Silica-carbonate stromatolites related to coastal hydrothermal venting in Bahía Concepción, Baja...

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Sedimentary Geology 1

Research paper

Silica-carbonate stromatolites related to coastal hydrothermal

venting in Bahıa Concepcion, Baja California Sur, Mexico

Carles Caneta,*, Rosa Marıa Prol-Ledesmaa, Ignacio Torres-Alvaradob, H. Albert Gilgc,

Ruth Esther Villanuevaa, Rufino Lozano-Santa Cruzd

aInstituto de Geofısica, Universidad Nacional Autonoma de Mexico, Cd. Universitaria, Coyoacan, 04510 Mexico, D.F., MexicobCentro de Investigacion en Energıa, Universidad Nacional Autonoma de Mexico, Temixco, Morelos, Mexico

cLehrstuhl fur Ingenieurgeologie, Technische Universitat Munchen, GermanydInstituto de Geologıa, Universidad Nacional Autonoma de Mexico, Cd. Universitaria, Coyoacan, 04510 Mexico, D.F., Mexico

Received 13 May 2004; received in revised form 25 November 2004; accepted 3 December 2004

Abstract

Submarine diffused seepage (from 5 to 15 m depth) and intertidal focused gasohydrothermal venting take place on the

West shore of the Bahıa Concepcion Bay, on Baja California, Mexico. The intertidal venting consists of a cluster of hot

springs that occur a few meters offshore, with vent temperatures up to 62 8C and a pH of 6.68. Two irregularly shaped

patches of silica-carbonate hot spring deposits occur around the main intertidal vent areas. In addition, a fossil bed of silica-

carbonate hot spring deposits of about 75 m long crops out along a cliff next to the active vent area. Both fossil and modern

silica-carbonate deposits are finely laminated, and form columnar, bulbous and smooth undulating microstromatolites up to

10 cm thick. Noncrystalline opal-A is the only silica phase present in the modern and fossil hot spring deposits and occurs as

microspheres up to 300 nm in diameter forming porous aggregates and irregular clusters, chains and spongy filament

networks. The silica supersaturation state of the thermal fluid necessary for opal precipitation is achieved by cooling when it

reaches the surface. The presence of preserved microbial remains (diatoms and possibly filamentous microbes) in both

modern and fossil deposits reflects the biological activity around the hot springs. The biological activity constrains the fabrics

and the textures of the deposit, and could mediate silica deposition. Calcite is the most abundant crystalline phase in the hot

spring deposits and forms discontinuous horizons of subhedral bladed crystals within the silica aggregates. Calcite crystals

are unusually enriched in 13C, with d13CV-PDB values between +3.0x and +9.3x. The large 13C enrichment is attributable to

a geothermal CO2 degassing process, which yields calcite supersaturation. The d18OV-PDB values in calcite, between �10.0xand �6.6x, indicate precipitation from a hot spring fluid that is a mixture of seawater and meteorically derived water. With

the methods applied in this study, no indication of biogenic influence on calcite precipitation has been found. Minor amounts

0037-0738/$ - s

doi:10.1016/j.se

* Correspon

E-mail addr

74 (2005) 97–113

ee front matter D 2004 Elsevier B.V. All rights reserved.

dgeo.2004.12.001

ding author. Tel.: +52 55 56 22 41 33; fax: +52 55 55 50 24 86.

ess: [email protected] (C. Canet).

C. Canet et al. / Sedimentary Geology 174 (2005) 97–11398

of barite occur in the fossil and modern hot spring deposits and precipitates when Ba2+-rich thermal water mixes with

seawater.

D 2004 Elsevier B.V. All rights reserved.

Keywords: Shallow hydrothermal vents; Microbialites; Sinter; Travertine; Opal-A; Carbon isotopes; Oxygen isotopes

1. Introduction

Silica and minor calcite finely laminated stroma-

tolitic deposits are a widespread surface feature of

many geothermal systems throughout the world.

Silica deposits (sinters) usually form in relation to

discharge of near-neutral alkali chloride waters, and

are composed mainly by opaline silica (e.g., Four-

nier and Rowe, 1966; Rodgers et al., 2004). For

example, silica stromatolitic sinters have been

described in the Taupo Volcanic Zone, New

Zealand (e.g., Renaut et al., 1996; Mountain et

al., 2003; Rodgers et al., 2004), in Iceland

(Konhauser et al., 2001), in the Yellowstone

National Park, Wyoming (e.g., Walter et al., 1972;

Walter, 1976; Guidry and Chafetz, 2003a), and in

the East African Rift (Renaut et al., 2002).

However, opaline stromatolitic sinters can also form

around acidic hot springs and, in this case, they

contain significant amounts of kaolinite, sulfur and

jarosite (Jones et al., 2000a).

Likewise, finely laminated calcium carbonate

deposits (tufa, travertine) are widely known in modern

subaerial and lacustrine thermal springs, for example,

in East African Rift basins (Renaut et al., 2002), in

Pyramid Lake, Nevada (Arp et al., 1999), and in the

Yellowstone National Park, Wyoming (Pentecost,

1990; Fouke et al., 2000). Additionally, several fossil

calcite travertine hot spring deposits have been

reported, for example, in Central Italy (Folk et al.,

1985) and in Mud Hills, California (Pedone and

Dickson, 2002). In hot spring environments, calcite

deposits form from neutral to alkali thermal waters

that are supersaturated with respect to calcite and

cannot precipitate in acidic conditions (Jones et al.,

2000b).

On the other hand, mixed silica-carbonate hot

spring deposits are much more rare (Campbell et al.,

2002). Among the best-studied silica-carbonate hot

spring deposits, those from Waikite (Jones and

Renaut, 1996; Jones et al., 2000b) and Ngatamariki

(Campbell et al., 2002), New Zealand, and a relict

deposit in Yellowstone, Wyoming (Guidry and Cha-

fetz, 2003b), can be mentioned.

Although many geyser and subaerial thermal

spring sinters and travertine deposits are well

documented, those formed in coastal and submarine

hydrothermal environments have received little

attention. Near Punta Mita, on the western coast

of Mexico, finely laminated calcite deposits occur in

10 m depth submarine gasohydrothermal vents

(Canet et al., 2003). Moreover, silica-rich precip-

itates have been reported in close association to

massive sulfides in a modern oceanic hydrothermal

vent system, in the Central Indian Ocean (Halbach

et al., 2002). Likewise, only few sublacustrine hot

spring deposits (sinter and travertine) have been

studied (e.g., Barrat et al., 2000; Renaut et al.,

2002).

Siliceous sinters are formed from hot spring

solutions below life’s upper temperature limit (e.g.,

Jones and Renaut, 1996; Konhauser et al., 2001),

and its close association with microbes has been

well established in many cases (Konhauser et al.,

2001 and references therein; Guidry and Chafetz,

2003c). For a long time, the role of microbes had

been considered passive in silica sinter precipita-

tion, assuming that it is an inorganic-physicochem-

ical process (Walter et al., 1972; Walter, 1976).

Nevertheless, recent research points out that micro-

organisms have a more active role in silica

precipitation, fixing silica and favoring its nuclea-

tion (e.g., Jones and Renaut, 1996; Konhauser et

al., 2001). In many cases, silica precipitation can be

attributed to a combination of both biotic and

abiotic mechanisms (Guidry and Chafetz, 2003a). In

the same way, calcite crystallization in thermal

spring deposits may be mediated by microbial

C. Canet et al. / Sedimentary Geology 174 (2005) 97–113 99

activity (e.g., Chafetz and Folk, 1984; Arp et al.,

1999; Chafetz and Guidry, 1999; Canet et al.,

2003). In any case, organo-mineralization products

contribute as a main component in many hot spring

deposits, and microorganisms usually are mineral-

ized and preserved as fossils (Walter and Des

Marais, 1993). Furthermore, there is no doubt that

the presence of microbes has a great influence on

the textures and development of hot spring deposits

(Mountain et al., 2003).

Thermophilic life forms, comparable to those

supported by the hot spring environments, have been

Fig. 1. Location of the studied silica-carbonate hot spring deposits of Bahıa

deposits.

proposed as the common ancestor of life on Earth

(e.g. Stetter et al., 1990). Therefore, the study of

organo-mineralization processes and their products in

hot spring deposits can yield information on the early

Earth lifestyles (Walter and Des Marais, 1993;

Konhauser et al., 2001, 2003; Guidry and Chafetz,

2003a).

In this paper, we provide morphological, minera-

logical, geochemical and carbon and oxygen stable

isotope data on unusual silica-carbonate stromatolitic

deposits related to coastal hydrothermal springs from

the Gulf side of the Baja California peninsula,

Concepcion. (a) Fossil hot spring deposits and (b) modern hot spring


Mexico, and examine the role of microorganisms in

their precipitation.

2. Geological setting

The studied silica-carbonate stromatolitic deposits

and coastal hydrothermal springs are located at the

West shore of the Bahıa Concepcion Bay, on the

Gulf coast of the Baja California Peninsula (Fig. 1).

Bahıa Concepcion is one of the largest fault-bound

bays in Baja California, and its half-graben config-

uration developed during Late Miocene extension, in

relation with the Gulf of California opening

(Ledesma-Vazquez and Johnson, 2001). The evolu-

tion of Bahıa Concepcion during the Tertiary was

constrained by a subduction setting. Most of the

Bahıa Concepcion area is made up of the volcanic

series of the Comondu Group, which are related to

the Tertiary forearc magmatism (Ledesma-Vazquez

and Johnson, 2001). The Comondu volcanic rocks

unconformably cover Cretaceous granitoids. Accord-

ing to Umhoefer et al. (2001), the age of the

Comondu Group is restricted between upper Oligo-

cene and middle Miocene. Three different units form

the Comondu Group: (a) a lower unit containing

coarse detrital continental series with minor interlay-

ered volcanics, (b) a middle unit mainly composed

of andesite lava flows and (c) an upper unit

composed of andesite lava flows interlayered with

massive volcanic breccias (Umhoefer et al., 2001).

In the East shore of Bahıa Concepcion Bay, late

Miocene to early Pliocene marls of the Tirabuzon

Formation crop out (Moran, 1984). Fossiliferous

shallow water limestones, conglomerates and cherts

of the Infierno Formation, of late Pliocene age, crop

out in the southeastern corner of the bay (Ledesma-

Vazquez et al., 1997). The cherts of the Tirabuzon

Formation probably formed in a shallow environment,

due to the interaction between hydrothermal fluids

and mangrove carbonate muds (Ledesma-Vazquez et

al., 1997; Ledesma-Vazquez and Johnson, 2001).

Early Pleistocene basaltic flows and pyroclastic

deposits are the most recent magmatic events in the

area (Moran, 1984).

Plio–Quaternary tectonic activity caused uplift of

the bay area and generated extensive rocky shorelines

(Johnson and Ledesma-Vazquez, 2001).

3. Methodology

Samples of stromatolites were collected from

intertidal gasohydrothermal springs and in an adjacent

fossil deposit along a cliff. Thin polished sections

were prepared for examination with optical and

electronic microscope.

Unpolished samples were examined on a Jeol

JSM-35C Scanning Electron Microscope (SEM), on

secondary electron mode and operating at 20 kV, at

the Instituto de Geologıa of the Universidad Nacio-

nal Autonoma de Mexico (UNAM). These samples

received a thin gold coating before SEM examina-

tion. In addition, back-scattered electron images and

EDS qualitative analyses were obtained from thin

polished sections using a Jeol JXA-8900R electron

microprobe equipment at the Instituto de Geofısica

(UNAM).

XRD analyses were performed at the Instituto de

Geologıa of the UNAM, on a Philips PW130/96,

stepping 0.028 2h from 4.008 to 70.008, and using

copper X-radiation generated at 30 kV and 20 mA.

Whole-rock chemical analyses were performed in

selected stromatolite specimens. Major and minor

element analyses were obtained by X-ray fluorescence

at the Instituto de Geologıa (UNAM).

Carbon and oxygen isotope analyses of calcite

were carried out at the isotope laboratory of Bayeri-

sche Staatssammlung fqr Pal7ontologie und Geologie,

Mqnchen, Germany. All analyses were performed

using an automated Thermo/Finnigan bGasbench IIQonline preparation device coupled to a Thermo/

Finnigan Deltaplus isotope ratio mass spectrometer

using a continuous flow mode. CO2 was produced by

reaction of CaCO3 with phosphoric acid at 72 8C. Allmeasurements are reported as d-values in per mil (x)

relative to V-PDB. The precision and accuracy of

isotope values is estimated at F0.2x.

Fluid mixing modeling and determination of the

saturation state of the hydrothermal solutions with

respect to mineral species were performed using the

program bThe Geochemist’s WorkbenchQ (Bethke,

1996). Activity coefficients were calculated using

the Debye-Hqckel model, considering that the ionic

strength of the thermal fluids range between 0.5 and

0.7 approximately. Saturation indexes were calculated

for modeled cooling reaction paths beginning at the

thermal fluid temperature and ending at 25 8C. No


mineral precipitation was allowed during these calcu-

lations (closed system).

4. Modern coastal hydrothermal activity at Bahıa

Concepcion

Submarine diffused seepage and intertidal focused

hydrothermal venting take place on the West shore of

the Bahıa Concepcion Bay, along a 500 stretch of a

rocky shoreline (Fig. 1). Locally, the shoreline cliffs

are exposed and controlled by the El Requeson fault

zone, which delineates the western margin of Bahıa

Concepcion, and acts as a conduit for hydrothermal

fluids (Forrest et al., 2003).

The submarine hydrothermally active area is easily

recognized by gas bubbling, and occurs at depths

between 5 and 15 m. It consists in diffuse fluid seepage

(gas and water) through the unconsolidated sediments

(sand and volcanic boulders and cobbles deposited

from the rocky cliffs) that cover the seafloor. The

Fig. 2. Photographs of the main vent sites. (A) Intertidal hot springs a

approximately 0.5 m. (B) Shallow submarine (about 0.5 m depth) silica-car

cm. (C) Detail of stromatolitic growths around intertidal hot spring ou

hydrothermal fluid seepage and gas bubbling at 5 m depth. Scale bar is a

temperature measurements of the submarine diffuse

vents yield values of 50 8C at the sea bottom, and up to

87 8C within the sediments, where pH attains 6.2. No

submarine mounds or chimneys are developed. How-

ever, in the areas with most intense submarine venting,

iron oxyhydroxides covers the volcanic boulders

(Canet et al., submitted for publication) and orange-

yellow biofilms veneer the sediments.

On the other hand, focused intertidal hot springs are

a shallower expression of the gasohydrothermal

activity in the bay. A cluster of hot springs occurs

about 500 m SE from the main submarine diffuse ven-

ting area (Fig. 1). These springs are located only a few

meters offshore. Two main vent areas are recognizable

and are separated about 20 m from each other. Both

areas are located along a fissure that can be followed for

a few tens of meters on the seafloor. Temperature

reaches 62 8C in the intertidal hot springs and pH is

6.68. A decimeter-thick chalcedony-calcite-barite

banded vein protrudes above sea level between the

two vent areas, roughly parallel to the fissure that hosts

nd associated silica-carbonate stromatolitic deposits. Scale bar is

bonate deposits covering the seafloor. Scale bar is approximately 15

tflow channels. Scale bar is approximately 5 cm. (D) Submarine

pproximately 25 cm.


the hydrothermal vents. Two irregularly shaped patches

of hot spring deposits occur around the main intertidal

vent areas, each extending about 10 m2 (Fig. 2). These

deposits are partially subaerial during low tide.

4.1. Hydrothermal fluid chemistry

The hydrothermal activity in Bahıa Concepcion

consists of water and gas venting and seepage by

several intertidal hot springs and through the sedi-

ment-covered seafloor (Fig. 2). The composition of

the hydrothermal solution from submarine and inter-

tidal sites is shown in Table 1. The vent water is of

sodium-chloride type and has high concentrations of

Ca, Mn, Si, Ba, B, As, Hg, I, Fe, Li, HCO3 and Sr

(Prol-Ledesma1 et al., 2004). The liquid composition

of the vents and hot springs results of a mixing

between local seawater and a deep circulating

meteoric water (Prol-Ledesma1 et al., 2004). The

different degree of mixing with seawater causes the

compositional differences between submarine and

intertidal hot springs. Na/Li, Na–K–Ca and Si geo-

thermometers yield a reservoir temperature of approx-

imately 200 8C (Prol-Ledesma1 et al., 2004).

Mineral saturation state calculations allowed the

relation between the hydrothermal fluid composition

and the minerals that form the hot spring deposits of

Bahıa Concepcion to be evaluated. Fig. 3 presents the

results of these calculations for the hot spring water

and for a continuous mixing of hydrothermal and

marine water. The fluid from the intertidal hot springs

is supersaturated with respect to barite and silica

(quartz, chalcedony and amorphous silica) for the

complete temperature range (68 to 25 8C). Calcite

supersaturation takes place above about 53 8C (Fig.

Table 1

Water analyses (major ions) in Bahıa Concepcion

Sample Origin pH T (8C) Ca Mg K Na

BC1 Submarine venting 5.95 54–87 23.3 35.8 12.7 39



BC10 Intertidal hot spring 6.68 62 28.9 25.0 12.2 33

BC9 Seawater 7.75 ~25 9.8 58.3 12.48 48

Concentrations in mmolal. SI, calculated saturation index (log Q/K): Cal,

Calculated fugacity of CO2 ( fCO2) in atm (after Prol-Ledesma1 et al., 20

The detection limits (mmol/kg) are: Ca—0.02, Mg—0.002, K—0.01, Na—

3A). The mixture of marine and hydrothermal waters

is clearly subsaturated with respect to calcite and

supersaturated with respect to barite (Fig. 3B).

Vent gas is mainly composed of CO2 (44%) and N2

(54%), with minor amounts of CH4, Ar, He, H2 and

O2 (Forrest and Melwani, 2003). The mean d13C

value for CO2 is �6x (Forrest and Melwani, 2003).

5. Hot spring deposit occurrences and morphology

Both fossil and modern, finely laminated silica-

carbonate hot spring deposits of pale-yellow color are

present around the hydrothermally active areas on the

shoreline of Bahıa Concepcion (Fig. 1).

A 75 m long fossil bed of silica-carbonate

stromatolites crops out along a cliff next to the active

vent area. The morphology of the fossil hot spring

deposits is variable; they form small columnar,

bulbous and smooth undulating microstromatolites,

up to 10 cm thick (Fig. 4). The stromatolites occur

irregularly upon the volcanic bedrock and frequently

incorporate clastic fragments.

Silica and carbonate aggregates are presently

depositing in the surroundings of the intertidal hot

springs, about 150 m southeast from the above

mentioned fossil hot spring deposits. These modern

hot spring deposits are much less extensive than the

fossil beds that crop out along the cliffs and remain

submerged during the high tides. They usually form

crusts and coalescing rims over volcanic pebbles and

boulders (Fig. 2). Around the main hot spring outflow

conduits, the stromatolitic aggregates coat a structure-

less aggregate formed of allochthonous material

(detrital grains of plagioclase and volcanic rock

Cl SO4 HCO3 Si SI fCO2

Cal Brt Op

4.5 458.4 17.0 4.9 3.1 �0.61 0.43 �0.04 0.153

4.7 500.7 21.2 4.3 2.1 �0.76 0.52 �0.15 0.109

8.9 493.6 20.6 4.5 2.4 �0.76 0.53 �0.11 0.124

4.0 409.0 12.4 1.9 4.5 0.10 0.27 0.11 0.020

5.9 527.5 26.6 1.6 0.0 0.03 �0.42 �1.94 0.001

calcite; Brt, barite; Op, amorphous silica.

04).

0.04, Cl—0.03, SO4—0.03, HCO3—0.04 and Si—0.07.

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

0.5

25

2.0

1.5

1.0

0.5

0.0

-0.530 35 40 45 50 55 60 65 70

0.0

-0.5

-1.0

-1.5

-2.0

Barite

Calcite

62 58.3 54.6 50.9 47.2 43.5 39.8 36.1 32.4 28.7 25

Mixing fraction

Satu

ratio

n in

dex

(log

Q/K

)Sa

tura

tion

inde

x (l

og Q

/K)

Hydrothermal Seawater

B

A Intertidal hot springs

Quartz

Chalcedony

Barite

Amorphous silica

Calcite

Temperature (ºC)

Temperature (ºC)

Amorphous si ical

Fig. 3. Mineral saturation indexes (SI) for the fluids of the intertidal hot spring of Bahıa Concepcion. (A) Variation of SI with respect to

temperature for the hot spring thermal water. (B) Variation of SI for a continuous mixing of hydrothermal and marine waters. (Calculations were

performed with the program bThe Geochemist’s WorkbenchQ, Bethke, 1996).


fragments) cemented by silica with minor amounts of

calcite, barite and Mn oxides.

The modern stromatolitic aggregates attain 1 cm

thickness and show a fine internal lamination (Fig. 4).

They present bulbous to smooth undulating external

morphologies and columnar forms are absent.

Due to the low energy conditions prevalent in the

Bahıa Concepcion Bay, the presently forming stro-

matolites are not affected by high-energy waves.

6. Bulk mineralogy and chemical composition of

hot spring deposits

X-ray diffraction patterns of silica-carbonate stro-

matolites show a broad hump centered at about 3.9 2and extending from 168 to 328 2h, which corresponds

to noncrystalline opal-A (Herdianita et al., 2000;

Rodgers et al., 2004). Opal-A is the principal phase by

volume in both modern and fossil hot spring

Fig. 4. Hand samples of silica-carbonate stromatolites. (A) Columnar microstromatolites from fossil hot spring deposits. Scale bar=2.5 cm. (B)

Vertical section of columnar microstromatolites from fossil hot spring deposits showing fine laminations. (C) Bulbous microstromatolites from

moderns hot springs. Scale bar=2.5 cm. (D) Vertical section of bulbous microstromatolites from the modern hot springs. The silica-carbonate

microstromatolite is finely laminated. The base of the microstromatolite consists of volcanic pebble with sand-sized grains cemented by silica.


stromatolites of Bahıa Concepcion. The width at half

maximum intensity of the ~4 2 diffraction line (D82h) is about 7.28 and 7.48 (0.125 and 0.131 nm) in

fossil and modern stromatolites, respectively. This

parameter indicates the degree of structural order/

disorder in opaline silica and, in both cases, it is in

Table 2

Chemical analyses of silica-carbonate microstromatolites collected in Bah

Sample Location SiO2 TiO2 Al2O3 Fe2O3

BCP-3 Fossil hot spring deposit 6.65 0.01 0.55 0.18



BCT-4 Modern hot spring deposit 75.83 0.02 0.47 1.12

(Analyses in wt.%)

Sample Rb Sr Ba Y Zr Nb

BCP-3 4 1481 91 b0.7 b0.7 b0.7

BCP-4 22 403 264 1 5 b0.7

BCP-6 17 917 166 b0.7 5 b0.7

BCT-4 10 335 921 b0.7 2 b0.7

(Analyses in ppm, b below limit of detection)

LOI, loss on ignition.

agreement with non-altered opal-A (Herdianita et al.,

2000).

Calcite lines are also shown by bulk sample

diffraction analyses, being the most abundant crystal-

line phase in modern and fossil hot spring stromato-

lites. In addition, feldspar diffraction lines can be

ıa Concepcion hot springs

MnO MgO CaO Na2O K2O P2O5 LOI Total

0.02 0.48 50.84 0.35 0.08 0.11 40.16 99.44

0.24 0.81 10.08 1.63 0.48 0.09 15.27 99.15

0.03 0.47 25.92 0.83 0.39 0.03 24.18 99.88

0.23 0.42 8.97 0.80 0.22 0.01 11.53 99.64

V Cr Co Ni Cu Zn Th Pb

2 b2 2 b0.7 12 101 b3 b5

8 b2 5 b0.7 11 17 b3 5

18 b2 5 1 11 31 b3 b5

10 b2 3 b0.7 81 39 b3 22


identified, corresponding to detrital grains of plagio-

clase. Barite, although present in the silica-calcite

stromatolites, was not identified by X-ray diffraction.

Bulk rock chemical analyses of samples of fossil

and modern hot spring stromatolites are presented in

Table 2. All the samples show high concentration of

CaO (between 8.9 and 50.8 wt.%), accordingly with the

high content in calcite of these hot spring deposits.

Fig. 5. Thin section micrographs and scanning electron microscope images

plagioclase; Si, opaline silica. (A) Micrograph of fine-layered silica-carbon

light. Field width 2.6 mm. (B) Micrograph of fine laminated silica-carbonat

nichols. Field width 2.6 mm. (C) Porous, finely laminated silica and calcit

SEM-BSE image. (D) Thin calcite layers within opaline silica. Fossil hot

upon an aggregate of detrital grains cemented by opaline silica and barite.

crystals coated by opal-A. Fossil hot spring deposit. SEM-BSE image. (G

Modern hot spring deposit. SEM-BSE image. (H) Spore-like body (right ar

calcite. Modern hot spring deposit. SEM-BSE image.

These CaO contents in the hot spring deposits of Bahıa

Concepcion are higher than in the calcite bearing silica

sinters of New Zealand (Campbell et al., 2002).

Most of the analyzed samples show significant

enrichment in Ba (up to 921 ppm) and the highest Ba

contents correspond to the samples with greater SiO2

concentrations. These high values agree with the

occurrence of barite crystals within the stromatolites.

of Bahıa Concepcion hot spring deposits. Ba, barite; Cc, calcite; Pl,

ate stromatolites from intertidal modern hot springs. Plane polarized

e aggregates replaced by coarse calcite. Plane polarized light, crossed

e aggregate with barite and detrital grains. Fossil hot spring deposit.

spring deposit. SEM-BSE image. (E) Silica-carbonate stromatolite

Modern hot spring deposit. SEM-BSE image. (F) Subhedral calcite

) Opaline silica forming highly porous spongy filament networks.

row) and possible coccoid microbe remains (left arrow) embedded in


Likewise, Mn is enriched (up to 0.23 wt.%) in the

samples with higher silica contents.

7. Microscopic description

The petrography and electron microscope obser-

vations of fossil and modern hot spring stromato-

Fig. 6. Scanning electron microscope images on secondary electron mode o

Calcite subhedral crystal aggregate. (B) Radial aggregates of calcite upon o

microspheres. (D) Pennate diatoms. (E) Opal-A microspheres coalesced i

microcrystalline aggregates probably of Fe oxyhydroxides.

lites from Bahıa Concepcion have not shown

significant differences on the minerals and textures

between them (Figs. 5 and 6). In both cases, the

stromatolites consist of stacked undulating fine

layers of opaline silica (between 5 and 10 Amthick), with high porosity and interlayered discon-

tinuous calcite horizons (Fig. 5). Barite is present in

minor amounts, and detrital bind grains and micro-

f the Bahıa Concepcion hot spring silica-carbonate stromatolites. (A)

pal-A microspheres. (C) Silica discrete crusts cemented by coalesced

n irregular clusters and chains. (F) Opal-A microspheres coated by

Table 3

Carbon and oxygen stable isotope compositions of calcite

Sample Site description d13C(V-PDB) d18O(V-PDB)

BCP-3a Fossil hot spring deposits 7.2 �3.7

BCP-3b 6.4 �2.9

BCP-7-a 4.6 �3.3

BCP-7-b 9.3 �2.6

BCT-4-a Modern hot spring deposits 5.1 �10.0

BCT-4-b 7.7 �5.1

BCT-4-c 5.3 �7.1

BCT-5-a 6.8 �7.6

BCT-5-c 3.0 �9.1

BCT-5-b 7.3 �6.4

BR-2 Aragonite marine cement 1.0 �4.2


fossils are common within the silica and calcite

laminae.

Opal-A silica occurs mainly as distinct micro-

spheres, up to 300 nm in diameter, which coalesce and

form porous aggregates of irregular clusters and

chains (Fig. 6B, C, E and F). In some cases, opal-A

microspheres are coated by microcrystalline aggre-

gates, probably of Fe oxyhydroxides (Fig. 6F).

Locally, the silica chains form highly porous spongy

filament networks (Fig. 5G). Silica also forms discrete

regular crusts, of about 500 nm in thickness, parallel

to the stromatolite lamination. These crusts are

cemented among them by coalesced microspheres

(Fig. 6C).

Calcite is the most common precipitate after

opal-A, and it is deposited in discontinuous layers

within opal laminae, mostly forming subhedral

bladed to equant crystals up to few tens of microns

in size (Figs. 5B, C and E and 6A). Calcite also

forms thin layers (of few microns in thickness)

within silica aggregates (Fig. 5D). Calcite crystals

are generally coated by silica aggregates (Fig. 5E).

Locally, calcite develops coarse granular sparitic

textures (grain size up to 500 Am), filling voids of

the stromatolitic aggregates as a late cementation

(Fig. 5B).

Minor amounts of barite occur in the fossil and

modern stromatolites and, in addition, in the struc-

tureless opal-cemented aggregates that underlies the

stromatolites around the modern hydrothermal dis-

charge channels (Fig. 5C and E). In the silica-

carbonate stromatolites, barite forms short tabular

aggregates (up to 500 Am in length) and scattered

radial and bow tie clusters of tabular euhedral

crystals.

Abundant detrital grains occur within the silica and

carbonate layers. These trapped grains are mainly

sand-sized, angular to sub-angular, plagioclase and

volcanic rock fragments. In addition, some chalced-

ony fragments occur within the fossil silica-carbonate

stromatolites.

The hot spring stromatolites of Bahıa Concep-

cion show preserved and fossilized microorganisms

and microbial features. Pennate diatoms, up to 30

Am long and 8 Am wide, are scattered throughout

the hot spring stromatolites, and are especially

abundant in porous silica aggregates (Fig. 6D). In

addition, some spore-like bodies with possible

internal septum have been found within the stroma-

tolites, and small ellipsoidal structures embedded in

calcite and silica, which can be attributed to coccoid

microbes (Fig. 5H).

8. C and O stable isotopes

Eleven carbonate-rich bulk samples were selected

for stable carbon and oxygen isotopic analyses. Four

samples correspond to the fossil hot spring stroma-

tolites and six samples to the modern hot spring

stromatolites. In addition, one sample of marine

aragonite cement was analyzed as a reference. This

sample corresponds to a heterometric, polimictic

breccia cemented by aragonite, which was collected

in the intertidal zone next to the submarine diffuse

vent area.

Stable carbon and oxygen isotopic analyses of

calcite are summarized in Table 3. All the analyzed

samples are enriched in 13C with respect to normal

marine carbonates, with d13C values up to +9.3x.

The d 8O values range between �2.6x and

�10.0x. The samples more depleted in 18O

correspond to modern stromatolites, whereas samples

of fossil hot spring stromatolites show a narrow

range of d18O variation, with values between �2.6xand �3.7x.

In a d18O vs. d13C plot, fossil and modern

stromatolite analyses define two different linear trends

(Fig. 7). Fossil stromatolite samples fall along a near-

horizontal regression trendline. In contrast, modern

stromatolite analyses define a trendline with higher

35

30

25

20

15

10

5

0

-5-7 -5 -3 -1 1 3 5 7 9 11

Seawater

Hot spring water

Aragonite marine cement

Modern hot spring

Fossil hot spring

∆ at

62º

C

CO

2

∆ at

62º

C

∆ at

25º

C

∆ at

25º

C

5

0

-5

-10

-15

-20

-25

-30

δ13C(PDB)

δ18O

(SM

OW

)

δ18O

(PD

B)

Fig. 7. Plot of carbon and oxygen stable isotope composition of calcite of the hot spring deposits. D represents calcite-water equilibrium

fractionations according to O’Neil et al. (1969).


slope, because of the positive correlation between

d18O and d13C.

9. Discussion

Atypical silica-carbonate deposits are presently

forming in a coastal environment, around the intertidal

hot springs of Bahıa Concepcion. However, these

deposits do not form in the submarine diffuse

gasohydrothermal vents (at 5–15 m depth) of the same

area. In addition, a fossil equivalent of these deposits is

found onshore, close to the hydrothermally active area.

The subaerial exposure of that fossil deposit can be

attributed to the Plio–Quaternary tectonic uplift of the

bay area (Johnson and Ledesma-Vazquez, 2001).

Both modern and fossil silica-carbonate deposits

can be considered intertidal stromatolitic sinters. The

term stromatolite is applied here according to the

definition of Riding (1991) bmicroscopically lami-

nated deposits that can be built by a variety of

microbesQ, in the same way that has been applied

before for some hot spring sinter deposits by several

authors (e.g., Walter and Des Marais, 1993; Jones et

al., 2000a; Campbell et al., 2002).

9.1. Mineralogy and processes of formation of the hot

spring deposits

Although silica (sinters) and calcite (tufa, traver-

tine) deposits usually form in geothermal systems

elsewhere, silica-carbonate deposits are uncommon

(Jones and Renaut, 1996; Jones et al., 2000b; Camp-

bell et al., 2002). In hot spring deposits, the

mineralogy is mainly controlled by thermal water

chemistry (e.g., Jones et al., 2000a; Campbell et al.,

2002). Thus, silica is deposited from near-neutral and

alkaline pH chloride-rich and seldom from acid sulfate

thermal waters (e.g., Jones et al., 2000a; Rodgers et

al., 2004). According to Fournier and Rowe (1966),

deep reservoir temperatures above 175 8C are

necessary to form extensive silica deposits in the hot

spring environments.

In the hot springs of Bahıa Concepcion, the

thermal fluid (gas and water) chemistry allows silica,

calcite and barite precipitation. The deep reservoir


temperatures calculated by Prol-Ledesma1 et al.

(2004) are sufficiently high to produce hot spring

silica deposits. The saturation state calculations show

that the intertidal hot spring water is supersaturated

with respect to barite and silica (quartz, chalcedony

and amorphous silica) for a range of temperatures

between 68 and 25 8C (Fig. 3A). Both temperature

and fluid composition are responsible for mineral

saturation. Silica solubility increases with rising

temperature and pH; thus, silica supersaturation in

rising hydrothermal solutions is easily achieved by

cooling before mixing with seawater (Renaut et al.,

2002). Likewise, Guidry and Chafetz (2002) proposed

that cooling is the predominant process in silica

precipitation in the hot spring sinters of Yellowstone

(Wyoming). Theoretical calculations for a continuous

mixing of hydrothermal and marine water show that

amorphous silica saturation index decreases with

increasing seawater dilution (Fig. 3B). This fact

agrees with the absence of silica deposits in the

subtidal vents, where extensive mixing with seawater

prevents its precipitation.

Noncrystalline opal-A, deposited mainly as

microspheres, is the only silica phase encountered

in the modern and fossil hot spring deposits of

Bahıa Concepcion. According to Fournier (1985),

the silica phase that is deposited depends on the

degree of supersaturation of the solutions. Silica

microspheres grow from highly supersaturated sol-

utions, in which homogeneous nucleation and

colloidal growth takes place (Fournier, 1985; Renaut

et al., 2002). So, the precipitation of opal-A micro-

spheres agrees with the calculation of saturation state

for amorphous silica. Noncrystalline opal-A is the

initial silica product that forms in most hot springs

when the hydrothermal solutions become super-

saturated (Rodgers et al., 2004). After opal-A

deposition, several maturation stepwise transforma-

tions take place: opal-A changes to opal-CTFopal-C

and finally yields microcrystalline quartz (chalcedo-

ny)Fmoganite (Herdianita et al., 2000; Rodgers et

al., 2004). The alteration of opal-A to opal-C and its

subsequent transformation to chalcedony take thou-

sands of years and at least 50,000 years, respectively

(Herdianita et al., 2000; Rodgers et al., 2004).

Therefore, considering that opal-A is the only

identified silica phase of the studied fossil hot

spring deposit, it must be very recent, in spite of

the existence of hydrothermally derived cherts

(Ledesma-Vazquez et al., 1997) in the vicinity of

the vents that suggest that the present coastal

hydrothermal activity has been long-lived.

On the other hand, calcium carbonate deposits on

hot springs form from neutral alkali thermal waters

with high Ca2+ and CO32� activities (Jones et al.,

2000b) and, in most cases, carbonate supersaturation

is attained by CO2 degassing (e.g., Friedman, 1970;

Julia, 1983; Arp et al., 1999) or by heating of ambient

seawater (Barrat et al., 2000). The slightly low pH

values measured in vent fluids (between 5.95 and

6.68) are near neutral at vent temperatures (Kw at 60

8C is 13.1076, Harned and Owen, 1958). Only for

temperatures above 53 8C, the thermal water of Bahıa

Concepcion is slightly supersaturated in calcite and

even the saturation indexes are too low to explain

calcite precipitation (Fig. 3A). Furthermore, the

mixture of marine and hydrothermal water is clearly

subsaturated with respect to calcite (Fig. 3B). Thus,

calcite precipitation should be mainly triggered by

CO2 degassing. In many travertine systems, the loss of

CO2 by degassing is the main cause of calcite

supersaturation (Chafetz et al., 1991). CO2 degassing

is an ongoing process as the collected gas samples

from the active vents have a high CO2 concentration

(Forrest and Melwani, 2003). It produces a drop of

CO2 fugacity and increases the saturation index of the

waters with respect to calcite in the intertidal hot

springs (Table 1).

The Bahıa Concepcion hot springs yield a rare

example of authigenic precipitation of barite on

stromatolitic deposits. Barite precipitates when Ba2+-

rich hydrothermal water mixes with cold SO42�-rich

seawater. Therefore, as evidenced by theoretical

calculations, mixing of hydrothermal and marine

waters increases de saturation index of water with

respect to barite, causing its precipitation (Fig. 3B).

Microbial remains and microfossils identified in

the studied silica-carbonate stromatolitic deposits

evidence the biological activity around the hot

springs, and comprise diatoms and possibly, coccoids

and spores. Furthermore, the chains and filaments that

built up the porous spongy silica networks could be

attributed to filamentous microorganisms (cyanobac-

teria or fungi) that have been silicified. Diatoms are

common in hot spring waters elsewhere (e.g., Jones et

al., 2000a; Renaut et al., 2002; Rodgers et al., 2004;


Guidry and Chafetz, 2003b); however, thermal envi-

ronment biota is dominated by fungi at acidic pH, and

by bacteria at near-neutral pH (e.g., Jones et al.,

2000a). Microbial mats can mediate silica precipita-

tion serving as templates for fixing and nucleation of

silica. This way of microbial mediation in silica

precipitation has been suggested in several hot spring

deposits with filamentous opaline textures (e.g., Jones

et al., 2000a; Konhauser et al., 2001). In contrast, the

lack of microbial fabrics on calcite, as calcitic shrubs

and clumps (Chafetz and Folk, 1984; Chafetz and

Guidry, 1999), fibrous crystals (Julia, 1983) and

porous aggregates (Riding, 1991), suggests that

CaCO3 precipitation in Bahıa Concepcion hot springs

is an inorganic-physicochemical process. In the same

way, for the Ngatamariki silica-carbonate hot spring

deposits, New Zealand, Campbell et al. (2002)

suggest a microbially mediated deposition process

for silica and an abiogenic process for calcite.

In the vicinity of the main hot spring outflow

conduits, a structureless aggregate of silica, calcite

and barite, which cements detrital fragments, under-

lies the stromatolites (Fig. 5E). Similarly, Renaut et al.

(2002) reported laminated silica crusts overlying

massive silica cemented detrital agglomerates in the

sublacustrine hot springs of Lake Baringo, Kenya. In

Bahıa Concepcion, the abiogenic deposition of silica,

calcite and barite forming structureless agglomerates

around the hot springs indicate that those minerals can

precipitate without microbial mediation, as predicted

by equilibrium thermodynamic calculations. This

implies that, where microorganisms are present,

although they do not actively induce mineral precip-

itation they are responsible of the finely laminated

fabrics of the deposit.

9.2. Carbon and oxygen isotopes

All the analyzed carbonates from the silica-

carbonate hot spring deposits are unusually enriched

in 13C, with d13C values up to +9.3x V-PDB. These

values indicate high 13C contents in the dissolved

inorganic carbon, considering the small fractionation

(about 1x at low temperatures) between HCO3� and

calcite (Romanek et al., 1992).

High d13C carbonates have been reported mainly

in lakes with high evaporation rates (Stiller et al.,

1985) and in hot spring-related carbonates (Valero-

Garces et al., 1999; Fouke et al., 2000; Melezhik and

Fallick, 2001). The precipitation of hot spring

carbonates is usually triggered by degassing of CO2

(e.g., Friedman, 1970; Arp et al., 1999; Chafetz et al.,

1991). Through CO2 degassing, a kinetic fractionation

process yield a strong 13C enrichment of dissolved

inorganic carbon and, therefore, of carbonate precip-

itates (Michaelis et al., 1985; Chafetz et al., 1991).

This non-equilibrium process can explain the 13C

enrichment in calcite of both modern and fossil silica-

carbonate hot spring deposits of Bahıa Concepcion. In

the same way, this process has been proposed by

Valero-Garces et al. (1999) to explain extreme 13C

enrichments in authigenic carbonates from Andean

lakes with geothermal activity.

The low d18O values of calcite from the modern

hot springs are due to the presence of a meteorically

derived hydrothermal fluid that is involved in calcite

precipitation. The range of d18O variation indicates

that calcite precipitates from a mixture of seawater

(cold, with d18O close to 0x V-SMOW) and hydro-

thermal fluid (62 8C, �3.11x V-SMOW, Prol-

Ledesma1 et al., 2004) in variable proportions. The

lowest d18O values (�10.0x V-PDB) can be

achieved by precipitation in isotopic equilibrium from

the hydrothermal fluid at temperatures near 60 8C,according to the fractionations established by O’Neil

et al. (1969) (Fig. 7). Otherwise, the highest d18O

values imply lower temperatures and a major seawater

component on calcite deposition. d18O and d13C

roughly define a positive correlation, so that the

analyses less depleted in 18O are the most enriched in13C (Fig. 7). This fact suggests an inverse temperature

dependence of the process of 13C/12C fractionation by

CO2 degassing. Kim and O’Neil (1997) observed that

the 18O/16O fractionation between calcite and water is

higher at high HCO3� concentration. In the modern

intertidal hot springs of Bahıa Concepcion, where the

hydrothermal fluid is enriched in HCO3� with respect

to seawater, this phenomenon could explain the poor

correlation between d18O and d13C.

In contrast, d18O values of calcite from the fossil

hot spring deposits show a very limited variation

(�2.6x to �3.7x V-PDB). The d18O values are

slightly higher than the values from calcite crystals of

the modern hot springs and are not correlated with

d13C variations. Taking into account that d18O on

calcite depends on the temperature and the isotope


composition of the water, the oxygen isotope compo-

sition of fossil hot spring calcite requires an 18O-

enriched water component and/or lower temperatures

of crystallization. The narrow range of variation of

d18O values suggests a limited process of mixing of

fluids during calcite precipitation. However, the

thermal fluid itself is a mixture of seawater and deep

circulating groundwater (Prol-Ledesma1 et al., 2004).

Thus, the high oxygen isotope values of the fluid can

be produced by a greater seawater component. More-

over, the seawater composition could have changed

throughout time and is subjected to local variations, so

that high evaporation rates and restricted water

exchange can produce heavier d18O in bay waters.

Dettman et al. (2004) measured d18O values up to

7.6x V-SMOW in tide pools in the northern Gulf of

California.

Other possible explanation of the O isotopic

composition observed in the fossil hot spring deposits

is to consider that the original d18O was not preserved

due to exchange reactions with seawater after cessa-

tion of the hot spring activity. However, at low

temperatures, rates of volume diffusion are very small;

therefore, simple isotopic exchange with fluids is

sluggish (O’Neil, 1987). Moreover, there are no

evidences of polymorphic changes (e.g., aragonite-

calcite) that could explain an isotopic exchange by

recrystallization.

10. Conclusions

The intertidal hot springs of Bahıa Concepcion

provide a rare example of silica-carbonate stromato-

litic sinter. In addition, a silica-carbonate deposit found

onshore can be considered the fossil equivalent of the

modern hot spring deposits. Moreover, a structureless

abiotic aggregate of silica, calcite and barite underlies

the stromatolites around the main hot springs.

Microbial remains and microfossils are abundant in

both modern and fossil silica-carbonate stromatolitic

deposits of Bahıa Concepcion, and provide evidence

that biological activity takes place around the hot

springs. The biological activity has an important role

in the development of the laminated fabrics and the

textures of the deposit.

Noncrystalline opal-A is the only phase of silica

present in the modern and fossil hot spring deposits

of Bahıa Concepcion. Opal-A is mainly deposited as

microspheres, suggesting that it precipitates from a

highly supersaturated solution. The silica supersatu-

ration state of the thermal fluid must be achieved by

cooling. Opal-A is also the only silica phase in the

fossil hot spring deposit, so that it must be very

recent (as maximum few thousands of years), as it

has not yet recrystallized to more stable silica

polymorphs.

In spite that the physicochemical conditions of the

hot springs allow a pure inorganic precipitation of

silica, microbes could mediate silica deposition serv-

ing as templates for fixing and nucleation of silica.

Calcite is the most abundant crystalline phase in

the hot spring deposits. The calculation of saturation

state shows that the mixed hydrothermal and marine

water is subsaturated in calcite, thus, calcite precip-

itation would be related to a loss of CO2 by degassing.

Calcite crystals are unusually enriched in 13C, with

d13C values up to +9.3x PDB. The 13C enrichment is

attributable to a CO2 degassing process, which yields

calcite supersaturation and triggers a kinetic fractio-

nation between CO2 and dissolved inorganic carbon.

The range of d18O values of calcite is in agreement

with precipitation from a mixture of seawater and

meteorically derived hydrothermal fluid. Unlike opal,

the lack of biological fabrics on calcite suggests that

its precipitation is an inorganic-physicochemical

process.

Acknowledgements

Funding was provided by the CONACyT projects

I39170-T and 32510-T, and PAPIIT IN-107003. The

SEM-EDS analyses were done in the Instituto de

Geologıa and in the Instituto de Geofısica of the

Universidad Nacional Autonoma de Mexico. We

thank M. Reyes Salas for her assistance during the

SEM analyses. X-ray diffraction and fluorescence

analyses were carried out in the Instituto de Geologıa

(UNAM). We acknowledge the help of U. Struck with

isotope analyses. We thank A. Camprubı for the

photographs. We thank D.I. Norman and J. Tritlla for

their explanations that improved the manuscript. The

authors thank M.A. Torres Vera, M.J. Forrest and J.

Ledesma Vazquez for their help during the collection

of the samples.


References

Arp G, Thiel V, Reimer A, Michaelis W, Reitner J. Biofilm

exopolymers control microbialite formation at thermal springs

discharging into alkaline Pyramid Lake, Nevada, USA. Sedi-

ment Geol 1999;126:159–76.

Barrat JA, Boulegue J, Tiercelin JJ, Lesourd M. Strontium isotopes

and rare-earth element geochemistry of hydrothermal carbonate

deposits from Lake Tanganyika, East Africa. Geochim Cosmo-

chim Acta 2000;64:287–98.

Bethke CM. Geochemical reaction modeling. Concepts and

applications. New York, USA7 Oxford University Press;

1996.

Campbell KA, Rodgers KA, Brotheridge JMA, Browne PRL. An

unusual modern silica-carbonate sinter from Pavlova spring,

Ngatamariki, New Zealand. Sedimentology 2002;49:835–54.

Canet C, Prol-Ledesma RM, Melgarejo JC, Reyes A. Methane-

related carbonates formed at submarine hydrothermal springs: a

new setting for microbially-derived carbonates? Mar Geol

2003;199:245–61.

Canet C, Prol-Ledesma RM, Rubio-Ramos MA, Proenza J,

Forrest MJ, Torres-Vera MA. Characteristics of Mn–Ba–Hg

mineralization at shallow hydrothermal vents in Bahıa

Concepcion, Baja California Sur, Mexico. Chem Geol 2004

[submitted for publication].

Chafetz HS, Folk RL. Travertines: depositional morphology and the

bacterially constructed constituents. J Sediment Petrol 1984;54:

289–316.

Chafetz HS, Guidry SA. Bacterial shrubs, crystal shrubs, and ray-

crystal crusts: bacterially induced vs abiotic mineral precipita-

tion. Sediment Geol 1999;126:57–74.

Chafetz HS, Rush PF, Utech NM. Microenvironmental controls on

mineralogy and habit of CaCO3 precipitates: an example from an

active travertine system. Sedimentology 1991;38:107–26.

Dettman DL, Flessa KW, Roopnarine PD, Schfne BR, Goodwin

DH. The use of oxygen isotope variation in shells of estuarine

mollusks as a quantitative record of seasonal and annual

Colorado River discharge. Geochim Cosmochim Acta 2004;

68:1253–63.

Folk RL, Chafetz HS, Tiezzi PA. Bizarre forms of depositional and

diagenetic calcite in hot-spring travertines, Central Italy. In:

Schneidermann N, Harris P, editors. Carbonate cements. Society

of economic paleontologists and mineralogists special publica-

tion, vol. 36; 1985, p. 349–69.

Forrest MJ, Melwani A. Ecological consequences of shallow-water

hydrothermal venting along the El Requeson Fault Zone, Bahıa

Concepcion, BCS, Mexico. GSA general meeting abstracts with

programs, Seattle, Washington, USA; 2003a, p. 236-10.

Forrest MJ, Greene HG, Ledesma-Vazquez J, Prol-Ledesma RM.

Present-day shallow-water hydrothermal venting along the El

Requeson fault zone provides possible analog for formation of

Pliocene-age chert deposits in Bahıa Concepcion, BCS, Mexico.

GSA cordilleran section abstracts with programs, Puerto

Vallarta, Jalisco, Mexico; 2003b, p. 35.

Fouke BW, Farmer JD, Des Marais DJ, Pratt L, Sturchio NC, Burns

PC, et al. Depositional facies and aqueous-solid geochemistry of

travertine-depositing hot springs (Angel Terrace, Mammoth Hot

Springs, Yellowstone National Park, USA). J Sediment Res

2000;70:565–85.

Fournier RO. The behavior of silica in hydrothermal solutions. In:

Berger BR, Bethke PM, editors. Geology and geochemistry of

epithermal systems. Rev econ geol, vol. 2. Littleton (CO, USA)7

Society of Economic Geologists; 1985. p. 45–61.

Fournier RO, Rowe JJ. Estimation of underground temperatures

from the silica content of water from hot springs and wet-steam

wells. Am J Sci 1966;264:685–97.

Friedman I. Some investigations of the deposition of travertine from

hot springs: I. The isotopic chemistry of a travertine-depositing

spring. Geochim Cosmochim Acta 1970;34:1303–15.

Guidry SA, Chafetz HS. Factors governing subaqueous siliceous

sinter precipitation: examples from Yellowstone National Park,

USA. Sedimentology 2002;49:1253–67.

Guidry SA, Chafetz HS. Anatomy of siliceous hot springs:

examples from Yellowstone National Park, Wyoming, USA.

Sediment Geol 2003a;157:71–106.

Guidry SA, Chafetz HS. Depositional facies and diagenetic

alteration in a relict siliceous hot spring accumulation: examples

from Yellowstone National Park, USA. J Sediment Res 2003b;

73:806–23.

Guidry SA, Chafetz HS. Siliceous shrubs in hot springs from

Yellowstone National Park, Wyoming, USA. Can J Earth Sci

2003c;40:1571–83.

Halbach M, Halbach P, Lqders V. Sulfide-impregnated and pure

silica precipitates of hydrothermal origin from the Central Indian

Ocean. Chem Geol 2002;182:357–75.

Harned HS, Owen BB. The physical chemistry of electrolytic

solutions. 3rd ed. New York, USA7 Chapman and Hall; 1958.

Herdianita NR, Rogers KA, Browne PRL. Routine instrumental

procedures to characterize the mineralogy of modern and

ancient silica sinters. Geothermics 2000;29:65–81.

Johnson ME, Ledesma-Vazquez J. Pliocene–Pleistocene rocky

shorelines trace coastal development of Bahıa Concepcion, gulf

coast of Baja California Sur (Mexico). Palaeogeogr Palae-

oclimatol Palaeoecol 2001;166:65–88.

Jones B, Renaut RW. Influence of thermophilic bacteria on calcite

and silica precipitation in hot springs with water temperatures

above 90 8C: evidence from Kenya and New Zealand. Can J

Earth Sci 1996;33:72–83.

Jones B, Renaut RW, Rosen MR. Stromatolites forming in acidic

hot-spring waters, North Island, New Zealand. Palaios

2000a;15:450–75.

Jones B, Renaut RW, Rosen MR. Trigonal dendritic calcite crystals

forming from hot spring waters at Waikite, North Island, New

Zealand. J Sediment Res 2000b;70:586–603.

Julia R. Travertines. In: Scholle PA, Bebout DG, Moore CH,

editors. Carbonate depositional environments. Tulsa (OK,

USA)7 Am Assoc Pet Mineral; 1983. p. 212–65.

Kim ST, O’Neil JR. Equilibrium and non-equilibrium oxygen

isotope effects in synthetic carbonates. Geochim Cosmochim

Acta 1997;61:3461–76.

Konhauser KO, Phoenix VR, Bottrell SH, Adams DG, Head IM.

Microbial-silica interactions in Icelandic hot spring sinter:

possible analogues for some Precambrian siliceous stromato-

lites. Sedimentology 2001;48:415–33.


Konhauser KO, Jones B, Reysenbach AL, Renaut RW. Hot spring

sinters: keys to understanding Earth’s earliest life forms. Can J

Earth Sci 2003;40:1713–24.

Ledesma-Vazquez J, Johnson ME. Miocene–Pleistocene tectono-

sedimentary evolution of Bahıa Concepcion region, Baja

California Sur (Mexico). Sediment Geol 2001;144:83–96.

Ledesma-Vazquez J, Berry RW, Johnson ME, Gutierrez-Sanchez S.

El Mono chert: a shallow-water chert from the Pliocene Infierno

Formation, Baja California Sur, Mexico. Spec Pap-Geol Soc

Am 1997;318:73–81.

Melezhik VA, Fallick AE. Palaeoproterozoic travertines of volcanic

affiliation from a 13C-rich rift lake environment. Chem Geol

2001;173:293–312.

Michaelis JE, Usdowski E, Menschel G. Partitioning of 13C and 12C

on the degassing of CO2 and the precipitation of calcite:

Rayleigh-type fractionation and a kinetic model. Am J Sci 1985;

285:318–27.

Moran ZD. Geology of the Mexican Republic. Studies in geology,

vol. 39. Tulsa (OK, USA)7 American Association of Petroleum

Geologists; 1984.

Mountain BW, Benning LG, Boerema JA. Experimental studies on

New Zealand hot spring sinters: rates of growth and textural

development. Can J Earth Sci 2003;40:1643–67.

O’Neil JR. Preservation of H, C, and O isotopic ratios in the low

temperature environment. In: Kyser TK, editor. Stable isotope

geochemistry of low temperature fluids. Short course hand-

book of the mineralogical association of Canada, vol. 13.

p. 85–128.

O’Neil JR, Clayton RN, Mayeda TK. Oxygen isotope fractionation

in divalent metal carbonates. J Chem Phys 1969;51:5547–58.

Pedone VA, Dickson J. Minor-element variations in lacustrine tufa,

Miocene Barstow Formation, California. AGU Fall Meeting

Abstracts with Programs, San Francisco, California, USA,

p. V22B–1031.

Pentecost A. The formation of travertine shrubs: Mammoth Hot

Springs, Wyoming. Geol Mag 1990;127:159–68.

Prol-Ledesma RM, Canet C, Torres-Vera MA, Forrest MJ, Armienta

MA. Vent fluid chemistry in Bahıa Concepcion coastal

submarine hydrothermal system, Baja California Sur, Mexico.

J Volcanol Geotherm Res 2004;137:311–28.

Renaut RW, Jones B, Rosen MR. Primary silica oncoids from

Orakeikorako hot springs, North Island, New Zealand. Palaios

1996;11:446–58.

Renaut RW, Jones B, Tiercelin JJ, Tarits C. Sublacustrine

precipitation of hydrothermal silica in rift lakes: evidence from

Lake Baringo, central Kenya Rift Valley. Sediment Geol 2002;

148:235–57.

Riding R. Calcified cyanobacteria. In: Riding R, editor. Calcareous

Algae and Stromatolites. Berlin, Germany7 Springer Verlag;

1991. p. 55–87.

Rodgers KA, Browne PRL, Buddle TF, Cook KL, Greatrex RA,

Hampton WA, et al. Silica phases in sinters and residues

from geothermal fields of New Zealand. Earth-Sci Rev 2004;

66:1–61.

Romanek CS, Grossman EL, Morse JW. Carbon isotopic fractio-

nation in synthetic aragonite and calcite: effects of temperature

and precipitation rate. Geochim Cosmochim Acta 1992;56:

419–30.

Stetter KO, Fiala G, Huber G, Huber R, Segerer A. Hyper-

thermophilic microorganisms. FEMS Microbiol Rev 75:1990;

117–24.

Stiller M, Rounick JS, Shasha S. Extreme carbon-isotope enrich-

ments in evaporation brines. Nature 1985;316:434–5.

Umhoefer PJ, Dorsey RJ, Willsey S, Mayer L, Renne P.

Stratigraphy and geochronology of the Comondu Group near

Loreto, Baja California Sur, Mexico. Sediment Geol 2001;144:

125–47.

Valero-Garces BL, Delgado-Huertas A, Ratto N, Navas A. Large13C enrichment in primary carbonates from Andean Altiplano

lakes, northwest Argentina. Earth Planet Sci Lett 1999;171:

253–66.

Walter MR. Geyserites of Yellowstone National Park: an example of

abiogenic stromatolites. In: Walter MR, editor. Stromatolites.

Amsterdam, The Nederlands7 Elsevier; 1976. p. 87–112.

Walter MR, Des Marais DJ. Preservation of biological information

in thermal spring deposits: developing a strategy for the search

for fossil life on Mars. Icarus 1993;101:129–43.

Walter MR, Bauld J, Brock TD. Siliceous algal and bacterial

stromatolites in hot spring and geyser effluents of Yellowstone

National Park. Science 1972;178:402–5.

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