Matrix-rich strata (20-70% mud matrix) have been increasingly recognized in deep-marine systems. These beds are thought to be deposited from mud-rich flows in a distal basin-floor setting; however they remain poorly understood, partly because details of lateral lithological changes are poorly known. In this study, matrix-rich strata are common in proximal basin-floor strata of the Neoproterozoic Windermere Supergroup. The objective of this thesis is to provide detailed description and interpretation of the lithological and mineralogical make-up and lateral facies trends of matrix-rich strata in in a unit 40 m thick and 800 m wide. Here, stratigraphic and petrographic analyses identified five facies: classic turbidites; sandstones; clayey sandstones; sandy claystones and fine-grained banded couplets, which laterally are arranged systematically from matrix-poor sandstones to thin-bedded turbidites. This lateral change is interpreted to represent a depositional continuum along the margins of an efflux jet that formed immediately downflow of an avulsion node.