Authors: Hanneke Heida (ICTJA, CSIC – Barcelona), Fadl Raad (CNRS Montpellier) and Athina Tzevahirtzian (Universitá di Palermo).
Last September our ESRs Hanneke Heida, Fadl Raad and Athina Tzevahirtzian had the opportunity to enjoy an Indian Summer investigating the fascinating Messinian outcrops of the island of Mallorca, in the Balearic archipelago.
What clues does Mallorca hold to understanding the Messinian Salinity Crisis (MSC)?
Mallorca constitutes the most important emerged portion of the Balearic Promontory, which is the north-eastern prolongation of the external zones of the Betic reliefs (south-eastern Spain) into the Mediterranean Sea. The island’s rocks are composed essentially by carbonate deposits, ranging from the late Carboniferous to the Quaternary periods, that is to say from about 300 million years ago (Ma) to recent deposits. The position between intermediate (Valencia Basin) and deep (Algerian) basins makes it a great area to investigate the relations between erosional stages and hypo- and hypersaline events during the Messinian Salinity Crisis.
Onland, the Messinian deposits are outcropping in several places along the magnificent southern coast of the island which gave us the opportunity to discover the story that these outcrops are telling us. It is thought that the Messinian outcrops range from 6.3 to 5.33 Ma, thus registering the whole Messinian Salinity Crisis (MSC). Buried below the Palma basin and into the offshore domain we find gypsum deposits of unclear stratigraphic position, and one of the few known instances of halite at intermediate depth in the Central Mallorca Depression, a fascinating key to the progression of the MSC.
Thanks to Guillem Mas, from Earth Sciences Research Group of the Universitat de les Illes Balears (UIB), we were able to visit and discuss the outcrops of interest. Sections studied include Porto Pi, Cala Santanyi, Cala Maioris, sections located in the beautiful village of Santa Eugenia as well as other outcrops found on the road connecting the mentioned sections, which each ESR approaching the fieldwork from their own area of expertise, sparking some interesting debates.
During the fieldwork, diverse discussions and sometimes (a lot of times!!) disagreements, helped us every day to be a little more confused about the dating of the sedimentary deposits and the reconstruction of the MSC. The Messinian continues to be a mess… but positive vibes and enthusiasm to study the geology remain! At the end of the tiring days of sampling and thinking on the hidden geological story of Mallorca’s rocks, we also enjoyed a relaxing swim in the turquoise sea of the island.
The work in Mallorca focused on various aspects of Messinian geology, from the stratigraphic correlation with Sicilian outcrops (Athina) to the continuation of the units offshore and their implications for post-Messinian local and regional deformation and uplift (Fadl and Hanneke).
Athina has been more than happy to observe the possible stratigraphical correlations that can be made between Mallorca’s and the Sicily’s outcrops. That’s why she sampled more than 100 rocks (heavy luggage…) for further laboratory analysis, hoping a lot of questions to be answered concerning the formation and the architecture of the different basins.
Fadl, who’s research focuses on the offshore aspect of the Balearic Promontory, had as a main objective to find a correlation and/or a possible connection between the MSC deposits onshore and the deposits seen in the seismic images south of the island. For this goal it was important to have a look on the geometries, facies and the exact location of the outcropping MSC deposits.
The tectonics of the northeastern area of the promontory are of big interest as well, especially the one that took place after the MSC. It is known that in this area the dominant post-Messinian movements along the faults are extensional. However, the last earthquake that took place on Mallorca island in 1851 has been associated to transpressive (strike-slip + compressive) movement along the Sencelles fault located in the heart of the island (see the figure with the map and the positions of the outcrops). Nevertheless, people in Mallorca look to be fearless and if you wonder why, just have a look below at the image of the house built above one of the active faults!!
The Balearic Promontory is also a key area in constraining vertical motions since the Messinian using numerical modelling, as the shallow carbonate reefs from Messinian times are still positioned close to sea level, providing important insights into the amount of isostatic adjustment to sedimentation and evaporite deposition that can have occurred in the region.
The translation of field observations to inputs for numerical models is an important step to constraining model boundary conditions, and requires an understanding of the complexities and uncertainties seen in the field. Whether erosion occurred at a certain stratigraphic level, whether it was regional or local, and if it points towards uplift caused by flexure or tectonics, sea level lowering or a combination of those factors proves to be challenging!
- Guillem Mas (Universitat de les Illes Balears)
- Antonio Caruso (University of Palermo)
- Agnès Maillard (Paul Sabatier University – Toulouse III)
- Carine Lezin (Paul Sabatier University – Toulouse III)
…for this beautiful journey and all the knowledge you are constantly transmitting to us!