Contributions to Geology 18.1
Early lithification of limestones in the Redwater Shale Member of the Sundance Formation (Jurassic) of southeastern Wyoming
KNUT A. ANDERSSON Department of Geology, University of Wyoming, Laramie, Wyoming 82071
Pages
1-18
Keywords
lithification, Sundance, Wyoming, Redwater, limestone
Abstract
Calcareous concretions, limestone cobbles, and limestone layers are present in
the Redwater Shale Member (Jurassic: lower Oxfordian) of the Sundance Formation
in southeastern Wyoming. Many of the typically ellipsoidal and discoidal
concretions are scattered through the shale where they formed. Layers of
limestone cobbles represent accumulations of reworked concretions. While exposed
on the sea floor, they were penetrated by rock-boring pelecypods and encrusted
by oysters and polychaetes. One of these cobble layers is represented throughout
an area several tens of kilometers in diameter. It is consistently found at the
boundary between the lower shale unit and the upper siltstone unit of the
Redwater. Its cobbles represent several lithologic groups. This implies
derivation from several different source beds, and the cobble layer probably
represents a lag deposit on an erosion surface. The average size of the cobbles
is about 12 cm x 8 cm x 4 cm. Other similar but less widespread layers are in
the lower shale unit of the Redwater.
Similar evidence for early lithification and intraformational episodes of
erosion is provided by some limestone layers and large boulders of oolite at the
base of the Redwater Shale Member at one locality, and bored layers of
fossiliferous limestone near the top of the member at two other localities.
These limestone layers are discontinuous and the surfaces of lateral truncation
are bored by pelecypods, and in one case encrusted by oysters. The limestones
became indurated and were freed from overlying sediments by wave erosion during
the Jurassic. Wave action on the limestones produced irregular ledges and
boulders. The exposed parts of the limestones were ideal substrates for boring
pelecypods and oysters.
Some large, flat boulders of fossiliferous limestone exhibit pelecypod borings
on all surfaces, but are bored most extensively on the underside. This
distribution of borings can be explained in two ways. Either the boulders were
resting on the substrate in such a way that water could circulate under them, or
they were overturned by storm waves.
Early lithification of limestones in the Redwater Shale Member of the Sundance Formation (Jurassic) of southeastern Wyoming
KNUT A. ANDERSSON Department of Geology, University of Wyoming, Laramie, Wyoming 82071
Pages
1-18
Keywords
limestone, Redwater, Sundance, Wyoming, concretions, pelecypods, oysters, shale
Abstract
Calcareous concretions, limestone cobbles, and limestone layers are present in
the Redwater Shale Member (Jurassic: lower Oxfordian) of the Sundance Formation
in southeastern Wyoming. Many of the typically ellipsoidal and discoidal
concretions are scattered through the shale where they formed. Layers of
limestone cobbles represent accumulations of reworked concretions. While exposed
on the sea floor, they were penetrated by rock-boring pelecypods and encrusted
by oysters and polychaetes. One of these cobble layers is represented throughout
an area several tens of kilometers in diameter. It is consistently found at the
boundary between the lower shale unit and the upper siltstone unit of the
Redwater. Its cobbles represent several lithologic groups. This implies
derivation from several different source beds, and the cobble layer probably
represents a lag deposit on an erosion surface. The average size of the cobbles
is about 12 cm x 8 cm x 4 cm. Other similar but less widespread layers are in
the lower shale unit of the Redwater.
Similar evidence for early lithification and intraformational episodes of
erosion is provided by some limestone layers and large boulders of oolite at the
base of the Redwater Shale Member at one locality, and bored layers of
fossiliferous limestone near the top of the member at two other localities.
These limestone layers are discontinuous and the surfaces of lateral truncation
are bored by pelecypods, and in one case encrusted by oysters. The limestones
became indurated and were freed from overlying sediments by wave erosion during
the Jurassic. Wave action on the limestones produced irregular ledges and
boulders. The exposed parts of the limestones were ideal substrates for boring
pelecypods and oysters.
Some large, flat boulders of fossiliferous limestone exhibit pelecypod borings
on all surfaces, but are bored most extensively on the underside. This
distribution of borings can be explained in two ways. Either the boulders were
resting on the substrate in such a way that water could circulate under them, or
they were overturned by storm waves.
A geostatistical evaluation for underground uranium mining
CHARLES
M. KEEFER Department of Geology, The University of Wyoming, Laramie, Wyoming
82071
LEON E. BORGMAN Department of Geology, The University of Wyoming, Laramie,
Wyoming 82071
Pages
19-32
Keywords
kriging, uranium, geostatistical, ore
Abstract
Kriging, a geostatistical method, was used to examine spatially correlated
geologic phenomena with respect to their geometrical influence in a uranium
underground mining region of Wyoming. Uranium exploration drill holes were
mathematically analyzed using accumulations over 15.2 m intervals as the
regionalized variables. Two dimensional, anisotropic variograms described the
zones of influence characteristic of each of the three levels studied in detail.
A comparison between kriging and the usual technique assuming independence of
the data showed that kriging gave lower mean estimates and corresponding
variances which are more representative of the sample distribution. This
geostatistical method also worked well when a randomly distributed, anomalously
high accumulation was present. The purpose of the study was to demonstrate the
use of kriging in developing an economically feasible underground mining
program. This was done by giving ore reserve evaluations in terms of an average
grade and error of the estimation within hypothetical tunneling geometries.
A geostatistical evaluation for underground uranium mining
CHARLES
M. KEEFER Department of Geology, The University of Wyoming, Laramie, Wyoming
82071
LEON E. BORGMAN Department of Geology, The University of Wyoming, Laramie,
Wyoming 82071
Pages
19-32
Keywords
kriging, uranium, geostatistical, variograms
Abstract
Kriging, a geostatistical method, was used to examine spatially correlated
geologic phenomena with respect to their geometrical influence in a uranium
underground mining region of Wyoming. Uranium exploration drill holes were
mathematically analyzed using accumulations over 15.2 m intervals as the
regionalized variables. Two dimensional, anisotropic variograms described the
zones of influence characteristic of each of the three levels studied in detail.
A comparison between kriging and the usual technique assuming independence of
the data showed that kriging gave lower mean estimates and corresponding
variances which are more representative of the sample distribution. This
geostatistical method also worked well when a randomly distributed, anomalously
high accumulation was present. The purpose of the study was to demonstrate the
use of kriging in developing an economically feasible underground mining
program. This was done by giving ore reserve evaluations in terms of an average
grade and error of the estimation within hypothetical tunneling geometries.
Summary
of Miocene vertebrate fossils of the Granite Mountains Basin, central
Wyoming
JENS MUNTHE Department of Paleontology, University of California, Berkeley, California, 94720
Pages
33-46
Keywords
Arikaree, Miocene, vertebrate, Granite, Wyoming, Split Rock
Abstract
Vertebrate fossils from the Miocene rocks of the Granite Mountains Basin
indicate early (Arikareean) to middle (Hemingfordian) Miocene age for the
Arikaree Formation and late (Clarendonian) Miocene age for the overlying
Ogallala Formation. Sixty-seven taxa of fossil vertebrates are now known from 27
localities in the Granite Mountains area. The Split Rock local fauna from the
uppermost Arikaree Formation consists of 59 vertebrate taxa from 11 localities
and correlates with the faunas from the Box Butte and Sheep Creek Formations of
northwestern Nebraska. The Split Rock local fauna is approximately 17 million
years old. This indicates that Arikaree-type sedimentation lasted three to four
million years longer in the Granite Mountain Basin than in nearby areas to the
north and east. The bones, jaws and teeth representing the Split Rock local
fauna were deposited under subaerial conditions and were transported little from
the places where the animals died. They are a relatively complete representation
of the vertebrate fauna which lived in the same area 17 million years ago.
Summary
of Miocene vertebrate fossils of the Granite Mountains Basin, central
Wyoming
JENS MUNTHE Department of Paleontology, University of California, Berkeley, California, 94720
Pages
33-46
Keywords
fauna,
Miocene, vertebrate, Granite Mountains, Wyoming
Abstract
Vertebrate fossils from the Miocene rocks of the Granite Mountains Basin
indicate early (Arikareean) to middle (Hemingfordian) Miocene age for the
Arikaree Formation and late (Clarendonian) Miocene age for the overlying
Ogallala Formation. Sixty-seven taxa of fossil vertebrates are now known from 27
localities in the Granite Mountains area. The Split Rock local fauna from the
uppermost Arikaree Formation consists of 59 vertebrate taxa from 11 localities
and correlates with the faunas from the Box Butte and Sheep Creek Formations of
northwestern Nebraska. The Split Rock local fauna is approximately 17 million
years old. This indicates that Arikaree-type sedimentation lasted three to four
million years longer in the Granite Mountain Basin than in nearby areas to the
north and east. The bones, jaws and teeth representing the Split Rock local
fauna were deposited under subaerial conditions and were transported little from
the places where the animals died. They are a relatively complete representation
of the vertebrate fauna which lived in the same area 17 million years ago.
The Hay-Romer camel debate: fifty years later
MICHAEL
E. NELSON Department of Earth Sciences and Sternberg Memorial Museum, Fort Hays
State University, Hays, Kansas 67601
JAMES H. MADSEN, JR. Paleontology Branch Antiquities Section, Division of State
History, Salt Lake City, Utah 84101
Pages
47-50
Keywords
camel,
radiocarbon, Great Basin, Utah
Abstract
A
radiocarbon date of 11,075 + 255 years b.p. was obtained from the right palatine
and maxilla of a camel skull collected from a lava cave in Millard County, Utah.
This date supports Romer's (1928; 1929) conclusions that camels existed in the
Great Basin region of the western United States until relatively recent times.
Petrography of White River Group (Oligocene) in northwest Nebraska and adjacent
Wyoming
CHARLES
R. SINGLER Department of Geology, Youngstown State University, Youngstown, Ohio
44555
M. DANE PICARD Department of Geology and Geophysics, the University of Utah,
Salt Lake City, Utah 84112
Pages
51-68
Keywords
Oligocene, Chadron, Brule, Nebraska, Wyoming
Abstract
The
Chadron and overlying Brule formations (Oligocene) in northwest Nebraska and
adjacent Wyoming consist of fluvial and eolian deposits. Fine-grained rocks are
dominant, although sandstone, conglomerate, limestone and tuff are present. The
Chadron Formation contains the largest amount of mudstone and claystone; the
Brule Formation contains large amounts of siltstone and lesser amounts of
sandstone and mudstone.
Rocks of the White River Group contain quartz, feldspar, smectite, mica, heavy
minerals, glass shards, calcite cement, and other, less abundant, minerals. In
general, these rocks are texturally and mineralogically immature. The course
clastics of the Chadron Formation are arkosic, and those of the Brule Formation
are arkosic to subarkosic. The abundance and kind of quartz and feldspar
indicate a granitic-metamorphic provenance similar to the Hartville
Uplift-Laramie Range.
Glass shards in the fine-grained rocks, tuff in the Chadron Formation, and
volcanic minerals throughout the stratigraphic sequence indicate considerable
volcanic activity on the west during the Oligocene.
Regional uplift in eastern Wyoming during late Eocene or early Oligocene time,
and an increasingly arid climate through the Oligocene were the major controls
of deposition of the White River beds in northwest Nebraska and eastcentral
Wyoming. The influence of the Black Hills of South Dakota was minor.
Factors affecting fluorine content of fossil bones and teeth
HEINRICH TOOTS Department of Geology and Geography, C. W. Post College,
Greenvale, New York 11548
RONALD B. PARKER Sammen Sheep Farm, Rt. 1, Henning, Minnesota 56551
Pages
69-70
Keywords
fluorine, fossil, teeth, permeability, enamel
Abstract
The
amount of fluorine acquired by a bone or tooth during fossilization is not
entirely time dependent. It varies with the rate at which fluoride ions are
transported to the fossil, the rate at which the ions diffuse into the fossil,
and the total available fluorine. The rate of supply of fluoride to the fossil
is a function of the permeability of the surrounding sediment and other
hydrologic factors. We have found that the influence of sediment permeability
exceeds that of age. The rate of diffusion of fluoride into the fossils is
controlled by the physical properties and the thickness of the phosphatic
tissue. Bone and dentine are permeable and fluoridization is aided by
circulation. In enamel, only the slow process of diffusion is effective. In a
given amount of time, a thin bone or layer of enamel acquires more fluorine than
a thick bone or thick layer of enamel.
