Growth‐faults from delta collapse – structural and sedimentological investigation of the Last Chance delta, Ferron Sandstone, Utah

Abstract

Investigations of syn‐sedimentary growth faults in the Last Chance delta (Ferron Sandstone, Utah, USA) show that fault‐bounded half‐grabens arrested high amounts of sand in the mouth bar and/or distributary channel areas. Fault‐controlled morphology causes changes in routing of the delta top to delta front drainage towards the long axis of half‐grabens. Faulting was spatially and temporally non‐systematic, and polyphase, with 3D cusp/listric fault geometries instigated by linkage of variously oriented segments. Hanging wall rollover folds consisting of wedge‐shaped syn‐kinematic sand attest to rapid <1‐m slip increments on faults followed by mild erosion along crests of fault blocks and sedimentary infill of adjacent accommodation. Triangle‐zones in prodelta to delta front muds are located underneath steeper faults and interconnected rotated fault‐flats. Their geometry is that of antiformal stack duplexes, in an arrangement of low‐angle‐to‐bedding normal faults at the base, replaced by folded thrusts upwards. These faults show a brittle, frictional flow deformation mechanism ascribed to early compaction of mud. For syn‐kinematic sand, there is a change from general granular/hydroplastic flow in shear zones to later brittle failure and cataclasis, a transition instigated by precipitation of calcite cement. Extensional faulting in the Last Chance delta was likely controlled by gravity driven collapse towards the delta slope and prodelta, as is commonly observed in collapsing deltas. The trigger and driving mechanism is envisioned as localized loads from sand deposited within distributary channels/mouth bars and fault‐controlled basins along the delta top. A regional tilt and especially displacement of compacted mud below sand bodies towards less compacted muds also contributed to the faulting.

Architecture, deformation style and petrophysical properties of growth fault systems: the Late Triassic deltaic succession of southern Edgeøya (East Svalbard)

“…This type of depositional setting would have favoured differential compaction‐driven subsidence between the prodelta and the relatively more proximal zones, leading to the creation of landward‐dipping listric growth faulting at the delta toe (Back & Morley, ; Braathen et al., ). In this framework first order and larger‐scale (seismic) faults with spacing in the order of kilometres would provide a counter‐regional, monoclinal slope dipping towards the delta system.…”

“…This general arrangement is not always observed, and in several cases the growth faults domains are bounded by counter‐regional, landward dipping, large‐scale listric faults (Pochat et al., ; Rouby, Raillard, Guillocheau, Bouroullec, & Nalpas, ; Sapin, Ringenbach, Rives, & Pubellier, ), a pattern also replicated in analogue models (McClay, Dooley, & Lewis, ; McClay & Ellis, ). Such situations have been related to local to regional differential compaction and sedimentary loading between the finer, water‐saturated outer prodelta and the inner, coarser delta front‐top zones (Back & Morley, ; Braathen et al., ).…”

“…from less than 1 mm to the size of the outcrop) syn‐sedimentary deformation mechanisms of growth faulting at shallow crustal conditions (< than 1 km burial), are underrepresented in the current literature, partially due to the relative scarcity of favourable exposures. A few exceptions are available (Bhattacharya & Davies, ; Bouroullec et al., ; Braathen et al., ; Onderdonk & Midtkandal, ; Zecchin, Massari, Mellere, & Prosser, ), and usually describe neo‐tectonic faulting in poorly consolidated lithologies (Bense & Person, ; Heynekamp, Goodwin, Mozley, & Haneberg, ; Loveless, Bense, & Turner, ; Mozley & Goodwin, ; Rawling & Goodwin, , ). This outcrop‐based study presents the results of a combined structural‐stratigraphic and petrophysical analysis the superbly exposed, Late Triassic growth fault system cropping out in the southern part of Edgeøya, Svalbard (Arctic Norway).…”

Mesozoic‐Cenozoic Regional Stress Field Evolution in Svalbard

“…Syn‐sedimentary Triassic normal faults on Edgeøya and Hopen (Braathen, Midtkandal, et al, ; Maher et al, ; Ogata et al, ; Osmundsen et al, ; Smyrak‐Sikora et al, ), and offshore (Anell et al, ), provide potential insight into crustal stresses at that time. These faults can be separated into two groups, thick‐skinned versus thin‐skinned, a division introduced by Anell et al () and adhered to herein.…”

“…In addition to this northwest prograding deltaic system, Worsely () suggests an additional Late Triassic sediment source to the north of Svalbard. During Carnian deposition of the Tschermakfjellet and De Geerdalen formations (Table ), both thick and thin‐skinned normal faulting occurred in eastern Svalbard (Osmundsen et al, ; Braathen, Midtkandal, et al, , Figure ). Late Jurassic transgression yielded a thick sequence of organic rich shales across the region (Anell et al, ; Dypvik et al, ; Koevoets et al, ).…”