In general, how do the differences in bed thickness relate to changes in environmental conditions during deposition?
Only partially. Thickness also depends upon any subsequent erosion.
I see this question a lot and my answer is that a thicker unique and identifiable bed represents a stable environment at both the coast and the uplands. So the environmental changes are minimal as each bed represents a pattern at work during the beds deposition. When the conditions change the beds character will change. The change could indicate a receding coast line or a state of erosion levels in the uplands. For example when a sandstone bed starts to turn arkose--more feldspar fragments this indicates a maturing erosion cycle upland when the erosion surface cuts into the plutonic core of the headlands of the delivery drainage system. We would not or course consider these to be the same beds. Beds are measured from demarcation to demarcation. Conversely, a succession of thinner beds-- alternating between grain sizes( less mature) or composition( silt vs sandstone) indicates a less stable , more dynamically changing environment; e.g. a change in coastline (aka sea level) and/or mountain uplift/wasting/erosion in the forelands. An uncomformity between beds represents a drastic change of no deposition and probable erosion. ...
A rock is a mineral, or aggregate of minerals, that forms an essential part of the earth's crust. Rocks differ from minerals in that rocks are merely physical mixtures of minerals, while the minerals themselves are chemical compounds of fairly uniform composition. Any rock can be classified as one of three types: igneous, sedimentary, or metamorphic. This method of classification is based on the mode of formation of the rock. Igneous rock is formed from a molten state. The sedimentary rocks are formed from sediments or erosion fragments deposited in lake and ocean beds. Metamorphic rocks form when great heat and pressure, caused by deep burial, alter the physical condition of sedimentary, igneous, or another metamorphic rock. Fine grained (dense) igneous rocks form when rapid cooling occurs. Conversely, coarse-grained rocks cooled slowly and crystals grew large. Extrusive rocks are formed by volcanic activity at the surface of the earth. These rocks cool rapidly. Examples of some common igneous rocks are: rhyolite, andesite, basalt, granite, diorite, gabbro. Sedimentary rocks are classified based on the size of the particle of the sediment, or fragment. Shale (dense, fine particles), sandstone (particles distinguishable to the naked eye) and conglomerate (pebbles and gravel cemented together) are examples of sedimentary rocks. When broken, a metamorphic rock usually breaks along the plane of foliation. Metamorphic rocks are classified based on their grain size and degree of foliation. Some examples of metamorphic rocks are: slate, schist, gneiss. Hence the bed thickness depends on the type and naturally have a bearing on the environmental conditions too. More information in source. Sarayu.
