Abstract
The Upper Cretaceous Capacete Formation, from the intracratonic Sanfranciscana Basin, central Brazil, consists of epiclastic sediments with a significant aeolian contribution. This unit has been traditionally interpreted as deposited by alluvial fans distally grading to braided rivers in an arid- to semiarid climate within the central part of southwestern Gondwana. Locally, some expositions with wide lateral extension show architectural elements indicative of deposition in meandering rivers, such as floodplain fines (FF) interbedded with crevasse splay (CR), lateral-accretion macroforms (LA), and channels (CH). Bioturbation within the meandering fluvial deposits is commonly associated with the floodplain element, mainly occurring in fine-grained sandstone and mudstone. The lateral-accretion elements and channel deposits are barren of trace fossils. Sandstone with climbing ripples (Sr) from the element CR show low bioturbation of meniscate trace fossils assigned to Taenidium, Beaconites, and Scoyenia ichnogenera. Simple vertical and horizontal burrows identified as Skolithos and Palaeophycus occur associated with Taenidium and Camborygma in sandstone facies (Sr, St and Sh), as well as rhizoliths, representing the Scoyenia ichnofacies. The predominance of trace fossils related to the FF and CR architectural elements attests to the colonization mostly by insects in episodic and vegetated flood plains of meandering river system from the Capacete Formation. Thus, despite the primarily arid to semiarid conditions interpreted for the inner parts of the newly formed South American continent during the Upper Cretaceous, our new data support deposition under humid conditions in some intervals of the Capacete Formation from Sanfranciscana Basin.
Highlights
The Upper Cretaceous Capacete Formation is an exclusively continental unit deposited by the reworking of the coeval volcanic rocks from the Santonian–Campanian Patos Formation (83.6 ± 1.4 Ma, Gibson et al, 1995)
Considering the scarce palaeoichnological and sedimentological studies focusing on the Capacete Formation, this manuscript aims to: (1) record the first occurrence of invertebrate trace fossils in this unit; (2) apply the study of the trace fossil assemblage as an auxiliary tool for the environmental reconstitution of continental successions; and (3) contribute to the palaeoclimatic reconstitution of the inner part of the newly formed South American continent
Trace fossils were prospected in all stratigraphic horizons, and their descriptions were based on the ichnotaxobases proposed by Bromley (1996)
Summary
The Upper Cretaceous Capacete Formation is an exclusively continental unit deposited by the reworking of the coeval volcanic rocks from the Santonian–Campanian Patos Formation (83.6 ± 1.4 Ma, Gibson et al, 1995). This unit is classically interpreted as deposited in distal alluvial fans that grade to braided fluvial systems, with a substantial contribution of aeolian sediments (Campos and Dardenne, 1997a). Vertebrate tracks (e.g., Carvalho and Kattah, 1998, Mescolotti et al, 2019) and brief descriptions of invertebrate trace fossil (Taenidium in the Três Barras Formation of the underlying Areado Group, Mescolotti et al, 2019). Considering the scarce palaeoichnological and sedimentological studies focusing on the Capacete Formation, this manuscript aims to: (1) record the first occurrence of invertebrate trace fossils in this unit; (2) apply the study of the trace fossil assemblage as an auxiliary tool for the environmental reconstitution of continental successions; and (3) contribute to the palaeoclimatic reconstitution of the inner part of the newly formed South American continent
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