marker bed (key bed, chronohorizon, chronostratigraphic horizon, datum) A thin bed of a distinctive character, often widely distributed and capable of being recognized and traced over a large geographical area. Marker beds are taken to be the results of either (geologically speaking) very short episodes of deposition (e.g. a thin coal seam), or of almost instantaneous events (e.g. turbidity deposits (see TURBIDITY CURRENT), or bentonite beds derived from volcanic ash falls). Such beds are thus very valuable as time markers in stratigraphic correlation.
More From encyclopedia.com
Hepatomegaly , hepatomegaly Enlargement of the liver as a result of congestion (e.g. in heart failure), inflammation or fatty infiltration (as in kwashiorkor). hepa… Alum , alum (ăl´əm), any one of a series of isomorphous double salts that are hydrated sulfates of a univalent cation (e.g., potassium, sodium, ammonium, ce… Hygroscopic Nucleus , hygroscopic nucleus Microscopic particle (e.g. of sulphur dioxide, salt, dust, or smoke) in the free air, on which water vapour may condense to form… Silicate , silicate silicates The most important and abundant group of rock-forming minerals, which can be classified according to the structural arrangement of… Psilophytales , Skip to main content Psilophytales Psilophytales (psilophytes) Primitive pteridophytes, which were the earliest vascular plants, from the Silurian an… Vegetables , The term vegetables can have three distinct meanings when applied to plants. The first as in "animal, vegetable, or mineral" refers to the entire kin…
About this article
Updated About encyclopedia.com content Print Article