Southeastern Missouri Research Articles

Alteration of organic matter in the Viburnum Trend lead-zinc district of southeastern Missouri

Organic petrography and elemental analyses were used to study alteration of organic matter in the Bonneterre Formation dolostones. Reflectance measurements and petrographic characteristics of organic particles define an alteration zone about 20 km wide, centered on the Viburnum Trend ore deposits. Within this zone, bitumen has been generated from kerogen. In contrast, no evidence of local bitumen generation was observed in samples located more than 10 km from the Viburnum Trend. This could indicate a level of thermal maturity significantly greater than the regional background level.The organic matter in the Bonneterre Formation consists primarily of amorphous marine kerogen, algal remains (alginite), and solid bitumen. In the absence of vitrinite, relative levels of thermal maturity were determined from the reflectance, fluorescence, and state of preservation of fossil unicellular algae. Within the alteration zone the alginite has been impregnated with bitumen, and there is convincing petrographic evidence that the bitumen was locally generated. Outside of the alteration zone, the algae are well preserved and exhibit the bright yellow fluorescence characteristic of immaturity. There is also petrographic evidence of increased solid bitumen reflectance due to interaction with pore fluids, both within and outside the alteration zone. Elemental analyses suggest that organic matter has been oxidized throughout the study area.Although there is no direct evidence linking the organic maturation and alteration with ore deposition, the association of the alteration zone with a major Mississippi Valley-type deposit permits the hypothesis that the regional flow of hot brines associated with the deposit was the cause of the anomalous heating, and that the evolution of methane and other gases during this process played a role in the ore deposition.

Factors controlling the distribution of a subtropical corn borer,Diatraea grandiosella(Lepidoptera: Pyralidae)

During this century the southwestern corn borer, Diatraea grandiosella (Lepidoptera: Pyralidae), has extended its range from subtropical Mexico into the United States, below 38° N latitude. This maize‐feeding insect is now found from Arizona east to Alabama and north to Kansas, Missouri, and Tennessee. The species has adapted to the shorter growing seasons, longer summer daylengths, and lower winter temperatures present in the southern US than are present in Mexico. Life history, morphological, and behavioral traits were compared for populations of D. grandiosella from southeastern Missouri and southcentral Mexico and revealed differentiation in a suite of characters, some of which show clear adaptation to a northern climate while others are obviously less adaptive. An electrophoretic comparison of enzymes from D. grandiosella from the central portion of its range in the US and from a population from southcentral Mexico indicated that considerable genetic differentiation has occurred. Quantitative genetic...

Hierarchical Levels of Heterogeneity in a Mississippi River Meander Belt and Application to Reservoir Systems: Geologic Note (1)

Six hierarchical levels of sand heterogeneity that would be present in analogous reservoirs are recognized in a Mississippi River meander-belt system in southeastern Missouri: (1) meander belt, (2) meander scroll, (3) channel, point bar, and splay, (4) lobe sheet, (5) bedding unit, and (6) laminae. Heterogeneity level 1 is similar in size to an oil field and consists of (1) 9 million ac-ft (11.1 billion m{3}) of high-permeability channel sands in numerous meander scrolls and (2) 4 million ac-ft (4.9 billion m{3}) of low-permeability clay plugs (in numerous abandoned channels) that separate a field into isolated pools and reservoirs. Overbank flood-plain muds capping the meander-belt system are barriers to vertical migration of fluids. Heterogeneity level 2 is the size of pools within a field and has 1.2 million ac-ft (1.5 billion m{3}) of highly permeable, laterally accreted channel and point-bar sands, partly or wholly isolated from other sand bodies by low-permeability, abandoned-channel clay plugs. Abandoned mud-filled chutes impede lateral migration of fluids in the upper pa ts of the meander scroll. The third level of heterogeneity is composed of about 70,000 ac-ft (86.3 million m{3}) of individual, permeable channel, point-bar, and crevasse-splay sand bodies, with numerous thin sheets and lenses of low-permeability muds and silts (derived from chute fill and mud drapes) that impede vertical migration of fluids. Heterogeneity level 4 is the lobe sheet unit (reservoir pay zone about 450 ac-ft or 555,000 m{3} in volume) comprising channel, point-bar, and splay sand bodies. The fifth level of heterogeneity is the single bedding unit (about 10 ac-ft or 12,000 m{3}) at the scale of a reservoir flow unit or perforated interval. Permeable, cross-bedded sand bundles are separated by low-permeability, inclined and horizontal mud-silt layers and lenses present along bed-set boundaries. Heterogeneity level 6 is individual sand laminae (grain-flow lenses or grain-fall sheets) separated by textural variations (and hence permeability-porosity variations) and isolated mud-silt laminae. Permeabilities range from 90-160 d in sand; several millidarcys to 50 d in muddy sand, silt, and sandy silt beds from the levee, crevasse, and abandoned-channel fill; and less than 10 md in muddy silts and muds from abandoned-channel and chute-fill mud sheets and laminae. At all levels within a fluvial meander-belt system, these permeability heterogeneities are the principal controls on productivity throughout the life of a reservoir.

Integrating paleontology, geothermometry, and sedimentology in determining the history of the Reelfoot Basin, southern midcontinent, U.S.A.

The northeast-trending Reelfoot basin, extending from northeast Arkansas and westernmost Tennessee into southeastern Missouri, southernmost Illinois, and westernmost Kentucky, is geologically, and socioeconomically, significant because it is co-extensive with the New Madrid Seismic Zone, one of the most seismically active areas of the central and eastern United States. The basin has been periodically active from its inception as a rift basin in the Proterozoic to the present and has accumulated up to at least 5,000 m of sediment, including up to at least 1 km of Cretaceous and Tertiary sedimentary strata near the head of the Mississippi Embayment. Structural and stratigraphic interpretations within the subsurface pre-Mesozoic part of the basin have been based almost entirely on geophysical and physical stratigraphic criteria; these interpretations have been loosely constrained due to an extreme sparsity of drillhole data through the Paleozoic sequence. Recent analysis of Cambrian and Ordovician fossils (conodonts, palynomorphs, brachiopods, and trilobites) from cuttings and core from a very few drillholes allows establishment of the beginnings of a verifiable stratigraphy for this part of the sequence. The paleontological data also provide (1) biofacies evidence for interpretations of the depositional setting during part of the Late Cambrian and Early Ordovician interval and (2) thermal maturation data pertaining to the post-depositional geothermal history of these strata.Upper Cambrian phosphatic brachiopods and trilobites provide improved correlations between strata in the basin, the Ozark shelf to the northwest, and the Upper Mississippi River Valley. Cold-water-realm palynomorphs and trilobites from siliciclastic rocks of turbiditic origin in the central part of the Reelfoot basin support an interpretation, based on sedimentary structures in a short interval of core, of a deep-water basinal origin for these strata.Lower Ordovician conodonts provide a biostratigraphy for the carbonate rocks of this part of the sequence; correlations can be made with the shallow-water sequences of the Knox, Prairie du Chien, and Arbuckle Groups, and the Ozark sequence of the adjacent shelf areas to the east, north, and west. The uppermost Lower Ordovician strata in the basin record a short-term incursion of cooler water environments, reflected by the character of both the conodont fauna and the lithofacies. The youngest Paleozoic dates known from the basin south of the Pascola arch are latest Ibexian (Early Ordovician).Thermal alteration indices of both the Cambrian palynomorphs (organic-walled microphytoplankton) and Ordovician conodonts in the deeper parts of the basin, corroborated by fluid inclusion thermometry, vitrinite reflectance, and other geochemical techniques, are of higher values than predicted using any published estimates of overburden burial. These maturation values most likely reflect burial enhanced by the passage of hydrothermal fluids on a regional scale; they place constraints on interpretations of the tectonothermal evolution of the basin.

Thinning effects on diameter growth in black and scarlet oak as shown by tree ring analyses

In the period 1953–1954, five levels of thinning were imposed as part of a crop tree release study on a 32-year-old mixed stand of scarlet oak ( Quercus coccinea Muench.) and black oak ( Quercus velutina Lam.) located in southeastern Missouri. In winter 1985, 162 live trees were felled (90 scarlet oaks and 72 black oaks). A section of 10 cm thickness was cut from the base of each butt log. Dendrochronological techniques were used to gather and prepare data to compare treatment responses. Although there was a significant differential treatment response attributable to thinning, the timing of this response varied between the two species. Black oaks had a 10 year period of increased differential growth immediately after the thinning whereas the scarlet oaks, with a 12 year differential growth period, lagged 6–7 years behind. This was not apparent using the standard inventory techniques of periodic diameter measurements.

Water relationships among wetland habitat types in the Mingo Swamp, Missouri

The hydrologic relationships of 15 lowland hardwood wetland habitat types in the Mingo Swamp of southeastern Missouri were analyzed using principal component analysis (PCA) and clustering multivariate techniques. Both the PCA and cluster analyses defined significant differences among wetland types. In all PCAs, the percentage of total water coverage, percentage of water 30 cm deep had the highest loading in factor I and were most useful in separating wetland types. Typically, open water habitats were classified at one extreme in the analyses and pin oak/hickory habitats at the opposite extreme. Dead tree, open marsh, ditch, and river habitats were usually closely grouped; however, all green-tree reservoir habitats were hydrologically shifted toward deeper, more permanently flooded conditions, especially in fall and early winter.

The Butler Hill Caldera: a mid-Proterozoic ignimbrite-granite complex

Abstract Uplift along rift-related faults in the eastern St. Francois igneous terrane of southeastern Missouri exposes a high-level anorogenic igneous complex consisting of 1.5 km of intracaldera ignimbrites, a zoned central pluton, and late-stage ring plutons. A collapse structure, named the Butler Hill Caldera (BHC), formed in response to eruption of comenditic ignimbrites of the Lake Killarney Formation which attains an intracaldera thickness of 400 m. Continued peralkaline volcanism resulted in an additional 1000 m of Grassy Mountain Ignimbrite within the caldera and a thin, but widespread, outflow sheet. Following degassing of the magma chamber, the central pluton forcefully intruded the intracaldera volcanic sequence producing arcuate folds concentric to the caldera axis. Remnants of the original magma chamber roof are not preserved. The final igneous event related to the BHC involved intrusion of amphibole-granitoids in an annular pattern within, and concentric to, the caldera walls. The latter bodies probably merge, with depth, into a single ring pluton. The petrographic zoning exhibited by the mildly peraluminous central pluton of the BHC consists of: (1) a roof-zone of fine-grained, brick-red, hypersolvus granophyre with abundant miarolitic cavities which is nearly devoid of hydrous minerals; (2) a transitional zone of pink fine- to medium-grained seriate granite in which granophyric intergrowths are common and plagioclase and biotite are present in trace amounts only; and (3) a border zone of medium- to coarse-grained pink to grey subsolvus biotite granite with rapakivi texture. The paradoxical association of peralkaline and peraluminous suites with hypersolvus and subsolvus petrographic traits at the same structural level is recognized in other high-level anorogenic complexes. The common factor in these terranes, regardless of their age, appears to be that initial magmas were hot, relatively dry, low in CaO and high in F. These compositional features favor ascent of hypersolvus magmas to subvolcanic levels where saturation is accomplished by influx of meteoric water. Field, chemical, isotopic, and petrographic evidence indicate that BHC rocks have experienced at least two periods of subsolidus metasomatism. The resulting metasomatic features are typical of anorogenic ignimbrites and high-level granitoids elsewhere and must be quantified before existing chemical data can be applied to questions of igneous petrogenesis.

Cold hardiness of larvae of the southwestern corn borer, Diatraea grandiosella

AbstractThe cold‐hardening capacity of field‐collected larvae from southeast Missouri and laboratory‐reared larvae of the southwestern corn borer, Diatraea grandiosella Dyar, was examined. Supercooling points of non‐diapause and diapause larvae collected from maize plants grown in Missouri (36° 30′ N lat.) were ca. –7.0 °C. The hemolymph melting points of diapause field larvae (–0.8 °C) were significantly lower than those of non‐diapause larvae collected in July (–0.5 °C). The supercooling points of hemolymph from non‐diapause and diapause field larvae ranged randomly from –10° to –18 °C. Supercooling points of non‐diapause laboratory larvae increased from –13° to –10 °C prior to pupation, whereas those of diapause larvae increased similarly before the onset of diapause, but then decreased during diapause to ca. –17 °C. No change in supercooling points or capacity to survive in the presence of ice was observed in diapause laboratory larvae acclimated at 4 °C for 63 days. Laboratory and field larvae began to freeze at ca. –1.5 °C in the presence of ice, but survived to several degrees below their melting points. The high supercooling points of field larvae appeared to be due to the presence of an environmental ice‐nucleator. Although data for laboratory larvae indicate sufficiently low supercooling points to permit winter survival in southeastern Missouri, considerable larval mortality occurs in the field due to inoculative freezing and the presence of an ice‐nucleator.

Late Quaternary paleoecology and paleoenvironments of the Central Mississippi Alluvial Valley

A radiocarbon-dated sediment core from Powers Fort Swale, located in the Western Lowlands of southeastern Missouri, provides sedimentological and palynological evidence for dynamic changes in fluvial regime and vegetation in the Central Mississippi Alluvial Valley during the late Pleistocene and Holocene intervals. During the late Wisconsinan glacial maximum, glacial meltwater carried by the Mississippi River maintained active braided streams. Sand grains in full-glacial and late-glacial sediments of Powers Fort Swale show evidence of reworking by eolian activity, with late Pleistocene formation of sand dunes continuing until 11,600 yr B.P. within the Western Lowlands. The sedimentological sequence indicates a progressive, stepwise loss of glacial meltwater and coarse sediment supply during the late-glacial interval, resulting in abandonment of braided-stream terraces. The initial, partial diversion of Mississippi River flow occurred in the late-glacial interval, possibly as early as 16,300 yr B.P., as the Mississippi River shifted from the Western Lowlands through the Bell City-Oran Gap in Crowleys Ridge and into the Eastern Lowlands. By 14,500 yr B.P., the complete diversion of meltwater through this gap coincided with a change in the Powers Fort sediment core from a spruce-dominated to an oak-dominated pollen assemblage. At 11,500 yr B.P., sedimentological changes reflected a changeover to a meandering river regime. The transition to pollen assemblages characteristic of Holocene temperate swamp forest occurred at 9500 yr B.P.

Paleomagnetic age of the central Missouri barite deposits and its genetic implications

In the Central Missouri barite district, barite samples were taken from four barite deposits and carbonate samples from the Lower Ordovician Jefferson City and Gasconade Dolomites in two road cuts and from the Mississippian Burlington Limestone in a quarry. The samples were tested paleomagnetically using detailed alternating field and thermal demagnetization and saturation isothermal remanent magnetization methods. An A magnetization direction of declination = 153.5 degrees , inclination = 17.6 degrees (N = 35, k = 17, alpha 95 = 4.8 degrees ) is carried by pseudosingle domain magnetite in the barite-rich zones of three open-pit mines as an ore-synchronous component, in the Jefferson City Dolomite as a secondary component, and in collapse breccia blocks of probable post-Middle Devonian age in the dolomite to give a negative conglomerate test. The A paleopole at 121.0 degrees E, 36.6 degrees N (dp = 2.6 degrees , dm = 4.9 degrees ) falls within the Kiaman reversed magnetic polarity interval on the Late Pennsylvanian to early Early Permian part of the apparent polar wander path for North America. A B magnetization direction of declination = 36.8 degrees , inclination = 77.8 degrees (N = 21, k = 13, alpha 95 = 92 degrees ) is found in the other units. It is a hybrid magnetization dominated by hematite produced by weathering and by viscous remanence in magnetite, both of Quaternary origin. The Kiaman magnetization in the barite ores and host rocks of the Central Missouri district agrees with known Kiaman magnetizations in the lead-zinc ores and host rocks of the adjacent Southeastern Missouri and Northern Arkansas districts. This agreement provides strong support for the Ouachita tectonic uplift model of genesis for the origin of the Mississippi Valley-type ore deposits in the midcontinental region of the United States.

Bootheel lineament: A possible coseismic fault of the great New Madrid earthquakes

A remote sensing examination of the New Madrid seismic zone has revealed a feature, the Bootheel lineament, that may be the surface expression of one of the coseismic faults of the great New Madrid earthquakes of 1811 and 1812. The lineament extends about 135 km in a north-northeast direction through northeastern Arkansas and southeastern Missouri. The morphology and pattern of the lineament suggest that it reflects a fault with strike-slip displacement. Field data indicate that liquefied sand was injected along the lineament, probably in 1811 and 1812. The Bootheel lineament does not coincide with any of the major arms of New Madrid seismicity, possibly indicating that the current seismicity does not precisely reflect the faults that ruptured in 1811 and 1812.

Stable carbon isotopes and the study of prehistoric human diet

Mass spectrometric analysis of the stable carbon isotope composition (13C/12C or delta 13C) of bone collagen from human remains recovered at archaeological sites provides a direct chemical method for investigating dietary patterns of prehistoric human populations. This methodology is based on the facts that (1) different food items within the human diet have distinct delta 13C values, and (2) the delta 13C value of human bone collagen is determined by the delta 13C value of the diet. Studies of the development of subsistence patterns based on corn agriculture, one of the most significant developments in North American prehistory, can benefit from the use of stable carbon isotope techniques because corn has a high delta 13C value relative to other components of the human diet. Measurements of delta 13C of bone collagen from prehistoric human skeletal remains from southeastern Missouri and northeastern Arkansas indicate that intensive corn agriculture began in this region around A.D. 1000, that the incorporation of corn into the human diet was a rapid phenomenon, and that 35 to 77% of the human diet from A.D. 1000 to A.D. 1600 consisted of corn. Results from an isochronous population in southeastern South Dakota (A.D. 1400) suggest that 78 to 90% of the diet of this group consisted of corn, with no difference between males and females. Coupled with more traditional archaeological methods, stable carbon isotope analysis of bone collagen can significantly enhance reconstruction of dietary patterns of prehistoric humans.

Diagenesis, thermal maturation and burial history of the Upper Cambrian Bonneterre dolomite, southeastern Missouri; an interpretation of thermal history from petrographic and fluid inclusion evidence

In this report, fluid inclusion, thermal alteration index (TAI) and petrographic data are used to interpret thermal maturation and burial history of the Bonneterre Formation of southeastern Missouri. TAI visual estimates, based on indigenous Upper Cambrian acritarchs, indicate maximum thermal exposure into the mid-upper peak gas window. This interpretation is in agreement with maximum fluid inclusion homogenization temperatures which average 235°C (455°F or an approximate vitrinite equivalent of 1.7% R 0). Thin-section petrography and fluid inclusion evidence further indicate that three separate episodes of burial have occurred. Initial burial, of unknown depth or thermal exposure, culminated in a period of uplift and karstic subaerial exposure possibly during Late Ordovician time. Maximum burial and thermal exposure to the mid-upper peak gas window followed, and is represented in the rock by a high-temperature (235°C), randomly oriented two-phase fluid inclusion population in matrix dolomite. Subsequent uplift, possibly coincident with Ouachita overthrusting, resulted in a variety of diagenetic fabrics, including late burial cements and fractures. Secondary two-phase fluid inclusions within these late calcite cements and those occurring in linear trains that cut across matrix dolomite record lower average homogenization temperatures than their unoriented precursors (average T h = 170°C, or an approximate equivalent of 1.3% R 0), further indicating that a significant amount uplift has occurred since maximum burial. Present-day bottom hole temperatures of only 74°C (an approximate equivalent of 0.7% R 0) indicate that uplift has occurred after this second burial episode. This event probably coincides with the development of the New Madrid Fault system during the Tertiary, which still active today. These results demonstrate the utility of fluid inclusion microthermometry complex burial/thermal histories.

Geoarchaeological evidence of strong prehistoric earthquakes in the New Madrid (Missouri) seismic zone

Sand blows and fissures that cover >10,500 km{sup 2} in northeastern Arkansas and southeastern Missouri attest to the severity of the 1811-1812 earthquake series in the New Madrid seismic zone. However, except for one occurence near New Madrid, Missouri, the region has been devoid of any evidence of other major shocks for at least 1.3 ka prior to 1811 and possibly for >9 ka. Stratigraphic relations and radiocarbon dating at a recently excavated archaeological site near East Prairie, Missouri, have revealed liquifaction phenomena attributable to a shock dated to within about 100 yr prior to A.D. 539 and a probable second one dated between about A.D. 539 and 991.

Dolomitization and Dolomite Neomorphism in the Back Reef Facies of the Bonneterre and Davis Formations (Cambrian), Southeastern Missouri

The back reef facies of the Bonneterre and Davis Formations consists of dolomitized cryptalgalaminates and partially dolomitized peloid mudstones. These subfacies were deposited on tidal flats and in shallow lagoons that existed in the St. Francois Mountains of southeast Missouri during late Cambrian time. The back reef facies is bounded on the seaward side by dolomitized algal bioherms and grainstone banks which host the southeast Missouri Mississippi Valley-type (MVT) lead-zinc-copper ore deposits. Cryptalgalaminates are replaced by both fine crystalline, planar dolomite and coarse crystalline, nonplanar dolomite. Peloid mudstones are partially replaced, but mainly by coarse crystalline, nonplanar dolomite. Planar dolomite, replacing cryptalgalaminates, shows gradational transitions into coarse crystalline, nonplanar dolomite. The transitions are accompanied by progressive increase in average crystal size and an increased skewness toward the coarse size fraction. Planar dolomite is enriched in 18 O relative to stratigraphically equivalent marine limestones. Coarse crystalline, nonplanar dolomite, which replaces both cryptalgalaminates and peloid mudstones, has delta 13 C and delta 18 O values transitional between those of planar dolomite and late dolomite cements associated with MVT mineralization. Fluid inclusion analysis of nonplanar dolomite and associated dolomite cements indicates precipitation at elevated temperatures (60 to 114 degrees C) by saline, basinal fluids. These data indicate that the back reef facies was subjected to a complex diagenetic history involving both early and late diagenetic dolomitization and dolomite neomorphism. Fine crystalline, planar dolomite was formed during early diagenetic dolomitization of the cryptalgalaminate subfacies by a fluid approaching seawater composition. Coarse crystalline, nonplanar dolomite was formed as a result of neomorphism of pro-existing planar dolomite and dolomitization of peloid mudstones, after burial, accompanying MVT mineralization in southeast Missouri.

Rich Fen Bryophytes in Missouri: Ecological Comments and Three State Records

Aneura pinguis (L.) Dum., Calliergonella cuspidata (Hedw.) Loeske, and Campylium stellatum (Hedw.) C. Jens. are reported new to Missouri from calcareousfens of the eastern Ozarks. Aneura occurs farther south in Arkansas and Oklahoma, but the Calliergonella and Campylium are disjunct and at the southernmost known limits of their ranges in the Midwest. It is probable that these fens in Missouri provide relict habitats for species that were more widespread in the lower Midwest during Pleistocene full glacial time. Calliergonella is documented from Alberta, Canada as well. Fens are grass-, sedge-, or reed-dominated, peat- forming ecosystems that develop under the influ- ence of mineral-rich ground water (Crum 1988). Like bogs, fens are systems in which productivity exceeds decomposition and hence peat, rich in or- ganic material, accumulates. Fen peat forms a sub- strate upon which unique assemblages of plants are found. These include a diversity ofbryophytes, from peat mosses of the genus Sphagnum that dominate in acidic poor fens to brown mosses, mostly of the families Amblystegiaceae and Brachytheciaceae, that dominate in alkaline, rich fens. Fens are most abundant in boreal landscapes that, in North Amer- ica, have been recently glaciated. As temperatures increase, decomposition rates increase (Damman 1979); therefore, farther south in temperate North America fens decrease in abundance. In the central Midwest, they form a minor component of the land- scape. Missouri fens are calcareous communities that occur mainly in the unglaciated Salem Plateau re- gion in the Ozarks of southeastern Missouri (Kurz

Geochemical and petrographic evidence for fluid sources and pathways during dolomitization and lead-zinc mineralization in southeast Missouri: A review

Regional geological studies in southeastern Missouri have made a significant contribution to knowledge of the origin of Mississippi Valley-type mineralization and the late diagenetic history of sedimentary rocks throughout this part of the Midcontinent. In addition to mineral exploration, investigations such as these provide insights into basinal processes such as migration and distribution of petroleum, dolomitization, and porosity modification of carbonate petroleum reservoir rocks.

Effects of Temper on Strength of Ceramics: Response to Bronitsky and Hamer

Results of strength tests on sand- and shell-tempered ceramics reported by Bronitsky and Hamer (1986) are difficult to interpret because of flawed experimental procedures and have questionable relevance to the archaeological record. Results from an improved procedure suggest shell-tempered ceramics as produced in prehistoric southeastern Missouri were stronger and tougher than sand-tempered counterparts.

Facies, Depositional, and Diagenetic Environments of Golconda Group (Mississippian) in Southwestern Illinois and Southeastern Missouri: ABSTRACT

In southwestern Illinois and southeastern Missouri, the Golconda Group (Late Mississippian) is composed of interbedded calcareous and noncalcareous shales, bioclastic and oolitic limestones, and quartz siltstones and sandstones, in order of decreasing abundance. These were deposited on a shallow-marine shelf under the influence of a fluvial-deltaic complex originating from the north. The primary factors responsible for the abundance and lateral variability of these lithologies were environmental energy level and terrigenous sediment supply. These factors contributed to the formation of 12 distinct Golconda lithofacies (two siliciclastic and ten carbonate facies). They formed in a variety of shallow shelf environments. Localized bioclastic and oolitic accumulation, resulting in shoal formation, and storm surges were the predominant depositional processes for limestones on this shelf. Environmental energy appears to have increased toward the southwest with a corresponding decrease in water depth. This was the result of an area of emergence toward the southwest, from which minor fine-grained, siliciclastic sediment may have been supplied to the basin. Based on petrographic observations, the diagenetic sequence of the Golconda was as follows: eogenesis, marine phreatic and freshwater phreatic succeeded by a fresh/saline water mixing zone; mesogenesis, shallow to deep subsurface zone; and telogenesis, freshwater vadose to phreatic surficialmore » zone. Exposure to each of these zones resulted in a variety of diagenetic products, the most significant of which were freshwater cements, dolomite, and sutured grains.« less

Geoarchaeological Evidence for Prairie-Mound Formation in the Mississippi Alluvial Valley, Southeastern Missouri

AbstractArchaeological materials in several prairie mounds in the northern Western Lowlands of southeastern Missouri indicate that mounds began forming prior to ca. 5000-3000 yr B.P. The mounds subsequently were inundated and built up to their modern configuration by aggradational and reworking processes. Human use of the mounds may have been tied to exploitation of aquatic animals residing in backwater habitats during periods of prolonged flooding. Principal features of the sampled portion of the mound field include preoccupation topographic highs, early occupation (ca. 5000-3000 yr B.P.) layers that drape the topographic highs, and later occupation (ca. 3000-950 yr B.P.) layers that drape earlier occupation layers and extend onto intermound areas.