Near Narita airport, Japan A single train of symmetrical ripples, almost but not quite starved...

Near Narita airport, Japan

A single train of symmetrical ripples, almost but not quite starved (there’s some sediment in the troughs).

Wappinger Gp (Cambrian), I84, Fishkill, New York

Note the rather complex internal structure of these symmetrical ripples.

Wappinger Gp (Cambrian), I84, Fishkill, New York

This ripple is almost symmetrical, but its internal lamination shows that the ripple is shifting from right to left.

Chapel Island Fm (Cambrian), Newfoundland

A train of mildly asymmetrical ripples, moving from left to right.

Moenkopi Fm (Triassic), Gale Hills, Nevada, east of Las Vegas

Ripples climbing at a low angle. How do you tell between oscillatory-flow ripples and unidirectional-flow ripples, when you can’t see the full ripple profile? One tip-off: the sets are very regular, and they extend for long distances in the streamwise direction.


Another good example of (presumably) oscillatory-flow ripples climbing at a low angle.


The angle of climb is somewhat greater than in the preceding photo, but you can’t quite see the full ripple profile.


Ripples climbing at an angle steep enough that you can see the entire ripple profile. The ripples are almost but not quite symmetrical.


Nearly symmetrical ripples climbing at a middling angle. The thickness of the bed is unusually large. In what kind of environment can the conditions of flow and aggradation stay so similar for a long time?


Fairly large ripples climbing at a high angle.

Ferron Ss (Cretaceous), Utah

The thickness of this rippled bed is large relative to the scale of the ripples. One has the impression that the angle of climb is high, but the details of ripple geometry and movement vary upward through the bed.

San Rafael Swell, Utah

Symmetrical ripples climbing almost vertically. The conditions of oscillatory flow must have remained the same while sediment was showered from above for a long period of time. (It’s unlikely that the sediment could have been deposited in a very short time, because the ripples would probably not have been able to exist under those conditions.)


Another example of a very high, almost vertical, angle of climb. Such situations are very uncommon in the sedimentary record.

Moenkopi Fm (Triassic), Gale Hills, north of Lake Mead, Nevada

It’s more common to see a lot of irregularity in an oscillation-rippled bed like this one, in contrast to the several preceding photos.

Another example of an irregularly oscillation-rippled bed.

Wood Canyon Fm (Proterozoic–Cambrian), southern Nopah Range, California

A growing (fairly small-scale) hummock.


A lager growing hummock.

A hummock with gentle slopes, replaced upward by a swale.


A swale growing upward, continuously, into a hummock.

Wood Canyon FM (Neoproterozoic–Cambrian), southern Nopah Range, California

A piece from a bed with medium-sale hummocky cross stratification. The geometry of the bed top is clearly hummocky–swaly.

Cretaceous, Book Cliffs, Utah

A hummocky cross-stratified bed showing the characteristic lateral transition from a truncation surface to conformable lminae.

Rainstorm Mbr, Johnnie Fm (Neoproterozoic), southern Nopah Range, California

Another example of the same effect.


A representative large-scale hummocky cross-stratified bed.


Another example. Note the upward transition from swale to hummock on the left, and the lateral transition from truncation to conformability in the center.

Cretaceous, Book Cliffs, Utah (courtesy of John Harms)

This photo was used early on by Harms to illustrate the sedimentary style he termed “hummocky cross stratification”.


A good example of large-scale hummocky cross stratification.


A swale that is ironed out by deposition with time.


Follow the through-going truncation surface from left to right. This style of hummocky cross stratification might be described as “scour-and-drape” HCS: a hummocky–swaly erosion surface is draped by later sedimentation.

Thermopolis Sh (Cretaceous), Cody, Wyoming

Smallish-scale HCS. Although you can’t get a good three-dimensional view of the bed top, it is three-dimensional. The laminasets are clearly multidirectional.

Near Narita airport, Japan A single train of symmetrical ripples, almost but not quite starved...

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