Palaeoshoreline for the Late Cretaceous Marine Platform in the Iberian Trough (Leonese Area, Spain) Deduced from Outcrop and Subsurface Analysis

Cent. Eur. J. Geosci. • 4(3) • 2012 • 395-415 DOI: 10.2478/s13533-011-0067-6

Central European Journal of Geosciences

Palaeoshoreline for the Late Cretaceous marine platform in the Iberian Trough (Leonese Area, Spain) deduced from outcrop and subsurface analysis

Research Article

Antonio Herrero-Hernández1∗, Fernando Gómez-Fernández1†

1 Universidad de León, Departamento de Tecnología Minera, Topográﬁca y de Estructuras. C/ Jesús Rubio 2, 24004-León, Spain

Received 18 November 2011; accepted 12 March 2012

Abstract: The location of the Late Cretaceous paleoshoreline in the Leonese Area (Iberian Trough, Spain) has been investigated by seismic analysis through isobath and isopach maps. The succession can be divided into two depositional sequences: DS-1 and DS-2. These sequences are composed of fluvial systems at the base, with paleocurrents that flowed eastward and north-eastward. The DS-1 sequence (Late Albian-Middle Turonian) shows intertidal to subtidal and offshore deposits at the top, while the DS-2 sequence (Late Turonian-Campanian) presents intertidal to subtidal, tidal flat and shallow marine and lacustrine deposits at its top. The stratigraphic cyclicity based on systems tracts shows that these two depositional sequences exhibit remarkable eustatic control. Both sequences start at the base with a significant sedimentary supply from fluvial systems, related to eustatic fall episodes, and conclude at the top with transgressive periods. The evolution of the basin reveals the history of base-level changes and associated shifts in depositional trends during successive stages. The deeper sectors of the DS-1 sequence are located towards the northeastern part of the study area while the proximal portion of the basin-margin is located to the southwest. The paleoshoreline is placed in a direction oriented at 120. The variations in thickness are elongated in orientations between 030 and 050 and are mainly related to paleovalleys and tributary fluvial networks that supply sediment through the shoreline. It is possible that these variations may be related to active synsedimentary faults. Depocenters move toward the northeast and east during the DS-2 sequence while the proximal portion of the basin-margin moves to the southwest. The paleoshoreline has an orientation of 155 direction and moves basinward. The isopach maps show a group of corridors oriented at 130-140 and 165-170, interpreted as result of accumulation of sandy bodies such as inter and subtidal bars. The fluvial systems are transversal to the paleoshoreline direction. Keywords: shoreline, sequence stratigraphy • isobaths and isopachs maps • seismic lineaments • Late Cretaceous • Iberian Trough © Versita sp. z o.o.

∗ †

E-mail: [email protected] E-mail: [email protected]

395 Palaeoshoreline for the Late Cretaceous marine platform in the Iberian Trough (Leonese Area, Spain) deduced from outcrop and subsurface analysis

1. Introduction consideration. Lastly, this paper analyzes the main factors controlling the sedimentary evolution of the area and their implications for understanding the Late Cretaceous. 2. Data and methodology During Late Cretaceous time (Late Albian to Maastrichtian) marine and continental sediments were deposited in the western margin of the Iberian Trough, in the so-called “Castilian ramp” [1]. This is thought of as an extensional sedimentary basin that was The sedimentological and sequence stratigraphic analysis developed after Jurassic rifting. During this period there has been based on the interpretation of twelve was an active rifting segment in the Bay of Biscay related stratigraphic logs (Figs. 2 and 3) made in Cretaceous to the Atlantic opening (Fig. 1), while along the Iberian outcrops to the north of the study area and measured over Massif (Iberian Ranges, Maestrazgo and Central System a total of over 4,000 meters thickness. Lithology, texture, of Spain) sediments were deposited which are similar to sedimentary structures, including trace fossils, and fossil those defined and analyzed in this article [2–5]. content were described. The recognition of stratigraphic discontinuities, and cyclicity trends marked by paleosols The Mesozoic deposits in the western margin of the were also used for stratigraphic correlation. A set of rocks Iberian Trough (Leonese area, Spain) are presently were sampled for petrographic, granulometric and pollen located between the Cantabrian Mountains represented analysis. by the Variscan Domains (Cantabrian Zone and West-Asturian-Leonese Zone) and the Cenozoic deposits A grid of seventeen 2D seismic reflection profiles were of the Duero Basin. The Late Cretaceous succession crops used to investigate the materials in the subsurface, with out at the surface as a thin (150 to 650 m thick) and seismic profiles distributed in two orthogonal directions discontinuous E-W band, 60 km long and 5 km wide, which (Fig. 4). Seismic data interpretation has allowed the includes fluvial, transitional and shallow marine deposits definition of two new depositional sequences (see section (Fig. 2). 4), and has been used to make the isopach maps of these units. The isopach maps were made using the technique Many previous studies [1, 6–15], have described the Late of map subtraction with a contour interval of 50 m, and Cretaceous succession in the Leonese area. However, the mapping of faults affecting these units has also been palaeogeographic distribution of the different sedimentary carried out. environments and the location of coastline have not been The average location of the paleoshoreline is determined studied in detail, mainly due to the outcrop limitations. It in the subsurface using a combination of field is therefore necessary to analyze subsurface data to obtain sedimentological data and isopach maps. palaeogeographic and palaeotectonic reconstructions of the sedimentary basin. The Late Cretaceous sediments in the Leonese area were deposited in fluvial systems and carbonate platforms that Obtaining lineaments from geophysical data is a common occupied the same palaeogeographic positions throughout technique in studies of the subsurface, especially those the Late Cretaceous with minor variations mainly due to related to fracture patterns and other tectonic features. changes (rise or fall) in sea-level and structural trends. Lineament analysis can also be useful in identifying The presence of coastal sedimentary facies can be used palaeogeographic and sedimentological features, such as the evidence of the paleoshoreline in the field. as coastline position, the orientation of fluvial channel networks, as well as the location of the main depocentres The resolution of the seismic profiles does not allow the of the basin. presence of the coastal sedimentary environments to be determined and so two sectors have been defined, in order The main purpose of this paper is to analyse the Late to establish the average position of the paleoshoreline Cretaceous succession in the subsurface to determine in the isopach maps. These sectors are: (1) the the palaeogeographic distribution (in space and time) proximal portion of the basin-margin which generally of sedimentary environments and the mean location of contains alluvial, deltaic and shallow-marine depositional the coastline. High quality seismic data has enabled systems; and (2) the distal (basinward) portion, containing the creation of the isobath and isopach maps for the outer-shelf, slope and deeper water depositional systems. differentiated units. The sequence stratigraphic analysis has taken the lithostratigraphical and sedimentological Two premises have been taken into account in this study: characteristics of the deposits, the sea level fluctuations, (1) the lateral facies shift between marine and continental and the position of the fluvial-marine transitional zone into environments is located in the field between stratigraphic 396 Antonio Herrero-Hernández, Fernando Gómez-Fernández

Emerged areas 6 Open platform and deep basin Shallow carbonate platform 30° Coastal deposits 4 Siliciclastic coastal deposits 2 3 5 1 1-Hesperian Massif 2-Iberian Trough 3-Ebro Massif 4-PyreneanTrough 5-Lusitanian Basin 25° 6-Central Massif

Study area Transform faults Rift axis segments

Figure 1. Paleogeographic map of the Iberian Trough (Late Turonian). Modiﬁed after [16, 17, 18].

profiles 4, 5, 6 and 7 (Fig. 3); and (2) the existence of a The paleogeographic and paleoclimatic context of the lineament that separates the sector where the isolines are region consists of fluvial systems and carbonate platforms more homogeneous (open-trace isolines) from the sector developed in a hot and humid climate with tropical where highs and lows are grouped (closed isolines) in characteristics, and approximate latitude of 25-30° N the isopach maps. This lineament is considered the [21, 22]. A change from a warm humid climate during the average position of the paleoshoreline, which separates Early Cretaceous to an arid desert climate during the Late the western sector, with sediment thicknesses less than Aptian-Early Cenomanian is determined in the eastern 200-300 m, from the eastern one, where the thicknesses sector of Iberia [23, 24]. are greater. Occasionally, to the west of this lineament Two tectonic contexts can be differentiated in the region some marine deposits outcrop (Brugos de Fenar), marking during Alpine orogenesis. The first one is due to the the peak of the Late Cretaceous transgression. The evolution of the region during the Late Cretaceous and it is seismic profiles show that this lineament and the change associated with a post-rifting phase in the Gulf of Biscay, in thickness on both sides are not related to the mapped with an extensive tectonic regime controlled by normal faults, but can be interpreted as result of the increase in faults mainly aligned NE-SW and NW-SE (see Fig. 1). depositional thickness of sediments in the area. The Porma and Yugueros Faults (NE-SW) (Fig. 2) and the 3. Regional stratigraphy, Ventaniella Fault (NW-SE) may be in this group, which depositional environments and is also formed by major faults of the Lusitanian Basin and the Iberian Trough (Fig. 1). The second tectonic context tectonic framework is a compression stage superimposed on the previous context. Subsequently, during the end-Cretaceous and early Cenozoic, the collision of the Iberian and Eurasian tectonic plates took place. The region was subjected to compressive stress with the formation of (1) an uplifted The Cretaceous units are separated from the basement by block to the north, the Cantabrian Zone where some a basal unconformity, under which a kaolinitic alteration Variscan faults and thrusts were slightly reactivated; and mantle was developed. The upper limit of this succession (2) a foreland basin to the south, the Cenozoic Duero is an unconformity or a disconformity with the overlying Basin [25]. The cross-sections of both geological domains Cenozoic deposits of the Duero Basin [19, 20]. show the geometry of this boundary (Fig. 5). This The general stratigraphic organisation is composed of two Alpine compression took place mainly in NE-SW and lithostratigraphic units, the Voznuevo Member and the N-S directions and caused an internal deformation in the Boñar Formation. The Boñar Formation passes laterally Mesozoic succession, confirmed by evidence such as La into the Voznuevo Member, with a change in lithology from Losilla Anticline and Las Bodas Syncline (Fig. 2). These detrital-carbonate materials (eastern sector) to exclusively folds are associated with a backthrust rotated by simple detrital materials (western sector). The Boñar Formation shear related to the larger thrust responsible for the uplift is absent west of Brugos de Fenar (Fig. 2, 3). of the mountain range [26]. 397 Palaeoshoreline for the Late Cretaceous marine platform in the Iberian Trough (Leonese Area, Spain) deduced from outcrop and subsurface analysis Cistierna 4.749.000 4.746.000 4.743.000 4.740.000 Q P N Yugueros 42°40' 52 42°50' 12 40 85

GUARDO Yugueros Fault Yugueros 0 10 20 km

La Estación 5°00'

75 5°00'

318.000 318.000 La Ercina

Sabero-Gordón Fault

CISTIERNA

t t 52 Las Bodas Syncline

44 t 12

La Acisa de La Arrimadas Las

t t

t 27 40

t 11

8 t 50 10

40 t

10 t 7 CENOZOIC OUTCROPS QUATERNARY OUTCROPS QUATERNARY T 9 M3 P C1

8 t C1 9 M2 M1 t

t M4 40 80

35 312.000 t 312.000

Boñar

5°30' t Barrillos de Arrimadas Las T 5°30' 28 25 5 70 35 Las Bodas

30 22

42 t 30 4 38 La Losilla

t 35 C1 Q M2

t s M4 M1

t t 45

P t T 20

23 t

28 s

C1 s

Q t 65

s La Devesa de Boñar

t 2 s 27

40 t

t t s 35

t s 40 3 T LA ROBLA LA

t 28

t Palazuelo de Boñar

38 s PALEOZOIC ROCKS (CANTABRIAN ZONE) ROCKS (CANTABRIAN PALEOZOIC PALEOZOIC ROCKS (CENTRAL IBERIAN ZONE) ROCKS (CENTRAL PALEOZOIC MESOZOIC OUTCROPS t

s t 1

Llamera

306.000 t 306.000 42°50' 42°40' P 76 30 36 24 M4 M3

Q Porma Fault Porma La Losilla Anticline La Losilla T 80 Quaternary rocks (Q) (T) Cenozoic Units Dolomitic Member (M-4) Heterolithic Member (M-3) Argillaceous & Sandy Member (M-2) Calcarenitic Member (M-1) Member (C-1) Voznuevo Paleozoic rocks C1 80 Campohermoso IBERIAN RANGE M4 100 km

M3 Q

300.000 300.000 85 6 MADRID P 85 M3 Sabero-Gordón Fault M4 C1 T 40 LISBOA 60

La Valcueva 80 DUERO BASIN

294.000 Q 294.000 CANTABRIAN MOUNTAINS CANTABRIAN BOÑAR FORMATION VOZNUEVO MEMBER Cenozoic basins 5 35 18 C1 70 M4 Paleozoic & Mesozoic rocks Q 80 C1 C1 P T Robledo de Fenar Q M4

N 288.000 0 2 Km1 288.000 Fenar 80 Brugos de AFRICA EUROPE 4.749.000 4.746.000 4.743.000 4.740.000

Figure 2. Detailed geologic map of the Late Cretaceous successions showing the distribution of the main units, the local tectonic setting and the locations of logged sections (numbers 1 to 12). Compiled from [14].

398 Antonio Herrero-Hernández, Fernando Gómez-Fernández

WEST 4 5 6 7 8 9 10 11 12 EAST Base level Top erosive of preserved sections rise fall SD HST 2 Dolomitic Member (M-4) MFS ? TST 2 DS - 2 MRS LST 2 BOÑAR BSFR HST 1 MFS FORMATION 3 Heterolithic Member (M-3) TST 1 MRS SD

Argillaceous-Sand y Member (M-2) 1 2 LST 1

DS - 1 Calcarenitic Member (M-1) MEMBER VOZNUEVO

100 m

Voznuevo Member (C-1) 50 m

0 m 10 Km 0 Dolomitic Member (M-4)

BOÑAR Heterolithic Member (M-3) FORMATION Argillaceous-Sandy Member (M-2) Calcarenitic Member (M-1) VOZNUEVO Voznuevo Member (C-1) MEMBER

Figure 3. Cross-section with sequence stratigraphic framework for the Late Cretaceous strata in the Leonese Area, Iberian Trough, (see ﬁgure 2 for section location). On the far right is the interpreted relative sea-level curve. Abbreviations: LST-lowstand systems tract; HST-highstand systems tract; TST-transgressive systems tract; BSFR- basal surface of forced regression; MFS-maximum ﬂooding surface; MRS-maximum regressive surface; SD-subaerial discontinuity.

Also, various E-W and NW-SE thrusts and faults, such faults appear at the surface (cross-section 1, Fig. 5). Most as the Principal and the El Campillo Thrusts, affect all of these faults do not seem to have a syn-sedimentary the Mesozoic and Cenozoic sediments. These thrusts and activity during the Mesozoic stage, as tectonic movements faults are associated with a thick-skinned deformation are not observed in relation with variations in thicknesses. style, having a kilometric length and south vergence. The variations of thickness in the isopach maps can be Their emplacement involves the Paleozoic basement and related to the sedimentary dynamics and the formation of produces the uplift of the Cantabrian Range during the sub-basins. Cenozoic stage [25] as a result of the movement of Variscan 3.1. The Voznuevo Member: facies and structures to the south. depositional environments The compressional end-Cretaceous-Cenozoic stage masks the prior extensional stage, generating a deformation that caused the reactivation of Variscan and Mesozoic faults The thickness of this unit is 350 m in the western sector and the formation of new faults and thrusts affecting the of the studied area [28] and 150 m in the central sector main seismic reflectors. The inversion of some of the [29, 30]. The unit encompasses conglomerates, sands and previous Variscan faults also often occurs, passing from lutites and essentially is composed of white, reddish and normal to reverse. yellowish sands weakly cemented by iron oxides (Figs. Six different groups of faults have been defined in the 7A, 7B and 8). It was deposited by fluvial systems with subsurface from the seismic sections [27], with NW-SE (N source areas located to the west and southwest. The 90-120) average directions. These faults and thrusts affect Voznuevo unit was defined for the first time by [8] and is mainly the Mesozoic units (Fig. 6) although some of them equivalent to the Arenas Utrillas unit, defined by [31] in penetrate Cenozoic units. In the northwestern area these the Iberian Range, and is classified here as local member, 399 Palaeoshoreline for the Late Cretaceous marine platform in the Iberian Trough (Leonese Area, Spain) deduced from outcrop and subsurface analysis

FIGURE 6A, 6B 5°00' 5°30'

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DR85-04V �

� EL CAMPILLO DR85-02V 42°40' 42°40'

ALMANZA DR87-11V

Torio R. Torio Carrión River Carrión

Bernesga River Bernesga DR87-02VD

LEÓN DR85-08V

DR85-05V SALDAÑA 42°30' 42°30' Porma River DR85-06V Cea River DR87-17V Esla River DR87-19V DR87-13V DR85-01V DR85-07V SAHAGUN Órbigo River LEÓN-1BIS N VALENCIA DE LEÓN-1 DON JUAN DR87-16V

FIGURE 6C

5°00'

5°30'

� QUATERNARY OUTCROPS � 0 10 20 km MAJOR THRUST CENOZOIC OUTCROPS PETROLEUM WELLS MESOZOIC OUTCROPS LOCATION SEISMIC SECTIONS PRE-MESOZOIC ROCKS

Figure 4. Generalized geologic map and location of the seismic sections and of the main petroleum wells.

following nomenclature of [32]. system, changing from meandering and braided to more The age of the Voznuevo Member is inferred by its position channelised conditions and with more stable flood plains. with respect to the underlying and overlying units and was One cannot rule out the existence of a significant break in determined in the Iberian Range to be from the Middle and the sedimentation; it should be marked by the presence Late Albian to the Turonian. However, in the study area of one or multiple levels of paleosols with some lateral the upper part of this unit has been dated with pollen continuity. The result is the presence of much finer data to the beginning of the Late Cretaceous [9]. In other materials in the upper part of the Voznuevo Member. In sectors of the Iberian Trough this unit extends from the both parts a set of terrigenous facies and subfacies with Aptian [33] to the Santonian [34]. vertical and lateral repetitions have been found. This separation was established in the Leonese area [11, 35] The Voznuevo Member can be divided into two parts based and in the Iberian Range [36]. on the presence of vertical changes in sedimentological features, such as: variations in grain size, changes in The interpretation of the Albian clastic units in the paleocurrents directions and a considerable variation in western margin of the Cretaceous Iberian Trough varies the energy conditions in the sedimentary environments. from delta fan environments [37], to deltaic environments These variations may be a response to a change in dominated by tides [38] and tidal flat facies and other sedimentary conditions, which would evolve vertically coastal deposits [39]. In the Iberian Range, an extensive and laterally, which would vary the type of fluvial desert system existed, based on the occurrence of dunes 400 Antonio Herrero-Hernández, Fernando Gómez-Fernández

2 3 Porma Fault Boñar Ventaniella 1 4 Fault La Robla

N Cistierna Guardo

0 10 20 Km

1 2

1 Km 1 Km 0 0 -1 -1 -2 -2 -3 -3 3 4 1 Km 0 1 Km -1 0 -2 -1 -3 -2 -3

Cenozoic Cretaceous Precambrian and Paleozoic

Alpine thrusts Angular syntectonic unconformity

Figure 5. N-S cross-sections showing the geological structure of the deposits at the northern boundary of the Duero Basin. Modiﬁed by [26].

and other aeolian deposits, with coeval shallow marine of conglomerates and sands, which would travel in traction deposits3.1.1. The [23, lower24, 40 part]. of the Voznuevo Member as bedload. The deposits within the fluvial channels come from clear water streams, and have both longitudinal bars of low relief as well as transversal bars with a well-developed avalanche face and a certain slope. Often, The lower part of the Voznuevo Member is made up these bars are subsequently colonized by vegetation and of a fining-upward lower-order terrigenous sequence of animals, whose roots and activity caused the development conglomerates and sandstones, which are badly classified, of soil-forming processes and bioturbation of freshly and a few lutites that are found more towards the top of deposited sediments, generating well-developed paleosol this part. The sediments are moderately to well-sorted horizons. with sedimentary structures that are sometimes marked by the presence of some conglomerates, or by alternating In the western sector (Rioseco de Tapia, 10 km west of colours. La Robla), and on top of the unit we find fluvial channels The base of the facies association corresponds to the filled with epsilon cross bedding, a characteristic of high filling of fluvial channels, mainly braided, that eroded the sinuosity channels. This suggests evolving depositional substrate, sometimes strongly. The top of this association conditions with an increase in the sinuosity of the river represents flood plain deposits with frequent features of channels due to the proximity of the base level. These high subaerial exposure and bioturbation. sinuosity channels are unique and they migrate between floodplain sediments. The sedimentation took place within broad channels; the sediment would be moved by currents in the shallow Moving laterally form the central sector analyzed (section waters with high carrying capacity and high values of 4, Figs. 2 and 3), some deposits have been found in tidal kinetic energy. These channels were stable and had a subenvironments in the upper layers of the unit. Cross high width/depth ratio, and were mainly low-sinuosity. bedding sands with laminae with very low inclination The concentration of sediment was high, mainly a mixture angles, between 2 and 10°, with wedge shaped cross-sets 401 Palaeoshoreline for the Late Cretaceous marine platform in the Iberian Trough (Leonese Area, Spain) deduced from outcrop and subsurface analysis

S DR 85-02V N Common deep point A wo-way travel time (s) travel wo-way T

S DR 85-02V N B 0.0 0.0 0.2 0.2 0.4 0.4 0.6 0.6 0.8 0.8 1.0 1.0 1.2 1.2 1.4 1.4 1.6 1.6 1.8 1.8 2.0 2.0 0 20 Km

Paleogene and Neogene Seismic Units (PgSU and NgSU) DS-2 Depositional Sequence Paleozoic Seismic Unit (PzSU) DS-1 Depositional Sequence

C DR 85-07V S Common deep point N 0.0

0.2

0.4 Paleogene and Neogene Seismic Units (PgSU and NgSU) 0.6

0.8

1.0

wo-way travel time (s) travel wo-way DS-2 T

1.2 DS-1

1.4 Paleozoic Seismic Unit (PzSU) 0 Km 20 Km

Figure 6. A) Fragment of the DR 85-02 V seismic section and B) the interpretation. The location of the seismic section is depicted in figure 4. C) Fragment of a seismic section (DR 85-07V) showing the reflections in the Paleozoic Seismic Unit (PgSU), Mesozoic Seismic Units (depositional sequences DS-1 and DS-2) and Cenozoic Seismic Units (PgSU and NgSU). The location of the seismic section is depicted in figure 4. Seismic data courtesy of REPSOL-YPF.

402 Antonio Herrero-Hernández, Fernando Gómez-Fernández

A B

M-2 M-1 M-3 M-4

CENOZOIC

VOZNUEVO MEMBER

D Y E

Z M-4 M-3 X

1 mm CENOZOIC

Figure 7. A) Fluvial cross-bedded fine-medium sands of the Voznuevo Member, from section 2 (see location in Fig. 2) (see hammer handle for scale). B) Field view of fluvial deposits of the Voznuevo Member, from outcrop section 1 (see location in Fig. 2). (Z) sandy siltstones show paleosol features and (X) channelized clast-supported conglomerates with cross-bedding. The scale is given by the hammer in the circle. The top of the section is upward. C) Complete view of the four members of the Boñar Formation (M-1 to M-4) between the Voznuevo Member and the Vegaquemada Formation (Cenozoic ) in La Ercina town. D) Grainstone of the Calcarenitic Member (M-1) (Boñar Formation). (X) Bioclasts. (Z) Peloids. (Y) Quartz grain. Modified after Gómez Fernández et al. (2003). E) Complete view of the Dolomitic Member (M-4) between the Heterolithic Member (M-3) and Vegaquemada Formation (Cenozoic) in La Ercina town. Top section to the right.

and laminae in opposite directions have been found. These The paleocurrent measurements in the western sector traits are due to the migration of dunes due to tidal (sections 1 to 4, Figs. 2 and 3) show a prevailing flow currents, swash flows and backwash in tidal channels direction3.1.2. The from upper the west. part of the Voznuevo Member and sand tidal flats. Their appearance points are the swash zone of a beach. Occasionally, areas of scattered accumulations of organic matter can be found. These correspond to plant fragments that have been transported In contrast, the upper part of the Voznuevo Member through a limited area where they accumulated, in an is formed by materials with a much finer grain: abandoned channel of inter-supratidal areas. The vertical more or less sandy silt, and intercalated sands, distribution of these sedimentary subfacies , where muds more dispersed conglomerates and microconglomerates with carbonaceous residues passes into coarse to medium with coarse to fine grain sizes. These sediments sands with swash type cross bedding and further towards form fining-upward sequences with greater lithological the surface, fine sands with wave ripples, helps to interpret variability, meaning that, in some sections there are the succession of facies as a terrigenous tidal flat, with more sand intercalations present and in others, more both intertidal and subtidal subenvironments. intercalations of conglomerates. 403 Palaeoshoreline for the Late Cretaceous marine platform in the Iberian Trough (Leonese Area, Spain) deduced from outcrop and subsurface analysis

80 h

h 50 h VOZNUEVO MEMBER

40 FLUVIAL

h LATE ALBIAN-EARLY LATE ALBIAN-EARLY CONIACIAN

20 h

Carboniferous: slates and limolites 0 m L/m Af Ag C M W P G

Conglomerates Large-scale cross bed. Carbonate nodules Sands Small-scale cross bed. Carbonate reticular Lutites Chanelized surface Rhizoliths Marls Lateral wedging Limestones Clay/oxide migrations Imbricated clasts Grainstones Burrows Normal gradding Dolostones h hidromorphy Sandy Marls Clay nodules Paleocurrents Marly-limestones Carbonate cement

Figure 8. Sedimentological log of the lower part of the Voznuevo Member near to Soto y Amío town, (section 1; see Fig. 2 for location).

404 Antonio Herrero-Hernández, Fernando Gómez-Fernández

There is generally an abundance of fine sediments, representing deposits on the floodplain by overflows along the main channels and the subsequent processes of fine material settling from suspension. The different processes of pedogenesis are constant and are often linked to redox processes of iron. Different mineralogical transformations & LACUSTRINE? occur that result in the genesis of paleosols of different DOLOMITIC MEMBER types, with accumulation of iron and/or manganese oxyhydroxides and the neoformation of kaolinite. This TIDAL FLAT T O SHALLOW MARINE flood plain is crossed by fluvial channels where sand bars and conglomerates accumulate. The sedimentation in the flood plain suggests a relatively high sedimentation rate, most likely related to deposition from flows with some clay loading. The presence of soil characteristics such as vertically oriented root bioturbation suggests a strong colonization of the MAASTRICHTIEN EARLY CONIACIAN-

ﬂoodplain by plants. - 2 SEQUENCE DEPOSITIONAL

The paleocurrent measurements in the western sector WITH T O SUBTIDAL

(sections 1 to 4, Figs. 2 and 3) show a prevailing ﬂow HETEROLITHIC MEMBER direction from the southwest. INTERTIDAL

3.2. The Boñar Formation: facies and INFLUENCES TERRIGENOUS depositional environments

The Boñar Formation is made up of limestones, CRETACEOUS dolostones, and some shaly, marlstone and sandstone intervals, with a maximum thickness of 385 m (Figs. 7C, FORMATION BOÑAR 7D, 7E and 9). This unit disappears westward from the town of placeCityBrugos Fenar (the edge of the marine MEMBER basin). OFFSHORE TRANSITION TRANSITION OFFSHORE

This unit has been divided into four lithological members SANDY AND ARGILLACEOUS LATERAL SHIFT TO FLUVIAL DEPOSITS LATERAL SHIFT TO FLUVIAL [14] who are: the Calcarenitic Member (M-1), the Argillaceous and Sandy Member (M-2), the Heterolithic T O Member (M-3) and the Dolomitic Member (M-4). SUBTIDAL The exact dating of the Boñar Formation is not MEMBER INTERTIDAL DEPOSITIONAL SEQUENCE - 1 SEQUENCE DEPOSITIONAL possible because the lack of precise paleontological CALCARENITIC 25 m data. Nevertheless, the correlation with successions located to the east of the region [13], allows Members ALBIAN-EARLY CONIACIAN LATE M-1 and M-2 to be assigned an Early ConiacianAcutostrea age. FLUVIAL MEMBER 0 m VOZNUEVO Datingacutirostris in the calcarenitesPraeradiolites of the M-3 plicatus Member assigns 150-300 m aOrbignya Santonian microstyla age with littoral faunaOrbignya [30] as cf. striata NILSSON,Cyclolites sp LAJARD, Figure 9. Representative log and interpreted depositional DOUVILLE, environments of the members of the Boñar Formation. Modiﬁed after [14]. DEFRANCE, . These correlations also allow an apparentLacazina Early Santonian to Late SantonianOrbignya heberti age to beverneuili attributed to the M-3 sequence. The M-4 Member contains , teeth of selacean and DOUVILLE, among other rudistes and they allow a Campanian age to be assigned. In the Iberian Range the paleontological data is more 405 Palaeoshoreline for the Late Cretaceous marine platform in the Iberian Trough (Leonese Area, Spain) deduced from outcrop and subsurface analysis

precise [13, 32, 41–50] and the lithostratigraphic beige-ochre tones, with mudstone textures, and to a lesser correlation can be established with appropriate extent wackestone and packstone textures. Dolomitization considerations of the separation distance. has been less intense in its upper half. In general, the strata are of metric thickness (up to 1 m) with exceptions In the eastern sector, the Calcarenitic Member (M-1) at the base, where they can exceed 2 m thick. This lies over the Voznuevo Member, with a distinct and member shows intercalations of marls, marly limestones, irregular contact, at times marked by calcareous grey clays, and to a lesser extent some calcareous microconglomerates. This member consists mainly of conglomerates, which are more frequent in the upper sandy bioclastic grainstone (calcarenites and calcirudites) layers. In various occurrences in the upper part, oolitic of brown, grey and ochre-colored tones. These grainstones with cross bedding has been observed. grainstones alternate with marls, sandy marls, marly limestones and, to a lesser extent, micritic limestones. From the petrographic point of view, the M-4 Member is This member has a maximum thickness of 175 m. Its mainly made up of dolomitized mudstone and occasionally layers form upward fining sequences on a metric and wackestone from bioclasts can be found (gastropods, decametric scale and have frequent internal medium ostracods, thin shelled bivalves and foraminifera), pellets and large-scale cross bedding, where paleocurrent flow (biopelmicrites), irregularly distributed (bioturbation) in a direction is towards the west. In the upper part there are micritic matrix (55-60%), where a tiling of spar cement fills frequent levels of oolitic limestone. the primary (10-12%) and secondary porosity. There are concentrations of iron oxides in stylolites and secondary The Argillaceous-Sandy Member (M-2) is between 60 and porosities that stain the bioclasts and matrix. 90 m thick in the eastern sector (sections 8 to 11, Figs. 2 and 3). It usually corresponds to areas that are covered or From the sedimentary point of view, the Boñar Formation poorly exposed, and it is constituted by clay-marls in its is a homoclinal marine ramp (north-Castilian ramp), that lower part and mostly sandstones in its upper part. The was open to the east. The accumulation of ooids, sandstones are generally medium-grained, well sorted, marine benthic fauna and reworked siliciclastic material and generally have abundant muscovite grains. They also with cross bedding that appear in the M-1 and M-3 have frequent medium-scale cross-bedding. Members are interpreted as intertidal bars to very shallow subtidal bars. The marl and bioturbated biomicrites with The Heterolithic Member (M-3) is 75-155 m thick. restricted marine fauna correspond to subtidal deposits. It is formed by alternating marls, micritic limestones, These characteristics may correspond to the formation calcarenites and sandstones. The marls contain thin of beach-lagoon-barrier islands [12] or by the general grey clay intercalations and abundant grains of muscovite restricted circulation that can characterize these types of and carbonaceous fragments, sometimes concentrated in platforms [51]. levels. Limestones range from biomicrites (mudstone and wackestone with bioclasts) to grainstone with a high The marls and clays of the lower part of the M-2 content of siliciclastic grains (calcarenites and calcirudites Member were deposited from suspension, in low-energy rich in quartz, orthoclase and occasionally glauconite and environments below the wave base level, in the muscovite), and they appear in banks, usually with a offshore-transition area. The top of this member consists strong lateral continuity. Sandstones are grey and beige, of sandstones with cross-bedding and carbonaceous sometimes with carbonate cement. fragments, which display a coarsening-upward trend. The top layers of the member are interpreted as From the petrographic point of view, the limestones foreshore-shoreface facies, beach deposits and fluvial of the M-1 and M-3 Members are sandy with grains channels. that are medium-fine to coarse, that are moderately well sorted, and have grainstone textures (biosparites, Often, the terrigenous supply from inland areas bio-oosparites sandstone). 35-40% of the total rock is contaminates the carbonate sedimentation in the marine bioclastic (echinoderms, brachiopods, bryozoans, molluscs platform, aborting it at various times (M-2 and M-3). and pellets), some of which have a thin oolitic covering, This terrigenous sediment has an abundance of feldspar and 20-25% is siliciclastic (quartz, feldspars -mainly and mica particles, from plutonic rocks from the west and orthoclase- and to a lesser extent glauconite and southwest produced mostly during times of low sea level. muscovite). Spar cement, tiling and isopach crust The M-4 Member consists of dolomitized mudstones completely seal the abundant primary interparticle (Fig. 7D) and occasionally bioturbated wackestones with porosity (35-40%). bioclasts (gastropods, ostracods, thin shelled bivalves The Dolomitic Member (M-4) has a maximum thickness and foraminifera) and pellets (biopelmicrites). This M-4 of 95 m. It consists of dolomitized limestones with Member is defined as deposits of tidal flats and lagoon 406 Antonio Herrero-Hernández, Fernando Gómez-Fernández

facies. towards the NW (continuous line in Fig. 11), represents 4. Depositional sequences and the enclosure of the 200 m thick isoline and delimits these sectors. Towards the northeast of this lineament lineaments analysis the sequence shows a thickness between 200 m and 800 m. Up to half a dozen corridors (passageways) can be found transversal to this lineament. They are identified by the warped shape of isolines 150, 200, and 250 m, In previous papers [25, 52] the regional stratigraphic forming incoming and outgoing V-shaped patterns. These architecture has been summarized in four seismic units: corridors are oriented between 030 and 050 and are less the Palaeozoic Seismic Unit, the Mesozoic Seismic Unit, than 250 m wide (dotted lines in Fig. 11). The wider the Palaeogene Seismic Unit and the Neogene Seismic corridors (between 350 and 800 m thick) can be found Unit. These units correspond to higher-order sequences parallel to these lines (broken lines in Fig. 11). in the hierarchy of stratigraphic sequences. In the present The lowstand system tract (LST-1) is represented by a paper, the Mesozoic Seismic Unit (MzSU) is analyzed fluvial braided system, with bars and channels and flood (Fig. 6). plain deposits (Voznuevo Member), with more than 300 Following the terminology proposed among others by m thickness of sediments (Fig. 3). The paleocurrent [53–56], and based on sedimentological data and seismic directions of E and NE and the orientation 030-050 of analysis, the Voznuevo Member and the Boñar Formation the isopachs (see dashed lines in Fig. 11) shows that the can be interpreted as corresponding to two depositional mouth of the marine basin was located towards the NE sequences: the DS-1 sequence (Lower Mesozoic Seismic with a greater thickness of sediments in this area. Unit) and the DS-2 sequence (Upper Mesozoic Seismic The second stage corresponds to the transgressive system Unit) (Figs. 3 and 6). tract (TST-1), which is represented by the M-1 Member The DS-1 comprises the lower part of the Voznuevo of the Boñar Formation (Fig. 3). It corresponds Member in the western sector, and the Voznuevo to tidal environments and represents the termination Member and the Calcarenitic (M-1) and lower part of towards the continent (landward) of the carbonate the Argillaceous-Sandy Member (M-2) of the Boñar platforms that developed more widely to the east. The Formation in the eastern sector. The DS-2 sequence microconglomerates of the M-1 member correspond to the encompasses the upper part of the Voznuevo Member from maximum regressive surface (MRS), transgressive surface stratigraphic section 6 to the west, and the upper part of for other authors, [57] and represent a coastal onlap. The the Argillaceous-Sandy (M-2) and the Heterolithic and MRS marks the fluvial to tidal transition, thus defining Dolomitic Members (M-3, M-4) of the Boñar Formation the transition from LST-1 into the TST-1. to the east. In next sections, the sedimentary evolution of The deposits in the HST-1 are deeper than the previous these two depositional sequences is interpreted based on ones (TST-1) and indicate a new change in shoreline the stratigraphic data (Fig. 3) and isopach maps obtained position which migrates landward. The HST-1 is mainly from seismic analysis (Figs. 6, 10, 11 and 12). characterized by low energy offshore-transition facies The Late Cretaceous successions are thinner in the west associations and low energy carbonate platform deposits and southwest sectors (see isopach map in Fig. 10), while (base of M-2 Member). It corresponds to a stage of the average thickness of this succession is 800 m in the base level rise and generates a normal regression of the NE sector. The region is divided into two sectors by a shoreline. HST-1 shows a retrogradational dispersal of northward line oriented at 155 (broken line in Fig. 10) the facies belts and represents a transgressive maximum that passes through the Boñar town. In the western sector, in the Late Cretaceous, which can be correlated with the the succession is generally less than 600 m thick, whereas Cenomanian transgression seen along the Iberian Range. in the eastern sector two depocentres can be recognized with thicknesses around 1,000 m and 1,900 m near to The facies associations in the upper layers of the lower Saldaña and Guardo towns, respectively. part of the Voznuevo Member allow us to interpret the 4.1. DS-1 depositional sequence sedimentary environment as a terrigenous tidal flat, with both intertidal and subtidal subenvironments. To the east there is a lateral facies shift identified in section 7 (Fig. 3), passing laterally into the marls and clays of the base of the The isopach map for the DS-1 sequence (Fig. 11) shows M-2 Member (offshore-transition facies). In alluvial strata, values lower than 200 m thickness located in the west and the maximum flooding surface (MFS) is represented by the southwest sectors. A lineament oriented at 120 that curves onset of marine processes [58]. In this sense, the maximum 407 Palaeoshoreline for the Late Cretaceous marine platform in the Iberian Trough (Leonese Area, Spain) deduced from outcrop and subsurface analysis

4760000 FIGURE 2 PORMA FAULT VENTANIELLA FAULT N 155 BOÑAR PRINCIPAL THRUST EL CAMPILLO THRUST LA ROBLA CISTIERNA GUARDO 4740000

1250 PEÑA-1 EL CAMPILLO

ALMANZA 4720000 LEÓN UTM Y (HUSO 30 N) SALDAÑA VILLAMERIEL

0 250 4700000

500

750 LEÓN-1BIS

LEÓN-1 4680000 260000 280000 300000 320000 340000 360000 380000 400000 Major faults and thrusts in N Alpine thrusts in the Variscan basement UTM X (HUSO 30 N) subsoil 0 Km 20 Km

Figure 10. Isopach map of the Mesozoic Seismic Unit (MzSU). The broken line corresponds to the 155 direction. Contour interval of 50 m. See text for discussion.

N 30-50 4760000 FIGURE 2 N 30-50 PORMA FAULT VENTANIELLA FAULT

BOÑAR PRINCIPAL THRUST LA ROBLA CISTIERNA EL CAMPILLO THRUST GUARDO 600 4740000 PEÑA-1 EL CAMPILLO

500 ALMANZA 4720000 LEÓN

UTM Y (HUSO 30 N) SALDAÑA VILLAMERIEL 0

4700000 500

LEÓN-1BIS 300 400 100 200 LEÓN-1 4680000 260000 280000 300000 320000 340000 360000 380000 400000 N 120 N Major faults and thrusts in UTM X (HUSO 30 N) Alpine thrusts in 0 Km 20 Km subsoil the Variscan basement

Figure 11. Isopach map of the DS-1 sequence. The continuous line corresponds to the 120 direction that curves towards NW. The dotted lines correspond to the 30-50 directions with thickness less than 250 m. The broken lines correspond to the 30-50 directions with thickness higher than 350-800 m. Contour interval of 50 m. See text for discussion.

408 Antonio Herrero-Hernández, Fernando Gómez-Fernández

transgressive shoreline (maximum flooding surface, MFS) transversal to the main lineament which is oriented at at the base is located in the Brugos de Fenar section, 155. These zones represent the distal zones of the as suggested by the preserved shoreline deposits in this terrigenous supply from the continental areas, given area. Further west, the landward portion of the basin is that these transversal directions coincide with the fluvial affected by the rise of the fluvial base level, with more drainage patters defined earlier for the Voznuevo Member. space in the basin for accommodation and evolution of a The invasion of the marine platform by terrigenous complex high-sinuosity fluvial system. materials from fluvial systems occurs at end of this phase, The position of the paleoshoreline in the isopach map at top of the M-2 Member. These fluvial sandstones during the DS-1 sequence is placed oriented to 120, re-establish the non-marine sedimentation and they are and curves towards NW (Fig. 11). This paleoshoreline formed during sea-level fall. The shoreline is forced is located in the SW sector of the study area. The to regress by the falling of the base level. Several differences in thickness between corridors with less than different names have been suggested for packages of 250 m (oriented between 030 and 050, dotted lines in Fig. strata formed during this stage. Following the terminology 11) and corridors of greater thickness (between 350 and proposed by [55, 56, 59, 60], among others, the deposits 800 m) can be found parallel to these lines (broken lines in accumulated during a sea-level fall are: the FSST (falling Fig. 11). These differences in thickness are also observed stage systems tract) or early LST. In this case the lower in the field, where no outcrop or very thin outcrops of M-1 boundary is the sequence boundary. According to [61, 62] and M-2 Members (Boñar Formation) are found (5, 6, 7 the deposits accumulated during the sea-level fall are and 12 sections, Figs. 2 and 3). deposits from the late HST. We prefer early lowstand The highs and lows of the isopach maps are initially systems tract (LST-2) because it refers to the relative fall difficult to relate to faults and paleogeographic thresholds of sea level that can be directly deduced from the facies associated with basement faults. They may be related to pattern of the systems tract. the sedimentary dynamic and formation of sub-basins with The lower boundary of the LST-2 is a sequence the internal stacking of sediments. However, some of the stratigraphic surface, and is marked by the basal surface variations in thickness may be caused by movements along of forced regression (BSFR). Landward, the BSFR is faults as can be observed in the seismic profiles (Fig. 6). accompanied by a considerable variation in the energy These thresholds would be oriented between 030 and 050, conditions of the fluvial environments, which vary from concordant with the Porma and Yugueros Faults (Fig. 2). 4.2. DS-2 depositional sequence meandering and braided to more channelised conditions with more stable flood plains. In fluvial architectural elements, changes such as type of fluvial system, paleosols, etc., may be useful for correlation. These limits may be used to define sequence boundaries [63]. The isopach map obtained for the DS-2 sequence (Fig. Basinward, no erosional processes have been observed at 12) shows a clear lineament oriented at 155, coinciding this level. with the position of the 250 m isoline (continuous line in Fig. 12), which separates the thinner regions of the DS-2 At top of the LST-2 the transition between regression sequence to the southwest from the greater thicknesses and subsequent transgression is indicated by a maximum (up to 850 m) to the northeast of this line. regressive surface (MRS). Some corridors appear in the NE sector, oriented between The following stages are represented by M-3 Member 130-140 and 165-170 (broken lines in Fig. 12) and (TST-2) and M-4 Member (HST-2). The paleogeographic subparallel to the isoline of 250 m. The observed features change in the Boñar Formation. In these stages thicknesses here are very high, reaching as much as new conditions exist with the near-shore and coastal plain 650 m in this area and it is interpreted as the result sub-environments. A second transgression, which was of accumulation of sandy bodies, such as the inter and more extensive towards the west, occurred (sections 4, 5 subtidal. bars of the M-3 Member of the Boñar Formation and 6, Figs. 2 and 3). These system tracts suggest a rapid (TST-2), that run parallel to the direction of the tidal change of depositional environment from fluvial systems to currents In addition, within these corridors another sector intertidal and lagoonal facies. can be observed oriented at 130-140 (dotted lines in Fig. The deposits in the TST-2 are marls, micritic limestones, 12), where the thickness decreases all the way down to calcarenites and sandstones and are interpreted as 250 m. intertidal bars to very shallow subtidal bars, with In the SW sector various embayments can be observed orientations parallel to the direction of the tidal currents. with thicknesses between 200 and 300 m and directions Marls and bioturbated biomicrites correspond to subtidal 409 Palaeoshoreline for the Late Cretaceous marine platform in the Iberian Trough (Leonese Area, Spain) deduced from outcrop and subsurface analysis

4760000 FIGURE 2 PORMA FAULT VENTANIELLA FAULT N 155 BOÑAR PRINCIPAL THRUST LA ROBLA EL CAMPILLO THRUST CISTIERNA GUARDO 600 4740000 800 500 PEÑA-1

EL CAMPILLO LEÓN ALMANZA 4720000

UTM Y (HUSO 30 N) VILLAMERIEL SALDAÑA

300 400 4700000 0 200 100

LEÓN-1BIS LEÓN-1

4680000 260000 280000 300000 320000 340000 360000 N 130-140 400000 N 165-170 N Major faults and thrusts in Alpine thrusts in UTM X (HUSO 30 N) 0 Km 20 Km subsoil the Variscan basement

Figure 12. Isopach map of the DS-2 sequence. The continuous line corresponds to the 155 direction (isoline of 250 m). The broken lines correspond to the 130-140 and 165-170 directions with thicknesses as high as 650 m. The dotted lines correspond to thicknesses of 250 m. Contour interval of 50 m. See text for discussion.

deposits. This systems tract manifests a new change in oriented at 155 (Fig. 12), rotating about 35 degrees shoreline position which progressively migrates landward. in relation to its position during the DS-1 sequence. The accumulation of the fluvial system deposits continues The paleoshoreline is transgressive and moves landward inland in the upper part of the Voznuevo Member which is during the DS-2 sequence. The fluvial systems frequently formed under high-accommodation conditions. of LST-2 pass into deepening environments (TST-2), One change in the fluvial style towards anastomosing with a shallowing with progressively more restricted conditions occurs. The dominance of the flood-plain environments (HST-2) at the top of DS-2. deposits in this stage may point to high-accommodation 5. Discussion and conclusions conditions and vertical aggradation in the upper part of the Voznuevo Member. The comparison of the analyzed sediments with other examples of fossil depositional systems shows a Detailed analyses of the Late Cretaceous succession in sedimentary context (basinward) with banks or shoals of the Leonese Area of the Iberian Trough show a coastline carbonated sands surrounded by subtidal deposits [64, 65]. where interaction between marine and continental The top of TST-2 is the maximum flooding surface (MFS) domains took place in an environment subjected to represented by the boundary between the upper part of variations in sea level. Variations in sea level during this the Voznuevo Member and the M-4 Member of the Boñar stage are produced from proto-Atlantic and Tethys marine Formation (sections 4 to 12). It represents the surface that domains, which only sporadically remain connected [47, existed at the time of maximum transgression of the shelf 67, 68]. [66]. Stratigraphic profiles and new data obtained from analysis HST-2 includes dolomitized mudstones and bioturbated of reflection seismic sections allow the placement of wackestones with bioclasts deposited in tidal flats and the shoreline within the study area and its relative lagoons systems. HST-2 has been eroded and truncated displacement with time. In addition an offset of during subsequent Cenozoic stages. lineaments with different palaeogeographic and tectonic During the DS-2 sequence, the position of the interpretations have been observed. paleoshoreline was located in the central sector and The general stratigraphic organisation of these deposits 410 Antonio Herrero-Hernández, Fernando Gómez-Fernández

is composed of two lithostratigraphic units: Voznuevo with basement faults could exercise a direct control on Member and Boñar Formation. The first one is drainage basin evolution, continental sediment supply, characterized mainly by deposits made up from different distribution of sedimentary facies belts, and location of fluvial systems that drained the edge of the Iberian the depositional environment. Massif. Laterally, towards the east and the northeast, this Taking into account the isopach maps of both depositional unit passes into the Boñar Formation, which represents sequences, during DS-1 the shoreline was located in sedimentation in terrigenous-carbonate mixed platforms the SW sector and it was oriented in N at 120 and with shallow subtidal and intertidal areas on open shelf curves towards NW (Fig. 11). In the western area the depositional environments. seismic fabric of the basement and the disappearance Using seismic profiles, the internal stratigraphic of the DS-1 (León 1 and León 1 b boreholes) allow architecture of the Late Cretaceous is articulated across a paleorelief oriented at 120 excavated over Palaeozoic two low-frequency (2nd and 3rd order) depositional basement by the DS-1, to be observed. This lineament sequences, DS-1 and DS-2. Both of them show periods separates the deeper sectors of the marine basin towards of lowstand followed by two important transgressions the northeast and the proximal portion of the basin-margin which are shown by significant lateral changes of facies to the southwest. The isopach map of the DS-2 sequence and shoreline shifts. The overall shoreline retreat (Fig. 12) shows a lineament oriented at 155, which landward associated with transgressive units exceeds separates the thinner deposits of the southwest from the 10km to the west. thicker deposits to the northeast. The mean position of the paleoshoreline is located in the central area with The DS-1 sequence is made up of LST-1, TST-1 and that direction (Fig. 12). During the DS-2 sequence the HST-1. The LST-1 is characterized by large fluvial paleoshoreline has rotated about 35 degrees in relation plains crossed by low sinuosity channels, together with to that of the DS-1 sequence. paleosol development in extensive areas of the floodplain, and high sinuosity channels at the top. Between Boñar The low thickness of TST-1 and HST-1 (Fig. 3) and and Yugueros towns (sections 7 to 12) the vertical and the variations in thickness (see isopach map, Fig. 11) lateral facies relationships allow subdividing of the DS-1 following corridors with trajectories between 030 and sequence into TST-1 and HST-1. TST-1 is constituted 050, can be related to the sedimentary dynamics with by a group of facies produced by terrigenous tidal flat the accumulation of sediments in sub-basins elongated systems with intertidal and subtidal subenvironments. in these directions and predicts that the geometry of Marls and clays of HST-1 were mostly deposited in sand bodies would be extended in said directions (broken the offshore area. Both systems tracts show lateral line in Fig. 11). These directions are transverse to the facies shifts with tidal influence and beach deposits paleorelief oriented at 120 that is appreciable in seismic (upper layers of the lower part Voznuevo Member) which and well data. The DS-1 sequence is interpreted as a correspond to the first transgression in the region. result of channel fill in paleovalleys with tributary fluvial networks developed in a large area located to the west The DS-2 sequence is made up of LST-2, TST-2 and and southwest of the region. HST-2. At the base of DS-2 sequence LST-2 implies a surface of forced regression causing the migration of However, these variations in thickness, especially for the the shoreline towards the basin. Sandstones within DS-1 sequence, may be caused by movements along faults LST-2 were deposited in fluvial systems. The deposits (Fig. 6). They are possibly related to the existence of TST-2 indicate gradual rises of sea level, punctuated of paleogeographic thresholds probably influenced by by normal regressions (intertidal and subtidal bars) and basement faults, which would have orientations between the end of transgression is completed by HST-2 with tidal 030 and 050 (e. g. Porma and Yugueros Faults). These flats and lagoonal facies. These base-level fluctuations blocks created an uneven topography and significant imply landward differences in the fluvial style. It may thickness variations. be characterized by laterally interconnected amalgamated During DS-2 sequence the continuous and elongate channels with well preserved floodplain deposits (upper depocenters move towards the northeast and east. part of Voznuevo Member). The basinward sediment distribution shows a group of Sediment distribution and evolution of the paleoshoreline corridors oriented at 130-140 and 165-170 (broken lines in both depositional sequences was controlled by eustatic in Fig. 12), which are interpreted as the result of changes in sea level accompanied by lateral facies shifts accumulation of inter and subtidal sandy bars. Marine within the depositional sequences. Tectonic activity had flooding of the basin progressively forced the movement a minor influence, and topographic features associated of these bars towards the coastline, which indicates that 411 Palaeoshoreline for the Late Cretaceous marine platform in the Iberian Trough (Leonese Area, Spain) deduced from outcrop and subsurface analysis

eustatic changes control the sediment distribution and References facies belt distribution. The average paleocurrent trend also goes from southwest to northeast in the upper part of the Voznuevo Member. These directions may be indicated by the normal directions to the coastline position (oriented [1] Floquet M., Outcrop cycle stratigraphy of shallow at 155) and represent the entry of transversal fluvial ramp deposits: the Late Cretaceous series on the systems. Castilian ramp (northern Spain). In: de Graciansky P.C., Hardenbol J.,SEPM Jacquin Spec. T., PublVail P.R. (Eds.), The marine platform reached its greatest extent in Mesozoic and Cenozoic Sequence Stratigraphy of the Late Cretaceous, corresponding to the maximum European Basins. ., 1998, 60, eustatic sea level rise [69, 70]. Taking into account 343-361 the Exxon-Group global cycle chart and the depositional [2] ÁlvaroActa Geológica M., Capote Hispánica R., Vegas R., Un modelo de sequences defined in the Iberian Range [32, 42–44, 47–50], evolución geotectónica para la cadena Celtibérica. the correspondence with the different units used in this , 1979, 14, 172-181 paper has been established. The stratigraphic correlations [3] Salas R., Casas A., Mesozoic extensionalTectonophysics tectonics, are difficult because of the distance from the Iberian Range stratigraphy and crustal evolution during the Alpine and biostratigraphic dating has not available until now. cycle of the eastern Iberian basin. , However, as lithofacies in the Iberian Range are generally 1993, 228, 33-55 similar to those of the successions described above, [4] Casas-Sainz A.M., Gil-Imaz A., ExtensionalGeol. correlations were made using high-resolution sequence subsidence,Rundsch contractional folding and thrust inversion stratigraphy in combination with the evolution of the of the eastern Cameros basin, northern Spain. relative sea-level. The DS-1 sequence must correspond ., 1998, 86, 802-818 to the UZA-2 (Late Albian-Middle Turonian) of [69, 70] [5] Martín-Chivelet M., Berásategui X., Rosales I., Vilas and can be correlated with the Cenomanian transgression L., Vera J.A., Caus E., Gräfe K.U., Mas R., Puig seen along the Iberian Range. The subsequent eustatic C., Segura M., Robles S., Floquet M., Quesada S., fall is well recognized in many sectors in the Iberian Ruiz-Ortiz P.A., Fregenal-Martínez M.A., Salas R., Range and is used to separate 2nd order sequences. Arias C., García A., Martín-Algarra A., Meléndez The DS-2 sequence shows correlation with UZA-3 (Late M.A., Chacón B., Molina J.M., Sanz J.L., Castro J.M., Turonian-Campanian) of [69, 70]. During this sequence García-Hernández M., Carenas B., García-Hidalgo a second transgression occurred. HST-2 has been J.F., Gil J., Ortega F., Cretaceous. In: Gibbons W., completely eroded during subsequent stages, and is Moreno T., (Eds.), The Geology of Spain. Geological truncated at the top by Cenozoic units. Society of London, London, 2002, 255-292 Acknowledgements [6] Gómez de Llarena J., Algunos ejemplos de cobijaduras tectónicas terciarias en Asturias, León y Palencia. Boletín de la Real Sociedad Española de Historia Natural, 1934, 34 (2-3), 123-127 Partial financial support for seismic data analysis from [7] Ciry R., Etude géologique d’une partie des provinces the Duero Basin has been provided by ENDESA. de Burgos, Palencia, León et Santander. Bulletin de The microfacies study and cartography analysis were la Société d’Histoire Naturelle, Toulouse, 1939, 74, supported by the Excma. Diputación Provincial de León. 1-528 The authors acknowledge REPSOL-YPF for releasing [8] Evers H.J.,Leidse Geology Geology of the Mededelingen Leonides between the seismic data from the Duero Cenozoic Basin. This work Bernesga and Porma rivers. Cantabrian Mountains, has been supported by the ‘Consejería de Educación’ NW Spain. , 1967, 41, of the ‘Junta de Castilla y León’ through the project 83-151 LE289A11-2. This manuscript has improved after critical [9] Van Ameron H.W.J., Upper Cretaceous pollenPollen and reading and the suggestions and alterations to the sporesSpores assemblages from the so-called «Wealden» of terminology and concepts made by Dra. B. Bádenas the pronvience of León (Northern Spain). (University of Zaragoza). , 1965,Breviora 7, 89-93 Geológica Astúrica [10] Carballeira J., El Cretácico del SE de Cervera del Pisuerga. , 1969, 13, 41-45 [11] Jonker R.K., Fluvial sediments of Cretaceous age along the southern border of the 412 Antonio Herrero-Hernández, Fernando Gómez-Fernández

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