Giant submarine collapse of a carbonate platform at the Turonian–Coniacian transition: The Ayabacas Formation, southern Peru

Abstract

The Ayabacas Formation of southern Peru is an impressive unit formed by the giant submarine collapse of the mid‐Cretaceous carbonate platform of the western Peru back‐arc basin (WPBAB), near the Turonian–Coniacian transition (∼90–89 Ma). It extends along the southwestern edge of the Cordillera Oriental and throughout the Altiplano and Cordillera Occidental over >80 000 km2 in map view, and represents a volume of displaced sediments of >10 000 km3. The collapse occurred down the basin slope, i.e. toward the SW. Six zones are characterised on the basis of deformational facies, and a seventh corresponds to the northeastern ‘stable’ area (Zone 0). Zones 1–3 display increasing fragmentation from NE to SW, and are composed of limestone rafts and sheets embedded in a matrix of mainly red, partly calcareous and locally sandy, mudstones to siltstones. In contrast, in Zones 4 and 5 the unit consists only of displaced and stacked limestone masses forming a ‘sedimentary thrust and fold system’, with sizes increasing to the southwest. In Zone 6, the upper part of the limestone succession consists of rafts and sheets stacked over the regularly bedded lower part. The triggering of this extremely large mass wasting clearly ensued from slope creation, oversteepening and seismicity produced by extensional tectonic activity, as demonstrated by the observation of synsedimentary normal faults and related thickness variations. Other factors, such as pore pressure increases or lithification contrasts probably facilitated sliding. The key role of tectonics is strengthened by the specific relationships between the basin and collapse histories and two major fault systems that cross the study area. The Ayabacas collapse occurred at a turning point in the Central Andean evolution. Before the event, the back‐arc basin had been essentially marine and deepened to the west, with little volcanic activity taking place at the arc. After the event, the back‐arc was occupied by continental to near‐continental environments, and was bounded to the southwest by a massive volcanic arc shedding debris and tuffs into the basin.

The Northern Carpathians plate tectonic evolutionary stages and origin of olistoliths and olistostromes

“…A prograding series of olistostromes marks successive orogenic pulses, or punctuated orogenesis [13]. However, olistostrome deposits were also identified at block-faulted passive margins [7,16] and along strongly uplifted shoulders of rift basins [15,17,18]. Olistostromes containing exotic olistoliths derived from the basement rocks uplifted and exposed to mass wasting at basin margin are classified as allolistostromes, whereas endolistostromes contain fragments of the basinal sediments only, and are generated at oversteepened subaqueous slope of the basin [19].…”

“…Olistostromes from these units of the Outer Carpathians of Poland were rarely presented in publications because poor degree of exposure rendered field observations difficult. Interesting studies of olistostromes based on good outcrops or deep boreholes, and conducted in other regions and other orogens [9,10,12,14,15,16,20,21,22], provided detailed observations that more recently appeared helpful in the identification of such units in less-well exposed Outer Carpathians, even in some situations when exposure was fragmentary. In some cases, in-depth studies of the existing geological maps enabled to identify olistostromes and olistolithic megablocks there where their presence was previously unknown.…”

International Lateinamerika-Kolloquium 2009

“…In particular, a significant pulse of pluton emplacement occurred at ~62-61 Ma along a >300 kmlong segment of the arc (Mukasa, 1986;Quang et al, 2003). This pulse and the major reactivation of volcanism at ~91 Ma coincided with major increases in accumulation rate in the backarc basin (Sempere et al, 1997;Callot et al, 2008), strongly suggesting that magmatic growth of the arc caused an orogenic development that was large enough to increase subsidence in the backarc, and thus to regionally flexure the lithosphere.…”

“…A ≥700 m-thick succession of continental, coarse-to (reddish) fine-grained deposits sharply overlies the AlbianTuronian carbonate succession that had slowly accumulated in the backarc until then (Sempere et al, 2002). Whereas the latter is nearly devoid of volcanic intercalations or detritus, the former includes volcaniclastic deposits as well as tuffs and lava flows (Callot et al, 2008). This sharp turning point in the stratigraphic record is dated at ~91-90 Ma (Callot et al, 2008) and coincides with the only significant uplift known in coastal southern Peru (Wipf, 2006), and with the emplacement, between 91 and 70 Ma, of the most voluminous units in the Coastal Batholith (Mukasa, 1986).…”

Effects of mass waste events on thrust wedges: Analogue experiments and application to the Makran accretionary wedge

“…Fossil equivalents can be studied in outcrop in the Apennines [Pini, 1999;Bonini, 2006;Lucente and Pini, 2008], the Andes [Callot et al, 2008], and Makran [McCall and Kidd, 1982;Burg et al, 2008]. The Makran accretionary wedge (Figure 1) offers exceptionally clear exposures where the size, the stratigraphy, the morphology and the primary structures of the wedge can be studied without conjecture.…”