JACOBSVILLE SANDSTONE
The Jacobsville Sandstone (=
“Eastern Sandstone” in early geologic literature) is a mottled
reddish-pinkish-whitish, fluvial (river system) sandstone that outcrops in many
areas of Michigan's UP, especially in the Keweenaw Peninsula, Marquette, and
Munising areas. It dates to the late Mesoproterozoic (~1.03-1.07 billion
years). The Jacobsville principally varies in lithology from nearly pure
quartzose sandstone to arkosic
sandstone. Granules, small pebbles, and rip-up clasts may be seen in
some outcrops.
The two photos below show
nicely cross-bedded Jacobsville Sandstone outcrops at Miner's Beach, at the
mouth of Miner's River, Pictured Rocks National Lakeshore, east of Munising (see
map). The Jacobsville at Miner's Beach consists of light pinkish-gray
quartzose sandstones that are moderately well-sorted, with subangular to
subrounded, medium-grained quartz sand. Some of the quartz grains are
slightly pinkish.
Jacobsville Sandstone (above & below) -
cross-bedded quartzose sandstones from the ~uppermost Jacobsville Sandstone at
Miner's Beach.
Jacobsville Sandstone
Here's a Jacobsville Ss.
outcrop at Quincy Mill (see
map), in Michigan's Keweenaw Peninsula, near the towns of Hancock and
Houghton. The Jacobsville here is a mottled pinkish-reddish, moderately
sorted, fluvial arkosic sandstone. Lenses of coarse-grained sand,
granules, small pebbles, and reddish shale rip-up clasts are present in a few
horizons.
Jacobsville Sandstone - outcrop just northeast of
Quincy Mill, Keweenaw Peninsula, UP of Michigan, USA. The rocks here are
arkosic sandstones.
Jacobsville Sandstone (outcrop at Quincy Mill)
with dark red rip-up clasts of shale.
Jacobsville Sandstone (5.6 cm across) from
lakeshore outcrops along Marquette Bay, Lake Superior (see
map). This arkosic sandstone is rich in quartz and K-feldspar sand
grains, plus a few scattered muscovite micas. The sand is dominantly
subangular and coarse-grained to very coarse-grained.