Novaculite Research Articles

Current Research at Arkansas Archeological Survey’s Henderson State University Research Station

During 2017, the Arkansas Archeological Survey celebrated its 50th anniversary with a series of website postings (http://archeology.uark.edu/who-we-are/50moments/), a forum at the annual meeting of the Arkansas Archeological Society, and a symposium at the annual Southeastern Archaeological Conference in Tulsa. In addition, the Survey made strides in documenting and archiving its history and collections. The Survey’s Henderson State University (HSU) Research Station in Arkadelphia continued to inventory curated artifact collections and scan older paper records and color slides. Trubitt and Cinotto, assisted by volunteers during weekly Archeology Lab Days, are updating the station’s curated collections database with artifact counts and weights, and using identified diagnostic artifacts to revise temporal information in the AMASDA state site files database. We are also adding new information on novaculite projectile point distributions to the “Arkansas Novaculite” website (http://archeology.uark.edu/novaculite/index.html) database. Ultimately, the novaculite distribution map will be expanded to create maps for each time period. This attention to the station’s curated collections inventory has sparked several new projects. We inventoried over 10,000 artifacts from 1973 testing at the Spanish Diggings site (3GA48) in Garland County, the largest of the Ouachita Mountains novaculite quarries. Novaculite debris from this quarry can now be compared with excavated samples of chipping debris and in-process pieces from other quarries and habitation sites. Diagnostic dart points (Marshall and Gary, var. Gary) indicate use of the quarry at least during the Middle and Late Archaic and Early Woodland periods (ca. 6000-200 B.C.).

Experimental constraints on dynamic fragmentation as a dissipative process during seismic slip.

Various fault damage fabrics, from gouge in the principal slip zone to fragmented and pulverized rocks in the fault damage zone, have been attributed to brittle deformation at high strain rates during earthquake rupture. Past experimental work has shown that there exists a critical threshold in stress-strain rate space through which rock failure transitions from failure along a few discrete fracture planes to intense fragmentation. We present new experimental results on Arkansas Novaculite (AN) and Westerly Granite (WG) in which we quantify fracture surface area produced by dynamic fragmentation under uniaxial compressive loading and examine the controls of pre-existing mineral anisotropy on dissipative processes at the microscale. Tests on AN produced substantially greater new fracture surface area (approx. 6.0 m2 g-1) than those on WG (0.07 m2 g-1). Estimates of the portion of energy dissipated into brittle fracture were significant for WG (approx. 5%), but appeared substantial in AN (10% to as much as 40%). The results have important implications for the partitioning of dissipated energy under extreme loading conditions expected during earthquakes and the scaling of high-speed laboratory rock mechanics experiments to natural fault zones.This article is part of the themed issue 'Faulting, friction and weakening: from slow to fast motion'.

Comparison of the Elemental Geochemistry of the Arkansas Novaculite and the Boone Chert in their Type Regions, Arkansas

The name Arkansas Novaculite was proposed by A.H. Purdue, 1909 to replace the name Arkansas Stone assigned by L. S. Griswold, 1892, but deemed too generic, to an interval of Early Devonian-Early Mississippian, very fine-grained, even textured, siliceous sedimentary rock famous for use as whetstones. The interval is exposed along the margins of the Benton Uplift, south flank of the Ouachita Mountains, west-central Arkansas, where it reaches a maximum thickness of 243.8 m (800 ft). The Arkansas Novaculite comprises informal lower and upper members characterized by massive beds of nearly pure novaculite, separated by a shale-bearing middle member that spans the Devonian-Mississippian boundary. The formation represents deep water deposition below carbonate compensation depths, in contrast to contemporaneous chert-bearing intervals, such as the Early Mississippian Boone Formation in the southern Ozarks, with chert formed in shallower marine conditions, or as a replacement of associated limestone beds. Source of the prodigious quantities of silica forming the Arkansas Novaculite has been controversial. Geochemical analyses, using both EDX and trace element analysis, were performed using mass spectrometry and have identified a significant contribution by both aluminum and potassium, which would seem to eliminate a biogenic origin and favor a volcanic source, perhaps related to an island arc system that formed during the Ouachita Orogeny as Laurasia collided with Gondwana. Trace element analysis also suggests that the Arkansas Novaculite and the chert in the Boone Formation may have both been formed from the same volcanic source.

Taking it to the River: Arkansas Novaculite Quarrying and Archaic Period Tool Production

Arkansas Novaculite, outcropping on ridge tops in the Ouachita Mountains of Arkansas and Oklahoma, was a critical resource for Indians living in both mountains and coastal plains. We review recent archaeological research on novaculite quarries and the movement of toolstone away from outcrops, especially during the Middle and Late Archaic Period (6,100-650 BC). Toolstone procurement was intensive and extensive, as shown through mapping of quarry features at Spanish Diggings, a major quarry at the southeastern end of the Novaculite Uplift. Analysis of tool production debris at the Jones Mill Site on the Ouachita River focuses on identifying heat treatment and biface reduction as people moved novaculite from source to habitation.

The Organization of Novaculite Tool Production: Quarry-Workshop Debitage Comparisons

Arkansas novaculite, outcropping in the Ouachita Mountains of Arkansas and Oklahoma, has been an important regional lithic resource for thousands of years. Because of the stone’s durability, by-products of past novaculite procurement and tool production and use activities litter the landscape in southwest Arkansas. Recent work situates novaculite quarries in the broader context of tool production and exchange systems. This article focuses on the organization of tool production, and explores analytical techniques that can be used to identify spatial separation of the lithic reduction process between quarry, workshop, and habitation sites.

Titanium, vanadium, and niobium mineralization and alkali metasomatism from the Magnet Cove Complex, Arkansas

The Christy Ti-V-Nb deposit is hosted by the Arkansas Novaculite, adjacent to the carbonatite-alkaline Magnet Cove Complex. Mineralized rock contains up to 8 wt percent Ti, 2.68 wt percent V, and 0.124 wt percent Nb. Minor amounts of Li and Mo are present, and there is evidence for the preferential concentration of the middle to heavy rare earth elements (REE) in altered clay-rich dikes. Mineralized rock consists of (1) thermally recrystallized novaculite that is partly replaced by actinolite, sodic amphibole, taeniolite (KLiMg 2 Si 4 O 10 F 2 ), pyrite,and siderite, (2) brookite-bearing amphibole- and taeniolite-rich rock that contains siderite and pyrite, (3) quartz-brookite aggregates, and (4) goethite-rich rocks that form the oxidized zone of the deposit. Unaltered rock is scarce at the Christy deposit. Comparison of mineralized lithologies from the Christy deposit with those from two other areas of mineralization associated with the Magnet Cove Complex, the Magnet Cove Titanium Corporation deposit (Rutile deposit) and the Hardy-Walsh prospect, provides mineralogical and chemical evidence for the source of the mineralizing fluids at the Christy deposit.Massive clay-rich (kaolinite + or - smectite) dikes are in contact with the mineralized zones of the Christy deposit. The presence of relict K feldspar and pyrite in the least altered dikes and certain characteristic trace elements (e.g., Ba, Rb) suggest that the Christy dikes are related to less pervasively altered rutile-mineralized, pyrite-bearing carbonate-feldspar dikes fromthe Rutile deposit. The feldspar-carbonate dikes from the Rutile deposit may be the products of intense alkali metasomatism of alkaline igneous silicate rocks that were emplaced prior to the intrusion of the Magnet Cove carbonatite.The Christy deposit formed through a series of complex processes. The initial phase of mineralization is directly related to the infiltration of novaculite by alkali-rich fluids that were probably derived from carbonatite magma. Introduction of the metasomatic fluids preceded emplacement of massive feldspar- and pyrite-bearing dikes that were subsequently altered to the clay-rich masses Titanium, V, Nb, and Li were introduced by the alkali-rich fluids at temperatures that were, as indicated by fluid inclusion data (Willis et al., 1991), as high as 600 degrees C. During the initial stage of mineralization, V was concentrated in aegirine and sodic amphibole, Li was concentrated in taeniolite, minor amounts of Ti were concentrated in aegirine, and pyrite formed. The replacement of novaculite by the aforementioned minerals yielded excess silica, which precipitated as quartz in veins and as clear overgrowths on recrystallized, inclusion-rich (partly replaced) quartz. Niobium- and V-bearing brookite precipitated with the quartz. Minerals formed during the first stage reacted with a second fluid at temperatures of 100 degrees to 300 degrees C, as indicated by fluid inclusion data (Willis et al., 1991), and V was then concentrated in smectite and goethite. The isotopic composition of siderite [delta 18 O SMOW = 23.8-25.0ppm, delta 13 C PDB = -7.1 to -8.9ppm suggests that the second fluid was a mixture of low-temperature metasomatic fluid and ground water. Vanadium was further concentrated in clay minerals (Breit et al., 1992), in goethite, and in vug minerals as low-temperature alteration proceeded. Brookite is not totally resistant to weathering and it is at least partly replaced by other oxides in the oxidized zone.

Oxygen diffusion in a fine‐grained quartz aggregate with wetted and nonwetted microstructures

Oxygen grain boundary and bulk diffusion rates have been measured in a 1.2‐μm grain diameter quartz aggregate (Arkansas novaculite) preannealed in wetting and nonwetting fluids to determine the effect of microstructure. Samples were preannealed at 800°C and 150 MPa confining pressure for 6 to 12 days with pure water, pure CO2, or water + NaCl (∼6M) to produce equilibrium microstructures. The samples were then annealed at 450° to 800°C and 100 MPa confining pressure with 98%18O‐enriched water to determine the diffusion rates. Profiles of18O/(18O+16O) with depth from the surface were measured using an ion microprobe, and the product of the grain boundary diffusion coefficient (D′) and effective boundary width (δ) or the bulk diffusion coefficient (Dbulk) determined. Compared to the starting material, the D′δ values for samples texturally equilibrated with pure CO2(nonwetted microstructure) and pure water are about the same and about 4 times greater, respectively. Bulk diffusivities in samples preannealed with 6MNaCl (wetted microstructure) are 4 to 5 orders of magnitude greater than the bulk diffusivities in samples preannealed with pure CO2(nonwetted). In addition, the D'δ value for a sample texturally equilibrated first with 6MNaCl and then with pure CO2is about a factor of 3 greater than the value for the starting material, demonstrating that the textural equilibration process is essentially reversible. The results of this study indicate that transport rates are strongly influenced by the wetting characteristics of coexisting fluids in a polycrystalline aggregate. In nonwetted samples, changes in the effective grain boundary width or the formation of small isolated pores at triple junctions can change D′δ values. However, these effects are minor compared to the change in transport rate for samples with nonwetted versus wetted microstructures. The much faster rates for samples with a wetted microstructure are believed to be due to oxygen transport along the interconnected channels by ionic diffusion in a static fluid. The bulk diffusivities obtained for samples with a wetted microstructure are consistent with previously determined values for oxygen exchange at an igneous intrusive contact.

The effect of fluid chemistry on wetting textures in novaculite

We have performed two suites of experiments at 600°C and 200 MPa on samples of Arkansas Novaculite to investigate the effect of fluid chemistry on the local distribution of fluids amid grains of solid rock under crustal conditions. Analysis of texture before and after these experiments indicates that fluid chemistry has an effect on both equilibrium wetting angles and the degree of fluid connectivity along triple junctions. The first suite of experiments shows that triple grain junctions in low‐porosity (ϕ < 1%) novaculite have dihedral angles (Θ) less than 60° in the presence of 1 m MgCl2, 3 m KCl, and 3 m, 4 m, or 6 m NaCl solutions. In these samples wetted triple junctions observed under a scanning electron microscope in polished section were approximately 0.15 μm from corner to corner. In fracture surfaces the triple junctions appear to form an interconnected network of very fine tubules. Novaculite in the presence of CaCl2 solutions also contains wetted triple junctions with Θ < 60° but appears to be less wetting than the previous fluids. Novaculite in the presence of H2O and CO2‐H2O equilibrates to nonwetting textures (Θ ≥ 60°) and lacks interconnected tubules as observed in fracture surfaces. In the second set of experiments samples were equilibrated sequentially in two different fluids. After this treatment, samples exhibited textures characteristic of the second pore fluid, attesting to the reversibility of the textural equilibration process and suggesting that reversion of textures occurs rapidly (<24 hours) under these conditions.

Measurement of oxygen grain boundary diffusion in natural, fine-grained, quartz aggregates

Grain boundary diffusion measurements using fine-grained, natural, monomineralic aggregates offer several distinct advantages over techniques previously employed. Pure quartz aggregates (Arkansas novaculite), with 1.2 and 4.9 μm diameter grains, were annealed at 450–800°C and 100 MPa confining pressure in 18O-enriched water. Profiles of 18O ( 18O + 16O) with depth from the surface were measured using an ion microprobe, and data were collected from an area 68 μm in diameter in order to obtain a well-averaged value for many grain boundaries. Using graphical solutions appropriate to the boundary conditions employed, the product of the average grain boundary diffusion coefficient ( D′) and effective boundary width (δ) is obtained and is independent of the grain size, geometry, and grain boundary tortuosity. Arrhenius parameters for the 1.2 and 4.9 μm grain size samples are: D′ 0 δ = 2.6 and 3.4 × 10 −17 m 3/sec, and Q = 27 ± 1 and 26 ± 3 kcal/mol, respectively. Measured values of D′ δ were about three times greater for the 4.9 μm aggregate, although this might be due in part to thermal cracking while going to temperature. The activation energy of both samples, ~ 27 kcal/mol ( 113 kJ/mol), is significantly less than that for volume diffusion of oxygen in quartz, but greater than that for ionic diffusion in a static fluid. Measured D′ δ values are within the range of most previous estimates. For a representative effective grain boundary width of 1 nm, the oxygen grain boundary diffusion coefficients are 4 to 6 orders of magnitude greater than oxygen volume diffusion coefficients in quartz single crystals, and ~6 orders of magnitude less than ionic diffusion coefficients in a static fluid, over the temperature range of the experiments.

Textures of Paleozoic chert and novaculite in the Ouachita Mountains of Arkansas and Oklahoma and their geological significance

Scanning electron micrographs of cherts and novaculites from the Ouachita Mountain fold belt of Arkansas and Oklahoma show a sequential range in textures from cryptocrystalline, anhedral quartz < 1 µm in diameter in the nonmetamorphosed chert and novaculite, to coarse, polygonal triple-point, euhedral quartz 100 µm or more in diameter where the cherts have been thermally metamorphosed, the coarsest being in xenoliths. The textures have been correlated with similar texture and crystal sizes in the chert from a contact metamorphic aureole on the Isle of Skye, Scotland, where classic metamorphic mineral assemblages from talc through tremolite, diopside, and forsterite grades have been identified. Texture of chert thus can be used as an indicator of elevated temperature. Mean apparent crystal diameters measured of the quartz in the Arkansas Novaculite and associated cherts were plotted on a map of the Ouachita Mountain fold belt extending from Little Rock, Arkansas, to near Broken Bow, Oklahoma. The regional trend in texture parallels the structural core trend and, in addition, is strongly overprinted by localized areas of coarser crystallinity near Little Rock, Magnet Cove, and Potash Sulphur Springs, Arkansas, where igneous intrusions have occurred, and near Broken Bow, Oklahoma. Temperature estimates from studies of fluid inclusions, stable isotope ratios, mineral-chemical phase relationships in associated rocks, and novaculite as xenoliths suggest that maximum temperatures as high as 760 °C may have been reached by portions of the novaculite. Other examples of triple-point texture in chert collected from distant localities, which range in age from Precambrian to Tertiary, show that polygonal triple-point texture in chert is world-wide in occurrence. It follows that small samples of chert-novaculite can yield evidence of a history of elevated temperature. Such evidence may be used to estimate maturation or degradation of hydrocarbons in the rocks and to furnish clues during exploration for thermally related metallic and nonmetallic minerals.

Devonian Novaculites as Source of Oil in Marathon-Ouachita Thrust System: ABSTRACT

The Arkansas Novaculite of southern Oklahoma and the Caballos Novaculite of west Texas (both Devonian) form fractured reservoirs in the Marathon-Ouachita thrust system. These formations were examined to ascertain their petroleum potential. End_Page 318------------------------------ Findings include the following. (1) The thermal maturity of the thrust system conforms to the maturity of the sequence that it has overthrust, suggesting that this allochthonous facies is not anomalously mature. (2) Shale units within the novaculites contain oil-prone organic matter in sufficient concentrations to constitute source rocks. (3) The composition of oils from Isom Springs field in southern Oklahoma and from McKay Creek field in west Texas is virtually identical and generally resembles Devonian oils in Oklahoma and west Texas. We conclude that the Devonian novaculites of the Marathon-Ouachita thrust system are self sourcing and do not require a fortuitous juxtaposition of source rocks of a different age to produce a commercial deposit. End_of_Article - Last_Page 319------------

Hydrogeochemical exploration for barite, Ouachita Mountains, U.S.A.

Approximately 100 springs were sampled as part of a general geochemical survey in a 130 by 140 km multi-mineralized area of the Ouachita Mountains. The study area was subdivided into Area I and Area II based on differences in lithology and mineralization. Area I is composed primarily of the Paleozoic Stanley Shale and the Arkansas Novaculite Formation, and has considerable manganese (often present as psilomelane) and barite mineralization. The barite occurs primarily as replacement deposits in shale in Area I. Area II is composed of Paleozoic and Cretaceous sedimentary rocks, and Quaternary alluvium. Mercury, antimony, strontium and barite mineralization is present. The barite mineralization occurs as cement in the Cretaceous sandstone and gravel in this area. The widely prevalent barite cement in Area II is reflected by higher median and upper range values of barium concentration and also higher median and threshold % BaSO 4 saturation values. The presence of barite as cement in the sediments of Area II tends to mask the detection of the barite deposits in this area. Approximately 83% of the sites within 1.7 km of known barite mineralization in Area I were characterized by anomalous barium concentration, and 67% within 3.4 km. Anomalous % BaSO 4 saturation values and Ba/Sr ratios produced success rates generally similar to those of anomalous barium concentrations. Anomalous strontium concentrations did not prove effective in detecting barite mineralization.

Fluid Flow Through a Crack Network in Rocks

A network of cracks pervading a rock is modeled by a random distribution of two-dimensional intersecting, complex, narrow cracks. The percolation properties of the resulting network are studied as functions of the crack-area density and size of the medium. Gas flow commences at a finite value of the crack density which in Arkansas Novaculite rocks amounts according to our model to 670 cracks per cm2. The mean probability of finding at least one crack intersecting another is 0.57 at the threshold density. Above that, the rock gas-flow permeability increases superlinearly with crack density due to the enhancement of short percolative paths.

A Petrologic Examination of Some Resedimented, Coarse-Grained, Clastic Intervals in Ouachita Mountains, Arkansas: ABSTRACT

Several resedimented, coarse-grained clastic intervals exist in the strata of the Ouachita Mountains. A petrologic examination of selected units in the basal Stanley Shale, the Arkansas Novaculite, and the Missouri Mountain Shale yields information pertaining to provenance, transportation, and deposition. Twenty-five coarse-grained units sampled are categorized as massive sandstone, pebbly sandstone, clast-supported conglomerate, and matrix-supported conglomerate. Samples exhibit grading, imbrication, and stratification indicative of mass flow and fluidal flow-transport processes. Sedimentary rock fragments are the predominant clasts, with chert being the primary constituent. Other major constituents are detrital quartz, rip-up clasts, and shale fragments, of which the latter show signs of soft-sediment deformation. A metasedimentary source area is inferred. Paleoflow direction, estimated to be to the south and southwest, was ascertained by orientation of imbricated clasts and channel cuts. A vertical sequence change from a matrix-supported conglomerate to a bimodal, clast-supported conglomerate, both of which exhibit channeling, to a massive sandstone occurs at one locality. This fining-upward sequence is due to a change in source area, which may be the result of tectonism and/or glacio-eustatic sea-level fluctuations. End_of_Article - Last_Page 452------------

Structural and Stratigraphic Framework of Lower Mesozoic and Upper Paleozoic Strata, Northeast Texas: ABSTRACT

The lower Mesozoic and upper Paleozoic were investigated in a 19,430 sq km area centered about Ellis County, Texas, in an effort to define the pre-Cretaceous surface, determine the westward extent of Jurassic rocks, analyze thickness and lithic nature of the lowermost Cretaceous, delineate the extent of faulting, and evaluate the economic potential of the section studied. The pre-Cretaceous surface dips east-southeast and consists of Paleozoic rock in the updip third of the study area and Jurassic rock in the downdip two-thirds. Regional dip increases southeastward into the East Texas basin, but is interrupted by Balcones and Mexia-Talco faults. According to seismic data, many of these normal faults extend into the Paleozoic section. They are Jurassic and younger in age and formed along preexisting lines of weakness in response to the structural development of the East Texas basin. Jurassic rock extends updip beyond the Mexia-Talco system in an onlap fashion, each carbonate formation becoming more clastic as it nears its own pinch-out. The overlying Hosston Formation was deposited in a fluvial to nearshore environment, in the study area, on the basis o reported lithologies and isopach form. The interval studied has economic potential as geothermal, ground-water, and hydrocarbon sources. Possible hydrocarbon traps include fractured Arkansas Novaculite, updip pinch-out of and porous facies within the Upper Jurassic formations, and traps against the downdip sides of faults in the Hosston Formation and underlying Jurassic formations. End_of_Article - Last_Page 607------------

Dynamic tensile strength of lunar rock types

The dynamic tensile strengths of four rocks have been determined. A flat plate impact experiment is used to generate ∼1‐μs‐duration tensile stress pulses in rock samples by superposing rarefaction waves to induce fracture. A gabbroic anorthosite and a basalt were selected because they are the same rock types as occur on the lunar highlands and mare, respectively. Although these have dynamic tensile strengths which lie within the ranges 153–174 MPa and 157–179 –MPa, whereas Arkansas novaculite and Westerly granite exhibit dynamic tensile strengths of 67–88 MPa and 95–116 MPa, respectively, the effect of chemical weathering and other factors, which may affect application of the present results to the moon, have not been explicitly studied. The reported tensile strengths are based on a series of experiments on each rock where determination of incipient spallation is made by terminal microscopic examination. These data are generally consistent with previous determinations, at least one of which was for a significantly chemically altered (hydroxylated) but physically coherent rock. The tensile failure data do not bear a simple relation to compressive results and imply that any modeling involving rock fracture consider the tensile strength of igneous rocks under impulse loads distinct from the values for static tensile strength. Generally, the dynamic tensile strengths of nonporous igneous rocks range from ∼ 100 to 180 MPa, with the more basic, and even amphibole‐bearing samples, yielding the higher values.

Ouachita Facies, an Overview: ABSTRACT

Since the discovery of oil in the Arkansas Novaculite in Marshall County, Oklahoma, in February 1977, several significant wells have been drilled in southeastern Oklahoma and in Grayson County, Texas. Sands in the Stanley formation and parts of the Bigfork formation have proven to be productive. An unnamed sand zone in the Womble that occurs about 200 ft (60 m) below the Bigfork has had significant shows and indicates that it too will be productive. Structural problems and stratigraphic surprises will probably be exposed as wildcat drilling continues. End_of_Article - Last_Page 1500------------

Gas Potential of Ouachita Facies, Atoka and Pushmataha Counties, Oklahoma: ABSTRACT

End_Page 1498------------------------------Atoka and Pushmataha Counties lie along the westernmost exposure of the Ouachita facies in southeast Oklahoma. Eight gas wells have been completed in this isolated exploration area, and six exploratory tests are in the drilling or completion stage. Seven of the completed wells are productive from the Mississippian Stanley sands, and produce at low daily rates. In mid-summer of 1980, a gas well was completed from the Arkansas Novaculite of Early Mississippian-Devonian-Silurian age, and from the Bigfork Chert of Ordovician age. Although a production history is not available on this well, an extensive lease play has resulted, and increased exploratory drilling has begun. The Novaculite-Bigfork production appears to be primarily fracture controlled, but will deliver gas at commercial rate . Only five tests in this general area were ever drilled deep enough to penetrate the Novaculite and/or Bigfork in the past, with three reporting commercial flows of gas, but owing to being in an isolated area with no gas pipeline, exploration has at a lull since the late 1950s. With the new drilling technology known today, the greatly improved stimulation methods, and adequate gas market conditions, this area will provide new exploratory targets in the 1980s End_of_Article - Last_Page 1499------------

Stress corrosion and the rate-dependent tensile failure of a fine-grained quartz rock

Pre-cracked double torsion specimens of Arkansas Novaculite were deformed (1) in the load relaxation mode, and (2) at a fast cross-head speed using an Instron deformation machine to obtain stress intensity factor ( K I)-crack velocity ( v) data for stress corrosion in liquid water. The fracture toughness ( K Ic) was found to be 1.335 ± 0.075 MN m −3/2. At temperatures from 20°C to 80°C the stress corrosion index, n( v ∞ K n I was 25.1 ± 1.5 and the activation enthalpy for crack propagation was 69.5 ± 1.7 kJ mole −1. The K I-v data at 20°C were used to generate a diagram predicting the influence of strain rate on tensile fracture stress. These predictions were in good agreement with the fracture stress determined by bend experiments in liquid water at 20°C. Both the predictions and the experimental results are consistent with a monotonie reduction in tensile fracture stress from approximately 72 MN m −2 to 39 MN m −2 as strain rate is reduced from 6 · 10 −5 s −1 down to 10 −10 s −1. At strain rates faster than approximately 6 · 10 −5 s −1 stress corrosion does not influence the tensile fracture stress. It is unlikely that Novaculite will exhibit a fundamental fracture stress during deformation at even the slowest geological strain rates.

Oil Production from Fractured Cherts of Woodford and Arkansas Novaculite Formations, Oklahoma: ABSTRACT

The chert section of the Woodford Formation has been known to be productive of oil and gas for at least 30 years. However, little was known about the chert as a reservoir until 1969 when Jones and Pellow Oil Co. and Westheimer-Neustadt Corp. jointly developed the Northeast Alden pool extension in T7N, R13W, Caddo County, Oklahoma. Cores, thin sections, X-ray analyses, and combustion tube studies indicate that the Woodford Chert is a prime source bed for hydrocarbons, and when fractured is an excellent reservoir. In February 1977, Westheimer-Neustadt Corp. drilled the No. 1 Wallace in Sec. 2, T8S, R5E, to test the Arkansas Novaculite, which is similar to the Woodford Chert, and completed the well for a potential flow of more than 1,000 bbl of oil per day. The significance of the discovery has not been fully realized by industry in that it may have opened a new petroleum province in the Ouachita facies that extends from southeastern Oklahoma in a broad arch for over 600 mi (966 km) to the Marathon Mountains near the Mexican border. End_of_Article - Last_Page 754------------