Facies Analysis and Correlations - MyGeologyPage

Geology 109L
Lab 8: Facies Analysis and Correlations:
Sequence Stratigraphy in the Book Cliffs, Utah
Goal: In this lab, you will put together your knowledge of near-shore facies and sequence
stratigraphy to correlate sections and interpret facies changes in the Cretaceous stratigraphy of the
Book Cliffs.
Introduction
Facies analysis is an important part of any stratigraphic study. The basic idea is to
recognize how different depositional environments are expressed by the development of
characteristic structures, lithologies and organic components in sedimentary rocks. The usual way
to reconstruct the depositional history of an area is to group strata into facies assemblages; that is,
measuring numerous stratigraphic sections, examining the rocks, and assigning those rocks a
depositional environment based on sedimentary structures, paleontological evidence and lithology.
When this has been accomplished, the measured sections are correlated using the facies
assemblages and sequence stratigraphic concepts, and three dimensional models of deposition are
constructed. When doing this, the stratigrapher must not only be familiar with sedimentary rocks
and structures, but also bear in mind the regional history of the area.
It is important to consider facies changes when correlating measured sections. A facies
change is the natural gradation from one environment to another. For example, at a certain point of
sea level, the coastal plain of Hot-As-Heck, Texas grades into a tidal flat, which grades along the
shoreline into a beach, both of which grade out to the deeper waters of the Gulf of Mexico. The
sediments in these environments differ, but there are no clean breaks dividing the environments; the
sediments change continuously. Add to this a stream that flows out to the Gulf, and you add more
environments. When sea level rises or falls, those environments migrate, producing a vertical
stacking of the sediments deposited in these laterally contiguous environments.
Stratigraphy in the Book Cliffs
During Late Cretaceous time, a time of world-wide high sea level, the stable cratonic area of
North America was inundated by marine waters. The invasive body of water is called the Western
Interior Seaway, or the Great Cretaceous Seaway. It was approximately 4800 km long and up to
1600 km wide. At this time, the western side of the seaway was bordered by a foreland basin
formed by thrusting of the Columbian-Sevier orogeny (which runs through present day Nevada),
and on the east by a stable exposed platform. Several basins formed due to the weight of the thrust
sheets loading the crust and causing subsidence. The stratigraphy and lithofacies differ in the
different basins, but in all, coal and natural gas deposits are an important economic consideration.
(Did you know that the Denver area has abundant petroleum resources? They are from organics
deposited in this environment during Cretaceous time.) Understanding the depositional
environments and stratigraphy in these basins is very important for exploration for these resources.
They also provide information on the timing and influences of thrust sheet movement; by dating
sediments in these basins, the timing and location of tectonic activity along the western paleomargin
of North America can be accurately constrained.
ASSIGNMENT
1) Identify the facies assemblages on the measured sections that will be provided in lab and color
the units different colors. Remember to consider Walther’s Law: Neighboring environments
should appear next to each other vertically unless an unconformity is present.
2) Identify and correlate the unconformities between sections. Some do not appear in all sections.
Think about why and how to deal with the correlations.
Book Cliffs, Page 1

3) Correlate the facies and facies changes between sections considering the temporal significance
of the unconformities. Color the areas between sections with the facies you predict.
4) On the far right of the stratigraphic columns, construct an approximate sea level curve for the
area based on the location of unconformities and shifts in facies distributions.
5) Answer the questions at the bottom of the stratigraphic columns.
6) Turn in your correlations.
Important Note: The stratigraphic columns are taken from Yoshida (2000), who provided a
correlation similar to the one I am asking you to do. However, Yoshida (2000) also mapped facies
changes and unconformities along cliffs between sections. Thus, Yoshida (2000) had much more
information than you do, and the correlations in the paper show much more detail. Also, I slightly
changed the facies I am asking you to map out, because it was unclear to me how Yoshida (2000)
identified some of the facies. Why this matters to you: You are welcome to look up Yoshida’s
paper and look at the published correlations, but this is neither required nor particularly encouraged
(or discouraged). The paper may or may not help. It contains complex terminology, making it
difficult to read, and you should be able to do this lab without that additional information. If you do
choose to look up the paper, you still need to work through your own correlations based on the
information provided in the lab; they should not be the same as the published ones. I did not get the
published correlation when I tried the correlations myself. Please reference it by answering the
questions on the bottom of the strat section page. Please note that if you use the paper and do not
reference it, you will be guilty of plagerism, which broadly consists of using other people’s work
without acknowledging them. Your answers to the questions will NOT affect your grade, unless
you use the paper and do not say that you did.
Facies Assemblages for the Upper Blackhawk Formation and Lower Castlegate Sandstone
The following descriptions of facies are taken from Yoshida (2000). Use these descriptions and the
facies tables that follow them to interpret the depositional environments represented in the
stratigraphic columns that you will correlate for this lab.
Yoshida, S. 2000. Sequence and facies architecture of the upper Blackhawk Formation and the
Lower Castlegate Sandstone (Upper Cretaceous), Book Cliffs, Utah, USA. Sedimentary Geology,
v. 136, p. 249-276.
4. Lithofacies assemblages
This study divides the strata of the uppermost Blackhawk Formation and the Lower Castlegate
Sandstone between Horse Canyon and Coal Canyon into nine lithofacies assemblages (Table 1).
4.1. Assemblage A: braided-fluvial facies
Assemblage A dominates the lower part of the Lower Castlegate Sandstone, and comprises
superimposed sandstone sheets bounded by laterally extensive erosional surfaces (Figs. 3 and 4A).
On a single outcrop (e.g. hundreds of metres wide), thick sandstone sheets (e.g. 10–20 m)
commonly comprise a few, laterally extensive sand bodies. Paleocurrents measured from trough
cross-bedding within each sheet sandstone are unimodal, oriented to the south-east and east. Many
sand bodies within each sheet sandstone contain large-scale cross-bedding (2– 13 m high), dipping
in a direction parallel, oblique or normal to local flow. Log impressions, wood/ plant fragments, and
rare dinosaur/reptile bones occur at the base of sandstone sheets. Sandstone beds within the sand
bodies are thin (,20 cm) to thick (3–4 m), are mostly fine- to medium-grained, and typically have a
pale orange to brown colour. Abundant trough cross-stratification and convolute bedding with
minor current ripples occur within beds. Minor associated lithofacies include light-grey shale and
Book Cliffs, Page 2

siltstone beds. Each sandstone sheet shows an incomplete fining-upward profile. Assemblage A is
interpreted to be of braided fluvial origin.
4.2. Assemblage B: tidally influenced sandy fluvial facies
Assemblage B is characterized by lenticular to tabular sand bodies 2–11 m thick, which
commonly contain large-scale cross-bedding (1.5–11 m high) and mud drapes. Some of these can
be classified as inclined heterolithic strata (hereafter called IHS; Thomas et al., 1987) (Figs. 3, 5 and
6), but some lack the diagnostic mud/sand couplets. Sandstones exhibit a white to very light
grey/brown colour. They are mostly very fine- to fine-grained, but medium-grained sandstone with
abundant lag deposits (e.g. wood fragments and reptile bones) occurs near the erosional base of
some sand bodies (Fig. 4B). In many localities these sand bodies laterally coalesce to form a sheet
geometry in the lower part of the assemblage (Fig. 4A). Each sheet sandstone has an upward-fining
profile (Figs. 3 and 5). Trough cross-bedding and convolute bedding are the most common
sedimentary structures in this assemblage. Log impressions are common at the base of sheet
sandstones. Siltstones typically have a light grey to greenish grey colour. Shales are dark grey and
carbonaceous, and contain abundant vascular plant fragments. In addition to IHS, this assemblage
contains many sedimentary structures indicative of tidal influence (e.g. Shanley et al., 1992), such
as sigmoidal bedding (Fig. 7A), fine organic detritus along the cross-stratification (Fig. 7B),
oscillation/bidirectional ripples (Fig. 7C), flaser/wavy/lenticular bedding and multiple reactivation
surfaces. Trace fossils including Teredolites and various crawling/resting traces occur in the
sandstones, which also contain rare dinosaur footprints (Fig. 5). Paleocurrents measured from the
trough cross-bedding are commonly unimodal, oriented to the east and southeast. Dispersion of the
paleocurrent readings in this assemblage is, however, higher than those in Assemblage A, and
subordinate northwestward flow is indicated in cross-bedding in some localities. This assemblage
changes facies updip to braided-fluvial deposits of Assemblage A and downdip to muddy estuarine
deposits of Assemblage D (Fig. 3). Assemblage B is interpreted as tidally-influenced fluvial to
upper estuarine deposits.
4.3. Assemblage C: alluvial plain facies
Assemblage C, together with Assemblage D, comprises the Upper Mudstone Member of the
Blackhawk Formation (Figs. 3 and 8). This assemblage consists of isolated channel sand bodies
encased in mudstones and siltstones. The sandstone fill of the channels is mostly fine-grained,
commonly has red ferric silica cement, and displays the geometry of lateral accretion. Sandstone
beds in the channels are characterized by trough cross-bedding and convolute bedding with minor
current ripples, and are typically interbedded with thin mudstones or siltstones. Inter-channel
deposits comprise dominantly siltstones and shales. Siltstones are light grey to grey, massive to
thick-bedded, and often have parallel laminations and minor current ripples. Shales are light to dark
grey, and carbonaceous, with abundant vascular plant fragments. Rootlets, thin coals and minor
sideritic nodules occur within the shales and siltstones. Assemblage C is interpreted as fresh-water
alluvial plain deposits with meandering river systems.
4.4. Assemblage D: muddy marginal-marine facies
Assemblage D consists of interbedded siltstones and mudstones with subordinate sandstones
and thin coals (Figs. 3, 5, 6, and 9). Sandstones are very fine- to fine-grained, thin (,50 cm) to thickbedded
(1–2 m). Thick sandstones occur with thin mud drapes either as channel-fill deposits (Figs.
5 and 10A), or within upward-coarsening and upward-thickening clinoform units (Fig. 11) or as
lenticular sand bars with mud drapes (Fig. 12). Channel fills are commonly made of distinct,
concave-up IHS (Fig. 10A). Thin sandstone beds have horizontal to wavy parallel lamination and
contain abundant oscillation and current ripples and minor trough cross-stratification. Tidal
indicators such as wavy/flaser/lenticular bedding, sigmoidal bedding and bidirectional ripples are
common. Trace fossils Ophiomorpha, Thalassinoides, Teredolites, Skolithos, Chondrites, and
various crawling traces and log impressions are present in the sandstones and siltstones.
Book Cliffs, Page 3

Siltstones have a distinct greenish to light grey colour, or dark grey where carbonaceous, and
are commonly bioturbated to varying degrees. They are massive to laminated, contain abundant
vascular plant fragments and organic material. Shales are dark- to brownish-grey and carbonaceous,
have horizontal to wavy lamination with abundant vascular plant fragments, minor sideritic nodules
and large (,15 cm long) intraformational clasts. Body fossils of marine and brackish water fauna
(e.g. gastropods, pelecypods) are rare and only locally preserved in the muddy part of the thicker
intervals of this assemblage (e.g. Fisher et al., 1960; Maberry, 1971) (Figs. 3 and 9). Assemblage
D is interpreted to have been deposited in a wide range of low-energy, marginal marine
environments. Interpretation of depositional environments of Assemblage D (e.g. lagoon vs.
estuary) requires a regional context, including spatial relationships with other facies assemblages,
and a sequence stratigraphic framework (Fig. 3).
4.5. Assemblage E: upper-estuarine clinoform and channel facies
Assemblage E infills deep and narrow incised valleys (up to 18 m deep) associated with the
Desert sequence boundary (Fig. 3). This assemblage is characterized by stacked scoop-shaped
channels and/or sand bars (Miall, 1993) (Fig. 13A), and large-scale (,18 mthick), down-streamdipping
clinoforms (Fig. 13B). Assemblage E grades upward to muddy deposits of Assemblage D
interpreted to be of lagoonal origin (Fig. 3). Some clinoforms are traceable for several hundred
meters or more. In paleo-slope section of the incised valleys, this facies becomes thinner toward the
head of the incised valley system, and grades updip into alluvial plain deposits (Assemblage C)
(Fig. 3).
Assemblage E is dominated by inclined, medium- to fine-grained sandstones with thin (typically
,20 cm thick) carbonaceous mud drapes. These sandstone/ mudstone beds form sandy IHS at some
localities. Upward-fining trends occur to varying degrees, both as individual sandstone–mudstone
couplets of IHS and in overall successions of this assemblage. Sandstone units have abundant
trough cross-bedding, current/ bidirectional ripples, convolute bedding, low-angle/ flat parallel
laminations and rare sigmoidal bedding. Fine organic detritus is commonly present along the crossstrata
of sandstone beds. The occurrence of mud drapes, bidirectional ripples and rare Teredolites
and Skolithos trace fossils may indicate tidal influence (Shanley et al., 1992). However,
paleocurrents measured from cross-bedding indicate dominantly unimodal flow in the SE direction,
and brackish-water/marine fossils have not been found by this study fromthis assemblage west of
Tusher Canyon. Assemblage E is interpreted as channel deposits of a large, sandy bayhead delta in
the upper estuary.
4.6. Assemblage F: backshore/back barrier sandstone facies
Assemblage F commonly has a white flaggy with subtle to moderate upward-coarsening
profiles (Fig. 14A), or thin to thick (1–5 m) tabular and massive sandstone (Fig. 14B). This
assemblage pinches out updip into lagoonal deposits of Assemblage D, and grades downdip into
shallow open marine sandstones of Assemblage H. Sandstones are very fine- to fine-grained and
well to moderately sorted, and contain horizontal to low-angle parallel lamination with subordinate
trough cross-stratification and current ripples. Organic detritus and plant fragments are common.
Rootlets may be present, typically near the top of the facies. Paleocurrent data measured from cross
bedding and current ripples indicate a dominant updip (westerly) flow direction. Assemblage F is
interpreted as a complex of back barrier environments composed of backshore, wash-over fan and
flood tidal delta.
4.7. Assemblage G: tidal inlet channel facies
Assemblage G occurs as isolated channels in the uppermost part of the Lower Castlegate
Sandstone in some localities east of the Little Park Wash South section (Figs. 3, 9 and 10B). These
channels are filled with medium-fine grained sandstone, ripped-up siltstone flakes, and local
bioclasts including coquina. Paleocurrents measured from the axis of trough cross-bedding show a
dominant basinward (south-easterly) flow direction. Assemblage G is interpreted as having been
Book Cliffs, Page 4

formed in tidal inlets (ebb channels) in the lower estuary, and subsequently eroded at its upper part
by a marine ravinement surface associated with the transgressing Buck Tongue shoreface.
4.8. Assemblage H: shoreface to foreshore facies
Assemblage H is dominated by sandstone, which coarsens upward from very fine to fine grain
size (Figs. 3 and 13). The lower part of the succession comprises interbedded thin sandstone,
siltstone and ripples, and hummocky cross-stratification. This interval changes upward to thickbedded
sandstone with hummocky cross-stratification, which is then overlain by thick amalgamated
sandstone with swaley cross-stratification near the base, trough cross-bedding and inclined parallel
lamination in the middle, and flat to low-angle parallel lamination near the top. Various marine trace
fossils including Thalassinoides, Ophiomorpha and Skolithos occur, comprising the Skolithos and
proximal Cruziana ichnofacies (e.g. Pemberton and MacEachern, 1995). Assemblage H is
interpreted as a shoreface–foreshore deposit.
4.9. Assemblage I: muddy open marine facies
Assemblage I comprises most of the Buck Tongue (Fig. 3), and is made up of thick mudstones
and thin sandstones and siltstones. The mudstones are typically dark grey, carbonaceous, and often
laminated and silty. The sandstones and siltstones are light to moderate grey, and horizontal to wavy
laminated with rare oscillation ripples, but some are structureless due to intense bioturbation. The
upper part of the Buck Tongue contains thin (,50 cm) sandstones with hummocky crossstratification
(Fig. 3). Trace fossils including Ophiomorpha, Diplocraterion, Terebellina,
Teichichnus, and various crawling traces occur. Assemblage I represents deposition on the open
marine shelf and in the transition zone between the lower shoreface and the shelf.
Book Cliffs, Page 5