principle of original horizontality middle school

The principle of inclusions states that any rock fragments that are included in a rock must be older than the rock in which they are included. But sediments can also terminate against faults or erosional features (see unconformities below), so may be cut off by local factors. The principle of lateral continuity states that sediments are deposited such that they extend laterally for some distance before thinning and pinching out at the edge of the depositional basin. Source: AntanO (2017) CC BY 4.0 view source The delta foresets are labeled “Delta deposits” in this figure, and you can quickly see that the front face of the foresets are definitely not deposited horizontally. Figure 19.6 A cross-section through a river delta forming in a lake.

The same holds true of delta foreset beds (Figure 19.6). For example, cross-bedding forms at an appreciable angle, where sand is deposited upon the lee face of a ripple. At a broad scale this is true, but at a smaller scale it may not be. The principle of original horizontality indicates that sediments are originally deposited as horizontal to nearly horizontal sheets. This situation may not be true, though, if the sequence of rocks has been flipped completely over by tectonic processes, or disrupted by faulting. The principle of superposition states that sedimentary layers are deposited in sequence, and the layers at the bottom are older than those at the top. These situations are generally rare, but they should not be forgotten when unraveling the geological history of an area. But caution must be taken, as there may be situations in which the rules are not valid, so local factors must be understood before an interpretation can be made. There are a few simple rules for doing this. The simplest and most intuitive way of dating geological features is to look at the relationships between them. 19.2 Relative Dating Methods Relative Dating Principles

Principle of original horizontality middle school