Allochems

Table 5.4. Classification of carbonate sediments based on texture and nature of allochems according to Folk (1962).

Both classifications are based on the depositional texture of the limestone Folk s emphasis is on the similarity of carbonate sedimentation to that of sandstones, resulting in a scheme employing as variables the lime mud spar cement ratio and allochem composition. Allochems may be intraclasts, ooids, fossils or... 

Figure 5.4. Classification of mixed siliciclastic-carbonate sediments proposed by Mount (1985). It is an unfolded tetrahedron in which the apices are siliciclastic sand, carbonate allochems, siliciclastic mud, and carbonate micrite. For comparison with Folk s (1962) classification, the classification of pure fossiliferous limestone is also plotted.

Sandstones with abundant carbonate grains constitute an important petrofacies in many sedimentary sequences (ZufFa, 1987). One class of such sandstones has abundant contemporaneous intrabasinal carbonate particles which include bioclasts, ooids, peloids and intraclasts (allochems, sensu Folk,... 

It is interesting that the product distribution from the reaction of the o-methoxyphenyl complex with diethylacetylene was found to be dependent on alkyne concentration. One equivalent of alkyne, slow addition of alkyne, or low absolute concentration of alkyne favors the indene product. Reactions performed with excess or high concentrations of alkyne favor benzannulation. The observation, reffered to as the allochemical effect, was explained as resulting from coordination of reaction intermediates by the alkyne. Thus excess alkyne acts as a ligand to stabilize intermediates along the path to benzannulation. Finally, it was noted that the product distribution was not substantially altered by addition of phosphines, phosphine oxides or sulfides. 

Mullin, C.A. (1986). Adaptative Divergence of Chewing and Sucking Arthropods to Plant Allochemicals. Plenum Press, New York. 

Carbonate sedimentary rocks are dominantly of marine origin. Many limestones are composed of fossilised shell debris in various states of comminution, some fine grained carbonates such as chalk (q.v.) may be entirely composed of sub-microscopic phytoplankton. Algal mats secrete aragonite particles and coral reefs are CeiCO structures which may be preserved, fossilised, intact or degraded to produce other limestones. As discussed above, allochems such as faecal pellets and ooliths may be... 

A further application of this calorimeter was for airbom irritations like attrac-tants, toxic compounds, anaesthetics or allochemicals on individual insects [47]. Larvae of the cabbage looper Trichoplusia ni) were tested against microgram amounts of benzene. They produced a strong, but short exothermic effect because the benzene was washed out by the air stream. A young male of the rootworm Diabrotica longicomis answered with a pronounced exothermic heat output to the exposure to pheromones prepared as extracts from female com rootworms. Moreover, the male moved immediately towards the source of the stimulant. 

---