Monday, January 5, 2009

Ichnology and Sequence Stratigraphy. Part A: The Ferron Sandstone

In May 2007, I got the chance to attend a very small meeting held in Price/Utah, USA “Ichnological Applications to Sedimentological and Sequence Stratigraphic Problems” organised by the SEPM.

In the first place, I gave my first scientific talk there and, more important, I gained precious experience in ichnology and sequence stratigraphy of siliclastic shallow marine systems. I do not really know where the word “gorgeous” is derived from but “gorge” might be a good guess and Utah is a excellent place to prove it. For me, geologically grown up in well covered, un-exposed Europe, the southwestern U.S. are somewhat my “promised land”. Nearly everything is visible and I really don't know where to go first. Awesome!

The succession visited at several localities during the congress fieldtrips included the Ferron Sandstone and the Panther Tongue Member. Both successions represent marginal to shallow marine sand wedges that prograded into Western Interior Seaway during the Cretaceous.

The well exposed Ferron Sandstone member gave textbook-like insights into shallow marine system dynamics and the feedback of organisms as recorded by trace fossils. However, the fieldtrip was predominantly focused on sedimentology. I learned a lot there and I really improved my skills in siliclastics just by sharing these three days in an inspiring landscape. It is not up to me telling the sedimentary evolution of the Ferron and Panther tongue sandstones but I would like to show some field pictures including some suggestions what you are expected to see there. The excursion was very well guided by Janok Bhattacharya from the University of Houston.

Ivie Creek Section

A general look on the Ferron Sandstone. This is a clinoform set comprising a whole prodelta to deltaplain succession. The slope, covered by float represents mudstones of the shelf. The lower part of the cliff face introduces the deltaic succession with heterolithic prodelta deposits. The bright sandy portion in the middle of the cliff face represents stacked delta front sandstones (Ivie Creek, N' of I-70).

Sandstone showing Hummocky Cross Stratification and low angle truncation Trace fossils are rare and include Thalassinoides, Ophiomorpha and Planolites. This low-diverse suite is typical for sediments generated by events such as storms. These sediments are interpreted as deposits of proximal, storm-domianted and wave-influenced prodelta (Ivie Creek Section ,near I-70).

Sandstone in lower bedding plane view with Thalassinoides, a dwelling/?feeding burrow produced by crustaceans. Such mass occurrences are probable related to short-term colonisation after storm events when floculated muds provide an excellent food resource (Ivie Creek Section near I-70).

This is a beautifully exposed fluvial point bar embedded in coal-deposits of the floodplain (Mr. Charles Howell for scale).

Willow Springs Wash

A more proximal facies of the Ferron is exposed at Willow Springs Wash. In the middle of this picture you can see a thick multistorey channel representing the distributary system for highly river-dominated delta lobes. Although there is some float covering the underlying deposits, you may notice that this channel incised underlying strata. I am somewhat confusing my field notes here; I am not sure if this channel is interpreted as a highly entrenched distributary or as regressional valley incision. Sorry, I will come back to this one. Suggestions welcome.

Probably my first real Dinosaur bone. This is just a fragment found at the base of the channel deposits from the picture above

A large specimen of Arenicolites within river-dominated prodelta to delta-front facies.

1 comment:

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