| CHALK CANYON, HICKEY &
OTHER FORMATIONS |
|
Hickey Formation (HF)
(~9.2 to 16.2 My) Miocene
The Hickey formation is the name given by geologists Anderson &
Creasey in 1958, to a sequence of basaltic flows and associated red-brown
sedimentary rocks exposed on Hickey Mountain. Potassium-argon dating
(1971) indicates the the formation ranges in age from about 14.6 My to 10.1 My at
Hickey Mountain and is therefore considered to be late Miocene and early
Pliocene in age.
Basalts from the formation were erupted at a number of places in the region
and formed local accumulations which included the BCC, Big Bug, Estler, Mingus
Mtn. and Prescott areas.
The Basalt volcanism part of the formation is dominantly subalkaline (a rock
that contains no alkali minerals other than feldspars). The lower sedimentary
part of the formation consists mainly of pebble to bolder conglomerate,
sandstone & siltstone interbedded with olivine basalt.
NOTE: There is some controversy over the age of the lower sediments in the
Hickey Formation (Ths) some geologists thing the sediments may be older than Tertiary.
Chalk Canyon Formation (CCF)
(~15.4 to 23.3 My) Miocene
The Chalk Canyon formation (informal name) consists of deposition of
interstratified volcanic, alluvial, and lake beds in Black Canyon City, Cave Creek
and Chalk Mtn. area.
The CCF was named by Ernest Gomez of
(NAU) in 1978, for exposures in Chalk Canyon, a tributary to cave creek which is
north of phoenix arizona. Exposures of the formation are found throughout the
area with excellent exposures in the slopes beneath Black Mesa (not the mesa
along I-17), New River Mesa, and skull Mesa. The overall thickness of the
formation changes little from west to east, although large differences are seen
in the thickness of the members. A maximum thickness of more than 300 meters is
found near the black mesa, and new river mesa. Generally
the CCF represents a sequence of early Miocene alkaline (a igneous rock that has
an excess of sodium & potassium) basalts, felsic tuffs and
fluvial-lacusteine sediments.
Their is a upper and lower member. The lower member sits on a thin
fanglomerate or trachyte layers which rests on early Proterozoic basement.
Tuff of the CCF is mostly reworked, although some airfall tuff is present.
Airfall tuffs are white. An intermediate to silica rich source is suggested, for
the reworked tuffs.
Only the upper layer is present in the BCC area. It has been reported that
there is a 2-5 meter thick soil layer between the Upper CCF and the HF.
Correlation between units
The Hickey sediments, from there stratigraphic position beneath Hickey basalt
correlate with parts of the Chalk Canyon Fm, mainly with the upper member but
perhaps with some parts of the lower member as well. The basalts are mainly
alkalic with smaller amounts on the tholeiitic side.
Red Conglomerate / Fanglomerate layer
(~33-38 My ?) Oligocene / Eocene
This new found layer, near BCC, of Oligocene well cemented, course, poorly sorted,
crudely to poorly stratified
rock locally underlies the volcanic and sedimentary rocks of the CCF.
This fanglomerate contains only protozoic detritus, no Tertiary volcanics are present.
Its deposition is interpreted to mark the onset of an episode of strong
regional uplift before the CCF formation existed. This layer sits directly
on protozoic basement schist with the white air-fall ash above it. This one location
is the only place around BCC that has this layer. Normally the white ash sits on the
Proterozoic basement. Note; see the column 1 chart on this site.
There are also exposures of this layer near Cave Creek and at two locations
in Bloody Basin.