3-D sedimentary architecture of a Quaternary gravel delta (SW-Germany): Implications for hydrostratigraphy

摘要

This paper investigates a Quaternary Gilbert-type gravel delta that was formed in an ice-marginal environment at the end of the last glacial period. Outcrop, sediment core and ground-penetrating radar (GPR) studies reveal the sedimentary facies and depositional architecture of the delta that comprises three major units: (1) a 2-5 m thick, gravelly topset with an erosional base, formed by accretion of bedload sheets in a braided river; (2) an up to 40 m thick, steeply inclined (13-35°) foreset, dominated by gravelly lithofacies being the product of cohesionless debris flows and debris falls as well as gravity slides while sandy lithofacies was deposited by traction currents; and (3) a 10-20 m thick, sandy bottomset comprising low-density turbidites. Syn-to postdepositional deformation of parts of the bottomset deposits largely resulted from rapid deposition of overlying gravels and differential loading of the prograding foreset beds. The development of the delta was most likely controlled by a high sediment supply and lake level fluctuations. The overall coarsening-upward succession reflects delta progradation and aggradation into a glaciolacustrine environment. Outcrop sedimentology served as a direct analogue in order to characterise the three-dimensional sedimentary and hydraulic architecture of the nearby gravel-delta aquifer. Applying a multidisciplinary approach, sedimentological, geophysical, and hydrogeological data were integrated within the 3-D modelling package Gocad (Earth Decision Sciences) to develop high-resolution 3-D aquifer models.