Tidal and seasonal controls in the formation of Late Miocene inclined heterolithic stratification deposits, western Amazonian foreland basin

Abstract

Upper Miocene strata in the Acre sub-basin, Brazil, consist dominantly of various types of inclined heterolithic stratification and pedogenic horizons. These strata were sedimentologically and ichnologically described to: (i) study different temporal controls responsible for inclined heterolithic stratification generation and their variation in a distal-proximal trend; and (ii) delineate the depositional setting. For this purpose, nine representative outcrops were sedimentologically and ichnologically studied, and their facies associations described. Thickness variations of the heterolithic strata of various orders (lamina, lamina bundles and beds) were analysed by statistical methods (Fourier transform). The deposits were interpreted as tidally and seasonally influenced estuarine or delta-related and continental strata. The inclined heterolithic stratification deposits represented vastly different settings ranging from tidally dominated, brackish-water ichnofossils-bearing channels to seasonally controlled, articulated Purussaurus (a freshwater alligator) fossilbearing channels. Several time cycles were distinguished in the strata, including semi-diurnal, fortnightly and seasonal. Tidal imprint was best observed in low-energy brackish-water settings, whereas seasonal rhythmicity was distinguishable throughout the depositional system. However, the latter was most apparent in riverine channels proximal to the inferred fluvio-tidal transition. The different temporal controls commonly had distinguishable impact on sedimentological and ichnological properties in the studied sediments. The differing properties included: (i) the degree and nature of lateral variability with respect to lithology and bedforms in inclined heterolithic stratification; (ii) the lateral continuity of inclined heterolithic stratification; (iii) the nature of sedimentary contacts between the inclined heterolithic stratification members; (iv) thickness variation of inclined heterolithic stratification members within a set; (v) the cyclicities observed in inclined heterolithic stratification series; (vi) the degree of bioturbation; (vii) the types of trace fossils observed; and (viii) the distribution of bioturbation in adjacent inclined heterolithic stratification members.

Evidences for a Paleocene marine incursion in southern Amazonia (Madre de Dios Sub-Andean Zone, Peru)

“…In a tidal environment, 436 they can be characteristic of tidal inlet infillings in the fluvial-tidal transition zone of estuaries 437 (Dalrymple et al, 1992;Hovikoski et al, 2008). Flood dominated Climbing 438…”

The Nazca Ridge and Uplift of the Fitzcarrald Arch: Implications for Regional Geology in Northern South America

“…The oldest sediments outcropping on the Fitzcarrald Arch area are Miocene in age and part of the Ipururo and Madre de Dios Formations in Peru (Kummel 1948), and of the Solimões Formation in Brazil (Oppenheim 1946;Silva 1988 (Espurt et al 2006;Antoine et al 2007); 2, Sepa River; 3, Urubamba River; 4, Purus River (Räsänen et al 1995, Hovikoski et al 2008; 5, (Cozzuol, 2006); 6, Patos Inca (Cozzuol 2006); 7, Alto Purus River (Campbell et al 2001); 8, Manú River; 9, Madre de Dios River; 10, Inambari River (Roddaz 2004;Roddaz et al 2006;Hovikoski et al 2005); 11, Tambo River; 12, Chicosillo River (Espurt et al 2006); 13, Las Piedras River (Campbell et al 2001); 14, Lower Madre de Dios River (Roddaz 2004); 15, Ucayali River (Dumont et al 1991 (Hovikoski et al 2008). Consequently, from the late Middle Miocene to the Late Miocene, the Fitzcarrald Arch area was completely fl ooded and its sediment deposition was controlled by tidal currents.…”

“…On the eastern fl ank of the Fitzcarrald Arch, the outcrops of the Solimões Formation have been described by Räsänen et al (1995) and Hovikoski et al (2008) along the Jurua and Acre Rivers and the Purus River (8.80610°S, 68.80330°W) (see Fig. 6.3).…”

“…6.3). These Miocene sediments commonly consist of various types of tidally infl uenced inclined heterolithic stratifi cation (IHS)-bearing channel deposits that are intercalated with pedogenically altered horizons (Hovikoski et al 2008). The palaeocurrents are variable between localities but are mainly toward the southeast and northeast (Räsänen et al 1995;Hovikoski et al 2007).…”

The Development of the Amazonian Mega‐Wetland (Miocene; Brazil, Colombia, Peru, Bolivia)

“…month cycles (e.g. Rebata et al 2006;Hovikoski et al 2005Hovikoski et al , 2007Hovikoski et al , 2008Hovikoski 2006) and are further discussed in Chapter 9.…”