Geology of the Walnut Miss.-Tenn. 7.5 minute topographic quadrangle.

Mississippi Mineral Resources Institute 220 Old Chemistry Building, University, Mississippi 38677

Stratigraphic units of Cretaceous, Tertiary and Quaternary age crop out within the geographic bounds of the Walnut Miss.-Tenn. 7.5 minute quadrangle. The Cretaceous unit cropping out in the map area consists of the late Cretaceous Owl Creek Formation with the Cretaceous-Tertiary boundary forming the upper contact. The Tertiary section consists of the basal Clayton Formation, Porters Creek Formation, and the Naheola Formation of the Midway Group with the Meridian Sand of the Claiborne Group stratigraphically overstepping the older Midway formations. Significant flood plain deposits associated with the existing fluvial systems comprise the sediments of the Quaternary. The outcrop belts are generally oriented in a northerly direction and dip toward the west. Local structure has influenced both the dip of the units and the outcrop patterns. The major structural feature is the Muddy Creek Fault Zone located along the trend of Muddy Creek. The small anticlinal structure just west of Walnut, Mississippi, is likely associated with the adjacent Muddy Creek Fault Zone.

This investigation is part of a joint effort by the Mississippi Mineral Resources Institute (MMRI) and the University of Mississippi's Department of Geology and Geological Engineering to map Cretaceous and Tertiary stratigraphic units in northern Mississippi. The purpose of the mapping effort is to provide a source of updated information to the public, the mining industry and local planning commissions, and to aid regional economic development. The mapping also fulfills an educational purpose by providing first-hand knowledge of field stratigraphy and mapping techniques to graduate students.

The mapping of the geological units was accomplished using U.S. Geological Survey topographic base maps with a relative fraction scale of 1:24,000. Earlier geologic mapping, such as that done by Conant and McCutcheon (1941), did not have access to topographic maps and so the use of the topographic base is a significant step to refining the outcrop patterns. More detailed geological maps also allow natural hazards, such as expansive clays, to be incorporated into regional planning and zoning.

Previous Geological Mapping--Tippah County was previously mapped by Conant and McCutcheon (1941) and the northern-most area adjoining the Mississippi-Tennessee line was mapped by E.E. Russell (E.E. Russell, oral communications, 2001), in the course of geological mapping for the State of Tennessee. Herrick and Rima (1968) also published a map including the northern-most edge of the quadrangle in a report on the Foraminifera from the Clayton Formation in Hardeman County, Tennessee. The adjacent Falkner and Chalybeate quadrangles (Mississippi) have been mapped by Swann (1997, 1999) and the adjoining Camp Hill and Whitten Town (Mississippi) quadrangles were mapped by Thompson (2000a, b). The surface geology of adjoining Benton County was reported by Lusk (1956).

Area of Study--The Walnut Quadrangle includes areas of northern Tippah County, Mississippi, and the southern extreme of Hardeman County, Tennessee (Fig. 1). The town of Walnut, the largest municipality in the study area, is located in the northern half of the quadrangle. The major transportation corridor is U.S. Highway 72, traversing the study area from east to west and passing through Walnut. The Holly Springs National Forest comprises much of the western third of the study area. Geological mapping was focused on the study area, but additional mapping was carried out in adjacent quadrangles to allow smooth transitions of contacts across map boundaries. The northward flowing Muddy Creek is the major fluvial component in the study area. Relief within the quadrangle is approximately 240 feet. The lowest elevations are along Muddy Creek and the highest are in the hilly terrain of the northwestern corner of the study area.

Surface Stratigraphy--This stratigraphic analysis supports and updates the general stratigraphic relationships described by Conant and McCutcheon (1941) and the geological mapping by Lusk (1956) in adjoining Benton County, Mississippi. The MMRI-Martindale No. 1 stratigraphic test well (Fig. 2) was drilled in the northwestern quarter of the study area (sec.35, T1S, R3E) to aid in stratigraphic analysis. The well was cored to a total depth of 370 feet (112.5 m) and a suite of down-hole geophysical logs was obtained to aid between-well correlations. The stratigraphic units assigned to the core included the Cretaceous Ripley and Owl Creek Formations, the Tertiary Clayton, Porters Creek, Naheola Formations, and the Meridian Sand. The Ripley Formation, oldest unit recognized in the core, does not crop out in the study area. The remaining units crop out within the study area.

The Ripley Formation (Selma Group), in Mississippi, is divided into several members with the Chiwapa Sandstone the youngest. The core between the depths of 269 feet (82 m) and 370 feet (112.8 m) was assigned to the Ripley Formation. A typical Chiwapa lithology of phosphatic, glauconitic and fossiliferous, interbedded sand, sandy limestone and calcareous sandstone was encountered between the depths of 306 feet (93 m) and 360 feet (109.4 m). It is interesting to note that the Chiwapa Calcareous beds are approximately 40 feet (12.2 m) below the upper formational contact rather than comprising the upper-most Ripley section, its typical stratigraphic position. The top of the Chiwapa (i.e., the Ripley-Owl Creek formational contact) is unconformable and the basal Owl Creek sand often contains the trace fossil Ophiomorpha sp. (fossil burrow of the ghost shrimp, Callianassa major).

The oldest stratigraphic unit cropping out within the quadrangle is the Cretaceous Owl Creek Formation, the youngest formation of the Selma Group (Fig. 3). The Owl Creek comprises the top of the Cretaceous section with the Cretaceous-Tertiary boundary as its upper contact; a basal sand marks its lower, unconformable contact with the Ripley Formation. The Owl Creek is poorly represented in the study area with only very limited outcrops along the eastern valley wall of Muddy Creek and highly weathered exposures along the eastern edge of the study area. The Owl Creek typically consists of dark-to medium-gray, silty clay with a locally abundant molluscan fauna. Carbonaceous plant fragments are typically present near the upper contact. Fifty-three feet (16.5 m) of core (216 feet [65.7 m] to 269 feet [82 m] in depth) in the MMRI-Martindale test well were assigned to the Owl Creek Formation and consist of medium-gray, silty clay to friable, glauconitic clay. Molluscan fossils are sparse. The base of the unit consist of a four-foot, medium- to finegrained, glauconitic sand. The upper contact is typically sharp in outcrop when defined by the basal, fine-grained to gravelly sand of the Clayton Formation. In the MMRI-Martindale, No. 1 core, the Clayton-Owl Creek contact was marked by a sharp change from a dark gray, silty, sandy clay with carbonized plant debris of the Owl Creek to the fine-grained, glauconitic sands of the basal Clayton Formation.

The Clayton Formation is the oldest formation of the Paleocene Midway Group. MacNeil (1946) proposed the Chalybeate Limestone Member to include the Clayton facies containing sand and limestone verses the chalk facies further south in its outcrop belt. The entire formation in the study area is assigned to the Chalybeate Limestone Member.

The Clayton's primary outcrop belt coincides, for most part, with the Muddy Creek valley walls. North of Highway 72 the Clayton crops out on both sides of the Muddy Creek valley, but south of this point it is largely confined to the eastern valley wall. Increasing displacement along the Muddy Creek Fault Zone is interpreted as being a major controlling factor influencing the width and orientation of the Clayton outcrop pattern.

Lithologically, the Clayton typically consists of a thin basal sand or gravelly sand, a fossiliferous limestone unit of varying thickness, and a thick unit of fine-grained, glauconitic sand which makes up the majority of the formation (Conant and McCutheon, 1941; Swann, 1999). The basal sand is typically less than one foot (0.3 m) in thickness and if the gravel component is missing, careful field work is required to distinguish it from the sand-enriched facies of the Cretaceous Owl Creek Formation. The limestone section was particularly well exposed during road construction associated with the expansion of Highway 72. In the western valley wall of Muddy Creek (eastern 1/2, sec. 33, T1S, R4E) the limestone required ripping to construct the road grade. This section consisted of a light gray to light greenishgray, fossiliferous, sparry limestone and an overlyingbed of sparsely fossiliferous, glauconitic, fine-grained sand. Although there were several molluscan taxa present as molds and casts in the limestone section, only Ostrea pulaskensis was identifiable. The fossils in the sand section were molds and casts and could only be identified as bivalves. The glauconitic, fine-grained sands comprise most of the Clayton section and are the most common lithology in exposures.

In weathered exposures, this upper Clayton sand is an argillaceous, massive clay, with a red color derived from the weathering of glaueonite, and with sparse Ophiomorpha sp. In the MMRI-Martindale core, the Clayton was assigned 16 feet (4.9 m)of section i.e., from 208 feet (63.4 m) to 216 feet (65.9 m) in depth.

The Paleocene Porters Creek Formation (Midway Group) conformably overlies the Clayton Formation. The Porters Creek forms the most extensive outcrop belt of all the mapped units and is located in a northerly trending belt near the center of the study area. In this study, the Porters Creek was subdivided into two sections, a sandy lower section (Tippah Sand Lentil and equivalent sections) and the typical clay upper section with a thin bed of indurated claystone marking this interformational boundary. Placing the indurated claystone within the Porters Creek Formation varies with Conant and McCutcheon (1941), who used it as the lower Porters Creek formational boundary. Their decision to use the claystone (which they identified as a sandstone) is unfortunate, because applying it as the formational boundary would place the Tippah Sand Lentil in the Clayton Formation. Conant and McCutcheon describe a typical exposure of the claystone bed north-east of Tipplersville (their exposure number 2, page 33) which lies within the study area. This claystone bed is clearly within the lower Porters Creek section with the massive, glauconitic sands of the Clayton well below the claystone. The lower lithologic units of the Porters Creek are best exposed in the northern half of the study area and the upper clay section is best exposed in the southern half. A total of 171 feet (52 m) (from a depth of 208 feet [63.4 m] to 37 feet [11.3 m]) of section was assigned to the Porters Creek Formation in the MMRI-Martin dale No. 1 stratigraphic test well.

The Clayton-Porters Creek contact is conformable and so the two lithologies are intercalated. The fine-grained, glauconitic sands of the upper Clayton section become more argillaceous and thin clay beds become common in the transition zone. In this mapping, the fine-grained sands have been retained in the Clayton and the interbedded sand and clay section was assigned to the lower Porters Creek Formation. The base of the lowest clay bed in the transition zone was chosen as the contact for mapping purposes.

The lower Porters Creek section is developed more fully in the study area than any other area in Mississippi. A total of 59 feet (18 m) (from depths of 208 feet [63.4 m] to 149 feet [45.4 m]) was assigned to the lower Porters Creek section in the MMRI-Martindale No. 1 test well. The lower Porters Creek consists of a series of fine-grained sands, clay beds and indurated claystones representing beach to nearshore marine conditions. The sand beds appear to represent very near shore barrier bar to beach depositional environtments. The Tippah Sand Lentil is a formally named concentration of sand within the lower Porters Creek section. The upper 15 feet (4.6 m) of the Tippah Sand at the type section (SE 1/4, see. 12, T2S, R3E) are exposed in road cuts on the southern valley wall of Hurricane Creek. The Tippah Sand lithology here consists of very well sorted, micaceous, fine-grained sand containing laminations and Ophiomorpha sp. (Fig. 4) in addition to the upper Porters Creek clays and a thin section of basal Meridian Sand. Reineck and Singh (1975) would assign facies such as the Tippah Sand at the type section to middle shoreface depositional environments. Up the dip, the equivalent lower Porters Creek section (NW 1/4, sec. 21, T2S, R4E) is more argillaceous and contains wavy bedding and abundant burrows (Fig. 4). This facies suggests more near shore, intertidal depositional environments (Reineck and Singh, 1975) such as a coastal salt marsh.

[FIGURE 4 OMITTED]

A thin claystone overlies the beach deposits and represents the base of the upper Porters Creek section. The claystone is of particular interest as it contains sparse, abraded bivalve fragments (Venericardia sp.) and represents the transgressional phase, flooding the near shore sediments of the lower Porters Creek. Above the claystone is a thick clay section typical of the lithology often associated with the Porters Creek Formation.

The typical clay lithology of the Porters Creek consists of medium to dark gray clay which breaks with a conchoidal fracture. This clay section comprises the majority of the Porters Creek section and is a section of economic interest. The clay section appears massive upon initial examination, but when dried, laminations and thin silty, micaceous partings are obvious. The laminations can be well developed locally, even to casual observation throughout the section. Fossils are sparse and typically poorly preserved. There are at least two glauconite-enriched zones that subdivide this clay section. The glanconitic zones, when weathered, are often marked by black concretions consisting of manganese and iron oxides, and quartz sand grains. The clay section may also contain small, isolated channel sands of local extent. The clays are also highly expansive and have been responsible for foundation problems in structures not properly constructed to accommodate the movement associated with clay expansion and contraction.

The clay section becomes increasingly silty near the upper contact with the Naheola Formation, but retains its medium to dark gray color, conchoidal fracture and laminations typical of the Porters Creek lithology. It should be pointed out that Thompson (2000a, b) correlates the Matthews Landing Member of the Porters Creek into the adjoining Camp Hill and Whittentown Quadrangles. The brief description in the map legend indicates a lithology consisting of interbedded to interlaminated, pale yellow sand with common siderite concretions and nodules. This correlation is suspect as the lithologic description given by Thompson (2000a, b) is typical of the overlying Naheola Formation rather than the Porters Creek. The following evidence is offered as a discussion of this difference in interpretations.

(1) Formational Boundaries As the Matthews Landing Marl Member is the uppermost unit in the Porters Creek Formation, the upper formational contact has a direct bearing on its presence or absence. A primary lithologic characteristic of the Naheola Formation is the interbedded pale yellow sand and clays which often exhibit a greenish-gray color. The Porters Creek consists of laminated dark gray clays with only minor; local sands. The description of the Matthews Landing provided by Thompson (2000a, b) is consistent with the lithologic description of the younger Naheola Formation. This description leads to the conclusion that his Porters Creek-Naheola contact has been placed within the basal Naheola Formation, rather than lower in the section at the point of lithologic change. Restricting the interbedded sand and clay section to the Naheola is traditional, dating to the work of Mellen and McCutcheon (1939), and the work of MacNeil (1946) in his work through Mississippi and Alabama, and more recently by Swann (1999), and Moyse (1999).

(2) Lithology--The Matthews Landing lithology is a fossiliferous, marine marl. Although the Porters Creek is marine and sections of the Naheola are also marine, there is no calcareous unit which could be assigned to a marl lithology. Within the Walnut Quadrangle, macro fossils are sparse in both the lower Naheola and the upper Porters Creek section unlike the description of the traditional Matthews Landing. Toulmin (1977), does not recognize the Matthews Landing Member in his cross section which begins in Tippah County and MacNeil (1946) specifically states on his cross section that the Matthews Landing is absent in North Mississippi.

(3) Siderite Nodules and Concretions--Thompson (2000a, b) states siderite is common in his Matthews Landing section. The Matthews Landing is a marine unit, yet siderite is typically formed in freshwater depositional environments due to chemical considerations. Bemer (1971) states (p. 199) "... as a result marine siderite is rare. It has never been observed forming in modern marine sediments." The presence of siderite nodules suggests that the Matthews Landing section described by Thompson is not the marine depositional environment which is consistent with the traditional stratigraphic concept of both the Porters Creek and Matthews Landing. The Naheola Formation, however, does contain lignite beds and facies that could represent fresh water depositional environments which would be consistent with Thompson's descriptions.

These facts suggest that the "Matthews Landing Marl Member" of Thompson is actually higher in the section and part of the Naheola Formation, which also places his Porters Creek-Naheola contact west of where it would be if traditional stratigraphic assignments were used. Based on this mapping and previous work, there is no lithology consistent with the Matthews Landing Marl Member of the Porters Creek Formation present in the quadrangle or in Tippah County.

The Naheola Formation is the youngest unit of the Midway Group and conformably overlies the Porters Creek Formation. Recognition of the Naheola Formation in northern-most Mississippi is a result of the most recent mapping such as by Thompson (2000a, b). Earlier mapping assigned the lithologies now associated with the Naheola to various other units, most commonly some part of the Wilcox Group. Recent mapping has, therefore, separated the Naheola as a distinct mappable unit.

The Naheola outcrop belt is confined to the central and western half of the study area and extends into the adjoining Whitten Town and Camp Hill Quadrangles (Thompson, 2000a, b). Thompson subdivided the Naheola into its component Oak Hill and Coal Bluff Members. No attempt was made to map the subordinate Naheola members in this investigation, but Thompson's subdivision appears valid as there does appear to be a lithological basis for subdividing the formation.

The Naheola-Porters Creek contact is conformable and is defined by the lowest occurring sand bed above the gray, laminated clays of the Porters Creek section. The Naheola sands are typically fine-grained and often cross bedded, and are easily distinguished from the clay section of the Porters Creek. The Naheola clay beds are often a greenish-gray color and are interbedded with fine-grained sands. Iron oxide concretions are common in some parts of the Naheola section and represent weathered siderite nodules. An exception to the fine grain sizes is a zone near the middle of the Naheola which may contain coarse-grained sand and granules or clay clasts up to boulder size (Swann, 1999). A very thin Naheola section was cored in the MMRI-Martindale No. 1 well (only 12 feet [3.6 m]) near the top of the well. The overlying Meridian Sand is distinguished from the Naheola by a marked grain size change from the fine-grained sands and greenish-gray clays in the Naheola to the granule-containing, coarse- to medium-grained sands in the overlying Meridian Sand.

The Meridian Sand is the basal stratigraphic unit of the Claiborne Group and stratigraphically oversteps the older Wilcox and, more rarely, onto the Midway Group. This overstep was first suspected by Conant and McCutcheon (1941). Brown (1947, p. 34) also supported the overstep interpretation of the Meridian in his discussion of the Wilcox Group, "These strata are covered by overlap of the Meridian sand member of the Tallahatta formation in northern Mississippi." and states the outcrop pattern is "1 to 15 miles wide" in northern Mississippi. Lusk (1956) agreed with the overstep concept in adjacent Benton County as he mapped Meridian Sand to the Benton-Tippah County line. The Meridian overstep was also recognized in Tippah County in mapping conducted by Swann and others (1995), Swann (1999) and in Union County mapping by Moyse (1999). Although not mapped separately, Tourtelot (1964) also thought that some of the coarse-grained sands in the Tippah-Benton Bauxite District could be assigned to the basal Tallahatta Formation, i.e., the Meridian Sand. In contrast, Thompson (2000a, b) breaks with traditional interpretations of the stratigraphic section and does not recognize Meridian Sand in either the adjacent Camp Hill or Whitten Town Quadrangles, but, rather places the contact further west in the Slaydon and Holly Springs Quadrangles. Unfortunately, the reasons for this major reinterpretation of the section are unknown as there is no explanatory text accompanying his geological maps. Due to the lack of explanation for the reinterpretation of the Meridian section the fact that the historic interpretation of several previous investigators support a Meridian Sand overstep, and the traditional interpretation for a Meridian Sand overstep appears to be a valid lithostratigraphic interpretation based on the stratigraphic code, the interpretation of Thompson (2000a, b) cannot be supported.

The Meridian Sand consists of fine- to coarse-grained sand with scattered granules or small gravel, typically cross-bedded, and with subordinate clay lenses. The lower contact is perhaps the most notable in the study area with marked erosional relief beneath it, particularly where it oversteps the clays of the Porters Creek Formation. In some areas the clays underlying the contact are weathered, indicating the development of a paleosol. The relief associated with the erosion along the lower contact also complicates its mapping as it is seldom possible to project contacts with any accuracy.

The eastern edge of the Meridian Sand outcrop belt is characterized by a series of large channels or "channel complexes" incised into the underlying stratigraphic units and extending up dip onto older units forming the stratigraphic overstep discussed earlier. Centered on the town of Walnut, there is a large outlier that has been mapped as Meridian that overlies both lower Porters Creek and Clayton. This outlier was assigned to the Meridian due to its lithology, i.e., a cross bedded, medium-to coarse-grained sand, containing sparse, well rounded quartz gravel at its base. This lithology not consistent with younger terrace deposits as it lacked rounded, iron oxide cemented clasts, silt beds and did not contain the fining upward sequences characteristic of these Quaternary deposits. The Walnut outlier is also on trend with a large Meridian channel that continues westward into an eastward extension of the Meridian outcrop mapped by Lusk (1956).

Quaternary flood plains have also been mapped along the major fluvial components. These flood plains are typically well developed and are particularly broad in the Porters Creek outcrop belt. The largest flood plain is associated with Muddy Creek, a northward flowing tributary to the Hatchie River. Ditching and channelization along Muddy Creek dates from 1912 (United States Department of Agriculture, 1976).

The flood plains can vary significantly in lithologic characteristics, but typically consist of a fining upward sequence with clays at the surface. Outcrops are not common other than within the stream bottom or stream banks. The contact between the flood plain and valley walls is based, in part, on geomorphic criteria. The slope change, however, from flood plain to valley wall is so gradual in the Porters Creek outcrop that the geomorphic criteria were difficult to apply with great confidence.

Structure--The primary structural element in the study area is the Muddy Creek Fault Zone (Fig. 3) which has a northerly trend along Muddy Creek. Conant and McCutcheon (1941) suspected faulting in the Walnut-Muddy Creek area, but a lack of topographic maps made it difficult to identify fault trends or displacement. The environmental impact statement prepared for channelization work along Muddy Creek (United States Department of Agriculture, 1976) was more definitive, stating that there was structure in the Walnut area and noting a potential for hydrocarbons, though production was regarded as speculative. Bicker (1974) included a questionable fault trending northeasterly into northern Tippah County in his northern Mississippi cross section. There is, however, a significant difference in orientation between his fault and the Muddy Creek Fault Zone. Recent mapping adjacent and south of the study area has better defined the Muddy Creek Fault Zone and its southern terminus near Ripley, Mississippi (Swann and others, 1995; Swann, 1997, 1999). The northern terminus of the fault zone is unknown as it continues north of the study area into Tennessee. The Muddy Creek Fault Zone is interpreted as consisting of a set of en echelon faults rather than a single fault. The unusually straight valley walls of Muddy Creek appear to parallel projected component faults and may represent a fault line scarp.

[FIGURE 3 OMITTED]

Two parallel faults were mapped in the northwest corner of the study area in sec. 26 and 27, T1S, R3E. These faults displace Naheola and Porters Creek Formations, but the displacement is estimated at less than 20 feet (6.1 m). Another fault was mapped in sec. 14 and 15 T2S, R3E. This fault trends almost east to west and displaces both the Porters Creek Formation and the overlying Meridian Sand. Displacement appears to be approximately 20 feet (6.1 m) with the downthrown block to the north.

A small northerly trending fault is mapped on the southern boundary of the map area (crossing Turkey Creek) and is the continuation of a fault originally described in Swann (1999). This fault lacks sufficient offset to completely displace the Porters Creek Formation, so displacement is difficult to determine. It is estimated to have 20 feet (6.1 m) or less displacement.

The top of the lower section of the Porters Creek Formation is often marked by an indurated, glauconitic siltstone or mudstone that can be used as a marker bed for structural mapping. Structure contours based on the elevation of this marker bed illustrate an elongate, northerly trending, positive structure situated west of the town of Walnut (Walnut Anticline). The crest of the structure is situated in part of sections 19, 30, and 31 of TIS, R4E; sections 25 and 36 of T1S, R3E; section 1, T2S, R3E; and section 6, T2S, R4E. The Blackwell No.1 and the Melton No. 1, hydrocarbon test wells were drilled on structure, but south of its crest. The Martindale No. 1 well was drilled off the west flank of the structure but little is known of the stratigraphy encountered in this old hydrocarbon test. The Melton No. 1 well reported oil shows in the thick Paleozoic carbonate section. All of these wells were plugged and abandoned.

The Walnut Anticline is interpreted largely from surface mapping and could also be interpreted as a fault block associated with the adjacent Muddy Creek Fault Zone. The anticlinal interpretation is preferred because the lower Porters Creek siltstone marker bed elevation change is gradual rather than abrupt as would be expected if a fault boundary were crossed.

Hydrocarbon and Mineral Resource Potential-The hydrocarbon potential of northern-most Mississippi is largely unknown due to lack of exploration. There are no records, for example, from adjoining Benton County to indicate that there has ever been a hydrocarbon test well drilled within the county. The northern-most tier of counties in Mississippi (including Tippah County) is considered to be within the northern-most edge of the Black Warrior Basin. Present production (mostly gas) is south and east of the study area.

The Tertiary and Cretaceous sections in the study area, as is generally the case in the Black Warrior, are founded on an indurated Paleozoic section. The depth to the Paleozoic section is typically 1,100 feet (334.4 m) to 1,400 feet (425.6 m) in depth. From the few hydrocarbon test wells present in Tippah County, the stratigraphic assignments to the Paleozoic section are not without question, but it has been suggested that the top of this section is of Ordovician age. Some interpretations, however, assign at least parts of the Cretaceous subcrop to the basal Iowa Group (Mississippian). Regardless, the section consists of a thick sequence of limestones and dolostones with subordinate shales. The literature regarding the subsurface Paleozoic section in Mississippi is extensive, but work by Jennings (1994), Henderson (1991), Henderson and Gazzier (1989), and Schwalb (1982) should provide an overview.

The Memphis Equipment Co., No. 1 Melton well is probably the most important hydrocarbon test in the study area. The No. 1 Melton has a total depth of 5,302 feet (1,611.8 m) encountering the Paleozoic section (Ordovician?) at a depth of 1170 feet (355.7 m) and bottomed in what has been assigned to the Cambrian Copper Ridge. The Melton No.1 also contained a section referred to as the "reef facies." Examination of the cuttings from the Melton No. 1 are of poor quality so it was difficult to determine the nature of this "reef facies." The cuttings did yield two fragments from the "reef" interval that appeared to be poorly preserved, algal limestone. The Smackco. Ltd., No. 1 Blackwell, test well (with a total depth of 3200 feet [972.8 m]) is located approximately one half mile from the Melton well. An excellent set of cuttings sample descriptions was worked by the late Jack Henderson of the Mississippi Office of Geology for the No.1 Blackwell (sample descriptions are available from the Mississippi Office of Geology or the Mississippi Mineral Resources Institute). The "reef facies" is noted as consisting of chalk or "chalky limestone."

The presence of the Walnut Anticline, hydrocarbons shows in the cuttings of the Melton No. 1, and a potential algal facies are important factors for possible hydrocarbon trapping and production. The presence, however, of only two wells on which to base evaluations, and the lack of a clearly defined seal in the upper section of the Paleozoic carbonates are of concern. The Paleozoic section below the Melton No. 1 is virtually unknown and may be worthy of further investigation.

Other mineral resources within the quadrangle include industrial clays and sands. These resources are associated with the Porters Creek Formation and the Meridian Sand respectively. The thick clay section of the Porters Creek is currently being used as a agricultural carrier, an absorbent, and for various specialty products. The wide Porters Creek outcrop belt suggests there is an abundance of reserves in the study area.

The Meridian Sand is used most often as a construction sand but may also have other applications. Outside the study area, washing the sand yields a usable masonry sand and it may also be suitable for specialty market sands such as filter sands (coarser grain sizes). The lower section of the Porters Creek Formation also contains sands, but they are typically fine- to very fine-grained and not as thick or laterally as extensive as those of the Meridian Sand. These sands are probably of limited economic significance.

CONCLUSIONS

Geological mapping in the Walnut, Mississippi-Tennessee, topographic quadrangle has identified five Cretaceous and Tertiary units cropping out with the quadrangle. These include the Cretaceous Owl Creek Formation the Tertiary Clayton, Porters Creek, Naheola Formations and the Meridian Sand. The Wilcox Group is not present in the study area with the Meridian Sand in unconformable contact with stratigraphic units of the Midway Group. This Meridian Sand overstep mapped in the study area supports earlier work in Tippah County and adjoining Benton County. The flood plains associated with existing fluvial components were mapped as a separate unit.

The Muddy Creek Fault Zone is the major structural feature and is interpreted as series of en echelon faults trending northerly along the course of Muddy Creek. The fault zone influences the outcrop pattern of the units of the Midway Group and appears to control the orientation of Muddy Creek, its flood plain and its eastern valley wall. The Muddy Creek Fault Zone continues into Tennessee, so the northern terminus is unknown. Other structures, such as the Walnut Anticline, are adjacent to the Muddy Creek Fault Zone and may be structurally related.

A structure contour map constructed using the claystone bed dividing the upper and lower Porters Creek Formation as a marker bed, suggests a positive structure west of Walnut (Walnut Anticline) with a northerly trend. All of the hydrocarbon test wells (three) are associated with this structure. The Memphis Equipment Co., Melton No. land the Smackco Ltd, Blackwell No. 1 wells all went to total depth in carbonate rocks of Paleozoic age. Oil shows were noted from the Melton No. 1, but little else is known. This structure may be worthy of additional investigations for the potential of deeper hydrocarbons. The Porters Creek Formation and the Meridian Sand contain industrial clay and sand, respectively, that are of economic significance to the region.

ACKNOWLEDGMENTS

The author would like to acknowledge the assistance of the Mississippi Office of Geology which obtained the core and cuttings from the MMRI-Martindale No.l well that proved instrumental to the investigation. Mr. Rob Stewart and Ms. Cathy Grace (presently with EMS, Albuquerque, N.M. and the University of Mississippi, Department of Geology and Geological Engineering, respectively) assisted in core logging. Mr. Paul Mitchell, Mississippi Mineral Resources Institute, Technical Design Specialist, constructed the illustrations, and helped with completion of the digital version of the geological map. Ms Carol Lutken, Staff Geologist and Mr. Stephen Ingrain, Sr., Research Associate, both of the Mississippi Mineral Resources Institute, provided editorial comments and suggested changes which improved the paper. Dr. Darrel Schmitz, Mississippi State University; Ms. Julie Kelley, U.S. Army Engineering Research and Development Center; and Mr. Rick Ericksen, Mississippi State Board of Registered Professional Geologists, served as external reviewers for the Journal. Their help is gratefully acknowledged and their comments and suggestions improved the paper. The author, however, bears the responsibility of the conclusions proposed in the paper and the implications thereof. The "words of wisdom" regarding Benton County geology provided by Mr. Tracy Lusk, were greatly appreciated. The University of Mississippi Geoinformatics Center allowed us the use of their equipment and provided useful advice as we experimented with more efficient methods of producing digital geological maps.

LITERATURE CITED

Berner, R.A., 1971. Principles of Chemical Sedimentology McGraw-Hill Book Company, New York, New York, 240 pp.

Bicker, A.R., 1974. East-west cross section--Tishomingo County to Tunica County Mississippi. Mississippi Office of Geology, CS-2, one sheet.

Brown, G.F.,, 1947. Geology and artesian water of the alluvial plain in northwestern Mississippi. Mississippi State Geological Survey, Bulletin 65,424 pp.

Conant, L.C., and T.E. McCutcheon, 1941. Tippah County mineral resources. Mississippi State Geological Survey, Bulletin 42, 228 pp.

Henderson, K.S., 1991. Cambro-Ordivician subsurface stratigraphy of the Black Warrior Basin in Mississippi.Mississippi Office of Geology, Report of Investigations 2, 51 p.

Henderson, K.S., and C.A. Gazzier, 1989. Preliminary evaluation of coal and coalbed gas resource potential of western Clay County, Mississippi. Mississippi Bureau of Geology, Report of Investigations 1, 31 pp.

Herrick, S.M., and D.R. Rima, 1968. Foraminifera from the Clayton Formation (Paleocene) in southeastern Hardeman County, Tennessee. U.S. Geological Survey, Professional Paper 600-C, pp. C69-C74.

Jennings, S.P.,, 1994. Hydrogeology and aquifer potential of the Paleozoic rocks of Northeastern Mississippi. Mississippi Office of Land and Water Resources, Hydrologic Investigations Report 94-1, 54 pp.

Lusk, T.W., 1956. Benton County Geology. Mississippi State Geological Survey, Bulletin 80, 104 pp.

MacNeil, F.S., 1946. Summary of the Midway and Wilcox stratigraphy of Alabama and Mississippi. U.S. Geological Survey, Strategic Minerals Investigations Preliminary Report (3-195), 29 pp.

Mellen, FF., and T.E. McCutcheon, 1939. Winston County Mineral Resources. Mississippi State Geological Survey, Bulletin 38, 169 pp.

Moyse, M.M., 1999. The geology and land use recommendations of the Myrtle, Mississippi, 7.5 minute topographic quadrangle. Unpublished Master of Science thesis, University of Mississippi, 96 pp.

Reinck, H.E. and I.B. Singh, 1975. Depositional sedimentary environments. Springer-Verlag, New York, New York, 439 pp.

Schwalb, H.R., 1982. Paleozoic geology of the New Madrid area. U.S. Nuclear Regulatory Commission, NUREG/CR-2902, 61 pp.

Swann, C.T., F.S.M.R. Faruque, and J.L. Harding, 1995. The engineering and environmental geology of the Ripley Mississippi area--A guide for small municipalities. Mississippi Mineral Resources Institute, Open-file Report 95-1, 54 pp.

Swann, C.T., 1997. Geology of the Chalybeate Topographic Quadrangle, Tippah and Alcorn Counties, Mississippi. Journal of the Mississippi Academy of Sciences, 42:142-150.

Swann, C.T., 1999. Geology of the Falkner Topographic Quadrangle, Tippah County, Mississippi. Journal of the Mississippi Academy of Sciences, 44:206-215.

Thompson, D.E., 2000a. Geologic map of the Camp Hill Quadrangle, Benton and Tippah Counties, Mississippi, and Hardeman County, Tennessee. Mississippi Office of Geology, Open-File Report 95, I sheet.

Thompson, D.E., 2000b. Geologic Map of the Whitten Town Quadrangle, Tippah and Benton Counties, Mississippi. Mississippi Office of Geology, Open-File Report 94, 1 sheet.

Tourtelot, H.A., 1964. Bauxite deposits of the Tippah-Benton District Mississippi. U.S. Geological Survey, Bulletin 1199-C, 31 pp.

Toulmin, L.D., 1977. Stratigraphic distribution of Paleocene and Eocene fossils in the eastern Gulf Coast region. Geological Survey of Alabama, Monograph 13,602 pp. (2 vols).

United States Department of Agriculture, 1976. Environmental impact statement for Muddy Creek Watershed, Tippah County, Mississippi and Hardeman County, Tennessee. U.S. Department of Agriculture, 84 pp.