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Field trip 2

Topic: Facies, Depositional Sequences and Sea Level Changes in the Late Cenomanian - Turonian Platforms at the Center of Spain

Authors: José F. García-Hidalgo, Javier Gil and Manuel Segura (University of Alcalá - Spain)

Field trip leaders: José F. García-Hidalgo and Manuel Segura (University of Alcalá - Spain)

Date: Monday 01 June 2015, 08:00 - 18:30 hrs.

Field trip description

The Hesperian coast of the Iberian basin during the late Cenomanian-Turonian provides excellent examples of siliciclastic-carbonate sedimentation controlled by sea-level changes. These sediments are composed of three major group of facies: continental-coastal terrigenous sandstones, claystones and marls (and minor conglomerates, dolostones and dolomitic sandstones), an alternation of shelf carbonates and coastal marls, and relatively deep-water, hemipelagic marls. Stratigraphic architecture was mainly aggradational. This region was characterized by generally low rates of subsidence, and the depositional systems here were very sensitive to even small-scale relative sea-level changes. These eustatic sea level changes (low and high order) produced a hierarchical arrangement of four scales of both deepening- and shallowing-upwards, unconformity-bounded depositional sequences (from 2nd to 5th order; although the most prominent and visible in field outcrops are 4th order ones), that spread along much of the Iberian Basin. They are identified by widespread surfaces of exposure, minor erosive surfaces, abrupt landward or basinward shifts in facies belts (mainly of shoreface sandstones), patterns of facies progradation and retrogradation, and shoreline onlap.

The stratigraphical arrangement and age determination of 4th-order depositional sequences suggests that the presence of cyclic, astronomical, processes controlled the sedimentary record. This orbital forcing, in the Milankovitch frequency band (long eccentricity cycles of 400 ka for the 4th-order sequences), acted as a major factor that controlled climate and sea-level, which in turn influenced depositional environments. These highfrequency changes were superimposed on a long-term, 3rd and 2nd-order evolution of the relative sea level. Due to all these sea-level changes, the processes driving sediment accumulation along the coastal and shelf environments were discontinuous over 4th-order sequence scales. Thus, a more complex facies patterns arise when the geometry and stratal relationships on the building 4th-order sequences rather than 3rd-order ones are studied in detail, with interdigitation of siliciclastics and carbonates at different scales. In this sense, the increasing use of outcrop information in the surficial and subsurficial interpretation and modelling of sedimentary sequences of siliciclastic-carbonate systems demands more detailed and precise data in order to facilitate a correct sequence stratigraphic breakdown and to predict the geometries of facies units. In this field trip, we examine some issues that are important in understanding the coastal and shelf stratigraphic record for oil exploration and a broader perspective for future outcrop studies, such as the variability in architecture, evolution and stacking pattern of depositional mixed systems, and the origin and evolution of sediments in relation to changes in the relative sea-level.

Specific objectives of the field trip are to: describe and interpret the depositional environments of the late Cenomanian-Turonian sediments at the southern margin of the Spanish Central System; interpret their depositional environments from terrigenous-carbonate coastal sediments, to fine-grained outer shelf sediments or carbonate platform deposits; describe the geometry and stratal architecture of this margin; and illustrate the cycle stacking patterns of individual stratigraphic sections, integrating these with stratigraphic and sedimentological features in order to identify and correlate depositional sequences.


Somolinos section

 

Tentative itinerary Monday 01 June
07:45 Registration at IFEMA
08:00 Departure from IFEMA
09:30 Stop: Veguillas
11:15 Stop: Alcorlo reservoir
  Lunch Break *
14:30 Stop: Somolinos
18:30 Arrival at IFEMA

* Lunch bag will be included