At the Castle Creek study area a remarkably well exposed section in the Isaac Formation, Windermere Supergroup, was measured to document potential lateral and vertical changes in facies. Here, a consistent lateral succession of facies was observed consisting of matrix-poor sandstone to clayey sandstone to bipartite bed to sandy claystone, collectively overlain by a thin-bedded turbidite and mudstone cap. These changes are interpreted to reflect particle settling in a negligibly-sheared sand-mud suspension following detachment from the margins of an avulsion jet. Vertically, similar facies stack to form packages 2-7 beds thick implying temporary stabilization of jet-margin dynamics. At a larger scale facies stack to form three stratal assemblages. SA-1: intercalated matrix-rich and matrix-poor strata and SA-2: matrix-rich strata stack vertically and laterally but then are sharply overlain everywhere by classical turbidites of SA-3, indicating a dramatic change from deposition immediately downflow of an avulsion node to conventional levee deposition.

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.

This study investigates the lithological characteristics, and lateral and vertical facies trends of poorly understood, deep-marine matrix-rich sedimentary rocks. Two laterally extensive, well-exposed outcrops of slope and proximal basin floor deposits were investigated from the Neoproterozoic Windermere Supergroup. Significantly, matrix-rich beds have been found to undergo the same lateral trends (over ~200-650 m) in both outcrops. Initially, thicker, clayey sandstone transitions laterally to a bipartite bed with the development of an upper, planar-based, more matrix-rich unit. Further laterally, the basal unit progressively thins until it pinches out, and all that remains is the upper, more matrix-rich unit – a sandy claystone. It too thins and then pinches out. Draping the entire transect is a thin, matrix-poor structured unit overlain by a mudstone or claystone cap. These trends are interpreted to reflect a progressive but rapid lateral evolution of flow structure controlled primarily by particle settling, namely sand, from mud-rich avulsion-related flows.

Deep-marine sandstones containing significant (> 10%) detrital mud (silt and clay) matrix have become increasingly recognized, but mostly in drill core or poorly exposed outcrops where details of their vertical and lateral variability are poorly captured. Exceptional vertical and along-strike exposures of matrix-rich and associated matrix-poor deposits in deep-marine strata of the passive margin Neoproterozoic Windermere Supergroup and foreland basin Ordovician Cloridorme Formation, provide an unparalleled opportunity to document such characteristics. In both study areas, strata form a 100s m long depositional continuum that at its upflow end consists of thick-bedded matrix-poor sandstone (<20% matrix) that transforms progressively downflow to medium- to thick-bedded muddy sandstone (20 – 50% matrix) to medium-bedded bipartite facies with a basal sandy (30 – 60% matrix) part overlain sharply by a muddier part (40 – 80% matrix), and then to thin-bedded sandy mudstone (50 – 90% matrix). This depositional continuum is then overlain everywhere by a thin- to very thin-bedded traction-structured sandstone and/or silty mudstone cap. This consistent lithofacies change is interpreted to reflect particle settling in a rapidly but systematically evolving, negligibly-sheared sand-mud suspension developed along the margins (Windermere) and downflow terminus (Cloridorme) of a high-energy, mud-enriched avulsion jet. Stratigraphically upward, beds of similar lithofacies type succeed one another vertically and transform to the next facies in the depositional continuum at about the same along-strike position, forming stratal units 2–9 beds thick whose grain-size distribution gradually decreases upward. This spatial and temporal regularity is interpreted to be caused by multiple surges of a single, progressively waning turbidity current, with sufficient lag between successive surges for the deposition of a traction-structured sandstone overlain by mudstone cap. Furthermore, the systematic backstepping or side-stepping recognized at the stratal unit scale in both the Windermere and Cloridorme is interpreted to be driven by a combination of knickpoint migration and local topographic steering of the flows, which continued until the supply of mud from local seafloor erosion became exhausted, the main channel avulsed elsewhere, or a new stratal element developed.