Interplay of Autogenic and Allogenic Processes On the Formation of Shallow Carbonate Cycles in a Synrift Setting (Lower Pliensbachian, Traras Mountains, NW Algeria)

Abstract

Meter-scale shallowing-upward cycles are recorded in many carbonate successions around the world. It is often difficult to recognize whether they represent autocycles, formed through intrinsic controls, or allocycles, resulting from orbital forcing or tectonic movements, or both. Here, we review the criteria used in the identification of the two types of cyclicity and apply them to two newly described lower Pliensbachian outcrops in the Traras Mountains, northwestern Algeria. Throughout the investigation of six sections, the deposits are suggested to have formed in intertidal–supratidal to shallow subtidal environments on a tropical ramp in the Western Tethys. In this area, shallowing-upward small-scale peritidal and subtidal cycles have been shown to be, and are assumed to be, ordered. The carbon isotope data mirror the recorded cycles and indicate different lengths of subaerial exposures. These cycles, in a developed within synrift setting, have been interpreted as produced mainly by autocyclic processes, but interacting with allocyclic factors. Peritidal cycles are thought to be generated by progradation of intertidal and supratidal flats into lagoonal sediments, while subtidal cycles are interpreted to have been controlled by lateral migration of shoals. The impact of the minor fluctuations of eustatic sea level is weakly marked, and only long subaerial exposure can reveal the contribution of these fluctuations to the formation of the recorded cycles. Tectonic movements resulting from spreading of the Tethys are interpreted to have controlled cycle distribution and thickness at a regional scale. However, synsedimentary tectonic features are rare in the studied area; this suggests that sediment transport would control the thickness and duration of cycles instead of the rate at which accommodation was created.

Orbital cycles, differential subsidence and internal factors controlling the high-frequency sequence architecture in a Sinemurian shallow carbonate platform (Mallorca island, Spain)

“…Therefore, a probably combination of tectonically and orbitally driven accommodation changes controlled the generation of medium-scale sequences of the studied early Sinemurian to earliest late Sinemurian platform Stage-1. This interaction has also been Traras Mountains, Algeria, Belkhedim et al, 2019) where cycles or sequences similar to our medium-and large-scale sequences have been interpreted as a result of local or regional tectonic subsidence and orbitally driven sea level variations (Table 2). In Mallorca island a clearer influence of tectonic activity has been deduced for the overlaying late Sinemurian platform Stage-2 (Sevillano et al 2019).…”

“…For example, if the small-scale sequences culminate with subaerial exposure at the sequence boundary, as is the case of peritidal small-scale sequences recorded here (Fig. 8), the time of non-deposition or erosion involved in the sequence boundary can be longer than 20 kyr (Sadler, 1981(Sadler, , 1994, resulting in "missed beats" in the cyclostratigraphic record (Belkhedim et al, 2019;Strasser, 2019). In other cases, facies such as high-energy oolitic bars can migrate laterally within the inner platform or be displaced during events such as storms or spring tides (e.g.…”

“…However, as a whole, the variability in the estimated time duration of small-scale sequences, thickness, Journal Pre-proof J o u r n a l P r e -p r o o f and facies stacking (Fig. 8) indicate a strong imprint of autocyclic processes inherent to the sedimentary system (e.g., progradation of tidal flats, Ginsburg, 1971;Belkhedim et al, 2019; lateral migration of sedimentary bodies and local erosional processes, Pratt and James, 1986;Strasser 1991). For example, if the small-scale sequences culminate with subaerial exposure at the sequence boundary, as is the case of peritidal small-scale sequences recorded here (Fig.…”

“…The Lower Jurassic peritidal to shallow marine carbonate platform successions developed around the western Tethys usually display a hierarchical stacking of highfrequency depositional sequences that have been related to allocyclic and/or autocyclic mechanisms. In most of these platforms, a combination of factors controlling the cyclicity and the internal facies stacking has been suggested: orbital-driven sea-level changes, local or regional tectonic subsidence, and variations in local sediment supply and tidal flat progradation (Crevello, 1990(Crevello, , 1991Walkden and De Matos, 2000;Bosence et al, 2000Bosence et al, , 2009Pomoni-Papaioannou and Kostopoulou, 2008;Pomoni-Papaioannou and Karakitsios, 2016;Bádenas et al, 2010;Aurell and Bádenas, 2015;Brandano et al, 2015;Belkhedim et al, 2019). Similar high-frequency depositional sequences have been described in the Sinemurian shallow platform successions of Mallorca (Es Barraca Member, Balearic Islands, Spain) (Barnolas and Simó, 1984;Sevillano et al, 2013).…”

Differentiate allogenic and autogenic controls on the formation of parasequences and depositional sequences of a tide‐ and wave‐dominated carbonate platform (Lower Cretaceous, Kopet‐Dagh Basin, Iran)

“…The formation of facies and facies associations—including their composition, texture and internal erosional surfaces, the nature of the bounding surfaces of parasequences, and at a higher level, the formation of sequence boundaries and system tracts—holds valuable information about the depositional setting and controlling factors in a sedimentary basin. The effect of local and internal factors (e.g., tide‐dominated, wave‐dominated, or fluvial‐dominated sedimentary processes, oxygen level, water circulation, nutrient supply, local change in sedimentation rate) and local shifts in carbonate productivity can result in lateral changes of facies, the formation of internal erosional surfaces, change in the stacking pattern of the sedimentary packages, and the formation of the parasequences marked by minor flooding surfaces (e.g., Angulo & Buatois, 2012; Baniak, Gingras, Burns, & Pemberton, 2014; Bayet‐Goll et al, 2018; Belkhedim et al, 2019; Catuneanu, 2019; Plink‐Björklund, 2019). Large‐scale changes in facies belts, carbonate productivity zone, depositional environments, and even depositional systems—with the subsequent formation of the system tracts and medium–large‐scale cycles—are mainly controlled by allogenic factors, including tectonic regime (passive vs. active), eustatic, and climate changes (e.g., Belkhedim et al, 2019; Catuneanu, 2019; Sharafi et al, 2019; Sharafi, Longhitano, Mahboubi, Moussavi‐Harami, & Mosaddegh, 2016; Sharafi, Mahboubi, Moussavi‐Harami, Ashuri, & Rahimi, 2013; Sharafi, Mosaddegh, Bayet‐Goll, & Ahmadi, 2020).…”