Eocene inversion history of the Sandown Pericline, Isle of Wight, southern England

Abstract

Study of the composition and distribution of derived lithoclast and fossil suites collected from the Selsey, Barton and Becton Formations in Whitecliff Bay, Isle of Wight has enabled a detailed reconstruction of Mid-Late Eocene uplift of 500 m + on the northern limb of the Sandown Pericline. The stratigraphical distribution of clasts and fossils derived from older formations demonstrates the erosion of progressively older Eocene, Palaeocene and Cretaceous sediments during growth of the structure. The presence of delicate reworked fossils and clasts, together with limited palaeocurrent data support very local derivation from the south. The preservational state of the derived materials is used to identify the diverse processes of erosion and transport. Two phases of uplift (Lutetian, Bartonian), separated by a period of quiescence and peneplanation have been identified; rates of Eocene uplift of about 100 m Ma – 1 are postulated to have taken place.

New insights into the structure and evolution of the Isle of Wight Monocline

“…The present-day level of erosion on the Isle of Wight Monocline is such that the evidence for mid-late Eocene erosion has been removed by later Tertiary uplift and erosion. However, we do not see a problem in the amount of Eocene uplift proposed by Gale et al (1999), or accommodating their model into the general model of reverse faulting representing the last major control on the structure of the folds' northern limbs. Although sandbox models of inverted planar and listric detachment faults and domino faults reveal the reverse faulting in post extension strata occurs soon after inversion commences ( Fig.…”

“…The reverse fault zones come to crop just to the north of the Chalk within the steeply dipping Cenozoic strata and may have up to 560 m displacement at top Chalk levels, a figure similar to that of Gale et al (1999) for the mid-late Eocene uplift that they postulate exposed the Chalk in the crest of the Sandown Anticline. The present-day level of erosion on the Isle of Wight Monocline is such that the evidence for mid-late Eocene erosion has been removed by later Tertiary uplift and erosion.…”

“…The inversion structures have long been thought of as Mid-Tertiary (Miocene) in age but this was questioned by the existence of erosion of the Bembridge Limestone (Daley and Edwards, (1971) and there is increasing evidence of a more complex history of uplift from Palaeogene times into the Quaternary (Gale et al, 1999;Newell and Evans, this volume). Inversion and some folding may even have commenced in Late Cretaceous times (Mortimore, 1986;Mortimore andPomerol, 1991, 1997), although this is questioned by Gale et al (1999).…”

“…Previously, the northern limb of the Monocline was seen as controlling the outcrop of what have often been viewed as a largely continuous sequence of steeply dipping 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 9 to overturned Cretaceous and Cenozoic strata on the northern limbs of the Sandown and Brighstone anticlines (e.g. BGS, 1975BGS, , 1995Gale et al, 1999). Seismic interpretations (e.g.…”

“…Earlier studies of this important zone of folding have tended to emphasise the role of the reversal of movement on the underlying Permian to Mesozoic extensional down-to-the-south normal faults during Tertiary (Alpine) compression, which produced a northerly-verging and generally unfaulted monoclinal folding in the overlying late Cretaceous to early Cenozoic strata (e.g. Whittaker, 1985;Chadwick, 1993;Underhill and Patterson, 1998;Gale et al, 1999). The studies did not fully depict the development or the presence of a major reverse fault zone on the steep to overturned northern limb of the two anticlines forming the overall Isle of Wight monoclinal structure ( Fig.…”