LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

36 LOWER CRETACEOUS DEPOSITS INT CALIFORNIA AND OREGON
EMBAYMENT CURRENTS
That currents would be set up within the embayment there can be no
doubt. These would arise both from the inflowing water from tho Yolla
Bolly basin and River, and from tho tides entering the embayment from
the sea. A complete analysis of these effects cannot be undertaken here.
To what degree the sorting action of the currents would be effective upon
the sediments is a matter for both deductive reasoning and observation.
Currents arising from the inflow from the Yolla Bolly basin would vary
with the seasons, and their carrying power would vary with distance from
the point of debouchure. Heavy materials would be dropped sooner, and
the coarser detritus should be found near its entrance upon the delta.
Farther away the materials would be progressively finer, and thus the
sediments would vary from conglomerates to sandstones and shales as the
drift was followed southward along its course.
The tidal currents entering the embayment at the south would meet the
southward-moving currents and partially check them, and at the same
time they would themselves be driven eastward against the eastern shore
of the embayment, which in effect they would follow northward with
gradually diminishing force of current.
Ebb tides would stimulate the currents from the north along the western
shore of the embayment and increase their carrying power, whereas
marine waters would linger along its eastern margin, where brackish
water would scarcely penetrate. Such action would continue throughout
Cretaceous time. Each inflowing stream from the west would add its
contribution of water and sediment to the general volume of drift. In
this way there would be set up a system of circulating currents with a
maximum southward flow along the western border and a more gentle
northward flow along the eastern side of the embayment. The effect of
these currents would be felt not only by the sediments of the embayment
but also by the molluscan inhabitants that had entered it with the tides
through whatever portal was then open to admit them.
With regard to the defcrital sediments, the sorting effects of the currents,
and the distribution of the materials, they conform for the most part to
deductive principles, with some modification. From the delta head the
normal sorting action is recognizable as far south as Thomes Creek, at
which point a second, though smaller, stream had entered the embayment
from the west. Farther south other streams came in from the same direction,
and the sorting action of the currents met interference. Although
the positions of various streams active during Cretaceous time can be
recognized, many others have been greatly altered by faulting, or piracy,
or other causes, and the records are not complete. Nevertheless the
principals of sedimentation are not thereby invalidated, and much information
can be derived by careful study of the facts.