Uraian soal storm deposit dibawah ini bagus, aku ambil dari sebuah website
Storm deposit merupakan deposit (tubuh batuan) yang cukup tebal, dibentuk
dalam waktu yang sangat-sangat singkat ... lamanya saja storm ... ngga akan
berbulan-bulan waktunya. Dalam setahun ada musimnya tetapi bukan proses yang
kontinyu ...
Selingan shale yg sangat tipis (mungkin bisa ~ hanya 5 %) tetapi jauuuh
lebih lama pembentukannya, bayangkan kalo mencari 'keong' nya di shale ini,
mungkin settingnya sudah sangat berbeda antara sandstone dengan shale
interbednya dalam lingkungan pengendapannya.
Dan yang menarik juga, uraian Samodro :
>menurut istilah yang dipakai di sini...storm deposit adalah endapan
>seperti channel (tapi bukan channel) yang ditemukan di daerah yang more
>distal than delta plain (delta front/prodelta...)
Bagaimana sebenernya geometri dari sebuah endapan storm ? karena biasanya
relatif singkat tentunya geometrinya mungkin akan menyerupai ketika
diendapkan
rdp
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Storms in the Foreland Basin.
(Foreknobs shelf environment)
The Foreknobs formation contains the shelf deposits of the clastic
wedge. It is filled with thousands of sandstone beds stacked on on top of
the other, like the ones to the left, containing hummocky sequences, each
one the result of a storm, like a hurricane or, on our modern Atlantic
coast, a "nor'easter". Thousands of sandstones means thousands of storms,
but just how frequent is that? Do all these sandstone deposits laid out one
after the other in the rock record imply that this was a continuously roiled
up and riled coastline being pounded incessantly with storms, and little
else happening in between?
To get an answer to this we can use storms on a modern shelf as a
model. For reasons that will become clear below, the modern Atlantic coast
is not necessarily a good model for the Catskill, but it is familiar to most
of us and will give some idea of what we might expect.
Every year there is a hurricane season, and anywhere from a few to a
few dozen hurricanes are born and wander their way across the oceans. But as
most of us know, any one spot of coastline does not feel the impact of all
these storms. Indeed, a spot of coast may go for a decade, or many decades,
without having any significant storms attack it (like the Carolina Outer
Banks recently).
So, what is being deposited on the shelf during all these quiet years?
Practically nothing, or perhaps a few millimeters of mud washed down with
the rivers. But, then comes the big storm that just happens to hit this
particular spot on the coast. The wind howls and waves crash with great
energy, ripping and eroding the sand, transporting some of it offshore. And
there the waves work the sand beds into sandbars with hummocky sequences,
the signature of a storm deposit. And then all goes quiet again for another
decade, or more.
The point is, even though there are many storms each year any one spot
of coast receives a major storm infrequently. And the major storms probably
crossed any one point on this Devonian Foreknobs shelf no more frequently
than they cross the Atlantic shelf today. Yet it is possible to be fooled
when looking at an outcrop of rock; sandstone after sandstone seems to point
to storm after storm, as indeed it does, but the outcrop skews our sense of
time. Each sandstone is probably the result of at most only a few day of
strong wave action, while the shale in between represents years of slow,
quiet accumulation. And most days of the year produce no rock record at all.
The geologic record is, in fact, mostly gaps.
So, now imagine the sea to the west in the Devonian being pounded
occasionally by large storms. But it is not quite that simple.
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