Rocks detritic

Ellwood B. B., Crick R. E., El Hassani A., Benoist S. L., and Young R. H. (2000) Magnetosusceptibility event and cyclostratigraphy method applied to marine rocks detrital input versus carbonate productivity. Geology 28, 1135-1138. 

Rutile Oxides Igneous and metamorphic rocks detrital sediments quartz inclusion C Very stable in soils, but some mobility of T rarely alters to other oxides... 

Residual sedimentary rocks Detritic or terrigeneous rocks... 

Primary porosity—porosily formed at the time the sediment was deposited. Sedimentary rocks that typically exhibit primary porosity are the clastic (also called fragmental or detrital) rocks, which are composed of erosional fragments from older beds. These particles are classified by grain size. 

Detrital or epiclastic <30 >50 Denudation products of continental rocks... 

Ferromanganese nodules found in freshwater lakes show concentric, alternating, iron- and manganese-rich bands radiating out from a central nucleus of detrital rock (e.g. Harriss Troup 1970). The nodules are found primarily in shallow (1-5 meters depth) regions of lakes, in regions with little to no finegrained sediment accumulation (e.g. Kindle 1935). 

The basement is made up of crystalline schists of the meso-metamorphic Somes Series. Sedimentation started during Permian with detritic deposits interbedded with rhyolites. The overlying Triassic deposits are unconformable and include detritic formations (Lower Triassic) and massive layers of carbonate rocks (Middle Triassic). The absence of the Upper Triassic is due to the uplift of the region during the Kimmeric tectonic phase. 

From the perspective of the global rock cycle (Figure 1.2), volcanic activity is the ultimate source of minerals comprising the crust. The crust is 27.7% by mass silicon and 46.6% oxygen, so it is not surprising that silicates are the dominant mineral type. Weathering of these minerals generates siliclastic particles. These are also referred to as detrital silicates. 

The cations become a component of river water and are eventually transported to the sea. About 45% of the dissolved solids entering the ocean are derived from the weathering of detrital silicates. Feldspars are the most important somce rock for terrigenous clays as illustrated by the following reaction... 

Feldspars are the most abundant minerals of igneous rocks, where their ubiquity and abundance of their components influence normative classifications. They are also abundant in gneisses, and may be observed in several facies of thermal and regional metamorphic regimes. Notwithstanding their alterability, they are ubiquitously present in sedimentary rocks, as authigenic and/or detritic phases. Only in carbonaceous sediments is their presence subordinate. 

In terms of a petrologic description, BA represents more closely a type of rock of detritic origin composed of phases that had undergone very different conditions of formation, and that subsequently was subject to a short low-pressure/high-temperature metamorphism where only partial melts occurred. 

Si, Fe and Fe is variable. Illite also appears to be the early product of weathering in cycles of intense alteration or one of the stable products under intermediate conditions (Jackson, 1959). It is apparently stable, or unaffected by transport in rivers for relatively short periods of time (Hurley, et al., 1961) but does change somewhat in the laboratory when in contact with sea water (Carroll and Starkey, 1960) it has been reported to be converted to chlorite or expandable minerals upon marine sedimentation (Powers, 1959). However, Weaver (1959) claims that much sedimentary illite is "reconstituted" mica which was degraded to montmorillonite by weathering processes. It is evident that a certain and usually minor portion of illite found in sedimentary rocks is of detrital origin (Velde and Hower, 1963) whether reconstituted or not. 

Thus detrital sediments can contain illite of at least four origins material crystallized during weathering reconstituted degraded mica, detrital mica formed at high temperatures and of course unaffected detrital illite from sedimentary rocks. 

Figure 11 indicates the necessary change in composition which a muscovite would need to become stable under conditions in a sedimentary rock where chlorite is present (x to y). The solid solution for mica-illites is delimited by the shaded area which represents a much larger variation than is possible under metamorphic or igneous conditions. The detrital muscovite (composition x) is in itself stable if the bulk composition of the sediment as projected into the coordinates is found at x. 

The AG between the assemblage of muscovite + chlorite at composition y and illite of this is likely to be relatively small and the tendency to recrystallize the muscovite from x to y compositions will be small at sedimentary conditions. However, as more thermal energy is added to the rock system, under conditions of deeper burial, the recrystallization will proceed more rapidly as temperature is increased. Evidence for such an effect can be found in Millot (1964) where sedimentary rocks coming from deeply buried or slightly metamorphosed series show the "chloritization" or kaolinitization" of detrital mica grains in splendid photographs. 

Figure 31b indicates the compositional spread of chlorites from six rocks in the illite-montmorillonite mixed layered mineral facies and from the illite-chlorite zone in the French Alps (Velde, unpublished). The grains analyzed with the microprobe are chlorites replacing isolated grains of detrital mica or were newly formed grains. They are usually 15 microns in the smallest dimension. 

In sum, one can say that 14 8 trioctahedral brucitic chlorite is largely unstable in most weathering environments, but aluminous soil chlorites are common under acid conditions. The bulk of chlorite found in sediments is certainly detrital in origin. 7 and 14 8 chlorites can be formed from 50°C upward in temperature until above 100°C where 14 8 chlorite becomes one of the most common minerals in sedimentary rocks. 

Analcime occurs only in the upper lagoonal complex in beds 150-300 m thick. It is most widespread in the cement of sandstones and fills the pores of many chemogenic rocks associated with them. The widespread occurrence of analcime in the upper complex and its absence in the. lower complex (despite the similar composition of detrital matter and the identical conditions of formation) would have been unaccountable were it not for one peculiar feature of the heavy mineral fraction. The heavy mineral content of rocks of the upper complex varies from fractions of a percent to 2 or 2.5%. Up ot 50% of the heavy mineral fraction consists of fresh, monoclinic pyroxene and amphibole. 

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