Stratigraphy, sedimentary patterns, and reservoir characteristics of Jurassic carbonate successions in the Lusitanian Basin

The Jurassic of the Lusitanian Basin (LB) is instructive for interpreting reservoir and source potential in carbonate ramp successions. Selected examples from the Lower, Middle, and lower Upper Jurassic of the LB are used here to illustrate a complete range of carbonate facies across the ramp system, from outer-ramp (Rabaçal), inner–mid-ramp (Maciço Calcário Estremenho and S. Pedro de Moel), and mixed non-marine, paralic and shallow-marine (Cabo Mondego) settings. Each example is used to demonstrate the interaction of tectonics and eustasy in controlling depositional facies, diagenesis, sedimentary patterns, and stratigraphic evolution. Emphasis is placed on the reservoir and/ or source-rock potential of each major depositional system. Outcrops are visited in the regions of: i) Maciço Calcário Estremenho (limestone hills in the eastern part of the LB); ii) Rabaçal, near Coimbra, also in the eastern part of the LB; and iii) Cabo Mondego and S. Pedro de Moel, both located in the western part of the basin (shoreline). In the Maciço Calcário Estremenho region, Middle Jurassic shallow-water facies (ooliteand skeletal-dominated sandbodies, coral–algal biostromes, and lagoonal, peritidal, and calcrete sediments) are examined. At Rabaçal, a Lower Jurassic hemipelagic succession is presented, supported by an integrated and detailed stratigraphic analysis emphasizing aspects related to the evolution of the Lower Jurassic series at the basin scale. At the coastal section of Cabo Mondego, the main features of interest are the Middle–Upper Jurassic basinwide disconformity, which shows the effects of a major forced regression, and various marginalto non-marine Oxfordian facies, including source rocks. At S. Pedro de Moel, the focus is on Sinemurian restricted-marine facies with text-book examples of stromatolites.


Introduction
The Lusitanian Basin (LB) is located in the Western Iberian Margin and is a marginal basin associated with the opening of the North Atlantic Ocean. Most of the basin fill is Jurassic in age, but Upper Triassic to Upper Cretaceous sediments occur, with a Tertiary cover (Fig. 1). Two main episodes of extension and rifting are recorded in the LB, one during the Late Triassic followed by a more major episode during the Late Jurassic-Early Cretaceous (e.g., Wilson et al. 1989;Leinfelder & Wilson,1998;Rasmussen et al. 1998, Reis et al., 2000Alves et al., 2002). The post-Triassic rift stage (Early-Middle Jurassic) was characterized by deposition that became increasingly marine over time, chiefly shallow-to deep-marine limestones and marls, dolostones, and bituminous shales, developed on a carbonate ramp depositional system (Soares et al., 1993;Azerêdo, 1998Azerêdo, , 2007Duarte et al., 2001Duarte et al., , 2004Azerêdo et al., 2002Azerêdo et al., , 2003Azerêdo et al., , 2010Duarte & Soares, 2002;Azerêdo & Wright, 2004;Duarte, 2007). The Middle Jurassic is separated from the Upper Jurassic by a basinwide disconformity (e.g., Azerêdo et al., 1998Azerêdo et al., , 2002Leinfelder & Wilson, 1998). The Triassic to Upper Jurassic lithostratigraphy of the LB is rather complex; a simplified scheme, in which some of the units are informal, is presented in Figure 2. Regarding the Lower and Middle Jurassic, formal units have been defined and described by Duarte & Soares (2002) and Azerêdo (2007), respectively, and are used throughout this guidebook.
Selected examples from the Lower, Middle, and lower Upper Jurassic of the LB are used to illustrate carbonate facies across the ramp system. These LB Jurassic series rocks are instructive for interpreting reservoir and source potential in carbonate ramps.
The examples are used to show the interaction of carbonate factory behaviour, tectonics, and eustasy in controlling depositional facies, diagenesis, sedimentary patterns, and stratigraphic evolution. Emphasis on reservoir and source-rock potential is made as appropriate. Outcrops are visited in the regions of: i) Maciço Calcário Estremenho (MCE, limestone hills in the eastern part of the LB); ii) Rabaçal, near Coimbra, also in the eastern part of the LB; and iii) Cabo Mondego (CM) and S. Pedro de Moel (SPM), both in the western part of the LB (shoreline). The outcrops are visited according to the plan given below (Fig. 1).
Stop 1 One of the main aims of this excursion is to examine some examples of well-exposed Middle Jurassic deposits in the east of the basin, namely, in the MCE region, an area of limestone hills (Fig. 1). The lithostratigraphic arrangement of the MCE successions as defined by Azerêdo (2007) is shown in Figure 3. Previous mapping work by Manuppella et al. (2000) has helped in arriving at this lithostratigraphic organization.
The field stops focus on parts of the following formations. The Chão das Pias Formation, including the Calcários de Vale da Serra Member and the  (Stop 1), features graded grainstones/rudstones and dolomitic facies types. The Serra de Aire Formation is characterized mainly by lagoonal and peritidal lithofacies (Stops 2 and 5). The Santo António-Candeeiros Formation is composed of high-energy barrier facies (Stops 2 and 3). A view of the landscape will also be made (Stop 4) encompassing the open-marine Barranco do Zambujal Formation and extending to the mid-ramp deposits of the lower Chão das Pias Formation (Fig. 3).

Dolomitos de Furadouro Member
In particular, inner-ramp oolite-and skeletal-dominated sandbodies, coral-algal biostromes, and lagoonal and peritidal sediments occur, defining several lithofacies and facies associations (Azerêdo, 1998). These shallow-water carbonate facies form successions measuring several hundreds of metres thick, representing a high-energy carbonate ramp depositional system under the influence of storms but dominated by wave activity. The sandbodies most commonly crop out as thick units of superimposed sets of oolitic and bioclastic grainstones, with rare intercalations of other facies types. The cross-sets comprise multistorey units, with common lateral and vertical variations in cross-stratification types and scales (Azerêdo, 1998(Azerêdo, , 2004(Azerêdo, , 2007. The barrier sandbodies are thought to have developed under a microtidal regime dominated by waves and longshore drift currents with frequent storm influence. The scale of the peritidal cyclothems associated with these sandbodies suggests a microtidal regime (Azerêdo, 1998). The peritidal facies association occurs in close association with the lagoonal facies association, and this entire range of deposits may be interbedded with storm layers. The thick inner-ramp succession was deposited as the result of a strong progradational stage, exhibiting pedogenic carbonates in the eastern part of the LB (see Stop 5) and well-exposed peritidal and dolomitic facies in the western part (Stops 1.1 and 1.2; Fig. 5). In addition, the evolution of the system was chiefly progradational-aggradational, with a high rate of production by the shallow-water carbonate factory (Figs 4 and 6) and rarer retrogradational episodes.  (Azerêdo, 2007).
At this stop, white, commonly graded, oolitic and coarser-grained oncolitic-intraclastic grainstones and rudstones, also exhibiting skeletal material (corals, algae, and molluscs), may be observed (Fig. 5). These limestones, which belong to the Calcários de Vale da Serra Mb of the Chão das Pias Fm, show good examples of low to moderate, heterogenous secondary porosity, namely, intraparticle, oomoldic, vuggy, and fracture porosity types. Dolomites and dolomitic limestones with good examples of recrystallization, fracturing, brecciation, and very large late calcite crystals may also be seen.

Stop 1.2. Vale de Chã Quarry Dolomites
The Vale de Chã Quarry (the Dolomitos de Furadouro Mb of the Chão das Pias Fm) contains good examples of dolomite rocks as well as porosity and permeability features to be examined (Fig. 5). These dolomites, cream to reddish in colour, range from massive dolomites and dolomitized, recrystallized coral limestones (mainly in the upper part of the quarry) to fenestral dolomicrites with oncoidal lenses showing vadose cements and microbially laminated dolomicrites (the lower part of the quarry). Porosity occurs at different scales, namely, well-developed vuggy, fracture, channel, and mouldic porosity. However, several low-porosity zones are also present, and faulting and later karstification further contribute to a complex permeability pattern.

Brief palaeoenvironmental interpretation:
The micrite-supported facies association reflects a lagoonal or marginal-marine environment, with episodes of intermittent, rapid subaerial exposure but usually favouring the development of shallow-water benthic faunal and floral communities. The grain-supported limestones reflect wave-and storm-associated depositional conditions. The amalgamated pattern of many of these layers and their lateral discontinuity are also features commonly reported in shallow-water storm deposits. The bioturbated wacke/packstones represent sedimentation lag-time intervals between the dominant high-energy intervals.

Stop 3. Fórnea: a panoramic view over an outer-ramp marl-limestone succession
A spectacular large-scale geomorphological landform can be observed here, namely, the deep and wide Fórnea "amphitheatre", formed by the Fórnea Creek in a marly limestone succession of the Lower to Middle Jurassic (Fig. 7). This site allows a good perspective to be gained over the furthermost outer-marine units in this region, known in the stratigraphic literature as the Barranco do Zambujal section. This section is important for its palaeontological content, namely, ammonoids, which makes it a biostratigraphic reference section for the Lower-Middle Jurassic transition through the Aalenian and Bajocian (Ruget-Perrot, 1961;Henriques, 2000;Manuppella et al., 2000). The section corresponds to a thickening-and shallowing-upwards outer-marine succession, the middle part of which comprises siliceous nodules.

Stop 4. Vale Florido oolitic-skeletal limestones and coral biostromes: facies, geometric configurations, and diagenetic features from a reservoir perpective (Sto. António-Candeeiros Fm, lower Bathonian)
Along the road that links the two small localities of Vale Florido and S. Bento (Fig. 1), lithofacies and biofacies typical of high-energy, high-sedimentation-rate settings crop out, namely (Azerêdo, 1998(Azerêdo, , 2004: coral-rich biolithites, bearing large in situ branched corals, smaller cup-shaped corals and coral fragments, associated with calcareous algae and other abundant skeletal material, and locally interspersed with peloidal-intraclastic packstones as internal sediment; finer-grained, mainly oolitic grainstones, with fewer bioclasts and other allochems, exhibiting planar and small-scale low-angle cross-sets, wave ripple cross-laminations, and gradations of these into low-or higher-angle cross-laminations; and massively bedded, crudely graded, coarse-grained, bioclastic-dominated grainstones and rudstones, with intraclasts and oncoids as well as planar or slightly undulatory laminae. The prominent biostrome units may be draped by, or grade laterally into, amalgamated, uneven bioclastic-intraclastic grainstones, and all the lithofacies may interfinger with each other (Fig. 8).
Most of the sandbody and biostrome deposits show low porosities but likely had varied primary porosities as indicated by the range of allochem types and sizes and the depositional fabrics. These deposits were subsequently affected to varying degrees by diagenesis, so there are also cases of higher porosity, even locally excellent (though usually poorly connected), in these lithofacies. These examples of high-porosity correspond to multi-phase, late secondary dissolution, usually, but not necessarily, associated with dolomitization (mouldic, intraparticle/intracrystal, and vuggy porosity; Fig. 8). Mechanical and chemical compactional features do occur, though rarely, as a result of dominant and significant early or multi-generation cementation. These issues can be exemplified and discussed by examining the outcrops at this stop, coupled with petrographic information and other relevant data introduced during the excursion.   Brief palaeoenvironmental interpretation: the sandbody and biostromal units are interpreted as typical barrier and peri-barrier deposits, with the biostromes having been formed mainly on the outermost side of the barrier, grading into oolite and skeletal sand sheets deposited between and on the flanks of the biogenic accumulations and small bioconstructions, in a highly dynamic sedimentary setting (Fig. 9). The cross-bedded, mainly oolitic grainstone clearly implies deposition from wave-dominated processes, above the fair-weather wave-base (upper shoreface). In contrast, the coarser-grained, massive to crudely graded planar laminated beds of skeletal grainstones/rudstones suggest a powerful, mainly unidirectional flow, influenced by storms, above the storm wave-base (lower shoreface). The peloidal-intraclastic interstitial sediment is interpreted as washed-in material from storm clouds.

Stop 5. Galinha Quarry: pedogenic, organic-matter-rich, peritidal carbonate succession (Serra de Aire Fm, lower Bathonian)
The previously active Galinha Quarry, which is located in the Fátima region (~30 km southeast of the Porto de Mós; Fig. 1), is nowadays a conservation site classified as a natural monument because of the excellent examples of sauropod trackways (Santos et al., 1994). These tracks are recorded in very shallow marginal-restricted lagoonal carbonate beds, towards the upper part of a pedogenic-peritidal-lagoonal marine carbonate succession assigned to the latest Bajocian?-lower Bathonian transition. The succession contains macrofossils (gastropods and bivalves) and microfossils (foraminifers, ostracods, calcareous algae, and cyanobacteria), several layers of microbial laminites, and fenestral structures (Azerêdo et al., 1995(Azerêdo et al., , 2015. The stop focuses mainly on the lower part of the section, which is characterized by pedogenic-peritidal deposits. This lower part of the section exhibits clear calcretes (massive, laminar, nodular, and brecciated, all with black clasts) interbedded with, and grading laterally or vertically into, a range of other deposits. Limestones and marly-clayey limestones, ranging from massive to nodular or laminar macrofabrics, and composed of clotted micrite, peloidal-intraclastic sediment, black clasts, fenestral carbonate, and scattered bioclasts, are seen either interbedded with or grading laterally into organic-or coal-rich, marly/ clayey seams and lenses, locally with carbonate nod-   ules and microbial laminites (Fig. 10). Hardgrounds are also observed. Microscopic examination shows a range of typical calcrete fabrics and a few evaporite traces (Azerêdo et al., , 2015. This pedogenic-dominated facies association grades upwards into peritidal cyclothems and lagoonal limestones with gastropods, ostracods, and other fossils. Only very rarely have freshwater ostracods and charophytes been found, at the base of the section. Many beds are bounded by undulated surfaces, and late compaction effects are also recorded. The upper part of the section corresponds to more fossiliferous limestones, with bivalves, gastropods, rare solitary corals, and ostracods, as well as microbial laminites, but no pedogenic evidence is recorded (Azerêdo et al., , 2015. Brief palaeoenvironmental interpretation: The palaeoenvironment resembles more the modern strongly seasonal Coorong setting, perhaps with less marked aridity, rather than a seasonal wetland setting . The organic facies and overall sedimentary characteristics, including evaporites, suggest small ponds and subaerial terrestrial zones in a low-relief landscape subjected to seasonally sub-arid-sub-humid climatic conditions, affected by wildfires, that later evolved to peritidal and restricted lagoonal settings as a result of gradual marine inundation of the previous lowstand system (Azerêdo et al., 2015).

Introduction
The Lower Jurassic in the LB is well exposed in almost all sectors of the basin (Fig. 1). Generally, the upper Sinemurian-upper Toarcian is dominated by hemipelagic deposits, represented by marl-limestone alternations, rich in nektonic and benthic macrofauna and controlled by an accurate ammonite biostratigraphy. The vertical facies variation observed between the Jamesoni and the Aalensis zones allows four main formations to be defined: the Vale das Fontes Fm (Jamesoni to Margaritatus Zone), the Lemede Fm (top of Margaritatus Zone to lowermost Polymorphum Zone), the S. Gião Fm (Polymorphum Zone to lowermost Meneghinii Zone), and part of the Póvoa da Lomba Fm (Duarte & Soares, 2002) (Fig. 11). The integration of several stratigraphic and sedimentological parameters (e.g., lithofacies analysis, stratonomy, microfacies, sequence evolution, ichnofossils, and palaeontological evolution) at the basin scale leads to the conclusion that the deposition occurred in a carbonate ramp setting (homoclinal ramp) dipping towards the northwest (e.g., Duarte, 1997Duarte, , 2007 (Fig. 11).
The Rabaçal-Coimbra region, located in the northeastern part of the LB (Soares et al., 2005;Fig. 11), is one of the most important sectors for the study of the Lower Jurassic in Portugal (e.g., Mouterde 1964-65;Duarte, 2004). In this region, most of the Toarcian belongs to the S. Gião Fm and to the base of the Póvoa da Lomba Fm. The S. Gião Fm has its type-section at Rabaçal (Fig. 12), a succession that has been analysed in detail over the last two decades in the different domains of stratigraphy and sedimentary geology (e.g., Duarte, 1997;Duarte et al., 2001Duarte et al., , 2007Perilli & Duarte, 2006;Suan et al., 2010;Cabral et al., 2013a;Comas-Rengifo et al., 2013a). Therefore, this stop is focused on examining this section at different scales, including the high diversity of hemipelagic facies and their vertical and lateral arrangement in terms of cyclicity and sequence evolution. Particular attention is paid to the sedimentary and geochemical record observed in the lower Toarcian and the related discussion of the Toarcian anoxic event.
The Vale das Fontes Fm (Jamesoni to Margaritatus Zone) is composed of alternations of decimetreto metre-scale marl and centimetre-scale limestone, particularly rich in brachiopods, bivalves, ammonites, and belemnites. This unit comprises several facies, such as black shales and lumpy bioclastic marls and limestones. In the Rabaçal type-section, only the upper part of the succession is observed, being composed mainly of greyish marls locally enriched in organic matter.
The Lemede Fm (top of Margaritatus(?) Zone to the extreme base of the Polymorphum Zone) is composed of bioturbated alternations of centimetre-scale marl and decimetre-scale limestone. The unit is very rich in belemnites and ammonites, amongst other benthic macrofauna (bivalves and brachiopods). This formation reaches around 20 m in thickness in the Rabaçal section (Fig. 13A).
The S. Gião Fm is dominated by marly facies and ranges in age from early Toarcian (lowermost Polymorphum Zone) to late Toarcian (Meneghinii Zone). The formation is subdivided into five informal members, as outlined below: the marly limestones with "Leptaena" facies (MLLF) Mb.; the thin, nodular limestones (TNL) mb; the marls and marly limestones with Hildaites and Hildoceras (MML-HH) mb; the marls and marly limestones with sponge bioconstructions (MMLSB) mb; and the marls and marly limestones with brachiopods (MMLB) mb. The S. Gião Fm is easily recognizable across a large area of the LB and is defined in terms of different stratonomic, sedimentological, and palaeontological (macrofauna and ichnofauna) characteristics (Duarte & Soares, 2002;Fig. 12). The formation at Rabaçal is around 145 m thick and is well controlled by ammonites (Mouterde et al., 1964-65;Rocha et al., 1987). The MLLF mb (7 m; Polymorphum Zone) is characterized by alternations of decimetre-to metre-scale marly beds and centimetre-scale marly limestones, greyish in colour (Fig. 13B). This member contains a very rich benthic and nektonic macrofauna, characterized by an abundance of small brachiopods, belemnites, pyritized ammonites (dactylioceratids), bivalves (mainly Plicatula sp.), and Zoophycos.
The TNL mb (7m; base of the Levisoni Zone) is composed of thin (centimetre-scale) alternations of limestones and marlstones, grey to brownish in colour (Fig. 13B). The limestones include calcilutites to fine calcarenites, with irregular surfaces (amalgamated structures), locally with laminations, cross-bedding (Fig. 13C), and symmetrical current ripples. The thin (<14 cm) calcareous levels are usually strongly bioturbated; Thalassinoides and Chondrites are common, but ammonites are rare (some Hildaites sp.).
The MMLHH mb (63 m; Levisoni Zone-Bifrons Zone interval) is composed of decimetre-to metre-scale alternations of marls, marly limestones, and micritic limestones, with the micritic limestones increasing towards the top of the unit (Fig. 13B). The nektonic (ammonites) and benthic (brachiopods and bivalves) faunal association is a persistent feature of this unit, but with low diversity throughout. The brachiopods, mainly rhynchonellids (Soaresirhynchia sp.) and terebratullids (Telothyris jauberti), are very rich at the base of the member, corresponding to the Levisoni Zone. Some horizons of the uppermost part of the Levisoni Zone are very rich in thin-shelled bivalves (Bositra sp.; Fig. 13D).
The MMLSB mb (43 m; Bifrons Zone to the base of the Bonarellii Zone interval), with the exception of the marly base (Fig. 13E), is composed of regular alternations of decimetre-to metre-scale marly beds and centimetre-to decimetre-scale marly limestones. The occurrence of small siliceous sponge mud mounds (Fig. 13F), preferentially associated with calcareous lithofacies, is a typical and dominant feature throughout the member (Duarte et al., 2001). The macrofauna shows high diversity, locally with high concentrations of ammonoids, rhynchonellids, crinoids, and bivalves.
The MMLB mb (22 m; Bonarellii Zone-base of the Meneghinii Zone interval) is composed primarily of marls with very rare limestone levels. The occurrence of brachiopods is the most important palaeontological feature of this unit.
The base of the Póvoa da Lomba Fm is composed of bioturbated marl-limestone alternations, with an upward increase in the proportion of calcareous (biomicrite-wackestone, locally packstone) facies. This part of the unit (MST4B in Duarte, 1997), ranging in age from the Meneghinii Zone to the Opalinum Zone, is indicated by the occurrence of siliceous sponge bioconstructions (Duarte et al., 2001), preferentially associated with the tops of fourth-order sequences (Fig. 13G). Another important feature that characterizes this unit in this area is the ichnofacies composed of the association of Chondrites, Zoophycos (Fig. 13H), Planolites, and Thalassinoides.

Sequence stratigraphy of the Toarcian succession
The Pliensbachian and Toarcian deposits of the LB are subdivided into two second-order transgressive-regressive facies cycles (SP and ST;Figs 11 and 12). The thickness of these sequences is highly variable, dependent on the palaeogeographic position of each sector in the basin, controlled by the ramp profile and accommodation space. In both second-order sequences, the thickness increases from the southeast (Tomar region) to the northwest (Figueira da Foz-Cantanhede sectors), following the dip direction of the ramp (Fig. 11).
ST is dated from early Toarcian to early Aalenian and includes the S. Gião Fm and the lowermost part of the Póvoa da Lomba Fm, and it is subdivided into four third-order depositional sequences (ST1 to ST4; Duarte et al., 2001Duarte et al., , 2004a, each one bounded by regional discontinuities, recognized over most parts of the LB (Figs 12 and 13B). The base of ST corresponds to an abrupt flooding event and is represented by a generalised marly accumulation across the whole basin (Fig. 13A). The marly dominance observed at the top of the Levisoni Zone marks the peak transgression of the Toarcian second-order sequence, coupled with the occurrence of Bositra sp. (Fig. 13B and D). The upper Toarcian-lower Aalenian succession shows a regressive trend, with the sequence ending with an upward increase in calcareous and bioclastic content (Fig. 13G). The discontinuity is dated from the Opalinum Zone and shows different sedimentary records in the basin (Duarte, 1997;DA1 in Duarte et al., 2001).  Fig. 15, representing the Callovian-Oxfordian disconformity and succession at Cabo Mondego (from Azerêdo et al., 2002).
In this sedimentary context, we emphasize the facies change observed between the MLLF and TNL members (DT2; across the Polymorphum-Levisoni chronozone boundary) (Fig. 13B). This disconti-nuity defines the most important sedimentological and palaeontological change recorded in the whole Lower Jurassic succession of the LB (Duarte, 1997;Duarte et al., 2004a) and reflects significant tectonic activity (e.g., Duarte, 1997;Kullberg et al., 2001). Corresponding approximately to the Polymorphum-Levisoni chronozone boundary (Duarte, 1997), this discontinuity marks an abrupt decrease in the evolution of Δ 13 C (Duarte et al., 2004a(Duarte et al., , 2007Suan et al., 2010).  Wright, 1985). Fa: facies associations of Azerêdo et al. (2002); Es: erosion surfaces (Wright, 1985). The key is given in Fig. 14. er-ramp facies ("Brenha" in Fig. 2; Cabo Mondego Fm sensu Azerêdo et al., 2003) are sharply overlain by a carbonate sandbody and then by mixed non-marine-paralic-shallow-marine facies corresponding to the Cabaços Fm (Wright, 1985(Wright, , 2004Azerêdo et al. 2002;Azerêdo & Wright, 2004). The sharp-based carbonate sandbody is 28 m thick, with extensive Thalassinoides-type burrows, and is overlain by a 6-m-thick package of coral-bearing sandstones, coral rudstones and packstones (locally red in colour with evidence of coral leaching), oyster-rich mudstones, in situ oyster-coral bioherms, and bioclastic limestones (Figs 14 and 15; Wright, 1985Wright, , 2004. Upwards into the Cabaços Fm, through a thickness of more than 100 m, sandstones, mudstones, shales, and lignites, as well as micritic-marly limestones with mainly non-marine bivalves, gastropods, abundant ostracods, and charophytes, are found interbedded with microbial laminites, organic-rich marls, and laminites, with local occurrences of thin calcite-replaced gypsum layers. This field-trip visits only the lower part of this thick package. Some of the organic-rich sediments present high total organic carbon values (reaching 30.7 wt.%), and palynofacies studies indicate that the particulate organic matter is mostly of continental origin punctuated by minor events of marine influence (Silva et al., 2011(Silva et al., , 2013. The overall features suggest that part of the Cabaços Fm. may be regarded as a potential source rock (e.g., Wright, 1985;Silva et al., 2011Silva et al., , 2013. Brief palaeoenvironmental interpretation: This sharp shift from open-marine to carbonate sandbody and then to non-marine deposits is interpreted as clear evidence for a forced regressive episode marking the Middle-Upper Jurassic transition, which is associated with a disconformity recorded at several locations across the basin (e.g., Azerêdo et al., 2002;and references therein). Reflooding led to the development of a complex pattern of depositional conditions throughout the basin from freshwater and brackish lagoonal environments to marginal-and shallow-marine settings. At Cabo Mondego, in particular, the input of siliciclastics (probably from the west) reflects erosion related to tectonism and basement uplift. The combination of oysters and corals, lensoidal sandstones, and coarse coral debris, overlain by carbonate-dominated sediments with non-marine fossils, probably represents mixed coastal marginal fresh to brackish water and restricted marine lagoonal settings, periodically affected by deltaic influxes and storms (Wright, 1985(Wright, , 2004Azerêdo et al., 2002;Azerêdo & Wright, 2004).

Stop 8. São Pedro de Moel region: stromatolites within a restricted marine succession (Coimbra Fm, Sinemurian)
This stop examines part of a more than 100 m thick, thin-to medium-bedded Lower Jurassic (Sinemurian) carbonate succession cropping out along the cliffs of two contiguous beaches in the S. Pedro de Moel region (Praia Velha and Praia da Concha; Fig. 1). This succession, belonging to the lower part of the Coimbra Fm (e.g., Mouterde et al., 1981;Rocha et al., 1987;Duarte et al., 2008;Azerêdo et al., 2010), is affected by faulting and tectonic deformation and reveals some interesting features, including excellent examples of stromatolitic mounds. The lowermost part of the series has not yet yielded age-diagnostic fossils, but it is overlain by marine marl-limestone deposits bearing the first ammonoid faunas recognized in the basin (Obtusum Zone, earliest late Sinemurian; Mouterde et al., 1981;Dommergues et al., 2004Dommergues et al., , 2010. The sedimentary succession has been described and interpreted in detail (with an emphasis on microbialites) by Azerêdo et al. (2010). The succession comprises (Fig. 16): dolomites; marly, argillaceous and/ or dolomitic limestones, either massively bedded or laminated, locally with undulating boundaries; stromatolites and a few tabular microbalite layers; fossil-iferous/skeletal limestones (bivalves, gastropods, and ostracods), graded in some places, with an erosive base and bioclastic lags and coquinas at the top; and a few marls and shales (Fig. 17). Bioturbation is also common. In contrast to the relatively even-bedded deposits both below and above, the succession contains many decimetre-to metre-scale brownish-reddish microbial structures, whose external and internal morphologies allow them to be classified as stromatolites.
Brief palaeoenvironmental interpretation: The overall depositional setting is interpreted as a mainly low-energy, shallow to moderately deep subtidal marine setting (distal inner-and mid-ramp), punctuated by higher-energy (storm/flooding) episodes, particularly in the middle and upper parts of the section. Some type of physical constraint, coupled with the low gradient of the ramp system, would presumably have defined an embayment environment in which circulation was relatively restricted for most of the time (favouring the microbial community), except when affected by externally induced events. Towards the upper part of the succession, progressive environmental openness leading to a gradually stronger marine influence, alternating with frequent environmental restriction, is inferred from the composition of palaeobiota and changes in diversity (Azerêdo et al. 2010;Cabral et al., 2013b).