Lagoon microbialites on Isla Angel de la Guarda and associated peninsular shores, Gulf of California...

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Lagoon microbialites on Isla Angel de la Guarda and associated peninsular shores,Gulf of California (Mexico)

Markes E. Johnson a,!, Jorge Ledesma-Vázquez b, David H. Backus a, Maria R. González c

a Dept of Geosciences, Williams College, Williamstown, MA 01267, USAb Facultad de Ciencias Marinas, Area de Geología, Universidad Autónoma de Baja California, Apartado postal 453, Ensenada, CP 22800, Baja California, Mexicoc Facultad de Ciencias, Escuela de Biología, Universidad Autónoma de Baja California, Km. 107, Carretera Tij-Ens, Ensenada, CP 22860, Baja California, Mexico

a b s t r a c ta r t i c l e i n f o

Article history:Received 5 December 2010Received in revised form 5 September 2011Accepted 6 September 2011Available online 17 September 2011

Keywords:RecentQuaternaryPlioceneClosed lagoonsCyanobacteriaOligotrophic ecosystems

Examples of two closed lagoons with extensive growth of Recent microbialites showing variable surfacemorphology and internal structure are found on Isla Angel de la Guarda in the Gulf of California. Comparablelagoonal microbialites also occur ashore from Ensenada El Quemado on the adjacent peninsular mainland ofBaja California. The perimeters of all three lagoons feature crusted structures indicative of thromboliteswith a knobby surface morphology 2 cm to 3 cm in relief and internal clotting without any sign of laminations.Outward from this zone, thrombolitic construction thins to merge with a white calci!ed crust below which asoft substratum of dark organic material 4 cm to 6 cm in thickness is concealed. The substratum is laminatedand heavily mucilaginous, as observed along the edges of extensive shrinkage cracks in the overlying crust. Thethrombolitic crust is anchored to the shore, while the thinner crust and associated stromatolitic mats "oat onthe surface of the lagoons. Laboratory cultures of the dark organic material yielded the solitary cyanobacteriumChroococcidiopsis as the predominant taxon interspersed with !lamentous forms. In decreasing order ofabundance, other morphotypes present include Phormidium, Oscillatoria, Geitlerinema, Chroococus, andprobably Spirulina. The larger of the two island lagoons follows an east–west azimuth and covers 0.225 km2,while the smaller lagoon has a roughly north–south axis and covers only 0.023 km2. The salinity of water inthe smaller lagoonwasmeasured as148 ppt. Pliocene strata along the edge of the smallermodern lagoon includesiltstone bearing calci!ed platelets suggestive of a microbial origin. Dry lagoons abandoned during the laterQuaternary occur inland at higher elevations on the island, but retain no fossils except for sporadic whitecrusts cemented on cobbles around distinct margins. Raised Quaternary lagoons parallel to the big lagoonon Isla Angel de la Guarda are partly obscured by "ood damage, but still easily mapped from aerial photos.These features suggest that Isla Angel de la Guarda experienced Quaternary uplift similar in scale to manyother gulf islands onwhichmarine terraces are preserved. Closed lagoons around the Gulf of California representa stable oligotrophic ecosystem affected by extreme aridity and hypersalinity, punctuated episodically bythe injection of"oodwater from tropical storms. The taxonomic and geographic ranges ofmicrobial communitiesthroughout the larger region remain to be explored.

© 2011 Elsevier B.V. All rights reserved.

1. Introduction

Considered the oldest traces of life on Earth, stromatolites are sedi-mentary structures with laminations formed by microbial associationsthat !rst appeared in Archean time. Allwood et al. (2006) studied vari-ations in stromatolite shape and other features from the 3.43 billion-year-old Strelley Pool Chert of Western Australia and related themto facies that formed in rocky-shore and associated peritidal envi-ronments. During Proterozoic times, stromatolites formed some ofthe largest organic structures preserved on our planet as representedby ramp build-ups with an accumulated thickness of 300 m in the

MackenzieMountains of Canada (Batten et al., 2004). In the Phanerozoicrock record, thrombolites are a common variation on stromatolitesin which laminae are absent and the structure is clotted or blotchy inappearance (Riding, 2000). Burne and Moore (1987) introduced theterm microbialites for organosedimentary deposits formed from inter-action between benthicmicrobial communities and detrital or chemicalsediments, the latter quali!ed as the product of chemical changes asso-ciated with photosynthesis.

Stromatolites became known from their extensive fossil recordlong before sensational discoveries were made of living representa-tives, such as the loaf-shaped and club-shaped microbialites fromHamlin Pool in Shark Bay, Western Australia (Logan, 1961; Playfordand Cockbain, 1976). Microbialites have been discovered in fully ma-rine conditions, for example sub-tidal channels off Lee Stocking Islandin the Bahamas where strong bottom currents are active (Dravis,

Sedimentary Geology 263–264 (2012) 76–84

! Corresponding author.E-mail address: [email protected] (M.E. Johnson).

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1983; Feldmann and McKenzie, 1998) and cryptic reef settings suchas found in the Caribbean (Zankl, 1993), Tahiti (Montaggioni andCamoin, 1993), and Australia's Great Barrier Reef (Webb et al.,1998). Microbialites from both cryptic and open-benthic settings inthe semi-closed lagoon of the Tikehau atoll of French Polynesia aremeticulously documented (Sprachta et al., 2001; Abed et al., 2003a,2003b; Gautret et al., 2004). Microbial mounds from the MessinianStage (Upper Miocene) in western Sicily (Saint Martin et al., 1996)grew under open benthic conditions similar to those found living onthe "anks of pinnacle reefs in the Tikehau atoll (Sprachta et al., 2001).The terminal carbonate complex, however, is marked by a generalshift from Messinian coral reefs to oolite shoals to stromatolites. Thecomplex is widely recognized in the Upper Miocene throughout thewesternMediterranean (Esteban, 1979). Miocenemicrobialites formedthick laminar deposits under conditions excluding all other life alongthe open coast of Menorca when Mediterranean waters became hyper-saline during the Messinian crisis more than 6 million years ago(Johnson et al., 2011). Microbial communities in restricted coastalsettings appear to have thrived especially well under oligotrophicconditions that limit competition from plants and animals.

Previously documented examples of living microbial mats from theBaja California peninsula of Mexico are scarce and the region remainslargely unexplored with respect to living and fossil forms. Two localitieson the Paci!c coast and a single area in the southern Gulf of Californiahave yielded results (Fig. 1a). Laguna Figueroa (also known as LagunaMormona) near Colonia Vicente Guerrero on the Paci!c coast is the !rstplace where microbial mats were reported (Horodyski and VonderHaar, 1975; Horodyski, 1977; Margulis et al., 1980; Stolz, 1983). Theother is at Guerrero Negro, where the same kind of mat was subjectedto various biological and chemical analyses (Des Marais, 2003; Spearet al., 2003; Omoregie et al., 2004). The microbes in both localities aredominated in the lower supratidal by Lyngbya sp., which constructsmatted structures without surface topography. The upper supratidal ischaracterized by Calothrix sp., which formsmatswith a pustular surface.Unlike the calci!ed examples from Shark Bay and channels around LeeStocking Island, microbial mats from the Paci!c coast of Baja Californiashowno associatedmineralization and, thus, have very limited potentialfor preservation in the fossil record. De!ned as incipient thrombolites,pro-thrombolitic structures show grains of varied sizes embeddedwithin a !ne-grained micritic matrix. Associated with !lamentous

TijuanaMexicali

Ensenada

Loreto

La Paz

Los Mochis

1140W 1110

Pacific Ocean

270N

300

BAJA

BAJA

SUR

CALIFORNIA

ARIZONA

N

a

0 50 100

Km

CALIFORNIA

Gulf of C

alifornia

Isla Tiburon

Isla Angelde la Guarda

Isla San José

Bahía deLos Angeles

Colonia Vicente Guerrero

Guerrero Negro

saltpans

Known stromatolite sites (Pacific & Gulf coasts)

Sites with closed lagoons (Gulf coast)Ensenada El Quemado

SONORA

b

Km

0 1 2

Isla Estangue

South-east end of Isla Angel de la Guarda

small lagoon

big lagoon

29o 15’

29o 00’

113o 08’

N

25 m

50 m

Ballenas Canal

Fig. 1. Maps for the Gulf of California and Isla Angel de la Guarda: (a) overview showing the Gulf of California, (b) inset enlarged from box on the regional map to show lagoons onthe south-east end of Isla Angel de la Guarda. Note that starred localities with closed lagoons are listed by name in Table 1.

77M.E. Johnson et al. / Sedimentary Geology 263–264 (2012) 76–84


microbes, such as Microcoleus chtomoplasters and Oscillatoria limosa,pro-thrombolitic structures were described for the !rst time fromseveral localities around El Mogote, the huge sand bar protecting LaPaz Bay on the Gulf of California (Siqueiros-Beltrones, 2008).

The present contribution on lagoonal microbial structures was theunanticipated result of awide-ranging survey over the Gulf of Californiaregarding Pliocene to Recent coastal ecosystems that include coralbiostromes, coral reefs, rhodolith banks, molluscan-bivalve banks,and carbonate dunes (Johnson and Ledesma-Vázquez, 2009). Here,we announce the discovery of extensive thrombolites and microbialmats from closed lagoons in the northern Gulf of California on IslaAngel de la Guarda and at Ensenada El Quemado on the peninsularmainland near Bahía de Los Angeles. Similar closed lagoons occurscattered throughout the entire Gulf of California, which leads us tospeculate on the broader distribution of microbial mats and throm-bolites in a relatively stable oligotrophic system. A geomorphologicalobservation of parallel signi!cance from our study is that raised depres-sions adjacent to themodern lagoons but at progressively higher eleva-tions suggest a history of uplift for Isla Angel de la Guarda. The pattern istectonically consistent with raised marine terraces widely tracedthroughout the Gulf of California.

2. Geographical, climatic, and geological settings

Isla Angel de la Guarda is the second largest island in the Gulf ofCalifornia, having an area of 936 km2. It sits off Bahía de Los Angelesnear the Baja California peninsula (Fig. 1a), and is dominated byMioceneandesite rocks. Two closed lagoons are developed at the southeast endof the island (Fig. 1b). The larger of the two lagoons is elongate on aneast–west azimuth and covers an area of 0.225 km2. The big lagoon isfully separated from the open sea by a north-facing berm that is1.25 km long. The berm is composed of gravel and cobble-size rocksthat rise 4 m above mean sea level on a 50-m wide base. Duringour initial visit to the island (March 17–19, 2007), the water levelin the lagoon was well above mean sea level. An inner berm formsthe south boundary of the lagoon, rising to an elevation about7.25 m above mean sea level. A veneer of pebble-size rocks coversthe inner berm and demarcates a dry moat that runs for much ofthe same length on the landward side. The "oor of this linear featureis pan-like and sits at an elevation about 5.25 m above mean sealevel.

The smaller of the two lagoons on the southeast end of Angel de laGuarda has a roughly north–south axis that extends for 375 m, and islikewise fully isolated from the open sea by a berm composed of smallboulder-size rocks on the exposed seaward side and by gravel-sizerocks forming a beach on the inner side. The height and base of theouter berm are similar in dimensions to the berm on the big east–east lagoon. The width of the small lagoon is variable from 50 m to75 m across, giving it a crudely triangular shape with an area of0.023 km2. Unlike the big lagoon with its distinct inner berm, thesmall lagoon has a landward margin formed by high cliffs dominatedby siltstone and !ne-grained sandstone but with some conglomeratelayers that include Pliocene fossils. During our visits, the water levelwithin the small lagoonwas somewhat belowmean sea level. The salin-ity of water in the smaller lagoon was found to be 148 ppt as measuredalong the inside shore.

Ensenada El Quemado (Fig. 1a), where another small lagoon sitsbehind the beach, is located at an indentation on the east side of theSierra Las Animas isolated from Bahía de Los Angeles by major faultblocks of Cretaceous granodiorite, Miocene andesite, and Pliocene ba-salt. The area of the lagoon is 0.024 km2 and it is closed from the opensea by a 30-m wide berm composed of mixed pebbles and cobbles.

Regarding climate, Bahía de los Angeles borders the San FelipeSubregion of the Sonora Desert, one of the most arid parts of theBaja California peninsula receiving the highest annual percentage ofsunshine and an average annual rainfall amounting to only 5 cm

(Roberts, 1989). Tropical storms andhurricanes cross the Baja Californiapeninsula from the Paci!c Ocean and enter the Gulf of California onan episodic basis every few years, typically during the season fromlate August through October. About 10% of the hurricanes that hitthe Paci!c coast of Mexico from 1966 to 2004, followed a parabolic tra-jectory from the south bringing torrential rain to the upper Gulf ofCalifornia (Romero-Vadillo et al., 2007). Such storms are known locallyas chubascos, and they cause extensive erosion of streambeds that nor-mally remain dry for years at a time.

On a regular seasonal basis, strong winter winds affect the Bahíade los Angeles area during the winter season, typically fromNovemberto April. These are stimulated by the passage of high-pressure sys-tems across the American Southwest that send south-directed burstsof air down the axis of the Gulf of California on an intermittentbasis lasting from two to three days at a time. Surface winds pushsouth-directed sea swells over a considerable fetch on the Gulf ofCalifornia. These impact north-facing shores on islands and peninsularheadlands, causing coastal erosion. This is signi!cant in terms of thegeomorphology related to construction of closed lagoons in areas ofpersistent long-shore currents.

3. Observed variations in microbialite surface morphology

Differences in the morphological structures formed by microbeswere reviewed by Riding (2000), who distinguished between stro-matolites, thrombolites, and other fabrics. Technically, stromatolitesshow the build-up of sheeted laminae on "at or mounded surfaces.Microbial structures that accumulate on "at surfaces often makemats. Those that accrue under the in"uence of tides, as in Shark Bay(Logan, 1961; Playford and Cockbain, 1976), form loaf-shaped struc-tures that permit the"owofwater between adjacent structures. Colum-nar (or club-shaped) structures that include branching cones also arecommonly found in the Hamlin Pool of Shark Bay and represent theform taken by many Lower Paleozoic stromatolites (Burne and Moore,1987; Riding, 2000). Laminations typical of mat stromatolites includethin layers of trapped and bound sediments uncharacteristic of throm-bolites. In present-day settings, however, the internal structures thatdifferentiate fossil stromatolites and thrombolites are hard to differenti-ate without access to petrographic thin sections or polished slabs.

Both the large and small lagoons on Isla Angel de la Guarda, aswell as the lagoon at El Quemado, exhibit extensive microbial growthwith surface expression ranging between more knob-like and morestratiform examples as co-extensive lateral facies. A general modelfor the arrangement of microbial facies applies to all three of theclosed lagoons (Fig. 2). The type of microbialite with raised and knob-by surfaces (Fig. 3) occupies a ring about 2 m to 3 m wide around the

Outer berm

Inner berm

Beach

Open water

Lan

dwar

d

Sea

war

d

4 to 5 m above mean sea level

6 to 8 m above mean sea level

Thrombolites

Micritic crust with shrinkage cracks

Fig. 2. Generalized model for zonation of microbialites in closed lagoons on the penin-sular shores and islands in the Gulf of California (not to scale).

78 M.E. Johnson et al. / Sedimentary Geology 263–264 (2012) 76–84


outer circumference of the lagoons. During our visits to the three la-goons, this zonewas fully exposed to the air as a thick crust of carbonatematerial and it was !rmly attached to the ground. Maximum topo-graphic relief on the branching knobs is between 2 cm and 3 cm. Theeroded edges of these structures show no evidence of internal lamina-tions. This zone pinches-out against a low beach below the landwardinner berms, and abuts against the outer berms on the seaward marginof the lagoons where it tends to become narrow or even discontinuous.Many of the cobbles or small boulders in the lower 0.5 m of the outerberms also show encrustations of white calcareous patches that rangein size from 0.5 cm in diameter to the entire exposed surface of anygiven rock. This material is similar to the white crust on the adjacentknobby structures.

An inner ring of more clearly matted microbial material is devel-oped toward the center of the lagoons, but may not form a continuouszone around the full perimeter (Fig. 2). During our visits, about 2-mto 3-m width of this zone was exposed to the air and the mats were

incised by shrinkage polygons that varied from 40 cm to 75 cm in diam-eter. The exposed part of this zone also is coated by a crust of calcareousmaterial, less than 1 cm thick with an upper surface of low relief cov-ered by small bubbles or pustules. The shrinkage cracks reach downseveral centimeters, and are outlined in black (Fig. 4). Dark organic ma-terial in layers 4–5 cm thick may be peeled back from the edges of theshrinkage polygons. This material is heavily mucilaginous, but holds to-gether with internal consistency. It is devoid of any calcareous content,although pinnate diatoms provideminor siliceous content. Themicrobi-almats extend outward over the lagoonwaters, where they remainwetand show a surface change in color from bleached-white to pink. Thepink surface appears to represent the living surface where active calci!-cation may be taking place.

From the outer to inner microbial zones, the surface becomes in-creasingly "exible and yields to the weight of a person crossing to-wards the open water. The water meeting the outer edge of thecalcareous crust is turbid green, where the crust and underlying mats"oat on the surface. It is not possible to see clearly at any depth, butthe lagoon bottom drops off rapidly. The actual depth of thethree lagoons is unknown.

4. Biological analysis: methods and results

Microbialite-bearing lagoons were discovered in March 2007 dur-ing a routine excursion to study the geology of Isla Angel de la Guardaand the region south of Bahía de Los Angeles on the Baja Californiapeninsula. Because proper permits were not in force for collection ofbiological materials at that time, itwas necessary to return inNovember2007 expressly for the purpose of collecting live samples of microbialcommunities from the lagoons. Four core samples were retrievedusing a plastic tube with a diameter of 4 cm and a length of 15 cm.Two samples were retrieved from the smaller lagoon on the south endof Isla Angel de la Guarda and two samples were taken from the lagoonon the peninsular mainland at Ensenada El Quemado (see Fig. 1a).Extraction was facilitated by pressing the tube through the super!cialcrust into the softer laminated sediments underneath to a depth of 8–10 cm and capping the tube (Fig. 5). Separate samples were takenfrom the seaward and landward sides of both lagoons. Care was takento make certain that all extractions occurred in places slightly sub-merged by water.

A petrographic thin section was made from a sample of knobbycrust similar to those shown in Figs. 3 and 5, but collected from thelagoon at El Quemado. The thin section reveals a mixture of micro-clots and calcimicrobal crusts with an overall texture that is irregular

Fig. 3. Thrombolite with knobby surface expression from the small lagoon on Isla Angelde la Guarda (coin with diameter of 2.4 cm for scale).

Fig. 4. Microbialite mat cut by desiccation polygons from the big lagoon on Isla Angelde la Guarda.

Fig. 5. Core sample collected from the south end of the small lagoon on Isla Angel de laGuarda. The coring tube has a diameter of 4 cm and a length of 15 cm. Calci!ed knobbycrust above the dark mat is very similar to that shown in Fig. 3. The dark matter collect-ed from this site (see Fig. 1b) was cultured under laboratory conditions.



and clearly lacks distinct laminae (Fig. 6). Although a hint of septal al-veolar structure is present in the lower part of the image that may beconstrued to represent fungal activity associated with plant roots, thesample has an indisputable origin on the edge of a lagoon setting. Athrombolite structure is interpreted for these bleached crusts.

Progressive isolates were taken from the surface crust and the mi-crobial mat in each of the four samples in order to verify the occurrenceof dominant taxa. Unialgal cultures were grown under laboratory con-ditions at the School of Biology, Faculty of Sciences, UniversidadAutónoma de Baja California in Ensenada, using an F/2 mediumwith !ltered seawater. Mucilage, pinnate diatoms, and the cyanobac-teria constitute the key components in all four samples. The solitary cy-anobacterium Chroococcidiopsis is the predominant taxon interspersedwith !lamentous forms. This genus is distinguished by a unicellular,non-heterocyst differentiating organization. The single cells are coccoid,or globular in shape (Fig. 7). On average, each colony varies from 21 to42 !m in diameter, but individual cells are 2–4.7 !m in diameter. Cul-tured growth of Chroococcidiopsis was luxuriant, "oating free on thewater surface, as well as !xed to "ask walls and bottoms.

Listed in order of decreasing abundance, the othermicrobialmorpho-types found in association with Chroococcidioopsis include Phormidiumand Oscillatoria (no sheaths) and thin !laments of Geitlerinema,Chroococus, and probably Spirulina. Filaments tentatively identi!edas Phormidium, comprise the second most abundant microbe in thecultured samples (Fig. 8). The tendency of Phormidium to occur inmats of tangled !laments that can detach from a !rm substrate and

"oat to the surface in rivers and lakes (Gugger et al., 2005) !ts ourobservations of bog-like "oating mats on the closed lagoons on IslaAngel de la Guarda.

5. Physical model for a sustainable oligotrophic ecosystem

Development of lagoonal microbialites in the Gulf of California(Fig. 2) is a biological reality that relies on a physical framework fora sustainable oligotrophic ecosystem. Such a framework may be mod-eled on the geomorphology of the big lagoon on Isla Angel de la Guarda,asmapped from an aerial photo taken January 24, 2007 and augmentedby elevation values subsequently collected during !eldwork (Fig. 9).The broad base of the outer berm forms a strong, continuous barrieralong the full length of the lagoon. Measured at 4 m above mean sealevel, the height of the berm assures that normal seawater rarely over-tops from the seaward side. Evidence of scour marks left in loose gravelon the inside face of the berm, however, indicates that stormwaves co-incidental with high tide are capable of washing over the berm into thelagoon. Nowhere along the inside length of the beam is there evidenceof sustained overwash capable of eroding deep channels. The only otherpossible source of replenishment by normal seawater is by seepage atdepth below the 50-m wide foundation of the berm.

An intriguing feature captured by our aerial photo is a shallowcove, approximately 50 m wide and 85 m long that indents towardthe southeast corner of the big lagoon. The low grade of the exposedsurface that declines into the cove like a ramp suggests that the fea-ture is a functional spillway for stormwater that enters the big lagoon

Fig. 6. Petrographic thin sectionmade fromknobby surface crust collected on themarginsof the lagoon at Ensenada El Quemado (Fig. 1b). Scale bar represents 200 !m.

Fig. 7. Cell colonies of the solitary cyanobacterium Chroococcidiopsis cultured fromsamples collected on Isla Angel de la Guarda. The three colonies in this image havean average diameter of 30 !m.

Fig. 8. Cell colonies of the!lamentous cyanobacterium Phormidium cultured fromsamplescollected on Isla Angel de la Guarda. The !laments in this image have a width of about10 !m.

N

Overflowchannel

30 m

5 m

10 m

20 m

15 m

25 m

500 m

Big Lagoon

Outer bermsInner berms

Quaternary lagoons

outwash zones

+ 5.25 m

+ 4 m

+7.25 m 5 m

Fig. 9. Landscape around the big lagoon at the southeast end of Isla Angel de la Guarda,mapping the position of active berms and older berms that outline the parallel locationof Quaternary lagoons.



as run-off during hurricanes. The most recent major storm to encroachon Isla Angel de la GuardawasHurricaneMarty,which crossed the tip ofthe Baja California peninsula and traversed nearly the full length of theGulf of California between September 18 and 24, 2003. Although thestorm was downgraded from hurricane status long before it passedthe eastern and northern shores of Angle de la Guarda, it droppedenough rain in a single, 24-hour period to quickly saturate the thin,sandy soil and cause "ash "oods. The natural watershed adjacent tothe big lagoon is partly contained by the 25-m contour in topography,where slopes on the east and west sides of the basin steepen due tothe transition from regolith to basement andesite rocks. This transitionoccurs farther upslope to the south. The overall size of the drainage areaamounts to approximately 2 km2. Water running down slope towardthe big lagoon to the north is channeled through three main outwashzones that pass through or around raised linear structures composedof unconsolidated gravel. Patterns of stream "ow on the areal photoshow that"oodwater is prevented fromdirectly entering the big lagoonbywhatwe de!ne as the lagoon's inner berm. This feature forms awideand continuous barrierwith an average elevation of 7.25 m abovemeansea level. Water may be dammed by this feature for a brief time, butmakes a detour to enter the lagoon from the east and west ends. Beforethe water level in the lagoon reaches the top of the outer berm, it isrouted through the small cove at the southeast corner of the lagoon,which serves as an over"ow channel (Fig. 9).

Several years may elapse before the next hurricane passes nearbya closed lagoon (Romero-Vadillo et al., 2007). Thus, the injection ofrainwater will eventually return to a hyper-saline condition due tothe region's extreme aridity and the limited amount of normal seawaterseeping through the outer bern into the lagoon. The outer berm is underseasonal repair by the ongoing introduction of coarse clastics trans-ported by strong long-shore currents from the more northerly parts ofthe island to its southeastern terminus (Fig. 1a). Although no onehas witnessed the episodic "ooding of the big lagoon by fresh water,the deep imprint of shrinkage polygons on themicrobialite crust sur-rounding the lagoon (Fig. 4), suggests that such changes betweencomparatively rare "oods and long intervals of extreme aridity ac-companied by hypersalinity take place. Mineral nutrients mayenter the lagoon during "oods, but the oligotropic nature of the la-goons will be maintained by the physical dynamics of the lagoonwith its restraining berms and corrective over"ow channel. Terraincan be expected to vary fromone closed lagoon to another. For example,the smaller nearby lagoon on Angel de la Guarda is closely surroundedon three sides bymuch steeper slopes, whichmeans that the size of thewatershed draining to this lagoon is much smaller (Fig. 1b).

6. Mapping Quaternary paleolagoons

Expression of the inner berm stretched along the big lagoon(Fig. 9) is worthy of consideration as a geomorphological problem,by itself. The origin of the modern outer berm is clear enough throughthe mechanics of vigorous long-shore drift, but why should a lagoonbecome enclosed between an outer and an inner berm? The continuousraised structure that extends along the south margin of the big lagoonwith an average elevation of 7.25 m abovemean sea level is a distinctivefeature that can easily be viewed in its entirety from a higher elevationwith a north-facing perspective (Fig. 10). Our interpretation is that theinner berm of the modern lagoon also is the former outer berm of aprevious lagoon that developed in a now inland but parallel position.Dark patches of ground on the inner side of this extensive barrier sitat an elevation 5.25 m above mean sea level toward the eastern endof the trough, and are devoid of vegetation (Figs. 9 and 10). The formerQuaternary lagoon retains its own inner berm, which has beenbreached by "oodwaters in three places (Fig. 9). Trails of loose sedi-ments deposited over the low ground clearly show the various path-ways of "oodwater on its way to the big lagoon. These incursionshave partially destroyed the structural integrity of the former lagoon.

The possible existence of an older Quaternary lagoon is suggested byremnants of yet another berm segment located at the back of thebasin within the con!nes of the 5-m contour line (Fig. 9).

Essentially, a kilometer-long embayment at the southeast end ofIsla Angel de la Guarda was progressively enclosed by a series ofberms constructed by pebbles and cobbles eroded from shores farthernorth on the island and transported by storm-driven long-shore drift.Uplift of the lagoons proceeded apace with tectonic forces related tothe ongoing development of the Gulf of California. So far as weknow, this kind of geomorphological relationship has not been previ-ously recognized in the Gulf of California. Themode and scale of discon-tinuous uplift is similar to patterns left by "ights of marine terracescorrelated along the gulf coast of the Baja California peninsula andvarious islands (Ortlieb, 1991). Unlike marine terraces that charac-teristically retain platform deposits with progressively older Pleisto-cene fossils, the Quaternary lagoons on Isla Angle de la Guardapreserve no de!nitive fossil microbialites except for white crustscemented on cobbles found sporadically around the margins. Otherfossils indicative of normal-marine conditions are completely absentfrom these abandoned lagoons.

7. Possible Pliocene microbialites on Isla Angel de la Guarda

Stratigraphic units exposed in the cliff face adjacent to the smallerlagoon on the south side of Isla Angel de la Guarda (Fig. 11, units 2and 6) account for nearly a meter's accumulation of laminated siltstonewith a peculiar fabric of calci!ed plates preserved in an interwoven net-work. In vertical pro!le, laminae fromunit 2 have an appearance similarto living and fossil microbialites formed by alternating layers of silt andplaty material consisting of original aragonitic micrite (Fig. 12). Similarfeatures have been interpreted as a primary precipitate (Burne andMoore, 1987, their Fig. 4a, b). It was not possible tomake a petrographicthin section for detailed study of this delicate material, but alternativemethods of study of the deposits in these intervals are ongoing. One ofthe conglomerate layers higher in the 9.25-m thick section (Fig. 2, unit13) includes marine fossils such as pecten shells, barnacles, and sanddollars. The sand dollars belong to the species Encope angelensis, de!nedbyDurham (1950) as an index fossil for theUpper Pliocene in theGulf ofCalifornia. We propose this succession re"ects conditions of Pliocenesubsidence that alternated from a closed lagoon hosting microbialitesmuch like the modern lagoon at its side and other intervals, duringwhich coarse clastic material was introduced under a setting open tomarine circulation.

8. Discussion

8.1. Comparison with microbialites from open and semi-restrictedsettings

Microbialites from closed lagoons on Isla Angel de la Guarda andthe peninsular gulf coast at El Quemado register biological activity

Fig. 10. View north over the modern lagoon at the southeast end of Isla Angel de laGuarda and raised Quaternary lagoons.



under conditions of high aridity and hypersalinity punctuated by in-cursions of fresh water at rare intervals. In particular, the polygonalpattern of shrinkage cracks found over an extensive zone inside thebig lagoon on Isla Angel de la Guarda (Fig. 4) strongly resembles poly-gons described and illustrated from ancient and modern microbialmats on sandy beaches (Noffke, 2008). Oscillation cracks are one ofseveral microbially induced sedimentary structures (MISS) found,for example, on modern beaches in Tunisia and paleobeaches fromthe 2.9 Ga Pongola Supergroup in South Africa (Noffke, 2008, Fig. 1Aand B). According to Noffke et al. (2001), polygonal cracking occursin microbial mats that accumulate in hot, semiarid climates character-ized by seasonal rainfall in response to periodically changing degreesof moisture. Past and present open beaches may be able to supportmicrobial mats, where the tidal range is large or the gradient onbeaches is suf!ciently low to promote hypersalinity in the upper tidal

to supratidal zones. Conditions in the Gulf of California are far moreextreme, but episodic "ooding of the microbial crusts may be a keyfactor in the development of deeply incised shrinkage cracks.

Loaf-shaped and club-shaped stromatolites from Hamlin Pool inShark Bay, Western Australia (Logan, 1961; Playford and Cockbain,1976) are known to thrive in semi-restricted waters with a salinityof 65 ppt under a climate with low precipitation (15 to 23 cm/year)and high aridity. These factors go far to explain the relative biologicalexclusivity of the Hamlin Pool. Examples of microbialites fromwhat istechnically a lagoon setting with near normal ocean salinities rangingfrom 35.8 to 36.4 ppt are thoroughly documented from the Tikehauatoll in French Polynesia (Sprachta et al., 2001; Abed et al., 2003a,2003b; Gautret et al., 2004). Compared to coastal lagoons on conti-nental shores, the Tikehau atoll is enormous, having a diameter ofabout 28 km. A channel to the open ocean assures the exchange ofnormal ocean water. Dome-shaped stromatolites up to 20 cm in di-ameter and 10 cm in height are well established living on the "anksof pinnacle reefs within the lagoon at depths from 13 m to 26 m(Sprachta et al., 2001). This scenario clearly obviates the argumentthat exposed benthic microbialites are limited to settings with elevatedsalinities that preclude greater biological diversity.

The geological history of the western Mediterranean Sea duringtheMessinian crisis in the Late Miocene provides a geographic scenarioakin to a truly gargantuan closed lagoon slowly passing through hyper-salinity to reach the widespread precipitation of evaporates (Esteban,1979). From Messinian deposits in western Sicily, Saint Martin et al.(1996) reported dome-shaped microbialitic mounds several meters indiameter that developed in an open benthic setting associated withcemented bivalves and crustose bryozoans. The setting may havebeen similar to the essentially normal-marine conditions of the Tikehauatoll. The Sicilian succession, however, concludes with stromatoliticlimestone capped by gypsum (Saint Martin et al., 1996, Fig. 2). UpperMessinian limestone on the northwest coast of Menorca in the BalearicIslands is dominated by thick microbialitic mats that covered rockyshores with a relatively diverse fauna of endolithic organisms (Johnsonet al., 2011).

A natural replacement sequence from rhodolites nucleated aroundbroken coral branches to an end stage with thick encrustations bymicrobialites is documented from Late Pleistocene deposits that accu-mulated in back-reef lagoons on San Salvador Island in the Bahamasand the Caribbean island of Grand Cayman (Jones and Hunter,1991). The conclusion reached through this study was that the suc-cession occurred with progressively shallower-water and lower-en-ergy conditions associated with the beginning drop in sea level atthe end of the last inter-glacial epoch. In effect, the environment inthese lagoons became increasingly restricted and conducive to thedevelopment of exposed microbialites due to a change in sea level.Microbialites are able to thrive under normal marine conditions(Sprachta et al., 2001), but are mainly limited to cryptic settings with-in coral reefs today (Montaggioni and Camoin, 1993; Zankl, 1993;Webb et al., 1998). By nomeans de!nitive, it appears thatmany openlybenthic microbialites are abetted by special circumstances that insureprotection from competing organisms. From this point of view, themicrobialites from closed lagoons in the upper Gulf of California appearto represent an endpoint in an oligotrohic ecosystem.

8.2. Other possible microbialite lagoons in the Gulf of California

Presently, there are three closed lagoons in the Gulf of Californiathat !t a general model of microbialites (Fig. 2). The site at El Quemadois not as impressive as the lagoons on Isla Angel de la Guarda, in part be-cause the thrombolitic zone showing a more knobby outer surface isless well developed. Nonetheless, the occurrence of thrombolites andmicrobial crusts on the peninsular shores in the same region showsthese features are more widely distributed than on a single island.This induced us to undertake a brief geomorphological survey of the

Lithology Description Thickness (m) Unit

Total thickness: 9.25 m

0

1

2

3

4

5

6

7

8

1

23

4

56

7

9

10

11

12

8

9

13

14

14 Sandstone, tan, laminated, fn. gr. with vertical ichnofossils......................................... 1.10

13 Conglomerate, clast supported, well rounded volcanic pebbles (0.3 to 0.5 cm in diameter), fossils include sand dollars, pectens, and barnacles................... 0.50

12 Pumice conglomerate, beige, well rounded pebbles (5 cm in diam.)............... 1.00

11 Sandstone, brown, fn. gr., grades upward to granules (1 mm in diameter)................................................... ........ 0.80`

10 Sandy siltstone, light brown........................ 0.60

9 Sandstone, tan, fn. gr. with scattered volcanic pebbles (5 cm diameter)............. 0.50

8 Conglomerate, brown, volcanic clasts with bimodal distribution (0.2 cm and 0.9 cm diameters on average)..................... 0.45

7 Siltstone, gray, interbedded with sandstone containing granules up to 2.5 mm in diameter.................................. 0.50

6 Siltstone, gray, 2mm laminations, microbiolite in origin.................................... 0.35

5 Pumice breccia, beige, gradational to siltstone........................................................ 0.30

4 Siltstone, pinkish tan with 1 mm granules floating in matrix.......................... 1.90

3 Sandy siltstone, gray....................................... 0.14

2 Siltstone, gray, 2 mm laminations, microbiolite in origin..................................... 0.60

1 Pumice conglomerate, beige, with clast size 1 cm in diatmer on average in a silty matrix.................................................................. 0.50

Fig. 11. Pliocene succession of strata at the south end of the small lagoon on Isla Angelde la Guarda (see map in Fig. 1b for lagoon location).

Fig. 12. Thin-bedded to laminated layers from the succession of Pliocene strata (seeFig. 11 for context) bordering the small lagoon at the southeast end of Isla Angel dela Guarda; pick-head for scale (30 cm).



islands and gulf shores of the Baja California peninsula using satelliteimages in search of similar closed lagoons with the potential to supportmicrobial growth. In addition to the three principal localities described,herein, Table 1 lists 10 other localities that range from the farthest northand south lagoons in the Gulf of California comparable on the basis ofberm width and overall area.

Table 1 provides only a partial listing of lagoons that potentiallycould host microbialites. Speci!cally excluded are mangrove lagoonsthat require open circulation with the sea. Also excluded are lagoonsthat arti!cially have been altered to allow ingress of seawater to feedcommercial saltpans. However, it can be noted that one commercialoperation we have visited features pits where none-calcifying micro-bial growth luxuriates. The closed lagoon near Punta Coloradito(Table 1) is known to contain a Pliocene gypsum deposit (Johnsonand Ledesma-Vázquez, 2001), the base of which now must be re-examined for a possible transition from microbialites. We speculatethat the distribution of living microbial associations in the Gulf ofCalifornia is more extensive than presently known, due to wide-spread conditions similar to those in the lagoons on Isla Angel de laGuarda and Ensenada El Quemado. It is understandable why micro-bialites from such closed lagoons have not been reported, heretofore.Viewed from boats passing along the coast, it is impossible to see intothe lagoons on account of the high berms that isolate them from thesea. From the air, the lagoons are easily mistaken for saltpans. Thesmall-scale structures generated by microbial assemblages typicallyregarded as thrombolites and stromatolites by geologists and paleontol-ogists require on-site inspection. Until the additional closed lagoonslisted in Table 1 and others like them are visited on foot, the potentialfor greater distribution of microbialites within the Gulf of Californiamust remain untested. Like the hypersaline waters of the westernMediterranean Sea during the Messinian crisis more than 6 millionyears ago (Esteban, 1979; Saint Martin et al., 1996; Johnson et al.,2011), the closed lagoons of modern Gulf of California present amuch smaller, but isolated setting where microbial mats can thriveunder isolation from competing marine invertebrates and algae.

8.3. Biological implications

Members of the genus Chroococcidiopsis are widely characterizedby a pronounced ability to withstand the lethal effects of desiccationand exposure to high levels of ultraviolet radiation. In nature, thesecyanobacteria thrive in arid deserts under extreme variations inhigh and low temperatures. Much of the time, they survive in a desic-cated (or even frozen) state. High brine salinities also are well

tolerated by this morphotype. Such hardy attributes can be expectedto insure an effective geographic distribution throughout the Gulf ofCalifornia, assuming possible wind transport of dehydrated particu-late matter.

8.4. Paleontological implications

The only published study that describes fossil stromatolites fromNeogene strata of Baja California's gulf-coast region is by Miranda-Avilés et al. (2005) in reference to the lower member of the Boleo For-mation at Santa Rosalía. Discovery of Recent thromobites from ElMogote in La Paz Bay (Siqueiros-Beltrones, 2008) and thewell-calci!edmicrobialites in the lagoons on Isla Angel de la Guard and at El Quemado(this paper) suggest there is signi!cant potential for more fossil discov-eries in the gulf region of the Baja California peninsula.

9. Conclusions and agenda for future studies

Previous detailed reports on live microbial communities fromthe Baja California peninsula are from the Paci!c coast, wheremat ecology was studied by Horodyski and Vonder Haar (1975),Horodyski (1977), and Stolz (1983) at Laguna Figueroa near ColoniaVicente Guerrero and by Des Marais (2003), Spear et al. (2003), andOmoregie et al. (2004) at the salt lagoons of Guerrero Negro. More re-cently, Siqueiros-Beltrones (2008) described the !rst microbialitesfrom El Mogote on La Paz Bay in the southern Gulf of California.

This note gives the !rst evidence of live microbial associationsfrom closed lagoons in the Gulf of California and the !rst account ofthrombolites with a knobby surface morphology potentially capableof fossilization. The same lagoonal conditions probably prevailed onIsla Angel de la Guarda in the Late Pliocene and Quaternary, basedon stratigraphical and geomorphological relationships. Protectionafforded by closed lagoons appears to be the key to the success of variedmicrobial associations living under enforced oligotrophic conditions inthe Bahía de Los Angeles area. The dominant taxon sampled from thisregion is an environmentally hardy morphotype of Chroococcidiopsis.We predict that Chroococcidiopsis and some of the associated !lamen-tous morphotypes such as Phormidium will be found to have a signi!-cantly wider geographic distribution in the Gulf of California.

Most especially, future biological research in the Gulf of Californiarequires the application of protocols for nucleic acid sequencing thatenable the detailed taxonomic mapping of cyanobacterial morpho-types (Abed et al., 2003a).

Future efforts to re!ne the general model for the framework of la-goonal microbialites are anticipated, particularly from the stand pointof geomorphology, whereby a better understanding may be gainedregarding sedimentological processes under which such stalwartberms are constructed and maintained.

From a practical point of view, the closed lagoons harboringmicrobialites also appear to have left behind a record of tectonic uplifton Isla Angel de la Guarda. More survey work is needed to determineif abandoned lagoons of Quaternary age may match the utility ofraised marine terraces in the study of regional tectonics on the islandsand lands around of the Gulf of California.

Acknowledgments

The authors acknowledge the donors of the Petroleum ResearchFund (American Chemical Society) for grant support that made ourtrips to Isla Angel de la Guarda possible in March and November2007. Peter W. Tierney (Williams College student) served as a !eldassistant during studies in March. Additional travel funds weremade available to Backus and Tourney from the Science Divisionand from the Department of Geosciences at Williams College. Ourthanks also go to the Universidad Autónoma de Baja California inEnsenada for additional logistical support. We also thank the director

Table 1Partial list of closed lagoons in the Gulf of California with potential to support livingstromatolites. These sites were surveyed using satellite images available from GoogleEarth and include the big and small lagoons on Isla Angel de la Guarda, as well as atEl Quemado (this study), for comparison. Lagoon areas and berm widths were mea-sured from ASTER images using the measurement tool of the image-processing soft-ware ENVI 4.3.

Name Latitude Longitude Area(km2)

Berm width(m)

Big lagoon (A. de la G.) 29° 03" 13# N 113° 06" 36# W 0.225 50Small lag. (A. de la G.) 29° 02" 22# N 113° 06" 42# W 0.023 60Ensenada El Quemado 28° 56" 53# N 113° 25" 29# W 0.024 30Punta Bufeo 29° 45" 54# N 114° 15" 57# W 0.078 50Punta Final 29° 45" 55# N 114° 16" 03# W 0.110 35–60Punta Remedios 29° 15" 18# N 113° 37" 44# W 0.118 40Punta Cardon 29° 06" 38# N 113° 34" 13# W 0.160 30SW Isla San Lorenzo 28° 35" 19# N 112° 35" 19# W 0.022 13Punta Ballena 28° 28" 17# N 112° 54" 40# W 0.011 35SE of Punta Coloradito 26° 43" 48# N 111° 37" 36# W 0.035 40NW Isla San Jose 25° 02" 10# N 110° 42" 44# W 0.435 30Isla Espiritu Santo 24° 29" 17# N 110° 18" 37# W 0.163 90Punta Colorado 23° 34" 47# N 109° 31" 06# W 0.012 25



for Area de Protección Flora y Fauna Isla del Golfo de California forgranting the permits for our visits. Gabriel Rendon (Centro de Investiga-ción Cientí!ca y de Educación Superior de Ensenada) prepared the pet-rographic thin sections. Gudveig Baarli (Williams College) assistedwiththe drafting of Figs. 2 and 9. Comments and suggestions by two anony-mous reviewers helped to substantially improve the manuscript.

References

Abed, R.M.M., Golubic, S., Garcia-Pichel, F., Camoin, G.F., Lee, S.-J., 2003a. Identity andspeciation in marine benthic cyanobacteria: the Phormidium-complex. AlgologicalStudies 109, 35–56.

Abed, R.M.M., Golubic, S., Garcia-Pichel, F., Camoin, G.F., Spfrachta, S., 2003b. Character-ization of microbialite-forming cyanobacteria in a tropical lagoon: Tikehau Atoll,Tuamotu, French Polynesia. Journal of Phycology 39, 862–873.

Allwood, A.C., Walter, M.R., Kamber, B.S., Marshall, C.P., Burch, I.W., 2006. Stromatolitereef from the Early Archean Era of Australia. Nature 441, 714–718.

Batten, K., Narbonne, G.M., James, N.P., 2004. Early Neoproterozoic (Tonian) ramp car-bonates and microbial buildups, Little Dal Group, Northwest Territories, Canada.Precambrian Research 133, 249–269.

Burne, R.V., Moore, L.S., 1987. Microbialites: organosedimentary deposits of benthicmicrobial communities. Palaios 2, 241–254.

Des Marais, D.J., 2003. Biogeochemisry of hypersaline microbial mats illustrates the dy-namics of modern microbial ecosystems and the early evolution of the biosphere.The Biological Bulletin 204, 160–167.

Dravis, J.J., 1983. Hardened subtidal stromatolites, Bahamas. Science 219, 385–386.Durham, J.W., 1950. Megascopic paleontology and marine stratigraphy. 1940 E.W.

Scripps Cruise to the Gulf of California, Part 2: Geological Society of America Memoir,43. 216 pp.

Esteban, M., 1979. Signi!cance of the Upper Miocene coral reefs of the western Mediter-ranean. Palaeogeography, Palaeoclimatology, Palaeoecology 29, 169–188.

Feldmann, M., McKenzie, J.A., 1998. Stromatolite–thrombolite associations in a modernenvironment, Lee Stocking Island, Bahamas. Palaios 13, 201–212.

Gautret, P., Camoin, G., Golubic, S., Sprachta, S., 2004. Biochemical control of calciumcarbonate precipitation in modern lagoonal microbialites, Tikehau Atoll, FrenchPolynesia. Journal of Sedimentary Research 74, 462–478.

Gugger, M., Lenoir, S., Berger, C., Ledreux, A., Druarat, J., Humbert, J., Guette, C., Bernard, C.,2005. First report in a river in Franceof thebenthic cyanobacteriumPhormidium favosumproducing anatoxin-a associated with dog neurotoxicosis. Toxicon 45, 919–928.

Horodyski, R.J., 1977. Lyngbya mats at Laguna Mormona, Baja California, Mexico; com-parison with Proterozoic stromatolites. Journal of Sedimentary Geology 47,1305–1320.

Horodyski, R.J., Vonder Haar, S.P., 1975. Recent calcareous stromatolites from LagunaMormona (Baja California) Mexico. Journal of Sedimentary Petrology 45, 894–906.

Johnson, M.E., Ledesma-Vázquez, J., 2001. Pliocene–Pleistocene rocky shorelines tracecoastal development of Bahía Concepción, gulf coast of Baja California Sur (Mexi-co). Palaeogeography, Palaeoclimatology, Palaeoecology 166, 65–88.

Johnson, M.E., Ledesma-Vázquez, J. (Eds.), 2009. Atlas of Coastal Ecosystems in theWestern Gulf of California. University of Arizona Press, Tucson, Arizona. 189 pp.

Johnson, M.E., Baarli, B.G., Santos, A., Mayoral, E., 2011. Ichnofacies and microbial build-ups on Late Miocene rocky shores from Menorca (Balearic Islands), Spain. Facies57, 255–265.

Jones, B., Hunter, I.G., 1991. Corals to rhodolites to microbialites — a community re-placement sequence indicative of regressive conditions. Palaios 6, 54–66.

Logan, B.W., 1961. Cryptozoon and associated stromatolites from the Recent, SharkBay, Western Australia. Journal of Geology 69, 517–533.

Margulis, L., Barghorn, E.S., Ashendorf, D., Banergee, S., Chase, D., Francis, S., Giovannoni, S.,Stoltz, J.F., 1980. The microbial community at Laguna Figueroa, Baja California,México: does it have Precambrian analogues? Precambrian Research 11, 93–123.

Miranda-Avilés, R., Beraldi-Campesi, H., Puy-Alguiza, M.J., Carreño, A.L., 2005.Estramatolitos, tufas y travertinos de la sección El Morro: Depósitos relacionadoscon la primera incursón marina en la Cuenca de Santa Roslía, Baja California Sur.Revista Mexicana de Ciencias Geológicas 22, 148–158.

Montaggioni, L.F., Camoin, G.F., 1993. Stromatolites associated with coralgal communi-ties in Holocene high-energy reefs. Geology 21, 149–152.

Noffke, N., 2008. Turbulent lifestyle: microbial mats on Earth's sandy beaches — todayand 3 billion years ago. GSA Today 18, 4–9.

Noffke, N., Gerdes, G., Klenke, T., Krumbein, W.E., 2001. Microbially induced sedimentarystructures indicating climatological, hydrological and depositional conditions withinRecent and Pleistocene coastal facies zones (southern Tunisia). Facies 44, 23–30.

Omoregie, E.O., Crumbliss, L.L., Bebout, B.M., Zehr, J.P., 2004. Determination of nitro-gen-!xing phylotypes in Lyngbya sp. andMicrocoleus chthonoplastes cyanobacterialmats from Guerrero Negro, Baja California, Mexico. Applied and EnvironmentalMicrobiology 70, 2119–2128.

Ortlieb, L., 1991. Quaternary vertical movements along the coasts of Baja California andSonora. In: Dauphin, J.P., Simoneit, B.R.T. (Eds.), The Gulf and Peninsular Provincesof the Californias: American Association of Petroleum Geologists Memoir, 47, pp.447–480.

Playford, P.E., Cockbain, A.E., 1976. In: Walter, M.R. (Ed.), Modern Algal Stromatolites atHamelin Pool, A Hypersaline Based Basin in Shark Bay, Western Australia: Devel-opments in Sedimentology, 20. Elsevier Science, Amsterdam, pp. 389–411.

Riding, R., 2000. Microbial carbonates: the geological record of calci!ed bacterial-algalmats and bio!lms. Sedimentology 47, 179–214.

Roberts, N.C., 1989. Baja California Plant Field Guide. Natural History Publishing Company,La Jolla, California. 309 pp.

Romero-Vadillo, E., Zaytsev, O., Mofrales-Pérez, R., 2007. Tropical cyclone statistics inthe northeastern Paci!c. Atmosfera 20, 197–213.

Saint Martin, J.P., Conesa, G., Cornée, J.J., 1996. A new type of Messinian compositemicrobialitic build-up (Salemi, Sicily, Italy). Sedimentary Geology 106, 51–63.

Siqueiros-Beltrones, D.A., 2008. Role of pro-thrombolites in the geomorphology of acoastal lagoon. Paci!c Science 62, 257–269.

Spear, J.R., Ley, R.E., Berger, A.B., Pace, N.R., 2003. Complexity in natural microbial eco-systems: the Guerrero Negro experience. The Biological Bulletin 204, 168–173.

Sprachta, S., Camoin, G., Golubic, S., Le Campion, T., 2001. Microbialites in a modern la-goonal environment: nature and distribution, Tikehau atoll (French Polynesia).Palaeogeography, Palaeoclimatology, Palaeoecology 175, 103–124.

Stolz, J.F., 1983. Fine structure of the strati!ed community at Laguna Figueroa, BajaCalifornia, Mexico. I. Methods of an in situ study of the laminated sediments. Pre-cambrian Research 20, 479–492.

Webb, G.E., Baker, J.C., Jell, J.S., 1998. Inferred syngenetic textural evolution in Holocenecryptic reefal microbialites, Heron Reef, Great Barrier Reef, Australia. Geology 26,355–358.

Zankl, H., 1993. The origin of high-Mg-calcitemicrobialites in cryptic habitats of Caribbeancoral reefs — their dependence on light and turbulence. Facies 29, 55–60.


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