Stratigraphy. „The potential Upper Jurassic aquifer ranges from 3992 – 4404 m MD. Yellowish-brown micritic limestones containing residues of siliceous sponges were developed here from 3992 – 4280 m MD, a dark-grey micrite with sponge needles (basinal limestones) from 4280 - 4375 m MD, xxxxx calcisiltites down to 4404 m MD, and Dogger rocks down to 4450 m MD. In place of the expected Xxxxxxx limestones (Helvetian facies), Swabian sponge mass facies were found. Dolomites causing the good permeabilities in the eastern Molasse Basin could only be observed subordinately. Indications of karstification, open porosities and fractures were only scarce. Increased quantities of transparent calcites could be observed only at 4070 m MD and from 4150 – 4210 m MD; white calcites observed from 4315 – 4335 m MD indicate a fault zone with closed fractures.“ (Xxxxxxxxx et al., 2015).
Stratigraphy. The bedrock in the Mill Creek Watershed is entirely of sedimentary origin. These rocks are primarily of the Allegheny and Pottsville Groups of Middle and Lower Pennsylvanian age. The Shenango sandstone of the lower Pocono Group outcrops in the stream valleys of Mill Creek near its mouth as well as at the mouths of several of the western tributaries to Mill Creek. The Xxxxx Chunk Formation and Xxxxxxx sandstone have been entirely removed by erosion or were never deposited in this area, creating disconformity between the Shenango member and the overlying Pottsville rocks. Coals and clays in the watershed usually occur in beds less than five feet thick. The sandstones and shales in the watershed are quite variable with some beds reaching a thickness of 50 feet or more. The sandstones and shales frequently grade into each other vertically and horizontally with no distinct delineation between beds. The sandstones are often massive and are very abundant. Limestone beds in the watershed are almost non-existent, and those beds encountered are usually thin and impure. The Allegheny Group was formerly known as the Lower Productive Coal Measures because of the numerous mineable coal seams that it contains. This group contains a variable sequence of shale, sandstone, limestone, clay, and valuable beds of coal. Sandstones are much less prominent than in the overlying Conemaugh Group or underlying Pottsville Group. The Allegheny Group includes all the strata between the top of the Upper Freeport coal and the base of the Brookville underclay. In areal extent this group covers nearly the entire watershed. Erosion has removed the upper portion of the group throughout much of the watershed and has removed these rocks entirely in the deeper valleys of the major streams, exposing the underlying Pottsville and Pocono Groups. Although there is considerable variation between members of the Allegheny Group, it has a relatively uniform thickness of about 325 feet. Due to the variable vertical sequence of this group and the inconsistant lateral extent of beds in the watershed, it is impractical to rely on a generalized geologic column as such a column would probably be quite different at any two locations. The Allegheny Group has been divided into three formations: the Freeport, extending from the top of the Upper Freeport coal to the top of the Upper Kittanning coal; the Kittanning, extending from the top of the Upper Kittanning coal to the base of the clay underlying the Lower Ki...
Stratigraphy. Besides the alluvial cover, the rock sequence at Twin Creeks consists of four main elements (MacKerrow et al., 1997): · A group of Penn-Permian Exxxxxx Formation mixed carbonate lithologies in depositional contact with: · A tectonic unit (Leviathan Thrust Sheet) of possible Devono-Mississippian age, thrust eastward over: · A tightly folded presumed Upper Ordovician group of predominantly basaltic sxxxx and flows (with minor interbedded shales and tuffs), and: · An equally tightly folded presumed Lower Ordovician group of predominantly shaley rocks (with minor mafic and basaltic igneous rocks). The Penn-Permian Exxxxxx Formation was divided functionally into three Members, and is the principal host in Vista Pit, with occasional extensions into northern Mega Pit. The formation is a transgressive sequence, showing a basal Lower Member of siliciclastic-dominated carbonate, a medial Middle Member dominated by massive biomicritic limestones and dolomites, and an Upper Member composed of siliciclastic sand-and-siltstones. The Devono-Mississippian Leviathan Thrust Sheet consists of an informal Upper Member comprised mostly of exceptionally thick sequences of pillow basalts, and an informal Lower Member dominated by interbedded greenstones, cherts & tuffs. The Lower Member of the sheet crops out along the west wall of Mega Pit, where it dips about 20 degrees to the west, and sporadically appears as an east-dipping remnant along the northeast wall, suggesting that the Leviathan Thrust surface defined a north-trending antiform now cored by Mega Pit. The Ordovician package is coherently folded into an overturned, eastward-verging Z. This package consists of three elements: a generally flat-lying, mildly arched and warped Upper Limb on the west side of Section 19 known as the Conelea Anticline, an overturned Middle Limb with no name, and a mildly arched upright Lower Limb on the east side of Section 19 known as the Tapper Anticline.
Stratigraphy. As a means of assessing soil horizon development and therefore artifact depositional integrity, detailed profile descriptions will be made. The descriptions, along with cultural material distributions, are designed to aid in prehistoric occupation surface definition and natural and cultural stratigraphy. Site use chronology will be established through the use of absolute (e.g., radiocarbon, luminescence) and relative (e.g., historical types, tephrochronology, stratigraphic) dating techniques. Radiocarbon dating may be applied to conventional materials such as charcoal and bone, as well as lesser dated materials and samples such as organic sediment fractions. In addition, occupation chronological information may be obtained through luminescence dating of fire- modified rock. Obsidian hydration analyses will be conducted for potential relative dating of obsidian materials. Lithic Analysis Lithic implement and debitage analysis, at a minimum, is divided into three major problem areas:
Stratigraphy shall include the stratigraphic column, determination of environments and age for each of the formations drilled.
Stratigraphy. The Tweed Heads 1:250,000 geological map shows that the site is underlain by the Lismore Basalt Formation. Our boreholes drilled on the site intersected fill and aeolian dune sand overlying weathered basaltic rock. In one borehole a firm clay of apparent alluvial/marine origin was observed overlying the weathered basalt. This clay could also be a weathered interflow layer from within the basaltic rocks that underlie the site. The general stratigraphy of the site is presented in a cross section geotechnical model presented in Figure 2. Further details of the materials intersected by the boreholes are provided in the Engineering Logs presented in Appendix A.
