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Sandstone petrography of continental depositional sequences of an intraplate rift basin: western Cameros Basin (North Spain)

Arribas Mocoroa, José and Alonso Millán, Ángela and Mas, J.R. and Tortosa, A. and Rodas González, Magdalena and Fernández Barrenechea, José María and Alonso Azcárate, Jacinto and Artigas, Rosana (2009) Sandstone petrography of continental depositional sequences of an intraplate rift basin: western Cameros Basin (North Spain). Journal of sedimentary research, 73 (2). pp. 309-327. ISSN 1527-1404

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Abstract

The Cameros Basin in Central Spain is an intraplate rift
basin that developed from Late Jurassic to Middle Albian time along
NW–SE trending troughs. The sedimentary basin fill was deposited
predominantly in continental environments and comprises several depositional
sequences. These sequences consist of fluvial sandstones that
commonly pass upward into lacustrine deposits at the top, producing
considerable repetition of facies. This study focused on the western
sector of the basin, where a total of seven depositional sequences (DS-
1 to DS-7) have been identified.
The composition of sandstones permits the characterization of each
sequence in terms of both clastic constituents and provenance. In addition,
four main petrofacies are identified. Petrofacies A is quartzosedimentolithic
(mean of Qm85F2Lt13) and records erosion of marine
Jurassic pre-rift cover during deposition of fluvial deposits of DS-1
(Brezales Formation). Petrofacies B is quartzofeldspathic (mean of
Qm81F14Lt5) with P/F > 1 at the base. This petrofacies was derived
from the erosion of low- to medium-grade metamorphic terranes of
the West Asturian–Leonese Zone of the Hesperian Massif during deposition
of DS-2 (Jaramillo Formation) and DS-3 (Salcedal Formation).
Quartzose sandstones characterize the top of DS-3 (mean of
Qm92F4Lt4). Petrofacies C is quartzarenitic (mean of Qm95F3Lt2) with
P/F > 1 and was produced by recycling of sedimentary cover (Triassic
arkoses and carbonate rocks) in the SW part of the basin (DS-4, Pen˜ -
acoba Formation). Finally, depositional sequences 5, 6, and 7 (Pinilla
de los Moros–Hortigüela, Pantano, and Abejar–Castrillo de la Reina
formations, respectively) contain petrofacies D. This petrofacies is
quartzofeldspathic with P/F near zero and a very low concentration of
metamorphic rock fragments (from Qm85F11Lt4 in Pantano Formation
to Qm73F26Lt1 in Castrillo de la Reina Formation). Petrofacies D was
generated by erosion of coarse crystalline plutonics located in the Central
Iberian Zone of the Hesperian Massif. In addition to sandstone
petrography, these provenance interpretations are supported by clay
mineralogy of interbedded shales. Thus, shales related to petrofacies
A and C have a variegated composition (illite, kaolinite, and randomly
interlayered illite–smectite mixed-layer clays); the presence of chlorite
characterizes interbedded shales from petrofacies B; and Illite and kaolinite
are the dominant clays associated with petrofacies D.
These petrofacies are consistent with the depositional sequences and
their hierarchy. An early megacycle, consisting of petrofacies A and B
(DS-1 to DS-3) was deposited during the initial stage of rifting, when
troughs developed in the West Asturian–Leonese Zone. A second stage
of rifting resulted in propagation of trough-bounding faults to the SW,
involving the Central Iberian Zone as a source terrane and producing
a second megacycle consisting of petrofacies C and D (DS-4, DS-5, DS-6, and DS-7). Sandstone composition has proven to be a powerful tool
in basin analysis and related tectonic inferences on intraplate rift basins
because of the close correlation that exists between depositional
sequences and petrofacies.


Item Type:Article
Uncontrolled Keywords:Sandstone; Rift basin; Petrography; North Spain
Subjects:Sciences > Geology > Petrology
ID Code:12764
Deposited On:25 May 2011 10:43
Last Modified:13 Dec 2012 08:47

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