Josep Serra-Kiel

Late Cretaceous–Paleocene formation of the proto–Zagros foreland basin, Lurestan Province, SW Iran

Late Cretaceous emplacement of ophiolitic-radiolaritic thrust sheets over the Arabian passive margin was the first manifestation of the protracted closure of the Neotethys Ocean, which ended with the continental collision between Arabia and central Iran and the formation of the present Zagros fold belt. This tectonic stacking produced a flexural basin (the Amiran Basin: 400 × 200 km in size) in the northwest Zagros that was filled with a 1225-m-thick shallowing-upward detrital succession made up of the Amiran, Taleh Zang, and Kashkan Formations. This succession sits unconformably above the Late Cretaceous Gurpi Formation and is overlain by the Oligocene-Miocene Shahbazan-Asmari carbonate succession. Dating of the Amiran-Kashkan succession is based on detailed biostratigraphy using large foraminifera and calcareous nannoplankton. The Cretaceous-Tertiary (K-T) boundary is located within the uppermost 25-45 m of the Gurpi Formation. The overlying Amiran and Taleh Zang Formations have been dated as Paleocene in age. However, the base of the Paleocene within the Gurpi Formation lacks NP1 and NP2 zones, implying a hiatus of ∼2 m.y. at ca. 65.5 Ma, which is inferred to correspond to an early folding phase near the Cretaceous-Paleocene boundary. The upper part of the Kashkan Formation is dated to the earliest Eocene by palynostratigraphy. A large hiatus (or very slow deposition) lasting about 15 m.y. occurs between the Kashkan and Shahbazan Formations in the studied region. The base of the prograding Shahbazan platform deposits is dated by 87Sr/86Sr stratigraphy at ca. 33.9 Ma. The upper part of the Asmari Formation is dated as early-middle Miocene using foraminifera associations. Reconstruction of the Amiran-Taleh Zang-Kashkan succession of the Amiran Basin indicates a thickening of the basin fill from the southern pinch-out along the SE flank of the Kabir Kuh anticline to SW of the Khorramabad anticline, where the flexure is at least 900 m. In contrast, the NE part of the basin underwent coeval contraction and uplift of ∼1300 m. Superimposed smaller undulations onto the large-scale flexure are interpreted as Late Cretaceous-Paleocene folds. Regional comparisons (SE Zagros, Oman, and Turkey) indicate that Late Cretaceous-Early Tertiary deformation affected the entire NE margin of Arabia but that compression was not synchronous, being younger in Lurestan than in the NW Persian Gulf where inversion tectonics occurred from Turonian to mid-Campanian times. The long sedimentary hiatus spanning most of the middle and late Eocene must have been related to deep lithospheric processes linked to the initial events of the protracted closure of the Neotethys Ocean between Arabia and central Iran. The tectono-sedimentary history recorded in the Zagros Basin may help to understand early foreland basin growth in other orogens in which subsequent continental collision has obliterated these early events.

QUANTIFYING THE KINEMATICS OF DETACHMENT FOLDS USING THREE-DIMENSIONAL GEOMETRY : APPLICATION TO THE MEDIANO ANTICLINE (PYRENEES, SPAIN)

The kinematics of detachment folds have been described by three different models: (1) hinge migration is responsible for fold amplification, (2) fold amplification is due to limb rotation, and (3) both hinge migration and limb rotation cause fold amplification. A numerical method is proposed to determine which of these mechanisms is responsible for the formation of natural detachment folds. This procedure consists of measuring and plotting geometric data collected from cross sections constructed across the termination of a fold where shortening dies out laterally, or in an area with a lateral shortening gradient. Assuming that observed spatial variations in fold geometry reflect temporal geometric evolution, the procedure allows determination of equations that govern the kinematics of the particular detachment fold analyzed. To validate the results obtained from the application of this technique to natural examples, they must be contrasted with other indicators of fold-amplification mechanisms such as microstructures, mesostructures, and syntectonic sediment patterns. This analysis is applied to an asymmetric growth fold, the Mediano anticline in the Southern Pyrenees of Spain, and shows that it grew due to limb rotation and minor hinge migration. These data, coupled with analysis of the growth stratal patterns using reverse and forward modeling techniques, are used to derive deformation rates and to display the kinematics of this fold.

Quantified vertical motions and tectonic evolution of the SE Pyrenean foreland basin

Abstract Local isostatic backstripping analysis is performed across the eastern part of the Ebro foreland basin between the Pyrenees and the Catalan Coastal Ranges. The subsidence analysis is based on two well-dated field-based sections and four oil-wells aligned parallel to the tectonic transport direction of the eastern Pyrenean orogen. The marine infill of the foreland basin is separated into four, third-order, transgressive-regressive depositional cycles. The first and second depositional cycles are located in the Ripoll piggy-back basin and the third and fourth ones are located south of the syn-depositional emergent Vall-fogona thrust. Subsidence curves display a typical convex-up shape with inflection points recording the onset of rapid tectonic subsidence. Inflection points coincide roughly with the base of depositional cycles. Rates of tectonic subsidence are less than 0.1 mm a−1 in distal parts of the basin and up to 0.53 mm a−1 in proximal parts during second depositional cycle. Younger depositional cycles show maximum rates of tectonic subsidence of 0.26 mm a−1. The locus of subsidence within the basin migrated southward at a rate of c. 10 mm a−1. This flexural wave crossed the complete Ebro foreland basin in 10–11 Ma. The intraplate Catalan Coastal Ranges at the southeastern margin of the Ebro foreland basin produced an increase of tectonic subsidence rate at 41.5 Ma. Maximum rates of tectonic subsidence coincide with deep-marine infill of the basin, maximum rates of shortening and thrust front advance, and low topographic relief orogenic wedge. Transgressive-regressive depositional cycles can be controlled partly by reductions of available space within the basin during tectonic thickening of the sedimentary pile by layer parallel shortening, folding and thrusting. Although much less constrained, an approximation of post-thrusting exhumation and isostatic and tectonic uplift, as well as a first determination of possible amounts of eroded material of parts of the Ebro basin illustrate the impact of post-depositional erosion and uplift on the foreland.

Basin architecture and growth folding of the NW Zagros early foreland basin during the Late Cretaceous and early Tertiary

Abstract: We present and use the chronostratigraphy of 13 field logs and detailed mapping to constrain the evolution of the early Zagros foreland basin, in NW Iran. Large foraminifera, calcareous nannofossil, palynological and 87Sr/86Sr analysis supplied ages indicating a Campanian–early Eocene age of the basin infill, which is characterizd by a diachronous, southwestward migrating, shallowing upwards, mixed clastic–carbonate succession. Growth synclines and local palaeoslope variations indicate syndepositional folding from Maastrichtian to Eocene time and suggest forelandward migration of the deformation front. We also illustrate the basin architecture with a synthetic stratigraphic transect. From internal to external areas, time lines cross the formation boundaries from continental Kashkan red beds to Taleh Zang mixed clastic–carbonate platforms, Amiran slope deposits and basinal Gurpi–Pabdeh shales and marls. The foreland basin depocentres show a progressive migration from the Campanian to Eocene (c. 83–52.7 Ma), with rates of c. 2.4 mm a−1 during the early–middle Palaeocene (c. 65.5–58.7 Ma) increasing to c. 6 mm a−1 during the late Palaeocene–earliest Eocene (c. 58.7–52.8 Ma). Coeval subsidence remained at c. 0.27 mm a−1 during the first 12.7 Ma and decreased to c. 0.16 mm a−1 during the last 4.2 Ma of basin filling. Finally, we integrate our results with published large-scale maps and discuss their implications in the context of the Zagros orogeny. Supplementary material: Tables with dating results are available at http://www.geolsoc.org.uk/SUP18439.

Cenozoic tectosedimentary evolution of Mallorca island

AbstractThe results of recent biostratigraphic, sedimentologic and structural work concerning the island of Mallorca have led us to elaborate a synthesis of the Cenozoic tectosedimentary evolution of this area. The recognition in the field of several unconformities enabled us to distinguish four Depositional Sequences embracing the pre and syntectonic deposits.From Paleocene to part of Middle Eocene there was no sedimentation in the Mallorca area. This stratigraphie gap follows the onset of Africa-Europe convergence.The area was stable during the first sequence (Upper Lutetian-Bartonian), which is trangressive towards the NW. Tectonic activity is recorded by the conglomeratic wedges of Depositional Sequence 11 (Priabonian-Lower Chattian). A dramatic paleogeographic change ocurred between Depositional Sequence II and III. Observed thrusts and unstable platform sediments of Depositional Sequence III (Upper Chattian-Lo-wermost Burdigalian) indicate the onset of thrust tectonics in the area. Turbiditic deposi...

Chronostratigraphy of the Boltaña anticline and the Ainsa Basin (southern Pyrenees)

The Ainsa Basin (south-central Pyrenees) is an exceptional example of a syntectonic foreland basin where structures oblique to the Pyrenean trend are well preserved. The absence of a complete chronostratigraphic frame motivated us to perform a detailed magnetostratigraphic study in the Ainsa Basin, including the shallow-marine–continental transition. Three sections covering almost the entire Eocene sedimentary fill were sampled (Ara, Coscollar, and Mondot), covering 2450 m of the sedimentary pile, with more than 1000 demagnetized specimens (sample spacing of 2.7 m). Data from previous magnetostratigraphic studies (Eripol section) allow us to complete the Eocene record with an 840-m-long profile within the Bartonian–Priabonian interval overlying the sampled sequence. Characteristic remanent magnetization (ChRM) directions were effectively isolated between 300 and 500 °C. Magnetite is the main magnetic carrier, with variable iron sulfide content and occasional hematite. Fold tests indicate a prefolding magnetization. Biostratigraphy based on shallow benthic foraminifera (15 localities) and a locality with abundant charophyte gyrogonites help to constrain the local magnetostratigraphic record (20 reversals) between the early Ilerdian and the middle Priabonian. A global correlation based on a magnetostratigraphic composite section derived from this work allows us to propose a complete chronostratigraphic frame for the Ainsa Basin infill between 55 and 45 Ma. Accumulation rates range from 2 to 53 cm/k.y., responding to retrogradational to progradational features during the early Lutetian, and a progressive increase from the middle Lutetian onward related to overall continentalization of the basin. Westward migration of subsidence is associated with progressively younger synsedimentary structures nucleating westward of the older ones in the South Pyrenean Basin.

Marine and Transitional Middle/Upper Eocene Units of the Southeastern Pyrenean Foreland Basin (NE Spain)

The stratigraphic basis of this work has allowed the use of larger foraminifers in the biostratigraphic characterisation of the new Shallow Benthic Zones (SBZ). This part of the volume presents a description of the sedimentary cycles formed by the transgressive-regressive systems of the Lutetian and Bartonian in the southeastern sector of the Ebro Foreland Basin.Concerning the Lutetian deposits studied in the Amer-Vic and Emporda areas, four sedimentary cycles have been characterised. The first and second are found within the Tavertet/Girona Limestone Formation (Reguant,1967;Palli,1972), while the third and fourth cycles cover the Coll de Malla Marl Formation (Clavell et al.,1970), the Bracons Formation (Gich,1969,1972), the Banyoles Marl Formation (Almela and Rios,1943),and the Bellmunt Formation (Gich,1969,1972). In the Bartonian deposits studied in the Igualada area,two transgressive-regressive sedimentary cycles have been characterised in the Collbas Formation (Ferrer,1971),the Igualada Formation (Ferrer,1971),and the Tossa Formation (Ferrer,1971). The Shallow Benthic Zones (SBZs)recognised within the Lutetian are the following:SBZ 13, from the Early Lutetian, in the transgressive system of the first cycle;SBZ 14,from the Middle Lutetian, in the second cycle and the lower part of the transgressive system of the third cycle; SBZ 15,from the Middle Lutetian, in the remaining parts of the third system; SBZ 16, from the Late Lutetian,throughout the fourth cycle.The association of larger foraminifers in the first and second cycles of the Bartonian in the Igualada area has been used as the basis for the definition of SBZs 17 and 18 recognised in the Bartonian of the western Tethys.

The Bartonian-Priabonian marine record of the eastern South Pyrenean Foreland Basin (NE Spain) : a new calibration of the larger foraminifers and calcareous nannofossil biozonation

This study presents a combined biostratigraphic (calcareous nannofossils, larger foraminifers) and magnetostratigraphic study of the Middle and Late Eocene marine units of the Igualada area, eastern Ebro Basin. The studied sections of Santa Maria de Miralles and La Tossa encompass the complete marine succession of the Santa Maria Group, where assemblages rich in larger foraminifers have been studied since the early 1950s. A total of 224 paleomagnetic sites and 62 biostratigraphic samples were collected along a 1350m-thick section that ranges from chron C20n to chron C16n (~43Ma to ~36Ma). The resulting magnetostratigraphy-based chronology challenges existing chronostratigraphic interpretations of these units and results in a new calibration of the biostratigraphic zonations. The base of calcareous nannofossil Zone NP19-20 is pinned down to an older age than its presently accepted attribution, whereas the time span assigned to Zone NP18 is significantly reduced. A revised calibration of larger foraminifers indicates that Zone SBZ18, formerly assigned exclusively to the late Bartonian, extends its range to the earlymost Priabonian, the Bartonian stage being almost entirely represented by Zone SBZ17. A division of Zone SBZ18 into two subzones is proposed.

An inventory of the marine and transitional Middle/Upper Eocene deposits of the Southeastern Pyrenean Foreland Basin (NE Spain)

In the southeastern Ebro Foreland Basin, the marine deposits of Lutetian and Bartonian age show excellent outcrop conditions, with a great lateral and horizontal continuity of lithostratigraphic units. In addition, the rich fossil record -mainly larger foraminifers-, provides iostratigraphic data of regional relevance for the whole Paleogene Pyrenean Basin, that can be used for the Middle Eocene biocorrelation of the western Tethys. This contribution is a sedimentary and biostratigraphic synthesis of the basic outcrops and sections of the Lutetian and Bartonian marine and transitional deposits in the southeastern sector of the Ebro Foreland Basin.

Evolutionary patterns of Clavatoraceae (Charophyta) in the mesogean basins analysed according to environmental change during Malm and lower cretaceous

Evolutionary patterns of Clavatoraceae during the Malm and the Lower Cretaceous can be understood by considering how palaeoecological constraints of these charophytes were affected by palaeoenvironmental change. Speciation of Clavatoraceae reached maxima in the Tithonian and especially in the Lower Barremian, coinciding with an important areal extension and environmental diversification of freshwater swamps. Extinction reached a peak in the Upper Barremian, coinciding with the marine flooding of freshwater environments in Mesogea, and continued through the Aptian and Albian due to substitution of carbonatic freshwater swamps by terrigenous deltaic environments and probably by development of highly competitive aquatic flora of angiosperms. Anagenetic change within species attained maxima during the Berriasian and Lower Barremian, when freshwater environments became extensively developed. Absence of change (stasis) was marked during the Valanginian and Hauterivian, in a geological context of environmental s...