Style and timing of surface faulting on the Meers , southwestern

ANTHONY J. CRONE U.S. Geological Survey, Denver, 80225 KENNETH V. LUZA Oklahoma Geological Survey, Norman, Oklahoma 73019

ABSTRACT Multiple radiocarbon ages of -humus fully documented only during the past few years samples from the Canyon Creek trenches and even though Harlton (1951) originally mapped Stratigraphic relations and radiocarbon the ponded-alluvium sites show that the last the fault in rocks in the late 1930s. A ages of deposits exposed in several trenches surface faulting occurred 1,200-1,300 yr ago. prominent scarp on late Quaternary deposits is and excavations help to establish the timing, Limited geologic evidence, however, indi- evidence that the fault may have generated large sense of slip, and style of the deformation that cates a long-term recurrence interval on the in the geologically recent past resulted from late Holocene surface faulting order of 100,000 yr or more. (Donovan and others, 1983; Ramelli and on the in southwestern Okla- The youthful surface faulting compared to Slemmons, 1986; Ramelli, 1988) and might be homa. The eastern half of the scarp is formed the apparently long recurrence interval pre- capable of doing so in the future. The presence on relatively ductile Hennessey sents a difficult problem for regional seismic- of a possible major seismogenic fault in south- Shale and Quaternary alluvium, whereas the hazard assessments. Hazard assessments that western Oklahoma raises questions about the western half is formed on well-lithified, rela- rely on the long-term slip rate might seriously presumed tectonic stability and the potential for tively brittle Permian Post Oak Conglomer- underestimate the hazard if the behavior of damaging earthquakes in the entire southern ate in the Slick Hills. the fault is characterized by a temporal clus- midcontinent region. At Canyon Creek on the eastern half of the tering of events, and if the late Holocene sur- Gilbert (1983a, 1983b) first drew attention to scarp, the shale and alluvium in two trenches face faulting signals the beginning of a period the tectonic significance of the scarp on Quater- are deformed mainly by monoclinal warping. of frequent faulting. Conversely, if strain ac- nary deposits along the Meers fault. Subsequent These trenches contain stratigraphic evidence cumulates steadily on the Meers fault and is studies have shown that some of the relief on the of one surface-faulting event that produced released regularly over time intervals of scarp is the result of late Holocene surface fault- about 3 m of throw. At this site, the amount 100,000 yr or more, then the hazard may be ing (Crone and Luza, 1986; Madole, 1986, of throw in middle Holocene and middle low because much of the stored strain was 1988). Despite this new information on the re- deposits is similar. Lateral dis- released only about 1,000 yr ago. Improved cency of faulting, the amount, sense, and recur- placement is difficult to detect in these -hazard assessments in much of rence of Quaternary movement on the fault trenches, most likely because of plastic de- the central and in stable intra- remain controversial (Ramelli and Slemmons, formation in the shale and alluvium. plate settings worldwide require a better un- 1986; Ramelli, 1988; Tilford and Westen, 1985; In contrast, trenches and excavations on derstanding of the long-term and short-term Westen, 1985). This paper describes our studies the western half of the scarp show that the behavior of seismogenic intraplate faults. to help resolve this controversy by clarifying the Holocene surface faulting produced at least Quaternary history of movement on the fault as much lateral as vertical displacement At INTRODUCTION and the style of deformation. We discuss the two sites, the scarp has dammed small gullies results of a trenching study (Crone and Luza, and ponded fine-grained alluvium upslope The southern midcontinent region is widely 1986; Luza and others, 1987) and other efforts from the scarp. The channels of the gullies at regarded as part of the tectonically stable central to quantify the amount of Holocene displace- these ponded-alluvium sites have been separ- interior of the United States. The dispersed, rela- ment on the fault. These investigations are some ated 3-5 m left-laterally since they were tively weak seismicity in the region can only of the first detailed studies of the late Quaternary dammed. The lateral displacement on the gul- generally be related to specific geologic struc- history of the fault. Future studies will certainly lies is 3.3 to 1.6 times as much as the vertical tures (Nuttli, 1979; Algermissen and others, revise details of this history. displacement. In a pit excavated into the col- 1982; Gordon, 1988), and until recently, Qua- luvium on the downthrown side of the scarp, ternary surface faulting had not been confirmed GENERAL GEOLOGIC SETTING subhorizonta! striae on conglomerate clasts (Howard and others, 1978). Thus, seismic along the fault plane provide evidence of source zones in the midcontinent have been de- The geologic history of south-central and nearly pure strike-slip movement. The age of fined mainly by the location of historic earth- southwestern Oklahoma has been dominated by the striae is unknown, but they are believed quake epicenters (Coppersmith, 1988) with a the presence of the southern Oklahoma aula- to be Quaternary in age because it is unlikely limited contribution from geologic and geophys- cogen—a deep, elongate, west-northwest-trend- that such delicate striae could be preserved in ical data. ing trough that extends into the craton from the soluble carbonate rock in a near-surface The geologic and geomorphic evidence of southern margin of North America (Ham and weathering environment for many hundreds Quaternary movement on the Meers fault in others, 1964; Ham and Wilson, 1967; Hoffman of thousands of years. southwestern Oklahoma (Fig. 1) has been care- and others, 1974; Walper, 1977). The

Geological Society of America Bulletin, v. 102, p. 1-17, 17 figs., 1 table, January 1990.

1 2 CRONE AND LUZA

may be part of a larger west-northwest-trending subsidence (Ham and others, 1964; Wickham, deep parts of the basin (Ham and Wilson, tectonic zone named the "Wichita megashear" 1978). 1967). Clastic debris eroded from the uplift col- or "Wichita lineament," which extends from From Early into Permian lected in the (Johnson and Den- south-central Oklahoma to western Colorado time, block faulting, uplift, and syntectonic sed- ison, 1973) during Pennsylvanian and Early (Budnik, 1986; Larson and others, 1985). imentation occurred in the aulacogen (Ham and Permian time. When this sedimentation ceased, The early history of the aulacogen was char- Wilson, 1967; Wickham, 1978; Budnik, 1986). the Anadarko basin was filled with more than acterized by rifting, deep-seated faulting, and During this time, a 700-km-long network of 11 km of sedimentary rocks (Ham and Wilson, bimodal magmatism (Wickham, 1978; Gilbert, faults formed across south-central Oklahoma 1967), making it one of the deepest basins in 1982). In late Precambrian or Early and the Panhandle. The location and North America. time, large gabbroic bodies (Raggedy Mountain west-northwesterly orientation of these faults The Meers (originally named the "Thomas Gabbro Group) intruded the upper crust, and were probably controlled by zones of crustal fault" by Harlton, 1951) and the Mountain basalt (Navajoe Mountain Basalt-Spilite Group) weakness that developed during the initial - View faults (Harlton, 1963; Ham and others, erupted onto the surface. This magmatism was ing. These faults separate deep Paleozoic basins 1964) are two of the principal faults in the followed, first by erosion, and later by eruption from adjacent uplifts throughout Oklahoma Frontal Wichita fault system. Other major faults of the Carlton Rhyolite Group and intrusion of (Fig. 1); the throw on individual faults locally (Fig. 1) include the Blue Creek Canyon the Wichita Granite Group in Middle Cambrian exceeds 7.5 km (Ham and Wilson, 1967). (Donovan, 1982), the Cement (Harlton, 1960), time. In southwestern Oklahoma, this network of the Cordell (Harlton, 1972), and the Duncan- Subsidence and basin filling dominated the faults was first mapped by Harlton (1951,1963, Criner (Ham and others, 1964) faults. The next stage of the aulacogen's history. From Late 1972) and named the "Frontal Wichita fault amount of Paleozoic-age throw on fault system Cambrian to Late time, the Ana- system." The frontal fault system is the structural and on individual faults is poorly known. Ham darko basin subsided continuously and was boundary between the Wichita-Amarillo uplift and others (1964) estimated 6.4 km of net throw filled with as much as 6 km of mostly nonclastic to the southwest and the Anadarko basin to the on the frontal fault system, whereas Powell and sediment. Although there is little direct evidence, northeast. The cumulative throw across the fault Fisher (1976) estimated 9.1 km of throw on the many of the faults that formed during the initial system accounts for most of the more than 12 Meers fault. rifting probably were reactivated during this km of structural relief between the uplift and In addition to the vertical displacement, struc- tural and stratigraphic relations have been cited to support varying amounts of Paleozoic left slip on selected faults related to the aulacogen (Moody and Hill, 1956; Tanner, 1967; Thor- man, 1969; Wickham, 1978; Butler, 1980; McLean and Stearns, 1983; Harding, 1985; Budnik, 1986; Cox and VanArsdale, 1988). The total lateral displacement on the entire system is difficult to measure and therefore is controver- sial. For example, Viele (1986) and Budnik (1986) argued for more than 120 km of left- lateral displacement along the entire system, whereas McConnell and others (1986) and McConnell (1987) considered the lateral-slip component to be secondary to the dip-slip com- ponent. The amount of lateral displacement on individual faults is also controversial. Tanner (1967) and Wickham (1978) cited stratigraphic evidence of about 65 km of left-lateral dis- placement on the Washita Valley fault (Fig. 1), yet Cox and VanArsdale (1988) and Perry (1989) favor only about 5 km of lateral dis- placement. The pattern and orientation of folds and faults along the Washita Valley (Harding, 1985) and other faults of the Frontal Wichita fault system (Moody and Hill, 1956; Butler, Prominent scarp on Meers fault Fault-Bar and ball on downthrown side, arrows 1980; Donovan and others, 1983) are typical of indicate sense of lateral slip on selected fault those produced by strike-slip faulting. Despite the diverse opinions, there is enough evidence to Figure 1. Map showing selected basins, uplifts, and faults in southwestern Oklahoma. The show that some left-lateral displacement oc- Frontal Wichita fault system separates the Anadarko basin from the Wichita-Amarillo uplift. curred on many faults in the aulacogen during Major faults in this system are labeled as follows: Meers, M; Blue Creek Canyon, BCC; late Paleozoic time. Mountain View, MV; Cement, CE; Cordell, CO; and Duncan-Criner, D-C. Faults on the south flank of the uplift are labeled as follows: Waurika-Muenster, W-M; North Fork, NF; Altus, The history of post-Paleozoic movement on A; and Burch, B. Other structural features include the Washita Valley fault (WVF) along the the faults along the Wichita-Amarillo uplift is Arbuckle uplift, the Oklahoma City uplift (OCU), and the McClain County fault zone (MCFZ). difficult to assess in Oklahoma, because few HOLOCENE SURFACE FAULTING ON THE MEERS FAULT, OKLAHOMA 3 rocks younger than Permian age are preserved in and prominent on the resistant conglomerate cal and instrumental earthquakes are useless in the region. In the Panhandle region of Texas, (Fig. 3), whereas it is more rounded and assessing the seismic potential of the fault. however, faulted Triassic rocks and syntectonic subdued on the relatively nonresistant shale. The Meers and other faults in the Frontal deposits within the late Miocene Ogallala For- Recurrent Quaternary movement on the fault Wichita fault system seem to be favorably mation are cited as evidence that selected faults is evident from the geomorphic expression of the oriented for movement in the contemporary along the uplift were reactivated in Mesozoic scarp on the Post Oak Conglomerate (Crone, regional stress field. The maximum regional hor- and Cenozoic time (Budnik, 1987). 1987; Ramelli, 1988). The highest scarps on the izontal compressive stress inferred from well- The seismotectonic significance of faulted conglomerate are generally from two to three bore breakouts (Dart, 1987) and in situ stress Quaternary deposits along the trace of the Meers times higher than the scarps formed on latest measurements (Zoback and Zoback, 1980) is fault remained unappreciated for decades. In Quaternary alluvium in the valleys of nearby oriented from northeast to east-northeast, which their study of wrench-fault , Moody ephemeral streams. In addition, some of the favors left-lateral movement on west-northwest- and Hill (1956) noted the presence of a scarp on highest scarps on the conglomerate have over- oriented fault planes. In this stress regime, many Quaternary deposits but did not discuss its tec- steepened segments near their mid-points (Fig. faults in the Frontal Wichita fault system are tonic implications. Gilbert's (1983a, 1983b) ob- 4) that may be the most recent surface rupture favorably oriented, yet the Meers is the only servations of the scarp formed on Quaternary superposed on an older, partly degraded scarp. fault that has documented late Quaternary deposits stimulated studies that confirmed youth- These oversteepened segments and the higher movement. These observations raise two ques- ful (Holocene) movement on the fault (Madole, scarps on older geologic units are good evidence tions about seismic hazards in the region: (1) is 1988; Crone and Luza, 1986). Additional of repeated movement during Quaternary time. there unrecognized evidence of Quaternary studies have led to speculation about possible Despite the geologic evidence of recent movement on other faults in the Frontal Wichita reactivation of other faults in the Frontal Wich- movement, the Meers fault is historically aseis- fault system, or (2) is the Meers fault uniquely ita fault system (Nielsen and Stern, 1985; Cox mic (Lawson, 1985; Luza and others, 1987). In susceptible to movement? Accurate regional and VanArsdale, 1988). fact, only a few widely scattered earthquakes seismic-hazard assessments depend on determin- spatially coincide with the entire Frontal Wich- ing which of these possibilities is correct. CHARACTERISTICS OF THE SCARP ita fault system (Gordon, 1988). Thus, histori- A first step in evaluating these two possibili-

The scarp along the Meers fault trends N60°W (Fig. 2) and is extremely linear despite 98° 30' variations in the topography, which indicates that the subjacent fault must be nearly vertical (Fig. 3). The conspicuous scarp is continuous for 26 km, but recent low-sun-angle photography shows that it may be as long as 37 km (Ramelli and Slemmons, 1986; Ramelli and others, 1987; Ramelli, 1988). In contrast, the geophysical ex- pression of the fault is about 70 km long (Slem- mons and others, 1985), whereas it can be traced for 83-109 km using subsurface data (Harlton, 1963). Near the center of the promi- nent 26-km-long scarp, the maximum vertical displacement is almost 5 m (Ramelli and Slem- mons, 1986; Ramelli and others, 1987). In con- trast to the net down-to-the-north throw during 34° 45' Paleozoic time, the scarp shows that Quaternary displacements have been down to the south. Displaced stream channels and topographic ridges show that Quaternary movements have also had a significant component of left slip. Accurately measuring this lateral component is [ | Permian Hennessey Shale Cambrian granite, gabbro, difficult, but Ramelli and Slemmons (1986) and and rhyolite, undifferentiated Ramelli and others (1987) have estimated that rs-oi Permian Post Oak Conglomerate the lateral slip is 3 to 5 times greater than the Selected faults, dashed where vertical displacement. Cambrian and -- inferred; hachured on sedimentary rocks, downthrown side of Meers The scarp is formed on two rock types, the undifferentiated Post Oak Conglomerate and the Hennessey Shale (Fig. 2), both Permian in age (Havens, Figure 2. Generalized geologic map in the area of the Meers fault scarp (modified from 1977). The Post Oak Conglomerate, which is Havens, 1977). Blue Creek Canyon fault is BCC. PA/CP is location of ponded-alluvium sites exposed in the Slick Hills, is a well-indurated and two of three pits in colluvium. CP is location of the third pit-in-colluvium site. See text for limestone-pebble conglomerate in a limestone explanation. Figure 3 is aerial photograph showing ponded-alluvium sites and the easternmost matrix. The Hennessey Shale is an easily eroded, pit in colluvium. Oblique aerial photograph and surfirial geologic map of Canyon Creek trench generally red shale. The scarp is sharp, linear, site (CCT) are shown in Figures 5 and 6, respectively. 4 CRONE AND LUZA

ties is to clarify the Quaternary behavior of the Meers fault. To this end, two trenches were ex- cavated across the scarp near Canyon Creek (Fig. 5). The trenches provide valuable informa- tion about the style of near-surface deformation and the age of the most recent faulting event. They also offer some insight into the recurrence of surface faulting. Our other studies have fo- cused on determining the amount and sense of late Quaternary slip on the fault.

DESCRIPTION OF THE CANYON CREEK TRENCHES

The two trenches are located in the SWV4SW/4 sec. 24, T. 4 N., R. 13 W, Co- manche County, Oklahoma. At the trench sites, the scarp strikes N64°W. The trenches were ex- cavated in Quaternary deposits of significantly different ages. Trench 1 was excavated in the youngest Holocene deposits known to be dis- placed by the fault, whereas trench 2 was exca- vated in deposits believed to be Pleistocene in age (Fig. 6).

WPA Stratigraphy of Canyon Creek Trench 1 (CCT-1) Trench 1, 22 m long and —2.5 m deep, was excavated about 150 m east-southeast of Can- yon Creek, a major drainage in the area (Fig. 5). The scarp is about 2.4 m high, has a surface offset of about 2.2 m, and has a maximum slope angle of 9°20' (Fig. 7). The scarp height and surface offset measured from the profile in Fig- ure 7 are minimum estimates of the throw, be- cause the stratigraphy in the trench shows that the topographic relief of the scarp has been re- duced by post-faulting alluviation on the down- thown side of the scarp. The deformed sediments in trench 1 are the upper part of the Browns Creek Alluvium (Ma- dole, 1986, 1988), which is probably mid- to early Holocene in age. The East Cache Allu- vium (Madole, 1986, 1988), believed to be la- test Holocene in age, is not deformed or faulted at Canyon Creek or at other nearby drainages. About 30 m east of the trench, a small ephem- eral stream (Fig. 6) has incised a shallow gully into the scarp and deposited a small alluvial fan at the base of the scarp. At the bottom of the trench, weathered Hen- nessey Shale (unit 3a, Fig. 8) was exposed on both sides of the fault. The shale is a soft, plastic, Figure 3. Low-sun-angle aerial photograph of the northwest-trending Meers fault scarp red (2.5 YR 4/6)1 slightly silty clay in which the showing the linear trace and expression in the Post Oak Conglomerate. Sites discussed in text are labeled as follows: easternmost pit in colluvium, CP; west-ponded-alluvium site, WPA; and 'Color descriptions in this report are based on the east-ponded-alluvium site, EPA. Photograph courtesy of A. R. Ramelli and R. A. Whitney, Munsell Soil Color Chart (Munsell Color Co., Inc., University of Nevada, Reno. Baltimore). All colors are for dry samples. HOLOCENE SURFACE FAULTING ON THE MEERS FAULT, OKLAHOMA 5 primary bedding has been obliterated by near- surface weathering. Local spots of reduced iron Northeast Southwest produce mottled orange, yellow, and gray col- ors. The most extensive area of iron reduction is adjacent to the fault where the shale is light gray (5Y7/2) and very calcareous (unit 3b). The Browns Creek Alluvium (unit 2, Fig. 8) lies on the shale. The alluvium is a generally fining-upward sequence of lenticular, interfin- gered pebble-cobble gravel (unit 2e), sand (unit 2c), silt (unit 2b), and clay (unit 2d) that grades upward into a strong brown (7.5 YR 5/6) clayey silt (unit 2a). The basal gravel (unit 2e) is matrix supported, strong brown (7.5 YR 5/6) to yel- lowish red (5 YR 4/6), and contains mostly rhyolite with rare limestone and sandstone clasts Figure 4. Topographic profile of Meers fault scarp on the Post Oak Conglomerate. The 5-10 cm in diameter. The interfingered sand oversteepened segment near midpoint of scarp may be evidence of recurrent Quaternary (unit 2c), silt (unit 2b), and clay (unit 2d) are movement. Scarp height (SH) and surface offset (SO) are dimensions defined by Bucknam and strong brown (7.5 YR 5/6) to yellowish brown Anderson (1979) and shown graphically by vertical arrows. Dots on profile show ends of (ION? 5/6), massive, calcareous, and mottled individual profile segments measured in the field. Profile was measured at westernmost pit-in- with 2-3 mm manganese concretions. Units coUuvium (CP) site shown in Figure 2. 2b-2e are relatively high-energy fluvial deposits of Canyon Creek. The overlying clayey silt (unit on the upper part of the scarp and depositing it vium; the amount of brittle deformation (crack- 2a) is massive, calcareous, and also mottled with along the base. ing and displacement on faults) is minor. A manganese concretions. It is a relatively low- 2-m-wide zone of brittle deformation (faulting) Style of the Deformation in Canyon Creek energy, flood-plain deposit that probably con- is located near the midpoint of the scarp and is Trench 1 tains some loess. The loess content of unit 2a bounded by two faults, the one on the southwest probably increases upward, and the upper part Nearly all of the deformation exposed in the has a reverse separation, and the one on the may contain a large amount of loess. trench is from flexing and warping of the allu- northeast has a normal separation (Figs. 8 and On the upthrown block, a weak soil com- posed of an A horizon and a calcareous C hori- zon has formed on the silt (unit 2a). The uppermost part of unit 2a has been reworked into the massive, noncalcareous, brown to dark brown (7.5 YR 4/4) A horizon (unit la) of the modern soil. Calcium carbonate leached from the A horizon has accumulated in the lower part of the clayey silt (unit 2a) and formed stage 1+ soil carbonate morphology (Gile and others, 1966; Birkeland, 1984, p. 358). After deposition of the Browns Creek Allu- vium, movement on the fault warped the allu- vium into a monocline. Tension cracks and faults with small displacements formed near the crest of the monocline. This deformation is de- scribed in the following section. After the scarp formed, the nearby ephemeral stream (Fig. 6) apparently flowed along its base, eroded much of the clayey silt (unit 2a) from the downthrown side of the scarp, and deposited a sequence of interbedded fine gravel, sand, silt, and clay (unit 1). These fluvial deposits (units lb and lc) generally fine upward and interfinger with and grade into a thick, dark brown (7.5 YR 3/2), Figure 5. Oblique aerial photograph of Canyon Creek trench sites on the Meers fault. View cumulic A horizon (upper part of unit la on to the north-northwest. Trench sites are shown as numbered lines that correspond to the downthrown side). The cumulic A horizon is number of the trench in text. Trench sites are labeled CCT in Figure 2. Road along the right derived mainly from sheetwash and downslope edge of the photograph is State Highway 58. Photograph courtesy of D. B. Slemmons, Univer- creep removing A-horizon material from the soil sity of Nevada, Reno. 6 CRONE AND LUZA

98° 31" 45" I I Residuum, colluvium, and sheetwash, undifferentiated; locally contains bedrock FPl East Cache Alluvium Fault-related fan alluvium I | Browns Creek Alluvium Eiiiii Kimbell Ranch Alluvium Po"S9J Porter Hill Alluvium Contact, dashed where inferred —V Fault, dotted where inferred; ball on downthrown side 1 1 • Trench, numbered as discussed in text; not to scale 34° 48' "

Figure 6. Map of surficial deposits near the Canyon Creek trench sites (modified from Madole, 1988). Sites are labeled CCT on regional map in Figure 2. See Madole (1988) for description of alluvial deposits.

sey Shale (unit 3a). Similarly, under the silt, a small pod of gravel (unit 2e) has been down- dropped at least 0.4 m into the shale. Thus, the entire stratigraphic section of Browns Creek Al- luvium has been dropped downward in this fault zone. The amount of dip slip (0.1 m on the top of 9). These faults are secondary features that (N64°W) of the scarp. The zone of reverse fault- the Hennessey Shale) on this fault is too small to formed in response to the warping, and they ing is narrow near the bottom of the trench and explain the amount of downward movement of may be similar to bending-moment faults wider upward. The reverse displacement across the gravel (0.4 m), silt (0.8 m), and the A- (Yeats, 1986). The displacement on these faults this zone probably results from localized near- horizon material (1.15 m). The best explanation in the trench accounts for only 8% to 13% of the surface compression during formation of the for these relations is that a sliver of Browns total vertical deformation across the scarp. Be- monocline (Yeats, 1986). In this zone, a finger- Creek Alluvium collapsed into an open fissure cause they are secondary features, the sense of like pod of A-horizon material (unit Id) extends as the monocline formed. The resulting vertical displacement on these faults may not directly through the clayey silt (unit 2a) and into the displacement of the alluvial units in the sliver reflect the sense of displacement on the subja- underlying gravel (unit 2e). This pod extends was greater than the throw on the top of the cent Meers fault. 1.15 m below the base of the soil horizon (unit shale. This collapse interpretation is supported The fault with reverse separation has only 0.1 la) from which it was derived. Like the A- by the lack of internal disruption and shearing of m of throw on the top of the Hennessey Shale horizon material, a pod of clayey silt (unit 2a) alluvial units in the sliver and the sharp contacts (Fig. 9). It strikes N59°W and dips 49°NE. This extends downward about 0.8 m through the between the sliver and the adjacent alluvium, strike is compatible with the local trend gravel (unit 2e) and into the underlying Hennes- which shows that there was minimal differential

Northeast Southwest SH: 2.4 m

METERS

Figure 7. Topographic profile of scarp at Canyon Creek trench 1. Shaded area on the profile shows superposed position and approximate dimensions of trench 1. Figure 8 is map of trench wall. Scarp height (SH), surface offset (SO), and maximum slope angle (0) are dimensions defined by Bucknam and Anderson (1979); Figure 4 shows graphic representation of SH and SO. Dots on profile show ends of individual profile segments measured in the field. Stratigraphic throw measured in the trench was 2.7-2.8 m. HOLOCENE SURFACE FAULTING ON THE MEERS FAULT, OKLAHOMA 7

Northeast Southwest METERS

4 6 8 10 12 14 16 18 20

Unit 1: Holocene Fault-related and Unit 2: Holocene Browns Creek Unit 3: Permian Hennessey Shale Post-faulting Deposits Alluvium

ia Silty fine sand, sandy silt, and 2a Massive clayey silt :3a: Red, plastic shale clayey silt

Pebble gravel, sandy gravel and [J2bjj Clayey silt Gray, bleached shale coarse sand

Stratigraphie contact, dashed where plclSj Clayey silt 2CY/{ Clayey sand "— gradational or subtle jA Fault, dashed where inferred; arrows Sandy silt; A-horizon material ty show general sense of movement filling earthquake-induced cracks 2d Silty clay Top of Browns Creek Alluvium after erosion by ephemeral stream ® Selected feature discussed in the text H Location of radiocarbon sample

Figure 8. Simplified map of wall of Canyon Creek trench 1. Alluvium exposed in the trench is part of the Browns Creek Alluvium (Madole, 1988). Some stratigraphic contacts are shown within single lithofacies units (for example, unit 2e); these contacts are based on subtle lithologic variations observed in the field.

Northeast Southwest movement at these contacts. Finally, the pro- ^l-'JM P " posed fissure is nearly perpendicular to the bed- SPOIL ding in the alluvium, as would be expected for an extensional crack. The fault with normal separation (at 11 m on Fig. 8) probably formed in response to extension near the crest of the monocline (Yeats, 1986). This near-vertical, down-to-the-south fault ver- 1570 cal. tically displaces both the top of the shale and the «H gravel by about 0.1 m. An open fissure, now filled with A-horizon material (unit Id in Fig. 9), formed at the surface above this fault.

Figure 9. Photograph of warped and faulted strata in Canyon Creek trench 1. View is east wall of trench. Trench is about 1.8 m deep near the faults. Figure 8 is a map of the wall of the trench; numbers and letters cor- respond to stratigraphic units labeled on map of trench wall. 8 CRONE AND LUZA

Another open fissure formed between the Age of Faulting in Canyon Creek Trench 1 ephemeral stream occurred shortly after the normal and reverse faults and is now marked by scarp formed. a small, triangular-shaped pod of gravel that col- Two radiocarbon dates on soil humus from These 14C ages are maximum ages for when lapsed into the underlying shale (Fig. 9) and a trench 1 (Fig. 8) show that the faulting at this the scarp formed because they are on soil narrow finger of A-horizon material (unit Id) site is late Holocene in age. A sample of the humus. The humus in these two samples did not that filled the fissure near the surface. A-horizon material in the fissure adjacent to the have a radiocarbon age of zero years when it The total stratigraphie throw measured in the reverse fault (Figs. 8 and 9) has a l4C age of was deposited. Ideally, the organic components trench was 2.7 to 2.8 m, but this is a minimum 1,570 cal. yr (Table l)2. This soil material fell in a soil at the surface achieve an equilibrium value because the fluvial gravels (unit 2e) on the into the fissure when the scarp formed, and so its between the rate at which they form and the rate downthrown side were still tectonically tilted age should be similar to the time of faulting. The at which they are destroyed by chemical and where they extended below the bottom of the second radiocarbon date is on soil humus from biological attack. For this simple discussion, we trench (Fig. 8). A distinctive, dark layer in the the basal fluvial clayey silt (unit lc in Fig. 8) that divide the soil organic material into two major silty clay (unit 2d) on both walls of the trench was deposited at the toe of the scarp by the components: (1) a short-lived component (pro- (feature A near meter 19 in Fig. 8) had a 17°SW ephemeral stream shortly after faulting. This teins, amino acids, and so on) that is dissolved, dip. If the trench had been extended farther humus is locally derived organic material that oxidized, or decomposed relatively quickly southwest (perhaps several meters) to where the was concentrated in the fine-grained silt. This (perhaps a few years to decades) and (2) a long- beds were undeformed, the total measured strat- sample has a 14C age of 1,646 cal. yr, which, lived component, soil humus, that is compara- igraphie throw would probably be 3 m or more. within the limits of the analytical error (Table tively insoluble and chemically stable. The The deformation at this site is dominated by 1), is comparable to the age of the soil material radiocarbon age of modern (assumed to be warping, which means that the scarp never had in the fissure. The similarity of these ages is evi- at equilibrium) may range from hundreds to a a large free face. Without a prominent free face, dence that the scour and backfilling by the few thousand years (Paul and others, 1964; Ger- 14 the degrading scarp did not generate colluvial asimov, 1971). The C age of a modern soil is a deposits that are commonly used to identify in- combined measure of the age of both the short- dividual surface-faulting events. The stratigraph- 2A11 radiocarbon-dated soil samples were pre- lived and long-lived components. In a buried ie relations between the faulted Browns Creek treated to remove inorganic carbonate and soluble or- soil, the short-lived components have been de- 14 Alluvium and postfaulting fluvial deposits (Fig. ganic contaminants. Radiocarbon ages in the text are stroyed, and the C age is largely based on the dendrochronologically calibrated radiocarbon ages, 8), however, show strong evidence of one age of the soil humus. The antiquity of modern which we cite as cal. yr. Table 1 lists all ages and soils primarily results from the slow destruction surface-faulting event. briefly describes the calibration process.

TABLE I. SUMMARY OF SELECTED RADIOCARBON DATES ON THE MEERS FAULT

Field site Radiocarbon age* Calibrated age^ Sample description and comments (yr) and (cal. yr) laboratory no. with two a uncertainty limits

Canyon Creek 1,660 ± 50 1,570 ± 120 Humus from soil that fell into open crack in scarp. Needs AMRT§ trench 1 (DIC-3180) correction. Closely dates time of scarp formation. 1,730 ± 55 Humus from soil in basal part of postfaulting deposit. (DIC-3266) Needs AMRT correction.

Canyon Creek 1,360 ± 50 1,290* Humus from buried soil A horizon located -4 m downslope from scarp. 110 trench 2 (DIC-3183) Needs AMRT correction. Postdates faulting. 250 ± 55 Humus from A horizon of modern soil located ~4 m downslope from scarp. (DIC-3324)

West-ponded 385 ± 40 Humus from modern A horizon at depth of 12 cm in test pit. alluvium (P11T-0050)

710 ± 30 Humus from depth of 38 to 40 cm in test pit. (PITT-0051)

1,090 ± 70 Humus from depth of -65 cm in test pit. Upper part of reddish-brown (prrr-0047) silt. 1,040 ±40 Humus from depth of -90 cm in test pit. Lower part of reddish- (PITT-0048) brown silt. 1,690 ± 45 Humus from depth of -120 cm in test pit. Postdates faulting. (PITT-0049) Needs AMRT correction.

East-ponded 1,225 ± 75 I.™:}« Humus from depth of 77 to 88 cm in south trench. Middle of reddish- alluvium (PITT-0338) brown silt.

1,480 ± 35 1.354 Humus from depth of 137 to 147 cm in south trench. Middle of brown (PITT-0339) silt beneath reddish-brown silt. 1,640 ± 50 Humus from depth of 162 to 172 cm in south trench. Lower part of I'539-!529 (PITT-0340) brown silt beneath reddish-brown silt. Postdates faulting. Needs AMRT correction. 1,865 ± 25 1,816^ Humus from depth of 190 to 200 cm in south trench. Interpreted as (P1TT-0114) channel fill that predates faulting. Needs AMRT correction.

"Radiocarbon age is the age reported by the radiocarbon laboratory. The cited uncertainty limits are for analytical uncertainties and are not corrected for isotopic fractionation. ^Calibrated age is dendrochronologically corrected for atmospheric variations in '^C production using the computer program of Stuiver and Reimer (1986). This correction converts conventional radiocarbon age to calibrated calendar years. §AMRT refers to average mean residence time for humus in a soil. See text for explanation. HOLOCENE SURFACE FAULTING ON THE MEERS FAULT, OKLAHOMA 9 of soil humus compared to the rapid destruction Browns Creek Alluvium as defined by Madole On the upthrown side of the fault, the gravels of less resistant components. The average time (1988). (units 2c-2e) are overlain by as much as 60 cm that humus resides in a soil is called the "appar- of clayey sand (unit 2b) and sandy silt (unit la; ent mean residence time" (AMRT), and it varies CANYON CREEK TRENCH 2 (CCT-2) modern A horizon) that may be largely aeolian. with climate. Subtracting the AMRT from the On the stable surface on the upthrown block, a radiocarbon ages of soil-humus samples pro- Stratigraphy of Canyon Creek Trench 2 soil with an argillic B horizon (unit 2b) has vides a better estimate of the time when the formed on the alluvium. This degree of soil de- scarp formed. Canyon Creek trench 2, located about 200 m velopment and the elevation of the alluvium The AMRT of the humus in these samples is east-southeast of trench 1, was excavated in Por- higher above the modern channel of Canyon unknown, but we use 300 yr as a reasonable ter Hill Alluvium (Fig. 6), which is probably Creek are evidence that the Porter Hill Alluvium estimate based on three lines of evidence. First, middle Pleistocene in age (Madole, 1986,1988). is substantially older than Browns Creek Allu- in his study of the Meers fault, Madole (1988) The scarp at this site is 3.4 m high, has a surface vium (Madole, 1988), which was exposed in estimated an AMRT of several hundred years offset of 3.0 m, and a maximum slope angle of Canyon Creek trench 1. (-100 to 500) by comparing radiocarbon dates 9° (Fig. 10). On the downthrown side of the fault, a buried of soil humus and charcoal fragments in fault- Bedrock was exposed only on the upthrown soil, composed of a B and an A horizon (units related deposits at Canyon Creek. Second, the side of the fault in the 19-m-long trench (Fig. 2b and 2a, respectively), define the prefaulting modern A horizons at trench 2 (discussed next) 11). Most of the bedrock was Hennessey Shale ground surface. The soil is now buried by collu- and at the west-ponded-alluvium site (discussed (unit 3a), but an enigmatic block of light brown vium derived from the fault scarp and the mod- below in this report) have radiocarbon ages of dolomite (unit 3b) was exposed adjacent to the ern A horizon (units la, lb, lc, Id). Units Id 308 cal. yr and 432 cal. yr, respectively. Al- fault zone. A high water table prevented deepen- and lc are interpreted as relatively intact frag- though these A horizons may contain some 14C ing the trench to bedrock on the downthrown ments of the buried B and A horizons, respec- contamination from nuclear testing, their ages side. Nevertheless, stratigraphic units within the tively, that were thrust onto the prefaulting are consistent with an estimated AMRT of 300 Porter Hill Alluvium (unit 2) could be traced ground surface and partially overridden by the yr. Third, at the Lubbock Lake site on the High across the fault zone. fault-zone gravel (unit le). These fragments are Plains of Texas, a surface soil and a soil buried The Porter Hill Alluvium in this trench is a now buried by younger colluvium (units lb, la) by alluvium that contains historical material 2.5-m-thick sequence of fluvial pebble and cob- shed off the scarp. The soil on these postfaulting have radiocarbon ages of 160 ± 60 and 220 + ble gravels (units 2c, 2d, 2e in Fig. 11) that rests colluvial deposits (units lb, la) is slightly less 50 yr, respectively (Holliday and others, 1983). on weathered Hennessey Shale. The red to dark developed than the buried soil. The AMRT may vary by 100 yr or more be- red (2.5 YR 4/6), massive to crudely stratified tween individual samples, but we use 300 yr as a gravel is subdivided on the basis of the amount Style of the Deformation in Canyon Creek working value. After correcting for AMRT, the of interstitial sand, silt, and clay. In the upper- Trench 2 two radiocarbon ages from samples in trench 1 most unit (2c), the gravel is completely plugged show that the scarp formed about 1,200 to with matrix; successively deeper units (2d, 2e) Stratigraphic units in the trench end against a 1,300 yr ago. contain progressively less matrix. We attribute fault zone (unit le) that has a reverse sense of The weak soil developed on the warped allu- much of the matrix to soil-forming processes displacement. The fault zone dips 56°NE and vium is supporting evidence that the deforma- and postdepositional infiltration of sand, silt, and strikes N64°W, which is identical to the region- tion is geologically youthful. On the upthrown clay into the gravel. The boundaries between the al strike of the scarp. The Porter Hill Alluvium side of the fault, the soil has only an A and C units are typically irregular and gradational; in the fault zone is dark red (2.5 YR 3/6), horizon. This weak development implies that therefore, changes in the thickness of the strati- massive, poorly sorted, matrix-supported gravel. the alluvium is Holocene in age and probably graphic units across the fault zone are not consid- Discrete shear planes were impossible to identify correlates with the younger alluvial unit in the ered to be valid evidence of lateral slip. in the fault zone because of the coarse-textured

Northeast Southwest SH: 3.4 m

METERS

Figure 10. Topographic profile across scarp at Canyon Creek trench 2. Shaded area on the profile shows superposed position and approximate dimensions of trench 2. Figure 11 is map of wall of trench. Scarp height (SH), surface offset (SO), and maximum slope angle (0) are dimensions defined by Bucknam and Anderson (1979); Figure 4 shows graphic representation of SH and SO. Dots on profile show ends of each profile segment measured in the field. Stratigraphic throw measured in the trench was 3.2-3.3 m. 10 CRONE AND LUZA

Northeast METERS Southwest 3 5 7 9 11 13 15 17 19

Unit 1 : Holocene Fault-related and Unit 2: Pleistocene Porter Hill Alluvium Unit 3: Paleozoic Rocks Post-faulting Deposits Sandy silt; buried A horizon that 1a Silty sand; modern A horizon Pi defines pre-faulting ground sur- 3a Permian Hennessey Shale m/à face on downthrown side of fault

Clayey sand; colluvium derived Clayey sand; on downthrown side of 1b 2b Dolomite boulder mainly from unit 2b fault, part of buried B horizon

Peb Stratigraphie contact, dashed where 1c Sandy silt; fragment of unit 2a thrust t^fgc»^' ble-cobble gravel plugged with onto pre-faulting ground surface matrix gradational or subtle

Clayey sand; fragment of unit 2b I»".*:*! Pebble-cobble gravel enriched with •f Fault, dashed where inferred; arrows thrust onto pre-faulting ground [,*.r2dv matrix show general sense of movement surface Mf.' #

Matrix-supported gravel of fault • £ : | Pebble-cobble gravel with abundant Location of radiocarbon sample •1e: B zone !v> matrix

Figure 11. Simplified map of wall of Canyon Creek trench 2. Faulted alluvium exposed in the trench is part of the middle Pleistocene Porter Hill Alluvium (Madole, 1988). gravels, but a few elongate clasts were reoriented (units 2a and 2b) on the prefaulting ground sur- with the estimate of 1,200-1,300 yr from subparallel to the direction of movement. face rests on gravel of the Porter Hill Alluvium. samples in trench 1. The stratigraphie throw measured in the This soil is truncated by the fault zone and is trench was 3.2 to 3.3 m, but this is a minimum buried by a single colluvial unit that is capped PONDED-ALLUVIUM SITES value because the stratigraphie units were still by the modern soil (units la and lb). slightly warped at both ends of the trench (Fig. 11). Nevertheless, the measured throw is similar Age of Faulting in Canyon Creek Trench 2 About 2.9 km northwest of the Canyon to the 3.0 m of throw (surface offset) estimated Creek trenches, surface faulting has disrupted from the scarp profile (Fig. 10). The throw The surface faulting in trench 2 is Holocene in the gradient of three small gullies and ponded across the fault zone is only between 0.5 and 1.0 age. The radiocarbon age of 1,290 cal. yr of the fine-grained alluvium behind a scarp of Post m. Thus, warping accounts for about 70% to buried A horizon (unit 2a) is a minimum date Oak Conglomerate. In two of these gullies, re- 85% (about 2.2-2.8 m) of the deformation at for the time of faulting. This soil was buried by ferred to as the west-ponded-alluvium (WPA) this site. The amount of brittle failure is greater scarp-derived colluvium about 1,000 yr ago and east-ponded-alluvium (EPA) sites (Fig. 3), in the Porter Hill Alluvium than in Browns (after subtracting 300 yr for an AMRT). The we excavated a pair of trenches to the top of the Creek Alluvium (trench 1). The fragments of the sampling site, however, was 2-3 m downslope conglomerate. At each site, the trenches were buried soil that were thrust onto the prefaulting from the fault where, most likely, the soil was parallel to the fault with one trench on either ground surface (units lc and Id) show that there not buried immediately after the faulting event. side of the scarp. The configuration of the bed- was enough brittle failure in the Porter Hill Al- The soil may have remained exposed for a cen- rock surface in the bottom of each trench ap- luvium to form at least a small free face on the tury or more before it was buried by the pro- proximately defines the shape of the channel scarp. grading colluvial wedge. Adding a minimum of eroded into the conglomerate. The vertical and As in trench 1, the stratigraphie relations in a century to the AMRT-corrected time yields an lateral displacement on the fault can be esti- this trench support one surface-faulting event. estimate of 1,100 yr for the time when the scarp mated by comparing the position of the channels On the downthrown side of the fault, the soil formed. This minimum estimate is consistent on either side of the scarp. HOLOCENE SURFACE FAULTING ON THE MEERS FAULT, OKLAHOMA 11

Assumptions about the prefaulting morphol- ogy of the channels make these measurements only general estimates of the displacement. For example, the estimates of throw assume that the channel between the two trenches had no gra- dient prior to faulting. Although geologically un- likely, this assumption permits estimates of the minimum throw. The estimates of lateral dis- placement assume that the thalwegs were orig- inally straight; yet, similar gullies in this drainage basin that are unaffected by the faulting have channel meanders with amplitudes of about 1.5 to 2 m. In spite of their limitations, these esti- mates help to quantify the lateral and vertical displacement in latest Quaternary deposits across the fault. The only other reported dis- placement measurements are those of Ramelli and others (1987) and Ramelli (1988), but their measurements are based on misaligned ridge crests, which are older Quaternary features that record a longer history of fault movement. At the west-ponded-alluvium site, the scarp on Post Oak Conglomerate is 1.1 m high (Fig. 12). The asymmetric distribution of the allu- vium and the mismatch in the bedrock surface on either side of the scarp are evidence of a component of sinistral separation on the fault Figure 12. Map of west-ponded-alluvium site. Bar and ball at base of scarp is on down- (Fig. 13). Unfortunately, the trenches were not thrown side of fault; fault is dotted where concealed. Colluvium is derived from the Post Oak dug across the entire bedrock channel, but a Conglomerate. Stipple pattern shows perimeter of alluvium; distribution of alluvium on either prominent inflection in the bottom of each side of the scarp indicates a component of sinistral slip. Trend of northeast-flowing gully before trench is interpreted as the break in slope be- it was dammed is unknown. Configuration of bedrock surface in north and south trenches is tween the thalweg and the channel margin. shown in Figure 13. Stars show inflection points in buried thalweg margin (seen in trenches) These inflection points serve as a piercing point that are matched to estimate amount of displacement. Location of site is shown in Figure 2; to estimate the vertical and lateral slip of the aerial photograph of site is shown in Figure 3. Stratigraphy in test pit is shown in Figure 16. thalweg (Fig. 13). The thalweg is vertically displaced a min- imum of 0.7 m, assuming no gradient in the thalweg between the two trenches. We calculate a thalweg gradient of 7 cm/m from the depth to WEST EAST bedrock in the test pit and in the south trench 1 1 1 1 1 1 i i i i i i i i (Fig. 12). Projecting this gradient between the NORTH TRENCH SOUTH TRENCH north and south trenches indicates a vertical (Upthrown side of fault) (Downthrown side of fault) separation of 1.5 m. The thalweg is separated 5.0 m left-laterally, 1 GROUND SURFACE GROUND SURFACE assuming the original channel was perpendicular co to the scarp (Fig. 12). Unfortunately, the trend oc 0 0.7 m vertical LiJ of the gully before it was dammed is not obvious separation njyu' Lu -1 from the morphology of the hillslope above the J ponded alluvium. Without knowing this trend, POST OAKSr- / the estimated lateral separation cannot be re- -2 "CONGLOMERATE 5 fined. Nevertheless, the measurements at the left-lateral separa ion west-ponded-alluvium site show much more lat- i i i i i i ili eral than vertical separation. -6 -4 -2 0 2 4 6 8 At the east-ponded-alluvium site (Fig. 14), METERS the fault apparently divides into two strands, be- cause only one scarp is visible on the Post Oak Figure 13. Configuration of bedrock surface in north and south trenches at west-ponded- Conglomerate directly northwest of the ponded alluvium site. Vertical and lateral separation are estimated by matching thalweg margin (stars) alluvium; but southeast of the alluvium, two in each trench. The vertical separation is a minimum value; see text for explanation. Location parallel scarps are about 4-6 m apart (Fig. 14). of trenches is shown in Figure 12. The cumulative scarp height across both strands 12 CRONE AND LUZA

is about 1.9 m. The trenches were located to record the total displacement on both strands. Unlike the west-ponded-alluvium site, here the alluvium on either side of the scarp does not appear to be laterally displaced. The thalweg (the deepest point) in the two trenches provides a piercing point to estimate the amount of latest Quaternary slip on the fault. The vertical displacement on the thalweg is at least 2.1 m (Fig. 15). We have no control points to calculate a thalweg gradient at this site, and so we cannot refine this estimate of the vertical displacement. The estimates of lateral displacement vary depending on the trend of the thalweg that is projected between the trenches (Fig. 14). If the thalweg was originally perpendicular to the fault, then the left-lateral separation is 1.6 m. The outline of the alluvium upslope from the scarp, however, has a trend slightly oblique to the scarp. If this trend (fine dashed-dotted line A in Fig. 14) is projected through the thalweg in the south trench, then the left-lateral component of slip is about 3.4 m, which is the value we prefer. The gully, which is eroded into the bed- 10 m rock above the ponded alluvium, has an even more northeasterly trend. If this trend is pro- • Location of channel thalweg _._ Projection of trend of ponded jected through the thalweg trench (fine dotted alluvium line B in Fig. 14), then the left-lateral compo- Projection of trend of gully nent of slip is about 5.1 m. upslope from scarp Despite uncertainties in the measurements, the thalwegs at both ponded-alluvium sites show Figure 14. Map of east-ponded-alluvium site. Bar and ball at base of scarp is on down- evidence of left-lateral displacement. At the west thrown side of fault; fault is dotted where concealed. Colluvium is derived from the Post Oak site, the ratio of lateral to vertical displacement is Conglomerate. Stipple pattern marks perimeter of alluvium. Gully drains to the northeast. about 3.3:1 (5.0 m lateral to 1.5 vertical). At the Solid stars show channel thalweg in both trenches. Figure 15 shows configuration of bedrock east site, the ratio of lateral to vertical displace- surfaces in north and south trenches. Fine dotted-dashed line (A) is projection of elongation of ment ranges between 2.4:1 and 1.6:1 (5.1 m and ponded alluvium through thalweg in south trench to north trench, which shows 3.4 m of 3.4 m lateral to 2.1 m vertical). These ratios are left-lateral separation. Fine dotted line (B) is projection of trend of gully in bedrock above similar to the average ratios of 3:1 to 5:1 esti- ponded alluvium through thalweg in south trench to north trench, which shows 5.1 m of mated by Ramelli and Slemmons (1986) and left-lateral separation. Figure 2 shows location of site; Figure 3 is aerial photograph of site. Ramelli (1988). When the scarp formed, the transport and WEST EAST storage of sediment in the gulies above the scarp changed abruptly; this change is reflected in the stratigraphy of the test pit and the trenches south

Figure 15. Configuration of bedrock surface in north and south trenches at east-ponded-alluvium site. Solid stars show channel thalweg in both trenches. Trenches are superposed to show direction of separation of thal- weg between the two trenches. For simplicity, ground surface at the trenches is not shown. Figure 14 shows location of trenches.

-4 -2 0 2 4 6 8 10

METERS HOLOCENE SURFACE FAULTING ON THE MEERS FAULT, OKLAHOMA 13 of the scarp at both ponded-alluvium sites (Fig. porarily stored in the channel before it was silt to the pebble-free silt is the stratigraphic level 16). The basal 0.5 to 0.6 m of material is dammed. Similar-sized, undammed gullies in that corresponds to the time at which the gully yellowish-red (5 YR 4/6) pebble and cobble this small drainage locally contain 30 cm or was dammed. Before damming, the through- gravel in a matrix of sandy silt that is residuum more of pebbly, brown alluvium overlying the flowing drainage transported sand and pebbles and colluvium derived from weathering of the residuum. At both ponded sites, the pebble and that were deposited with the silt. After dam- underlying conglomerate. This basal gravel is sand content of the brown silt diminishes ming, only pebble-free silt was deposited in the overlain by a few tens of centimeters of pebbly abruptly upward, and most of the ponded allu- low-energy ponded area. and sandy, dark brown (7.5 YR 3/4) to dark vium is pebble-free, dark-brown (7.5 YR 3/4) to Poor water drainage through the ponded al- reddish-brown (5YR 2.5/2) silt that was proba- dark reddish-brown (5YR 3/3) silt. We believe luvium has helped to preserve the organic matter bly humus-rich alluvium and slopewash tem- that the transition from the sandy-pebbly brown (in the form of soil humus) that was washed in with the alluvium. A series of radiocarbon dates on humus in the alluvium helps determine when the scarp formed (Fig. 16; Table 1). As discussed WEST PONDED EAST PONDED above, these radiocarbon dates should be cor- ALLUVIUM ALLUVIUM rected for AMRT by about 300 yr. At the east DEPTH site (Fig. 16, right column), the dark brown, (in cm) (test pit) (south trench) pebbly silt above the colluvial gravel has a radi- 0 r ocarbon age of 1,816 cal. yr. Above the pebbly 432 cal. yr silt, the basal part of the relatively pebble-free, dark brown silt has an age of 1,539 cal. yr. MODERN These two ages (adjusted for AMRT) bracket 676 cal. yr the time when the scarp formed. A sample 30 A HORIZON so cm higher from the middle of the brown silt has an age of 1,354 cal. yr and is undoubtedly a 1011 cal. yr DARK BROWN minimum date for the time of faulting. At the west site, the time of faulting is not TO REDDISH 1167 cal. yr 967 cal. yr well defined, because the basal sample was col- 100 BROWN SILT lected from the stratigraphic interval that we now believe contains humus from both the pre- faulting, brown, sandy silt and the postfaulting, 1606 cal. yr dark-brown, relatively sand-free silt. This com- posite sample, however, has an age of 1,606 cal. 150 yr, which is consistent with the inferred age of faulting from the east site. Within the pebble-free silts, a subtle but sig- nificant color change separates the brown silt from an overlying reddish-brown (5YR 3/2- 5YR 4/6) silt (Fig. 16). This color change prob- 200 ably results from less humus in the reddish- brown silt compared to the brown silt. We do not believe that the color change is caused by pedogenic processes (that is, soil oxidation) for two reasons. First, the reddish-brown silt lacks 250 structural or textural changes that would imply any significant amount of pedogenesis. Sec- ondly, the current geomorphic setting of the

^o.^c.vr' ponded areas inhibits any substantial soil devel- opment, because the ground surface is continu- ously aggrading as the sediment washed from the surrounding hillslopes collects behind the Sample interval for radiocarbon date Abrupt boundary dams. The relatively low humus content of the | Diffuse boundary Unconformity reddish-brown silt could be explained by a cli- matic event or a tectonic event. A period of Clear to gradual boundary relatively dry climate could cause deposition of the reddish-brown silt because decreased precip- Figure 16. Schematic diagram comparing stratigraphy at the west- and east-ponded- itation would reduce the vegetative cover. Less alluvium sites. Stratigraphy of the west site is from test pit shown in Figure 12; stratigraphy of vegetation would generate less humus and east site is from deepest part of south trench shown in Figure 14. Radiocarbon ages are would also increase the surface runoff (Schumm, calibrated ages shown in Table 1. 1977, p. 29). The net effect would be an increase 14 CRONE AND LUZA in the supply of humus-poor sediment into the was concentrated in a 2-m-wide zone that con- drained, generally dry ridge crest minimizes the ponded basin. tained a mixture of clay gouge and pervasively amount of water that infiltrates into the collu- Alternatively, deposition of the reddish-brown sheared, brecciated bedrock. This zone is flanked vium. Because they are on a ridge crest, the silt could be related to a second faulting event. by numerous small-displacement faults. The striae are most likely the result of tectonic In this case, the scarp from the first event would main fault plane, which was near the mid-slope movements rather than nontectonic processes, be completely buried by alluvium in the ponded position of the scarp, was marked by a 20- to such as slope failure or downslope creep. basin, and excess alluvium would be transported 30-cm-thick, dark red to orange-red, massive, The age of the striae is unknown, but because over the scarp and down the gully. At this stage, plastic clay gouge that had no obvious tectoni- of their low rake angle, it is doubtful that they humus might accumulate in the brown silt be- cally induced fabric. In the lower 40 cm of the formed during the most recent faulting event, cause of the relatively low sedimentation rate pit, the contact between the gouge and the up- considering the 2-3 m of late Holocene throw and stable surface in the ponded basin. A second thrown (north) block of the fault was marked by measured at Canyon Creek. We believe that the faulting event would rejuvenate the dam by in- a relatively intact bedrock surface having a striae formed during a Quaternary faulting creasing the height of the scarp. All of the sedi- strike of N60°W and 76°NE dip. event, because it seems unlikely that such fine, ment from the surrounding hillslopes would The bedrock surface in the bottom of the pit delicate features could be preserved in soluble now be trapped behind the dam. The humus had many fine, subhorizontal striae on protrud- carbonate rock in a near-surface weathering en- content in the newly trapped sediment would be ing clasts in the conglomerate (Fig. 17). Nine- vironment for several hundreds of thousands of less than that in the underlying alluvium because teen striae were distinct enough to measure rake years. the damming suddenly increased the sedimenta- angles. The mean and median values of the an- Interpretations of the stratigraphy in the other tion rate in the ponded basin. gles were less than 1°NW (that is, essentially two pits in colluvium (0.6 km and 1.8 km Radiocarbon dates of 967 cal. yr and 1,011 horizontal), even though the extreme values northwest of the ponded-alluvium site) support cal. yr at the west site, and 1,167 cal. yr at the ranged from 8°SE to 12°NW. Because the either one or two late Holocene faulting events. east site show that the reddish-brown silt was measurements were from the northern (up- In both of these pits, upper Holocene deposits deposited slightly less than 1,000 yr ago (correct- thrown) block of the fault, southeasterly rakes (<2,000 yr old), considered to be scarp-derived ing for AMRT). If the reddish-brown silt were a indicate left-lateral movement, and northwest- colluvium, are truncated by an overhanging depositional response to a second faulting event, erly rakes indicate right-lateral movement. Al- fault plane. One interpretation of these relations then these dates are minimum ages of the fault- though the absolute sense of slip determined relies on a single faulting event in which lateral ing event. If the silt was deposited in response to from the striae remains uncertain, they do record movement has brought the colluvium out of the a climatic event, then the dates imply a period of an episode of nearly pure lateral slip. plane of the exposure and positioned it against reduced precipitation about 1,000 yr ago. This The preservation of these striae is attributed to the fault plane. An alternative explanation in- interpretation agrees with the paleoecologic and their burial by calcareous colluvium and their vokes two faulting events: one faulting event, sedimentologic evidence of a drier climate in the location on a ridge crest. Burial by calcareous deposition of the colluvium, and a second fault- region starting about 1,000 yr ago (Hall, 1982, colluvium minimizes dissolution of the striae by ing event. We cannot preclude either interpreta- 1986). Thus, although the tectonic explanation meteoric water, and their location on a well- tion based on the stratigraphy in these pits, but cannot be excluded, similar ages for the onset of a drier regional climate and deposition of the reddish-brown silt favor attributing the color change to climatic effects.

EXCAVATIONS IN FAULT-SCARP COLLUVIUM

Examination of the Post Oak Conglomerate along the scarp revealed poorly preserved fea- tures that appeared to be striae or small mullions on the fault, but dissolution and pitting of the limestone conglomerate made interpretation of these features equivocal. These features showed that studies in the Post Oak Conglomerate held promise for determining the sense and timing of slip on the fault. Therefore, we excavated pits in the colluvium (CP, Fig. 2) at the base of the scarp at three sites located about 0.1 km, 0.6 km, and 1.8 km northwest of the ponded-alluvium sites, respectively. The easternmost pit (Fig. 3) was 2 m deep and was excavated on the downthrown side of a 1.6-m-high scarp. After a backhoe removed Figure 17. Striae on clasts in Post Oak Conglomerate exposed in easternmost pit in collu- most of the colluvium in the pit, we dug into the vium. Location of pit is labeled PA/CP in Figure 2 and CP in Figure 3. The inch/cm scale is fault zone by hand and examined all parting horizontal. Near-horizontal rake angles of striae are evidence of nearly pure lateral surfaces for slip indicators. Most of the faulting displacement. HOLOCENE SURFACE FAULTING ON THE MEERS FAULT, OKLAHOMA 15 we favor the single-event interpretation because ling evidence of late Holocene movement on the moment magnitude of slightly more than 7 for we found no stratigraphic evidence of two Meers fault. The best estimate for the time of last the Meers fault using reasonable values for the events in the Canyon Creek trenches (about 4 surface faulting is about 1,200-1,300 yr ago. shear modulus, average displacement, rupture km to the east), and because the late Holocene The material used to estimate the age of a length, and downdip width of the rupture. We surface faulting had a major component of lat- surface-faulting event rarely yields the exact emphasize that the above-cited magnitude esti- eral slip. Until more conclusive data are availa- time of the event; commonly, the material pro- mates must be considered cautiously because the ble, we favor the conservative interpretation of a vides the age of a stratigraphic horizon, which seismogenic potential of Meers fault has still not single late Holocene event that is documented in then brackets either maximum or minimum age yet been firmly established. this paper and by Madole (1988). Future studies for the faulting. Of the sites discussed here, the are needed to determine if more than one late soil material that fell into the open crack at Can- Recurrent Faulting on the Meers Fault Holocene event may have occurred on the yon Creek trench 1 most closely corresponds to Meers fault. the time of faulting. Presumably, this material The information on the long-term (pre- fell into a crack that was deep enough to mini- Holocene) history of the fault is very limited, but DISCUSSION mize contamination by younger insoluble soil it indicates a long recurrence interval for surface organic material. Our estimate relies heavily on faulting. The best information is from the Can- Geologic relations in the Canyon Creek the age of this soil material (1,570 cal. yr) minus yon Creek trenches, but it must be interpreted trenches and at the two ponded-alluvium sites the 300-yr AMRT. carefully, because only the dip component of show that a late Holocene surface-faulting event All other dated samples provide minimum movement is recorded in these trenches. The fol- on the Meers fault had a left-lateral reverse sense ages for the faulting event. Based on their strati- lowing discussion assumes that all surface- of displacement. Despite large uncertainties in graphic positions, the samples that best define faulting events have a significant dip-slip com- the lateral and vertical separations measured at the time of faulting are the 1,646 cal. yr age at ponent, even though the subhorizontal striae in the ponded-alluvium sites, the measurements Canyon Creek trench 1, the 1,606 cal. yr age at the pit excavated into fault-scarp colluvium sup- show that the amount of lateral slip is equal to the west-ponded-alluvium site, and the 1,539 port an episode of nearly pure lateral slip. or greater than the vertical slip. cal. yr age at the east-ponded-alluvium site. The colluvial stratigraphy in the Canyon We found no strong evidence of lateral dis- After correcting for AMRT, the minimum age Creek trenches strongly supports only one placement in the Canyon Creek trenches. In for faulting at each site is 1,346, 1,306, and surface-faulting event. The stratigraphic throw trenches such as those at Canyon Creek, which 1,239 yr ago. These ages are virtually identical in both trenches is similar (more than 2.7 to 2.8 are excavated perpendicular to the scarp, abrupt when one considers the errors in the age deter- m in trench 1 and 3.2 to 3.3 m in trench 2). The changes in the thickness or character of strati- minations and the probable variation in AMRT warped Browns Creek Alluvium in trench 1 is graphic units across fault zones would be con- for each sample. middle Holocene in age, and the faulted and sidered as good evidence of strike-slip move- The date of the last surface faulting from this warped Porter Hill Alluvium in trench 2 is ment (Sylvester, 1988). The relatively uniform study (1,200-1,300 yr ago) agrees with that de- thought to be middle Pleistocene (790,000- thickness and similar character of stratigraphic termined by Madole (1988). Madole's eastern- 130,000 yr) in age (Madole, 1986, 1988). The units on both sides of the fault do not favor a most site (Browns Creek site) and our west- vertical displacement is about the same in mid- substantial amount of lateral slip. This conclu- ernmost site (west-ponded-alluvium site) are dle Holocene alluvium and in alluvium that is sion is inconsistent with the amount of lateral located 12.3 km apart along the central part of probably more than 100,000 yr old. This implies displacement documented at the ponded-allu- the scarp. Considering the distribution of these that no substantial vertical movement occurred vium sites, which are only about 3 km away. sites and the scarp's geomorphic expression, it on the fault for at least 100,000 yr prior to the The apparent lack of lateral slip at Canyon seems likely that the surface rupture from the late Holocene surface faulting. Creek may be related to the relatively ductile last event was 26 km long, and may have been The geomorphic expression of the fault is behavior of the Quaternary alluvium and Hen- 37 km long (Ramelli and others, 1987; Ramelli, consistent with a long recurrence interval even nessey Shale compared to the brittle behavior of 1988). though the most recent surface faulting was the Post Oak Conglomerate at the ponded- The size of the earthquake that may have 1,200-1,300 yr ago. The absence of a major alluvium sites. The deformation in the Canyon caused the Holocene surface rupture on the topographic or geomorphic escarpment coinci- Creek trenches is dominated by warping and Meers fault can be generally estimated by using dent with the fault argues against vertical flexing, which produces the vertical relief on the empirical relations that compare the length of movements with a regular recurrence of hun- scarp. Considering this style of ductile behavior, surface faulting with magnitude for historical dreds to a few thousand years throughout the it is possible that a considerable amount of lat- earthquakes (Bonilla and others, 1984). A sur- Quaternary. The biggest scarps along the fault eral displacement could have occurred in the face rupture 26-37 km long on a reverse or are only about 5 m high, and the maximum subsurface, but it was absorbed and concealed reverse-oblique slip fault would be associated lateral separation of ridge crests in the Slick Hills by plastic deformation in the shale and alluvium. with an earthquake of about Ms7 based on these is less than 25 m (Ramelli and Slemmons, 1986; In contrast, the late Quaternary deformation in rupture length versus magnitude relations. As Ramelli, 1988). If a typical faulting event has the Post Oak Conglomerate is mostly brittle Bonilla and others (1984) noted, however, the 1.5-2 m of vertical and 3-5 m of lateral slip failure that is concentrated in a zone of clay correlation between magnitude and rupture (based on the late Holocene displacement at the gouge and sheared bedrock a few meters wide. length are statistically poor for reverse and ponded-alluvium sites), then the cumulative dis- Lateral displacement on the fault is easier to reverse-oblique slip faults. placement since the modern topography and detect and measure in the Post Oak Conglomer- The seismic moment and the associated mo- drainage system formed in the Slick Hills could ate than in the Hennessey Shale because of the ment magnitude (M of Hanks and Kanamori, result from as few as three to as many as six conglomerate's brittle behavior. 1979) may also be used to estimate the size of events. Estimation of the age of the modern Multiple radiocarbon dates provide compel- earthquakes on the Meers fault. We calculate a landforms in the Slick Hills is difficult, but based 16 CRONE AND LUZA

on the distribution and inferred age (middle to seriously underestimate the hazard. Alterna- fault emphasizes the need for a systematic re- early? Pleistocene) of the Lake Lawtonka Allu- tively, perhaps the strain on seismogenic faults in view of major faults in the central United States vium (Madole, 1986; Luza and others, 1987, "stable" intraplate settings accumulates steadily, for evidence of Quaternary movement. Such a p. 21), 500,000 yr is a conservative estimate. and is released regularly. In this case, realistic review might modify our impression of the neo- The modern landscape may be much older. hazard assessments can be derived from know- tectonics in a large part of the United States and Three to six faulting events distributed over ing the long-term slip rate and the time of the our assessment of the associated earthquake 500,000 yr yield a long-term recurrence interval last event. Our present knowledge of the spatial hazards. of about 100,000 yr, which is similar to that and temporal pattern of earthquakes in the cen- inferred from the Canyon Creek trenches. tral United States and in stable continental inte- ACKNOWLEDGMENTS These results imply that the short time that riors worldwide is very poor (Coppersmith, has elapsed since the last faulting event is not 1988; Denham, 1988). Obviously, better earth- This study was partially supported by U.S. typical of the long-term behavior of the fault. In quake-hazard assessments in intraplate settings Nuclear Regulatory Commission Contract No. fact, the long-term behavior of the Meers fault will rely on a greater understanding of both the NRC 04-82-006-01 to the Oklahoma Geologi- may be very different from the behavior of other long-term and short-term behavior of seismo- cal Survey. We thank David Kimbell and seismically hazardous faults in the central and genic faults. Charles Oliver of the Kimbell Ranch for their eastern United States. The inferred recurrence of Our inference that the Meers fault is capable interest and their permission to excavate all of large earthquakes on the Meers fault is more of generating large damaging earthquakes (de- the trenches on their property. Douglas Lemley than an order of magnitude longer than those spite its aseismic condition) assumes that the and Kathleen Haller provided valuable assist- estimated for the scarp is connected to a major fault that extends ance in the field. Irene Stehli (Dicarb Radioiso- (600-700 yr) (Russ, 1979) and for earthquakes to hypocentral depths. The large amount of topes, Inc.) and Robert Steckenrath (University near Charleston, South Carolina (1,000-1,800 strain energy released during major earthquakes of Pittsburgh Radiocarbon Laboratory) were yr) (Obermeier and others, 1985; Talwani and can be stored only in high-strength rocks, that is, especially cooperative in providing the radio- Cox, 1985). Both the New Madrid and Charles- in rocks buried several kilometers deep (Das and carbon dates. Alan R. Ramelli and David B. ton areas have abundant microseismicity in con- Scholz, 1983). An important goal of future stud- Slemmons kindly provided the photographs in trast to the aseismic Meers fault. The lack of ies should be to determine the relationship Figures 3 and 5, respectively. The thoughtful microseismicity and the long recurrence interval between the fault scarp and nearby major deeply reviews and constructive comments by Craig M. might mean that strain is stored and released penetrating faults, because without knowing this dePolo, Michael N. Machette, Richard F. Ma- differently on the Meers fault than it is in the relationship, we do not know if severe, damag- dole, Alan R. Ramelli, Roy VanArsdale, and New Madrid and Charleston areas. ing ground motion would accompany surface Robert S. Yeats have improved the presentation rupture on the fault. of ideas in this paper. Earthquake-Hazard Assessments The geologic evidence of Holocene move- ment on the Meers fault was overlooked and The youthful surface faulting on the Meers undocumented for more than four decades de- REFERENCES CITED fault compared to its apparently long recurrence spite bedrock mapping along the fault that Algermissen, S. T., Perkins, D. M., Thenhaus, P. C., Hanson, S. L., and Bender, interval raises important and difficult questions began nearly 50 yr ago. If other faults in the B. L., 1982, Probabilistic estimates of maximum acceleration and veloc- ity in rock in the contiguous United States: U.S. Geological Survey about how hazard assessments should deal with region had been microseismically active, then Open-File Report 82-1033,99 p. differences in the long-term versus short-term this evidence might have been recognized ear- Allen, C. R., 1975, Geological criteria for evaluating seismicity: Geological Society of America Bulletin, v. 86, no. 8, p. 1041-1057. behavior of seismogenic faults. In the past few lier. Nevertheless, the oversight raises the possi- Birkeland, P. W., 1984, Soils and geomorphology: New York, Oxford Univer- years, an increasing number of paleoseismologic bility that other faults in the Frontal Wichita sity Press, 372 p. Bonilla, M. G., Mark, R. K., and Lienkaemper, J. J., 1984, Statistical relations studies have shown that the temporal pattern of fault system or elsewhere in the southern mid- among earthquake magnitude, surface rupture, and surface fault dis- placement: Seismological Society of America Bulletin, v. 74, no. 6, earthquakes on some faults is not uniform and continent may have produced major earth- p. 2379-2411. that earthquakes on these faults cluster in time Bucknam, R. C., and Anderson, R. E., 1979, Estimation of fault-scarp ages quakes during the Quaternary, but the geologic from a scarp-height-slope-angle relationship: Geology, v. 7, no. 1, (Wallace, 1984, 1987; Knuepfer, 1987; Ma- evidence of those earthquakes has yet to be p. 11-14. Budnik, R. T., 1986, Left-lateral intraplate deformation along the Ancestral chette, 1987; Swan, 1988; Jacoby and others, recognized. —Implications for late Paleozoic plate motions: Tec- 1988; Sieh and others, 1989). The long-term tonophysics, v. 132, p. 195-214. The Meers fault emphasizes two valuable les- 1987, Late Miocene reactivation of Ancestral Rocky Mountain struc- behavior of these faults is characterized by two tures in the Texas Panhandle—A response to Basin and Range exten- sons. First, although many potentially hazardous sion: Geology, v. 15, p. 163-166. or more faulting events within a relatively short faults are microseismically active and therefore Butler, K. R., 1980, A structural analysis of the Cambrian-Ordovician strata on the north flank of the , Oklahoma: Geological So- period of time followed by a relatively long pe- can be easily recognized, other hazardous faults ciety of America Abstracts with Programs, v. 12, no. 1, p. 2. riod of quiescence. The possibility of two late Coppersmith, K. J., 1988, Temporal and spatial clustering of earthquake activ- may be aseismic and can be identified only by ity in the central and eastern United States: Seismological Research Holocene faulting events (as noted in the exca- geologic studies (Allen, 1975). Secondly, the Letters, v. 59, no. 4, p. 299-304. Cox, R. T., and VanArsdale, R. B., 1988, Structure and chronology of the vations in fault-scarp colluvium) may be evi- long-held notion that much of the midcontinent Washita Valley fault, southern Oklahoma aulacogen: Shale Shaker, dence that temporal clustering occurs on the (with the exception of the New Madrid, Mis- v. 39, no. 1, p. 2-13. Crone, A. J., 1987, The Meers fault, SW Oklahoma—Evidence of multiple Meers fault. If so, does the late Holocene surface souri, seismic zone) is tectonically stable is now episodes of Quaternary surface faulting: Geological Society of America faulting indicate the onset of a period of rela- Abstracts with Programs, v. 19, no. 7, p. 630. suspect. Previously, only low- to moderate- Crone, A. J., and Luza, K. V., 1986, Holocene deformation associated with the tively frequent earthquakes? If the fault is in a Meers fault, southwestern Oklahoma, in Donovan, R. N., ed., The Slick magnitude earthquakes were considered likely Hills of southwestern Oklahoma—Fragments of an aulacogen?: Okla- period of frequent earthquakes, then hazard as- throughout most of the region. The conclusive homa Geological Survey Guidebook 24, p. 68-72. Dart, R. L., 1987, South-central United States well-bore breakout-data catalog: sessments that rely on long-term slip rates might evidence of Holocene movement on the Meers U.S. Geological Survey Open-File Report 87-405,95 p. HOLOCENE SURFACE FAULTING ON THE MEERS FAULT, OKLAHOMA 17

Das, Shamita, and Scholz, C. H., 1983, Why large earthquakes do not nucleate Howard, K. A., Aaron, J. M , Brabb, E. E„ Brock, M. R., Gower, H. D , Hunt, southwest Oklahoma [M.S. thesis]: Reno, Nevada, University of Ne- at shallow depths: Nature, v. 305, p. 621-623. S. J., Milton, D. J , Muehlberger, W. R., Nakata, J. K., Plafker, G., vada, 123 p. Denham, David, 1988, Australian seismicity—The puzzle of the not-so-stable Prowell, D. C , Wallace, R. E., and Witkind, I. J., 1978, Preliminary Rameili, A. R., and Slemmons, D. B., 1986, Neotectonic activity of the Meers continent: Seismological Research Letters, v. 59, no. 4, p. 235-240. map of young faults in the United States as a guide to possible fault fault, in Donovan, R. N., ed., The Slick Hills of southwestern Donovan, R. N., 1982, Geology of Blue Creek Canyon, Wichita Mountains activity: U.S. Geological Survey Miscellaneous Field Studies Map Oklahoma—Fragments of an aulacogen?: Oklahoma Geological Sur- area, in Geology of the eastern Wichita Mountains, southwestern Okla- MF-916, 2 sheets, scales 1:5,000,000 and 1:7,500,000. vey Guidebook 24, p. 45-54. homa: Oklahoma Geological Survey Guidebook 21, p. 65-77. Jacoby, G. C, Sheppard, P. R., and Sieh, K. E, 1988, Irregular recurrence of Rameili, A. R., Slemmons, D. B., and Brocoum, S. J., 1987, The Meers Donovan, R. N., Gilbert, M. C., Luza, K. V., Marchini, D., and Sanderson, D„ large earthquakes along the —Evidence from trees: foult—'Tectonic activity in southwestern Oklahoma: U S. Nuclear Reg- 1983, Possible Quaternary movement on the Meers fault, southwestern Science, v. 241, p. 196-199. ulatory Commission NUREG/CR-4852,25 p. Oklahoma: Oklahoma Geology Notes, v. 43, no. 5, p. 124-133. Johnson, K. S., and Denison, R. E., 1973, Igneous geology of the Wichita Russ, D. P., 1979, Late Holocene faulting and earthquake recurrence in the Gerasimov, I. P., 1971, Nature and originality of paleosols, in Yaalon, D. H., Mountains and economic geology of Permian rocks in southwest Okla- area, northwestern : Geological Society of ed., Paleopedology—Origin, nature and dating of paleosols: Jerusalem, homa: Oklahoma Geological Survey, Guidebook for Geological Society America Bulletin, v. 90, no. 11, p. 1013-1018. Israel, International Society of Soil Science and Israel Universities Press, of America Field Trip No. 6 (1973 Annual Meeting), 33 p. Schumm, S. A., 1977, The fluvial system: New York, John Wiley and Sons, p. 15-27. Knuepfer, P.L.K., 1987, Changes in Holocene slip rates in strike-slip environ- 338 p. Gilbert, M. C., 1982, Geologic setting of the eastern Wichita Mountains with a ments, in Crone, A. J., and Omdahl, E M., eds., Proceedings of Confer- Sieh, Kerry, Stuiver, Minze, and Brillinger, David, 1989, A more precise chro- brief discussion of unresolved problems, in Gilbert, M. C., and Dono- ence 39—Directions in Paleoseismology: U.S. Geological Survey nology of earthquakes produced by the San Andreas fault in southern van, R. N., eds., Geology of the eastern Wichita Mountains, southwest- Open-File Report 87-673, p. 249-261. California: Journal of Geophysical Research, v. 94, no. Bl, p. 603-623. ern Oklahoma: Oklahoma Geological Survey Guidebook 21, p. 1-30. Larson, E. E., Patterson, P. E., Curtis, G., Drake, R., and Mutschler, F. E., Slemmons, D. B., Rameili, A. R., and Brocoum, S. J., 1985, Earthquake 1983a, The Meers fault—Unusual aspects and possible tectonic conse- 1985, Petrologic, paleomagnetic, and structural evidence of a Paleozoic potential of the Meers fault, Oklahoma: Seismological Society of Amer- quences: Geological Society of America Abstracts with Programs, v. 15, rift system in Oklahoma, New Mexico, Colorado, and Utah: Geological ica, Eastern Section, Earthquake Notes, v. 55, no. 1, p. 1. p. I. Society of America Bulletin, v. 96, no. 11, p. 1364-1372. Stuiver, Minze, and Reimer, P. J., 1986, A computer program for radiocarbon • 1983b, The Meers fault of southwestern Oklahoma—Evidence for pos- Lawson, J. E., Jr., 1985, Seismicity at the Meets fault: Earthquake Notes, age calibration: Radiocarbon, v. 28, no. 2B, p. 1022-1030 (Rev 2.0). sible strong Quaternary seismicity in the midcontinent: EOS (American Eastern Section, Seismological Society of America, v. 55, no. 1, p. 2. Swan, F. H., 1988, Temporal clustering of paleoseismic events on the Oued Geophysical Union Transactions), v. 64, no. 18, p. 313. Luza, K V., Madole, R. F., and Crone, A. J., 1987, Investigation of the Meers Fodda fault, Algeria: Geology, v. 16, no. 12, p. 1092-1095. Gile, L. H., Peterson, F. F., and Grossman, R. B., 1966, Morphological and fault, southwestern Oklahoma: Oklahoma Geological Survey Special Sylvester, A. G., 1988, Strike-slip faults: Geological Society of America Bul- genetic sequences of carbonate accumulation in desert soils: Soil Publication 87-1,75 p. letin, v. 100, no. 11, p. 1666-1703. Science, v. 101, p. 347-360. Machette, M. N., 1987, Changes in long-term versus short-term slip rates in an Talwani, Pradeep, and Cox, John, 1985, Paleoseismic evidence for recurrence Gordon. O. W., 1988, Revised instrumental hypocenters and correlation of extensional environment, in Crone, A. J., and Omdahl, E M., eds.. of earthquakes near Charleston, South Carolina: Science, v. 229, earthquake locatioas and tectonics in the central United States: U.S. Proceedings of Conference 39—Directions in Paleoseismology: U.S. p. 379-381. Geological Survey Professional Paper 1364,69 p. Geological Survey Open-File Report 87-673, p. 228-238. Tanner, J. H., 1967, Wrench fault movements along Washita Valley fault, Hall, S. A., 1982, Late Holocene paleoecology of the Southern Plains: Quater- Madole, R. F., 1986, The Meers fault—Quaternary stratigraphy and evidence Arbuckle Mountain area, Oklahoma: American Association of Petro- nary Research, v. 17, p. 391-407. for late Holocene movement, in Donovan, R. N., ed., The Slick Hills of leum Geologists Bulletin, v. 51, p. 126-141. 1986, Late Quaternary alluvial chronology of the Southern Plains: southwestern Oklahoma—Fragments of an aulacogen?: Oklahoma Thorman, C. H., 1969, Wrench faulting in southern Oklahoma [abs.]: Geologi- Geological Society of America Abstracts with Programs, v. 18, no. 6, Geological Survey Guidebook 24, p. 55-67. cal Society of America Special Paper 121, p. 571. p. 625. 1988, Stratigraphic evidence of Holocene faulting in the Midcontinent— Tilford, N. R.t and Westen, D. P., 1985, The Meers fault in southwestern Ham, W. E„ and Wilson, J. L., 1967, Paleozoic epeirogeny and orogeny in the The Meers fault, southwestern Oklahoma: Geological Society of Amer- Oklahoma—Implications of the sense of recent movement: Association central United States: American Journal of Science, v. 265, p. 332-407. ica Bulletin, v. 100, no. 3, p. 392-401. of Engineering Geologists Abstracts and Program, 28th annual meeting, Ham, W. E., Denison, R. E., and Merritt, C. A., 1964, Basement rocks and McConnell, D. A., 1987, Paleozoic structural evolution of the Wichita uplift, Winston-Salem, N.C., p. 77. structural evolution of southern Oklahoma: Oklahoma Geological Sur- southwest Oklahoma [PhD. thesis]: College Station, Texas, Texas Viele, G. W., 1986, The subduction of Texas: Geological Society of America vey Bulletin 95, 302 p. A&M University, 219 p. Abstracts with Programs, v. 18, no. 6, p. 779. Hanks, T. C., and Kanamori, Hiroo, 1979, A : Journal McConnell, D. A., Beauchamp, W. H., Donovan, R. N., Marchini, W.R.D., Wallace, R. E., 1984, Patterns and timing of late Quaternary faulting in the of Geophysical Research, v. 84, tto. B5, p. 2348-2350. and Sanderson, D. J., 1986, Structural evolution of the Frontal fault Great Basin Province and relation to some regional tectonic features: Harding, T. P., 1985, Seismic characteristics and identification of negative zone, Wichita uplift, southwestern Oklahoma: Geological Society of Journal of Geophysical Research, v. 89, no. B7, p. 5763-5769. flower structures, positive flower structures, and positive structural in- America Abstracts with Programs, v. 18, no. 6, p. 687. 1987, Grouping and migration of surface faulting and variations in slip version: American Association of Petroleum Geologists Bulletin, v. 69, McLean, Richard, and Stearns, D- W., 1983, Fault analysis in Wichita Moun- rates on faults in the Great Basin Province: Seismological Society of no. 4, p. 582-600. tains [abs.]: American Association of Petroleum Geologists Bulletin, v. 76, America Bulletin, v. 77, no. 3, p. 868-876. Harlton, B. H., 1951, Faults in sedimentary part of Wichita Mountains of no. 3, p. 511-512. Walper, J. L., 1977, Paleozoic tectonics of the southern margin of North Oklahoma: American Association of Petroleum Geologists Bulletin, Moody, J. D„ and Hill, M. J., 1956, Wrench-fault tectonics: Geological Society America: Gulf Coast Association of Geological Societies Transactions, v. 35, no. 5, p. 988-999. of America Bulletin, v. 67, no. 9, p. 1207-1246. v. 27, p. 230-241. 1960, Stratigraphy of Cement pool and adjacent area, Caddo and Nielsen, K. C., and Stern, R. J., 1985, Post-Carboniferous tectonics in the Westen, D. P., 1985, Recognition criteria for young multiple surface ruptures Grady Counties, Oklahoma: American Association of Petroleum Geol- Anadarko basin, Oklahoma—Evidence from side-looking radar imag- along the Meers fault in southwestern Oklahoma [M.S. thesis]: College ogists Bulletin, v. 44, no. 2, p. 210-226. ery: Geology, v. 13, no. 6, p. 409-412. Station, Texas, Texas A&M University, 69 p. 1963, Frontal Wichita fault system of southwestern Oklahoma: Ameri- Nuttli, O. W.. 1979, Seismicity of the central United States, in Hathway, A. W„ Wickham, John, 1978, The Southern Oklahoma aulacogen, in Structural style can Association of Petroleum Geologists Bulletin, v. 47, no. 8, and McClure, C. R., eds., Geology in the siting of nuclear power plants: of the Arbuckle region: Geological Society of America South-Central p. 1552-1580. Geological Society of America Reviews in Engineering Geology, v. 4, Section field trip no. 3 guidebook, March 8-9,1978, p. 8-41. 1972, Faulted fold belts of southern Anadarko basin adjacent to frontal p. 67-93. Yeats, R. S., 1986, Active faults related to folding, in Active tectonics: Washing- Wichitas: American Association of Petroleum Geologists Bulletin, v. 56, Obermeier, S. F., Gohn, G. S., Weems, R. E, Gelinas, R. L., and Rubin, Meyer, ton, D.C., National Academy Press, p. 63-79. no. 8, p. 1544-1551. 1985, Geologic evidence for recurrent moderate to large earthquakes Zoback, M. L., and Zoback, Mark, 1980, State of stress in the conterminous Havens, J. S., 1977, Reconnaissance of the water resources of the Lawton near Charleston, South Carolina: Science, v. 227, p. 408-411. United States: Journal of Geophysical Research, v. 85, no. Bl 1, quadrangle, southwestern Oklahoma: Oklahoma Geological Survey Paul, E. A., Campbell, C. A., Rennie, D. A., and McCallum, K. J., 1964, p. 6113-6156. Hydrologic Atlas 6, scale 1:250,000,4 oversized plates. Investigations of the dynamics of soil humus utilizing carbon dating Hoffman, P., Dewey, J. F., and Burke, K., 1974, and their genetic techniques: 8th International Congress of Soil Science, Transactions, relation to geosynctines, with a example from Great Slave Bucharest, Romania, p. 201-208. Lake, Canada, in Dott, R. H., and Shaver, R. H., Modern and ancient Perry, W. J., 1989, Tectonic evolution of the Anadarko basin region, Okla- geosynclinal sedimentation: Society of Economic Paleontologists and homa: U.S. Geological Survey Bulletin, 1866-A, p. A1-A19. Mineralogists Special Publication 19, p. 38-55. Powell, B. N., and Fisher, J. F., 1976, Plutonic igneous geology of the Wichita Holliday, V. T., Johnson, Eileen, Haas, Herbert, and Steckenrath, Robert, magmatic province, Oklahoma: Oklahoma Geological Survey, Guide- 1983, Radiocarbon ages from the Lubbock Lake site, 1950-1980— book for Geological Society of America Field Trip No. 2 (South- MANUSCRIPT RECEIVED BY THE SOCIETY NOVEMBER 30,1988 Framework for cultural and ecological change on the Southern High Central Section meeting), 35 p. REVISED MANUSCRIPT RECEIVED JUNE 7,1989 Plains: Plains Anthropologist, v. 28, no. 101, p. 165-182. Rameili, A. R., 1988, Late Quaternary tectonic activity of the Meers fault, MANUSCRIPT ACCEPTED JUNE 13,1989

Printed in U.S.A.