The Coastline between Staithes
and Port Mulgrave
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FORMATION |
MEMBER |
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Whitby Mudstone |
Alum Shale |
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Cleveland Ironstone |
Kettleness |
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Staithes Sandstone |
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Redcar Mudstone |
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Perhaps one of
the most famous Jurassic sites in Northern England is on the North Yorkshire
coast between Staithes and Port Mulgrave.
The rocks exposed are Lower Jurassic, all of which were deposited in marine
conditions of varying depth. The formations and members are illustrated in
the table above. Check the tides before doing this traverse! Photo to the left shows part of Staithes village and Staithes Sandstone
Formation sandstones/siltstones |
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The Staithes Sandstone Formation (SSF) consists of shallow marine
sandstones and siltstones. Notable features, as seen in the illustration to the
right, are well bedded coarser sandstones alternating with finer sediments
where the bedding has been destroyed due to bioturbation. Cowbar
Nab is the type locality for this formation. |
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Above the
SSF is the Cleveland Ironstone Formation (CIF),
so named because of the ironstone seams which were once quarried or mined. |
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Another interesting feature to be seen within the the
CIF in Jet Wyke are the so called "striped
beds" with infilled gutters. The gutters can be seen below the Raisdale Seam in plan view, to
the right, and cross section, as illustrated below. The striped beds and
gutters are believed to have been caused by storm conditions, and are known
as "tempestites". |
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The coastline between Staithes and Port Mulgrave is
quite fossiliferous. It is, however, a Site of Special Scientific Interest
and therefore collections must only be made from loose material. Examination
of the Main Seam will reveal many horizontal U shaped burrows, above right,
believed to have been made by a shrimp like creature named Rhizocorallium. The Grey Shale
Member is best exposed in Brackenberry Wyke. Here, specimens of the zonal ammonite Dactylioceras tenuicostastum
can be found. |
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Many of the Jurassic ironstones contain ooliths
consisting of concentric layers of chamosite, an
iron silicate, or their derivatives, berthierine or
goethite. They are formed by the precipitation of minerals around a nucleus, e.g. a shell fragment being rolled around by
oscillating currents. The concentric structure of the mineral results in a
cruciform extinction pattern when viewed under the microscope with cross
polarised light. The illustration to the left shows an oolith
which is 1mm in diameter. |
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From Brackenberry Wyke
to Rosedale Wyke at Port Mulgrave
the overlying Mulgrave Shale and Alum Shale Members are exposed in the
cliffs. Pieces of jet, a hard black type of lignite derived from wood
belonging to auracarian trees resembling the modern
day Monkey Puzzle tree, can occasionally be found among the rocks on the
shore in Rosedale Wyke. More information about this area can be found in the following excellent
guides: the G.A. guide "The Yorkshire Coast", the Y.G.S. guide
"Yorkshire Rocks and Landscape". Details can be found on the
Recommended Reading page To
return to the Jurassic period, click here. |
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