# Width of strata in stratigraphic column

I am trying to understand whether there is one "standard" meaning of the width of represented strata in stratigraphic columns, but I can find nothing online or in my geology books.

I notice that, sometimes, under stratigraphic columns there can be legenda explaining how the width of the represented strata relates to the measure of the clasts of a conglomerate, but I have also found stratigraphic columns with no stratum of conglomerate or breccia where not all the strata are equally large.

Is the width of strata usually an increasing function of the area occupied by the respective stratum? Can width represent other characteristics of the described stratum?

• Can you clarify what you mean by 'largeness'? I think you mean width (horizontal size on the page), but it's not clear. I'll have a go at answering anyway. Commented Dec 29, 2014 at 21:04
• Indeed. What is "largeness"? Commented Dec 29, 2014 at 21:45
• Excuse me: I didn't remember the correct English word. Edited Commented Dec 31, 2014 at 9:47

The width of a unit in a stratigraphic column, or 'log', sometimes represents the average grainsize of the rock. I can imagine it being keyed to some other property, but grainsize is common. You'll find lots of examples with a quick search for 'sedimentary log'.

The height of a unit typically represents thickness if the vertical axis is length, height or depth. Alternatively, if the vertical axis is time, then the height of a unit corresponds to time duration.

I've tried to illustrate some of the typical layouts here:

On a wireline log, the horizontal axis is some physical property such as natural gamma-ray emission rate or bulk density. Check the legend.

There's no reason not to represent other parameters with the horizontal axis (or the vertical one, or the colour), but then you'd need to be careful about labelling things clearly.

Footnote: often colour is keyed to lithology. This may or may not closely follow the grainsize. Symbols may be added to represent other relevant characteristics of the rock, such as sedimentary structures and fossils.

At least in Germany, another approach is very common („Verwitterungsprofil“): the width of layers shows their competence (resistance to weathering/erosion). So competent rocks (which don’t weather easily) “stand out” opposed to soft rocks. This is a very idealised representation of what a “real”, weatherd outcrop could look like.

Edited to add: my experience with “German columns” is that grain-size profiles are indicated by a labeled axis at the top or bottom (as in kwinkunks’s answer). If there is no indication, it usually is a competence profile.

• This is also true for a lot of older literature. Especially (?) Quaternary logs. It can be confusing sometimes. Commented Apr 20, 2015 at 19:15
• Very interesting, and very pertitent to one of my more specific interests: Alpine geology (I live on the westernmost edge of the Apennines and the Alps of the Sestri-Voltaggio area are in front of my house)! Commented Apr 20, 2015 at 19:30
• In some cases, when a real outcrop is presented (instead of a idealised stratigraphic or “normal” profile), the width and shape of the layers in the colum may show the actual appearance of the profile, i.e. layers standing out, eroded parts (e.g. at the bottom by a river), etc. Commented Apr 21, 2015 at 8:30