The Westernmost Tethys Blog

07/26/2019

Source areas in the Agost Basin (Betic Cordillera)

Filed under: Betics,Tectonosedimentary model — Tags: , , , — messinianalicante @ 7:52 AM

A new work to illustrate a changes in source areas related with pull-apart basin  in the Betics. Here the link to the work in researchgate.

Sedimentary and mineralogical analyses were performed in the Neogene Agost Basin (External Domain, Betic Cordillera) to reconstruct relationships between tectonics and sedimentation, and source areas evolution over time.

Geological Setting

Figure 1) A: Index map; B: Geological sketch showing the main zones and units of the Betic Cordillera; C: Geological map based on the main sedimentary cycles proposed by Vera (2004).

 

The sedimentary analysis allowed defining two sedimentary sequences: (1) Lower Stratigraphic Unit, Serravallian p.p. and (2) Upper Stratigraphic Unit, post Lower Tortonian (Upper Miocene p.p.)separated by an angular unconformity. They consist of marine (lithofacies L-1to L-3) and continental (lithofacies L-5to L-8) deposits respectively (Figure 2).

Figure 2. Lithostratigraphic record and correlations of four representative successions (logs 1 to 4) of the Agost Basin. The two main sequences (Lower Stratigraphic Unit, LSU and Upper Stratigraphic Unit, USU) separated by an angular unconformity are evidenced. Depositional environments, supplies and the isochronous lines T1-T5 are also indicated.

 

The analysis of mineralogical assemblages and some XRD parameters of the sedimentary sequences (Figure 3) and older formations (Figure 4) allowed recognizing a sedimentary evolution controlled by the activation of different source areas over time.

Figure 3. Mineralogical results of the Neogene sedimentary record of the Agost Basin (LSU and USU, given as the average value from the set of samples (n) in each lithofacies L-1 to L-8 included in tab. 2 for the whole rock and the <2 µm grain-size fraction (in wt. %). Ranges and average values of the intensities ratio of the Qtz(001)/Qtz(101) peak areas of quartz, and Sme(003)/Sme(002) peak areas of smectite and Ill(002)/Ill(001) peak areas of illite under ethylene glycol solvation are included.

 

Figure 4. Mineralogical results concerning the source areas given as the average value from the set of samples (n) in each Sedimentary Cycle included in tab. 1 for the whole rock and the <2 µm grain-size fraction (in wt. %). Ranges and average values of the intensities ratio of the Qtz(001)/Qtz(101) peak areas of quartz, and Sme(003)/Sme(002) peak areas of smectite and Ill(002)/Ill(001) peak areas of illite under ethylene glycol solvation are included.

 

In particular, the Ill+Kln±Sme+Chl clay-mineral association characterizes the supply from Triassic formations; the Ill+Kln+Sme association from Albian formations; the Sme+Ill±Kln+(I-S) and Sme+Ill±Kln associations from Upper Cretaceous p.p.formations; and the Sme+Ill±Kln+(I-S) association from Paleogene formations, testifying a tectonic mobility of the basin margins differentiated over time (Figure 5).

 

Figure 5. (A) Comparative plots of XRD parameters, traceable mineral phases, and clay-mineral associations of the Neogene sedimentary record of the Agost Basin (LSU and USU, including the lithofacies L-1 to L-8) and source areas (Sedimentary Cycles I to VI as Triassic p.p., CI; Albian p.p., CIV; Cenomanian-Turonian p.p., CV-CT; Upper Cretaceous p.p., CV-S; and Paleogene p.p., CVI); purple, green, and orange dotted lines identify supplies from predominant Triassic, Cretaceous, and Upper Cretaceous-Paleogene source areas, respectively. The ternary plots for the whole-rock (B) and the <2 µm grain-size fraction (C) mineralogy, given as the average value (in wt. %) from the set of samples in each Sedimentary Cycle (tab. 1, fig. 4) and lithofacies (tab. 2, fig. 5), show three compositional fields corresponding to predominant Triassic like (TR), Albian like (AL), and Upper Cretaceous-Paleogene like (CP) mineralogical associations mixing in variable proportions to determine the mineralogical associations from L-1 to L-8. Samples with gypsum and chloride as typical Triassic mineral phases to identify the Triassic influence in F-1 to F-8 are indicated.

 

This reconstruction leads to propose detailed relationships between types of deposits and provenance and not a classic “unroofing”, as follows: (i) the lithofacies L-1 (lithofacies L-2 and L-3 were not analysed) is characterized by the Ill+Kln+Sme mineralogical association indicating an origin from the Albian formations; (ii) the lithofacies L-4 shows a mixture of Ill+Kln+Sme and Sme+Ill+Kln associations sourced from the Albian and Upper Cretaceous formations; (iii) the lithofacies L-5 is characterized by the Sme+Ill±Kln+(I-S) association indicating a provenance from the Upper Cretaceous and Paleogene formations; (iv) the lithofacies L-6 to L-8 are characterized by the Ill+Kln±Sme+Chl association indicating a supply mainly from Triassic deposits. The evolutionary sedimentary model reconstructed for the Agost Basin, which improves a previous contribution about the same area, has been correlated with those reported in other intramontane Neogene basins in the Betic-Rifian Arc studied with similar resolution, so obtaining useful information for regional reconstructions.

Figure 6. Tectono-sedimentary evolutionary model with location of source areas of the Agost Basin and surrounding areas. A: Middle Miocene stage (Lower Stratigraphic Unit); B: Late Miocene stage (Upper Stratigraphic Unit).

 

 

Cite as: Martín-Martín, M., Guerrera, F., Alcalá, F. J., Serrano, F., Tramontana, M. (2018): Source areas evolution in the Neogene Agost Basin (Betic Cordillera): implications for regional reconstructions. Italian Journal of Geoscience. 2018, 137(3): 433-451. doi:10.3301/IJG.2018.14

 

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