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Lawrence C. Craig

Publications and source records attributed to Lawrence C. Craig.

4 recordsLinked to original sources
USGS1955

Stratigraphy of the Morrison and related formations, Colorado Plateau region, a preliminary report

Three subdivisions of the Jurassic rocks of the Colorado Plateau region are: the Glen Canyon group, mainly eolian and fluvial sedimentary rocks; the San Rafael group, marine and marginal marine sedimentary rocks; and the Morrison formation, fluvial and lacustrine sedimentary rocks. In central and eastern Colorado the Morrison formation has not been differ- entiated into members. In eastern Utah, northeastern Arizona, northwestern New Mexico, and in part of western Colorado, the Morrison may be divided into a lower part and an upper part; each part has two members which are di1Ierentiated on a lithologic basis. Where differentiated, the lower part of the Morrison consists either of the Salt Wash member or the Recapture member or both; these are equivalent in age and inter tongue and intergrade over a broad area in the vicinity of the Four Corners area of New Mexico, Colorado, Arizona, and Utah. The Salt Wash member is present in eastern Utah and parts of western Colorado, north- eastern Arizona, and northwestern New Mexico. It was formed as a large alluvial plain or 'fan' by an aggrading system of braided streams diverging to the north and east from an apex in south-central Utah. The major source area of the Salt Wash was to the southwest of south-central Utah, probably in west-central Arizona and southeastern California. The member was derived mainly from sedimentary rocks. The Salt Wash deposits grade from predomi- nantly coarse texture at the apex of the 'fan' to predominantly flne texture at the margin of the 'fan'. The Salt Wash member has been arbitrarily divided into four facies: a con- glomera tic sandstone facies, a sandstone and mudstone facies, a claystone and lenticular sandstone facies, and a claystone and limestone facies. The Recapture member of the Morrison formation is present in northeastern Arizona, northwestern New Mexico, and small areas of southeastern Utah and southwestern Colorado near the Four Corners. It was formed as a large alluvial plain or 'fan' by an aggrading system of braided streams. The Recap- ture deposits grade from predominantly coarse texture sedimentary rocks to predominantly fine texture and have been arbitrarily divided into three facies: a conglomeratic sandstone facies, a sandstone facies, and a claystone and sandstone facies. The distribution of the facies indicates that the major source area of the Recapture was south of Gallup, N. Mex., probably in west-central New Mexico. The Recapture was derived from an area of intrusive and extrusive igneous rocks, metamorphic rocks, and sedimentary rocks. The upper part of the Morrison formation consists of the Westwater Canyon member and the Brushy Basin member. The Westwater Canyon member forms the lower portion of the upper part of the Morrison in northeastern Arizona, northwestern New Mexico, and places in southeastern Utah and southwestern Colorade near the Four Corners, and it intertongues and intergrades northward into the Brushy Basin member. The Westwater Canyon member was formed as a large alluvial plain or 'fan' by an aggrading system of braided streams. The Westwater deposits grade from predominantly coarse-textured sedimentary rocks to somewhat finer textured sedimentary rocks, and have been arbitrarily divided into two facies: a conglomeratic sandstone facies and a sandstone facies. The distribution of the facies indicates that the major source area of the Westwater was south of Gallup, N. Mex., probably in west-central New Mexico. The Westwater was derived from an area of intrusive and extrusive igneous rocks, metamorphic rocks, and sedimentary rocks. The similarity of the distribution and composition of the Westwater to the Recapture indicates that the Westwater represents essentially a continuation of deposition on the Recapture 'fan'; the Westwater contains, however, considerably coarser materials. Whereas the S

Bulletin↗
USGS1949

Lower middle ordovician of south-central Pennsylvania

Broad paleostructural development in south-central Pennsylvania and Maryland was similar to that of central and eastern New York during the deposition of lower Middle Ordovician beds. Thick marine limestones of the easternmost belts of outcrop in the Cumberland Valley indicate the southward extension of the Champlain miogeosyncline. Thin and, in part, coarse-textured limestones in belts of outcrop just west of the Cumberland Valley indicate the extension of the Adirondack arch. Intermediate correlation shows the development of a relatively shallow platform east of the Adirondack arch and marginal to the Champlain miogeosyncline during part of the Bolarian (Kay, 1947) and Trentonian epochs. Detailed description, definition and correlation of the stratigraphic units are presented. The Pinesburg and Fannettsburg members (new) of the Shippensburg formation (redefined), the Housum and Kauffman members (new) of the Mercersburg formation (redefined), the Oranda formation (Cooper and Cooper, 1946) and the lower Martinsburg exhibit westward thinning by overlap or convergence or both from Champlain miogeosynclinal sections in eastern belts to sections on the Adirondack line in Path Valley. The Doylesburg member (new) of the Shippensburg is believed truncated to extinction southeastward from Path Valley by pre-Mercersburg regional unconformity. Argillaceous material in southeasternmost exposures of Oranda begins the Middle Ordovician transgressive clastic deposits resulting from the Vermontian disturbance. Correlations indicate Shippensburg is post-middle Chazyan to pre-Chaumont in age, Mercersburg is Rockland and Kirkfield, Oranda is Shoreham, and lower Martinsburg is Denmark.

Pennsylvania↗