The Status of Surface Geologic Mapping in Mississippi
Total Page：16
File Type：pdf, Size：1020Kb
THE DEPARTMENT OF ENVIRONMENTAL QUALITY Office of Geology P. 0. Box 20307 Volume 15, Number 3 Jackson, Mississippi 39289-1307 September 1994 THE STATUS OF SURFACE GEOLOGIC MAPPING IN MISSISSIPPI David T. Dockery Ill, Michael B. E. Bograd, and David E. Thompson Mississippi Office of Geology INTRODUCTION and locating areas suitable for waste disposal. The Office of Geology intends also to pull together the At the current rate of production of detailed surface work ofother geologists and publish their maps to make them geologic maps, coverage ofthe entire state of Mississippi will available to all potential users. be accomplished in about 100 years. Now that we have your attention, some explanation is in SCALE AND OUTPUT OF GEOLOGIC MAPS order as to our plans for improvement. The Mississippi Office ofGeologycurrently has four surface mapping projects under With all the mapping underway, it might seem that geo way. Two ofthese are centered along the Wilcox outcrop belt logic map coverage of the whole state should be forthcoming. in Lauderdale, Kemper, Winston, and Noxubee counties with So, what's the holdup? There are four aspects of the current plans for expansion northward to the Tennessee state line. The mapping program that make for slow going. First, the maps are Wilcox Group contains important clay and lignite resources at being published at a scale of l :24,000 - the same as that of a and near the surface, is a source of oil in the subsurface of 7.5-minute topographic quadrangle. This allows much greater southwestern Mississippi, and is an important source for detail than is possible at the scale of previously published drinking water in the central and northwestern parts of the county geologic maps. At this scale, 837 quadrangle maps are state. The third mapping project is along the Catahoula required to cover Mississippi. That's a lotofmaps to be done! outcrop belt in south-central Mississippi. The Catahoula Is this much detail really necessary? Yes; many users in Formation contains clay resources, and its sandstone units construction, environmental remediation, agriculture, and even have been utilized as building stones (e.g., the stone wall at home buyers would like to see geologic maps ofmuch greater Piney Woods School and the Old Capitol in Jackson). Most detail, even at the scale of I: 12,000. In some areas around importantly, sands of the Catahoula Formation are a major Jackson, such resolution would allow a prospective buyer to source ofd ri nking water for southern Mississippi. The fourth determine ifa home or business were on or offtheY azoo Clay mapping project is in Jackson County where population ex outcrop belt and allow a better assessment ofpossible founda pansion is placing new demands on local resour~es; geologic tion problems. At this point we must define what we mean by information is needed concerning drinking water resources "detailed" geologic maps. We define detajJed geologic map- ping as that done and printed at the scale of I :24,000, or one digital products are convenient, modifiable, and preferred by inch on the map represents 2000 feet on the ground. Greenl y many users. they are more efficiently done by full-time data and Williams ( 1930) stated that only in very simple areas processing technicians. Having no DP technicians available could a scale of I :20,000 be regarded as detailed. Compton for the surface mapping projects, geologists must create and ( 1962) defined detailed geologic (or topographic) mapping as digitize their own finished maps. The finished digital product being at scales larger than I inch = 200 feet (I :2400). He requires more of the geologist's time than does the field referred to the scales I :24,000 to I :62.500 as intermediate mapping and test hole drilling. This is complicated by the fact scales. The U.S. Geological Survey'sgoals under the National that all must use the same equipment. Funding of a DP Geological Mapping Act are to see the entire country mapped technician will free up three geologists to devote their full time at the scale of I :24.000. to geologic mapping. At present, 29 geologic quadrangles are available as open-file reports or otherwise, leaving 808 to be done. Some THE VALUE OF GEOLOGIC MAPS of this number straddle state lines and may be published with adjacent maps. Stil l. at an optimistic estimate of producing 8 Why bother to map the state's geology in the first place? per year with our current programs, coverage ofthe whole state The best answer to that question is in another question- what will require I 0 I years. Because of reasons below, it is ifwe had no idea of the nature ofthe strata below our feet. The expected that this output will increase. Biblical parable comes to mind about the wise man who built The second aspect slowing ma p output is that the current his house upon the rock and the fool who built upon the sand. programs have targeted the state's most difficult geologic The fool in Matthew 7: 24-27 did not know his surface terrains. These are areas where the present State Geologic geology. A storm came; the sand gave way; the foundation Map (Bicker, 1969) is inadequate or incorrect. Once these failed, and great was the fall thereof. Many a structure today terrains or outcrop belts are satisfactorily completed, interven suffers a similar fate. Maps showing unconsolidated alluvium ing areas can be done with greater ease. are in demand by emergency management agencies. In plan The third aspect is also related to geologically difficult ning fora major earthquake occurrence along the New Madrid areas of the state. In the past, local formational names were Seismic Zone, emergency management agencies need maps of given to sections of the Wilcox Group where traditional units these and other potentially unstable areas in order to place could not be readily distinguished. These local names were shelters, staging areas, and field hospitals on solid ground that used by some and rejected by others. The present mapping can withstand the aftershocks. programs in the Wilcox outcrop belt utilize only those form a A second important use of geologic maps is in the explo ti ons recogni zed in the group's type area in Wilcox Count y, ration for mineraJ resources. Mississippi's first oil field at Alabama. This provides a uniformity in nomenclature from Tinsley was found while mapping the surface geology of western Georgia to Mississippi and better reflects the geneti Yazoo County. The Tinsley Field was a major oil find and is cally related depositional packages- or. in layman terms, what still in operation today. A fault mapped in Wayne County was the real geology is like. Mapping of these formatio ns into laterthe site ofa successful oil well. Even though the domestic northern Mississippi becomes more difficult as the units tend oil industry is underappreciated, the state has reaped hundreds to look more alike there. Careful field work. the drilling of of millions of dollars in severance taxes on oil production and core holes, geophysical log analyses, and analyses of micro in lease sales on state-owned land. scopic fossil pollen and dynocysts are necessary to guarantee Geologic maps are also important in the exploration for success. Sometimes maps have to be changed with the arrival materials used by the construction industry every day such as of new data. sand and gravel. brick and ceramic clays, lightweight aggre The care mentioned above. while time consuming. is gate, and crushed stone. Most of these materials have a low important to our mapping program. Geologic maps are unit value, which requires that their source be close to the job required to stand the scrutiny of paleontological (fossil) ex site. For example, land transportation costs on gravel from aminations, dera iled surface correlation, and test hole data. Tennessee would be considerable for use on a job in southern Only then are they considered reliable geological documents. Mississippi. Geologic maps showing graveliferous units are No geologic map is expected to be 100% perfect in the needed around every metropolitan center where demand is depiction of its geological outcrops. This is not the issue that high. Other materials with a low unit value include limestone concerns us. The disastrous error is that of a geologic map for cement and agricultural lime and lignite. Lignite is not lacking well-defined stratigraphic units - a meaningless or mined in Mississippi at present but may soon be used to fuel misleading document. new electric power plants. The fourth aspect is one that substantially slows our Mineral resources in the state with a high unit value geologic mapping program . Our maps are now produced (meaning they can be economically shipped over great dis digitally using AutoCA D software after the geologist has tances) include bentonite, tripoli, heavy mineral sands, and completed field and office work and map sketching. While mineral clays. Of these, only bentonite and mineral clay are 38 MISSISSIPPI GEOLOGY, V . 15, No. 3. SEPTEMBER 1994 MISSISSIPPI OFFICE OF GEOLOGY (MISSISSIPPI GEOLOGICAL SURVEY) 1994 mined at present. Tripoli was once mined in the state, and been published and accompany the county geologic reports heavy mineral exploration is ongoing. Heavy minerals are (bulletins); the first was pub Ii shed in 1939 and the most recent shipped from Australia for use in plants on the Mississippi in 1988. The quality ofthes e maps varies with the better ones Gulf Coast. A local source would be much better. Mineral being the most recent, but these maps are generally the best clays from the Bucatunna Formation in Smith County are heat source of information on the geology of any area.