AN INTEGRATED ENVIRONMENT ANALYSIS - LITHOFACIES, CHEMOFACIES, BIOFACIES - OF THE OLIGOCENE CALCAREOUS-SILICICLASTIC SHELF DEPOSITS IN NORTHERN GERMANY

During the Oligocene monotonous fine-grained siliciclastic and calcare ous shelf sediments of the Septaria Clay Fm. were deposited in the Nor th German Basin. The uniform grain size spectrum and the homogeneous o utward appearance of these sediments forces environmental analysis to be based on a joint investigation of the inorganic and organic facies. The transgression of the Rupelian sea caused tidal sand sheets to for m off the mouth of estuaries. Upon deepening of the basin the benthoni c oxygen content of the bottom water diminished and inner shelf muds w ere deposited. Following this early transgression, a conspicuous chang e may be recognized when a siliciclastic shelf was replaced by a calca reous-siliciclastic shelf upon shoaling of the basin and warming of th e seawater. These outer shelf conditions persisted until fine-grained elastic sediments became more and more dominant during the early Late Oligocene. Their depositional environment may be described as shallow lagoon. In the succeeding formation of the Oligocene tidal bars and es tuarine sands are characteristic. The uppermost formation penetrated b y the drill hole in the Gartow area contains estuarine channel sands. In conclusion, the Oligocene sedimentary record reflects a symmetrical facies pattern showing calcareous-siliciclastic cyclothems in the cen tral section and siliciclastic shelf deposits below and above, reflect ing the cyclical nature of the Oligocene sea in a dominantly tidally-i nfluenced depositional environment. The use of clay minerals, heavy mi nerals, carbonates, phosphates and sulphides together with dinocysts, nannofossils and foraminifera has proved to be a successful tool in pa laeoecological and palaeoenvironmental analyses. (C) Elsevier Science B.V. All rights reserved.