Donna S. Anderson¹, Timothy A. Cross¹

(1) Colorado School of Mines, Golden, CO

ABSTRACT: Climatic and Stratigraphically-Sensitive Geomorphic Controls on Stratigraphic Architecture, Hornelen Basin (Devonian), Norway

Strong climatic and stratigraphically-sensitive geomorphic controls on stratigraphic architecture, in addition to the well-known tectonic control, are recognized from recent work in the Hornelen Basin (Devonian), western Norway. An interpretation of climatic controls is based on a largely in-phase relationship of sediment supply from two different, orthogonal sources. Intrabasinal sources along the fault-controlled basin margin supplies small sediment volumes to the transverse alluvial fan system. An extrabasinal source supplies a large sediment volume to the axial braided river system. Mapping shows that as alluvial fans prograde and fan toes migrate basinward, the axial fluvial system also expands laterally toward the fan toes, while intervening lakes disappear. Hence, sediment volume synchronously increases in both the alluvial fan and braided river facies tracts. This in-phase relationship of two different sediment supplies is most likely related to a common change in hydrologic budget across a wide region: a change that is ultimately controlled by climate.

Stratigraphically-sensitive geomorphic control is inferred from a consistent reciprocal relationship between facies of the higher gradient alluvial-fan facies tract and those of the lower gradient braided-river facies tract. During the early stages of alluvial-fan retreat, decreasing gradients at fan toes permit lateral expansion of the braided-river facies tract up the former fan surface. In this configuration, the alluvial fan and braided-river facies tracts migrate in tandem: one facies tract replaces the other in a reciprocal relationship. Because this relationship exists at specific times (early base-level rise) across four scales of stratigraphic cycles, it demonstrates a stratigraphic control on the position and type of geomorphic elements that occupy the fan to braided-river transition zone.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado