284 Gulf Coast Association of Geological Societies Transactions, Volume 55, 2005

Distribution and Origin of Fault-Line Scarps of Southwest Louisiana, USA

Heinrich, Paul V.

Louisiana Geological Survey, Louisiana State University, Baton Rouge, Louisiana 70803

Abstract

Compilation of fault-line scarps and traces from existing geologic mapping and revision ofthe resulting compilation using remote sensing data and various aerial images revealed a complexpattern of Quaternary fault-line scarps within southwest Louisiana. Numerous, generally east-west trending, fault-line scarps form a 24 km wide east-west trending belt lying south of a linebetween Ville Platte, Louisiana and Kirbyville, Texas. The southern edge of it is marked by a rela-tively continuous set of fault-line scarps associated with the Tepetate fault zone. Numerous fault-line scarps occur between the Tepetate fault zone and the shoreline of the Gulf of Mexico. How-ever, these fault-line scarps lack any regional pattern, and many are associated with local saltdomes and growth faults. The northernmost fault-line scarps found within southwest Louisianaconsist of a narrow belt of prominent east-west trending scarps within southern Rapides Parish.

Many of these Quaternary fault-line scarps are the surface expressions of known Tertiarygrowth faults, a number of which are associated with roll-over structures containing oil and gasfields. Such oil and gas fields were formed as the result of reactivation of the faults during thePleistocene. The reactivation of these faults and the associated formation of these scarps representthe results of the loading of the Gulf of Mexico margin starting in Late Pliocene time. This loadinghas had the effect of reactivating regional fault trends such as the Tepetate fault zone and causingthe renewed flowage of deep-seated salt.

Introduction

Southwest Louisiana consists of a series coastal terraces underlain by Pleistocene allostrato-graphic units, which the Louisiana Geological Survey has grouped into the Intermediate and Praireallogroups (Fig. 1). A deeply dissected strip of Pliocene coastal plain sediments of the Willis Formationlies along the northern edge of the Pleistocene terraces between the Sabine and Calcasieu rivers. Betweenthe Calcasieu River and the eastern valley wall of the Mississippi Alluvial Valley, younger Pleistocenesediments cover the eroded edge of these Pliocene age sediments (Heinrich and Autin 2000, Snead et al.,2002a, 2002b, McCulloh and Heinrich 2002, Heinrich et al., 2002, 2003, McCulloh et al., 2003).

Within southwest Louisiana, the coast-parallel units comprising the Intermediate Allogroup, inorder of descending elevation and decreasing age, consist of the Lissie, Elizabeth, and Oakdale allofor-mations. These alloformations consist of early to middle Pleistocene fluvial deposits of the Calcasieu,Mississippi, Sabine, and Red rivers, their tributaries, and coastal plain streams. Alloformations have rel-atively flat, but highly dissected, terrace surfaces lacking any remnants of original constructionaltopography. Intermediate Alloformation is bounded updip by the Willis and Fleming formations andonlapped gulfward by the sediments of the Prairie Allogroup. Near the Mississippi River flood plain,Sicily Island and Peoria loesses blanket the Intermediate Allogroup (Snead et al., 2002a, 2002b,McCulloh et al., 2003). Along the Red River and between it and the Mississippi River, the IntermediateAllogroup consists of the Pleistocene fluvial sediments of Fisk's (1948) Montgomery and Bentley for-mations (McCulloh and Heinrich 2004).

© 2006 by The Gulf Coast Association of Geological Societies

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Figure 1. Geologic map of southwest Louisiana showing known fault traces and fault-line scarps. Compiledand generalized from McCulloh and Heinrich (2002), Saucier and Snead (1989), and various published andunpublished 1:100,000 scale Louisiana geologic quadrangles cited in text. Note: ch = China segment, C = Cam-eron Meadows salt dome, H = Hackberry salt dome, J =Jefferson Island salt dome, Je = Jennings salt dome,mb = Marsh Bayou segment, t = Topsy segment, and V = Vinton salt dome.

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The Beaumont Alloformation consists of Sangamon coastal plain deposits. A diverse assemblageof fluvial and deltaic sediments of the Calcasieu, Mississippi, Sabine, and Red rivers, their tributaries,and coastal plain streams; barrier sands that comprise Houston ridge; and estuarine and marine sedi-ments comprise this alloformation. Unlike the alloformations that compose the Intermediate Allogroup,the surface of the Beaumont Alloformation, although degraded by various surficial processes, exhibitsrecognizable constructional landforms including coastal ridges, relict channels, and a barrier islandridge. It is onlapped gulfward by Holocene sediments of the Mermantau Alloformation. The AvoyellesAlloformation occurs as isolated terrace fragments and comprises the southeast corner of the PrairieAllogroup along the western valley wall of the Mississippi Alluvial Valley. Its surface exhibits the relictmeander-belt morphology of the relict Lafayette meander-belt of the Mississippi River. The Big CaneAlloformation consists of Red River sediments intermediate in age, stratigraphy, and elevation betweenthe Avoyelles Alloformation and modern Mississippi River floodplain. Peoria loess covers the surfacesof the Avoyelles and Big Cane alloformations and the western part of the Beaumont Alloformation adja-cent to the Mississippi River Alluvial Valley (Heinrich and Autin 2000, Heinrich et al., 2002, 2003,McCulloh et al., 2003, McCulloh and Heinrich 2004).

The Deweyville Allogroup consists of Wisconsinan fluvial deposits intermediate in age andstratigraphic position between Holocene fluvial sediments underlying the modern floodplains of theCalcasieu and Sabine rivers and the Prairie Allogroup. The surface of the Deweyville exhibits well-pre-served meander scars that are substantially larger than those of adjacent modern flood plains. Gulfward,these surfaces dip beneath the floodplains and sediments of the river valleys along which they are found.Multiple units of alloformation rank have been recognized and mapped within the Deweyville Allo-group (Blum et al., 1995, Heinrich et al., 2002, 2003).

For this paper, the alluvial valleys of the Calcasieu, Mississippi, Sabine, and Red rivers and theirtributaries, the fluvial sediments underlying them are left undifferentiated. Within the Mississippi RiverAlluvial Valley, unnamed Pleistocene valley train deposits occur, which are also not discussed. Theremainder of the Holocene sediment consists of the deposits of the Mississippi River delta and the Mer-mentau Alloformation.

The Mermentau Alloformation, originally defined as the "Mermentau Member" by Jones et al.,(1954), underlies the chenier plain of southwest Louisiana. It consists of dark-colored marine muds,sandy and shelly beach deposits, organic marsh clays, and lacustrine and bay muds that underlie theLouisiana chenier plain. This alloformation extends westward along the coast of the Gulf of Mexico intoTexas as far west as Galveston Bay and eastward to Vermilion Bay (Jackson et al., 1954, Heinrich inpress, in preparation).

As discussed by Heinrich (2005), Howe and Moresi (1931) mapped the first fault-line scarpwithin southwest Louisiana. They interpreted this scarp to be a terrace boundary between their Pensa-cola and Hammond terraces. Later, Bernard (1950) was apparently the first person to recognize thepresence of fault-line scarps within the southwest Louisiana region by mapping fault-line scarps justacross the Sabine River in Texas within Newton County. Later, Heinrich (1988) postulated that a scarp,the Dequincy scarp, within southwest Louisiana interpreted by Fisk (1948) to be a terrace scarp, was, infact, tectonic in origin. As reported by Heinrich (1997, 2000), the tectonic origin of one of these scarps,the De Quincy scarp, was confirmed by STATEMAP funded drilling conducted for Snead et al., (1995).Since then, fault-line scarps within southwest Louisiana have been mapped for and illustrated by several1:100,000 scale geologic quadrangles, i.e. Heinrich and Autin (2000), Snead et al., (2002a, 2002b), Hei-nrich et al., (2002, 2003), and Heinrich (in press, in preparation). In addition, McCulloh et al., (2003)briefly described these fault-line scarps.

Methodology

A map of fault-line scarps within southwest Louisiana was compiled from existing geologicmaps and from new mapping created from recently available remote sensing data. The remote sensingdata consisted of digital elevation models (DEMs) prepared from LIDAR (LIght Detection And Rang-ing) data available at Atlas: The Louisiana Statewide GIS at http://atlas.lsu.edu/ and National ElevationDataset (NED) available at http://seamless.usgs.gov/. Previously mapped fault-line scarps wereobtained from Heinrich and Autin (2000), Snead et al., (2002a, 2002b), Heinrich et al., (2002, 2003),

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Heinrich (2005), and Heinrich (in press, in preparation). The locations of these fault-line scarps as indi-cated on original draft 1:24,000 geologic maps for these sources were consulted and reviewed againstLIDAR images produced using MacDEM, Version 1.0. In addition, analyses of the LIDAR DEMs usingGlobal Mapper, Version 5.07, and visual inspection of MacDEM LIDAR images were used to map thelocation of additional fault-line scarps. The locations of these potential fault-line scarps were examinedrelative to features identifiable from USGS Digital Orthophoto Quarter Quadrangles, soils surveys, andavailable subsurface data. The height of fault-line scarps was estimated using Global Mapper, Version5.07 from the LIDAR DEMs.

Results

Compilation and review of previously mapped fault traces and fault-line scarps and analysis ofimages produced from both LIDAR and NED DEMs revealed a number of previously unmapped faulttraces and fault-line scarps. The plotting of these features on 1;100,000 scale topographic and geologicmaps revealed three major regions of surface faulting. They are the Glenmora trend, Tepetate trend, andSouthern Fault-line Scarps and Traces region.

Glenmora trend

The northernmost set of fault-line scarps, the Glenmora trend, lies within southern Rapides Par-ish (Fig. 1). This trend consists of sets of east-west scarps, which lie within an area extending from justover a mile north of Lake Cocodrie westward past Glenmora, Louisiana, to the Rapides-Vernon parishline. Indistinct linear features on images made from LIDAR DEMs suggested the presence of the traceof another east-west fault trace lying about a mile south of the Allen-Rapides parish line.

Because of the dissected nature of the terraces associated with the Lissie and Oakdale alloforma-tions of the Intermediate Allogroup, it is difficult to determine the exact amount that the fault-line scarpsof the Glenmora trend have displaced the terrace surfaces. For the northernmost sets of scarps, heightvaries from 15 to 25 ft (4.6 to 7.6 m). The westernmost scarp segment of one set has a height varyingfrom 30 to 35 ft (9.1 to 11 m). The southernmost set of scarps has a height of only 8 to 10 ft (2.4 to 3.0m).

Available log data from water, oil, and gas wells is insufficient to confirm the presence faultsassociated with these scarps in the subsurface at this time. However, the morphology of these scarps,their east-west orientation, and their cross-cutting of terrace scarps separating the surfaces of the theLissie and Oakdale alloformations clearly show them to be fault-line scarps. One scarp segment, whichextends from the Lissie Alloformation across terraces of Tenmile Creek as a 3 ft (0.9 m) high scarpwithin southwest Rapides Parish, Sec. 31, T. 1 S., R.4 W. (Fig. 2). This and similar fault-line scarpswithin the Glenmora trend demonstrate the tectonic origin of these scarps and ongoing fault movement.

At this time there appears to be a gap of about 23 mi (37 km) separating the Glenmora andTepetate trends. A review of images made from NED DEMS, selected 1:24,000 scale topographic maps,and selected 1:24000 scale USGS Digital Orthophoto Quadrangles (DOQQ) revealed no evidence ofsignificant scarps within this gap. Detailed analysis of LIDAR data, when it becomes available, mightreveal scarps with heights below the resolution of the 1:24,000 scale topographic maps within this gap.Similarly with the currently available data, i.e. various aerial imagery and photographs, 1:24,000 scaletopographic maps, 1:24,000 scale DOQQs, and DEMs derived from these topographic maps, no evi-dence of fault-line scarps west of the Rapides-Vernon parish line could be discerned. However, thedetailed analysis of LIDAR data, when it becomes available, would be able to determine if the Glen-mora trend extends further west.

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Figure 2. Image produced from LIDAR DEM for the Steep Gulley 1:24,000 quadrangle showing fault-linescarp within the Glenmora trend. Arrows point to base of fault-line scarp. A = fault-line scarp cutting surfaceof Lissie Alloformation. B and C = scarp cutting terraces within the valley of Tenmile Creek within southwestRapides Parish.

Tepetate trend

Extending from the western valley wall of the Mississippi River alluvial Valley to the valley ofthe Sabine River, the Tepetate trend of fault-line scarps crosses across the surface of the Lissie andBeaumont alloformations westward into East Texas (Fig. 1). It consists of a 15 mi (24 km) wide zonecontaining several fault-line scarps. Except along its southern edge, the fault-line scarps that composethis trend apparently consist of discontinuous east-west scarps ranging from less than 1 mile (0.6 km) toabout 7 mi (11 km) in length. However, when LIDAR data become available for this part of Louisianacovering the bulk of the Tepetate trend, it is possible that more fault-line scarps will be found and knownones will be found to be more continuous and extensive than can be determined using the data nowavailable.

The southern edge of the Tepetate trend is defined by an almost continuous series of fault-linescarps composed of four segments, the De Quincy, Marsh Bayou, Topsy, and China segments (Fig. 1).The De Quincy, Topsy, and China segments consist of gulfward-facing fault-line scarps. In contrast theMarsh Bayou segment consists of an inland-facing fault-line scarp. Where these fault-line scarps of theDe Quincy and Topsy segments cross the Lissie Alloformation, they displace its surface by 25 to 30 ft(7.6 to 9 m) (Fig. 2). These fault-line scarps also displaced alluvium within the valleys, where they crossthem. Further west, fault-line scarps of the China segment displace the surface of the Beaumont Allofor-mation between 6 to 10 ft (1.8 to 3 m) within Acadia, Jefferson Davis, and Lafayette parishes. Near theAcadia-Jefferson Davis parish line, fault-line scarp within the China segment, displaces a terrace, possi-bly belonging to the Avoyelles Alloformation, along Bayou Nezpique by about 4 ft (1.2 m). The fault-line scarps of the China segment also displace several relict Pleistocene fluvial channels of the RedRiver.

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The fault-line scarps of the Tepetate trend are clearly associated with regional growth faults in thesubsurface. As discussed in detail by Heinrich (2000) and Miller and Heinrich (2003), the fault-linescarps of the De Quincy and China segments are clearly associated with the Tepetate fault zone in thesubsurface. Paine (1962) illustrated faulted alluvium of the Beaumont Alloformation exposed in theWolfe gravel pit at Indian Village, Jefferson Davis Parish, Louisiana. Heinrich (2000) documented sub-surface displacement of the alluvium comproing the Lissie Alloformation associated with a fault-linescarp of the De Quincy segment. The other fault-line scarps within the Tepetate trend are associatedwith regional growth faults as mapped by Lautier (1980, 1981), Lemoine (1989), Anonymous (2002),and others. Oil and gas fields associated with roll-over structures are often located immediately south offault-line scarps within the Tepetate trend (Holland et al., 1952, Paine 1962, Standfield et al., 1981,Anonymous 2002, Miller and Heinrich 2003).

Clear evidence of recent movement along fault-line scarps within the Tepetate trend exists withinsouthwest Louisiana. As illustrated by Miller and Heinrich (2003), subsidence has occurred where afault-line scarp of the China segment crosses a few floodplains of modern bayous and streams withinAllen Parish. For example, the floodplain of Bayou Serpent has been offset by almost 3 ft (1 m). Hein-rich (2000) found displacement of terrace surfaces within stream valleys where they cross the trace ofthe De Quincy segment in Calcasieu and Beauregard parishes. Images prepared from LIDAR data showthat the Holocene floodplains of many of the drainages crossing the De Quincy segment are offset bylow, but distinct, fault-line scarps (Fig. 3).

Figure 3. Image produced from LIDAR DEM for De Quincy 1:24,000 quadrangle, Calcasieu Parish, showingfault-line scarp along De Quincy segment within the Tepetate trend. Arrows point toward base of fault-linescarps. A = fault-line scarp cutting Lissie Alloformation. B = fault-line scarp cutting Holocene alluvium withinstream valleys. ? = possible scarps of inland facing antithetic faults.

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Southern fault trace and fault-line scarps region

Widely scattered fault-line scarps and fault traces occur south of the Tepetate fault-line scarptrend (Fig.1). They consist of a mixture of fault traces and gulfward- and inland-facing fault-line scarpslacking any discernible regional trends. Typically, these fault-line scarps face gulfward. The height ofthese scarps typically ranges from 2 to 4 ft (0.6 to 1.2 m) to 5 to 7 ft (1.5 to 2.1 m). They offset relict flu-vial landforms and coastal ridges found on the surface of the Beaumont and Avolleyes alloformations inmany places.

Although the majority of fault-line scarps found south of the Tepetate trend face gulfward, aseries of inland-facing fault-line scarps occurs within Sections 14-17, 19, and 20, T.9S., R.6W.; Sections15 and 22-24, T.9S., R.6W.; Sections 25-30, T.9S., R.5W.; and Sections 26-30, T.9S., R.4W., western-most Jefferson Davis Parish and easternmost Calcasieu Parish (Fig. 1). The relief on these fault-linescarps is quite low being in the range of 3 to 6 ft (0.9 to 2 m). As a result, they are not readily apparenton 1:24,000 scale topographic maps although they show up quite well in images made from LIDARdata. The tectonic origin of these scarps is consistent with their morphology and demonstrated by relictchannels and natural levees of the Red River, which they offset (Fig. 4).

Figure 4. Image produced from LIDAR DEM for Fenton 1:24,000 quadrangle, Jefferson Davis Parish, show-ing inland-facing fault-line scarp offsetting relict Red River channel. Arrows point toward base of scarps. A =scarp cutting Beaumont Allofromation. Dashed line = centerline of relict Red River channel.

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An extensive fault-line scarp system radiates from the Vinton salt dome in southwest CalcasieuParish (Fig. 1). From the Vinton salt dome, fault line scarps extend as far as 12 mi (20 km) to the north-east, 7.3 mi (12 km) to the southeast, and 3 mi (5 km) to the west. The height of the fault-line scarps tothe northeast and west is typically about 3 ft (0.9 m). In case of the longest of the northern fault-linescarps, the displacement of the fault reverses along its length such that it changes from an eastward-fac-ing scarp to a westward-facing scarp. The fault-line scarps to the southeast of the Vinton dome typicallyrange in height from 2 to 3 ft (0.6 to 0.9 m). The displacement of terrace surfaces, relict river channels,and coastal ridges by these scarps clearly demonstrate their tectonic origin.

Fault traces and fault-line scarps are also associated with three other salt domes within southwestLouisiana (Fig. 1). Within Iberia Parish, Heinrich (2005) described a less extensive radial pattern offault-line scarps associated with the Jefferson Island salt dome. Although the Hackberry salt dome alsohas fault-line scarps associated with it, they do not form the radial pattern seen in the other three saltdomes. The fault-line scarps associated with both the Hackberry and Jefferson island salt domes offsetrelict river channels. Within the Chenier Plain, Heinrich (in press) has mapped fault traces radiating outfrom the Cameron Meadows salt dome. In the case of the Cameron Meadows, Hackberry, and JeffersonIsland salt domes, the fault-line scarps correspond closely to known fault zones within the subsurface.

DiscussionThe trends and groups of fault-line scarps appear to represent differing responses to the loading

of the Louisiana coastal plain by the Mississippi, Red, and Sabine rivers. The factors determining thelocation of the Glenmora trend faulting are unclear given the lack of a major, mapped subsurface faultzone associated with it and the lack of accessible subsurface data. One possible explanation of the posi-tion of this fault trend is provided by the presence of the southern edge of the Comachean just north ofand paralleling the Glenmora trend (Adams 1985, Lopez 1995). Van Siclen (1978) suggested that fault-ing might be concentrated in front of the position of this former continental shelf edge, behind which thesediments are stabilized, in part, by the presence of thick carbonate sequences.

In case of the Tepetate trend, the fault-line scarps are clearly associated with pre-existing growthfaults. Detailed studies done by Heinrich (2000) along the China segment, by Hanor (1982) along theTepetate fault zone in Pointe Coupee Parish, and Durham and Peeples (1956) along the Baton Rougefault zone in Southeastern Louisiana, all indicated that the fault-line scarps are the result of the reactiva-tion of growth faults during the Pleistocene. These results are consistent with arguments by Nunn(1985) and, later, Dokka (2004), that the reactivation of these growth faults was the result of high sedi-mentation rates, which have occurred within the Louisiana coastal plain and continental shelf since thestart of continental glaciation. Nunn (1985) and Dokka (2004) argued that this loading has caused thereactivation of these faults as a result of a combination of tensional stress to which the underlying crustis being subjected within the Tepetate trend, gravity sliding of the Central Province of Peele et al.,(1995) under its own weight, and the reactivation of the flowage of deep-seated salt.

In the case of the fault traces and fault-line scarps south of the Tepetate trend, they are far toosouth to be explained by tensional stress on the underlying crust as suggested by Nunn (1985). The reac-tivation of these fault-line scarps, as argued by Dokka (2004) is readily explained as the result of gravitysliding and the flowage of deep-seated salt. The fault-line scarps associated with the Cameron Mead-ows, Hackberry, Jefferson Island, and Vinton salt domes quite likely reflect salt flowage at depthassociated with these domes.

ConclusionsThe compilation of data from Heinrich and Autin 2000, Snead et al., 2002a, 2002b, McCulloh

and Heinrich 2002, Heinrich et al., 2002, 2003, and Heinrich (2005, in press, in preparation) and the re-evaluation of this mapping using recent LIDAR DEMs found that Late Pleistocene faulting within thecoastal plain of southwest Louisiana is not limited to the Tepetate fault zone. The compilation of faulttraces and fault-line scarps from these sources defines three general groupings of these features, theGlenmora trend, the Tepetate trend, and the Southern Fault trace and Fault-line Scarp region, withinsouthwest Louisiana. Each of these groupings represents differing regional response to the loading ofthe Louisiana coastal plain.

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The presence of well-defined fault traces and fault-line scarps outside of the Tepetate fault zonedemonstrates that the potential for the damage to infrastructure within southwest Louisiana by faultmovement is greater than previously thought. Because there is no direct evidence of earthquake activityassociated with faults within southwest Louisiana, except possibly for the relatively minor 1983 LakeCharles earthquake, the hazard from seismic shaking is negligible. As a result, the main hazard posed byfaults within southwest Louisiana is from movement along these faults as a result of ongoing naturalsubsidence, possibly accentuated at times by excessive groundwater pumping. Over time, such move-ment can cause cumulative damage to buildings, roads, pipelines, railroads, and other infrastructurebuilt across them or associated antithetic faults.

Acknowledgements

The United States Geological Survey under their STATEMAP program funded the geologic map-ping, which made this research possible, under cooperative agreements no. 1434-94-A-1233, 1434-HQ-96-AG-01490, and 03HQAG0088. In addition, support from the Louisiana Geological Survey made thecompilation of the geologic map data and review of LIDAR and NED data possible. Finally, I thank Mr.Sidney Agnew, currently at the Department of Geology and Geophysics, Louisiana State University atBaton Rouge and Richard P. McCulloh of the Louisiana Geological Survey for sharing their ideas andexpertise fault-line scarps and the about the use of LIDAR in mapping them.

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Snead, J.I., P.V. Heinrich, and R.P. McCulloh, 2002b, The DeRidder 30 X 60 Minute Geologic Quadrangle: Louisi-ana Geological Survey, Baton Rouge. scale 1:100,000.

Standfield, C.P., E.L. McGehee, J.L. Snead, E.B. Millet, and E.L. Nichols, 1981, Oil and Gas Map of Louisiana.Louisiana Geological Survey, Baton Rouge. scale 1:380,160.

Van Siclen, D.C., 1978, Geologic Study of Faulting at Addicks Dam, Buffalo Bayou, Harris County, Texas: Unpub-lished report prepared for U.S. Army Corps of Engineers, Galveston District, under cooperative agreementno. DACW64-78-M-0027, Galvetson, Texas. 76 pp.

Erratum to ‘‘Distribution and origin of fault-line scarps of southwest Louisiana, USA‘‘

In the legend of figure 1 on page 285 of Heinrich (2005) , the Beaumont Alloformation is incorrectly labeled as the “Hammond alloformation.” The corrected legend is below.

Reference Cited:  Heinrich,  P.  V.,  2005a,  Distribution  and  Origin  of  Fault‐Line  Scarps  of  Southwest  Louisiana,  USA.  Gulf  Coast  Association  of Geological Societies Transactions. vol. 55, pp. 284‐293.