Abstract

Professor D. V. Ager writes: Concerning K. T. Pickering’s paper (1984) of the Helmsdale Boulder Beds of NE Scotland, it should be placed on record that by no means all of the Upper Jurassic shallow water fauna he refers to is comminuted. I have, for example, collected from these beds nearly perfect specimens of the giant and unusual brachiopods Russirhynchia sutherlandi (Davidson) and Rovillieria (?) joassi (Davidson) which are unknown elsewhere. I have earlier suggested (Ager 1965) that their very local occurrence may indicate adaptation to a rocky sea-floor environment where sedimentation did not occur and where, therefore, they are not preserved except in the very special circumstances of the Helmsdale succession. A rocky sea-floor may also be indicated by the oysters and regular echinoids. I suggest that the presence of these forms may imply tsunami or similar water movements, presumably triggered by earthquakes, which transported the benthos from a rocky shelf without necessarily implying any particular sedimentary process.

Dr K. T. Pickering replies: I agree with Professor Ager’s comment that not all the Upper Jurassic shallow water fauna is ‘comminuted’, and would point out that on p. 361 I state: ‘Fossils are common, mainly as shell detritus,...’ and on p. 372: ‘...the scarcity of possible in situ shell faunas, . . .’ thereby suggesting that shell comminution and disarticulation is considerably more prevalent than the occurrence of perfect/near-perfect specimens in the ‘Boulder Beds’. Implicit in these statements is the local occurrence of well-preserved shallow water, and deeper water, faunas.

With regard

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