Plio- foot rift (Mississippi Valley graben). However, it Pliocene–Pleistocene Unconformity Surface cene–Pleistocene age unconformity (top of the appears that southeast-trending faults also were Eocene–base of the Mississippi alluvium) (Fig. active during rifting because some of these faults In Figure 9 we project the Reelfoot Rift base- 7). The data were initially split into the Eastern are evident on seismic refl ection lines within the ment faults to the Pliocene–Pleistocene uncon- Lowlands and Western Lowlands and contoured rift. These southeast-trending faults have been formity surface. In addition, we have included separately utilizing universal kriging within mapped in the Ozarks of Arkansas and Missouri the base of the Pliocene Upland Gravel on ArcGIS™. Surfaces were cropped based upon as Proterozoic basement faults that predate Crowley’s Ridge in our Pliocene–Pleistocene the data extent and fl ood plain limits. Reelfoot rifting (Sims et al., 1987). Stark (1997) unconformity surface. Thus, the Eastern and Relief on the Pliocene–Pleistocene uncon- proposed that these southeast-trending faults Western Lowlands and Crowley’s Ridge were formity suggests the presence of both erosional originated within the 1.8 Ga Central Plains oro- contoured together in Figure 9. The Pliocene– and tectonic features (Fig. 8). A prominent low gen basement. Pleistocene unconformity surface is an ero- extends along the eastern side of Crowley’s The Reelfoot rift is subdivided into eight sional surface that has been tectonically modi- Ridge that we believe is due to Pleistocene fault-bound blocks (Fig. 6). At the largest scale, fi ed. In the Eastern Lowlands, Quaternary uplift ancestral Mississippi or Ohio River incision as the rift consists of two basins divided by a struc- has occurred along the Reelfoot fault (Grand described by Saucier (1994). This river course tural high. This intrarift high is bound on the River tectonic zone) to form the Lake County can be traced beneath Sikeston Ridge at right north by the Osceola fault zone and on the south uplift, along the Axial fault to affect regional angles to the trend of that ridge (Figs. 8 and 9). by the Bolivar-Mansfi eld tectonic zone. Major drainage, and along Joiner ridge. Tectonic sub- Since there is no evidence that this river course changes in strike of the Eastern Rift Margin sidence in the Eastern Lowlands has occurred has been altered by tectonic uplift, we con- and Western Rift Margin faults occur near their beneath Reelfoot Lake, northwest of the Axial clude that the overlying Sikeston Ridge is pre- intersection with the Bolivar-Mansfi eld tectonic fault, and perhaps immediately east of Joiner dominately erosional in origin. A topographic zone and the Osceola fault zone, also indicating ridge. In the Western Lowlands there are one

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Figure 7. Distribution of 5077 borings used to map the Pliocene–Pleistocene unconformity (base of Mississippi River alluvium). WL—West- ern Lowlands, EL—Eastern Lowlands, B—Big Lake, S—Lake St. Francis. IL—Illinois, KY—Kentucky, MO—Missouri, MS—Mississippi, TN—Tennessee. DEM—digital elevation model.

and perhaps two major structural basins that appear to divide Crowley’s Ridge into sections, fault) has undergone Quaternary uplift. Cox et are separated by an apparently uplifted block as one would expect if the faults were active al. (2001, 2006) documented that the Eastern bound by the Axial fault and a possible exten- during the Quaternary. Rift Margin faults have undergone up-to-the- sion of the Eastern Margin faults southwest of Hence, based on Figure 9 and neotectonic northwest Quaternary displacement. Relative the White River fault zone. Perhaps most dra- studies conducted in the Eastern Lowlands, it up-to-the-southeast Quaternary displacement matic in Figure 9 is the elevation of Crowley’s appears that the entire Reelfoot rift has been tec- along the Axial fault appears to have been Ridge. Upon viewing Figure 9 stereoscopically tonically active during the Quaternary (Fig. 10). responsible for local impoundment of the St. (see Animation 2), it becomes apparent that Speciﬁ cally, we believe that the southeastern Francis and Little Rivers to form Lake St. Fran- most of the basement faults produce saddles, or half of the Reelfoot rift (southeast of the Axial cis and Big Lake respectively, within the general

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Figure 8. Pliocene–Pleistocene unconformity structure contour map. B—Big Lake, S—Lake St. Francis, J—Joiner ridge. AR—Arkansas, IL—Illinois, KY—Kentucky, MO—Missouri, MS—Mississippi, TN—Tennessee.

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Figure 9. Pliocene–Pleistocene unconformity surface with Precambrian Reelfoot rift faults. B—Big Lake, S—Lake St. Francis, CR—Crow- ley’s Ridge, J—Joiner ridge, GRTZ—Grand River tectonic zone; CMTZ—Central Missouri tectonic zone; OFZ—Osceola fault zone; BMTZ—Bolivar-Mansﬁ eld tectonic zone; WRFZ—White River fault zone. EM—Eastern Rift Margin faults, AF—Axial fault, WM—West- ern Rift Margin fault, RF—Reelfoot fault, NM—New Madrid. AR—Arkansas, IL—Illinois, KY—Kentucky, MO—Missouri, MS—Missis- sippi, TN—Tennessee. Tiptonville dome is a culmination on the Lake County uplift. Crowley’s Ridge south of lat 35°N not shown.

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thus, the fault intersections have acted as initiation gated upward from Central Plains orogen rocks points for the stepovers (Talwani, 1999; Gango- through the overlying granites and rhyolites of padhyay and Talwani, 2005). the Eastern Granite Rhyolite Province, as proposed by Stark (1997) (Fig. 3). The northeast- CONCLUSIONS and southeast-trending faults that bound the Reelfoot rift and interior subbasins locally have Late Proterozoic through Cambrian rifting as much as 3 km of vertical displacement (Par- across southeastern North America created the rish and Van Arsdale, 2004). The Rift appears northeast-trending Reelfoot rift. Proterozoic to step up to the north at its northern end across southeast-trending faults of the Ozarks appear the Grand River tectonic zone (Reelfoot nor- to pass through the Reelfoot rift and were active mal fault), has a central intrarift uplifted block Animation 2. If you are viewing the PDF of during rifting (Fig. 6). We speculate that the bound by the Osceola fault zone and Bolivar- this paper or reading it ofﬂ ine, please visit southeast-trending faults may have propa- Mansﬁ eld tectonic zone, and steps up to the http://dx.doi.org/10.1130/GES00107.S2 or the full-text article on www.gsajournals.org to view Animation 2.

area called the sunklands (Van Arsdale, 1998; Mihills and Van Arsdale, 1999; Guccione et al., 2000). In the Western Lowlands, our proposed Quaternary uplift of the southeastern half of the Reelfoot rift is coincident with the high that is bound by the Axial fault and the southwestern projection of the Eastern Margin faults (Fig. 9). Similarly, it appears that the northwestern half of the Reelfoot rift has undergone Quaternary subsidence. This interpretation is supported by the basin in the Western Lowlands that is bound by the Axial and Western Margin faults and down- to-the-southeast displacement on the Western Rift Margin fault near Jonesboro, Arkansas (Van Arsdale et al., 1995) and near New Madrid, Mis- souri (Baldwin et al., 2005). The New Madrid seismic zone has been explained as being caused by right-lateral shear along the Axial fault and the Western Margin fault north of New Madrid, Missouri, with a left-step- ping compressional stepover being the Reelfoot fault. However, the Reelfoot thrust earthquakes and deformation continue southeast beyond the Mississippi River valley beneath a thick loess blanket to near the Eastern Rift Margin faults (Figs. 1 and 10) (Van Arsdale et al., 1999; Cox et al., 2001). Thus, a more accurate assessment would be that there is either one large stepover zone from the Eastern Margin faults to the West- ern Margin fault or two stepovers separated by the Axial fault. In assessing the remaining Reelfoot rift area, it appears that there are an additional two aseismic north-trending left stepovers. The most obvious one is the southern half of Crowley’s Ridge, which is documented as being bound by young faulting (Van Arsdale et al., 1995), and the Figure 10. Interpreted deformation of the Pliocene–Pleistocene unconformity surface. Black second one is Joiner ridge. Crowley’s Ridge steps lines—faults, J—Joiner ridge, GRTZ—Grand River tectonic zone; CMTZ—Central Mis- between the West Rift Margin fault and the East souri tectonic zone; OFZ—Osceola fault zone; BMTZ—Bolivar-Mansﬁ eld tectonic zone; Rift Margin faults, whereas Joiner ridge steps over WRFZ—White River fault zone, EM—Eastern Rift Margin faults, AF—Axial fault, WM— between the East Rift Margin faults and the Axial Western Rift Margin fault, RF—Reelfoot fault. AR—Arkansas, KY—Kentucky, MO— fault. We propose that these three stepovers are Missouri, MS—Mississippi, TN—Tennessee. Inset map shows a restraining bend (van der associated with Reelfoot rift fault intersections; Pluijm and Marshak, 2004).

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potential fi eld imagery, in van der Pluijm, B.A., and Guccione, M.J., Prior, W.L., and Rutledge, E.M., 1990, The Ter- south across the White River fault zone. Thus, Catacosinos, P.A., eds., Basements and basins of east- tiary and early Quaternary geology of Crowley’s Ridge, the southeast-trending faults appear to be fun- ern North America: Geological Society of America in Guccione M., and Rutledge, E., eds., Field guide to the damental structures that were involved in the Special Paper 308, p. 33–44. Mississippi Alluvial Valley northeast Arkansas and south- Autin, W.J., Burns, S.F., Miller, B.J., Saucier, R.T., and east Missouri: Fayetteville, Arkansas, Friends of the Pleis- formation of the Reelfoot rift. Snead, J.I., 1991, Quaternary geology of the lower tocene South-Central Cell, p. 23–44. The Pliocene–Pleistocene unconformity Mississippi Valley, in Morrison, R.B., ed., Quaternary Guccione, M.J., Van Arsdale, R.B., and Lynne, H.H., 2000, nonglacial geology; conterminous United States: Boul- Origin and age of the Manilla high and associated Big beneath the Mississippi River alluvium is an der, Colorado, Geological Society of America, Geol- Lake “sunklands” in the New Madrid seismic zone, erosional unconformity that has been tectoni- ogy of North America, v. K-2, p. 547–582. northeastern Arkansas: Geological Society of Amer- cally altered at different scales. On a regional Baldwin, J.N., Barron, A., Kelson, K.I., Harris, J.B., and ica Bulletin, v. 112, p. 579–590, doi: 10.1130/0016- Cashman, S., 2002, Preliminary paleoseismic and geo- 7606(2000)112<0579:OAAOTM>2.3.CO;2. scale, local fi eld studies and inspection of Figure physical investigation of the North Farrenburg Linea- Guinness, E.A., Arvidson, R.E., Strebeck, J.W., Schulz, 9 suggest that the southeastern half of the Reel- ment; primary tectonic deformation associated with K.J., Davies, G.F., and Leff, C.E., 1982, Identifi cation foot rift has undergone Quaternary uplift while the New Madrid North Fault?: Seismological Research of a Precambrian rift through Missouri by digital image Letters, v. 73, p. 393–413. processing of geophysical and geological data: Journal the northwestern half has undergone subsidence. Baldwin, J.N., Harris, J.B., Van Arsdale, R.B., Givler, R., of Geophysical Research, v. 87, p. 8529–8545. On a more local scale, tectonic uplift has occurred Kelson, K.I., Sexton, J.L., and Lake, M., 2005, Con- Haley, B.R., Glick, E.E., and Bush, W.V., 1993, Geologi- straints on the location of the late Quaternary Reelfoot cal map of Arkansas: U.S. Geological Survey, scale on the Lake County uplift, along the Axial fault, and New Madrid North faults in the northern New 1:500,000. along the southern half of Crowley’s Ridge, and Madrid seismic zone, central United States: Seismo- Hendricks, J.D., 1988, Bouguer gravity of Arkansas: Reston, on Joiner ridge. Tectonic subsidence has occurred logical Research Letters, v. 76, p. 772–789. Virginia, U.S. Geological Survey, 31 p. 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QFITSM>2.0.CO;2. bon potential of the Reelfoot Aulocogen [Master’s the- The regional stress fi eld has imposed, and is Cox, R.T., Van Arsdale, R.B., Harris, J.B., and Larsen, D., sis]: Norman, University of Oklahoma, 109 p. imposing, right-lateral shear across the N45°E 2001, Neotectonics of the southeastern Reelfoot Rift Howe, J.R., and Thompson, T.L., 1984, Tectonics, sedimen- zone margin, central United States, and implications tation, and hydrocarbon potential of the Reelfoot Rift: striking East Rift Margin faults, Axial fault, for regional strain accommodation: Geology, v. 29, Oil and Gas Journal, v. 82, p. 179–190. and West Rift Margin fault. Essentially, the p. 419–422, doi: 10.1130/0091-7613(2001)029<0419: Johnston, A.C., and Schweig, E.S., 1996, The enigma of NOTSRR>2.0.CO;2. the New Madrid earthquakes of 1811–1812: Annual entire Reelfoot rift has undergone Quaternary Cox, R.T., Cherryhomes, J., Harris, J.B., Larsen, D., Van Review of Earth and Planetary Sciences, v. 24, p. 339– right-lateral transpression resulting in relative Arsdale, R.B., and Forman, S.L., 2006, Paleoseismol- 384, doi: 10.1146/annurev.earth.24.1.339. uplift and subsidence of the eastern and west- ogy of the southeastern Reelfoot Rift in western Ten- Kane, M.F., Hildenbrand, T.G., and Hendricks, J.D., 1981, nessee and implications for intraplate fault zone evolu- Model for the tectonic evolution of the Mississippi ern halves of the Reelfoot rift, respectively, and tion: Tectonics, v. 23, p. 1–17. Embayment and its contemporary seismicity: Geology, formation of compressional stepovers. The ste- Crone, A.J., McKeown, F.A., Hardin, S.T., Hamilton, R.M., v. 9, p. 563–568, doi: 10.1130/0091-7613(1981)9<563: pover that is currently seismically active is at the Russ, D.P., and Zoback, M.D., 1985, Structure of MFTTEO>2.0.CO;2. the New Madrid seismic source zone in southeastern Kisvarsanyi, E.B., 1984, The Precambrian tectonic frame- northern end of the Reelfoot rift. It is reasonable Missouri and northeastern Arkansas: Geology, v. 13, work of Missouri as interpreted from magnetic anom- to assume, however, that the different stepovers p. 547–550, doi: 10.1130/0091-7613(1985)13<547: aly map: Missouri Department of Natural Resources SOTNMS>2.0.CO;2. Contributions to Precambrian Geology, no. 14, p. 19. activate at different times, perhaps as shear dis- Csontos, R.M., 2007, Three dimensional modeling of the Langenheim, V.E., and Hildenbrand, T.G., 1997, Commerce placement propagates along the rift faults. Reelfoot Rift and New Madrid seismic zone [Ph.D. geophysical lineament—Its source, geometry, and dissertation]: Memphis, Tennessee, University of Mem- relation to the Reelfoot rift and New Madrid seismic ACKNOWLEDGMENTS phis, 92 p. zone: Geological Society of America Bulletin, v. 109, Dart, R.L., 1992, Catalog of pre-Cretaceous geologic drill- p. 580–595, doi: 10.1130/0016-7606(1997)109<0580: hole data from the upper Mississippi Embayment. A CGLISG>2.3.CO;2. Funding for this research was provided by the revision and update of Open-File report 90-260: U.S. Marshak, S., and Paulsen, T., 1996, Midcontinent U.S. fault National Science Foundation Mid America Earthquake Geological Survey Open-File Report 92.685, p. 253. and fold zones; a legacy of Proterozoic extensional tecto- Center, Memphis Stone and Gravel, and a University Dart, R.L., and Swolfs, H.S., 1998, Contour mapping of relic nism?: Geology, v. 24, p. 151–154, doi: 10.1130/0091- of Memphis Dunavant grant. 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