LOWER CRETACEOUS DEPOSITS CALIFORNIA AND OREGON

IS LOWER CRETACEOUS DEPOSITS INT CALIFORNIA AND OREGON
sedimentary aggregates they present difficulties in the matter of correlations
with other more concentrated columns in the Cretaceous deposits
of other countries, but these difficulties may be more apparent than real.
EMBAYMENTS OF THE TROUGH
GENERAL STATEMENT
The Cretaceous deposits within the Great Valley trough are found
chiefly on the west borders of its two major embayments, which lie in
opposite directions from a supposed marine entrance to it near San Francisco
Bay. These embayments may be known as the Sacramento and the
Joaquin, corresponding to the major parts of the Great Valley of the
present, although they are not proportional in dimensions.
In the Sacramento embayment both the physical and paleontologies!
records for the lower Cretaceous are more complete, extending from
Berriasian to late Albian time, the higher portions of the column being
partly lacking, the lower portions of the sequence here constituting the
Shasta series in its type areas.
In the Joaquin embayment both the stratigraphic and faunal records
of the Shasta series are incomplete. At the bottom, the column begins
with early Cretaceous deposits that represent a port of Valanginian time,
but for the most part its areas ore fragmented by faulting, Upon these
scattered deposits there is a succession of Upper Cretaceous strata, occupying
the span from late Albian almost to the close of the period. Between
these portions of the column there is a stratigraphic hiatus, in which
almost no Hauterivian, Barremian, or Aptian faunas have been found,
although this condition appears to be in part due to faulting. Nevertheless,
the facts seem to indicate a different sequence of depositions! and
of tectonic events than those found in the Sacramento embayment and
suggest the possibility that the two embayments were not so closely connected
during a part of Cretaceous time as the present aspect of the
Great Valley would indicate.
In the Joaquin embayment the volume of later Cretaceous deposits
(Albian to Maestrichtinn) far exceeds that of its early portion, attaining
a maximum thickness of more than 25,000 feet, although in some places
it does not exceed half this thickness. The faunal sequence is much less
complete than in the northern embayment, although in its upper part the
faunas are better developed, whereas in its lower four-fifths the faunas
are scanty and almost wholly post-Cenomanian.
JOAQUIN EMBAYMENT
General Statement—The view that the principal portal leading to the
Joaquin embayment was near San Francisco Bay may not be wholly
correct since it does not meet all factual requirements, especially for the
later Cretaceous deposits. These Cretaceous beds outcrop only along its