Channel facies

Channel Facies Thalweg Facies Slackwater Facies Diamicton Facies Backswamp Facies... 

Figure 4. A representative cross-section of channel facies sediment. The Chaperon, a filled side passage on Rose s Pass, Mammoth Cave, Kentucky. From Davies and Chao (1959).

Channel facies sediments are transported mainly as bedload. The varying particle sizes found from bed to bed appear to represent different flow regimes. The ability of any given flow regime to transport sediment is determined by the boundary shear between the moving water and the movable sediment bed. The boundary shear is related to flow velocity through Newton s stress law ... 

Figure 6. Series of stratigraphic columns along Columbian Avenue, Flint Ridge section of Mammoth Cave Kentucky showing lithologic characteristics of channel facies. Columns are keyed to core locations shown in figure 7. Note the total column thickness original columns were drawn to two different scales. Original data from Carwile and Hawkinson (1968).

The conduit that feeds Rock Spring is entirely in the phreatic zone. It has been explored by SCUBA diving for roughly 400 meters. The conduit carries a flux of clastic sediments. The diver reports a lift tube where the flow rises about 4 meters up a slope. Channel facies sediments collected from bottom and top of the lift tube were dried and sieved. The resulting grain size distribution (Fig. 9) reveals little difference between the bottom and the top of the tube. These sediments are being swept down the conduit by pipe flow and quite clearly follow undulations in the pipe. 

Clastic sediments deposited in conduit systems can be conveniently be divided into five facies depending on the mechanism of deposition. The channel facies comprises most observed sediment piles and can be subdivided further depending on the objectives of a particular investigation. Diamicton facies and slackwater facies are deposited from suspended loads. Channel facies and thalweg facies are transported as bedload. The backswamp facies is defined to describe those residual in infiltrated clastic sediments that are deposited in place with little horizontal transport. 

Cemented zones are most common near the top and base of sandstones. Areas having high percentages of calcite-cemented sandstone (>20%) occur along the margins of the sandstones, in levee, overbank and lobe deposits, where the sandstone pinches out into siltstone. The areas having the lowest percentage of calcite-cemented sandstone (<10%) occur where the sandstone is thickest, in the channel facies. The calcite layers may be associated with pulses of turbidite deposition. The source of... 

Garrels et al. (1973) believe that the BIF must have been formed in restricted basins in semi-enclosed water bodies, periodically communicating with the ocean via channels or over bars. Deposition of silica occurred mainly during evaporation, but deposition of iron was complex and is explained both by oxidation (hematite facies) and by evaporation (silicate and carbonate facies) and sulfate reduction (sulfide facies). It is suggested that the spatial distribution of the sedimentary facies of the BIF will correspond to the well-known scheme of James (1954), but to explain the similarity of banding in the face of different causes of precipitation of the iron raises difficulties. 

Slackwater facies are found in most cave deposits, usually as the final layer to be deposited. The slackwater facies appears at the top of the section in Figure 4 as the laminated clay overlying the channel deposits. Even when passages are nearly plugged... 

Fig. 6. Stratigraphical column showing details of the relationships between grain size, lithology, sorting and degree of cementation in sediments from the Chamisa Mesa and Canada Pillares Members. Note correlation between coarser and better sorted channel (CH) associations and good cementation. Nodular, platy and rod-shaped concretions are associated with crevasse splay (CS), paleosol (P), interdune facies (ID) and overbank fine (OF) sediments. Scattered ovoid to elongate concretions dominate in the cross-stratified aeolian facies (EC). Note that the coarser portions of aeolian sandsheets (ES) are preferentially cemented.

The Upper Lunde Member ( 850 m thick) marks another change in the depositional facies and style of these Upper Triassic continental beds. The lower boundary of this member is usually assigned to the base of the first marked fluvial-channel sandstone. The lower part of the upper member consists of braided stream channel sandstones and units of reddish-brown floodplain mudstones characterized by palaeosols with calcrete concretions. The upper part of the member also comprises middle-sinuous stream deposits, interchanging with rather mature reddish-brown, calcrete-rich palaeosols (Nystuen Fait, 1995). 

Triassic sediments are deposited only in the eastern and northern parts of the Sahara, in the Triassic Province. Triassic sandstones are mainly a combination of deltaic to prodeltaic facies represented by upper deltaic fluvial system deposits, lower distributary channel rivers, mouth bars, beach sands and tidal flat and prodeltaic shales. Typical marine Triassic shales are restricted in extent in the study area. Triassic Lower, Middle and Upper sandstones are stratigraphically separated by shale intervals, but occasionally also by carbonates or volcanic interbeds. They are often medium grained, and range from friable to cemented with clay mineral, carbonate, anhydrite and siliceous cement. Porosity ranges from 12 to 22%. With respect to mineralogical composition and maturity, Triassic sandstones are mature sublitharenite (Lower Triassic), sublitharenite to submature subarkose (Middle Triassic) and submature subarkose (Upper Triassic). 

The "Lo Hueco" fossil site includes an upper Campanian-lower MaasUichtian inteival in "Garumn" facies belonging to the upper part of the Villalba de la Sierra Formation and constituted by a succession of versicolor marly mudstone levels, partially cut by a sandy channel structure and two sulphated intervals. The succession of versicolor marly mudstone levels and the sandy channel structure contain an exceptional richness and diversity of fossils, and have to date provided more than 8500 macroremains, mainly... 

Graphitic conductors, pyrite concentrations, buried channels, fault structures Buried channels, fault, vein structures Sulphide minerals, clay mineralogy changes Geologic structures, regional and local facies changes buried channels, local unconformity mapping... 

---