Feature and duration of metre-scale sequences in a storm-dominated carbonate ramp setting (Kimmeridgian, northeastern Spain)

Sedimentary Geology 312 (2014) 94–108

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Feature and duration of metre-scale sequences in a storm-dominated carbonate ramp setting (Kimmeridgian, northeastern Spain) C. Colombié a,⁎, B. Bádenas b, M. Aurell b, A.E. Götz c, S. Bertholon a, M. Boussaha d a

Laboratoire de Géologie de Lyon, Université Claude Bernard, Ecole Normale Supérieure, CNRS, 2 Rue Raphaël Dubois, 69622 Villeurbanne Cedex, France Dpto. Ciencias de la Tierra, Universidad de Zaragoza, 50009 Zaragoza, Spain University of Pretoria, Department of Geology, Private Bag X20, Hatfield, 0028 Pretoria, South Africa d University of Copenhagen, Department of Geosciences and Natural Resource Management, Øster Voldgade 10, Copenhagen 1350, Denmark b c

a r t i c l e

i n f o

Article history: Received 9 August 2014 Accepted 11 August 2014 Available online 23 August 2014 Editor: B. Jones Keywords: Carbonate ramp Tempestite Cyclostratigraphy Late Jurassic Northeastern Spain

a b s t r a c t Metre-scale sequences may result from the combined effects of allocyclic and autocyclic processes which are closely inter-related. The carbonate ramp that developed northwest of the Iberian Basin during the late Kimmeridgian was affected by northwestward migrating cyclones. Marl–limestone alternations that settled in mid-ramp environments contain abundant mm to cm thick coarse-grained accumulations that have been related to these events. The aim of this paper is to determine the impact of storm-induced processes on the metre-scale sequence features. Four sections (R3, R4, R6, and R7), which are 5 to 7 m in thickness, were studied bed-by-bed along a 4 km-long outcrop, which shows the transition between the shallow and the relatively deep realms of the middle ramp. Metre-scale sequences were defined and correlated along this outcrop according to the detailed microfacies analysis of host, fine-grained deposits, palynofacies and sequence-stratigraphic analyses, and carbonand oxygen-isotope measurements. The evolution through time of sedimentary features such as the size of quartz grains and the relative abundance of grains other than quartz (i.e., muscovite, bivalve, ooid, and intraclast) does not correlate from one section to the other, suggesting that the finest as well as the coarsest sediment was reworked in these storm-dominated environments. Small- and medium-scale sequences are defined according to changes in alternation, marly interbed, and limestone bed thickness, and correlated from one section to the other. Because of the effects of storms on sediment distribution and preservation, sequence boundaries coincide with thin alternations and marly interbeds in the most proximal sections (i.e., R3, R4), while they correspond to thin alternations and limestone beds in the most distal sections (i.e., R6, R7). Field observations and palynofacies analyses confirm this sequence-stratigraphic analysis. The excursions in carbon- and oxygen-isotope values are consistent with the lithological correlations, but in themselves are not conclusive. Marl–limestone alternations, and small-, and medium-scale sequences are hierarchically stacked, suggesting an orbital control on sedimentation with alternations lasting 20 kyr, small-scale sequences, 100 kyr, and medium-scale sequences, 400 kyr. As biostratigraphic analyses and spectral analysis are not the most appropriate tools to validate this time calibration in such a short interval and highly dynamic system, an alternative approach is developed, which is based on the quantification of the rates of sediment accumulation, preservation, and sea-level rise. © 2014 Elsevier B.V. All rights reserved.

1. Introduction Sequence stratigraphy is an efficient stratigraphic tool to correlate coeval stratigraphic sections whatever the type of deposits they include and their (palaeo)geograpical location. Metre-scale sequences commonly occur in shallow-marine carbonate successions, and often result from eustatic sea-level changes driven by orbital forcing

⁎ Corresponding author. Tel.: +33 4 72 44 58 14; fax: +33 4 72 43 15 26. E-mail addresses: [email protected] (C. Colombié), [email protected] (B. Bádenas), [email protected] (M. Aurell), [email protected] (A.E. Götz), [email protected] (S. Bertholon), [email protected] (M. Boussaha).

http://dx.doi.org/10.1016/j.sedgeo.2014.08.002 0037-0738/© 2014 Elsevier B.V. All rights reserved.

(e.g. Spalluto (2011) in Hill et al. (2012)). These allocyclic processes are inferred via either sequence stacking patterns or spectral analysis. However, in storm-dominated shallow-marine environments, where current- and wave-reworked sediments dominate, hydrodynamic processes may control the variations of accommodation space and the sequence formation. The type and the amount of sedimentary input, which partly determines the accumulation rate and the sedimentary features of sequences, also depend on both autocyclic and hydrodynamic processes. These autocyclic processes lead to the formation of sequences, which have limited lateral continuity (Einsele et al., 1991). As the sedimentary record results from the interaction between alloand autocyclic processes, the metre-scale sequence interpretation has to combine both phenomena.

C. Colombié et al. / Sedimentary Geology 312 (2014) 94–108

Hill et al. (2012) used Carbonate GPM, which is a deterministic, three dimensional geological process model, to investigate the preservation of allocycles in shallow-marine carbonate sections in the occurrence of autocyclic processes. They showed that distinguishing allocyclic and autocyclic forcing is very difficult except when sediments are well-preserved and precisely dated. Colombié et al. (2012) showed that autocyclic phenomena sometimes reveal external forcing signals. They used a very detailed facies analysis and the hierarchical stacking pattern of Late Jurassic shallow-marine carbonate sequences. In this well-defined high-resolution stratigraphical framework, they showed that Milankovitch-scale sea-level cycles may result from the combined effects of cyclic changes in carbonate production and storm-induced processes. The carbonate ramp developed in the Iberian Basin during the late Kimmeridgian provides an excellent opportunity to investigate the effect of autocyclic processes on the generation of metre-scale sequences. The fine-grained marl–limestone alternations that characterise the middle area of this ramp include abundant coarse-grained accumulations. These accumulations were interpreted as tempestites (Bádenas and Aurell, 2001a). These mid-ramp successions are particularly well exposed in the outcrops located near the village of Ricla (northeastern Spain, Fig. 1). There, Bádenas et al. (2005) defined metre-scale sequences, which they called bundles and sets of bundles, on the basis of facies analyses. However, the diagnostic criteria determined LATEST KIMMERIDGIAN Eroded

?

Emerged areas

*

INNER-MIDDLE RAMP Oolitic and bioclastic facies and reefs ... Peloidal facies

.

MIDDLE-OUTER RAMP Limestones and marls with tempestites OUTER RAMP Limestones and marls OUTER RAMP-SLOPE Limestones with sponges OUTER RAMP-BASIN Organic rich laminated marls ZARAGOZA and lime mudstones with ammonites

EBRO MASSIF

*

?

* *

.

* SORIA

* *

. * ...

?

.

**

* *

IBERIAN MASSIF

* * *

. .

*

TERUEL

*

CUENCA

. .

IBERIAN BASIN Studied area

?

.

Sediment transport trend

* * *

ALBACETE

. 0

40 km

N

Fig. 1. Palaeogeographical map of the studied area during the latest Kimmeridgian (modified from Bádenas et al., 2005). The studied deposits, which are located north-west of the Iberian Basin, are mainly limestone beds and marly interbeds with tempestites, which formed in the middle–outer ramp. These deposits contain abundant detrital particles originated from the Iberian and Ebro massifs, located west and north of the studied area, respectively.

95

by Bádenas et al. (2005) are sometimes unsuitable for distinguishing between sequence boundaries and maximum-flooding surfaces/zones. On the other hand, the spectral analysis of bed thickness in the age equivalent outer ramp succession exposed in the Aguilón section (located 40 km offshore of Ricla) showed that bundles and sets of bundles probably originated from high-frequency sea-level changes controlled by the 20-kyr precession and the 100-kyr short eccentricity cycles, respectively (Bádenas et al., 2003). However, the possible assignment to the metre-scale sequences defined in the mid-ramp domain of Ricla to any of the orbital cycles is more open to discussion (Bádenas et al., 2005). The aim of this paper is to determine the impact of storm-induced processes on the feature of the late Kimmeridgian metre-scale sequences recorded in the middle areas of the Iberian carbonate ramp. Metre-scale sequences are defined and correlated along a 4 km-long outcrop located north of the village of Ricla, according to a very detailed microfacies analysis of host, fine-grained deposits, palynofacies analyses, sequence interpretation, and carbon- and oxygen-isotope measurements. The stacking-pattern analysis of these metre-scale sequences leads to an estimation of their duration. In the absence of precise biostratigraphic dating, the quantification of rates of preservation, sediment accumulation, and sea-level rise, and their comparison with previous results from literature give support to the cyclostratigraphic analysis proposed for the interval studied.

2. Geological setting During the late Kimmeridgian, the studied area was located in the northern part of the Iberian Basin, in the transition area between the middle and the outer carbonate ramp setting (Fig. 1). This ramp was open to the Tethys Sea towards the east, and was affected by cyclones. These cyclones were blowing from the southeast to the northwest along the Tethys Sea (Marsaglia and Klein, 1983). The storm-induced flows that affected the northern Iberian Basin resulted in the formation of storm deposits (i.e., tempestites), which are particularly well represented across the outcrops of Ricla (Bádenas and Aurell, 2001a). These tempestites characterise distal middle-ramp environments, and formed below the fair-weather wave base. The interval studied at Ricla belongs to the upper Loriguilla Formation (Fig. 2). This unit mainly consists of well-bedded lime mudstones with frequent tempestites (Bádenas et al., 2005). In Ricla, the Loriguilla Formation includes in its middle part the Ricla Member, a cross-bedded oolitic sandy grainstone unit. The boundary between the Ricla Member and the upper Loriguilla Formation is a prominent discontinuity, traceable at outcrop scale and building a stratigraphic marker horizon (Fig. 3B). This discontinuity corresponds to the lower boundary of the so-called Kim2 Sequence (Aurell et al., 2010) (Fig. 2). This sequence boundary is located around the Acanthicum and the Eudoxus ammonite zones (Bádenas and Aurell, 2001b) and was interpreted by Bádenas et al. (2003) to be coincident with Tethyan third-order sequence boundary Kim 4 of Hardenbol et al. (1998). The interval studied corresponds to the lower 7 m of the upper Loriguilla Formation and therefore corresponds to the lower part of the transgressive systems tract of the Kim2 Sequence that just follows the Ricla Member (Fig. 2). The fine-grained carbonates that form most of the studied upper Loriguilla Formation resulted from the combination of both pelagic mud and reworked mud derived from shallow-water environments by offshore directed, storm-generated density currents (Aurell et al., 1998). The presence within the muddy facies of scattered calcareous nannoplankton, as revealed by scanning electron microscopy, indicates a small pelagic contribution. They also contain abundant detrital particles, such as quartz, micas, plant remains or argillaceous minerals, which have originated from the neighbouring Iberian and Ebro massifs (Fig. 1).

C. Colombié et al. / Sedimentary Geology 312 (2014) 94–108

Ammonite zone

T-R cycle and

(Hardenbol et al., 1998)

sequence (Bádenas et al., 2005; Aurell et al., 2010)

154 155 156

Late

150.86

152.01 152.70

Early

153

Kimmeridgian

152

Tith.

153.54 153.98 154.63

Kim 5

HYBONOTUM

EUDOXUS

Kim 4 Kim 3 Kim 2 Kim 1 Ox 8

ACANTHICUM DIVISUM HYPSELOCYCLUM PLATYNOTA PLANULA BIMAMMATUM

et al., 2005)

?

?

R

BECKERI

Lithostratigraphy at Ricla Village (Bádenas

?

HST TST HST

silty limestones and skeletal packstones (inner ramp) lime mudstones with storm deposits (middle ramp) 1

Ricla Mb.

sandy marls and silty limestones (middle ramp)

Interval studied

(Hardenbol et al., 1998)

Loriguilla Fm.

Tethyan 3rd-order sequence boundary

KIM2 SEQ.

(Gradstein et al., 2012)

KIM1 SEQ.

Age in Ma and stage

T-R FACIES CYCLE 3.2

96

TST Sot de Chera Fm. marls (middle to outer ramp)

T 1

: oolitic sandy grainstones (inner-middle ramp)

Fig. 2. Stratigraphical location of the studied interval (modified from Bádenas et al., 2005). The studied interval corresponds to the base of the transgressive systems tract of Kim2 Sequence, which formed in the late Kimmeridgian, during the Eudoxus and the Beckeri ammonite zones. This interval just follows the Ricla Member, which corresponds to cross-bedded oolitic sandy grainstones of inner-middle ramp, and which constitutes a marker horizon for stratigraphic correlation.

In Ricla, the well-bedded lime mudstones and marly interbeds of the upper Loriguilla Formation group into bundles and sets of bundles (Bádenas et al., 2005). Bundles contain between 2 and 12 limestone beds, and are 1.4 m thick on average. Three to six bundles form sets of bundles, which are 4.5 to 8 m thick. These metre-scale sequences have been related to changes in carbonate export driven by high-frequency sea-level fluctuations (Bádenas et al., 2005). The deepening-shallowing evolution would be coeval to thinning-thickening trend of limestone beds, with maximum-flooding intervals being associated with thin limestone beds. The thinning-up trends would result from the progressive reduction in carbonate mud due to a decrease in carbonate production in shallow areas during flooding intervals (Bádenas et al., 2003, 2005). As a consequence, maximum-flooding surfaces are characterised by omission surfaces with abundant trace fossils. Omission surfaces also constitute diagnostic criteria for the definition of bundle boundaries. The sequence-stratigraphic correlation between the Ricla Village section and the Aguilón section, representing an upper Kimmeridgian outer ramp lime mudstone succession, is supported by biostratigraphic data (Bádenas et al., 2005). In Aguilón, facies, stratal, and spectral analyses led to the definition of bundles and sets of bundles (Bádenas et al., 2003). Bundles, which are 1 to 2 m thick, have been related to high-frequency sea-level changes controlled by the orbital precession cycle. Sets of bundles, which contain 5 bundles, and are 5 to 8 m thick, probably originated from high-frequency sea-level changes controlled by the short eccentricity cycle. Bundles and sets of bundles, which are defined both in Ricla Village and in Aguilón, would have lasted 20 and 100 kyr, respectively. 3. Materials and methods 3.1. Facies, sequence- and cyclostratigraphic analyses The sections studied (from R3 to R7) are located close to the village of Ricla, 50 km southwest of Zaragoza in northeastern Spain (Fig. 3A). These sections are distributed over a 4-km long outcrop, which shows the transition between coral and ooid-dominated proximal (i.e., the closest to the emerged land) and mud-dominated distal (i.e., the farthest away from the emerged land) environments (Bádenas and Aurell, 2001a) (Fig. 3B, Plate I). Fig. 4 shows the detailed bed-by-bed logging of sections R3, R4, R6, and R7, with thickness, number of sample, number of limestone bed, weathering profile, lithology, texture, sedimentary structure (including trace fossils), and content in grains. Sections R3 and R4 contain numerous outcrop gaps, which were interpreted as marly interbeds. Texture is after Dunham (1962). Eighty-five thin sections were analysed for the 4 sections studied: 24 in R3, 31 in R4, 16 in R6, and 14 in R7. The size of quartz grains

corresponds to the Pettijohn et al. (1987) maximum size, and their percentage was estimated from comparison with the Baccelle and Bosellini (1965) charts. Three divisions of size of quartz grains were defined between the coarsest and the finest grains of quartz observed in thin section: coarse (i.e., larger than 300 μm), medium (i.e., between 150 and 300 μm), and fine (i.e., smaller than 150 μm). The relative abundance of grains other than quartz equals 1 when grains occur at least once in a thin section, 2 when they occur at least once in each field of view of the microscope at a magnification of × 40, 3 when they occur at least twice in each field of view, and 4 when they occur more than twice in each field of view, the fields of view covering the entire thin section. Microfacies were defined on the basis of the above sedimentary features (Table 1), and were arranged between proximal and distal ramp environments according to the Bádenas and Aurell (2001a) facies model (Fig. 3B). Tempestite number was also determined in thin sections (Fig. 5). Each coarse-grained accumulation was interpreted as one tempestite because storm sequences are most of the time incomplete, and because the samples studied do not reflect all the events preserved. The high-resolution sequence- and cyclostratigraphic analyses are based on the Vail et al. (1991) nomenclature and on the Strasser et al. (1999) concepts. The evolution through time of the above sedimentary features but also of the thickness of limestone bed, marly interbed, and marl–limestone alternation allows small- and medium-scale depositional sequences to be defined (Figs. 4, 5). These sequences, which correspond to relative sea-level cycles, show a deepening-shallowing trend. Maximum-flooding surfaces coincide with the most distal environments, while sequence boundaries correspond to the most proximal environments. Alternations stack into small-scale sequences, which in turn group into medium-scale sequences. This hierarchical stacking pattern allows controlling factors on sedimentation and the sequence duration to be determined. 3.2. Palynofacies analyses Twenty samples from sections R3, R6, and R7 were studied with respect to their sedimentary organic matter content (Figs. 6, 7). All samples were prepared using standard palynological processing techniques, including HCl (33%) and HF (73%) treatment for dissolution of carbonates and silicates, and saturated ZnCl2 solution (D ≈ 2.2 g/ml) for density separation. Residues were sieved at 15 μm mesh size. Slides have been mounted in Eukitt, a commercial, resin-based mounting medium. For palynofacies analysis the sedimentary organic matter of the sections studied is grouped into a continental fraction including phytoclasts, pollen grains and spores, and a marine fraction composed

C. Colombié et al. / Sedimentary Geology 312 (2014) 94–108

97

N

A)

Zaragoza

Ebro river Jalon river

SPAIN

41°40'

ZARAGOZA

R3 R3

R3-R7 Ricla La Almunia

41°30'

1°00'

1°20'

10 km

upper Oxfordianlower Kimmeridgian

R4 Sot de Chera Fm. Torricilla Fm. Loriguilla Fm.

Kimmeridgian

Ricla Mb.

lower Cretaceous

R6 R7 1 km

Ricla

Jalon river

B) Proximal N

MIDDLE RAMP

Distal S

nt

ro

l

* * * * * * * * * * * H * * * * * * * *

0

1 km m

ro

p

co

K

no

ou

tc

10

D

0

J I

G

TFOt3 TFOt2

E

C

F

TFOt1

B A

R3

Loriguilla Fm. (lower part)

Ricla Mb.

R4

R6

R7

HST (Highstand Systems Tract) of KIM1 SEQUENCE TST (Transgressive Systems Tract) of KIM2 SEQUENCE G: oncolitic-bioclastic or skeletal packstones/ A: silty limestones and sandy marls floatstones B: cross-bedded and channeled oolitic-bioclastic sandstones * * H: coral and/or microbial patches

Torrecilla Fm.

C: cross-bedded oolitic grainstones

I: marl-limestone alternations with tempestites

D: large scale cross-bedded oolitic sandy grainstones

J: oolitic packstones-grainstones with ripples and bars Loriguilla Fm. (upper part) K: oolitic and bioclastic packstones-grainstones

E-F: sandy oolitic and bioclastic grainstones

R6-R4 R4-R3

t (ky) 133 344

h (cm) 250 450

hR4-R3 hR6-R4

Sea-level rise rate (cm.ky-1) 1.88 1.31

Mean rate of sea level rise = 1.59 cm.ky-1 Fig. 3. Geographical location of the studied sections (A) and facies distribution along the 4-km long studied outcrop during the uppermost and lowermost Kim1 and Kim2 sequences, respectively (B) (modified from Bádenas and Aurell, 2001a). Tempestites firstly occur in distal then in proximal sections, indicating the successive positions of the tempestite first occurrence (TFO) during the transgressive part of Kim2 Sequence, and allowing the calculation of the mean rate of sea-level rise.

of dinoflagellate cysts, acritarchs, prasinophytes and foraminiferal test linings. The relative percentage of these components is based on counting at least 400 particles per slide. Three palynofacies parameters were calculated to detect stratigraphic changes in the composition of sedimentary organic matter reflecting eustatic signals (Götz et al., 2008; Haas et al., 2010): (1) the proportion of marine phytoplankton. This parameter quantifies the

percentage rate of dinoflagellate cysts, acritarchs and prasinophytes in the sedimentary organic matter. It is linked to the marine conditions of the water column, depending on distance to coastline, water depth, temperature, salinity, and nutrient availability; (2) the ratio of opaque to translucent phytoclasts (OP/TR ratio). Opaque phytoclasts (OP) partly consist of charcoal originating from forest fires, but mainly develop by oxidation of translucent phytoclasts (TR). Another source

Plate I. Field and microfacies views of the Ricla outcrop, sections, and deposits. (1) The Ricla outcrop is 4-km long and includes sections R3, R4, R6, and R7, which range from the most proximal to the most distal areas, respectively; (2) The sections studied are mainly composed of marly interbeds that alternate with limestone beds; (3) The studied limestone beds contain abundant mm to cm thick coarse-grained accumulations (arrow), which are interpreted as tempestites; (4) The studied deposits contain abundant detrital particles that can be coarse grains of quartz (arrow), notably at the top of coarse siliciclastics, in the lower part of the studied sections (Fig. 5); (5) Microfacies types HD may be grainstones or wackestones–packstones with abundant coarse grains of quartz (Q) and ooids (O); (6) Microfacies types HG may be mudstones or wackestones with medium grains of quartz (Q) and various other grains in small amounts; (7) Microfacies types HK are mudstones that mainly contain fine grains of quartz (Q) and muscovites (M); (8) Microfacies types HL are mudstones with fine grains of quartz (Q) and various other grains in small amounts. HD, HG, HK, and HL are the most abundant microfacies types in the sections studied.

98

C. Colombié et al. / Sedimentary Geology 312 (2014) 94–108

C

D

E

F

Marly interbed Mudstone Wackestone/ fine sandstone Packstone/ medium sandst. Grainstone/ coarse sandst. Boundstone

30

?

29 19.1 28

19

6

A

5 alt

25

27 26 25

B

C

D

E

F

? 18

24 17

23 23 17

16 15

21

16

12.1

7 alt

18

23

C

D

E

F

G

19 11

22

18 17

mfs 10 17

13

4 to 6 alt

12

19

9

11b 15 11a 14 10

sb

3 to 6 alt

13

4 to 7 alt 10.4

14

13

mfs

16

2

6 5

10 9 8

8 7b

7 7a

6

14 11 7

9 5

8

8 alt

12

4 to 8 alt

11

7.3

10

2

5

1c

9

7

8

4a 2

7

3 to 4 alt

4

7 6

6 alt

5 2

4 3 2

3 1

1 0.5 0.6 0.8

1 0

0

0

3 FMC 0

3 0

?

1a 0.3 0.8

HL HA

Sample Limestone bed number number

0

0

0

1

4 FMC 0

4 0

HA

1

sb

5

5 1b

6

2

4

mfs

3

sb mfs

4 3 2

4 to 6 alt

1 0.5 0.12 0.6

HL

Sample Limestone bed number number

0

0

0

4 FMC 0

2 0

HL HA

1

2

2

3 alt

1

Sample Limestone bed number number

3

4 alt

3

6

3

Sample Limestone bed number number

5 alt

8

7.1

2

mfs 6

3a

4 to 5 alt

4

9

3b

5 5

3

0

sb

10

13

4

4

4

8 12

6

6

4b

1

4 to 8 alt

15

3 alt 10

5 alt

6 alt

17

7

9

II

18

11 10

5

15

9

12 10.2

7

16

16

11

8

7 alt

18

8

9

6

12

20

17

1214

10

sb

20

B

11.2

12

3

G

21

14

16 15

11

F

15

4 alt 4

E

27

19

13

D

21

23

19 14

C

26

A

20

B

25 24

21 20

A 28

C. Colombié et al. / Sedimentary Geology 312 (2014) 94–108

6 to 8 alt 22 22

5

COLUMN TITLE A limestone bed thickness (in m) B marly interbed thickness (in m) C alternation thickness (in m) D quartz size (from Fine to Coarse) E muscovite relative abundance F ooid relative abundance G microfacies type (cf. Tab. 1)

maximum abundance of marine phytoplankton

19

SHALLOWING Maximum-flooding surface (mfs) DEEPENING Sequence boundary (sb)

R7 distal mid ramp

Structure cm-thick skeletal eventite (>3 cm thick) sandy and/or oolitic eventite (> 3 cm thick) undiffrenciated bioturbation abundant Chondrites abundant Rhizocorallium abundant Planolites

top of coarse siliciclastics

G

24

18

Grain peloid ooid oncoid intraclast quartz undifferenciated bioclast oyster coral debris microbialite debris

1 km

Marly interbed Mudstone Wackestone/ fine sandstone Packstone/ medium sandst. Grainstone/ coarse sandst. Boundstone

20

R6

FACIES AT OUTCROP SCALE Lithology coral and/or microbial patch oncolitic-bioclastic packstone/ floatstone skeletal packstone/floatstone limestone bed marly interbed

G

21

7

2 km

Small-scale sequence

B

R4

Medium-scale sequence

A

1 km

Marly interbed Mudstone Wackestone/ fine sandstone Packstone/ medium sandst. Grainstone/ coarse sandst. Boundstone

Marly interbed Mudstone Wackestone/ fine sandstone Packstone/ medium sandst. Grainstone/ coarse sandst. Boundstone

Metre

R3 proximal mid ramp

4

0.5 0.3 0.6 0

0

0

FMC 0

4 0

HL

1

I

HA

99

Fig. 4. Main sedimentary features, resulting from field, microfacies, and palynofacies analyses, and sequence-stratigraphic correlation of host deposits from the most proximal to the most distal areas of the outcrop studied. According to thicknesses of limestone beds, marly interbeds, and alternations, small-scale sequences, containing 5 marl–limestone alternations on average, are defined. Four of these small-scale sequences form one medium-scale sequence. This hierarchical stacking pattern suggests an orbital control on sedimentation.

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C. Colombié et al. / Sedimentary Geology 312 (2014) 94–108

Table 1 Main sedimentary features of microfacies types. M: mudstone; W: wackestone; P: packstone; G: grainstone; B: boundstone.

Grain content

Texture

Quartz percentage

coarse (>300 µm)

mainly muscovites

W–P–G

25%

HB HC

Proximal

Quartz size

HA

environment

Microfacies type

mainly muscovites and bivalves

W–P

5%

coarse

mainly bivalves

M

some percent

coarse

various grains in small amounts

W–P

10%

HD

coarse

mainly ooid

G

20 to 30%

W–P

15 to 20%

HE

coarse

mainly intraclasts and ooids

W–P

20%

mainly intraclasts

W–P

5 to 10%

W–P

some percent to 5%

medium (from 150 to 300 µm)

mainly muscovites

M

5%

HG

medium

various grains in small amounts

M–W

some percent to 10 %

HH

medium

peloidal and clotted micrite

B

some percent

medium

mainly ooids

M–W

15%

medium

mainly intraclasts and oncoids

W–P

some percent

fine (<150 µm)

mainly muscovites

M

<1 to 10%

fine

various grains in small amounts

M

<1% to some percent

HJ HK HL

Distal

HI

environment

mainly intraclasts and oncoids HF

for opaque phytoclasts might be resedimentation of refractory particles. Generally, the ratio of opaque to translucent phytoclasts increases basinward due to fractionation processes and the higher preservation potential of opaque particles. Most of the oxidation is of subaerial, continental origin. However, in proximal high-energy shelf areas this trend may be reversed by in-situ (bio)oxidation at the seafloor, enhanced by the high porosity and permeability of coarse-grained sediments; and (3) the size and shape of plant debris (ED/BS ratio) are used to decipher proximal–distal and transgressive–regressive trends. Small, equidimensional (ED) woody fragments are characteristic of distal deposits whereas in proximal settings, large blade-shaped (BS) particles are quite abundant. In addition, proximal assemblages reveal a greater variety of particle sizes. Additionally, the AOM– Phytoclast–Palynomorph ternary plot after Tyson (1989, 1993) is used to detect and interpret proximal–distal settings.

3.3. Carbon- and oxygen-isotope analyses Carbon- and oxygen isotopes were measured on bulk carbonate samples from the 40 last metres of the Ricla Village section, from its lower part, which corresponds to section R7, from section R6, and from section R4 (Fig. 8). A total of 33 samples from Ricla Village (1 m sampling raster), 8 from R7, 10 from R6, and 12 from R4 (1 to 2 m sampling raster) were analysed. Carbon- and oxygen-isotope analyses were carried out on samples that tend to be more argillaceous in Ricla Village (percentage of CaCO3 ranges between 23 and 88%) than in R7, R6, and R4 (percentage of CaCO3 varies from 46 to 89%). Samples collected in Ricla Village were originally intended for the calcareous nannofossil and clay analyses, while those collected in R7, R6, R4, and R3 were intended for the limestone microfacies analysis. The analyses were processed at the Muséum National d'Histoire naturelle of Paris (France). The δ13C and the δ18O values were measured in a “Delta V Advantage” (Thermo) isotope ratio gas mass spectrometer directly coupled to a “Kiel IV” automatic carbonate preparation device (reaction at 70 °C under vacuum) and calibrated via the internal lab standard (Marbre LM, calibrated to NBS19) to the VPDB (Vienna Pee Dee Belemnite) scale. Standard deviations within each run range between 0.01 and 0.03‰ for carbon, and from 0.03 to 0.06‰ for oxygen. Isotopic results are reported in per mil deviation from the V-PDB (Vienna Pee Dee Belemnite) using the standard delta notation.

4. Results 4.1. Facies and palynofacies analyses In section R3, coarse-grained facies, including skeletal and oncolitic– bioclastic packstones/floatstones with poorly sorted reefal-derived debris and peloidal/intraclastic and/or sandy oolitic matrix dominate (Fig. 4). Downdip, sections R4, R6, and R7 mainly contain alternations of marly interbeds and limestone beds (Fig. 4, Plate I). Limestone beds are mainly mudstones, and include abundant coarse-grained accumulations, which are interpreted as tempestites (Bádenas and Aurell, 2001a) (Plate I). The changes through time in the marl–limestone alternation thickness resemble the changes in the marly interbed thickness in the most proximal sections (i.e., R3, R4), while they rather correlate with the changes in the limestone-bed thickness in the most distal sections (i.e., R6, R7) (columns A, B, and C of Figs. 4, 5). Twelve microfacies types (from HA to HL) have been defined according to the very detailed analysis of limestone beds (columns D, E, F, G of Fig. 4, Plate I, Table 1). They differ according to the quartz grain size, the content in grains other than quartz, such as muscovites, bivalves, ooids, and intraclasts, the texture, and the quartz grain percentage (Table 1). Few defined microfacies types comprise fine grains of quartz, which however form most of the studied samples (62.5%) (column D of Fig. 4, Plate I, Table 1). The observed microfacies types are mainly (i.e., relative abundance ranges between 2 and 4) made up of muscovites, bivalves, ooids or intraclasts, or may contain all these types of grains in small amounts (i.e., relative abundance equals 1) (columns D, E, F, G of Fig. 4, Table 1). All the texture types are present, from mudstones to boundstones, but mudstones and wackestones dominate (65% of the samples studied) (Fig. 4, Plate I, Table 1). Only one boundstone was observed in sample R4.4, which is mainly composed of peloidal and clotted micrite (microfacies type HH in column G of Fig. 4 and in Table 1). The percentage of quartz grains generally varies between less than 1% and 30% (Table 1). All samples studied yield sedimentary organic particles, phytoclasts being the dominant group (Figs. 6, 7). The sedimentary organic matter of sections R3, R6, and R7 shows in general a high degree of degradation of palynomorphs. The samples from the most proximal section (i.e., R3) are very poor in organic particles. However, the highest amount of (degraded) marine particles, corresponding to the highest amount of opaque, equidimensional phytoclasts, is detected in sample R3.5 (Fig. 7). Also in sections R6 and R7, this signal is very prominent (samples R6.7 and R7.4).

C

D

20

Marly interbed Mudstone Wackestone/ fine sandstone Packstone/ medium sandst. Grainstone/ coarse sandst. Boundstone

21

7

30

?

29 19.1

A

28 25

6

C

23 17 22

15

21

A

26

23

B

C

D

12 19

15 12.1

18

11

22

18

mfs

21

14

10

tR4-R3

11.2

17

20 18

17

17

16 15

4

13 12

9

19

11b 15 11a 14 10 13

1214

sb

14 17 13 10.2

mfs

16 8

11

15

10

9

TFOt2

9 8

tR6-R4

7

2

6 5

12

7

10

10 9 8

8 7b

7 7a

6

14 11

6

7 9

5

12

mfs

11

5

6

3a

5

8 7.3

10

2

5 7.1

3

1c

9

7

8

4a 2

7

4

7 6

6

sb

5 6

3 1b

5 2

4 3 2

3

0

2

1

1 0.5 0.6 0.8

1

Sample Limestone bed number number

0

0

0

0

?

1a

20

0.3 0.8

Sample Limestone bed number number

0

0

0

1

1

2

4

mfs

3

sb mfs

4 3 1

2 1 0.5 0.12 0.6

30 0

Sample Limestone bed number number

3

3

5 4

4

9 8

3b

6

4

1

sb

10

13

4

4b

Tempestite first occurrence at t1 (TFOt1)

II

18

9

12

11 10

5

15

10.4

8

11

16

16

12

3

6

20

A 23

19

13

sb

21

16

20

19 14

D

C

25 24

21 20

B

C. Colombié et al. / Sedimentary Geology 312 (2014) 94–108

5

SHALLOWING Maximum-flooding surface (mfs) DEEPENING Sequence boundary (sb)

27

23

22

COLUMN TITLE A limestone bed thickness (in m) B marly interbed thickness (in m) C alternation thickness (in m) D tempestite number

?

24

16

Structure cm-thick skeletal eventite (>3 cm thick) sandy and/or oolitic eventite (> 3 cm thick) undiffrenciated bioturbation abundant Chondrites abundant Rhizocorallium abundant Planolites

28

18

17

R7 distal mid ramp

19

24

18

1 km

Marly interbed Mudstone Wackestone/ fine sandstone Packstone/ medium sandst. Grainstone/ coarse sandst. Boundstone

19

TFOt3

27 26 25

B

R6

Small-scale sequence

B

2 km FACIES AT OUTCROP SCALE Lithology coral and/or microbial patch oncolitic-bioclastic packstone/ floatstone skeletal packstone/floatstone limestone bed marly interbed Grain peloid ooid oncoid intraclast quartz undifferenciated bioclast oyster D coral debris microbialite debris

Medium-scale sequence

A

R4

Marly interbed Mudstone Wackestone/ fine sandstone Packstone/ medium sandst. Grainstone/ coarse sandst. Boundstone

Marly interbed Mudstone Wackestone/ fine sandstone Packstone/ medium sandst. Grainstone/ coarse sandst. Boundstone

Metre

R3 1 km proximal mid ramp

0

0

0

30 0

2

2 1

Sample Limestone bed number number

0.5 0.3 0.6 0

0

0

35

1

I

0

101

Fig. 5. Spatial and temporal distribution of the tempestites identified in thin sections. Tempestites first occur in the most distal section and progressively in more proximal sections, indicating the successive positions of the tempestite first occurrence (TFO) during the transgressive systems tract of Kim2 Sequence. In section R7, the TFO is located 12 m below the base of the studied interval. According to the cyclostratigrapical interpretation proposed in this work, the time elapsed between two successive positions is calculated. Tempestites are more abundant in thick alternations than in thin ones, suggesting that thick alternations are better preserved and formed in more distal environments than thin alternations. Consequently, the thickest alternations would correspond to the maximum-flooding surfaces whereas the thinnest alternations would coincide with the sequence boundaries.

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Phytoclasts 95 I

10

R3

R3 R6 II

R7

R6

III

65 IVa VI

55

IVb

R7

40

IX

V

VII VIII

AOM

60

35

Palynomorphs

Fig. 6. Palynofacies data of sections R3, R6, and R7 plot in fields I, III, and V of the AOM–Phytoclast–Palynomorph ternary diagram, displaying deposits of a highly proximal (I), proximal (III), and distal (V) ramp setting.

4.2. Carbon- and oxygen-isotope measurements δ13C values vary between − 0.3‰ and 2.5‰ in the Ricla Village section (Fig. 8). These values equal 1.6‰, on average. The standard deviation, which is 0.7, reflects small variations. δ13C values are rather low and moderately fluctuate in the lower part of the section whereas they tend to increase and to slightly vary in the upper part (Fig. 8). The correlation between the Ricla Village and the Aguilón sections is based on the order of magnitude, on the fluctuations, and on the positive and the negative shifts of the δ13C values. According to the small variations that characterise the carbon-isotope signal, this chemostratigraphic correlation can perfectly fit with the sequence stratigraphic correlation proposed by Bádenas et al. (2005) between the Ricla Village and the Aguilón sections (Fig. 8). The lower part of the Ricla Village section coincides with section R7 (Fig. 8). However, carbon-isotope measurements were performed on samples that tend to be more argillaceous in Ricla Village section than in section R7. The δ13C values in section R7 range between 0.8‰ and 2.2‰ whereas the δ18O values vary between − 5.6‰ and − 5‰. The standard deviation equals 0.5 for δ13 C values and 0.2 for δ 18 O values, both reflecting small variations. Changes in δ13C values in section R7 are consistent with those recorded in the lower part of the Ricla Village section except for one value (corresponding to sample RV46) (Fig. 8). This value corresponds to negative shift b, which is correlated with negative shift b in the Aguilón section (Fig. 8). This negative shift does not appear in section R7, probably because of the low sampling resolution. The order of magnitude of the δ13C and δ18O values and of the standard deviation in section R6, as well as in section R3, are the same as in section R7.

5. Interpretation 5.1. Sedimentological interpretation During the late Kimmeridgian, the Iberian platform was subjected to the input of siliciclastics, which were resedimented offshore by storms (e.g., Bádenas and Aurell, 2001a). This sediment distribution probably explains why the changes in the alternation thickness resemble the changes in the marly interbed thickness in the most proximal sections (i.e., R3, R4), while they rather correlate with the

changes in the limestone bed thickness in the most distal sections (i.e., R6, R7) (columns A, B, C of Figs. 4, 5). As a whole, the studied interval shows coarse-grained facies, including quartz grains, skeletal grains, ooids, intraclasts, and oncoids in proximal areas whereas fine-grained facies dominate in distal areas of the Ricla outcrop (Bádenas and Aurell, 2001a) (Fig. 3B). According to not only this facies model but also on the basis of the size of quartz grains and the content in the grains other than quartz such as muscovites, bivalves, ooids or intraclasts determined in thin sections, the 12 microfacies types defined have been arranged from the most proximal to the most distal part of the ramp (Table 1, Fig. 3B). Proximal environments are characterised by limestones that mainly contain coarse grains of quartz and abundant grains other than quartz. The decrease in the size of quartz grains and in the content in grains other than quartz in limestones indicates more distal environments. Sedimentary organic matter of sections R3, R6, and R7 documents a clear proximal–distal trend, as interpreted from the AOM–Phytoclast– Palynomorph ternary plot (Fig. 6). The palynofacies data of the three sections plot along the phytoclasts–palynomorphs axis, and clearly display the change from proximal to more distal settings, i.e. from field I (highly proximal environment), to field III (proximal environment) and to field V (distal environment). The general high degree of degradation is interpreted as primary signal, e.g. from storm deposits in a shallow-marine setting. The most proximal samples (i.e., from section R3) are very poor in sedimentary organic matter - particles might be washed out from very shallow shoals, showing also a high amount of opaque phytoclasts. The highest amount of marine particles and opaque, equidimensional phytoclasts in sample R3.5 (Fig. 7) is interpreted as a major flooding signal. Also in the more distal sections R6 and R7 this signal is most prominent (samples R6.7 and R7.4). 5.2. Sequence interpretation Changes in depositional environments generally reflect changes in relative sea level. The most distal environments set during the most rapid relative rate of sea-level rises, which correspond to the maximum-flooding surfaces, while the most proximal environments set during the most rapid relative falls in sea level, which coincide with the sequence boundaries. In the present work, changes in the microfacies types defined, which reflect changes in depositional environments, do not correlate from one section to the other (column G of Fig. 4). This may be due to the fact that the finest as well as the coarsest sediment was reworked in these storm-dominated environments, and that reworked material probably composes the whole limestone beds. However, changes in the alternation thickness correlate from one section to the other (column C of Figs. 4, 5). Surfaces can be defined that coincide with thick or thin alternations and marly interbeds in the most proximal sections (i.e., R3, R4), and with thick or thin alternations and limestone beds in the most distal sections (i.e., R6, R7) (columns A, B, C of Figs. 4, 5). In places, condensed intervals, represented by surfaces of bioturbation, help to define the position of these surfaces (Figs. 4, 5). In sections R4, R6, and R7, the thickest alternations generally contain more tempestites than the thinnest alternations (column C and D of Fig. 5). Consequently, the thickest alternations would be the most preserved alternations (i.e., less affected by reworking and cannibalism from successive storm events). They probably formed in relatively distal environments, while the thinnest alternations would rather correspond to incomplete alternations that formed in relatively proximal environments. The thickest alternations would coincide with the maximum-flooding surfaces, while the thinnest alternations would indicate the sequence boundaries (column C of Figs. 4, 5). These diagnostic criteria allow the definition of three orders of depositional sequences, which are hierarchically stacked (Figs. 4, 5). Marl–limestone alternations correspond to elementary sequences, which stack into small-scale sequences. Small-scale

C. Colombié et al. / Sedimentary Geology 312 (2014) 94–108

Marine Plankton

Ratio ED/BS

Ratio OP/TR

103

R3

Highly Proximal Shelf

R3.8 R3.5 R3.4 R3.2 0

10 20 30 40 50 %

0

Marine Plankton

4

8

12

0

Ratio OP/TR

6

12

Proximal

R3.12

18

Ratio ED/BS

R6

R6.8 R6.73 R6.71 R6.7

Proximal Shelf

R6.6 R6.5 R6.4 R6.3 R6.2 R6.1 0

10 20 30 40 50 %

0

Marine Plankton

4

8

12

0

Ratio OP/TR

6

12

18

Ratio ED/BS

R7

R7.6

Distal Shelf

R7.5 R7.4 R7.3

Distal

R7.1 0

10 20 30 40 50 %

0

4

8

12

0

6

12

18

Fig. 7. Palynofacies parameters displaying transgressive–regressive trends: (1) the proportion of marine phytoplankton, (2) the ratio of opaque to translucent phytoclasts (OP/TR ratio), and (3) the size and shape of plant debris (ED/BS ratio). Samples from sections R3, R6, and R7 indicate maximum-flooding phases in R3.5, R6.7, and R7.4. Note the different percentages of marine phytoplankton with a maximum of 15% in the most proximal part and 35 and 45% in the more distal parts of the ramp setting. Opaque, equidimensional phytoclasts are most abundant within the intervals of maximum abundances of marine phytoplankton, indicating maximum-flooding phases.

R7 (= RICLA VILLAGE) Marly interbed Mudstone Wackestone/ fine sandstone Packstone/ medium sandst. Grainstone/ coarse sandst. Boundstone

Marly interbed Mudstone Wackestone/ fine sandstone Packstone/ medium sandst. Grainstone/ coarse sandst. Boundstone

Metre

Medium-scale sequence

104

R4

-1

? 19

δ13C (‰-VDP) 0 1 2 3

l

28

l

? 6

R6

18

27

Marly interbed Mudstone Wackestone/ fine sandstone Packstone/ medium sandst. Grainstone/ coarse sandst. Boundstone

17

j

23

j

21 20

i

16

5

23

k

k

26 25 24

i

19

15 22

h

18

20

17

13

4

g

12

19

11b 11a

g

16

15 18

10

14

9 17 8

13

f

f

16

3

15 12

7

e

e

14

d

11

d

6 10 13

5 4

2

c c

9 12

3b

b 11

a

b

3a 8 10

a

2 9 1c

7

8

1

7 6

6 5

5 4 1b

4

3

3 2

I 0

1a

Limestone bed -7 -5 0 2.5 number δ18O (‰) δ13C (‰)

Proximal environments

?

1

Limestone bed -7 -5 0 2.5 number δ18O (‰) δ13C (‰)

2 1

?

Limestone bed -7 -5 0 2.5 number δ18O (‰) δ13C (‰)

Distal environments

Fig. 8. Chemostratigraphic correlation between sections R4, R6, and R7 analysed in this work and the Ricla Village and Aguílon sections published by Bádenas et al. (2005). Changes in δ13C values in the lower part of the Ricla Village section are consistent with those recorded in section R7, which also records a slight positive shift in δ13C (which would correspond to c in Ricla Village) that just follows a slight negative shift (which would correspond to b in Ricla Village). Section R7 shows the same trend in carbon and oxygen-isotope values as also documented in sections R4 and R6. The grey/shaded areas on the oxygen and carbon-isotope curves correlate from section R4 to section R7.

C. Colombié et al. / Sedimentary Geology 312 (2014) 94–108

14

II

h

21

C. Colombié et al. / Sedimentary Geology 312 (2014) 94–108

105

Table 2 Mean sediment accumulation rate calculated for the studied interval.

Sequence 2

Sequence 3

Sequence 4

R4 R6 R7 R4 R6 R7 R4 R6 R7

Mean value Mean sed. rate (cm·ky−1) Mean sed. rate (mm·y−1)

A

B

C

D

E

F

G

H

I

J

K

10.00 17.50 9.58 35.00 28.75 33.00 16.67 25.83 27.33 22.63 1.13 0.01

7.90 15.83 7.92 11.66 26.26 17.00 11.25 24.58 14.33 15.19

15.80 18.09 16.53 6.66 18.27 10.30 13.50 19.03 10.49 13.43

8.05 5.03 7.62 1.87 3.06 2.21 4.20 3.41 3.22 3.51

2.25 13.50 7.00 11.00 19.00 18.00 6.80 13.50 27.00 13.12

0.28 2.68 0.92 5.88 6.21 8.14 1.62 3.96 8.39 3.74

3577.78 372.49 1088.58 170.13 161.10 122.90 617.52 252.36 119.26 267.51

20 20 20 20 20 20 20 20 20 20

50 50 50 50 50 50 50 50 50 50

0.006 0.054 0.018 0.118 0.124 0.163 0.032 0.079 0.168 0.075

0.014 0.134 0.046 0.294 0.310 0.407 0.081 0.198 0.419 0.187

A: alternation thickness (cm). B: limestone bed thickness (cm). C: limestone bed duration (=B × 20 / A in ky). D: thin section duration (=thin section size × C / B in ky). E: number of tempestites per sample. F: frequency (number of tempestites per ky). G: preservation interval (y). H: minimum recurrence interval (y). I: maximum recurrence interval (y). J: minimum preservation rate. K: maximum preservation rate.

sequences, which are 1.12 m thick, on average, form medium-scale sequences, which have a thickness close to 4 m. Five complete and the beginning of a sixth small-scale sequences and one complete and the beginning of a second medium-scale sequences have been defined (Figs. 4, 5). 5.3. Stratigraphic correlation and cyclostratigraphic analysis The sections studied are correlated using the top of the Ricla Member as a timeline and the sequence stratigraphic interpretation proposed in this work (Figs. 4, 5). Field data and the maximum abundance of marine phytoplankton support this sequence stratigraphic correlation. The variations in both δ18O and δ13C values are not contradictory to the other correlations, but are so slight to be, by themselves, conclusive. Small-scale sequence 1 mostly contains coarse-grained facies. The maximum-flooding surface of this sequence coincides with the top of coarse siliciclastics in sections R3 and R7 (Plate I, Figs. 4, 5). The maximum abundance of marine phytoplankton in section R3 corresponds to the first maximum abundance of marine phytoplankton in section R6, and with the deposition of lime mudstones in both sections. Small-scale sequence 2 is mainly formed by coarse-grained facies and coral-microbial facies in proximal sections (i.e., R3, R4), and by mud-supported facies in distal sections (i.e., R6, R7), reflecting the long-term sea-level rise (i.e., the TST of Kim2 Sequence). The maximum-flooding interval of this sequence coincides with significant facies changes in sections R3, R4 and R7, and with the second maximum abundance of marine phytoplankton in section R6. In small-scale sequence 3, relatively shallower coarse-grained and coral-microbial facies are only present in section R3, reflecting the transgressive trend during the long-term sea-level rise. Initial flooding interval of this small-scale sequence 3 led to the deposition of lime mudstones and covered marly interbeds in this shallower position, which is also coincident with the maximum flooding of the mediumscale sequence I. The maximum abundance of marine phytoplankton in section R7 does not coincide with this maximum-flooding surface, and might reflect the sampling resolution, hampering precise correlation of flooding signals. Small-scale sequences 4 and 5 also show coarse-grained facies in section R3, passing downdip to marl–limestone alternations. The sharp change between thicker coarse-grained limestone beds in small-scale sequence 4, to thinner coarse-grained limestone beds and covered marly interbeds in small-scale sequence 5,

also linked to a prominent bioturbated surface, correspond to the upper boundary of the medium-scale sequence I. The flooding at the upper boundary of small-scale sequence 5 is marked by the disappearance of coarse-grained facies and the deposition of marl– limestone alternations in all the studied sections. Each section contains a positive shift in both δ18O and δ13C values, which correlate from one section to the other (Fig. 8). According to the stratigraphic correlation between sections R3, R4, R6, and R7 proposed in the present work, small and medium-scale sequences correlate from one section to the other (Figs. 4, 5). The correlation of marl–limestone alternations from one section to the other is not possible because of the abundant tempestites (column D of Fig. 5). The thickness of small- and medium-scale sequences and the average number of marl–limestone alternations in a small-scale sequence are quite similar from one section to the other (Fig. 4). The stacking pattern analysis indicates that a small-scale sequence contains 5 marl– limestone alternations on average, and that the first medium-scale sequence includes 4 small-scale sequences (Fig. 4). This 1:4:5 stacking pattern suggests an orbital control on sedimentation. Marl–limestone alternations would correspond to the 20-kyr precession cycles, small- and medium-scale sequences, to the 100-kyr and the 400kyr eccentricity cycles, respectively. 6. Discussion 6.1. Duration of sequences The 1:4:5 stacking pattern determined in the present work on the basis of detailed microfacies analyses and sequence-stratigraphic interpretation and correlation is not consistent with the Bádenas et al. (2003) spectral analysis of Aguilón in the northern Iberia Ranges. They showed that small-scale sequences (which are as thick as their bundles) would last 20 kyr, and that the duration of medium-scale sequences (which have the same thickness as their sets of bundles) would be 100 kyr. As the interval studied in the present work is ten times shorter than the interval studied by Bádenas et al. (2003), which includes the entire late Kimmeridgian, time calibration is difficult. However, the differences of sequence duration between Ricla Village and Aguilón may be due to the effects of large-scale (or long-term) accommodation change on metre-scale (or short-term) cycles but also to the position of the interval studied on the ramp (or in the Iberian Basin). The interval studied

106

C. Colombié et al. / Sedimentary Geology 312 (2014) 94–108

Table 3 Carbonate sediment accumulation rates calculated for platform, margin, and basin environments. Type of deposit

Mean sedimentation rate (mm·y−1)

This work Late Jurassic Iberian platform Other Late Jurassic carbonate platforms Other ancient carbonate platforms

0.01 0.06 0.05 0.1

Holocene carbonate platforms

0.36

References Bádenas et al. (2003, 2005, 2012) Carcel et al. (2010), Colombié et al. (2012), Husinec and Read (2007), Rona (1973) McNeill (2005), Cozzi et al. (2004), Cunningham and Collins (2002), Elrick et al. (1991), Schwab (1976), Simo (1989) Elrick and Read (1991), Read et al. (1991), Lokier and Steuber (2008)

The values for this work, Late Jurassic and other ancient carbonate environments are not corrected for compaction. For Holocene carbonate platforms, the effect of compaction is minimal and can be ignored.

in the present work corresponds to the early transgressive systems tract of Kim2 Sequence (Fig. 2). This interval formed just after third-order sequence boundary Kim 4. The rates of sediment accumulation and of accommodation were still low, and the smallest cycles probably not preserved. Accordingly, Bádenas et al. (2003) suggested that bundles 44 and 45 from Aguilón, which formed during the late HST, just before third-order sequence boundary Kim5, were condensed due to an important loss of accommodation on the ramp. Moreover, Aguilón is in a more distal position on the ramp than Ricla Village (Bádenas et al., 2005). There, the accommodation was probably much higher than in Ricla Village, and allowed for the preservation of the smallest cycles. Consequently, the stacking pattern observed in the present work may have changed later into the stacking pattern observed by Bádenas et al. (2005). This is perfectly consistent with the result of Bádenas et al. (2005) who suggested that the stacking pattern in Kim2 Sequence is highly variable from one location of the Iberian Basin to the other.

6.2. Rate of sediment accumulation The rate of sediment accumulation calculated in this work corresponds to the ratio of the thickness to the duration of the alternations that form small-scale sequences 2, 3, and 4 (Table 2). On the basis of the above results and interpretations, the duration of alternation is 20 kyr. Small-scale sequences 2, 3, and 4 are complete and can be correlated from section R4 to section R7 (Figs. 4, 5). The sedimentation rate calculated in the present study equals 0.01 mm·y−1 (Table 2). Based on the sequence duration proposed by Bádenas et al. (2003, 2005) (i.e., 100 kyr for sets of bundles and 20 kyr for bundles) and on their thickness, the sediment accumulation rate equals 0.08 mm·y− 1 on average for Aguilón. However, according to this rate of sediment accumulation, the 45 bundles defined in Aguilón by Bádenas et al. (2003), which would last 900 kyr, would result in a succession much thicker than the section measured (i.e., 72 m instead of 63 m for Aguilón in Table 4 Sediment accumulation rate corrected for compaction calculated for the studied interval. A

B

C

Sequence 2

R4 10.00 7.90 19.75 R6 17.50 15.83 39.58 R7 9.58 7.92 19.80 Sequence 3 R4 35.00 11.66 29.15 R6 28.75 26.26 65.65 R7 33.00 17.00 42.50 Sequence 4 R4 16.67 11.25 28.13 R6 25.83 24.58 61.45 R7 27.33 14.33 35.83 Mean decompacted alternation thickness (cm) Mean sedimentation rate (cm·ky−1) Mean sedimentation rate (mm·y−1) A: mean alternation thickness (cm). B: mean limestone bed thickness (cm). C: mean decompacted limestone bed thickness (cm). D: mean marly interbed thickness (cm). E: mean decompacted marly interbed thickness (cm). F: mean decompacted alternation thickness (cm).

D

E

F

2.10 1.67 1.66 23.34 2.49 16.00 5.42 1.25 13.00

6.30 5.01 4.98 70.02 7.47 48.00 16.26 3.75 39.00

26.05 44.59 24.78 99.17 73.12 90.50 44.39 65.20 74.83 60.29 3.01 0.03

Bádenas et al., 2003). Moreover, Aurell et al. (1998) performed numerical modelling to better determine processes that controlled sedimentation. They showed that a significant part of the carbonates need to be pelagic in origin to explain such a high rate of sediment accumulation. However, the present study shows that the deposits studied do not contain calcareous nannofossils (F. Giraud, pers. comm., 2010). The sedimentation rate calculated in this work is also 7 times lower than the mean sedimentation rate measured from other Late Jurassic or ancient carbonate platforms (Table 3). Controls on the rate of sediment accumulation are the type and the amount of sedimentary input, the amount of accommodation available, the reworking of sediment by hydrodynamic processes, and the duration of the studied interval (e.g., Sommerfield, 2006). The studied sections comprise middle-outer ramp marl–limestone alternations that are frequently reworked by storms during the beginning of a third-order transgression. All these factors probably explain the low rates of sediment accumulation that are calculated in the present study. As the interval studied is short (i.e., no more than 600 kyr according to the above interpretations), the effect of the studied interval duration on the sediment accumulation rates is small. In view to the comparison with the rate of sediment accumulation in Holocene carbonate platforms, the sedimentation rate calculated in this work is corrected for compaction (Table 4). The original (or decompacted) thickness of alternation was estimated by using decompaction factors equal to 2.5 for carbonate mudstones and 3 for marls (Strasser and Samankassou, 2003). According to the mean decompacted alternation thickness and the duration of alternation defined in this work (i.e., 20 kyr), the sedimentation rate corrected for compaction is equal to 0.03 mm·y−1 on average (Table 4). The latter value is one order of magnitude lower than the mean sedimentation rate measured from Holocene successions, which results from the collection of depositional rates for different water depths and facies (Table 3). However, the Holocene sediment accumulation rates are one order of magnitude higher than ancient rocks (Wilson, 1975; Elrick and Read, 1991). Consequently, the sedimentation rate corrected for compaction calculated in this work is consistent with the mean Holocene accumulation rates.

6.3. Rate of preservation The rate of preservation is the ratio of the preservation interval to the recurrence interval (Keen et al., 2012). The preservation interval is the number of years between 2 storm events preserved in the sedimentary record. The recurrence interval is the return period for storms registered at the moment for a given location. The calculation of the preservation rate was performed on the basis of the following assumptions: 1) marly interbed sedimentation rate equals limestone bed sedimentation rate; 2) sedimentation rate is steady over the interval studied; 3) the number of coarse-grained accumulations reflects the number of events; and 4) the geological and oceanographic factors during severe storms in the Late Jurassic Iberian platform were the same as those that prevailed in the Gulf of Mexico during the Holocene such that the recurrence interval for large storms in the Late Jurassic Iberian platform was similar to the Gulf of Mexico (Keen et al., 2012).

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The limestone bed duration (C in Table 2) depends on limestone bed (B in Table 2) and alternation (A in Table 2) thicknesses and on the alternation duration, which equals 20 kyr according to the above results and interpretations. The 3 × 4 cm thin-section duration (D in Table 2) depends on the limestone bed thickness and duration and on the thin-section size, which depends on its orientation. According to the latter assumptions and relations, limestone bed and 3 × 4 cm thin-section durations (columns C and D in Table 2, respectively) are equal to 13.43 kyr and 3.51 kyr, respectively (Table 2). A thin section contains 13.12 tempestites on average (column E in Table 2). The frequency of tempestites is 3.74 per thousand years, and the preservation interval equals 267.51 years (columns F and G in Table 2, respectively). By using the Gulf of Mexico recurrence interval of 20–50 years (columns H and I in Table 2, respectively), the rate of preservation calculated in the present work ranges between 7.5 and 18.7% (columns J and K in Table 2). According to Bádenas et al. (2005), the alternation duration found in the lower part of Ricla Village would be equal to 2 or 3 kyr (e.g., bundles 1–14, which would last 100 kyr, consist of 2 to 12 couplets). However, with this alternation duration and the number of events determined in the present work, the preservation rate would be between 52 and 131%. These values are much higher than those generally calculated for ancient successions, and unlikely in stormdominated environments where reworking prevails. As stated above, the rate of preservation calculated in the present work is based on numerous assumptions but equals the preservation rate determined for Cretaceous storm-dominated sequences of Utah, which is comprised between 8 and 20% (Keen et al., 2012). The preservation rate calculated in the present work can also be used to correct the corrected sedimentation rate for compaction measured in this work, which is equal to 0.03 mm·y− 1 (Table 4). The corrected sedimentation rate varies between 0.4 (for a preservation rate equal to 7.5%) and 0.16 mm·y−1 (for a preservation rate equal to 18.7%). In the first case (i.e., for the lowest preservation rate), the corrected sedimentation rate is close to the mean Holocene accumulation rate (Table 3). 6.4. Rate of sea-level rise Changes through time of the features and of the number of tempestites may reflect changes in relative sea level but also could be linked to Milankovitch cycles via climate. For example, the current warming is leading to an increase in the cyclone intensity (Emanuel, 2005) while the cyclone frequency would decrease or remain unchanged (Knutson et al., 2010). However, as changes in climate are difficult to assess in ancient successions at such a high resolution, tempestites are used in the present study to infer sea-level variations. The boundary between the coarse-grained facies and the mud-supported facies is underlined by the tempestite first occurrence (TFO in Figs. 3B, 5). Tempestites first appear in the most distal section (TFOt1 in Figs. 3B, 5) then progressively in more proximal sections (TFOt2 and TFOt3 in Figs. 3B; 5), reflecting the sea-level rise that characterises the studied interval (i.e., the TST of Kim2 Sequence). In section R7, the TFO is located 12 m below the base of the studied interval. The calculation of the rate of sea-level rise was performed on the basis of the following assumptions: 1) the sedimentation rate is the same whatever the stratigraphic interval studied and the position of the section studied on the ramp, 2) the mean sedimentation rate calculated in this work, without decompaction of sediment thicknesses, is equal to 0.01 mm·y−1 (Table 2), and 3) the size of the ramp was the same as that published by Bádenas and Aurell (2001a) (Fig. 3B). tR6–R4 and tR4–R3 are the time elapsed between TFOt1 and TFOt2, and TFOt2 and TFOt3, respectively (Figs. 3B; 5). tR6–R4 and tR4–R3 are calculated according to the thickness of the sediment accumulated between TFOt1 and TFOt2, and TFOt2 and TFOt3, respectively (Fig. 5), and according to the above mean sedimentation rate. h R6–R4 and hR4–R3 are the distances between TFO t1 and TFO t2 , and TFOt2 and TFOt3, respectively, according to the size of the ramp model published

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by Bádenas and Aurell (2001a) (Fig. 3B). The rate of sea-level rise is the ratio of h on t, and is equal to 1.59 cm·kyr−1 on average (Fig. 3B). The same calculation with a sediment accumulation rate equal to 0.08 mm·y − 1 (i.e., considering 20-kyr bundles as proposed by Bádenas et al. (2003, 2005) instead of 100-kyr small-scale sequences as proposed in the present work) would result in a rate of sea-level rise that would be one order of magnitude higher (i.e., equals to 13 cm·kyr− 1) than the rate of sea-level rise obtained by numerical modelling for the Late Jurassic Iberian platform by Aurell and Bádenas (1994) and Aurell et al. (1995, 1998). Quantitative estimates of the rate of Phanerozoic sea-level changes are scarce. However, the rate of sea-level rise calculated in the present work is also close to the rate of sea-level rise at the boundary between the Pliensbachian and the Toarcian on the Yorkshire coast, which is equal to 1 cm by 1.2 kyr (Hallam, 1997). This latter value is consistent with the rate given by Pitman (1978) and Donovan and Jones (1979) for the sea-level variations due to tectonoeustatism. 7. Conclusions The detailed microfacies analyses of host, fine-grained deposits and the palynological, sequence-stratigraphic, and carbon- and oxygenisotope analyses of 4 Late Jurassic 5 to 7 m thick sections located along a 4 km-long outcrop showing the transition between the shallow and the relatively deep realms of a middle ramp, north of the village of Ricla (Zaragoza Province, northeastern Spain) reveal that: 1) the finest as well as the coarsest sediment was reworked in these storm-dominated environments, and resedimented material probably composes the whole limestone beds; 2) alternation, marly interbed and limestone bed thickness allow the definition of small- and medium-scale sequences that correlate from one section to the other. The distribution of siliciclastics across the ramp by storm-induced currents explains why the changes in the alternation thickness resemble the changes in the marly interbed thickness in the most proximal sections (i.e., R3, R4), while they rather correlate with the changes in the limestone bed thickness in the most distal sections (i.e., R6, R7). The most distal environments are also characterised by the thickest alternations that are the most preserved from reworking and cannibalism by successive storm events. Sequence boundaries therefore correspond to thin alternations and marly interbeds in the most proximal sections, while they coincide with thin alternations and limestone beds in the most distal sections (i.e., R6, R7). On the contrary, maximum-flooding surfaces correspond to thick alternations and marly interbeds in the most proximal sections, while they coincide with thick alternations and limestone beds in the most distal sections. Because of only very slight excursions in δ18O and δ13C values, the chemostratigraphy is not contradictory to the other correlation, but in itself is not conclusive; 3) the sections studied are very short and only one medium-scale sequence was defined. This medium-scale sequence contains 4 small-scale sequences that include 5 alternations on average. This stacking pattern suggests an orbital control on sedimentation: alternations would last 20 kyr, small-scale sequences 100 kyr, and medium-scale sequences 400 kyr; 4) a new approach based on the quantification of the rates of sediment accumulation, preservation and sea-level rise and on their comparison with previous results from literature validates this time calibration in the short interval studied. The duration of depositional sequences proposed in this work is not consistent with the bundle and set of bundle duration determined by Bádenas et al. (2003) in the outer-ramp carbonate-dominated succession of Aguílon section in the northern Iberia Ranges. This difference may be due to the effects of large-scale (or long-term) accommodation

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change on metre-scale (or short-term) cycles but also to the position of the interval studied on the ramp (or in the Iberian Basin). Bádenas et al. (2003) used spectral analysis, which is perhaps not the most appropriate tool to investigate such a complex and dynamic system. A better understanding of the sedimentary processes controlling this system requires more high-resolution facies and stacking pattern investigation, which is probably the best way to constrain the dynamics of the system studied at each step of its evolution and to determine the sequence duration. Acknowledgements We thank the Foundation MAIF, which financed this work. We are grateful to Ghislaine Broillet from the University Lyon 1 for the production of the thin sections of rocks, and to Dr. Marie Balasse and Joël Ughetto from the Muséum National d'Histoire naturelle of Paris, for having performed carbon- and oxygen-isotope analyses. We also thank Dr. Fabienne Giraud from the University Grenoble 1 and Dr. Johann Schnyder from the University Paris 6 for their help in the field. Dr. Fabienne Giraud is also greatly acknowledged for calcareous nannofossil analyses, and Dr. Stéphane Reboulet from the University Lyon 1, for his helpful comments on a preliminary version of this manuscript. Editor Brian Jones and two anonymous reviewers are thanked for their constructive comments. References Aurell, M., Bádenas, B., 1994. Facies and depositional sequence evolution controlled by high-frequency sea-level changes in a shallow-water carbonate ramp (late Kimmeridgian, NE Spain). Geological Magazine 141, 717–733. Aurell, M., Bosence, D., Waltham, D., 1995. Carbonate ramp depositional systems from a late Jurassic epeiric platform (Iberian Basin, Spain): a combined computer modelling and outcrop analysis. Sedimentology 42, 75–94. Aurell, M., Bádenas, B., Bosence, D.W.J., Waltham, D.A., 1998. Carbonate production and offshore transport on a Late Jurassic carbonate ramp (Kimmeridgian, Iberian basin, NE Spain): evidence from outcrops and computer modelling. In: Wright, V.P., Burchette, T.P. (Eds.), Carbonate Ramps. Geological Society of London, Special Publication. 149, pp. 137–161. Aurell, M., Bádenas, B., Ipas, J., Ramajo, J., 2010. Sedimentary evolution of 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. Baccelle, L., Bosellini, A., 1965. Diagrammi per la stima visiva della composizione percentuale nelle rocce sedimentarie. Annali della Università di Ferrarra, Sezione IX, Science Geologiche e Paleontologiche. 1, pp. 59–62. Bádenas, B., Aurell, M., 2001a. Proximal–distal facies relationships and sedimentary processes in a storm dominated carbonate ramp (Kimmeridgian, Northwest of the Iberian Ranges, Spain). Sedimentary Geology 139, 319–340. Bádenas, B., Aurell, M., 2001b. Kimmeridgian palaeogeography and basin evolution of northeastern Iberia. Palaeogeography, Palaeoclimatology, Palaeoecology 168, 291–310. Bádenas, B., Aurell, M., Rodríguez-Tovar, F.J., Pardo-Igúzquiza, E., 2003. Sequence stratigraphy and bedding rhythms of an outer ramp limestone succession (Late Kimmeridgian, Northeast Spain). Sedimentary Geology 161, 153–174. 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 ∂13Ccarb (Kimmeridgian, NE Spain). Sedimentology 52, 1253–1275. Carcel, D., Colombié, C., Giraud, F., Courtinat, B., 2010. Tectono-eustatic control on a mixed siliciclastic-carbonate platform during Kimmeridgian (La Rochelle platform, western France). Sedimentary Geology 223, 334–359. Colombié, C., Schnyder, J., Carcel, D., 2012. Shallow-water marl limestone alternations in the Late Jurassic of western France: cycles, storm event deposits or both? Sedimentary Geology 271–272, 28–43. Cozzi, A., Grotzinger, J.P., Allen, P.A., 2004. Evolution of a terminal Neoproterozoic carbonate ramp system (Buah Formation, Sultanate of Oman): effects of basement paleotopography. Geological Society of America Bulletin 116, 1367–1384. Cunningham, K.J., Collins, L.S., 2002. Controls on facies and sequence stratigraphy of an upper Miocene carbonate ramp and platform, Melilla basin, NE Morocco. Sedimentary Geology 146, 285–304. Donovan, D.T., Jones, E.J.W., 1979. Causes of world-wide changes in sea level. Journal of the Geological Society 136, 187–192. Dunham, R.J., 1962. Classification of carbonate rocks according to depositional texture. In: Ham, W.E. (Ed.), Classification of Carbonate Rocks. American Association of Petroleum Geologists Memoir. 1, pp. 108–121.

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