DAVID PLAISTED
I looked up some articles about varves and the Green River formation
in the literature. Here is what I found:
An example of a very well preserved fossil in the Green River formation,
from:
The first Esox (Esocidae : Teleostei) from the Eocene Green River
Formation, and a brief review of esocid fishes Grande L JOURNAL OF
VERTEBRATE PALEONTOLOGY 19 (2): 271-292 JUN 14 1999
Abstract: A new species of esocid, dagger Esox (Kenoza) kronneri
sp. nov., is described from the early Eocene Fossil Butte Member of
the Green River Formation, southwestern Wyoming. ... Although small
(118 millimeters long), the specimen is one of the best-preserved
fossil esociforms ever reported.
Discussion of the variable states of preservation of fossils in the
Green River formation; this claims that burial, or cold water without
much oxygen, explains the good state of preservation of the fossils.
From:
PALEOLIMNOLOGY AND TAPHONOMY OF SOME FISH DEPOSITS IN FOSSIL AND UINTA
LAKES OF THE EOCENE GREEN RIVER FORMATION, UTAH AND WYOMING FERBER CT,
WELLS NA PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY 117 (3-4):
185-210 SEP 1995
Abstract: In four sections in the lacustrine Eocene Green River
Formation in Utah (''Lake Uinta''), fish are preserved on carbonate
mudflats, along high-energy carbonate shorelines, in the littoral
zone, and in deeper profundal areas. Scattered bones and scales are
found throughout, dropped from disintegrating floating carcasses. Gar
scales typify shallow-water deposits, partly due to habitat
preference. Beach concentrations of greatly abraded bones and scales
grade offshore into storm lag layers and lenses, which grade to
loosely packed horizons or patches of unworn remains. Littoral fish
fossils range from dropped bones to good skeletons, with much
floating, lifting, and scavenging. Preservation improves away from the
waterline, not only into deep and cold profundal waters (where the
carcasses are protected from scavenging by anoxia and prevented from
floating by temperature and pressure), but also onto mudflats, where
stranding and burial of carcasses can also protect them.
A section through an isolated part of the Green River Formation in
Wyoming (''Fossil Lake'') also ranged from profundal to littoral with
minor emergence. Dropped body parts were found throughout, but
preservation quality of the best specimens improved with presumed
depth. The beds with the best specimens seem to have accumulated at
the bottom of a deep, stratified, warm-monomictic lake. Our Lake Uinta
sections were generally shallower and suggest more fluctuations in
water level, but this is not relevant to broad paleolimnological
interpretations because they represent marginal zones, which are
necessarily more sensitive to changes in depth. Overall, fish fossils
are especially informative in deeper waters, where sedimentary
distinctions fail.
An example of a well-preserved fossil in the Green River formation,
from:
A unique and complete polemoniaceous plant from the middle Eocene of
Utah, USA Lott TA, Manchester SR, Dilcher DL REVIEW OF PALAEOBOTANY
AND PALYNOLOGY 104 (1): 39-49 NOV 1998
Abstract: An extinct genus of the Polemoniaceae is described from one
complete fossil plant preserved in shale of the Eocene Green River
Formation, Utah. Combined vegetative and reproductive characters
including the taproot, basal and cauline pinnatifid leaves, primary
peduncular leaves, secondary peduncular bracts, pedicel bracts, fruits
in groups of three, and persistent calyx, support placement of this
plant close to the extant genus Gilia. Gilisenium hueberi gen. et
sp. nov. represents a rare record of an herbaceous plant, and the
oldest megafossil for the family Polemoniaceae.
Note -- I gave some web links earlier with other examples of well
preserved fossils from the Green River formation.
An article analyzing in which parts of the Green River formation well
preserved fossils are likely to be found:
DISCRIMINANT-ANALYSIS OF FISH-BEARING DEPOSITS IN THE EOCENE GREEN
RIVER FORMATION OF UTAH AND WYOMING WELLS NA, FERBER CT, OHMAN JC
PALAIOS 8 (1): 81-100 FEB 1993
Abstract: Principal components analysis and subsequent discriminant
function analysis helped interpret environments of some fish deposits
in the Eocene Green River Formation of Utah and Wyoming. The analysis
related 61 environmental variables to differing qualities of fish
preservation in 45 fish deposits. It greatly facilitated a Waltherian
or ''guilt by association'' type of facies analysis and it also served
to counteract observational biases and preconceptions. Analysis
indicates that completely preserved fishes are especially associated
with 1) environments that can also preserve fish coprolites, 2)
environments, probably deep, that exclude scavengers and physical
disturbances, and 3) abiotic mudflats with episodic inundations and
rapid burial.
The following article is the one claiming a million year record of
varves in the Green River formation, from:
CYCLICITY IN THE GREEN RIVER FORMATION (LACUSTRINE-EOCENE) OF WYOMING
FISCHER AG, ROBERTS LT JOURNAL OF SEDIMENTARY PETROLOGY 61 (7):
1146-1154 DEC 1991
Abstract: Basinal facies of the Green River Formation have two main
modes, lacustrine and playa. The lacustrine mode (Tipton and Laney
members) accumulated mainly varved oil shale. Here annual cycles are
recorded as varves. Variations in valve thickness demonstrate El Nino
(ENSO)-type and sunspot cycles (Ripepe et al., this
volume). Milankovitch-scale cycles are not obvious in lithic
variations, but gamma ray logs record 1) precessional variations with
a mean period (valve-timed) of 19.5 ka, and 2) a bundling of these in
the ca. 100 ka eccentricity cycle. In the plava mode (Wilkins Peak
Member), the lithic succession oil shale-trona-dolomitic marlstone
records the precessional drying up of a lake and is again bundled in
sets of 5, by the 100 ka eccentricity rhythm. The Tipton Member
persisted for 450 ka, the Wilkins Peak Member for ca. 1 Ma.
This also mentions that the varves are made of oil shale. This must
be the article that the folks at talk.origins have seized on to argue
that life is at least a million years old -- I agree that the
literature does not make much of this, in general, but it has to be
discussed because it is often used against Biblical creationists.
An article discussing possible microbial mats having an influence
in the Black Shale deposits of the Green River formation:
Microbial mats in terrigenous clastics: The challenge of
identification in the rock record Schieber J PALAIOS 14 (1): 3-12 FEB
1999
Abstract: Increasingly, microbial communities are recognized for
playing a potentially important role in defining and modifying surface
sediment characteristics in various settings, ranging from
terrestrial, through marginal marine, to continental margins. Whereas,
the presence of microbial mats can. be established with comparative
ease in modern terrigenous clastics, their recognition in sedimentary
rocks poses a big challenge.
... Possible ancient analogs occur in a variety of black shale
deposits (e.g. Jet Rock, Monterey Formation, Green River Formation),
with wavy to crinkly kerogen-rich Laminae being the main indication of
possible microbial mat origins. Although microbial mats clearly have
the ability to thrive in black shale environments, it will require
more research to firmly establish whether and how extensively, they
occupied this niche in, the geologic past.
A discussion of kerogen (a kind of organic material) in the Green
River formation:
OPTICAL DESCRIPTION OF AMORPHOUS KEROGEN IN BOTH THIN-SECTIONS AND
ISOLATED KEROGEN PREPARATIONS OF PRECAMBRIAN TO EOCENE SHALE SAMPLES
THOMPSONRIZER CL PRECAMBRIAN RESEARCH 61 (3-4): 181-190 MAR 1993
Abstract: This paper presents a limited study of Precambrian kerogen
and compares it to Phanerozoic kerogen. In both cases, most of the
kerogen is amorphous. While the specific biological precursors of
kerogen may be significantly different between the Precambrian and
Phanerozoic, the mode of degradation and preservation in shales may be
similar, and that is what is found in the description of the amorphous
kerogen. It is suggested that similar methods of sample preparation,
description and classification can be applied to all sedimentary
organic matter, regardless of age. Kerogen (disseminated organic
matter of sedimentary rocks that is insoluble in nonoxidizing acids,
bases and organic solvents, Hunt, 1979) occurs in many forms when
observed with a microscope. Structured kerogens include spores pollen,
unicellular algae, cuticle and cellular tissue of plants and coal
fragments. The majority of kerogens have no structures relatable to
precursor organisms and are called ''amorphous''. This paper describes
optical comparisons of various preparations of organic-rich
sedimentary rocks and the information that can be derived from them.
... Examples of amorphous kerogens from a variety of samples are
shown, including: thin section documentation of the occurrence of
oil-prone amorphous kerogen in laminae of the Eocene Green River
Formation: ...
I did not find any mention that well preserved fossils are found in
varves or laminae in the Green River formation -- I will have to look
more closely at Green River fossils in museums and books in the
future to see if this is the case.
Dave Plaisted
* * *
from a second email
Here are some references about fossils found in varves, but not in the
Green River formation. The first reference mentions fossils found in
varves and that generally they are not well preserved, but at certain
times the fossils were very well preserved, possibly because of very
cold conditions with poor circulation. It would be worth looking at
this one in more detail:
Seven centuries of taphonomic variation in Eocene freshwater fishes
preserved in varves: Paleoenvironments and temporal averaging Wilson
MVH, Barton DG PALEOBIOLOGY 22 (4): 535-542 FAL 1996
Abstract: Eocene lake beds of Horsefly, British Columbia, are
preserved in varves, or discrete yearly layers representing seasonal
changes in the lake. These varves allow study of temporal variation
and rates of change in morphological and ecological characters on a
very short time scale. One of the most sensitive indicators of the
paleoenvironmental conditions on the floor of the lake may be the
taphonomic condition of the fishes, which vary between perfectly
articulated and completely disarticulated skeletons. Patterns of
disarticulation correspond to those produced by scavengers. The
taphonomy supports the hypothesis that the lake was warm monomictic,
circulating in the winter, at which time scavengers could gain access
to the bottom of the lake. Larger-scale environmental events (on the
order of hundreds of years) are suggested by the fact that the
proportion of well-preserved specimens reached two peaks within the
seven centuries of deposition, one peak during the second century and
another during the fifth and sixth centuries. These results clearly
demonstrate two principles: that taphonomy can be a sensitive
indicator of paleoenvironmental conditions, and that temporal
averaging can affect the taphonomic properties of this fossil site,
and presumably of others with equal or lower time resolution.
The following article also discusses well preserved fossils in varves
(but not in the Green River formation) and gives a long chronology
which most Biblical creationists would dispute:
SHORT-TERM PALEOCLIMATIC FLUCTUATIONS EXPRESSED IN LOWER MISSISSIPPIAN
RAMP-SLOPE DEPOSITS, SOUTHWESTERN MONTANA ELRICK M, READ JF, CORUH C
GEOLOGY 19 (8): 799-802 AUG 1991
Abstract: Lower Mississippian ramp-slope deposits (Paine Member) of
southwestern Montana are composed of thin, rhythmically interbedded
limestone and argillaceous limestone (argillite). Millimeter-thick
graded layers typical of limestone beds represent distal storm
deposits, whereas argillite layers containing abundant whole, delicate
fossils represent quiet-water deposition during times of little or no
storm activity. Spectral analyses of the fluctuating insoluble-residue
content (quartz, muscovite-illite, organic matter) indicate a dominant
periodicity of 0.6-2.85 ka in the ramp-slope deposits; no spectral
peaks corresponding to typical Milankovitch-type periods
(approximately 20-100 ka) were observed. Similar approximately 2.5 ka
paleoclimatic periodicities are recorded in Quaternary continental and
alphine glaciers, Quaternary deep-sea sediments, C-14 variations in
Holocene tree rings, and Permian deep-water evaporite varves. These
short-term paleoclimatic fluctuations may represent one of several
harmonics of the precessional (19-23 ka) or obliquity (41 ka) orbital
cycles or may be related to variations in solar activity.
The following reference talks about problems in aligning different
varve chronologies; in general, they do not agree very well:
An evaluation of the late Weichselian Swedish varve chronology based
on cross-correlation analysis Holmquist B, Wohlfarth B GFF 120: 35-46
Part 1 MAR 1998
Abstract: The Swedish varve chronology is based on the correlation of
overlapping varve-thickness diagrams. The traditional visual match
between single diagrams has been based on, e.g., significant yearly
thickness variations or specific marker varves, but attempts to verify
these correlations by statistical methods are rare. To test if these
visual correlations can be regarded as correct, i.e. statistically
significant, we applied cross-correlation measures to overlapping
varve diagrams from two local varve chronologies established in
southeastern Sweden. Out of a total of 363 analysed connections, only
78 were found to fulfill the statistical requirements for a perfect
match. In 96 cases the statistical measures suggested alternative
placements to the published links. However, we found that for 179
correlations the published varve-diagram connections are statistically
not valid and that in 11 cases the overlap between diagrams is too
short to allow for valid cross-correlation analysis. This large number
of uncertain varve-diagram correlations in both local chronologies
shows that the derailed timing of the ice recession along the south
Swedish east coast can only be reconstructed through complementary
varve chronological investigations. Our investigations emphasize the
need to corroborate visual varve-diagram correlations through
statistical analyses, before the Swedish varve chronology can be
regarded as a valid, high-precision time scale.
[ March 14, 2002, 02:51 PM: Message edited by: Barnabas ]