A facies model for internalites (internal wave deposits) on a gently sloping carbonate ramp (Upper Jurassic, Ricla, NE Spain)

Sedimentary Geology 271-272 (2012) 44–57

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A facies model for internalites (internal wave deposits) on a gently sloping carbonate ramp (Upper Jurassic, Ricla, NE Spain) Beatriz Bádenas a,⁎, Luis Pomar b, Marc Aurell a, Michele Morsilli c a b c

Dpto. Ciencias de la Tierra, Universidad de Zaragoza, 50009 Zaragoza, Spain Departament de Ciències de la Terra, Universitat de les Illes Balears, 07122 Palma de Mallorca Illes Balears, Spain Dipartimento di Scienze della Terra, Università di Ferrara, 44100 Ferrara, Italy

a r t i c l e

i n f o

Article history: Received 2 March 2012 Received in revised form 27 May 2012 Accepted 28 May 2012 Available online 6 June 2012 Editor: B. Jones Keywords: Internalites Breaking internal waves Carbonate ramp Jurassic Iberian Basin

a b s t r a c t Internal waves are waves that propagate along the pycnocline, the interface between two density-stratified fluids. Even though internal waves are ubiquitous in oceans and lakes, their impact in the sedimentary record has remained largely unrecognized. Internal waves can remobilize the sediment from the depth at which the internal waves break onto the sea floor. In shelf, or ramp settings, internal wave deposits (internalites) have to be distinguished from tempestites while in slope and deeper settings internalites require distinction from turbidites. The Upper Kimmeridgian carbonate ramp succession cropping out near Ricla (NE Spain) provides some key evidence to differentiate the depositional processes induced by breaking internal waves from those related to surface storm waves. Sandy-oolitic grainstone eventites, previously interpreted as tempestites, contain evidence of reworking by turbulent events related to breaking internal waves. Underlying rationale are: 1) they occur in distal mid-ramp position, detached from the coeval shallow-water successions; 2) they do not have the characteristic coarsening- and thickening upward trend of storm deposits; 3) they gradually thin-out to disappear both up dip and down dip, interbedded with mid-ramp lime mudstones; and 4) they show little or no erosion towards the shallower areas. A facies model for internalites produced by two sediment populations, sand and mud, on a gently sloping carbonate ramp is proposed. The individual internalites occurring at Ricla include several architectural elements, sequentially organized in dip direction, which can be related to the flows associated with breaking internal waves: erosion in the breaker zone, swash run-up and tractive backwash flow. Individual internalites stack, with down- and up-slope shingling configuration, in dm-thick packages thought to reflect the up-slope and down-slope migration of the breaker zone, in turn related to depth variations of the palaeo-pycnocline. Packages occur in dm- to m-thick clusters suggested to reflect changes in sediment supply and/or variations in water stratification affecting the energy of internal waves. © 2012 Elsevier B.V. All rights reserved.

1. Introduction Among eventites, sediments reflecting the effects of turbulent events (Seilacher, 1982, 1991), tempestites and turbidites are the most frequently recognized. Tempestites and turbidites share some common features, namely an erosional phase, reflected by the basal erosion surface, and a subsequent depositional phase during waning of the turbulence which produces a graded sediment succession due to different settling velocities of the sediment grains. Internal waves are gravity waves that propagate along a pycnocline, the interface between two different density fluids (Munk, 1981; Apel, 2002). Any perturbation of the pycnocline, induced for example by surface waves, wind-stress fluctuations, tsunamis, tidal currents or river plumes flowing into a coastal ocean, propagates as an internal wave ⁎ Corresponding author. Tel.: + 34 976762247. E-mail addresses: [email protected] (B. Bádenas), [email protected] (L. Pomar), [email protected] (M. Aurell), [email protected] (M. Morsilli). 0037-0738/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.sedgeo.2012.05.020

(Small and Martin, 2002; Staquet and Sommeria, 2002; Nash and Moum, 2005; Santek and Winguth, 2007). Solitons, or “solitary internal wave packets” sensu Apel (2002), are ubiquitous wherever water currents and stratification occur in the neighbourhood of irregular topography, particularly near shelf edges, seamounts, sills and submarine canyons (Munk, 1981; Ostrovsky and Stepanyants, 1989; Global-OceanAssociates, 2004; Wolanski et al., 2004; Santek and Winguth, 2007). These conditions frequently happen in coastal regions, especially during summer months when a shallow thermocline develops. Solitons typically consist of rank-ordered wave packets, with number of cycles varying from a very few to a few tens, and with the largest amplitude and longest wave at the front and the smallest at the rear (Apel, 2002; Quaresma et al., 2007). Their amplitudes vary from a few up to 140 m and their maximum wavelengths from less than 100 m to more than 5 km (Apel et al., 2007; Quaresma et al., 2007; Santek and Winguth, 2007). Under thermohaline circulation, like in modern oceans, the pycnocline is induced primarily by temperature and secondarily by salinity gradients in the water column. The depth of the pycnocline

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Fig. 1. A) Palaeogeography of western Europe during the Late Kimmerdigian (modified from Dercourt et al., 1993; paleolatitude from Osete et al., 2011). B) Main facies belts in the northeastern Iberian Basin during the Late Kimmeridgian (adapted from Bádenas and Aurell, 2008). Numbers 1 to 6 indicate reference localities: 1 —Aldealpozo, 2 — Veruela, 3 — Ricla outcrop, 4 — Aguilón, 5 — Ariño and 6 — Calanda. C) Synthetic stratigraphy of the Kimmeridgian in the northern Iberian Basin (see location of reference localities 1 to 6 in B) including main facies belts and transgressive–regressive (T–R) sequences Kim1 and Kim2 (adapted from Aurell et al., 2010). Black box indicates the stratigraphic location of the studied interval at Ricla outcrop within the transgressive deposits of the Kim2 Sequence enlarged in Fig. 2.

in open oceans is highly variable, changing with latitude and season (from few to some 10's of metres in the case of the seasonal pycnocline, from 100 to some 100's of metres in the case of the permanent

pycnocline; Pomar et al., 2012). In small interior seas the seasonal pycnocline is commonly shallow (few- to some tens of metres) and strongly influenced by riverine discharge, wind regimes, and season,

Fig. 2. Facies architecture of the transgressive deposits (TST) of the third-order Kimmeridgian-2 Sequence (Kim2) in Ricla (updated from Bádenas and Aurell, 2001). Intervals rich in sandy-oolitic eventites are concentrated in the distal mid-ramp setting and are detached from shallower facies. The two studied intervals rich in eventites located between logs 5 and 7 are indicated (see Fig. 1 for location in a broader context).

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Fig. 3. A) Detail of the stratigraphic log 7 in Ricla (see Fig. 2 for location; adapted from Bádenas et al., 2005). The grey-shaded area denotes the two intervals with eventites analysed in this paper. B) View of the two studied intervals rich in sandy-oolitic and oolitic eventites. C) Microfacies image of an oolitic grainstone eventite, with quartz grains in their cores.

being sharper and shallower during summer (Brown et al., 1989). In a “greenhouse” world, the origin of the pycnocline was probably dominated by halothermal (salinity-driven) conditions (e.g., Kennett and Stott, 1991; Pak and Miller, 1992; Nunes and Norris, 2006). Internal waves and solitons propagating along the shallow-water pycnocline mostly dissipate over the continental shelf regions of the

world oceans (Wolanski et al., 2004; Quaresma et al., 2007; Lim et al., 2010). Refraction on the shelf strongly orients the packet crests along isobaths and retards their speed of advance (Emery and Gunnerson, 1973; Apel, 2002). Breaking of internal waves on sloping surfaces creates episodic and repetitive high-turbulent events and consequently erosion and transport of sediments (e.g., Pomar et al.,

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Fig. 4. Architectural elements in the sandy-oolitic internalites at Ricla. An internalite commonly contains three basic elements sequentially organized in a down-slope direction: a–b–c–b–a. Occasional elements (d and e) may also occur underlying element c.

2012). In contrast to tempestites (which occur in shallow shelf settings down to the storm-wave base sensu Seilacher, 1982), and turbidites (commonly accumulated on the basin floor), breaking of internal waves on sloping surfaces creates high-turbulent events in mid-shelf settings, when depending on the seasonal thermocline, or deeper on the continental slope and in submarine canyons when it relates to the permanent thermocline (Cacchione and Wunsch, 1974). Although internal waves in the interior of oceans and lakes are as common as surface waves (LaFond, 1966; Munk, 1981; Global-OceanAssociates, 2004; Thorpe, 2005), their impact in shaping sediments has remained largely unrecognized (see review in Pomar et al., 2012). Key evidence to differentiate the depositional processes induced by breaking internal waves from those related to surface storm waves can be gathered in the Upper Kimmeridgian carbonate ramp succession cropping out near Ricla (NE Spain). Sandy-oolitic deposits interbedded with mid-ramp lime mudstones and marls, previously interpreted as tempestites and storm lobes (Bádenas and Aurell, 2001; Bádenas

et al., 2005), are here reinterpreted as internalites (sensu Pomar et al., 2012), the product of breaking internal waves. Evidence indicating sediment reworking by internal waves has been obtained by characterization of the spatial distribution of the sandy-oolitic eventites at outcrop scale and the analysis of architectural elements and stacking pattern of individual eventites in two selected intervals rich in eventites. This work describes the detailed distribution of the architectural elements of eventites generated by breaking of internal waves on a gently sloping ramp sea floor. The character and along-dip relationship of architectural elements within individual internalites are related to variable hydrodynamic processes, with a more precise description and development of the general model on sediment dynamics during breaking of internal waves previously proposed in Pomar et al. (2012). The significance of the studied eventites in a broader context and the possible effects of depth variations of the pycnocline in carbonate ramp settings are discussed.

Fig. 5. Example of internalites 1 to 14 (letters in white denote the type of architectural elements; see Fig. 4). Internalite 1 consists of a lower discontinuous interval of rip-up clast floatstone (occasional d element) overlain by a bed with down-slope dipping cross-lamination (c element), with occasional rip-up clasts, that passes down slope into starved ripples (b element) and thin laminae (a element). Internalites 2 to 7 correspond to attached and detached starved ripples (b elements) separated by muddy layers, deformed by compaction. Internalites 3, 4 and 5 infill a depositional depression in front of internalite 1. Internalites 8 and 9, with down-slope dipping cross-lamination (c element), are separated by an erosional surface marked by occasional rip-up clasts; they pass down slope into starved ripples (b element). Note the erosion surface at the base of internalite 8. Internalites 10 to 13 are amalgamated levels of attached starved ripples (b elements), with minor intercalated muddy intervals. Internalite 14 corresponds to starved ripples (b element) passing down slope into a down-slope dipping cross-laminated bed (c element). An erosion surface underlying c element cuts into internalites 12 and 13, and an undulating top surface is blanketed by mud.

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Fig. 6. Decimetre-thick package of individual internalites 1 to 6 (letters in white denote the type of architectural elements; see Fig. 4). Internalites 1 to 3 are lenticular beds with down-slope dipping cross-lamination (c elements), separated by erosional surfaces. Internalite 4 corresponds to a rip-up clast floatstone bed (d element) with basal erosional surface cutting into internalites 2 to 3. Note the discontinuous muddy interval (see M) preserved from erosion. Lime mudstone rip-up clasts are usually concentrated in erosive furrows; they are variable in size and shape, from rounded (see rC) to angular (see aC). Clasts occasionally occur in down-slope dipping accumulations (see dC). Internalites 5 and 6 consist of down-slope dipping cross-laminated beds (c elements). Note basal erosional surfaces and occasional rip-up clasts (see oC).

2. Sedimentary context of the studied eventites 2.1. The Iberian Kimmeridgian carbonate ramp During the Kimmeridgian, a wide carbonate ramp developed in the Iberian Basin (Fig. 1), an intracratonic basin located in the northeastern part of the Iberian plate (e.g., Salas and Casas, 1993; Bádenas and Aurell, 2008; Aurell et al., 2010). This ramp was around 22° N palaeolatitude (Osete et al., 2011) and opened to the Tethys Ocean to the east, facing the trade winds of hurricanes and winter winds (Marsaglia and Klein, 1983; Price et al., 1995; Bádenas and Aurell, 2008). Shallow (inner- to proximal mid-ramp) settings included a wide range of reefal- and grain-supported skeletal, oolitic, oncolitic, peloidal and intraclastic facies, with intermittent input of siliciclastics supplied from the emerged Ebro and Iberian massifs. Offshore, the mid- to outerramp settings were characterized by monotonous successions of lime mudstones and marls, including a distal mid-ramp “transitional belt” characterized by sandy-oolitic-bioclastic eventites interbedded with the mud-dominant successions. In the Kimmeridgian succession cropping out near Ricla, the transition between shallow- and relatively deep deposits of the Iberian carbonate ramp can be analyzed along a 6-km continuous exposure. Here, the “transitional belt” includes abundant eventites deposited during a transgressive episode at the Eudoxus Zone (TST of the third-order Kim2 Sequence: Fig. 1B and C). These deposits are overlain by prograding (HST) shallow-water (high-energy and lagoonal) oolitic and bioclastic facies (Bádenas and Aurell, 2001; Aurell et al., 2010).

2.2. Spatial distribution of eventites in the Ricla outcrop The overall facies distribution in the TST deposits of the Kim2 Sequence across the Ricla outcrop is shown in Fig. 2. In proximal areas, these deposits include aggradational metre-sized coral-microbial buildups, with branching corals, chaetetid sponges, stromatoporoids and variable amounts of microbial crusts. These buildups are surrounded by skeletal- and oncolitic rudstone aprons composed of poorly sorted reefal-derived debris and in-situ growing oncoids within a sandy matrix with ooids and quartz grains (Bádenas et al., 2005). These facies gradually thin down dip to cm-thick skeletal- or oncolitic rudstones interbedded with lime mudstones and marls. Down dip, and detached from the skeletal/oncolitic rudstones, sandy-oolitic eventites, located in a distal mid-ramp position, range from fine/medium sandstones to pure oolitic grainstones, with quartz grains and ooids usually less than 1 mm in size, but locally with coarser grains such as echinoids, coral fragments, oncoids, quartzite pebbles and lime mudstone rip-up clasts.

The sandy-oolitic eventites of Ricla found in distal mid-ramp position were previously related to storm events and, based on grain size, thickness and sedimentary structures, were interpreted as storm lobes (dmthick cross-bedded deposits), proximal tempestites (cm-thick ripple beds) and distal tempestites (thin-sand laminae) (Bádenas and Aurell, 2001; Bádenas et al., 2005). It is obvious that the main components of these eventites (i.e., quartz grains, ooids) were derived from land or from the shallowest portion of the ramp, most probably via storm resedimentation (e.g., Bádenas and Aurell, 2001). However, based on the distribution of eventites at outcrop scale and relationships with shallower facies, Pomar et al. (2012) suggested that the resedimented grains were reworked by high-turbulent events generated in the midramp setting by breaking internal waves, so that the eventites actually correspond to internalites (Fig. 2). Their underpinning rationale includes: (1) sandy-oolitic eventites are concentrated in discrete intervals detached from the shallower-water reef-apron successions; (2) the eventites do not show a coarsening-thickening upward trend typical of storm-generated successions; (3) this distribution cannot be attributed to erosion effects (“cannibalism”) of repeated storm events because the eventites gradually thin and pinch out both up dip and down dip. 3. Architectural elements of internalites The architectural elements and stacking pattern of individual internalites have been studied in two stratigraphic intervals (2-m in total thickness) located c. 11 m above the lower boundary of the studied TST (Figs. 2 and 3). In this interval, the internalites are well developed in a continuously exposed outcrop covering, down dip, a c. 2-km wide mid-ramp segment (between reference logs 5 and 7 in Fig. 2). The sandy-oolitic internalites commonly contain three basic architectural elements (Fig. 4): (a) thin laminae, (b) starved ripples, and (c) a lenticular bed with down-slope dipping cross-lamination. When these three elements are present in an individual internalite, they are sequentially organized in the dip direction within the internalite, so that the thin laminae (a) pass down slope into starved ripples (b) and then into a lenticular bed with down-slope dipping cross-lamination (c) that thins out and passes again into starved ripples (b) and finally to thin laminae (a). Locally, other occasional elements may be associated with element c, the cross-laminated bed, namely a lenticular bed of rip-up clast floatstone (d), and a lenticular bed with up-slope dipping cross-lamination (e). A basal erosion surface, with several centimetres incision in the underlying sediments, usually occurs at the base of the elements c, d and e. These elements also occur on depositional depressions left by previous internalites (see Section 5). The down-slope dipping cross-laminated lenticular beds (c element), with S- to SE-directed palaeocurrents, are up to 20 cm-thick and extend for less than 5 m in a dip direction (Figs. 5 and 6). Rip-up clasts (lime

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Fig. 7. Examples of starved-ripples and thin-sand laminae in internalites (architectural b and a elements, in white; see Fig. 4). A) Internalites 1 to 5 form a package of amalgamated ripples (b elements), locally separated by muddy layers. Ripples have predominant downslope dipping cross-lamination. Internalite 3 consists of an isolated ripple with trough cross-lamination, located in the variably eroded depositional trough between detached ripples of internalite 2. Muddy rip-up clasts occur in internalite 5. Internalites 6 to 8 are discontinuous thin-sand laminae (a elements) within a muddy interval. Internalite 9 is an isolated internalite formed by attached ripples with down-slope dipping crosslamination and sharp (non-gradational) lower and upper boundaries. B) An isolated internalite consisting of attached asymmetrical starved ripples (b element), with mud offshoots on the stoss side and sand offshoots on the lee side. C) Top surface of an internalite consisting of attached asymmetrical ripples (b element) with sinuous crests blanketed by muddy sediment. Note regularity of ripple crest spacing.

mudstone fragments) are occasionally abundant, resting parallel to the inclined laminae. Grain-size trends of successive laminae are complex, usually encompassing several fining-, but locally also coarseningupward lamina sets. The upper boundary, when preserved, is a flat to

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undulating surface blanketed by muddy sediment. The c element thins both up- and down slope and passes into starved ripples (b element; Fig. 5). An individual cm-thick train of attached or detached starved ripples, with occasional rip-up clasts, forms the architectural b element (Figs. 5 and 7). It may locally include or be replaced by a lower interval with parallel- to low-angle lamination (Fig. 8). Extension in dip direction is highly variable, from a few decimetres to several tens of metres. Lower bounding surfaces are sharp and commonly flat, although concave-up shapes may result from loading deformation. Individual ripples are predominantly asymmetric, with down-slope dipping internal cross-lamination where preserved, and straight to sinuous crests with a NE–SW orientation (Fig. 7C). Occasional isolated ripples with concave base and trough cross-lamination occur in troughs of starved ripples of previous internalites (Fig. 7A). Ripple tops are sharp (non-gradational) and blanketed by muddy sediment. Mud offshoots within sand laminae on the stoss side of ripples are common (Figs. 7 and 8). Sand thready-fringes on the lee side of ripples interpenetrating lateral muddy sediments also occur (Fig. 9A). By analogy to “mud offshoots” definition (“mud drapes in ripple foresets”: Shanmugam et al., 1993), we have termed these sand threadyfringes as “sand offshoots”. Thin, mm-thick, sand laminae (a element) are frequent within the lime mudstones beds. Within the a–b–c–b–a down-slope succession (Fig. 4), the thin laminae represent either the up-slope or the down-slope element of a starved-ripple train (b element; Fig. 5). The extent of thin laminae is difficult to assess because they are discontinuous, their exposure is not complete and they are frequently bioturbated. Laminae are parallel to the bedding surfaces of limestone beds in which they are included. However, the local presence of down-slope dipping thin-sand laminae (Fig. 10), and thin‐sand offshoots in muddy-ripple foresets (i.e., mixed mud-sand ripples; Fig. 9B) indicates a certain degree of depositional inclination. Thinsand laminae underlying internalites are often disrupted as a result of interpenetration by fine sand- and muddy layers (see Fig. 8). The rip-up clast floatstone (occasional d element; Fig. 4) consists of a lenticular bed with thickness ranging from few- to 10 cm and variable down-slope extension, usually less than 5 m (see Figs. 5 and 6). Rip-up clasts are made from the lime mudstones in which internalites are intercalated including, in some clasts, fine-sand laminae. Size and shape of rip-up clasts are highly variable, from mm- to cm-sized subrounded to cm-sized flat and angular clasts. The rip-up clasts are usually irregularly distributed within the bed and concentrated in patches within erosive furrows, although they can occur as imbricated clasts dipping up slope, or forming down-slope dipping accumulations. Amalgamation of rip-up floatstone beds can locally produce complex internal structures. A lenticular bed with up-slope dipping cross-lamination (e element; Fig. 4) is occasionally recognized within the internalites (Fig. 10A). Thickness is up to 10 cm and extension in dip direction is usually less than 0.5 m. Where preserved, this element is overlain by the downslope dipping cross-laminated bed (c element) and separated by a flat to undulated erosion surface (Fig. 10A). The internal structure may locally be complex and formed by shingled stacking of individual beds separated by thin muddy intervals or by some rip-up clasts (Fig. 10B). 4. Interpretation: generation of architectural elements by breaking internal waves Breaking of internal waves on sloping surfaces creates episodic and repetitive high-turbulent events and consequently erosion and transport of sediments (Southard and Cacchione, 1972; Ribbe and Holloway, 2001; Apel, 2002; Fringer and Street, 2003; Bogucki et al., 2005; Thorpe, 2005; Gilbert et al., 2007; Bourgault et al., 2008; Boegman and Ivey, 2009; Lim et al., 2010). Thorpe and Lemmin (1999) have reported that the internal-wave surf zone has some, but

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Fig. 8. Examples of internalites containing an interval with parallel- to low-angle lamination (architectural b element; see Fig. 4). A) Internalite (2) interbedded with lime mudstones, overlies an erosion surface and includes: a lower interval (2.1) of fine-grained parallel laminae, a coarser middle interval (2.2) with parallel laminae and an upper interval (2.3) of asymmetrical starved ripples with internal down-slope dipping cross-lamination and mud offshoots on the stoss side. Interval (1) mostly consists of lime mudstones with thin-sand laminae (architectural a element) that progressively increase upward; in the upper part (1.2), thin‐sand and mud-laminae are disrupted. Interval (3) consists of lime mudstones with few thin-sand laminae. B) Internalite bed only consisting of a low-angle cross-laminated sandstone, isolated within muddy intervals.

possibly not all, the characteristics of the conventional “surface-wave” surf zone. Bourgault et al. (2005) have shown direct field observations of an internal solitary wave train impacting a shoaling bottom creating boluses of turbulent water that move onshore from the breaking zone and the creation of an intermediate layer that transports mixed water away from the mixing site. Southard and Cacchione (1972), based on laboratory experiments on breaking internal waves over a planar sloping bottom, have shown the waves to break abruptly as they shoaled, producing a breaker in the form of a turbulent and rapidly dissipating vortex. In these experiments, sediment moved up slope by the breakers, partly in suspension, and down slope by the compensating return flow, as bedload (swash and backwash phases in Cacchione and Pratson, 2004). Predominant flow at the bed and, therefore, also net sediment transport, was down slope. Based on these experiments, Pomar et al. (2012) proposed a preliminary model on sedimentary dynamics of breaking internal waves for the Ricla eventites, which consider three sedimentary phases: breaking, swash run-up and backwash. Turbulence and vortices induced by breaking internal waves on a muddy/sandy sea floor (i.e., breaking: Fig. 11A) induced erosion, the expression of which is the irregular erosive surface underlying thicker

architectural elements of c, d or e. Differential pressures on the seafloor generated by the internal wave trains, in a similar way to that produced by surface storm waves (e.g., Foda, 2003), might also facilitate erosion. The pressure distribution on the bottom sediment underneath nearbreaking or broken waves is transmitted into the porous bed, where it induces a flow and exerts a seepage force on the sediment grains within the bed. The horizontal component of this seepage force is related to the horizontal pressure gradient of the pressure distribution on the bottom and is therefore particularly pronounced under the steep front of a forward-leaning breaking wave and may, if sufficiently large, cause disruption of the bed (Schwab and Lee, 1988; Puig et al., 2004; Chen and Hsu, 2005; Madsen and Durham, 2007; Chang, 2011). An excess of pore-water pressure, and induced shear stress, exceeding the shear resistance of the overburden sediment can induce sediment disruption and liquefaction. Traction currents can transport more sediment once liquefaction has occurred (Clukey et al., 1985). Strachan and Evans (1991) suggested a sediment failure to have been triggered by excess of pore water pressures that might have been induced by internal wave action; the sediment body is thought to have failed by liquefaction acting retrogressively up slope. Laboratory experiments suggest fluidization of a

Fig. 9. Examples of sand offshoots in internalites and mixed mud-sand ripple lamination. A) Sand offshoots in the lee side of a ripple (architectural b element), passing down slope into mixed sand-mud lamination. B) Muddy interval with down-slope dipping sand offshoots (mixed sand-mud ripple lamination). Note sand offshoots disappearing both up- and down slope, and subsequent onlapping muds with parallel thin-sand laminae.

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Fig. 10. Examples of internalites including up-slope dipping cross-laminated beds (architectural e element; see Fig. 4). A) Package of internalites 1 to 6. Internalite 1 is a ripple bed (b element) which passes down slope into thin-sand laminae (a element). Ripples in internalite 1 are not well preserved due to erosion. Internalite 2 is a ripple train (b element) blanketed by a muddy interval that becomes thicker down slope (right of the picture) and contains low-angle down-slope dipping thin-sand laminae. Internalite 3 is formed by a down-slope dipping crosslaminated bed (c element) separated from internalite 2 by an erosion surface. Eventite 4 is formed by a lenticular bed with up-dipping cross-lamination (e element). Note lower erosion surface cutting into internalites 1 to 4 and the muddy interval. Internalites 5 and 6 are amalgamated and consist of ripples (b element) passing down slope into down-slope cross-laminated beds (c element). Internalites 4 and 5 are separated by an erosion surface; however, down slope, there is a muddy interval between them, preserved from erosion. B) Two packages of internalites (p1 and p2) separated by a muddy interval, but laterally amalgamated (p1+ p2). Package 1 includes internalites 1 and 2 in down-slope shingling geometry; each internalite is formed by a down-slope dipping cross-laminated bed (c element) passing down slope to a thin ripple and parallel-laminated bed (b element). Package 2 encompasses internalites 3 and 4. Internalite 3 consists of a lower part with a complex up-slope dipping cross-laminated bed (e element), deposited in the depositional depression left by package 1. Internalite 3 includes a thin upper part with down-slope dipping cross-lamination (c element) passing up slope into ripples (b element).

bed may take place on a very short timescale (around a second) when induced by a sudden negative pressure loading (Foda et al., 1997). On the Ricla ramp, pressure changes as internal waves travelled up ramp may have created high-shear stress on the seafloor, which induced also pressure changes in the pore waters and facilitated erosion and generation of rip-up clasts. The disrupted intervals underlying internalites could then be attributed to convolution of bottom sediment due to differential pressure. In the breaker zone, erosion of muddy and sandy sediments generated a turbid sediment-laden water mass. Rip-up clasts may have moved up slope a short distance but they rapidly settled near the generation area (i.e., “dumped heap”: Fig. 11B). The variable size and shape of rip-up clasts in the floatstone bed (d element) indicate variable abrasion and transport, but even rounded clasts underwent little transportation from the site of origin (Smith, 1972). The lenticular bed with up-slope dipping cross-lamination (e element) is associated with the swash run-up sediment transport. The bimodal character of the sediments facilitated segregation of grains from matrix, so that ooids and quartz grains were transported as bedload while the mud component was winnowed in suspension. Deposits generated during up-slope flow are only preserved within depressions (mostly erosive depressions produced in the breaker zone, but also depositional depressions left

following sedimentation of previous internalites), indicating the compensating return flow is the predominant agent in the net transport of sediments (backwash phase: Fig. 11C). Imbricated clasts dipping up slope, or forming down-slope dipping accumulations in the floatstone bed, also reflect reworking by the backwash flow. The sediment-laden backwash flow led the deposition of the lenticular bed with down-slope dipping cross-lamination (c element), the starved ripples with down-slope dipping internal crosslamination (b element), and the thin-sand laminae (a element). These sedimentary structures indicate transport of grains was predominantly by traction. The main body of the down-slope flow formed the cross-laminated bed (Fig. 11C), when it reached a depression on the seafloor, such as the erosion trough produced in the breaker zone or a bathymetric low created by deposition in the forefront of previous internalites. Thin-sand laminae and starved ripples occurring up slope of the cross-laminated bed accumulated from the sand remnants in the queue of the backwash flow. Those down slope of the cross-laminated bed formed from the sand remnants in the backwash flow, after deposition of the main cross-laminated body. The existence of fining- and coarsening-upward lamina sets within the cross-laminated bed indicates a pulsating regime of the tractive backwash flow. Rip-up clasts within the inclined laminae

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Fig. 11. Sketches depicting the sediment dynamics during breaking of internal waves on a shoaling surface (modified from Pomar et al., 2012), and the origin of the different architectural elements in the Ricla internalites (see Fig. 4). A) Breaking of internal waves creates turbulent vortices and entrainment of sandy oolites and mudstone rip-up clasts. B) Immediately after breaking, an intraclastic “dumped heap” (d element) and an up-slope dipping cross-laminated unit (e element) may form during the initial swash run-up. C) The compensating backwash flow transports sediments down slope as bedload, producing thin-sand laminae (a element), starved ripples (b element) and a down-slope dipping cross-laminated bed (c element). Thin-sand laminae and starved ripples occurring up slope accumulated from the sand remnants in the queue of the backwash flow; the main body of the down-slope flow formed the cross-laminated bed, when it reached a depression on the seafloor; down-slope starved ripples (locally with mud- and sand offshoots) and thin lamina formed from the sand remnants in the backwash flow, after deposition of the main c element.

also indicate some degree of reworking of previously generated clasts, such as erosion by the backwash flow of the “dumped heap” (e element) settled during the previous run-up flow. Up slope and down slope of the cross-laminated bed a “clearer” sediment-laden flow led to the deposition of starved ripples. Local intervals with parallel- to low-angle lamination underlying ripples probably were deposited with higher flow velocity, with Froude number ≥ 1. Ripples include both mud offshoots and sand offshoots interpenetrating lateral muddy sediments, which cannot be explained by alternating low- and high-energy conditions as proposed for sigmoidal mud offshoots by Shanmugam et al. (1993). These offshoots point to similar hydrodynamic behaviour and avalanching processes for mud and sand, and this requires flocculation of mud. Flocculation is affected by particle concentration within the fluid and intensity of turbulence. Floccule deposition is influenced by turbulence, bed shear stress, sediment concentration, and settling velocity. Swift moving (15–30 cm/s) muddy suspension is prone to flocculate over a wide range of salinities and sediment compositions, and the flocculated material travels as bedload and forms floccule ripples (Schieber et al., 2007; Schieber and Yawar, 2009). These authors have experimentally shown that muds

can be transported in bedload at current velocities that would suffice to transport and deposit sand. Floccule ripples are cross-laminated with geometries very similar to those produced in sandy sediments, but have higher water content. Mixed mud-sand ripples and thinsand inclined laminae occurring locally in Ricla evidence similar mud flocculation processes. An alternative to flocculation, in order to explain the similar hydrodynamic behaviour and avalanching processes for mud and sand, is to consider erosion processes generating sand-size mud fragments, similar to those obtained in flume experiments by erosion on soft-soupy muds (Schieber et al., 2010).

5. Stacking of internalites At the studied interval, internalites occur in two clusters encased in the muddy mid-ramp succession (Fig. 12A), into which several internalite packages gradually thin and, like fraying fringes, pinch out both up dip and down dip. These clusters are dm- to m-thick and 1- to more than 2 km of extension in dip direction and, at outcrop scale, correspond to the intervals rich in sandy-oolitic eventites (Fig. 2).

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Fig. 12. Stacking of internalites. A) Internalites occur in packages, in which the architectural elements are commonly organized in a similar way. A lower interval, with thin-sand laminae and ripples (a and b elements), is overlain by few cross-laminated beds (c elements) that, in turn, are often overlain by ripples. This vertical succession of architectural elements is repeatedly related to a down-slope shingled stacking of individual internalites, but up-slope shingling of internalites also occurs. These internalite packages are grouped in clusters encased in the muddy mid-ramp succession, detached from the shallower facies. Within these clusters, packages gradually thin and, interfingered with muds, pinch out both up dip and down dip. B) Internalite packages can be, locally, stacked in downlapping configuration (“lobe-like” progradation), infilling the forefront depression of a bulge on the seafloor created by a pile of previous internalites. C through E) Field sketch and photographs of two internalite packages (p1 and p2) with internal downlapping configuration of c elements of internalites, with an intervening wedge of isolated ripples (b elements).

Individual internalites concentrate in packages (Fig. 12A). The thickest part of an internalite package contains several stacked c elements (dm-thick and some 10's m extension in dip direction). Mostly, c elements are stacked in down-slope shingling configuration, suggesting each occurs in the forefront residual depression of the c element of a previous internalite, partially modified by erosion (Fig. 12A, see also Figs. 6 and 10B). However, physical tracking, in dip direction, of both single internalites and internalite packages, indicates that up-slope shingling also occurs. Within a package, the architectural elements are commonly organized vertically in a similar way (Fig. 12A, see also

Fig. 5): intervals consisting of thin-sand laminae and ripples (a and b elements) are overlain by few cross-laminated beds (c elements, occasionally d and e elements), often in shingling configuration, which in turn, can be overlain by ripples, and then by thin-sand laminae. This vertical stacking of internalites within a package results from the upand down-slope shift of stacked internalites. Unusually thick internalite stacks (up to 70 cm) occur in distal position within the Ricla outcrops (Fig. 12B to D). These stacks are “lobelike”, with lensoidal geometry in the depositional strike direction and marked sigmoidal shape having b20 m of extension in the dip

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direction. Within the “lobe-like” stack, two packages can be differentiated (p1 and p2 in Fig. 12C, D), based on the stacking patterns. Individual packages consist of downlapping c elements (down-slope dipping cross-laminated beds) of successive internalites bounded by mm- to cm-thick mud laminae, preferentially at the toe (Fig. 12C). At the toe of package p1 (Fig. 12D), a wedge of mud with ooliticsandy ripples (b elements) passes up dip to a thin mud layer and down dip to muds with thin-sand laminae (a elements). On top of package p2, dm-wide hummocks occur and bioturbation has locally destroyed the internal lamination. 6. Interpretation: fluctuations of the pycnocline Up- and down-slope shift of internalite packages points to the upand down-slope migration of the breaker zone, which can in turn be related to the fluctuation of the pycnocline. Bedding configuration and stacking patterns in “lobe-like” bodies result from the infill, by successive internalites, of a larger depositional depression at the forefront of a package characterized by vertical stacking of internalites (Fig. 12B). Vertical stacking of internalites would elevate the source point in the forefront of the package that would allow the successive internalites to stack in downlapping configuration. This depositional mechanism is coherent with the location of the “lobe-like” bodies in the distal position of the internalites accumulation. The two studied clusters of grainy internalites at Ricla encased in the muddy midramp facies are thought to reflect periods with enhanced sediment supply from shallow-water settings and/or variations of water stratification affecting the energy of the internal waves. The origin of the pycnocline and ocean circulation in the studied Kimmeridgian carbonate ramp was probably dominated by halothermal (primarily salinity-driven) conditions due to “greenhouse” climate, in contrast to modern open oceans where the pycnocline is mainly induced by temperature, and secondarily by salinity gradients (e.g., Kennett and Stott, 1991; Pak and Miller, 1992; Nunes and Norris, 2006). In interior seas, the seasonal pycnocline is commonly strongly influenced by riverine discharge. Low-salinity stratified water masses have been described in the northern Indian Ocean (Sri Lanka east coast), caused by the high seasonally varying precipitation and river runoff (Santek and Winguth, 2007). Therefore, it is plausible to suggest for the Ricla succession that the clusters of internalites accumulated during periods of increased riverine discharge that resulted in both sharpening of the pycnocline and hence internal waves as well as increased sediment delivery (quarz grains, quartzite pebbles) from the emerged areas of the Ebro and Iberian massifs (Fig. 1). The possible effects of storm activity on sediment supply and generation of internal waves in the Kimmeridgian carbonate ramp can also be considered. Storms would increase the input of landderived grains accumulated in shallower areas and shallow-water coarse grains (ooids, skeletal grains) into mid-ramp setting. In addition, storms

would generate perturbations in the pycnocline, as internal waves can be excited by storms (e.g., Staquet and Sommeria, 2002; Santek and Winguth, 2007). 7. Discussion: internalites vs. tempestites The coarse components of the mid-ramp eventites at Ricla were derived from land (quartz grains, occasional quartzite pebbles) and from the shallowest portion of the ramp (ooids, occasional bioclasts) by different processes, including hyperpycnal flows or storm-induced currents (Bádenas and Aurell, 2001). The analysis of the architectural elements and the stacking pattern of these eventites indicate internal-wave reworking and certain down-dip transport of sediments existing in mid ramp setting, in this case of previous resedimented deposits, and provide a facies model for deposits originated from breaking internal waves (Fig. 4). In mid-ramp settings, tempestites and/or internalites can occur interbedded within the mud-dominated successions. Some key criteria can be used to differentiate tempestites and internalites (Table 1): (1) Stacking of eventites. Internalites concentrate in discrete intervals in distal mid-ramp position detached from the shallowwater successions, gradually thinning-out to disappear both up dip and down dip (Pomar et al., 2012; Fig. 2). Individual internalite beds stack in up- and down-dip shingling configuration, reflecting the up- and down-dip migration of the pycnocline (and/or variable amplitude of the breaking wave). In Ricla, the fact that eventite-rich intervals are located in the lower part of the TST, with a progressive landward migration, is coherent with the progressive landward shift of the pycnocline intersecting the seafloor during transgression. In contrast, tempestites would increase to the shoreface and stack in thickening- and coarseningupwards succession, reflecting the shallowing-upward character of the surface-storm beds accumulation (e.g., Burchette and Wright, 1992). (2) Sedimentary processes. Both tempestites and internalites encompass an erosional phase and a depositional phase during waning of turbulence. a) Internalites are associated to erosion in the mid-ramp settings (breaker of the internal waves), whereas little or no erosion occurs in shallower settings. Contrarily, erosion processes due to storm waves dominate in shallower areas, so that “cannibalism” and/or amalgamation increases inshore in tempestites (Aigner, 1985). Rip-up clasts in internalites are derived from erosion in mid-ramp settings (breaker zone), but in tempestites can be derived from shallower settings. b) Internalite beds are deposited from tractive flows. Although predominantly down dip, internalites reflect both up- and down-dip transport processes (run-up and backwash flows).

Table 1 Key differences between the Ricla internalites and tempestites. Internalites generated by breaking internal waves in mid-ramp settings Stacking of eventites

Tempestites

Concentrated in discrete intervals in distal mid-ramp position, detached from Tempestite beds increasing to the shoreface, attached to shallowthe shallow-water successions water successions Gradually thins-out to disappear both up dip and down dip Up-slope increase of tempestites; down-slope decrease of tempestites Bed stacking in shingling configuration, reflecting up- and down-slope miThickening- and coarsening-upwards successions reflecting the gration of the pycnocline and/or variable amplitude of the breaking wave shallowing-upward character of storm beds accumulation Sedimentary Erosional Erosion localized in mid ramp position, associated to the breaker of the Predominant erosion in shallow areas processes phase internal waves Little or no erosion towards the shallower areas Increase of erosion (“cannibalism” and/or amalgamation) toward the shallower areas Rip-up clast from the internal-wave breaker zone (mid ramp) Rip-up clasts, if any, can be from shallower water Depositional Derived from tractive flow Derived from density and oscillatory flows phase Up-dip and down-dip transport, although preferentially down dip Down-dip transport Down-dip organization of the architectural elements, as product of bedload Vertical grading of grain size and sedimentary structures and the existence of depositional or erosional depressions indicating decreasing flow competence

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Recurrent organization of the architectural elements in dip direction (a–b–c–b–a; Fig. 4) responds to bedload differences in the different parts of the tractive flow, and to the existence of depressions (depositional or erosional) on the seafloor. Crossbedded elements formed by the main tractive flow and accumulated preferentially on seafloor depressions. Starved ripples and thin‐sand laminae are related to the sand remnants in the queue of the backwash flow. In contrast, tempestites derive from storm-generated density flows travelling down slope, combined with storm-wave action. The decreasing competence of the density flow and the storm-wave relaxation is reflected in the upward grading of grain size and associated sedimentary structures. The defined facies model for the Ricla internalites includes all the architectural elements (a–b–c–b–a) observed at the studied interval. However, other sandy-oolitic eventites in Ricla do not include the down-slope dipping cross-laminated bed (element c), and only thinsand laminae (element a) and cm-thick ripple beds (element b) are present. This is the case of most of the eventites found at the lowermost part of the studied TST in Ricla (Fig. 13). Thin-sand laminae and cmthick ripple beds are related in dip direction, indicating that they may correspond to “a–b–a” internalite type. In addition, they concentrate in distal mid-ramp position detached from shallower facies, with a gradual up-dip and down-dip decrease in number. The shingling configuration of these intervals rich in “a–b–a” internalites is coherent with a

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landward migration of the pycnocline during early transgression. The absence of the architectural element c could be related to small amount of sand-grain sediments. Lower riverine discharge might have controlled decreased coarse sediment delivery to mid-ramp settings (via hyperpycnal flows or storm-induced currents).

8. Conclusions Despite the ubiquity of internal waves in oceans and lakes, internal wave deposits (internalites) are seldom recognized in the sedimentary record. For shelf and ramp deposits, they require differentiation from tempestites, and from turbidites in deeper settings, with which they share some common features of a basal erosion surface and a subsequent depositional phase during the waning of turbulent conditions. Criteria for recognition of internalites, still to be fully developed, can be obtained by analyzing the spatial organization of architectural elements and associated sedimentary structures within eventite beds. A significant portion of eventites of Upper Kimmeridgian Ricla succession can be reinterpreted according to the processes associated to the break of internal waves on a sloping sea floor with bimodal sediment type, sand and mud. Breaking of internal waves on sloping surfaces creates episodic highturbulent events that remobilize sediment at the depth at which a pycnocline intersects the sea floor. Internalites are concentrated in discrete intervals in distal mid-ramp positions that are detached from

Fig. 13. Facies architecture based in the detailed logging and correlation across the lowermost part of the TST of the Kim2 Sequence at Ricla (see Fig. 2 for location; updated from Aurell et al., 2011). The number of sandy-oolitic cm-thick eventites in correlatable intervals is higher in distal mid-ramp setting, detached from shallower facies, indicating that they may correspond to internalites.

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coeval shallow-water successions. They do not have the coarseningthickening upward trend typical of storm-generated successions and they gradually thin-out to disappear both up- and down dip, interfingering with muddy mid-ramp lithofacies and little or no erosion towards shallower areas. Within internalites, diverse architectural elements can be related to breaking internal waves and associated turbulent flows: internal wave breaker zone (basal erosion surface), “dumped heap” in the surf zone (mud-chip floatstone bed: element d), up-dip swash (up-slope dipping cross-laminated bed: element e) and backwash flow (down-slope dipping cross-laminated bed: element c, isolated starved ripples: element b, and thin-sand laminae: element a). Individual internalites stack in packages, within which they are up- and down-slope shifted, often in shingling configuration. This staking pattern is suggested to reflect the landward and seaward migration of the internal waves breaker zone (fluctuation of the pycnocline). Clusters of internalite packages pinching out both up dip and down dip and encased in the muddy mid-ramp facies reflect changes in sediment supply and/or variations in water stratification affecting the energy of the internal waves. Acknowledgements This work is a contribution to the research projects Grupo Reconstrucciones Paleogeográficas (Aragón Government) and CGL201124546 (to B.B. and M.A.) and CGL2009-13254 (to L.P. and M.M.). We are grateful to the editor Brian Jones, and to Paul (Mitch) Harris and an anonymous reviewer for comments and suggestions on the original version of the manuscript. References Aigner, T., 1985. Storm depositional systems, dynamic stratigraphy in modern and ancient shallow-marine sequences. In: Friedman, G.C., Neugebauer, H.J., Seilacher, A. (Eds.), Lecture Notes in Earth Sciences. Springer, Berlin, pp. 1–171. Apel, J.R., 2002. Oceanic internal waves and solitons. In: Jackson, C.R. (Ed.), An atlas of internal solitary-like waves and their properties. Global Ocean Associates. Prepared for Office of Naval Research – Code 322 PO, Alexandria, VA, pp. 1–40. http://www. internalwaveatlas.com/Atlas2_PDF/IWAtlas_Pg001_Background&Theory.pdf. Apel, J.R., Ostrovsky, L.A., Stepanyants, Y., Lynch, J.F., 2007. Internal solitons in the ocean and their effect on underwater sound. The Journal of the Acoustical Society of America 121, 695–722. Aurell, M., Bádenas, B., Ipas, J., Ramajo, J., 2010. Sedmentary evolution o an Upper Jurassic carbonate ramp (Iberian Basin, NE Spain). In: van Buchem, F., Gerdes, K., Esteban, M. (Eds.), Reference models of Mesozoic and Cenozoic carbonate systems in Europe and the Middle East — stratigraphy and diagenesis: Geological society of London, special publication, 329, pp. 87–109. Aurell, M., Bádenas, B., Pomar, L. Colombié C., Caline, B., Ipas, J., Martínez, V., San Miguel, G., Al-Nazghah, M.H., 2011. The Kimmeridgian-Lower Tithonian carbonate ramps (Upper Jurassic, NE Spain): architecture, facies distribution and cyclostratigraphy. Geo-Guías 8, 45–86. Bádenas, B., Aurell, M., 2001. Proximal-distal facies relationships and sedimentary processes in a storm dominated carbonate ramp (Kimmeridgian, northern Iberian basin). Sedimentary Geology 139, 319–340. Bádenas, B., Aurell, M., 2008. Kimmeridgian epeiric sea deposits of northeast Spain: sedimentary dynamics of a storm-dominated carbonate ramp. In: Holmden, C., Pratt, B. (Eds.), Dynamics of Epeiric Seas: Geological Association of Canada, special paper, 48, pp. 55–71. Bádenas, B., Aurell, M., Gröcke, D.R., 2005. Facies analysis and correlation of high-order sequences in middle–outer ramp successions: variations in exported carbonate on basin-wide δ13Ccarb (Kimmeridgian, NE Spain). Sedimentology 52, 1253–1275. Boegman, L., Ivey, G.N., 2009. Flow separation and resuspension beneath shoaling nonlinear internal waves. Journal of Geophysical Research 114, C02018. Bogucki, D.J., Redekopp, L.G., Barth, J., 2005. Internal solitary waves in the Coastal Mixing and Optics 1996 experiment: multimodal structure and resuspension. Journal of Physical Oceanography 110, C02024. Bourgault, D., Kelley, D.E., Galbraith, P.S., 2005. Interfacial solitary wave run-up in the St. Lawrence Estuary. Journal of Marine Research 62, 1001–1015. Bourgault, D., Kelley, D.E., Galbraith, P.S., 2008. Turbulence and boluses on an internal beach. Journal of Marine Research 66, 563–588. Brown, J., Colling, A., Park, D., Phillips, J., Rothery, D., Wright, J.D., 1989. Seawater: its composition, properties and behavior. Pergamon Press and The Open University, Oxford. 238 pp. Burchette, T.P., Wright, V.P., 1992. Carbonate ramp depositional systems. Sedimentary Geology 79, 3–57. Cacchione, D., Pratson, L., 2004. Internal tides. American Scientist 2, 130–137.

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