Karstic Topography Research Articles

The formation and evolution of Al‐rich protoliths in the southern Ribeira belt, Brazil: Insights from remnants of a Precambrian paleoweathering surface

AbstractBauxitic clays, clayey bauxites and bauxites are residual products formed from the weathering of aluminosilicate‐rich parent rocks under wet and warm conditions. These deposits show a complex interplay between remobilisation of pre‐existing kaolinitic soils and depositional micro‐environments.In the southern Ribeira belt, Brazil, a paleoweathering surface developed on the continental shelf of the Capiru Group passive margin strata and on its basement/source rocks. This weathering cycle gave rise to a paleosol profile on the continental domain and a karstic paleotopography on the emerged carbonate shelf. The surface and karstic nets were later caped and filled with Al‐rich materials, typical of remobilised soils, bauxitic clays, clayey bauxites and pods of karst‐type bauxites.The age of the disconformity is Pre‐Brazilian/Pan‐African, implying a Neoproterozoic age for the weathering surface. In this study, we investigate the relationship among disconformities, paleosols and karst topography to better understand the stratigraphic control, chemical composition and mineralogy of the Al‐rich materials. We interpret this horizon as the remnants of a (meta‐)paleoweathering surface that can serve as a valuable key bed for stratigraphic correlation and paleogeographic reconstructions.We propose that the triggering process for the genesis of the paleosol profiles, bauxitic material and bauxite pods was a coupled mechanism between favourable climate and uplift along the northern margin of the Curitiba–Angola craton, creating a karstic topography that allowed the down‐plain transport of Al‐rich materials. In a later stage, these deposits were metamorphosed, developing a series of Al silicates in unusual paragenesis, typical of Al‐rich protoliths.The presence of these paragenesis, along with the recognition of the disconformity–paleoweathering surface pair, could be a useful tool to understand the paleoenvironmental and paleogeographic evolution of highly deformed terrains.

Geochemical and mineralogical features of karst bauxite deposits from the Alborz zone (Northern Iran): Implications for conditions of formation, behavior of trace and rare earth elements and parental affinity

The present study focuses on three outcrops of Upper Permian to Lower Jurassic karst bauxite deposits in the Alborz zone, north of Iran. The deposits occur as sharp semi-continuous lenses within the Upper Permian Ruteh Formation (Gheshlagh) and the Upper Triassic Elika Formation (Siahrudbar and Separdeh) carbonate rocks. Textural characteristics such as pelitomorphic matrix, local ooidic-pisoidic, fluidal, and clastic textures indicate authigenic-allothigenic origins. Mineralogically, kaolinite, boehmite, goethite, and hematite in the Gheshlagh, diaspore, hematite, and kaolinite in the Siahrudbar, and kaolinite, hematite, goethite, diaspore, siderite, and chamosite in the Separdeh deposits are the main phases. The distribution patterns of major elements normalized to the upper continental crust (UCC) depict enrichments of Al, Fe, and Ti in all three deposits. The three deposits are variably enriched in transition trace elements (Cr, Ni, Co, V), U, Th, and high field strength elements (Ga, Hf, Zr, Nb, Y) relative to UCC. The studied bauxites have average concentrations of rare earth elements (ΣREE, La-Lu) between 305.97 and 373.69 ppm. Geochemical data reveal progressive enrichment of REE and an intense (LREE/HREE)N fractionation toward the lower parts of the profile in the Separdeh deposit due to the alkaline conditions of the carbonate bedrock, and irregular distribution patterns at the Gheshlagh and Siahrudbar deposits due to water level and pH fluctuations. The positive Ce anomalies at Separdeh and Siahrudbar suggest oxidizing conditions in the upper parts of the profiles. At Gheshlagh, the negative to nil Ce anomalies reflect low intensity of oxidation. Based on previous geochemical analysis data, the Upper Permian basalts in the Gheshlagh, and the Upper Triassic basalts in the Separdeh and Siahrudbar areas were the most likely source materials. The local uplift of the Permian-Upper Triassic series led to the formation of karstic topography filled with materials derived from weathering of the basaltic rocks under humid tropical paleoclimate. The initial weathering converted the source rocks to kaolinitic soils characterized by the enrichment of Al, Fe, and Ti. Then, they were transferred to the karstic depressions and sinkholes and underwent in situ leaching and desilicification bringing about a relatively higher ore grade. The overall field and petrographic evidence demonstrate that these deposits were formed in shallow and swampy environments. In the eastern part of the Alborz zone (at Siahrudbar and Gheshlagh), better drainage conditions have enhanced the quality of ores.

Mineralogical and geochemical features of karst bauxites from Poci (western Henan, China), implications for parental affinity and bauxitization

The Poci bauxite deposits in western Henan, China, are hosted in the lower member of Upper Carboniferous Benxi Formation, unconformably overlying upon the paleokarst surface of the Ordovician Majiagou Formation. The orebodies comprise a high-grade bauxite horizon (characterized by the association of diaspore-illite-anatase) and a basal iron-rich horizon (diaspore-goethite-hematite-illite-anatase), sandwiched between the overlying clayey layer (illite-diaspore-goethite-anatase) and the underlying clayey layer (illite-diaspore-microcline-goethite). Geochemical investigations reveal that Rb, Cs, Ba, Cu, Zn are depleted, while B, Ga, Bi, V, Sc, Zr, Hf, Nb, Ta, W, U and Th are enriched in bauxite horizons. B is highly enriched in bauxite ores and clays (contents 176–1061 ppm) and positively associated with SiO2, indicating B is mainly hosted in clay components, e.g. dominantly illite, which are considered a mixture of authigenic minerals transformed from kaolinites during diagenesis and unaltered detrital minerals. Mass change calculations reveal that Hf, Zr, Nb, Ta, U, Th, Sc, Cr, and Ga are stable relative to TiO2 during the bauxitization process, indicating these elements are mainly associated with anatase and diaspore. The bauxite horizons and the underlying clays are more enriched in total REE contents (ΣREEs) and display more intense LREE/HREE fractionation than the overlying clays. Provenance analysis shows that parental materials of Poci bauxites were mainly derived from felsic-dominated igneous rocks along the southern margins of the North China Craton, with minor contribution from siliciclastic sedimentary rocks and argillaceous components of underlying carbonates. A conceptual model is proposed for the formation and evolution of Poci bauxites. Uplift caused by the North Qinling orogenesis along the southwestern margin of NCC led to the formation of karstic topography, allowing aluminum-rich source materials to be transported to the low karst plain and transformed into incipient bauxites under hot and humid tropical conditions. When the platform was submerged, Fe2+ ions were released from Fe/Al oxides/hydroxides under the reducing conditions associated with bacteria activity in an organic-rich environment, and redeposited as pyrites and siderites, generating a high-grade bauxite horizon and an iron-rich bauxite horizon. This marine modification resulted in further aluminum enrichment of bauxite ores.

The natural radioactivity of Istria, Croatia

Because of the geological structure of the Istrian peninsula which mainly consists of limestone that is characterized by karstic topography on its surface, it is expected that there are areas with elevated radon levels in soil gas as well as inside buildings (e.g. houses, kindergartens, schools). Recently, from autumn 2013 until spring 2015, more than 1200 radon measurements at about 500 randomly selected locations (in houses as well as in schools and kindergartens) were performed. The average value of indoor radon in homes is 102 Bq m−3 while the average radon concentrations in kindergartens (181 Bq m−3) and schools (208 Bq m−3) are approximately two times higher than in homes. In fact, in 15.5% of kindergartens and 21% of schools, the average indoor radon concentration is higher than 300 Bq m−3 which is the reference level in Croatia.Radon concentrations in soil gas in the Istrian peninsula were measured from 2013 to 2015 with the AlphaGUARD and RM-2 measuring systems. The obtained average value of 90 kBq/m3 and geogenic radon potential of 74 classifies the soil of Istria County into soil of high geogenic radon potential. It is important to emphasize that there are areas with radon concentrations up to 500 kBq m3. Soil samples were collected according to the standard procedures of the IAEA at 48 different locations. Activity concentrations of selected radionuclides were determined by means of gamma spectrometry by using an ORTEC HPGe detector system. The correlation between radon and its parents radium/uranium were investigated. The linear relationship between GRP and indoor radon per grid cell was found. The influence of climate condition on indoor radon concentration was observed. In accordance with the obtained results, areas with elevated indoor radon levels as well as levels of radon in soil gas were identified and geogenic and indoor radon maps were generated.

Mineralogical and geochemical evolution of the Bidgol bauxite deposit, Zagros Mountain Belt, Iran: Implications for ore genesis, rare earth elements fractionation and parental affinity

The present study focuses on the Late Cretaceous Bidgol bauxite deposit in the Zagros Simply Fold Belt, SW Iran. The orebody is located in the eroded major NW–SE trending Koh-e-Hosseyn anticline and hosted as discontinuous stratified layers and lenses within the upper member of the Cenomanian–Turonian Sarvak Formation. Detailed mineralogical analysis reveals that diaspore, hematite, goethite, anatase, clinochlore, chamosite, and calcite are the major mineral components accompanied by minor amounts of detrital and REE-bearing minerals such as rutile, zircon and parisite. The ore texture suggest that the bauxite material has an authigenic origin but in some parts it has been transported short distances from a primary in situ environment and redeposited in karstic depressions. The spheroidal pisolites of the Bidgol bauxite formed under conditions of low water activity, favouring the formation of large diaspore cores and a single dry-to-wet climatic fluctuation. The mass change calculations relative to the immobile element Ti show that elements such as Si, Fe, Mg, K, Na and Sr are leached out of the weathered system; Al, Ni, Zr, Ga, Cr and Ba are concentrated in the residual system; and Hf, Ta, Co, Rb, Cs, Be, and U are relatively immobile during the bauxitisation processes. The Nb, Th, Y, V, Sc, Sn and ΣREE are relatively immobile in the initial stage of bauxitisation processes in the bauxite ores, but were slightly mobile at the later stage of bauxitisation. Geochemical data reveal progressive enrichment of the REE and intense LREE/HREE fractionation toward the lower parts of the bauxite profile. Cerium behaves differently from the other REEs (especially LREE) and show positive anomalies in the upper horizons that gradually become negative in the deeper parts of the profile. The distribution and fractionation of trace elements and REEs during the bauxitisation process in the Bidgol deposit are mainly controlled by the presence of REE-bearing minerals, fluctuations in soil solution pH, REE ionization potential and the presence of bicarbonates or organic matter. Geochemical analyses confirm a protolith contribution from the bedrock argillaceous limestone and suggest that the source material for the Bidgol bauxite was provided from a siliciclastic material derived from a continental margin. The mid-Turonian uplift led to the formation of karstic topography, rubbly breccia and a layer of ferruginous–argillaceous debris that was affected by lateritic weathering under humid tropical climate. Subsequently, mobile elements are removed from the profiles, while Al, Fe and Ti are enriched, resulting in the formation of the pristine bauxite materials. When the platform subsided into the water again, the pristine bauxitic materials were partly converted to bauxite. During the exposure of bauxite orebodies on the limbs and crests of anticlines and subsequent eroding and accumulation in the karstic depressions during folding and faulting in Oligocene–Miocene, important factors such as intensity of the weathering, drainage and floating flow may have improved the qualities of the bauxite ores.

Genesis of the Permian karstic Pingguo bauxite deposit, western Guangxi, China

More than 0.5 billion tons of late Permian bauxite overlies the karstic topography of the Maokou Formation of western Guangxi in China. Here, we provide new mineralogical, geochemical, Sr–Nd–Pb isotopic, and pyrite S isotope and trace element compositional data for the Pingguo bauxite deposit, aiming to further our understanding of the genesis of Permian bauxite. The Pingguo bauxite contains three distinct layers: a lower layer dominated by ferric clay or weathered iron ore, a middle layer of cryptocrystalline and oolitic bauxite ore, and an upper layer dominated by argillaceous bauxite. The bauxite ore is mainly diaspore, pyrite, chamosite, and anatase, whereas the argillaceous bauxite contains diaspore, kaolinite, pyrophyllite, pyrite, and anatase. Two types of pyrite have been identified within the bauxite: fine-grained and framboidal pyrite (Py1) occurring in aggregates and coarse-grained and euhedral pyrite (Py2). Py1 is enriched in trace elements and is thought to have a diagenetic origin, whereas Py2 is deficient in trace elements and is considered to have formed by later recrystallization. The S isotopic composition of pyrite (−34.11 to −18.91‰) and visible ovoid microorganisms within the bauxite provide evidences of microbial activity during bauxite formation. The Sr–Nd–Pb isotopic composition of the bauxite indicates that these ores were generated by the weathering of basalts belonging to the Emeishan Large Igneous Province (LIP) and limestones of the Maokou Formation. Microorganisms were likely to have enhanced the dissolution and weathering of the parent rock and facilitated the precipitation of diaspore under near-surface conditions.

Exploration for a cave by magnetic and electrical resistivity surveys: Ayvacık Sinkhole example, Bozdağ, İzmir (western Turkey)

Geophysical survey techniques have been successfully applied to near-surface cave detection in karstic terrains. We used magnetic and electrical resistivity surveys to delineate the karstic structure of the Ayvacık Sinkhole, which may be considered to be a vertical cave. The magnetic-total-field-anomaly map helped reveal the metamorphic and sedimentary units in the study area. The total-horizontal-gradient map, which was based on a calculated pseudogravity anomaly, successfully identified the contact between the limestone unit and the cave system. Using these results, we positioned and carried out a vertical electrical sounding (VES) survey with a Schlumberger array along a line that consisted of 11 stations. The VES data were then processed using a 1D global optimization technique, which used a genetic algorithm and a 2D linearized least-squares algorithm. The results were generally in good agreement with each other, and together they pointed out three geologic layers: (1) an overburden layer ([Formula: see text]), (2) an approximately 25-m-thick alluvial fill (100–316 Ωm), and (3) a limestone unit (316–3162 Ωm); and also suggested the existence of a high-resistive anomaly ([Formula: see text]), possibly a karstic cave, located at the depth of approximately 40 m. Also, the results suggested that the buried limestone unit had an undulating karstic topography including a probable pinnacle structure. A synthetic modeling study was carried out, and it validated the reliability of the results. Finally, our findings indicated that the geophysical survey techniques used here were successful in detecting a cave located deep enough to make human exploration difficult.

Study of the effects of amphitheatre formations on the natural and human components in the Sorgun stream reservoir by using Geographical Information Systems

Abstract Although they are as large as ponor, uvala and polje, amphitheatres are least known interesting formations of karstic topography. In terms of formation styles and generated outcomes, amphitheatres affect the natural, human and economical life. The objective of this study is to introduce the mysterious amphitheatres “with a sample at former Aslanli Settlement” which are one of the important karstic terrain types integrating variety of natural beauties created as a result of their distinct karstic formations and at the same time this study intends to put forward how these amphitheatres ravage the public life in terms of economy and daily life of the inhabitants.

Assessing the repeatability of reflection seismic data in the presence of complex near-surface conditions CO2CRC Otway Project, Victoria, Australia

This study utilises repeated numerical tests to understand the effects of variable near-surface conditions on time-lapse seismic surveys. The numerical tests were aimed at reproducing the significant scattering observed in field experiments conducted at the Naylor site in the Otway Basin for the purpose of CO2 sequestration. In particular, the variation of elastic properties of both the top soil and the deeper rugose clay/limestone interface as a function of varying water saturation were investigated. Such tests simulate the measurements conducted in dry and wet seasons and to evaluate the contribution of these seasonal variations to seismic measurements in terms of non-repeatability. Full elastic pre-stack modelling experiments were carried out to quantify these effects and evaluate their individual contributions. The results show that the relatively simple scattering effects of the corrugated near-surface clay/limestone interface can have a profound effect on time-lapse surveys. The experiments also show that the changes in top soil saturation could potentially affect seismic signature even more than the corrugated deeper surface.Overall agreement between numerically predicted and in situ measured normalised root-mean-square (NRMS) differences between repeated (time-lapse) 2D seismic surveys warrant further investigation. Future field studies will include in situ measurements of the elastic properties of the weathered zone through the use of ‘micro Vertical Seismic Profiling (VSP)’ arrays and very dense refraction surveys. The results of this work may impact on other areas not associated with CO2 sequestration, such as imaging oil production over areas where producing fields suffer from a karstic topography, such as in the Middle East and Australia.

Seismic reflection survey for investigation of gypsum dissolution and subsidence at Hell Kettles, Darlington, UK

Abstract There are thick beds of gypsum in the Permian Zechstein sequence that forms the bedrock in the Darlington area. In this area, subsidence features attributed to gypsum dissolution are typically broad shallow depressions up to 100 m in diameter, and the ponds known as Hell Kettles [NZ 2814 1088] are the only recognized examples of steep-sided subsidence hollows around Darlington. We have acquired a loose grid of 11 2D seismic reflection profiles and a 3D seismic reflection survey in the area around the ponds. The 2D profiles have revealed evidence of foundering in the limestone of the Seaham Formation at depths of c . 50 m. The foundering is interpreted to have resulted from dissolution of gypsum in the Hartlepool Anhydrite Formation at c . 70 m depth. The reflection images of the gypsum itself are discontinuous, suggesting that its top surface has karstic topography. The 3D survey has revealed subcircular hollows in the Seaham Formation up to 20 m across, which are again attributed to foundering caused by gypsum dissolution. The results demonstrate the potential of the seismic reflection method for site investigation where there is a subsidence hazard because of the possible presence of subterranean cavities.

LOWER CRETACEOUS SEDIMENTARY SEQUENCES IN THE BASIN, NORTHEASTERN BRAZIL: A REVISION

The Araripe Basin in northeastern Brazil contain a 700 m-thick succession of JurassIc-Cretaceous strata. The 200 m-thick Lower Cretaceous is widely known for its fish-bearing concretions and gypsum deposits. Detailed field studies and core analyses provided data for revision of the Lower Cretaceous stratigraphy in the Araripe Basin. A regional disconfonnity within the Lower Cretaceous succession is described here for the flrst time. This surface divides the Aptian-Albian succession into two parts : 1. a lower sequence of black shale, laminated carbonate, algal mat carbonates, and evaporites in ascending stratigraphic order; and 2. an overlying sequence containing concretionary shale, limestone, and sandstone. These two stratigraphic divisions are herein defined as the Araripina Formation (new name) and the Santana Formation (revised), respectively. The expression of the disconformity varies across the basin. ln the southwest it is marked by caves formed in the gypsum and a karstic topography. Toward s the northeast, a 50 cm-thick layer of laminar calcareous and siliceous calcrete crust mark s th e disconformity surface.

Origin and subsidence of Guyots in Mid‐Pacific Mountains

Morphologic and magnetic data suggest that the Mid‐Pacific Mountains formed during Early Cretaceous time as a broad ENE trending double chain of midplate island seamounts over a mantle hot spot as the Pacific plate moved westward and slightly southward. Dredge, drill core, and reflection seismic data indicate that coral‐rudistid reefs grew on the subsiding seamounts and evolved to atolls and banks, largely burying the volcanic foundations. Magnetic data indicate that by late Aptian time, about 110 Ma, the seamounts were located at about 20°–25°S, which we suggest was near the fringes of the latitudinal zone of vigorous reef growth, where upward growth rates could just keep up with subsidence. A broad uplift probably related to the widespread regional emplacement of Aptian volcanics as oceanic plateaus, seamounts, and deep‐water flows and sills raised the Mid‐Pacific Mountain reefs out of the water, and both reflection seismic and isotopic data suggest that a karstic topography developed on many of the emergent reefs. As subsidence recommenced, the reefs could hot grow upward apace with subsidence. Renewed volcanism in Late Cretaceous time in the easternmost Mid‐Pacific Mountains maintained islands for a while, as at Horizon Guyot, but probably without large reefs. Elsewhere, pelagic conditions have prevailed as the guyots sank to their present‐day depths. These depths are systematically related to the inferred age of the volcanic foundations, being greatest on the youngest volcanoes.

Variations in Plant Communities With Topography Over Tropical Limestone Soils

Four line transects were investigated passing through primary and secondary forest near Belmopan, Belize, Central America. The transects ranged from 174 to 2012 m in length and are located in karstic topography with well-developed conical hills and depressions. Detailed quadrat and profile observations were made in order to interpret the vegetation pattern. Topo- graphy and drainage play a major part in determining this pattern, and summit areas are clearly distinguishable from hill slope, depressional and footslope areas. Plant succession following a major hurricane in 1961 can also be related to topography. An increased development of the accessible footslope areas is forecast in view of their better nutrient status, moisture levels and potential for rapid plant growth.

Le karst de Narinda (Madagascar)

Abstract. - Measuring during two years in North Madagascar brings us the proof that tropical dissolution is not so low, and that the highest values of CO3Ca content occur during the rainy season. There is a connection between the karstic topography and the lithological fades.

Données géomorphologiques sur la région de Fresh Creek, Ile Andros (Bahama)

A geomorphological study of the east coast of Andros (Fresh Creek area) shows the existence of a paleotopography represented by low-altitude hills (few metres). This paleotopography is protected by the presence of a calcitic Quaternary crust which covers Pleistocene calcarenite. In the western part of the area, there are long woody axes, oriented NE-SW, parallel to the channels of the creek. They end at two kilometres from the coast, along which is a second kind of lower hills, orthogonal to the first. The first axes can be interpreted as megaripples as seen at the present time on modern deposits (on the Great Bahama Bank) and fossilized by the upper crust. The second direction is made by accretion ripples along the coast. The surface of the Bahamian calcarenite has been studied. The Bahamian karst presents two topographical forms: “blue holes” like those outside the island, which are 60–80 m in diameter and both sparse and deep; and “washtub” dolines; these are numerous and shallow, and, from low altitude, exhibit a honeycombed aspect on the surface. This karstic topography with dolines and blue holes is also seen through the water of the Creek the hard bottom of which is covered only here and there with a few centimetres of sediments. Hence, there is a submerged karstic topography, made of the same elements as the aerial karst, but submerged by the Holocene transgression. The present karstic relief, in relation with the different eustatic levels of the Quaternary, has begun 120,000 years ago, according to the isotopic ages, and might be composed by different steps, difficult to show now, in the topography. The blue holes in the interior of the island of young and little evolved karst, were formed more by solution than by collapse of the karstic caves, because of the absence of a real river to drain the Andros shelf at the time of low sea levels. Blue holes of the inside of the island, as they are called, with submarine openings, have the same salinity as the water of the creek (17.5 g/l). The dolines with very low salinity (0.7 g/l to 3.8 g/l) are filled with stromatolites and charophytes, slowly forming sediments made up essentially of high-magnesian calcite. It seems that the Andros Island karst can be compared with that of the Yucatan, where there are round and deep open pits, called cenote, of which the Bahamian equivalent would be the blue holes which were drowned by the Holocene transgression.

Beachrock and associated carbonate sediments on the Fifty Fathom Flat, a submarine terrace on the outer continental shelf off Bombay

Beachrock and associated carbonate sediments were obtained by dredging and coring on the Fifty Fathom Flat, a submarine terrace at a depth of fifty fathoms (91·5 meters) on the outer continental shelf off Bombay. The beachrocks are iron stained calcarenites composed of oolites and skeletal material cemented together in a fine-grained carbonate matrix. Thin sections show that the rocks are oobiomicrite with a high grain to micrite ratio. The allochems are superficial oolites, skeletal matter and grapestone and pellet intraclasts all of which either charged with iron oxide or glauconitised. Associated sediments on the Flat are glauconitic sand, oolites and coral debris. The karstic topography which is evident from the echograms and the occurrence of beachrock implies that the Fifty Fathom Flat stood at sea-level, probably during the Pleistocene and is now submerged due to eustatic and/or tectonic causes.

Food Habits of the Silverjaw Minnow, Ericymba buccata Cope, in an Intermittent Stream in Kentucky

The feeding activity of the silverjaw minnow, Ericymba buccata Cope, is closely associated with that of the bluntnose minnow, Pimephales notatus (Rafinesque), and the stoneroller minnow, Campostoma anomalum (Rafinesque). Digestive tracts of 249 silverjaw minnows, taken from two stations on Plum Creek, Spencer and Bullitt counties, Kentucky, were examined and the contents identified. These data were analyzed according to the size of the fish, time of the year, and the availability of food. The food category occurring most often in digestive tracts of fish of all sizes was the order Diptera, chiefly chironomids, followed by detritus, Ephemeroptera, and Cladocera. Minnows 33 to 45 mm total length consumed more cladocerans and fewer mayflies while the reverse was observed in specimens 46 to 76 mm. A greater variety of organisms was eaten by all fish in the winter and spring. INTRODUCTION A complete understanding of community dynamics in the aquatic ecosystem depends upon a thorough knowledge of each species present. The family Cyprinidae contains more members than any freshwater group, most of which are considered to be forage species. An understanding of the biology of certain members of this family is of great value in fisheries management. The silverjaw minnow is a highly successful forage species occurring commonly in the eastern and southeastern United States (Forbes and Richardson, 1920; Moore, 1957; and Trautman, 1957). It occurs in large schools in gravelly or sandy-bottom streams of moderate gradients, feeds on benthos and detritus, and is preyed upon by various predators (Hoyt, 1969). The objectives of this study were to determine the kinds and numbers of food organisms consumed by minnows of different lengths and during different seasons. Observations were made on the availability of food organisms in the stream and were related to their utilization by the minnows. STUDY AREA Plum Creek is a small tributary of the Salt River in north-central Kentucky (Shelby, Bullitt, and Spencer counties). It flows over a belt of Ordovician limestone in the western section of the Outer Bluegrass Region, and as a result of this stratigraphy the area exhibits a relatively flat, mildly karstic topography with few forests and soils of fair 1 Contribution 128 (New Series) from the Department of Biology, University of Louisville, Louisville, Kentucky 40208, from a doctoral dissertation submitted to the University of Louisville, June 1969. 2 Present address: Biology Department, Western Kentucky University, Bowling Green 42101.