STATEMAP Field Blog Oct. 14 – 16, 2013

Hello all!

It was a rather wet week in the field this week.  Starting to see a little fall color as well, but still mostly green.  We worked in Weaver Creek which runs along that southwest/northeast lineation on the southern part of the Shirley quad.  It appears that the wide valley there and in the Middle Fork to the northeast is developed in a very thick shale sequence that is all dipping southeast, probably southeast of the major fault causing the lineation.  The valley can widen significantly in the shale, but once it reaches the 200+ feet thick, thin- to massive-bedded sandstone unit on the southeast side of the valley, it can’t go much farther.  Essentially the lineation is caused by the stream eroding upsection across the valley through the shale unit, until it reaches the contact with the thick sandstone unit above.  The lineation is therefore along the strike of (perpendicular to) the southeast dipping rock in this area.  One big question is what happens to the fault on the east side of the map where the lineation stops.  May have to wait to find out next year when we map the Parma quad.

Started out on Buffalo Hump, which I think may be a reference to a series of rounded “humps” along the end of Weaver Creek where the sandstone bluff is deeply incised by four drainages.   

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Saw several sets of non-vertical joints crossing each other in one of those drainages.  This usually indicates that there is a structure close-by, but we didn’t see anything unusual.

The next two days were rainy, so we stayed close to the highway so we could bale out in the event of a deluge.  The shaly unit was well exposed in the valley and displayed abundant soft-sediment deformation and load casts.

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It was difficult to ascertain the true dip of the rocks because this unit is a stack of very broad channels, so the beds dip consistently for a long way, then abruptly turn about 90 degrees and continue on like that for a ways, then switch back. The exposed edges of these channels typically dip sharply and are sandier.    Wish we had more time to study this unit to determine paleocurrent direction, facies, and depositional environment, but as usual, we’re just passing through.

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The channel-bedding continues into the sandy unit above as well.  The big question is what formation these units are in.  Now that we’ve worked our way south of the fault, we’re in a totally different section than we were in north of it.  Still haven’t seen anything that looks too familiar.  May have to pull well logs and work our way up from the subsurface to get started.

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Well, looks like better weather next week!  See you on the outcrop!

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