Lacustrine Carbonates – Beaches,
Microbes, & Chemical Precipitates
Rick Sarg, Suriamin, Mike Sweirenga, Katie Logan,
Carl Symcox, & Kati Tanavsuu-Milkeviciene
Colorado School of Mines
Paul Wright
Cardiff University
Eocene (50 Ma)
Eocene 50 Ma (52-48)
Lake Gosiute
Uinta Uplift Sevier
Thrust Front
CO
LOR
AD
O
UTA
H
WYOMING
Lake Uinta
Green River Paleogeography
Green River Lake Waters:
Brine Evolution and Chemical Divides
Green River Inflow Waters: Low temperature chemical weathering:
Minerals + dissolved atmospheric CO2 produce ions Na, Ca, Mg, K, Cl
HCO3, SO4 which then form chemical sediments in closed basin lakes.
HCO3 + CO3 > Ca
CaCO3 Precipitation, use up Ca, Mg; extra HCO3 + CO3
forms alkaline (pH 9-10) brines.
Precipitation of Na-carbonates,
i.e., nahcolite, trona, and halite
Accelerated chemical weathering with elevated
atmospheric CO2 in the Eocene (Smith et al., 2008)
Carbonate Stable Isotopes Co-vary –
A Closed System
• Piceance basin (~54 to ~48 Ma)
• Uinta basin (~54 to ~44 Ma)
• Divided into:
• 1. Members, based on lithofacies
• 2. Rich and lean zones (R/L), based on kerogen content
Modified after Self et al. 2010; Tänavsuu-Milkeviciene & Sarg 2012
Stratigraphy
Modified after Tucker & Wright, 1990
Carbonate Lake Environments
0 10 20 30 40 50 Kilometers Outcrops of Uteland Butte member
UTAH
UINTA BASIN
COLORADO
Vernal
3 1
4
8
10
15 14
2
13
5
9
12
11
6 7
16 17
to R
oo
seve
lt
Jensen
Hells Hole Canyon
Texas Creek
Missouri Creek Canyon
Evacuation Creek
Stat
e Li
ne
Missouri Creek 1 2 3 4 62 km
NBU 921-22M
5 m
C-Shale
D-Shale
4830
4840
4850
4860
4870
4890
4910
Core depths in feet
4880
4900 5 m
5 m
Oolitic & ostracod lime grainstones
Uteland Butte shoreline grainstones
Dolomitic intraclastic packstone
1mm
1mm
1mm
1mm
FA B
FA A
C S VF F M C VC GR PB CO
Mud Wacke Pack Grain Float Rud Bnd
1 mm
1 mm
Brazil & West Africa
Bioclastic Bar Deposits Comprise units >10m thick of grain supported, to densely packed molluscan calcrudites with thin (<5m) layers of bioclastic calcarenite and calclutite. No siliciclastic intercalations are present. This facies association forms thick deposits 20-550m thick.
These units are interpreted to result from the amalgamation of relatively thin (0.2-1m thick) cross bedded molluscan calcrudites deposited in shallow, high energy settings. They are mainly associated with steep sided palaeohighs and are believed to be the product of storms.
From Dolores de Carvalho M. et al. 2000 AAPG Studies in Geology 46, 245-256
Bioclastic Calcarenites/Beach Deposits
Comprise <10m thick units of bioclastic calcarenites associated with thinner (<5m) layers of siltstone, shale and calcilutite. Calcarenites show low angle cross bedding and comprise abraded bivalve fragments and rare gastropod fragments together with micrite envelopes. This facies association is generally 50-150m thick.
From Dolores de Carvalho M. et al. 2000 AAPG Studies in Geology 46, 245-256
Microbialites -Three Mile Canyon, Evacuation Creek
USGS: Johnson et al., 2010
Littoral Microbialite Deposits, Green River Fm., Three Mile Canyon
Color Key Orange: Intraclastic
rudstone/grainstone Yellow: Dendrolitic stromatolite Gray: Thrombolite/columnar
stromatolite Red: Agglutinated stromatolite Blue: Oolitic/peloidal
gnst/pkst/wackest Green: Spheroidal stromatolite White: Fine-grained stromatolite
Depositional Cycles
Basinward
Depositional Architecture
Lower Mid-Littoral Setting
Stromatolite bioherm
A. f. g. stromatolite with alternating dolomite and calcite lamina
B. Columnar stromatolite with dolomitized outer coating
C. Dendrolite layer D. Agglutinated
stromatolite with alternating dolomite and calcite lamina
E. Agglutinated stromatolite with dolomite and calcite lamina
F. Agglutinated stromatolite with irregular laminations
Stromatolite Microtextures
Thrombolite
Stromatolite Heads Dendrolite
Thrombolites & Stromatolites
A. Dolomitic thrombolite
B. Arborescent dolomitized thrombolite
C. Calcitic thrombolite with interstitial mud
D. Calcitic thrombolite
E. Partially dolomitized thrombolite clots
F. Fully dolomitized thrombolite
Thrombolite Microtexture
Intraparticle (after oogonia)
Enhanced fenestral
Dendrolitic framework
Interparticle
Interparticle & fracture
Vuggy framework
POROSITY
Carbonate-Claystone Cycles
Depositional environment - Lower sublittoral to upper profundal
Fine-grained Laminated Stromatolites
Photomicrograph of fine-grained, laminated stromatolite
Fine-grained Laminated Stromatolites – Upper Profundal
Brazil & West Africa
Stromatolite – Associated with Coarse Clastics; Mucua 1 well, Kwanza Basin, Angola
From Wasson M S et al., 2012 AAPG Search and Discovery Article #90153
Lacustrine Microbial Carbonates, Toca Fm. Lower Cretaceous, offshore Angola
Kambala Well A core: core is approx. 8.4 cm wide.
Profundal deposits
4 cm
61
cm
3 cm
Continuity of profundal deposits
Soft-sediment-deformed deposits
Laminated oil shale Oil shale breccia
Profundal deposits
Redox Conditions for Ferroan Dolomite
a (ankerite) = 0.1;
[Fe(II) aq] = 10-4
Inorganic C conc. = 10-2.7
Grosz et al. (2006) Geofluids 6, 137-153
Oil Shale
Shell 23X-2
Brazil & West Africa
Barra Velha Fm. carbonate components
Crystal shrubs –mm-cm-sized
Spherulites -mm-sized
Carbonate silt
Facies 1
Facies 2
Facies 3
Diaz J L B. Geoci. Petrobras, Rio de Janeiro, v. 13, n. 1, p. 7-25, nov. 2004/maio 2005
Shrubs - Campos Basin
Terra G J S et al. B. Geoci. Petrobras, Rio de Janeiro, v. 18, n. 1, p. 9-29, nov. 2009/maio 2010
Spherulites with silica and silicate matrices
Source – ANP Pre-Salt Libra Geological Assessment : 17/9/2013
IN situ spherulites, with stevensite
Terra G J S et al. B. Geoci. Petrobras, Rio de Janeiro, v. 18, n. 1, p. 9-29, nov. 2009/maio 2010
Spherulites with dolomite threads and pseudo-fenestral porosity
Textural “model”
Lacustrine Carbonates – Beaches,
Microbes, Springs, & Chemical
Precipitates
It’s all about the CHEMISTRY – driven
by climate, tectonics, & provenance
(ions to the lake)!
