Recognition of Deltas by Fitting Trend Surfaces to Upper Pennsylvanian Sandstones in North-Central Texas

Trends as a tool in stratigraphic research with lacustrine sedimentation as an example

“…No matter whether the studied variable is structure, isopach, or facies, the regional component of large areas is rarely described by a plane or surface of the first order in nature (Wermund & Jenkins, 1970). Referring to Fig 1, it is apparent that the used well distribution is not uniform.…”

“…In a regional distribution pattern, deltaic agents deposit their channel sands and distributary bars. A trend analysis of sand isopach percentages can be used to identify marine deltaic complexes, even in areas where stratigraphic sequences cannot be recognized or where well control is insufficient, according to Wermund & Jenkins (1970). For example, suppose the studied como posição estrutural, isópaca ou porcentagem de areia.…”

“…Em um padrão de distribuição regional, os agentes deltaicos depositam suas areias de canal e barras distributivas. Uma análise de tendência das porcentagens de isópacas de areia pode ser usada para identificar complexos deltaicos marinhos, mesmo em áreas onde as sequências estratigráficas não podem ser reconhecidas ou onde o controle do poço é insuficiente, de acordo com Wermund & Jenkins (1970). Suponha que o intervalo estudado não forme uma sequência natural de estratos, FORMAT, conforme definido por Forgotson (1957), ou um incremento genético de estratos (IGE), conforme definido por Bush (1971).…”

“…Concerning the distribution of the sands and the locality of deltaic agents, Wermund & Jenkins (1970) propose that the total studied interval be divided into genetic increments of strata (GISs), implying minute correlations and rigid control into recognizing deltas and their diverse environments. Arithmetic division of the total interval is recommended when such requirements cannot be met.…”

“…During the Special Projects Courses in Geology, held in 1971 and 1972, at the then Petrobras Higher Training Sector of Bahia (Setup/BA), pioneer regional stratigraphic analyzes were carried out on the lower Stages of the Recôncavo Series, that is, Rio da Serra Stage, in 1971, andDom João Stage, Andar Aratu andAndar Buracica, in 1972. The stratigraphic analysis tried to test the feasibility and limitation of Wermund & Jenkins's (1970) ideas, developed for marine deltaic deposition, for limnic deltas of the different faciological tracts of the accepted depositional system for these stages. Among other objectives, during the mentioned courses, it sought to establish a system for choosing the variables to be mapped.…”